Handbook of Cosmic Hazards and Planetary Defense 9783319028477

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_1-1 # Springer International Publishing Switzerland 2014

Solar Flares and Impact on Earth Mikhail Ya. Marova* and Vladimir D. Kuznetsovb a Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia b Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation, Russian Academy of Sciences, Moscow, Troitsk, Russia

Abstract The Sun exhibits different kinds of activity and its appearance is permanently changing, as it is revealed by numerous ground and space observations. The most well-known phenomenon is the 11-year solar activity cycle with an increasing and decreasing number of sunspots on the Sun surface over this period. These sunspots can be tens of thousands of kilometers across. They usually exist as pairs with opposite magnetic polarity alternating every solar cycle. A number of sunspots tend to peak at the solar maximum and are generally manifested closer to the Sun’s equator. Sunspots are darker and cooler than their surroundings because these are regions of the reducing energy convective transport from the hot interiors, which is inhibited by strong magnetic fields. The polarity of the Sun’s magnetic dipole changes every 11 years. This means that the North Magnetic Pole becomes the South one and vice versa. Because solar activity changes from one 11-year cycle to another, the doubled cycles (22 years and longer) are also distinguishable from each other. Irregularity is specifically manifested by a minimum of sunspots and solar activity during several cycles, as significantly occurred in the seventeenth century and is now known as the Maunder Minimum. These cycles strongly impact the Earth’ climate. During the last 11-year cycle, an unusual solar minimum occurred in 2008 and lasted much longer with lower amounts of sunspots than normal. Therefore, solar activity recurrence is not stable. Moreover, theory claims that magnetic instabilities in the Sun core could cause fluctuations with periods that could last tens of thousands of years. Solar flares, coronal mass ejection (CME), and solar proton events (SPEs) are the most characteristic phenomena of these changes in solar activity and their external manifestation. The activity rate as noted above is closely related with the 11-year solar cycle. These solar flare events are often accompanied by the huge ejected amounts of high-energy protons and electrons well exceeding the “normal” energy levels of solar-wind particles. Solar flares, coronal mass ejections (CMEs), solar proton events (SPEs), and normal ejections from the Sun known as “solar wind” have an effect throughout the solar system – especially its inner parts. These phenomena determine the state of geomagnetic fields of planets. Solar plasma and electromagnetic emissions thus have important interactions with the solar system bodies with particular significance for Earth. Solar weather processes impact the Earth’s upper, middle, and lower atmosphere and even can have negative impacts at the surface. Basically, solar activity events determine the space weather which influences planetary environment and, in particular, the life on Earth. This chapter addresses the known science that is associated with solar flares as well as how these solar flares play a key role in triggering other energetic and harmful solar phenomena. Finally it addresses how solar flares, CMEs, and SPEs in particular impact the Earth’s atmosphere and magnetosphere and especially how these phenomena can create significant negative impacts and major infrastructure risks to the world’s current economic and technological systems.

*Email: [email protected] Page 1 of 26

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_1-1 # Springer International Publishing Switzerland 2014

Keywords Carrington event; Coronal mass ejections (CMEs); Extreme-ultraviolet (EUV) radiation; Galactic cosmic radiation (GCR); Gamma radiation; Geomagnetically induced currents (GICs); Polar cap absorption (PCA) event; Solar corpuscular radiation (SCR); Solar energetic particles (SEPs); Solar and Heliospheric Observatory (SOHO) satellite; Solar flares; Solar proton events (SPEs); Solar wind; Sunspot; X-ray radiation

Introduction Solar flares (Fig. 1) are caused by the tearing apart and reconnection of the magnetic field lines (the so-called B-field) in the Sun’s chromosphere. This is accompanied by a rapid release of magnetic energy stored in the corona. A flare is a burst exhibited as an instantaneous and intense change in the Sun’s brightness in an active area on the Sun surface. The majority of the flares’ energy is not visible to the naked eye and must be observed with special instruments outside of the visible light range. Temperature inside a flare reaches 108 K, and energy release may reach nearly 1026 J – about a sixth of the total energy output of the Sun each second. This is the equivalent of 160 billion megatons of TNT or the same as the largest type of thermonuclear bomb known to humanity. Flare duration may be as long as 200 min. The typical solar flare is accompanied by strong intensity X-ray and gammaray releases of energy. This can and often does lead to a powerful acceleration of clouds of electrons, protons, and heavier particles that are ejected into space. The velocity of these plasma releases can approach a tenth of the speed of light. Unlike solar wind, particles generated by the violent flares and manifested as coronal mass ejections (CMEs) or solar proton events (SPEs) travel very fast, and when and if they reach Earth, they strongly disturb its environment and the atmosphere. Radiation from the flares can be extremely harmful to astronauts and to satellites and spacecraft and create other negative impacts that will be discussed later in this chapter. The exact relationship between the solar flare that originated below the corona and the ionic particle release known as a coronal mass ejections (CMEs) and solar proton events (SPEs) is not entirely understood. Solar flares, CMEs, and

Fig. 1 An example of solar flares over the Sun’s visible surface – photosphere (Credit: SOHO, ESA) Page 2 of 26

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_1-1 # Springer International Publishing Switzerland 2014

SPEs often occur together but are not always linked. The dynamic nature of the Sun’s magnetic fields is key to all of these phenomena. A CME represents the most powerful phenomenon in the solar system. They are originated in the corona and represent outbursts of the enormous volumes of the solar plasma also caused by the magnetic field lines reconnection. Some of them are associated with the solar flares or are related with the solar eruptive protuberances maintained above the solar surface by the magnetic fields. CME appears periodically and are composed of very energetic particles. Giant clots of plasma forming giant plasma bubbles expanding outside in the corona and its arms are thrown out in space. Billions and sometimes trillions of tons of matter are ejected and travel in the interplanetary medium with a velocity of greater than 1,000 km/s and form a detached bow shockwave at the front. CMEs are responsible for powerful magnetic storms on Earth. Due to plasma inflow the Earth’s magnetosphere can decrease from about 12 RE to about 6 RE. Solar flares and CME carry very harmful radiation, and in the case of CMEs, they generate a large amount of radiation as they hit the Earth’s atmosphere. Another phenomenon that is less violent than CMEs is solar proton events (SPE). They occur more often than typical solar flares and CMEs. The peak energies of generated proton ions are lower (i.e., typical energy levels are E ~ 30 MeV, and particle flux density is about 1010 cm
3) but SPE duration is longer. These events can last from a few hours to a few days. Whereas solar flares and CME are more characteristic for the maximum phase of the 11-year solar activity cycle, SPE occurs throughout the whole cycle. Their influence on the space environment and their impact on Earth is much lower than CMEs. Solar plasma and electromagnetic radiation impacting planets strongly influences their environment. The biggest impact is on their magnetosphere – either intrinsic or induced depending on whether a particular planet possesses a magnetic field. Such an interaction is referred to as solarplanetary coupling and is substantially dependent on the phase of the 11-year cycle of solar activity. Solar flares, especially when combined with CMEs, exert strong influence on the state of geomagnetic field and space weather on Earth. Changes in the solar activity result in changes to the geomagnetosphere’s shape and to the Earth’s radiation levels. These events can trigger magnetic storms and lead to major changes to the various upper atmosphere properties of the Earth as well. In particular, temperature of the Earth’s atmosphere in the height range 200–1,000 km can change by several times, from about 400 K to as high as 1,500 K, and change the atmosphere’s mass density by one to even two orders of magnitude. These solar storms can dramatically impact artificial satellite lifetime and threaten astronauts in orbit. These variations are caused by the solar flare’s extreme-ultraviolet (EUV) and soft X-ray radiation. Radio emissions from the Sun can be conveniently measured in the decimeter wavelengths. Solar activity can thus be indexed by measuring radiation in the 10.7 cm band. Radiation in this wavelength is today continuously recorded by simple radio antennas over the globe. This index (F10.7) changes from about 70 to about 180 W/m2Hz between solar activity minimum and maximum, respectively, and perfectly reflects the real physical processes depending on the solar energy input. Similarly, indexes of geomagnetic activity (Ap, Kp, Dst, and some others) are recorded by geophysical observatories. These measurements are used to characterize the Earth’s magnetic field disturbance. Solar flare effects on Earth (as well as CMEs) display themselves as auroras at high to moderate latitudes. In the case of particularly severe solar flares and CMEs, these auroras can be seen at much lower latitudes and with much greater vividness. Solar flares (as well as CMEs) can also result in the disruption of radio communications, breaks in electric power supply and destruction of electrical power transformers, blocking of radar operations, damage to spacecraft electronics, and

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_1-1 # Springer International Publishing Switzerland 2014

even disruption of underwater submarine cable operations. Many of these problems are occasioned by what are called geomagnetically induced currents (GICs).

Classification of Solar Flares Solar flare is a very explosive process. It involves energy release in the Sun’s atmosphere encompassing all its layers – photosphere, chromospheres, and corona. It manifests itself as a sudden brightening observed over the Sun surface or the solar limb. Basically, solar flare implies an event that is localized within an active region on the Sun (Fig. 2). In this way they are distinguished from CMEs which have much larger angular spans encompassing several active regions and enormous power of an explosive nature. The CME leads to an explosion of plasma ejected at a speed of thousand km per second. Flares involve the release of energy as electromagnetic radiation (i.e., extreme-ultraviolet X-rays and even gamma rays) that travels at the speed of light, while CMEs are ionic plasma that travels at speeds up to one-tenth of the speed of light. The top recorded speed of any recent CME was over 5.5 million km/h as registered by the Solar Dynamics Observatory (SDO). This was during a 31 August 2012 event that fortunately was largely directed away from the Earth’s path. Solar flares are extremely complex phenomena observed across the whole electromagnetic spectrum including extreme-ultraviolet and gamma-ray emissions as well as radio wavelength. Solar flares are classified depending on their size, duration, morphology or magnetic topology, and characteristic corpuscular radiation. There are two basic kinds of flares – impulsive and gradual. The duration of flares varies – from a few minutes to tens of minutes and even several hours. A fully developing flare is sometimes a combination of an impulsive and gradual event. A flare’s duration is indicative of its magnetic topology. While long-duration flares are linked to CMEs, impulsive flares are generally completely confined within the Sun’s lower atmosphere though some short-duration

Fig. 2 The massive solar flare X1.2-class on 7 January 2014. This image taken by SDO’s (Solar Dynamics Observatory) Helioseismic and Magnetic Imager shows location of two active regions on the Sun, which straddle a giant sunspot complex. The flare has forced the commercial spaceflight company Orbital Sciences to postpone the planned launch of a private cargo mission to the International Space Station (Credit: NASA/SDO) Page 4 of 26

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_1-1 # Springer International Publishing Switzerland 2014

Fig. 3 Solar flares defining space weather and affecting technological systems on the Earth and in space (Credit: L. J. Lanzerotti, Bell Laboratories, Lucent Technologies, Inc)

Fig. 4 Electromagnetic and corpuscular solar radiation and its effects (Credit: P. Brekke. Source: P. Brekke. Space Weather Effects. Presentation, ESTEC, 1 December, 2004)

flares may also have ionic plasma ejections of various scales. Solar satellite missions are seeking to understand better the relationship between flares and CMEs and SPEs and their causal relationships. There is widely used optical (Ha) classification system that is based on Ha emission line spectral observations, and this classification system addresses flare size (i.e., importance). The classification starts from a character S (means sub-flare) followed by Figs. 1, 2, 3, or 4 for successively larger flares Page 5 of 26

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_1-1 # Springer International Publishing Switzerland 2014

Table 1 Optical (Ha) classification system of flare size/importance S 1 2 3 4

A 1,600 km/s) CMEs do not produce type II bursts while some slow CMEs (~400 km/s) occasionally produce metric type II bursts. While the association between CMEs and metric type II bursts is controversial, the association between CMEs and decametric, hectometric, and longer wavelength has been established. A strong hierarchical relationship between CME kinetic energy and the type II wavelength has been found. Longer wavelength type II bursts are found to be associated with faster CMEs, which are also often associated with accelerating particles to higher energies (e.g., see Prakash et al. 2012; Gopalswamy et al. 2010b; and references therein).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_9-1 # Springer International Publishing Switzerland 2014

In Situ Observations of ICMEs in the IP Medium Soon after reaching the IP medium, ICMEs sweep large areas of space and can engulf the Earth, causing direct and indirect consequences. Studying ICMEs in situ mostly involves studying the plasma parameters (speed, density, temperature, plasma beta, ionization states, and elemental composition), magnetic fields (strength, direction), and the energetic particle energy spectrum. In situ sampling involves placing the spacecraft near Earth, either at L1 between the Sun and Earth or in an orbit with sufficient apogee time so that it spends most of the time in the IP medium ahead of the magnetosphere. NASA’s Advanced Composition Explorer (ACE), Wind, and the Interplanetary Monitoring Platform (IMP) series spacecraft are very good examples of in situ platforms that have largely enhanced our understanding of the IP medium and the solar transients over the last few decades. Arrival of IP shocks at the spacecraft is usually a good indicator of the driving ICME arrival. However, the angle at which the ICME arrives at the spacecraft affects what the spacecraft observes. Generally, ICMEs are characterized as flux ropes (field rotation) or non-flux ropes. A CME with a flux rope is referred to as a magnetic cloud (MC) if it has an enhanced magnetic field, smooth rotation of one of the components perpendicular to the Sun-Earth line, and a depressed proton temperature or beta plasma. One of the important aspects of in situ ICME observations is linking them back to their sources at the Sun, which allows us to understand the transport and acceleration processes that take place along their transit to Earth. However, the process is not straightforward. Multi-spacecraft observations could help in resolving this issue, which is still an ongoing research topic. STEREO observations from two opposite locations of the Sun-Earth line have confirmed the 3D structure of CMEs and their associated IP-driven shocks (see Gopalswamy et al. 2010b and references therein).

CMEs and Space Weather: Identifying the Hazards Instruments onboard spacecraft in the IP medium observe energetic particles, electrons, and ions at different intensities and energies and from different origins. These include anomalous cosmic rays, galactic cosmic rays, particles of planetary magnetospheres origin, particles accelerated at quasistationary shocks in the IP medium (e.g., from Corotating Interaction Regions, CIRs), and particles that are directly associated with events initiated at the Sun such as flares and CMEs: solar energetic particles (SEPs). SEPs pose hazardous radiation risks to both astronauts and instrumentation alike in the space environment. Although the Earth’s magnetosphere acts as a natural shield against most of energetic particles, it is still susceptible to the vast magnetic structure associated with the CME itself which when southward can cause intense geomagnetic storms in some cases. A CME is thus a double-hazardous phenomena with two key aspects of space weather, SEPs and geomagnetic storms. It is important to note that not all CMEs cause geomagnetic storms, and not all are associated with SEP events. Advanced instrumentation over the last two decades allowed intense investigations of CMEs and SEPs through solar cycle 23. Figure 5 shows the location sources of CMEs associated with SEPs and those that cause geomagnetic storms (e.g., see Gopalswamy 2009 for more details). The following section provides more details on each of the CME-associated phenomena.

Solar Energetic Particles SEPs are energetic ions and electrons that vary in energy between the suprathermal regime (tens of keVs) up to tens of GeV. SEPs are widely believed to be accelerated at the solar flare sites via the release of magnetic energy (flare-associated impulsive events) or the IP-driven shock waves in the Page 9 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_9-1 # Springer International Publishing Switzerland 2014

Fig. 5 Source location of CMEs producing geomagnetic storms (left) and SEP events (right) (Adapted from Gopalswamy (2009))

Table 1 Major differences between CME-associated and flare-associated events Particles 3 He/4He Fe/O H/He QFe Duration Longitude distribution Solar wind signature Event rate

Gradual Proton rich ~0.0005 ~0.15 ~100 ~14 Days Up to 180 Interplanetary shock ~10 per year

Impulsive Electron rich ~1 ~1.2 ~10 ~20 Hours Up to 30 None ~1,000 per year

coronal and the IP medium via diffusive acceleration (CME-associated gradual events). The difference between both types of SEPs has been now established after nearly two decades of in situ measurements. Table 1 summarizes the major properties of SEPs in both types of events (Kallenrode 2003 and references therein). See also Reames (2013) for a detailed observational study on their source origins. SEPs could be so energetic that they arrive at the Earth only a few minutes after they get accelerated and can affect space weather in two main aspects. (1) The relativistic proton fluxes can easily penetrate instrumentation shielding and cause permanent damage to the sensitive instrumentation as well as create radiation doses that might be hazardous or lethal to unprotected astronauts while traveling in space outside our protective magnetosphere. (2) SEP fluxes may impact the Earth’s middle atmospheric polar caps by producing enhanced ionizations, excitations, and dissociations of atmospheric atoms and molecules that cause, e.g., ozone depletions in the polar upper stratosphere (Schwenn 2006 and references therein). Figure 6 shows a double-halo CME at the Sun followed by an intense SEP enhancement at ACE instruments located at 1 AU. It is these particles that cause radiation hazards to the near-Earth environment and could affect instrumentation as well as astronauts’ health.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_9-1 # Springer International Publishing Switzerland 2014

Fig. 6 (a) A LASCO image of a double-halo CME that lifted off toward Earth on November 22–23 2001. Minutes after, enhanced fluxes of SEPs were observed by GOES satellites in Earth’s geostationary orbits (Credit: NASA, NOAA)

Geomagnetic Storms

Earth is enclosed in a vast space filled with the solar wind and the IP magnetic field that are always flowing outward from the Sun. Interactions between the Earth’s own magnetic field and these global features often cause distortions in the Earth’s geomagnetic field itself (Russell 2000). These distortions can have consequences on the Earth’s atmosphere as well. Northern lights, known as the Aurora, are impressive visual illustrations of the solar windmagnetosphere-atmosphere system interactions. These are caused by enhanced particle precipitation in the polar cusps due to the magnetic divergence in that region providing energy to the upper atmosphere. The geomagnetic field has field lines that are nearly open at the polar regions, extending into the IP medium. When the IP magnetic field turns southward, its field lines can temporarily connect with those of the Earth’s magnetic fields via magnetic reconnection. This process leads to additional open field lines and can move both cusps toward the dayside equator, in addition to injecting more solar wind into the polar regions. If a strong CME sweeps by and there is a southward IP component, two physical processes occur: (1) Magnetic reconnection will allow access of the CME-associated plasma directly into the magnetosphere, and (2) the ICME sheath compresses the magnetosphere as it engulfs it which can cause the magnetopause to move inward. If the field goes southward for a long time during an ICME ejecta or magnetic cloud, the ring current intensifies (the ring current is generated by energetic particle populations in the inner magnetosphere) and generates strong perturbations of the magnetic field on the ground particularly at low latitudes. This increase in geomagnetic activity is known as geomagnetic storms. The strength of a geomagnetic storm is usually monitored by the “Dst index,” which is derived from the instantaneous longitudinal average of the mid-latitude magnetic disturbances. A magnetic storm usually starts with a sudden increase in the geomagnetic field at the Earth’s surface that may last for several hours. This initial phase is followed by a decrease in Dst and a rapid first recovery phase followed by a long, slow second recovery phase. A typical geomagnetic storm lasts between 1 and 5 days (e.g., see Chian and Kamide 2007). It has been established that most geoeffective CMEs are observed as halo CMEs. However, predicting the occurrence and intensity of geomagnetic storms from CME observations is not currently possible. Figure 7 illustrates the effect of CME source locations on the strength of the geomagnetic storms. The figure shows a series of CMEs that arrived at Earth at different angles. The first two from the left originated close to the disc center and arrived at Earth as halo CMEs, causing

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_9-1 # Springer International Publishing Switzerland 2014

Fig. 7 (top) A sequence of CMEs observed by SOHO/LASCO during October to November 2003. (bottom) Dst index variation in response to the CMEs (Adapted from Gopalswamy et al. (2005))

intense geomagnetic effect (Dst indices of 363 and 401 nT). The last two CMEs originated near the west limb of the Sun and were observed as partial halos, causing much less magnetic disturbances. Table 2 Impacts of CME-associated events on the geospace and near-Earth space environment Coronal mass ejections Solar energetic particles Particle radiation Astronaut safety Aircraft crew and passenger safety Solar cell damage Semiconductor device damage and failure Faulty operation of semiconductor devices Spacecraft charging: surface and interior Atmosphere Low-altitude spacecraft drag Attenuation and scattering of wireless signals

Geomagnetic storms Ionosphere variations Induction of electrical currents in Earth Power distribution systems Long communications cables Pipelines Wireless signal reflection, propagation, attenuation Commercial radio and TV GPS systems Magnetic field variations Attitude control of spacecraft Radio direction finding Navigation (compass) Solar radio bursts Interference with radar Excess noise in wireless Communications systems

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_9-1 # Springer International Publishing Switzerland 2014

Effects of SEPs and geomagnetic storms from CME-associated events are manifested in different forms. More effects are becoming significant as the advancement of technology and miniaturized electronics pursues. Proper shielding is becoming a major issue in mission planning design. Table 2 below summarizes the effects of CMEs on space weather (see Lanzerotti 2007).

Conclusion CMEs are massive three-dimensional structures of magnetized plasma that liftoff from the solar corona into the interplanetary medium, often driving shocks and accelerating particles into very high energies. CMEs could cause geomagnetic storms that, along with SEPs, have key consequences on space weather at Earth and in the nearby space environment. We learn about CMEs mainly by remote sensing them during their departure from the Sun and by in situ measurements from instruments onboard spacecraft located in the interplanetary medium. Much of what we know about CMEs comes from the vast progress that was done over the last two decades. This chapter summarized the established properties of CMEs and highlighted their impacts on space weather. Major open CME questions remain, and the current fleet of active spacecraft, along with the anticipated missions over the coming decade, will likely fill some of the gaps in our CME knowledge. Some of these questions are: (1) What causes the CME to lift off and break into the IP medium? (2) How does a CME propagate in the IP space? (3) How can geomagnetic storms and SEPs be used to infer CME properties at the Sun? Space research is advancing fast; current missions are always providing unprecedented details about the Sun. As we progress in solar cycle 24, more CMEs will be observed and more research results will be confirmed. The ultimate goal would be to understand CME formation and propagation and to be able to predict them and provide the proper shielding against their associated hazards.

Acknowledgments The author would like to thank Heather Elliott for her constructive comments on the manuscript. This work was supported in part by NASA Award No. NNX13AE07G.

Cross-References ▶ Advanced Composition Explorer (ACE) (1997) ▶ Coronal Mass Ejections ▶ Medical Concerns with Ionizing Radiation and Radio-biological Effects ▶ NASA Wind Satellite (1994) ▶ Nature of Coronal Mass Ejections and Historical Patterns of their Occurrence ▶ Nature of the Threat / Historical Occurrence ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO) ▶ Solar Flares ▶ Solar Radiation and Spacecraft Shielding ▶ STEREO as a ‘Planetary Hazards’ Mission (1996)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_9-1 # Springer International Publishing Switzerland 2014

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Solar Radiation and Spacecraft Shielding David F. Medina* Directed Energy Directorate, AFRL/RDLE, U.S. Air Force Research Laboratory, Kirtland AFB, NM, USA

Abstract The space environment in the vicinity of spacecraft orbits is replete with a variety of natural and manmade threats from high-speed objects. Setting aside the massive objects such as meteorites and orbital debris, it is apparent that the seeming serenity left behind is still punctuated with a boiling assortment of invisible hazards in the form of high-energy charged particles, plasmas, and electromagnetic radiation. Effects from these can reach down into the atmosphere to high-altitude aircraft, ground technologies, and into the DNA of living systems. Here, focus is made on the spacecraft material itself including effects on the associated subsystems. The fundamental nature, source, and temporal-spatial variation of the radiation environment affecting present and future spacecraft traffic is the subject of much in-depth research but is described broadly in order to conceptualize the hazard. Spacecraft material damage is described as either localized material damage at the atomic level or damage to the overall satellite from charge accumulation and surface erosion. The localized hazards apply mostly to susceptible spacecraft sub-components at the particle level, particularly in solidstate microelectronics composed of miniaturized circuitry. The macro hazards have a broad effect over entire surfaces or can be an accumulation of localized damage over the mission of the spacecraft. Surface erosion and contamination is of less immediate consequence but can be eventually disruptive to mission objectives. The environmental sources and distribution of ionizing radiation are addressed including how they couple to the magnetic fields influencing their trajectories and flux concentrations. Given this background, the topic is concluded by addressing the established methods for radiation hazard avoidance and shielding.

Keywords Solar radiation; Spacecraft susceptibility; Microelectronics; Energetic particles; Coronal mass ejections; Solar flare; Spacecraft damage; Satellite; Galactic cosmic radiation; Shielding

Introduction Mankind’s first successful attempt to reach past the protective blankets enveloping earth occurred with the launch of Sputnik 1, on 4 October 1957 by the USSR. Simultaneous with this reach, however, humanity has had to recoil the other hand into a protective stance when facing the unmitigated brunt of the cosmic radiation environment. Historically, mankind is accustomed to the encroachments of massive objects such as asteroids and large meteorites since they are capable of trespassing, with impunity, our protective atmosphere. Ionizing radiation hazards, on the other hand,

*Email: [email protected] *Email: [email protected] Page 1 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

have been largely ignored prior to the space age since radiation is thankfully ameliorated in an exponential fashion on its way to the earth’s surface. Conversely, the stark vacuum of space is a free range for radiation energy to propagate, subject primarily to magnetic field constraints. The term “radiation,” in this context, serves to distinguish energy and particles of interest that have propagated sufficiently far from their source such that any prescribed spherical boundary through which they pass contains the same amount of energy regardless of the radial extent of the sphere. Modifying the term “radiation” with the term “ionizing” serves to further distinguish those components of the electromagnetic spectrum and subatomic particle population with sufficient energy to liberate or add electrons to the atoms or molecules of the material they strike leaving behind ions with a net electric charge. The most energetic radiation elements can also induce a cascade of secondary particles that can, in turn, be ionizing as well. The high-energy content, along with the charged state of these particles, acts in missile-like fashion to deliver a lethal payload. Principal damage mechanisms to technology include localized disruption of sensitive onboard electronics and computer memory states. This results when ions penetrate into the atomic structure, or when multiple penetrations lead to the accumulation of disruptive charge. Hazards exist on two fronts consisting of the localized atomic-level disruptions and broader effects such as body-wide charge accumulation and radiation ageing. The NOAA Space Weather Prediction Center (Speich and Poppe 2005) summarizes the scope of radiation effects on spacecraft to include: • • • • • • • • • •

Surface charging resulting in electrostatic discharge and/or contaminate accumulation Deep dielectric or bulk charging resulting from relativistic electron penetration Single event effect (SEE) and single event upsets (SEU) in particle penetration Spacecraft drag (3 composing 1 % of GCR flux Negatively charged electrons with a +1 (positron) or 1 (electron) charge and very small mass, electron beta particles moving near the speed of light are called “relativistic” Subatomic hadron particle, neutral charge, designation n0, GCR sources can have energies on the order of several joules Composed of photons at very small wavelengths, the corresponding energy can be approximated as E(eV) ¼ 1.24/l(mm) Produced by nucleon transition, designation, g, wavelengths are 1019 Hz, produced by a variety of causes but in space, principally the result of particle-photon or particle-particle collision Produced by electron orbital transition, wavelength of 0.01–10 nm and frequencies ranging from 3  1016 to 2  1019 Hz At the high UV spectrum, wavelengths in the range of 10–400 nm have sufficient energy to ionize and to break up nuclei

sources. This is discussed more below. Table 1 summarizes the types of particle and electromagnetic radiation, but does not include secondary particles resulting from collisions of space particles with the atmospheric such as pions and muons. These can, nevertheless, present a radiation hazard to high-altitude aircraft (Norbury 2010).

Sources of Radiation Ionizing radiation sources include galactic cosmic radiation (GCR) from outside our solar system and solar particle events (SPE) such as solar flares and coronal mass ejections from our sun. Both sources consist of electromagnetic and particle radiation. The relative abundances of the elemental composition of GCR compared to that of solar origin were compiled from various sources and reported by George et al. (2009) in Fig. 1. The abundance is scaled to silicon ¼ 1,000 which is intermediate in weight. Notable differences are the relative lack of hydrogen and helium from GCR sources and the abundance of light elements (lithium, beryllium, and boron) in GCR which are rare in the solar system.

Solar Contributions Clouds of subatomic particles emanating in sporadic surges from the sun are known as solar particle events (SPE). The US National Oceanic and Atmospheric Administration (NOAA) quantitatively defines SPEs to occur when instruments on the Geostationary Operational Environmental Satellite

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Fig. 1 Solar and galactic cosmic ray (GCR) composition (George et al. 2009)

Fig. 2 Giant prominence erupts 16 April 2013 (Figure Source: NASA)

(GOES) measure an average solar proton flux greater than or equal to ten particles/(cm2 ster s) in three consecutive 5-min periods (Friedberg and Copeland 2011). At these times, peak radiation contributions are a result of localized active regions on and near the sun’s surface often solar flares and coronal mass ejections (CME). The exact nature and precipitating causes of SPE is the subject of ongoing research, but SPEs tend to be random occurrences that vary in severity following the 11-year solar activity cycle. Particle distributions consist of high atomic number and energy (HZE) nuclei, protons, electrons, and other energetic ions. It is thought that HZE particles are accelerated by coronal mass ejections (Kahler 2003), but a causal relationship is still being investigated. The proton flux is the highest component of SPE; however, the energetic “relativistic” electrons constitute a formidable threat capable of penetrating spacecraft shielding and depositing accumulated charge on dielectric materials leading to harmful discharge events (Baker 2005) (Fig. 2).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Solar flares, with the sudden visible brightening, make for dramatic photography and news headlines, but hidden in this light show are ionizing particles and photons beyond the visible spectrum. Non-visible signatures can be detected at the earth’s surface even if the flare occurs on the back or side of the sun’s surface in areas not directly within the line of sight of the earth. After a solar flare occurs, particles start arriving to earth within tens of minutes with peak intensity occurring in a day or two. The ensuing clouds of charged particles, in addition to protons, include energetic electrons with some heavier elements interspersed. Of the heaviest elements such as iron (Z ¼ 26), there are about 27,000 protons for every iron particle (Shea) with similar ratios within one order of magnitude for carbon, nitrogen, and oxygen. In addition to particles, electromagnetic emissions include massless ionizing radiation in the form of X-rays and gamma rays. The ensuing release and acceleration of particles during an SPE can reach fluxes exceeding 100 particles cm2 s1 ster1 with energies greater than 10 MeV with some identified energies as high as 25 GeV. It would take 3  1010 of proton particles at this energy level to equal the kinetic energy of a baseball traveling at 90 mph. From 1970 to 2002, some catalogs record 253 SPEs with energy >10 Mev and peak fluxes of ten protons/cm2 s ster (Kurt et al. 2004). Lest the correct perspective be lost, it should be pointed out that solar flare activity and intensity has been fairly constant in the last ten million years (Shirley) only becoming relevant with the introduction of spaceborne technology.

Galactic Cosmic Sources Galactic cosmic radiation (GCR), originating from outside the solar system, is relatively stable and isotropic but contributes very high-energy particles, above 100 keV, to the total radiation environment. Particles from GCR consist mostly of atomic nuclei stripped of their electrons in the form of protons, alpha particles, and the nuclei of high Z elements. The most abundant particles are hydrogen and helium nuclei with fewer contributions from lithium, beryllium, boron, carbon, nitrogen, and oxygen in decreasing order of abundance. The GCR streams are relatively devoid of electron particles, which have been stripped by the magnetic fields surrounding the supernovae from which they originate (ASTM Special Technical Publication No. 330, Oct 1962). The species distribution of GCR particles is approximately 87 % protons, 12 % alpha nuclei (helium atoms), 1 % heavier nuclei, and 3 % high-energy electrons (Prantzos and Takahashi). The energy levels range from tens of MeV to about 1019 eV (Castellina and Donato 2010/2011), but the peak of the energy distribution is close to 0.3 eV. At these high energy levels, it would now only take 73 particles of 1019 eVenergy to equal the energy of a baseball traveling at 90 mph. The high-energy content can produce showers of secondary particles through the process of spallation as they impact the atmosphere or spacecraft materials.

Plasmas Plasmas in space consist of disassociated protons and electrons in similar quantities resulting in an overall neutral charge but highly conducting. Because the energy content of the plasma particles considered here is lower than particles capable of ionizing, the charge accumulation collects on the surface of exposed spacecraft rather than deeply penetrating. The accumulation of a surface charge can lead to disruptive and lethal electrostatic discharge (ESD) events. The particles which make up the plasmas are on the order of 1 keV for protons in contrast to the energetic particles of tens to Page 5 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

hundreds of keV capable of ion generation. Energy and density variation of the plasma environment ranges from about 0.1 eV and 103–105 particles/cm3 in LEO to 1 eV and 10–1,000 particles/cm3 in the magnetosphere to 1 particle/cm3 and thousands of eV in GEO (Valtonen 2005). Spacecraft surfaces such as solar panels and thermal control surfaces that start with a net positive charge will attract electrons from the plasma. This leads to a parasitic loss of power, surface charging, electrostatic discharge, and surface degradation over long-term exposure. Surface charging can encompass the entire satellite uniformly with a single potential relative to the ambient plasma potential, or it can consist of differential charge over the surface or between surfaces. Primary consequences of imbalanced spacecraft charges include disruption to onboard electronics and anomalous sensor signals but can also include material damage from arching. In addition, charged surfaces will attract contaminates, which affect thermal and optical properties of solar panels and optical sensors (Garrett and Whittlesey 2012). However, ESD was shown to be a primary cause of spacecraft mission anomalies and mission loss across the board of all potential causes. This conclusion was drawn from a survey of the cumulative number of anomaly reports across several agencies and databases (Koons et al. 2000).

Distribution of Radiation in Space Given the charged state of these particles, the spatial ordering in the vicinity of the primary satellite orbits is governed by the earth’s magnetosphere, which also acts as a global shield by attenuating all but the most energetic particles. As the earth’s magnetic field lines converge together near the poles, the amount of shielding decreases, affecting spacecraft in high-inclination orbits. To be expected, along with magnetic repulsion is the confluence of the entrapment potential as well. The Van Allen radiation belt consists of trapped energetic charged particles that follow the earth’s magnetic field lines. The outer belt extends from 12,000 to 25,000 km altitude with a region of high intensity 5,000 km wide centered at an altitude of about 17,000 km. The outer belt consists mostly of electrons and occupies more volume than the inner belt. The inner belt, consisting of mostly protons, ranges from 1,000 to 8,000 km centered at 3,000 km, the region of the highest density of particles. Relative to popular satellite orbits, the majority of the traffic residing in LEO overlaps with the low-altitude portion of the inner Van Allen belt outside of the severest region. Estimates of the total number of active satellites are difficult to obtain but range from 800 to 1,000 with 50 % residing in LEO, 40 % in geostationary orbits (GEO), and the rest dispersed around MEO and other elliptical orbits. The second largest quantity of active satellites, those in GEO, resides at 35,863 km altitude just above the outer belt. Areas of highest concentration are typically avoided by spacecraft. However, flight through the Van Allen belts and into space beyond the geomagnetic shielding is necessary for interplanetary flight. Despite the constraining nature of the earth’s magnetic field lines, the abundance of ionizing particles in the Van Allen belts is by no means static but is continuously relieved and replenished as they interact with the solar activity and neutral particles in the earth’s atmosphere. It is in the regions of highest concentration that disruption to sensitive electronics, disruption to command and control functions, and damage to satellite thermal and power systems and tracking systems are of most concern (Fig. 3).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Fig. 3 Van Allen belts (Figure Source: NASA)

Ionizing Radiation Effects on Electronics The race to achieve ever smaller electronic components is now graded by numbers of atoms. Innovative research has concluded that magnetic data storage unit sizes as small as 12 atoms are already feasible (Loth et al. 2012). As a result, radiation effects must also be resolved on a particleby-particle basis. Single-particle incursions causing an immediate localized effect are known as a single event effect (SEE). The path leading to a SEE begins upon particle penetration leading to the transfer of ionizing energy to the atoms in the electronic materials along its trajectory. This incursion results in the creation of secondary ions, which constitute the mechanism that induces an SEE. SEE encompasses a range of corresponding electrical disturbances (recoverable or permanent) typically in the form of a bit flip in memory or a register. Latch-up can occur when the ion particle charge leads to large currents through the parasitic base regions of integrated circuits. Integrated circuits affected in this manner typically apply the use of complementary metal-oxide-semiconductor (CMOS) technology. The latched region can be permanently disabled through thermal runaway. Nondestructive SEE results in soft errors which are recoverable and do not change the functionality of the device but can disrupt or damage system functionality through a chain of fault events. SEE events can be further categorized into single event upsets (SEU), single event functional interrupts (SEFI), and single event transients (SET). As microelectronic technology advances, new disruptive mechanisms will likely be identified (Maurer et al. 2008). Solar ultraviolet and X-ray radiation have less potential than high-energy particles and gamma rays for deeply penetrating spacecraft skin even during solar flares and are thus not a threat to interior electronics. However, they do play a role in surface degradation of solar panels or other exterior surfaces. Particles, on the other hand, with sufficient initial energy upon entry (>25 eV) to liberate or add electrons to the atoms they strike along their path can have hazardous effects on interior electronics. The depth of penetration is a function of the energy content of the particle. For electrons of 50 keV or less and 1 MeV for protons, the penetration depth into aluminum is on the order of 0.01 mm, and the result is that most of the charge is deposited at the surface. Internal charging requires energies >100 keV for electrons and >5 MeV for protons resulting in penetration depths Page 7 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Fig. 4 Mechanisms for single event effects (Sturesson 2009)

>0.1 mm (Valtonen 2005). The energy density along the strike path transferred into the ionization process is proportional to the energy lost as the particle is slowed along its trajectory into the material medium. As particles skid to a halt, the damage left in their wake includes the disruption of atoms in the medium potentially causing secondary ions. This is depicted in Fig. 4. The metric used to quantify the deposited energy is referred to as the linear energy transfer (LET) expressed as the differential dE/dx with units of keV/mm. The dependency of LET on the density of the traversed material can be taken into account by scaling LET with mass density resulting in LET units of MeV-cm2/mg. Cumulatively these lead to imbalanced charge states that upset the precise electronic states needed for binary control in microelectronics. In silicon, for example, an LET of 97 MeV-cm2 corresponds to a charge deposition of 1 pC/mm (Schwank et al. 2008). In semiconductor materials, silicon in particular, the energy gap or bandgap energy between the conduction band and the valence band is small enough that a few electrons can cross the gap into the conduction band. Radiation energy disrupts this feature by contributing to the creation of electronhole pairs when exciting an electron into the conduction band. The result is a hole left behind in the valence band which sets off a cascade of complex effects leading to a net charge buildup disrupting the state of the circuit. The disruption of the electron-hole pairs is cumulative and dependent on the total ionizing dose (TID) over the duration of the spacecraft mission. Maurer et al. (2008) describes the effects on digital microcircuits as being a result of a shift in metal-oxide-semiconductor (MOS) transistor threshold voltage (related to digital circuit power consumption and speed) from trapped charge. Linear microcircuits are said to exhibit performance changes as input bias current, offset, and drift are affected. Since the characteristics of the penetrating particle into the microelectronic material are initially fashioned by interaction with the spacecraft itself, an end-to-end assessment is necessary with computational methods that take into account the governing principles. The NASA HZETRN (Wilson et al. 1995) is one such code that allows the design engineer to study the effects of various shielding materials on the internal radiation environment of a spacecraft. The prediction of particle impact as a stochastic event warrants the selection of an appropriate probabilistic method such as Monte Carlo for assessing overall risk. Once this is determined, an understanding of the physics of particle interaction can be assessed as a function of material properties and then multiplied by the number of expected events to arrive at the total ionizing dose (TID) accumulated during mission duration. Evaluated together, an end-to-end hazard assessment is possible that enables appropriate protective hardening, operational maneuvers, or other protective measures to be incorporated into the design of shielding concepts and deployment strategies for satellites and space probes.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Spacecraft Charging Spacecraft charging research began in earnest with the launch of the SCATHA (Spacecraft Charging at High Altitudes), which sought to monitor the charging phenomena as a function of the parameters governing the plasma environmental and to detect the corresponding discharge events. Principle findings resulted in an understanding of the interaction of plasma and UV in the charging of dielectric materials and the need for incorporating enhanced conductivity in spacecraft materials (Fennel et al. 1985). Since then, advances in thin polyimide film research have led to specialized treatments such as indium tin oxide (ITO) coating or polyimide modifications such as Conductran™. Lai reports that current observations have further validated theoretical understanding of the critical electron temperature and voltage that delineates the onset of charging as predicted by a Maxwellian model (Lai 2007). Spacecraft charging effects generate the most interest for satellites at geosynchronous orbits. At these altitudes, communication satellites predominate in the presence of higher-energy plasma particles albeit of lower density. The exact plasma boundaries are dynamically influenced by solar events that push against the sun-facing magnetosphere and elongate the opposite side out to hundreds of earth radii. The distortion of earth’s magnetosphere fields is depicted in Fig. 5 obtained from “Planet and Comets” published by the Max Planck Institute for Solar System Research. Also shown are important research satellites (SOHO, Wind, Cluster, Polar, Geotail). For low earth orbits on the other hand, charging is not as much of a concern since the energy content of the plasma is less than an eV. Exceptions to this include spacecraft with differentially charged external components or large aspect ratios that move perpendicular to the magnetic field lines. Depending on the type and energy content of the radiation exposure, surface orientation, and material type, spacecraft charging can take the form of either deep dielectric charging or surface charging. Deep dielectric charging is primarily driven by relativistic electrons capable of deeper penetration than ions of similar energy states. Conductive materials are not affected below the

Fig. 5 Magnetosphere (Figure source: Max Planck Institute for Solar System Research) (http://www2.mps.mpg.de/en/ forschung/planeten/) Page 9 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Fig. 6 Sustained arcing damage on the EURECA solar panel array (Ferguson and Hillard 2003)

surface because penetrating electrons move back to the surface via Coulomb repulsion. However, surface charging can occur for both materials primarily as a result of less energetic particle plasma surface charge deposition. In both cases, detrimental effects can range in severity from electrical disturbances such as noise and anomalous measurements to mechanical damage from electrostatic discharge (ESD). Arching is induced by potential differences of 500 Vor greater. As stated above, ESD was shown to be a primary cause of spacecraft mission anomaly and mission loss across the board of all potential causes as evidenced in the cumulative number of anomaly reports across several agencies and databases (Koons et al. 2000). The Low Earth Orbit Spacecraft Charging Design Handbook (NASA-HDBK-4006) includes a rare photograph example of arc discharge damage sustained on orbit. This occurred on a solar panel on the European Space Agency (ESA) European Retrievable Carrier (EURECA) spacecraft that was recovered by the Space Shuttle (Figs. 6, 7, and 8). Spacecraft charging is mitigated with three basic approaches as described in the Low Earth Orbit Spacecraft Charging Design Handbook (NASA-HDBK-4006). “One is to place the structure at the most positive potential generated by the LEO spacecraft power system (the positive ground option). The second is to ground the structure by brute force to the ambient plasma (the plasma contactor solution). The third is to prevent any plasma exposure of high-voltage conducting surfaces (the encapsulation solution).” Other solutions derived from here are included in Ferguson et al. (2002).

Surface Erosion Damage Mechanical effects are an issue primarily with susceptible external surfaces in direct exposure. Radiation alone is not to blame. A coupled damage process occurs which includes debris impacts, Page 10 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

Fig. 7 Photograph of embrittled and cracked Teflon FEP retrieved from the Hubble Space Telescope (Figure Source: NASA Glenn Research Center)

Fig. 8 NASA image: ISS003E5863 – close-up of the experiment trays in MISSE, open and exposed to space

atomic oxygen interaction, and thermal cycling. Radiation contributes to the damage by inducing embrittlement. Because a majority of these surfaces are covered with various types of metalized polymer films, a great deal of research is focused on the development of resistant materials. This has led to a substantial amount of spacecraft material being composed of polymers and polymeric composites which exhibit favorable multipurpose characteristics. Prominent among the materials used are polybenzimidazole (high-performance fabrics such as space suits), polyimide (cables, multilayer insulation), polyether ether ketone or PEEK (cable insulation, high-vacuum applications), perfluorinated polymers (Teflon®, dielectric applications, coatings), epoxies, and silicones

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

because of their favorable electrical, thermal, and mechanical properties (Bhowmik 2011). Degradation from radiation can include either embrittlement or softening (loss of tensile strength), depending on whether the polymer chains are cross-linked or degraded. In both cases, undesirable outgassing is also a result (Miller 1959). More recently developed polymers include hightemperature polyimide PMR (polymerization of monomer reactants). Radiation induced hardening of the materials can be caused by ionizing particles, vacuum UV, and possibly the X-ray component. Atomic oxygen effects can work synergistically to degrade exposed surfaces already embrittled by radiation. Mechanical effects from particle incursions include regions of disrupted lattice ordering that can affect mechanical properties and point defects which can combine to impede free lattice motion. This results in hardening and embrittlement. An accumulation of individual impacts can exacerbate these effects depending on the type of material and the length of time they are exposed. Particularly susceptible are external multilayer insulation (MLI) surfaces that rely on maximum surface area for effective thermal control. Necessary properties of the surface material are high reflectance, low solar absorptance, and high thermal emittance which are salient properties of optimized films such as MLI Kapton# with vapor-deposited aluminum (VDA) coatings and Teflon fluorinated ethylene propylene (FEP) (Dupont). Surface measurements and detailed microscopy of exposed surfaces retrieved from the Long Duration Exposure Facility (LDEF, 5.8 years in space) experimental satellite in 1990 and the Hubble Space Telescope (3.6 years in space) indicate a synergistic effect between solar-induced embrittlement and atomic oxygen-induced erosion with thermal cycling also playing a role. The mechanism is thought to be enhanced erosion facilitated by a hardened condition (de Groh and Smith 1997; Guo et al. 2012). Starting in 2001, the Materials International Space Station Experiments (MISSE) investigated the response of over 1,500 samples to the space environment. In MISSE 1 and 2, trays consisting of holders for over 750 samples of candidate spacecraft materials arranged side-by-side were affixed to the exterior of the international space station. After up to 2 years of exposure, the samples were retrieved for analysis. Various stages of damage were observed in the plastics and coatings including embrittlement, darkening, and severe erosion. In addition to these localized damage effects, a secondary consequence could be the associated change in reflective properties of external surfaces which is referred to as space ageing. From the perspective of ground observation and tracking functions, the actual optical signature of a spacecraft affected by space ageing will diverge from the expected signature when pristine material conditions are assumed. Validation of mathematical models for predicting spacecraft signatures by comparison with observational data will erroneously differ, particularly around expected specular peaks, depending on the severity and surface area of the aged material. Recognizing this discrepancy, databases of optical properties for aged materials are being assembled (Khatipov 2006). Because of the large trade space available for external MLI blanket design, advanced materials research appears to be the best avenue for hazard mitigation. For highly developed materials composing microelectronics, other mitigating options are needed.

Total Ionizing Dose Rates The accumulation of single-particle events from both GCR and SPE must be taken into consideration over the mission life of spacecraft. Highest dose rates are encountered at geosynchronous altitudes, high-inclination orbits, and the inner radiation belt region, particularly following a major solar flare. Low-inclination orbits allow for better geomagnetic shielding of the GCR and solar radiation sources. The deposition of ionizing energy by a charged particle per time is known as the Page 12 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

dose rate measured as energy per mass per time. In terms of energy loss along the particle trajectory in the material (stopping power), the governing expression, known as the Bethe-Bloch formula, is extensive but has been reduced to a proportionality by Valtonen:

ðdE=dxÞ / nz2 Z = mv2 Where z is the charge number, m is mass, and v is velocity of the impacting particle, n is the number density and Z is the charge number of the medium (Valtonen 2005). Integrating this expression times the particle flux rate over the life of the mission provides the total ionizing dose (TDI). Although the overall dose rate is low for most spacecraft, ranging from 104 to 102 rad/s, the exposure time of typical spacecraft mission lifetimes can accumulate 105 rad depending on incident particle energy and the charge or Z of the particle (Maurer et al. 2008).

Shielding Concepts for Spacecraft The remarkable creativity seen in the development of various radiation shielding concepts invokes an analogy to ancient development of shield and armor defensive concepts against lethal projectiles. However, the simple analogy breaks down when considering the complex nature of radiation effects on spacecraft components. For this reason, decades of research have been required. First steps involve some type of passive shielding. Passive shielding relying on mass to deflect and absorb energetic particles has been the baseline concept for spacecraft radiation protection. Here also, the concept is not simple. Spacecraft shielding itself can contribute to secondary radiation as highly energetic particles transverse the atomic lattice of the shielding material creating secondary radiation. Studies (Kim et al. 1994) have shown that shielding materials composed of the least amount of nucleons (protons and neutrons) such as liquid hydrogen, water, and polyethylene provide more protection from secondary radiation than heavier elements such as aluminum or lead. Low nucleon materials will also minimize the occurrence of bremsstrahlung photons, but the shielding requires increased thickness to simultaneously shield against beta radiation incursion as well. One shielding concept that seeks to achieve high strength while leveraging on the benefits of low nucleon hydrogen suggests the need to apply high hydrogen polymers combined with boron nitride nanotube (BNNT) technology to formulate a composite material suitable for load bearing applications (Thibeault 2012). High-density shielding materials, on the other hand, have the advantage of requiring less volume, which is important in areas of restricted space such as compartments for microelectronic components. Additionally, there is the potential advantage of heat-sink cooling through the superior conductive properties inherent in high-density metals. In terms of electron repulsion, high Z atomic properties make these materials effective at reducing radiation from low-energy electrons and protons because they are more effective at scattering electrons. However, they are less effective at stopping the high-energy electrons and secondary ions resulting from cosmic rays. They also generate higher bremsstrahlung photons. Because of these additional considerations, high-density shielding has little effectiveness at preventing SEE. For now, mitigation of SEE is better achieved by a combination of error detection and correction (EDAC), anomaly detection and reboot, and redundancy. A combination of shielding, derating (intentionally reducing operating parameters such as supply voltage and junction temperature), and operational control is best suited for reducing cumulative ionization and displacement damage (Maurer et al. 2008).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

At first glance, the concept of active shielding against radiation appears futuristic. Active shielding, as opposed to passive shielding, involves dynamic protective measures that require some type of ongoing energetic or informational input to function. These types of shielding concepts have, in fact, been investigated for more than 40 years (Sussingham 1999). Most of the concepts are based on the fundamental property of electromagnetic deflection of charged particles. Initial concepts involved enveloping the spacecraft with an electric or plasma shield but were eventually abandoned for various reasons having to do with the complexity of the required systems. Other notional concepts involve the application of superconductors or artificial magnetospheres, but this is problematic due to high energy requirements. Viable concepts have yet to gain momentum. The achievement of an optimum balance of protective properties is the subject of intense continuing research and model development. But it can be broadly stated that optimization of passive shielding design must consider weight constraints, durability, flexibility, and particle stopping effectiveness to list a few. Simulation of secondary radiation effects has been practically applied to the engineering design of shielding concepts. A combination of first-principles transport codes and Monte Carlo probabilistic codes can address both the statistical nature of the impact and the physical phenomena occurring once the impact has taken place.

Forecasting the Space Environment An important aspect of spacecraft protection is the avoidance of the hazard in the first place. For this to be feasible, our current understanding of space weather requires a significant leap ahead. Having access to accurate space weather forecasts would reduce the need for costly shielding design by allowing overly conservative criteria to be relaxed. However, the advantages extend beyond shielding to include avoidance of continent-wide terrestrial power disruptions. For purposes of spacecraft protection, however, the origin, dynamic evolution, and forecasting of damaging radiation in the vicinity of spacecraft orbits are also an important motivating factor spurring the advancement of the space weather research. As the theoretical basis is better understood, we are gaining a significant hazard-avoidance advantage – the ability to forecast the space weather ahead of time. At present, the physical complexity of the coupled phenomena remains formidable. Normally, with theoretical model development, initial understanding can be gained with the application of empirically based methods, as used by Martin, to understand the magnetic field geometry of CME events (Martin and McAllister 1997). In 1997, the relationship between solar flares and CME was only beginning to be understood (Cane 1997). As the physics basis improves, so does the confidence and flexibility of application to a broader range of weather conditions that can be predicted further into the future. In 2002, Huston reported that uncertainties in the standard AP8 and AE8 models for predicting trapped proton and electron environments were a factor of two and an order of magnitude, respectively, when compared with several sets of flight data (Huston 2002). At the present time, protection schemes are primarily based on conservative designs to withstand the upper threshold of severity. This has functioned well up to now as there are few catastrophic failures among the multiple hundreds of civilian and military spacecraft (Baker 2005). Nevertheless, the ability to forecast space weather will be revolutionary for satellite protection.

Conclusion This chapter covers a broad range of multidisciplinary fields that only scratches the surface of the depth involved in each. However, it provides a bird’s-eye view of the enormity of the task needed to Page 14 of 17

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_10-1 # Springer International Publishing Switzerland 2014

take us to the point where we can forecast space weather as confidently as we do now with atmospheric weather. This is essential for long-term spacecraft protection. Present shield design has relied on conservative estimates, which have served well up to now. In the long term, shield design based on these conservative assumptions will become prohibitively expensive given the population increase in space and heavier reliance on ever-increasing miniaturization of microelectronic systems. High fidelity models based on an understanding of the governing physics will be necessary to optimize shield design and to estimate consequences. While radiation in space threatens the entire satellite, the consensus of research seems to point to microelectronic components (with the exception of biological systems) as the Achilles heel leading to mission failure. Research and development will have to make exponential progress to keep pace with the increasing access and sustainment needs of the space environment.

Cross-References ▶ Biological Hazards from Space ▶ Dashboard Display of Solar Weather ▶ Economic Challenges of Financing Planetary Defense ▶ International Sun Earth Explorers 1 and 2 ▶ International Sun-Earth Explorer-3 (ISEE) (1978) ▶ Medical Concerns with Ionizing Radiation and Radio-Biological Effects ▶ Nature of Coronal Mass Ejections and Historical Patterns of Their Occurrence ▶ NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Flares

References American Society for Testing Materials, committee E-10 on radioisotopes and radiation effects (1962). Space radiation effects on materials. (ASTM special technical publication no. 330) Philadelphia Baker DN (2005) Introduction to space weather. Lect Notes Phys 656:3–20 € Bhowmik S (2011) Effect of radiation and vacuum. In da Silva LFM, Ochsner A, Adams RA (eds), Handbook of adhesion technology (pp. 823–844). Berlin/Heidelberg: Springer Cane HV (1997) The current status in our understanding of energetic particles, coronal mass ejections, and flares. Appearing in the geophysical monograph 99 series, Coronal Mass Ejections, The American Geophysical Union Castellina A, Donato F (2011). Astrophysics of galactic charged cosmic rays. Springer Reference Library. doi:10.1007/978-94-007-5612-0_14 de Groh KK, Smith DC (1997) Investigation of teflon FEP embrittlement on spacecraft in low-earth orbit. NASA Technical Memorandum 113153 Fennel JF, Koons HC, Leung MS, Paul MF (1985) A review of SCATHA satellite results: charging and discharging. Air Force Systems Command (AFSC) report, SD-TR-85-27, 12 Aug 1985 Ferguson DC, Hillard GB (2003) Low earth orbit spacecraft charging design guidelines. NASA/ TP—2003-212287

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Ferguson DC, Hillard GB, Vayner BV, Galofaro JT (2002) High voltage space solar arrays. In: 53rd international astronautical congress of the International Astronautical Federation (IAF), Houston, IAC paper 02 IAA.6.3.03, 10–19 Oct 2002 Friedberg W, Copeland K (2011) Ionizing radiation in earth’s atmosphere and in space near earth. Final report DOT/FAA/AM-11/9, May 2011 Garrett HB, Whittlesey AC (2012) Guide to mitigating spacecraft charging effects, 1st edn. Wiley, Hoboken, # 2012 John Wiley & Sons George JS et al (2009) Elemental composition and energy spectra of galactic cosmic rays during solar cycle 23. Astrophys J 698:1666. doi:10.1088/0004-637X/698/2/1666 Guo A et al (2012) Embrittlement of MISSE 5 polymers after 13 months of space exposure. NASA/ TM—2012-217645, Sept 2012 Huston SL (2002) Space environments and effects: trapped proton model. NASA/CR-2002-211784 Kahler SW (2003) Energetic particle acceleration by coronal mass ejections. Adv Space Res 32(12):2587–2596 Khatipov SA (2006) Simulated aging of spacecraft external materials on orbit. In: Advanced Maui Optical and Space Surveillance (AMOS) technologies conference, Maui, Hawaii, 2006 Kim MY et al (1994) Performance study of galactic cosmic ray shield materials. NASA technical paper 3473, Nov 1994 Koons JE et al (2000) The impact of the space environment on space systems. In: 6th Spacecraft charging technology conference, Hanscom air force base, Massachusetts, 1 Sept 2001 Kurt V et al (2004) Statistical analysis of solar proton event. Ann Geophys 22:2255–2271 Lai ST (2007) Spacecraft charging – present situation and some problems. In: AIAA plasmadynamics and lasers conference, 28 June 2007, Miami, Fl Loth S et al (2012) Bistability in atomic-scale antiferromagnets. Science 335(6065):196–199. doi:10.1126/science.1214131 Martin SF, McAllister AH (1997) Predicting the sign of magnetic helicity in erupting filaments and coronal mass ejections. Coronal mass ejections, geophysical monograph 99, The American Geophysical Union Maurer RH, Fraeman ME, Martin MN, Roth DR (2008) Harsh environments: space radiation environment, effects and mitigation. John Hopkins APL Techn Digest 28(1):17–29 Miller AA (1959) Effects of high-energy radiation on polymers. Ann N Y Acad Sci 82:774–781. doi:10.1111/j.1749-6632 NOAA Space Weather Prediction Center Space weather prediction center topic paper: satellites and space weather. http://www.swpc.noaa.gov/info/Satellites.html Norbury JW (2010) Pion production data needed for space radiation. In: 40th international conference on environmental systems, Obtained from NASA Technical Reports Server (NTRS), 12–15 July 2010 Prantzos N, Takahashi J Cosmic rays (in the Galaxy). Springer Reference Library Schwank JR, Shaneyfelt MR, Dodd PE (2008) Radiation hardness assurance testing of microelectronic devices and integrated circuits: radiation environments, physical mechanisms, and foundations for hardness assurance. Sandia National Laboratories Documents, SAND-2008-6851P Shea MA Solar particle events. Springer Reference Library Shirley JH Solar flare. Springer Reference Library Speich D, Poppe B (2000) Space environment topics, satellite anomalies, space environment center, Boulder Co. Sturesson F (2009) Single Event Effects (SEE) mechanisms and effects. EPFL Space Center

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Sussingham CJ (1999) Forty years of development of active systems for radiation protection of spacecraft. J Astronaut Sci 47(3 and 4):165–175 NASA Technical Handbook, The Low Earth Orbit Spacecraft Charging Design Handbook (NASAHDBK-4006), (6 Jun 2007). https://standards.nasa.gov/documents/detail/3315626 Thibeault S (2012) Radiation shielding materials containing hydrogen, boron, and nitrogen: systematic computational and experimental study – Phase I, NIAC final report, 30 Sept 2012 Valtonen E (2005) Space weather effects on technology, in space weather: the physics behind a slogan. In: Scherer K, Fichtner H, Heber B, Mall U (eds), Lecture notes in physics, 656, pp. 241–274. Springer-Verlag, Berlin Heidelberg Wilson JW et al (1995) HZETRN: description of a free-space ion and nucleon transport and shielding computer program. NASA technical paper 3495

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NASA Wind Satellite (1994) Adam Szabo* Heliospheric Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA

Abstract The NASA Wind spacecraft, launched in November 1994, provides comprehensive and continuous in situ solar wind measurements while orbiting the Sun–Earth first Lagrange point upstream of Earth. The spacecraft has a full complement of instruments to measure the local magnetic and electric fields and thermal solar wind and high-energy charged particles at unprecedented high time resolutions. After nearly 20 years of operation, the spacecraft and most instruments are fully operational, and Wind is expected to remain in service for many years to come. While Wind provides real-time solar wind measurements for only about 2 h every day – thus it is not considered an operational space weather monitor – the high-quality and continuous Wind observations have been critical in developing current space weather forecasting techniques. In particular, Wind observations led to better understanding of the propagation and evolution of coronal mass ejections quantifying their distortions and deflections. Wind radio science results significantly added to the understanding of the inner heliospheric propagation of interplanetary shocks and high time resolution field and particle measurements revealed the mechanisms of how these shocks and magnetic reconnection can accelerate charged particles to very high and harmful energies. Wind is expected to continue its contribution to the development of future space weather forecasting capabilities as its measurements near two complete 11-year solar cycles allowing the identification of long-term trends.

Keywords Wind spacecraft; Solar wind; Interplanetary magnetic field; First Lagrange point; Coronal mass ejections; Magnetic cloud; Magnetic flux rope; Interplanetary shocks; Solar energetic particles; Solar flares; Magnetic reconnection; Heliosphere; Magnetosphere; Bow shock; Space weather; Type II radio burst; Solar cycle

Introduction NASA launched the Wind spacecraft in November 1994 to the Earth’s first Lagrange point (L1) as the interplanetary component of the Global Geospace Science (GGS) program within the International Solar Terrestrial Physics (ISTP) program. An orbit around the L1 point, upstream of Earth, toward the Sun, and four times further away than the Moon, provides a unique opportunity to observe the undisturbed solar wind before it impinges on the Earth’s magnetosphere (see Fig. 1). The original science objectives of the Wind mission were (1) to make accurate in situ measurements of interplanetary conditions upstream of the magnetosphere to complement measurements made inside

*Email: [email protected] Page 1 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 1 Artist depiction of the Wind spacecraft orbiting the Sun–Earth first Lagrange point observing the incoming solar wind. The two long booms hold the magnetometers and the four wire antennas, and two axial booms measure the electric magnetic field waves. The other instruments are housed inside of the spacecraft body

the magnetosphere by the Polar and Geotail spacecraft, other elements of the GGS program, and (2) to remotely sense interplanetary disturbances for possible future predictive purposes. The spin-stabilized Wind spacecraft – spin axis aligned with ecliptic south – carries eight instrument suites that provide comprehensive and continuous measurements of the thermal solar wind to solar energetic particles, quasi-static magnetic and electric fields to high-frequency radio waves, and g-rays. After nearly 20 years of operation, Wind is still returning all of these measurements that became essential for solar wind studies and serves as 1 AU baseline for deep space (inner and outer heliospheric) missions and as a reliable input for magnetospheric investigations long after the termination of the GGS and ISTP programs. The sections below review the rich contributions of the Wind mission to the subject of understanding the structure and propagation of coronal mass ejections (CMEs), interplanetary shocks, and corotating interaction regions (CIRs) and to the acceleration and transport of solar energetic particles (SEPs).

The Orbit of the Wind Spacecraft The first Sun–Earth Lagrange point, on the Sun–Earth line between the two objects, marks the position where the combined gravitational pull of the Sun and Earth provides precisely the centripetal force required to orbit with them. Thus a satellite at L1 will have a heliocentric orbit with a slightly smaller orbital radius but the same angular speed as Earth. In effect, the spacecraft will appear from Earth to be motionless, hovering 1.5 million km (or four times further than the Moon) upstream of Earth. In practice, the L1 Lagrange point – named after the eighteenth-century Italian mathematician and astronomer Joseph-Louis Lagrange – is not stable due to the eccentricity of the Earth’s orbit and other forces. Neither is it desirable to park a spacecraft exactly on the Sun–Earth line, making communication with it difficult due to intense radio emissions from the Sun. Fortunately, there exists a class of semi-periodic – not exactly repeating but bounded by a box – orbit around L1, called a Lissajous orbit that keeps the spacecraft outside of a 3–4 solar radio exclusion region, yet keeps it continuously upwind from Earth with minimal orbit correction requirements.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 2 The complex orbit of the Wind spacecraft between 2001 and 2004 in ecliptic coordinates. The plot is centered on Earth with the Sun to the left. The lunar orbit is marked by blue dashed lines

The Wind spacecraft was only the second mission to take advantage of this kind of an orbit after the very successful ISEE-3 mission (1978–1982). After a number of petal orbits and a double lunar swingby, Wind reached L1 in 1996. However, it did not stay in the vicinity of L1 for long as it was soon joined there by the Advanced Composition Explorer (ACE), another NASA solar wind mission. With Wind’s very large fuel reserve and with its spin axis perpendicular to the ecliptic (ACE’s spin axis is pointing at the Sun in constant need of realignment as the spacecraft is orbiting around the Sun), it was decided to relocate the Wind spacecraft to various, scientifically advantageous locations. In 1999 Wind executed a number of magnetospheric petal orbits that took it to the rarely sampled geomagnetic high latitudes. Between 2000 and 2002, Wind moved further and further away from the Sun–Earth line (and from ACE) reaching 2.3 million km to the side in a distant prograde orbit (see Fig. 2). Finally in 2003 it completed a second Lagrange (L2) point campaign, taking the spacecraft more than 1.5 million km downstream of Earth and ~3 million km downstream of ACE, to investigate solar wind evolution and magnetotail phenomena. Since 2004 Wind has remained at L1 in a Lissajous orbit bounded by +/ 600,000 km perpendicular to the Sun–Earth line in the ecliptic and +/ 120,000 km perpendicular to the ecliptic. It should be noted that this is a very large orbit as the maximum radius of the Earth’s geomagnetic tail is only around 150,000 km. Thus, propagating solar wind observations to Earth is a nontrivial task. The Wind spacecraft has enough fuel left to maintain its current orbit for almost 60 more years.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Spacecraft Design Wind was designed and manufactured by Martin Marietta of Astro Space Division in East Windsor, New Jersey. The satellite is a spin-stabilized cylindrical satellite with a diameter of 2.4 m and a height of 1.8 m (see Fig. 1). It has an approximately 3 s rotation period. With its 1,150 kg mass, two 50 m and two 7.5 m wire antennas, and two 12 m lanyard booms, the spacecraft has an immense angular momentum, rendering it an extremely stable platform, ideal for long-term, continuous solar wind measurements. Wind has body-mounted solar panels, only some of which see the Sun at any given time. At the beginning of the mission, the solar panels generated 472 W of power with a 100 W margin that allowed for ample aging degradation. The spacecraft will be able to operate all its subsystems simultaneously at least for the next 10 years. The instruments record their measurements to a tape deck, from which it is read back at high speed, nominally once a day for 2 h. This downlink telemetry takes place via an S-band system to the NASA Deep Space Network (DSN) at 64 kbps.

Instrumentation The Wind spacecraft carries eight instrument suites that provide comprehensive measurements of the solar wind thermal particles to solar energetic particles, quasi-static electromagnetic fields to high-frequency radio waves, and g-rays. Table 1 lists all of these instrument suites and their capabilities and current status. Wind’s complement of instruments was optimized for studies of solar wind plasma, interplanetary magnetic field, radio and plasma waves, and low energetic particles. The instrument suite is not equivalent to that on ACE, rather the two missions complement Table 1 The Wind spacecraft instrument suite and its current status Instrument Magnetic field investigation (MFI) Solar wind experiment (SWE) 3D plasma experiment (3DP)

Description Slowly varying vector magnetic fields (0–64,000 nT, 0–5.5 Hz) Density, velocity, and temperature of solar wind thermal ions (150 eV–8 keV) and electrons (5 eV–24.8 keV) Full 3D distribution function of solar wind ions and electrons (3 eV–30 keV) Energetic ions (25 keV–11 MeV) and energetic electrons (20 keV–1 MeV) Electric and magnetic field waves (0.3 Hz–14 MHz)

Radio and plasma wave experiment (WAVES) Suprathermal particle Suprathermal ions (H–Fe) in the energy range experiment (SMS) (0.5–226 keV/e)

High-energy particle Energetic particles (0.04–500 MeV/nuc) experiment (EPACT) KONUS High-time resolution gamma-ray detector Transient gamma-ray High spectral resolution gamma-ray detector in the spectrometer (TGRS) energy range 15 keV–10 MeV

Status Fully operational Ion sensors fully operational. Electron measurements limited to energies below 5 keV Fully operational

Fully operational

The low-energy SWICS sensor is not operational The STICS and MASS sensor fully operational Only the lower-energy detectors LEMT and STEP are operational (0.04–10 MeV/ nuc) Fully operational All the coolants used up. Instrument turned off

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

each other. Wind is the only near-Earth spacecraft capable of making remote radio wave measurements and hence tracking interplanetary shocks from the Sun to Earth. Moreover, Wind provides solar wind measurements with an unprecedented accuracy. It measures solar wind particle densities with three different instruments (SWE, 3DP, and WAVES) relying on different measurement techniques. Intercalibrating these three observations yields an absolute accuracy of better than 1 %. Wind also provides the highest time resolution measurements in the near-Earth environment (11 vectors/s for magnetic field and a 3 s cadence for plasma observations). Finally, Wind has accumulated solar wind observations for nearly two complete solar cycles (a solar magnetic cycle is ~11 years long). Thus, Wind is ideally positioned to study solar wind transients that have adverse space weather effects.

The Ambient Solar Wind The visible surface of the Sun, the photosphere, is at an effective temperature of 5,800 K, and it continuously emits charged particles called the solar wind. This solar wind – composed mostly of protons and electrons, 4 % (by number) helium nuclei (alpha particles), and traces of heavier ions – is heated to over a million degrees of Kelvin in the solar corona, 2,000 km above the photosphere. The solar wind particles are not only heated but also accelerated to 200–800 km/s of speed dragging with them the magnetic field of the Sun. This enormous speed (a fast bullet can reach 1 km/s and the fastest spacecraft launch ever was 16.26 km/s for New Horizon, a mission to Pluto) is faster than information can travel in this medium. Thus, as the solar wind flow approaches obstacles (like planets), information cannot flow upstream fast enough to divert the particles and they pile up forming a shock wave, not unlike a sonic boom in front of a supersonic airplane. In the case of Earth, this shock wave, called the bow shock, forms around 100,000 km, or 15 Earth radii upstream, toward the Sun. At this boundary, the solar wind particles abruptly slow down and change direction to flow around the planet (see Fig. 3). The Earth is a magnetized planet; thus, the obstacle that the solar wind plasma reacts to is not the surface of the planet, but its magnetic field that charge particles cannot cross. In turn, the shocked solar wind flowing around the planet compresses the Earth’s magnetic field into a large bubble, called the magnetosphere, till an energy balance is reached between the kinetic energy of the incoming solar wind flow and the magnetic energy of the magnetosphere. This energy balance boundary, the magnetopause, is just above 60,000 km at the subsolar point. Solar wind particles cannot cross through the magnetopause and thus cannot reach the surface of the Earth except near the magnetic poles where the vertically oriented magnetic field lines can exert only minimal pressure. But even at the magnetic poles, the extremely low-density solar wind of 10 particles per cubic centimeter (compared to 6  1023 particles/cm3 of the surface atmosphere) is quickly absorbed by the neutral atmosphere posing no danger to humankind. Therefore, it is not the ambient solar wind that represents a cosmic hazard. Rather, the large transients embedded in it that cause rapid variations in the compression of the magnetosphere are the chief culprit. These transients are discussed in the next sections.

Coronal Mass Ejections (CMEs) Coronal mass ejections (CMEs) are the most hazardous solar transients for man-made systems like electric power grids or oil pipelines. Sometimes as frequently as several times a day, but at least once every couple of weeks, the Sun ejects an extra dose of charged particles. Most of these CMEs Page 5 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 3 Artist rendition of the solar wind flowing around the Earth’s magnetosphere. The blue lines represent plasma flow directions. The yellow lines connected to Earth are magnetic field lines (Courtesy of K. Endo and Prof. Yohsuke Kamide)

originate from active regions on the Sun’s surface, such as groupings of sunspots associated with frequent solar flares. These regions have closed magnetic field lines, in which the magnetic field strength is large enough to contain the plasma. These field lines must be broken or weakened – probably via magnetic reconnection – for the plasma to escape from the Sun. The released CMEs have a wide range of velocities between 20 and 3,200 km/s. The slower ones are accelerated and the fast ones are decelerated by the solar wind so that by 1 AU the range of their speeds is much smaller. It takes between 1 and 3 days for them to reach Earth. Even though the average ejected mass in a CME is a staggering 1.6  1012 kg, it is the embedded magnetic field that is responsible for most of the geomagnetic response. CMEs expand their volume faster than the ambient solar wind – the solar wind expands nearly spherically resulting in a 1/r2 reduction in the solar wind density – thus by 1 AU their internal particle density is typically comparable or smaller than that of the ambient solar wind. However, the embedded magnetic field strength is several times – up to an order of magnitude – larger than the 1 AU interplanetary magnetic field. This extra field pressure compresses the Earth’s magnetosphere. Moreover, the CME internal magnetic field often takes a helical flux rope geometry – referred to as magnetic clouds (MCs) – with prolonged periods of large, ecliptic southward-pointing components. When squeezed against the northwardoriented subsolar magnetic field of Earth, they reconnect (cancel), weakening the internal magnetic pressure in the magnetosphere and thus rapidly further compressing the surface magnetic fields. These rapid magnetic fluctuations generate current in all conducting materials like a giant alternator. The amount of excess current generated is proportional to the length of the conducting material. Thus, electric power grid lines and oil pipelines that can span multiple states will experience the most excess current flows overloading transformers and weakening welding lines. Therefore, it is imperative to develop a forecasting capability that can accurately predict the arrival of the largest of these CMEs.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Current space weather monitoring spacecraft at L1 (like the ACE spacecraft or the future Deep Space Climate Observatory, DSCOVR) provide 15–45 min of warning time by measuring the local or in situ signatures of an incoming CME. To expand the forecasting interval to 1–3 days, the initiation of CMEs near the Sun has to be observed remotely and the propagation of these CMEs to 1 AU accurately modeled. The primary contribution of the Wind spacecraft to CME forecasting is in the area of developing these CME propagation and evolution models. While there is a very good correlation between CMEs at 1 AU and coronal CMEs (Gopalswamy et al. 2000) observed by white light coronagraphs, the reverse is not true. Even when limiting the study to only front-side full-halo CMEs, Michalek et al. (2004) found that only 83 out of 123 solar events had discernible 1 AU counterparts. What happened to a third of the CMEs? Were they processed by the solar wind so much that they became indistinguishable from the background flow? Or were they deflected by an unusual amount so that they missed Earth? Measurements made by Wind and other spacecraft give us some clues. Not every visible light CME observed near the Sun will maintain its dangerous magnetic flux rope topology by the time it reaches 1 AU. These irregular ejecta can still be identified by the Wind spacecraft by counter-streaming heat flux electrons, electrons with slightly more energy than the average solar wind component. These heat flux electrons travel faster than the solar wind but follow very precisely the interplanetary magnetic field lines. Thus, no matter what geometrical shape the CME takes at 1 AU, as long as both foot points of the internal magnetic field lines are still encored to the Sun, heat flux electrons will travel in both directions clearly delineating the CME from the ambient solar wind where only one end of the field lines is connected to the Sun, and thus heat flux electrons flow only in one direction. By identifying these irregular ejecta, the Wind measurements clearly identify that these CMEs dissipated harmlessly. What internal or external condition determines whether a CME dissipates or not is the subject of ongoing research. The most harmful CMEs preserve their magnetic flux rope configuration to 1 AU. However, even these powerful transients can be distorted by the ambient solar wind, changing their magnetic impact on the Earth system. Traditionally, CMEs are drawn as large horseshoe-shaped structures with embedded helical magnetic fields, with the field wound up much more near the surface and axial near the center (see Fig. 4). In contrast, STEREO white light images appear to show significant pancaking, not unlike some magnetohydrodynamic numerical simulations suggest (see Fig. 5). However, Wind magnetic field observations can be fitted rather well with simple circular crosssection flux rope models. In fact, even simultaneous three-spacecraft 3D reconstruction of the CME internal magnetic field lines, using magnetic field measurements from Wind and the two STEREO spacecraft, shows very little geometrical distortions. A recent, multi-spacecraft study has solved this dilemma by demonstrating that the white light images suffer from projection effects that make the CMEs look much more elongated than they are (Nieves-Chinchilla et al. 2012). This is a significant result, as it shows that those CMEs that do not dissipate will likely retain their near-circular cross section allowing more reliable forecasting. The shape of CMEs in the third dimension, along their symmetry axis, is much more difficult to observe at 1 AU. There are only a handful of fortuitous in situ observations of the same CME by multiple, well-separated spacecraft, as the CME has to lie nearly perfectly in the ecliptic and propagate toward Earth, a situation that happens only very rarely. But for these few cases, it has been shown that CMEs can twist and change the direction of their propagation significantly before reaching Earth (Möstl et al. 2012). Particularly during maximum solar activity years, when multiple CMEs are ejected in close proximity to each other, CMEs can interact with each other significantly deflecting their propagation. While multi-spacecraft observations cannot be relied on as a space

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

SUN CME

Magnetic Cloud

EARTH

Fig. 4 The idealized horseshoe shape of a CME magnetic flux rope. The internal magnetic field lines follow a helical direction with less and less winding toward the center of the structure (After Marubashi 1997)

Fig. 5 Global magnetohydrodynamic simulation of the evolution of a CME in the inner heliosphere. The injected CME is shown as an iso-surface at 25 % of maximum density. The color scale shows the flow velocities on the iso-surface and from the solar source surface. The small blue box toward the left of the figure shows the Earth’s position (Odstrcil et al. 2004) Page 8 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

weather forecasting technique, these cases serve as benchmark events for numerical and empirical space weather prediction models. Further insight into the global geometry of CMEs can be obtained using energetic particles as magnetic field line tracers. Solar flares, sudden releases of very energetic particles in the solar atmosphere, spew out simultaneously charged particles at different energies, thus speeds. If the flare happens at the foot point of the CME, the released energetic particles will follow the internal magnetic field lines of the CME with the more energetic and faster particles reaching the 1 AU observer – in this case the Wind spacecraft 3DP instrument – before the slower ones. The start of the energetic electrons is marked by a type III radio burst with the radio signal traveling in a straight line at the speed of light and measured by the Wind spacecraft radio antennas. Using these time differences, the length of the magnetic field lines from the Sun to 1 AU can be computed with great accuracy and compared to the predictions of helical flux rope geometry models. Such studies resulted in good agreements deep inside the CME, but not near the boundary (Kahler et al. 2011). This implies that, in addition to deflection and distortion, CME surface magnetic fields also reconnect with the ambient interplanetary magnetic fields, in effect peeling away one layer at a time of their structure. Thus, wind measurements, together with other spacecraft, have enabled the identification of the key processes of CME interplanetary propagation and evolution. It remains to distill these results into a space weather prediction model.

Interplanetary Shocks Besides CMEs any sudden pressure increase in the solar wind can compress the Earth’s magnetic field with negative consequences. Especially effective are interplanetary shocks where fast-moving solar wind streams overtake slowly moving parcels with a speed difference greater than any of the plasma wave mode speeds. At shocks, the plasma of the fast-moving stream piles up against the slow stream resulting in a density jump of up to a factor of four in a few seconds. Fast-moving CMEs can act like fast-moving pistons driving an interplanetary shock in front of them. Another source of interplanetary shocks is corotating interaction regions (CIRs) where a stream of fast solar wind overtakes a parcel of slow solar wind that was emitted from the Sun at an earlier time. During solar activity minimum years on the Sun, when the solar magnetic field is nearly dipolar, the Sun emits fast (~800 km/s) solar wind at high latitudes and much slower winds (300–450 km/s) near the magnetic equator (see Fig. 6). Since the magnetic dipole axis of the Sun is tilted with respect to its rotation axis, as the Sun rotates, fast streams are emitted behind slow parcels near the fast–slow wind boundary. These fast streams running into slow ones form CIRs, often steepening into fully formed shocks by 1 AU. During solar maximum years, the picture becomes much more complicated with fast and slow streams intermingling at all latitudes (see Fig. 6). Current global heliospheric models can accurately predict the arrival of CIR compression regions at Earth with about 3 days of warning time. Forecasting the arrival of CME-driven shocks is much more complicated. Moreover, unlike CIR shocks that are almost always aligned with the local Parker spiral direction (about 45 relative to the Sun–Earth line at 1 AU), CME-driven shocks can have almost any orientation. This introduces a large uncertainty in the predicted arrival times at Earth even from the L1 monitors (like ACE). As mentioned above, the L1 monitors orbit the L1 point that takes them several times further to the side than the diameter of the magnetosphere. For nonradially aligned structures, this requires the determination of the orientation of these fronts. Local surface normals can be computed based on the in situ measurements; however, these directions reflect the Page 9 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 6 Solar wind observations collected by the Ulysses spacecraft during two separate polar orbits of the Sun, 6 years apart at nearly opposite times in the 11-year solar cycle. Near solar minimum (left), the slow solar wind is limited to low latitudes. Near solar maximum (right), the fast and slow streams are more intermingled (Courtesy of Southwest Research Institute and the Ulysses/SWOOPS team)

small ripples on the shock surfaces, not their global orientation. Multi-spacecraft techniques have been successfully employed, combining measurements from Wind, ACE, SOHO, and the Genesis spacecraft, to reduce the prediction uncertainty from 10–15 min to 1–2 min. However, this technique does require four simultaneous real-time solar wind monitors to operate upstream of Earth. Fortunately, interplanetary shocks are strong radio emitters. The shocks accelerate electrons locally. The faster electrons race ahead, creating a plasma instability that through nonlinear wave–wave interactions produce the so-called type II radio emissions at the local electron plasma frequency and at its second harmonic. As the shock propagates away from the Sun and the local solar wind density drops, the frequency of these type II radio bursts also decreases. The radio receivers on-board the Wind spacecraft observe these radio signals (see Fig. 7) and thus are able to track shocks from the Sun all the way to 1 AU. Moreover, since the Wind spacecraft rotates in the ecliptic plane, it can determine the direction from which the signal is emanating (like a rotating radar dish). Combining the Wind radio measurements with those on STEREO, the signal can even be precisely triangulated to yield an exact location in space for each radio burst. The only unknown in this observational scheme is the precise radial solar wind density profile. Using global magnetohydrodynamic solar wind simulations to obtain the required solar wind density profiles and combining it with STEREO and SOHO white light images, the best current techniques are able to predict the arrival times of these shocks with an error bar of no more than a few hours, 1 or 3 days in advance. Current research is focusing on an interesting subclass of interplanetary shocks that are radio loud near the Sun – that is they produce a well-discernible type II radio emission – but result in no

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 7 Radio spectrogram of the August 24–27, 1998, CME observed by the Wind spacecraft. Red color represents high-intensity emissions. Shortly after 21:00 UT on August 24, the bright feature covering the full frequency range is a type III burst associated with a solar flare. The slowly descending feature is the type II burst related to the outwardpropagating CME-driven shock. The shock reaches the Wind and Earth just before 9:00 on August 26 (Courtesy of the Wind/WAVES team)

observable solar wind compressions in near-Earth, in situ measurements. It is postulated that these shocks somehow have deflected and completely missed Earth (Gopalswamy et al. 2012).

Solar Energetic Particles (SEPs) CMEs ringing the Earth’s magnetosphere are not the only space weather dangers emanating from the Sun. The Sun is also the source of a very wide energy spectrum of energetic particles – called solar energetic particles (SEPs) – ranging from tens of keV to well above 100 MeV. Besides solar flares directly injecting energetic particles onto interplanetary magnetic field lines just above the photosphere of the Sun, interplanetary shocks, discussed in the previous section, produce copious amounts of energetic ions and electrons as they propagate outward. While only the most energetic (~1 GeV) SEPs can reach the surface of the Earth due to the deflection of most charged particles by the protective magnetosphere, they represent a significant danger to astronauts, especially during future deep space missions. Also, SEPs cause havoc in modern satellite microelectronics causing memory bit flips, single-event upsets, and latchups that can significantly harm these components. Due to their near-speed-of-light velocities, SEPs arrive to the vicinity of Earth from the Sun in mere 15–30 min. Thus, viable forecasting schemes rely on remote observations of flares and interplanetary shocks. Tracking interplanetary shocks in the inner heliosphere has been discussed in the previous section. However, knowing the location and speed of a shock is insufficient to accurately predict SEP production rates. In fact, the precise physical mechanisms involved in SEP generation at shocks are not fully understood. The high time resolution solar wind measurements of the Wind spacecraft have recently resulted in a number of discoveries related to the acceleration of charged particles at interplanetary shocks. Analytical studies of the behavior of charged particles at solar wind shock discontinuities derived that the most energetic SEPs would have to be generated at shocks with such large jumps in density and magnetic field strength that are very rarely observed. Yet, even moderate-size shocks appear to be capable of producing harmful SEPs. In observing interplanetary shocks at 1 AU, Wind measurements revealed that shocks often are composed of multiple up/down steps or shocklets (see Fig. 8 Page 11 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 8 (Upper) Overview of the magnetic field profiles of a series of shocklets and SLAMS observed by Wind/MFI at an interplanetary shock. The green shaded region corresponds to the time period for the lower panel. (Lower) Ion velocity distribution showing contours of constant phase-space density (bulk flow frame) in the plane containing the average magnetic field direction (along the horizontal) and the solar wind velocity vector Vsw. Red peaks left of the plot center show accelerated ions (After Wilson et al. 2013)

upper panel). In observing the charged particles concurrently, evidence was found for diffusive shock acceleration (see Fig. 8 lower panel), whereby particles gain energy by traversing a shock ramp multiple times and diffuse in pitch angle and energy by scattering off of upstream and downstream shocklets or large fluctuations (Wilson et al. 2013). This process enables weaker shocks to still produce higher energy particles. Particularly effective are shock–shock interactions to produce copious amount of energetic particles. Catching the moment of interaction between two extremely fast-moving shocks in interplanetary space is highly unlikely. However, the Wind spacecraft, in cooperation with other near-Earth assets, can readily observe the moments when an interplanetary shock impinges on the Earth’s bow shock. It appears that one shock starts the acceleration process of the particles creating a pool of seed population that the second shock further accelerates to the higher energy ranges. In

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

effect, the two shocks as they collide form a magnetic trap that is particularly efficient at accelerating charged particles. Finally, Wind observations also shed some light on how magnetic reconnection in solar flares accelerates particles. Magnetic reconnection also operates in the 1 AU solar wind, though it is not nearly as energetic of a process as in solar flares. But 1 AU magnetic reconnection is readily observable by the Wind spacecraft. It appears that magnetic field lines do not have to be oriented precisely in the opposite direction in order to reconnect. In fact, component reconnection is much more prevalent than full magnetic cancelation (Gosling 2007). Wind observations also established that electron two-stream instability is the physical mechanism responsible for transferring magnetic energy of the reconnecting field lines to particle acceleration (Malaspina et al. 2013). These Wind observations and results pave the way for future predictive capabilities of SEP generation and forecasting.

Conclusion Over the past 20 years, the Wind spacecraft has collected valuable observations of the 1 AU solar wind, impinging on the Earth’s magnetosphere to advance our space weather prediction capabilities. Making most of its measurements while orbiting the Sun–Earth first Lagrange (L1) point, Wind has been collecting a comprehensive set of solar wind data at an unprecedented time resolution. The mostly multiply redundant instrumentation on the spacecraft has enabled in-depth studies of the structure and evolution of CMEs, interplanetary shock, and of the physical processes of particle acceleration at shocks and magnetic reconnection sites. Moreover, Wind radio wave observation of type II radio bursts generated by interplanetary shocks heading toward Earth has paved the way for future operational space weather forecasting capabilities with multiday lead times. The Wind spacecraft and its complement of instruments are still fully operational with enough fuel to maintain its current L1 orbit for nearly 60 years. Current NASA plans call for many more years of operations of this venerable spacecraft, most assuredly leading to more groundbreaking scientific discoveries.

Cross-References ▶ Advanced Composition Explorer (ACE) (1997) ▶ Coronal Mass Ejections ▶ Coronal Mass Ejections and their Cause and Nature ▶ Early Solar and Heliophysical Space Missions ▶ Interplanetary Monitoring Platforms (IMP) ▶ ISAS-NASA GEOTAIL Satellite (1992) ▶ Nature of Coronal Mass Ejections and Historical Patterns of Their Occurrences ▶ POLAR ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ STEREO as a Planetary Hazards Mission

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_13-1 # Springer International Publishing Switzerland (outside the USA) 2014

References Gopalswamy N, Lara A, Lepping RP, Kaiser ML, Berdichevsky D, St. Cyr OC (2000) Interplanetary acceleration of coronal mass ejections. Geophys Res Lett 27:145–148 Gopalswamy N, MaKela P, Akiyama S, Yashiro S, Xie H, MacDowall RJ, Kaiser ML (2012) Radioloud CMEs from the disk center lacking shocks at 1 AU. J Geophys Res 117:A08106 Gosling J (2007) Observations of magnetic reconnection in the turbulent high-speed solar wind. Astrophys J Lett 671:L73–L76 Kahler SW, Krucker S, Szabo A (2011) Solar energetic electron probes of magnetic cloud field line lengths. J Geophys Res 116:1104 Malaspina DM, Newman DL, Wilson LB III, Goetz K, Kellogg PJ, Kerstin K (2013) Electrostatic solitary waves in the solar wind: evidence for instability at solar wind current sheets. J Geophys Res 118(2):591–599 Marubashi K (1997) Interplanetary magnetic flux ropes and solar filaments. In: Crooker NU, Joselyn JA, Feynman J (eds) Coronal mass ejections, vol 99, Geophysical monograph. American Geophysical Union, Washington, DC, p 147 Michalek G, Gopalswamy N, Lara A, Manoharan PK (2004) Arrival time of halo coronal mass ejections in the vicinity of the Earth. Astron Astrophys 423:729–736 Möstl C, Farrugia CJ, Kilpua EKJ, Jian LK, Liu Y, Eastwood JP, Harrison RA, Webb DF, Temmer M, Odstrcil D, Davies JA, Rollett T, Luhmann JG, Nitta N, Mulligan T, Jensen EA, Forsyth R, Lavraud B, de Koning CA, Veronig AM, Galvin AB, Zhang TL, Anderson BJ (2012) Multi-point shock and flux rope analysis of multiple interplanetary coronal mass ejections around 2010 August 1 in the inner heliosphere. Astrophys J 758:10. doi:10.1088/0004-637X/758/ 1/10 Nieves-Chinchilla T, Colaninno R, Vourlidas A, Szabo A, Lepping RP, Boardson SA, Anderson BJ, Korth H (2012) Remote and in-situ observations of an unusual Earth-directed coronal mass ejection from multiple viewpoints. J Geophys Res 117:6106 Odstrcil D, Riley PC, Zhao XP (2004) Numerical simulation of the 12 May 1997 interplanetary CME event. J Geophys Res 109. doi:10.1029/2003JA010135 Wilson LB III, Koval A, Sibeck DG, Szabo A, Cattell CA, Kasper JC, Maruca BA, Pulupa M, Salem CS, Wilber M (2013) Shocklets, SLAMS, and field-aligned ion beams in the terrestrial foreshock. J Geophys Res 118(3):957–966

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Solar and Heliospheric Observatory (SOHO) (1995) B. Flecka* and O. C. St. Cyrb a Science Operations Department, European Space Agency, c/o NASA/GSFC Code 671, Greenbelt, MD, USA b NASA/GSFC, Code 670, Greenbelt, MD, USA

Abstract SOHO is the most comprehensive space mission ever devoted to the study of the Sun and its nearby cosmic environment known as the heliosphere. It was launched in December 1995 and is currently funded at least through the end of 2016. SOHO’s 12 instruments observe and measure structures and processes occurring inside as well as outside the Sun and which reach well beyond Earth’s orbit into the heliosphere. While designed to study the “quiet” Sun, the new capabilities and combination of several SOHO instruments have revolutionized space weather research. This article gives a brief mission overview, summarizes selected highlight results, and describes SOHO’s contributions to space weather research. These include cotemporaneous EUV imaging of activity in the Sun’s corona and white-light imaging of coronal mass ejections in the extended corona, magnetometry in the Sun’s atmosphere, imaging of far-side activity, measurements to predict solar proton storms, and monitoring solar wind plasma at the L1 Lagrangian point, 1.5 million kilometers upstream of Earth.

Keywords Sun; Heliosphere; CMEs; Space weather

Introduction SOHO, the Solar and Heliospheric Observatory, is a mission of international cooperation between ESA and NASA to study the Sun, from its deep core to the outer corona, the solar wind, and solar energetic particles. Together with Cluster (see chapter on ▶ Cluster (2000) in this volume), it forms the Solar-Terrestrial Science Program (STSP), the first “cornerstone” of ESA’s long-term program known as “Space Science – Horizon 2000.” STSP, in turn, was part of the International SolarTerrestrial Physics Program (ISTP), a cooperative scientific satellite project of NASA, ESA, and ISAS which aimed at gaining improved understanding of the physics of solar-terrestrial relations by coordinated, simultaneous investigations of the Sun-Earth space environment over an extended period of time. Science quality data, both archival and near real time, are available at the SOHO web sites (http://soho.nascom.nasa.gov and http://soho.esac.esa.int). Information about the mission as well as material suitable for education and public outreach are also available at the same locations. SOHO was designed to answer the following three fundamental questions about the Sun: What is the structure and dynamics of the solar interior? Why does the solar corona exist and how is it heated? Where is the solar wind produced and how is it accelerated?

*Email: bernhard.fl[email protected] Page 1 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

In the following paragraphs, the “original” SOHO mission will be described as it has been operated for over 15 years until the spring of 2011. Following the launch of NASA’s Solar Dynamics Observatory (SDO), which carries vastly improved versions of two of SOHO’s primary instruments, and in response to budget pressures, SOHO operations have been significantly reduced in recent years. A brief summary of the current status of SOHO and anticipated changes is also given. Detailed descriptions of all 12 instruments, the science operations and data products, as well as a complete mission overview can be found in Fleck et al. (1995). First an overview of the mission (spacecraft, orbit, payload, operations) is given, followed by a short summary of some of SOHO’s main scientific accomplishments. Then SOHO’s contributions to space weather research are discussed, which include the combination of coronal imaging in the EUV and white-light imaging of the extended corona, continuous mapping of the Sun’s magnetic field, imaging of active regions on the far side of the Sun, predicting the arrival of solar energetic particles (SEPs) based on measurements of energetic electrons, and in situ measurements of shock fronts of coronal mass ejections (CMEs) as they sweep over the Lagrangian point L1.

Mission Overview Spacecraft SOHO is a three-axis stabilized spacecraft that constantly faces the Sun. Its design is based on a modular concept with two main elements: the payload module, housing the 12 instrument packages, and the service module, providing essentials such as thrusters, power, and communications. SOHO’s mass at launch was 1,850 kg; its dimensions are 4.3  2.7  3.7 m3 (9.5 m with solar arrays deployed). Design life was 2 years, with consumables (hydrazine) onboard for another 4 years. The current hydrazine reserves in fact are sufficient for several more decades of normal operation, and the solar arrays should provide sufficient energy at least until the end of 2018. SOHO has excellent pointing performance, with errors typically smaller than 1 arcsec. SOHO was designed, assembled, and tested by a consortium of European space companies led by prime contractor Matra Marconi Space (now Airbus Defense and Space) under ESA management. NASA contributed the Atlas IIAS rocket on which SOHO was launched and is responsible for telecommunications (using NASA’s Deep Space Network, DSN) and daily operations, while ESA has overall responsibility for the mission. The focal point for spacecraft operations, science planning, and instrument operations is NASA’s Goddard Space Flight Center.

Orbit SOHO was launched on 2 December 1995 and inserted into a halo orbit around the Lagrangian point L1 in February 1996. There the combined gravity of Earth and Sun keep SOHO in an orbit locked to the Earth-Sun line. Nominal science operations started on 2 May 1996. The L1 halo orbit was chosen as it allows: (a) uninterrupted observations of our star, (b) sampling of the solar wind and energetic particles outside Earth’s magnetosphere, and (c) extremely good observing conditions for the detection of solar velocity oscillations with high accuracy and sensitivity by minimizing radial velocity variations.

Payload The payload consists of a set of 12 complementary instruments, developed and furnished by 12 international principal investigator (PI)-led consortia involving 39 institutes from 15 countries.

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Table 1 Instruments on SOHO and current PIs Instrument Global Oscillations at Low Frequency (GOLF) Na-vapor resonant scattering cell to measure global Sun velocity oscillations Variability of solar IRradiance and Variability (VIRGO) Active cavity radiometers and sun photometers for total and spectral irradiance Michelson Doppler Imager (MDI)a Fourier tachometer to measure velocity oscillation up to l = 4,500 Solar UV Measurements of Emitted Radiation (SUMER)a Normal incidence spectrometer; 500–1,600 Å; spectral res. 20,000–40,000 Coronal Diagnostic Spectrometer (CDS)a Normal and grazing incidence spectrometers, 150–800 Å Extreme ultraviolet Imaging Telescope (EIT) Full-disk images (1,024  1,024) in He II, Fe IX, Fe XII, Fe XV UltraViolet Coronagraph Spectrometer (UVCS)a UV lines (Ly a, O VI, etc.) in extended corona (1.3–3 RJ) Large Angle and Spectrometric COronagraph (LASCO) Overlapping externally occulted coronagraphs: 2–30 RJ Solar Wind ANisotropies (SWAN) Scanning telescopes operating in Ly a to measure solar wind mass flux Charge, Element, and Isotope Analysis System (CELIAS) Electrostatic deflection, time-of-flight measurements, solid-state detectors Comprehensive Suprathermal Energetic Particle analyzer (COSTEP) p, He: 0.04–53 MeV/n, e: 0;04–5 MeV; solid-state and plastic scintillator detectors Energetic and Relativistic Nuclei and Electron experiment (ERNE) p-Ni: 1.4–540 MeV/n, e: 5–60 MeV; solid-state and plastic scintillator detectors a

Principal investigator P. Boumier, IAS, F C. Fröhlich, PMOD/WRC, CH P. Scherrer, Stanford. Univ., USA W. Curdt, MPS, D A. Fludra, RAL, UK F. Auchère, IAS, F L. Strachan, SAO, USA R. Howard, NRL, USA E. Quémerais, LATMOS, F R. Wimmer-Schweingruber, Univ. Kiel, D B. Heber, Univ. Kiel, D

E. Valtonen, Univ. Turku, SF

No longer operated

Nine consortia are led by European PIs, the remaining three by US PIs. The payload weighs about 640 kg and consumes 450 W. SOHO’s 12 instruments, which represent the most comprehensive set of solar and heliospheric instruments ever developed and carried on the same platform, are listed in Table 1. The payload includes three helioseismology and solar irradiance instruments (GOLF, VIRGO, MDI) that have provided unique data for the study of the structure and dynamics of the solar interior, from the very deep core to the outermost layers of the convection zone; a set of five complementary remotesensing instruments, consisting of EUV and UV imagers, spectrographs, and coronagraphs (SUMER, CDS, EIT, UVCS, LASCO, SWAN), that have given us our first comprehensive view of the outer solar atmosphere and corona; and three in situ instruments (CELIAS, COSTEP, ERNE) making measurements of the composition and energy of the solar wind and charged energetic particles.

Cleanliness and Calibration UV instruments on earlier solar space missions have sometimes shown rather strong drops in responsivity after being exposed to solar radiation in space, due to polymerization of molecular contaminants. To avoid the danger of permanent degradation of the throughput of the SOHO

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

instruments and to protect the instruments observing the corona against particulate contamination, cleanliness was recognized early in the development of SOHO as a prime concern. As a consequence, a very stringent cleanliness program was implemented in order to assure clean environmental conditions for the sensitive experiments. Considerable effort went into making the radiometric response of the SOHO UV and EUV instruments directly traceable to a primary laboratory standard, namely, synchrotron radiation produced by storage rings. Because of unavoidable detector aging, a rigorous in-flight intercalibration program was implemented to monitor and maintain the calibration of instruments in orbit. For some instruments, that included suborbital intercalibration rocket flights. For details about SOHO’s cleanliness and calibration program, see Pauluhn et al. (2002).

Operations The SOHO Experimenters’ Operations Facility (EOF), located at NASA’s Goddard Space Flight Center (GSFC), served as the focal point for mission science planning and instrument operations. There the experiment teams received real-time and playback telemetry, processed those data to determine instrument commands, and sent commands directly from their workstations through the ground system to their instruments, both in near real time and on a delayed execution basis. From the outset, SOHO was conceived as an integrated package of complementary instruments, being once described as an “object-oriented” mission, rather than an “instrument-oriented” mission. There was therefore great emphasis on coordinated observations. Internally, this was facilitated through a nested scheme of planning meetings (monthly, weekly, daily), and externally through close coordination and data exchange for special campaigns and collaborations with other space missions and ground-based observatories over the Internet. In response to budget pressures and the increased feasibility of remote science operations via the Internet, the SOHO EOF and the SOHO Experimenters’ Analysis Facility (EAF) at GSFC were closed at the end of November 2010. Most remote sensing instruments are now being operated remotely from the PI home institutions. The SOHO spacecraft was originally designed for 24/7 manual operations. Starting in late 2006, SOHO engineers began an in-house reengineering effort to automate the spacecraft operations in an effort to reduce operations cost. This required the development of new ground software (pass generator, anomaly detection, and notification) as well as modifications of the Central On-Board Software. Since September 2008, all DSN contacts (except nonroutine passes such as station keeping and momentum management maneuvers) are automated.

Recent Mission Changes

NASA’s Solar Dynamics Observatory (SDO – see chapter on “▶ Solar Dynamics Observatory (SDO) (2010)” in this volume), which was launched on 11 February 2010, carries vastly improved versions of SOHO’s MDI and EIT instruments, as well as an EUV irradiance monitor. After the cross-calibration of EIT with SDO/AIA at the end of July 2010, the EIT image cadence has been reduced to two synoptic sets of images in all four wavelengths each day to track detector behavior and to maintain the uniform data set, spanning now over 1½ solar cycles. The telemetry bandwidth that had been used by EIT is now being used by LASCO to improve the cadence of its observations of the fastest CMEs. After the successful completion of the cross-calibration with SDO/HMI, MDI was commanded to stop taking science data on 12 April 2011 at 23:22:31UT. MDI operated exceptionally well for more than 15 years and has produced data that form the basis of over 1,700 papers in the refereed literature.

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On 23 January 2013, 17 years after the Ultraviolet Coronagraph Spectrometer (UVCS) obtained its first ultraviolet spectra of the extended solar corona, it was commanded to end operations because the detectors were no longer capable of producing scientifically meaningful observations. The SUMER detectors are very close to end of life and NASA’s Interface Region Imaging Spectrograph (IRIS), which was successfully launched on 27 June 2013, has vastly improved performance characteristics compared to SUMER. Following a final cross-calibration campaign in July 2014, SUMER science operations was terminated on 8 August 2014. CDS, which has been superseded to a large degree by Hinode/EIS, was commanded to end operations on 5 September 2014 because of budget constraints in the UK. All other instruments (VIRGO, GOLF, LASCO, SWAN, CELIAS, COSTEP, ERNE) are fully functional and continue to make unique and important contributions to the “Heliophysics System Observatory.”

Summary of Key Findings SOHO has provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, out to the solar wind and its interaction with the interstellar medium (e.g., Fleck et al. 2000, 2006). SOHO’s findings have been documented in an impressive and growing body of scientific literature and popular articles. It is impossible to do justice to the 4,900-plus articles published in the refereed literature (as of end of 2014) and an even greater number in conference proceedings and other publications, representing the work of more than 3,200 scientists worldwide. Here, only a brief summary of a few selected results based on data from SOHO can be given. In the following section, space-weather-related results will be discussed in some more detail. SOHO provided the first-ever images of structures and flows below the Sun’s surface and of activity on the far side of the Sun. Analysis of the helioseismology data from SOHO has shed new light on a number of structural and dynamic phenomena in the solar interior, such as the absence of differential rotation in the radiative zone, subsurface zonal and meridional flows, subconvection zone mixing, a very slow polar rotation, and shear zones in the solar rotation rate just below the surface of the Sun and at the tachocline (transition between radiative and convection zone). SOHO discovered sunquakes and eliminated uncertainties in the internal structure of the Sun as a possible explanation for the “neutrino problem.” It allowed the detection of sunspots in the deep interior of the Sun 1–2 days before they appeared at the solar surface. The ultraviolet imagers and spectrometers on SOHO have revealed an extremely dynamic solar atmosphere where plasma flows play an important role. They discovered new dynamic solar phenomena such as coronal waves and solar tornadoes and provided evidence for upward transfer of magnetic energy from the surface to the corona through a “magnetic carpet” (a weave of magnetic loops extending above the Sun’s surface). SOHO measured the acceleration profiles of both the slow and fast solar wind and identified the source regions of the fast solar wind. SOHO discovered that heavy solar wind ions in coronal holes both flow faster and are heated hundreds of times more strongly than protons and electrons and that they have highly anisotropic temperatures reaching hundreds of millions of degrees Kelvin in the direction perpendicular to the magnetic field. SOHO revolutionized our understanding of solar-terrestrial relations and dramatically boosted space weather forecasting capabilities by providing, in a near-continuous stream, a comprehensive suite of images covering the dynamic atmosphere and extended corona. SOHO has measured and characterized over 20,000 CMEs. CMEs are the most energetic eruptions on the Sun and the major Page 5 of 15

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driver of space weather. They are responsible for all of the largest solar energetic particle events in the heliosphere and are the primary cause of major geomagnetic storms. SOHO has measured for over 1½ solar cycles the total solar irradiance (the “solar constant”), spectral irradiance, as well as variations in the extreme ultraviolet flux which are important for the understanding of the impact of solar variability on Earth’s climate. High-precision visible light measurements of the Sun’s shape and brightness during two special 360 roll maneuvers of the SOHO spacecraft have produced the most precise determination of solar oblateness. Besides watching the Sun, SOHO has become the most prolific discoverer of comets in astronomical history: as of May 2014, over 2,700 comets have been found by SOHO, most of them by amateurs accessing SOHO near-real-time data via the Internet. Moreover, UVCS provided plasma diagnostic measurements of many of the sungrazing comets from both planned and serendipitous observations.

SOHO’s Contributions to Space Weather Research CMEs and Space Weather Before SOHO Coronal mass ejections, or CMEs, are eruptions of magnetized plasma from the Sun’s atmosphere. For recent reviews of many aspects of CMEs, see, e.g., Kunow et al. (2006), Chen (2011), Webb and Howard (2012), or the chapter on “▶ Coronal Mass Ejections and their Cause and Nature” in this volume. CMEs striking Earth’s magnetosphere are known to be the cause of the most significant geomagnetic storms. They also drive magnetohydrodynamic shocks that accelerate energetic particles and fill the heliosphere with energized particles. At the end of the 1980s, two developments highlighted the importance of understanding, or at least predicting, CMEs. The first was the collapse of the Hydro-Quebec power grid in 1989 due to a severe geomagnetic storm. This encouraged policy makers in the United States to formulate a cross-Agency National Space Weather Plan to coordinate resources and undertake new programs, such as NASA’s Living With a Star program. The second development was a shift in the research community from a focus on solar flares to CMEs as primarily important for solar-terrestrial physics. These developments set the stage for two space-based platforms that followed in the second half of the 1990s that revolutionized the understanding-driven science of solar and space physics into the applied science called space weather. Those two spacecraft were NASA’s Advanced Composition Explorer (ACE) and SOHO. ACE also resides at the Lagrangian point L1, and it was designed to send a continuous stream of highly compressed telemetry of in situ measurements of solar wind parameters just upstream of Earth’s magnetosphere that were relevant to the short-term (30–60 min) prediction of the onset of geomagnetic activity (see chapter on “▶ Advanced Composition Explorer (ACE) (1997) ” in this volume). For broader accounts of space weather, see Schwenn (2006), Bothmer and Daglis (2007), Schrijver and Siscoe (2009), or Song et al. (2001). CMEs were originally detected in the early 1970s when specialized telescopes called coronagraphs were first flown in space. Coronagraphs produce artificial eclipses of the Sun, occulting light from the million-times brighter solar disk so that the extended atmosphere, or corona, can be seen. As such, these telescopes are critically susceptible to stray light in order to detect the corona. Significant questions about CMEs remained unanswered prior to the launch of SOHO: What was their relationship to other forms of solar activity, particularly in terms of timing and causality? Although the morphology of some CMEs appeared to be a three-part structure (bright leading edge, dark trailing cavity, and bright prominence material trailing), what factors determined the variations of that form? Finally, there was the dispute about the interpretation (indeed, even the existence) of Page 6 of 15

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“halo” CMEs that surrounded the occulting disk and appeared to be directed toward the observer – could those events presage geomagnetic storms?

CMEs and Space Weather After SOHO

The questions posed above were answered within the first year of operation of SOHO’s LASCO and EIT, primarily due to significant improvements in these instruments compared to earlier ones. In Fig. 1, one can see a typical coronagraph series of images of a CME taken by LASCO C2. The dynamic range of LASCO’s CCD detectors was orders of magnitude larger than vidicon tubes used in previous coronagraphs, and the location of SOHO at L1 provided a greatly reduced and more stable stray-light background so that fainter CMEs could be detected and tracked than ever before. Earlier coronagraphs on Skylab, SMM, and P78-1 were in low-Earth, low-inclination orbits with 15 day-night transitions every 24 h. Two problems arose from this: (a) an approximately 40 % loss of coverage and (b) thermal distortions which resulted in a large and continuously changing stray-light background because of small changes in the sensitive alignment of the optical benches. The relatively rapid (e.g., 10–20 min) cadence of EIT images allowed many CMEs to be unambiguously associated with various forms of activity in the low corona for the first time. Of particular interest were the “EIT waves” that appeared to map the expansion of the CME across the solar surface (Fig. 2). Also, the intentional overlap (or nesting) of fields of view between EIT and LASCO’s C1-C2-C3 meant that events could be tracked from their initiation in the low corona out to the extent of the C3 field of view. The superior imaging capability of LASCO revealed that the threepart structure seen in many CMEs appeared to be a magnetic flux rope, thus giving physical insight to the myriad of morphologies that had been reported earlier (cf. Fig. 1). This understanding was critical to the subsequent physics-based modeling of the initiation and propagation of CMEs, and many of our current space weather forecasting tools are now built on this fact. The existence of halo CMEs (St. Cyr 2005) was confirmed because of the aforementioned improvements in detecting faint events. The combination of LASCO and EIT allowed observers to be able to distinguish between halo CMEs directed toward Earth and those originating on the far side. During the development of SOHO, as was evident from their original allocation of onboard resources, LASCO and EIT were considered “context” instruments for the spectrometric telescopes. However, during the first year of SOHO’s operation, it became clear that the significant improvements in image quality, combined with real-time return of LASCO and EIT images (almost 20 h per day), would define the “gold standard” for midrange (1–3 day) space weather forecasting (Fig. 3). SOHO operations personnel established a protocol to contact NOAA’s Space Environment Center (now Space Weather Prediction Center) with timely information on the appearance of Earth-directed CMEs. Many researchers then began using the LASCO and EIT data in various techniques, and combined with different auxiliary observations, to predict the arrival time of CMEs and interplanetary shocks. In 1998, additional telemetry was allocated to LASCO and EIT to improve the cadence of observations, and the midterm forecasting capabilities were significantly expanded.

Additional Scientific Understanding of CMEs from SOHO Observers have continued to populate the LASCO CME catalogue with information about the appearance, size, speed, and mass of individual events, now numbering more than 20,000, and researchers internationally compare these with their own observations of associated phenomena. With the growing size of that database and the launch of STEREO with multiple coronagraphs, some researchers began experimenting with the automated detection and measurement of CMEs. The algorithms were developed using archival data, and that has become a veritable cottage industry in recent years with almost a dozen technical approaches appearing to have some levels of success. Page 7 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 1 CME eruption in white light as observed by SOHO/LASCO C2. The relative size and location of the Sun can be seen by the inset cotemporaneous EIT image on the LASCO occulting disk. Two bright coronal streamers can be seen at the 4 and 7 o’clock position extending from underneath the LASCO occulting disk. The CME appears in the southwest streamer and proceeds to disrupt it (upper right frame at 10:29). Note the distinct magnetic flux rope structure which can be seen as a series of almost concentric windings in the 11:27 image (lower left). The CME is associated with a bright prominence that trails behind the flux rope (This and all subsequent images of this chapter are covered under the SOHO copyright policy, available at http://soho.nascom.nasa.gov/data/summary/copyright.html)

Another SOHO instrument has also provided significant new insights into CME research. UVCS was able to obtain spectroscopic observations of over 1,000 CMEs imaged by LASCO, during both planned and serendipitous observation. For the first time, UV emission lines of the pre- and posteruption coronal plasma, as well as the CME itself, have been observed, and diagnostics such as the line-of-sight velocity, density, composition, ionization state, and temperature allow researchers to link the CME onset characteristics to the coronal white-light images. Using the UVCS observations, the thermal history of the ejected plasma can be constrained, and realistic three-dimensional models of CMEs can be compared with simulations. Numerous shock waves and current sheets associated with CMEs have also been observed by UVCS, and this has allowed comparison of plasma densities and compression factors with radio bursts.

The Future of CME Research The heliophysics community wants to understand the initiation of CMEs, their propagation into the heliosphere, their impact at Earth and throughout the solar system, and the large-scale structure of the corona through a full magnetic cycle. The success of SOHO LASCO in advancing the understanding of CMEs, combined with the inherent limitations of a single vantage point in tracking events to Earth, led directly to the development of the STEREO mission (see chapter on “▶ Solar Terrestrial Relations Observatory (STEREO) (2012)” in this volume). The success of combining EIT and LASCO, as well as the high-cadence/high-resolution EUV imaging from the TRACE Small Explorer mission (1998–2010), led to the development of SDO. In order to further our Page 8 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 2 A time series of running difference images spanning 34 min in the Fe XII 195 Å channel of SOHO/EIT. Centered on a flaring active region just to the north on the central meridian, one can see a nearly circular disturbance (the “EIT wave”) as it propagates across the disk. The wave appears as the patchy bright features, leaving a region of reduced emission behind (dimming region) (Image covered under the SOHO copyright policy)

understanding and modeling of the initiation of CMEs, researchers are using high-cadence EUV and vector magnetic field information from SDO and combining them with white-light coronal data from SOHO/LASCO. Reconstructions of the propagation of CMEs into the heliosphere can only be modeled accurately using as many viewpoints as possible, for example, the two STEREO spacecraft and SOHO. Only LASCO provides a continuous record of the large-scale corona over more than an entire solar cycle from one viewpoint.

MDI Magnetic Field Maps

The Sun’s magnetic field is the driver of all solar activity. Without a magnetic field, there would be no flares, no particle events, no CMEs, and probably not even a corona. Knowledge of the Sun’s magnetic field is therefore of paramount importance for our understanding of energetic and eruptive events, and the only path to reliable predictive capabilities – the “holy grail” of space weather research – will be through measurements and understanding of the magnetic field topology throughout the Sun’s atmosphere, from the photosphere through the chromosphere to the base of the corona (e.g., Mackay and Yeates 2012). Unfortunately, magnetic field measurements in the chromosphere and corona are very difficult, and it may be many years until it will be possible to measure and interpret them reliably and on a routine basis. Most magnetic field measurements are therefore done in the photosphere and then extrapolated into the higher layers (e.g., Wiegelmann and Sakurai 2012), Page 9 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 3 Top left: MDI visible light image of the solar disk taken on 28 October 2003, where multiple large active regions can be seen. Top right: MDI magnetogram on the same day, illustrating the magnetic complexity of these active regions. Lower left: EIT Fe XII 195 Å image at the time of the X17 X-ray flare, seen as the bright emission just south close to the central meridian. The linear horizontal feature is an artifact due to saturation of the CCD detector. Lower right: LASCO C3 image at minutes after the flare (11:30 UT) where a halo CME completely surrounding the occulting disk is visible. The flare location and the existence of the halo CME were a clear indication that the event was heading toward Earth (Image covered under the SOHO copyright policy)

despite the considerable difficulties of transforming the forced photospheric magnetograms into adequate approximations of nearly force-free fields at the base of the corona. Since MDI provided only longitudinal magnetograms, extrapolations are limited to linear force-free field models. The Helioseismic and Magnetic Imager (HMI) on SDO, which superseded SOHO/MDI with several major improvements (significantly improved spatial resolution and image cadence), offers full Stokes vector magnetic field measurement capabilities and thus the application of nonlinear forcefree field models. While the primary objective of SOHO/MDI was to obtain spatially resolved velocity time series of the solar atmosphere for the helioseismic study of the Sun’s interior, as a by-product, MDI also generated longitudinal (line-of-sight) magnetograms in the photospheric Ni I 6768 Å line, formed at a height of about 100 km above t5000 = 1. MDI provided both full-disk magnetograms with a spatial resolution of 4 arcsec as well as higher-resolution (1.25 arcsec) magnetograms. The latter were limited to the MDI “high-res” field of view, a square of about 11  11 arcmin centered about 160 arcsec north of the equator. They were taken during special campaigns, when SOHO high rate telemetry was available. The temporal resolution of some of the MDI magnetic field data products

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

obtained during special campaigns is as short as 1 min. In addition to higher time resolution campaign data, MDI provided synoptic full-disk magnetograms at a regular cadence of 96 min (15 per day) throughout the mission. While there are magnetograms available with much higher spatial resolution (e.g., from the Stokes Polarimeter on Hinode, but also from ground), the unmatched consistency, availability, and coverage of the MDI 96-min full-disk magnetogram series have proven to be invaluable in nearly all research areas of solar physics, in particular also in space weather research. MDI synoptic magnetograms have been used in countless investigations aimed at reconstructing the magnetic field topology of active regions and eruptive events (e.g., Schrijver 2009). They form the basis of a large database of global potential field source surface (PFSS) models, which are frequently used as input for large-scale MHD models of the corona and heliosphere.

Far-Side Imaging of Active Regions by MDI and SWAN

Solar active regions are the centers of energetic phenomena that produce flares and coronal mass ejections, whose resulting electromagnetic and particle radiation interfere with telecommunications and power transmission on Earth and pose significant hazards to astronauts and spacecraft. Imaging of far-side solar activity allows anticipation of the appearance of large active regions more than a week ahead of their arrival on the East limb of the Sun, greatly improving midrange space weather forecasting capabilities from 1–3 days to 1–2 weeks. To use an analogy from terrestrial storm forecasting, far-side images of solar active regions would offer the space weather forecaster a similar lead time to potentially hazardous events as geosynchronous satellite data of a strong tropical depression or hurricane cell far out in the Atlantic. Just a little over 4 years after the launch of SOHO, in March 2000, scientists published an astonishing result: the first successful holographic reconstruction of features on the far side of the Sun. An active region on the far side reveals itself because its strong magnetic fields speed up the global sound waves. Because these waves travel from the near side of the Sun to the far side and back, they interfere with their multiple reflections. The result is a standing wave with a sharply defined frequency, called a p-mode (“p” for pressure), similar to the harmonics that resonate in an organ pipe. An active region can be compared to a small dent in the organ pipe, slightly reducing its internal volume and thereby slightly raising its resonant frequency. Soon after the initial publication of this result, the astonishing became routine, and MDI (and later also GONG and SDO/HMI) offered daily far-side images online. MDI was not the first SOHO instrument that provided information about activity on the Sun’s far side. Half a year before the MDI release, in June 1999, the SWAN team announced a new technique to map solar activity on the Sun’s far side. SWAN, short for Solar Wind Anisotropies, is used to map the whole sky in ultraviolet light. It sees a huge cloud of interstellar hydrogen that bathes the entire Solar System and interacts with the solar wind. The cloud is relatively tenuous – about 0.1 atoms per cc – yet it is thick enough to shine when illuminated by the Sun’s ultraviolet light (Ly a). This kind of observation is impossible from Earth because the atmosphere completely filters the shortwavelength ultraviolet light. Even spacecraft in orbit around the Earth are blinded to the hydrogen haze of the Solar System by a large swarm of hydrogen atoms that surrounds our planet (geocorona). SWAN full-sky maps reveal “hot spots” when the hydrogen cloud beyond the Sun glows more strongly than would be expected if the Sun were uniformly bright on its far side. The strong ultraviolet emissions from active regions on the far side of the Sun behave like beams from a lighthouse on the landscape (Fig. 4). They move in the sky in accordance with the Sun’s rotation, which takes about 28 days. This allows monitoring activity on the far side of the Sun without looking at it directly and is currently used by space weather researchers in France, in combination with Page 11 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 4 SWAN full-sky maps from 20 July 1996 (top) and 10 days later (30 July 1996; bottom). The left circles show the sky brightness in Ly a on the far side of the Sun, the right circles the same for the sky behind the spacecraft (i.e., behind Earth). Note the distinct bright patch in the upper left image, resulting from an active region on the far side of the Sun. Ten days later, when the Sun’s rotation has moved that active region to the visible face of the Sun (see lower right green EIT image), the sky behind the spacecraft is now illuminated (lower right blue image) (Image covered under the SOHO copyright policy)

MDI/GONG/HMI far-side helioseismology results to recreate the solar activity pattern at any time and any point on the Sun. With the two STEREO spacecraft (in combination with SOHO and SDO) providing full 360 coverage of the Sun, the far-side imaging techniques have been validated and hence are less frequently used for space weather predictions now than before the availability of STEREO data. However, in a few years, when the two STEREO spacecraft won’t be able to provide full 360 coverage anymore, these techniques will become very important and valuable again. The SWAN full-sky images are also used to predict the UV flux received by the Earth 2 weeks in advance and to compute the UV flux emitted toward any planet or object in the solar system. These values are produced on a regular basis and distributed through the SWAN web page. One application of this data set is the prediction of Earth’s thermospheric temperature, which is the main parameter used to compute the drag effect on satellites on low earth orbit. Multiple SOHO observations were then successfully used in October 2003 when some of the biggest active regions containing some of the largest sunspots of Cycle 23 appeared coming at the East limb of the Sun (Figs. 3 and 5) – already spreading X-rays, extreme ultraviolet radiation, high-energy particles, and coronal mass ejections into interplanetary space. At that time, space weather predictors had an earlier warning since the regions were seen on the far side of the Sun with seismic holography and other techniques developed with SOHO. The significance of that 2-week

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 5 A sequence of LASCO C3 images following the event depicted in Fig. 3 (“Halloween Storms” of 28 October 2003). In the upper left image (11:18), the halo CME is still behind the occulting disk. Planet Mercury is the bright feature at about 10 o’clock near the edge of the occulting disk; numerous bright coronal streamers can be seen extending out to the edge of the field of view; the dark linear feature at 7 o’clock is the shadow of the pylon holding the occulting disk; numerous stars are seen in the background. Upper right: The halo CME has emerged from behind the C3 occulting disk at 11:42. The remaining images are a time sequence showing the progression of the halo CME and the onset of one of the most intense energetic solar proton events in SOHO’s lifetime. The energetic protons are racing ahead of the CME plasma at nearly the speed of light and an hour after the eruption start bombarding the CCD detector. After about 12 h, the images are practically useless because of the intensity of the proton storm (Image covered under the SOHO copyright policy)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

outburst of solar activity has been documented in a NOAA Service Assessment (http://www.swpc. noaa.gov/Services/SWstorms_assessment.pdf). Not only were the MDI far-side techniques presaging intense activity on the Sun’s backside, but two other SOHO instruments also provided “early warning” that there was unusual activity on the Sun’s far side: the LASCO observers noted extremely fast CMEs without associated activity counterparts on the Earth-facing hemisphere of the Sun, and SWAN noted unusual EUV intensity coming from the Sun’s far side.

Predicting Solar Proton Events

Sudden increases in the fluence of >30 MeV protons in SEP events pose a hazard to human space activities and robotic space missions (cf. Fig. 5). A new method, based on SOHO/COSTEP measurements of relativistic (150 keV–10 MeV) electrons, permits up to an hour of warning for the later arriving protons in SEP events (Posner 2007). The electrons act as test particles by probing the continuously changing heliospheric transport conditions in the same region of the heliosphere through which the slower-moving protons have to propagate. The new method was for the first time tested under operational conditions during the February 2008 Space Shuttle Atlantis mission, which transported ESA’s Columbus laboratory to the International Space Station. NASA-Goddard’s Space Weather Research Center has included this method in its array of research-grade forecasting tools that routinely provide information to the human and robotic exploration fleet.

CELIAS Proton Monitor Measurements of the Solar Wind and ICMEs In addition to interplanetary shock fronts associated with CMEs, corotating interaction regions (CIRs) and their associated high-speed wind streams can drive geomagnetic activity. Upstream measurements of the solar wind plasma are therefore important for the short-term (30–60 min) prediction of the onset of geomagnetic activity. The CELIAS/MTOF proton monitor provides measurements of bulk speed, density, thermal speed, and north/south flow direction in near real time during DSN contact times. The only other available real-time data set is from ACE, which is seriously degraded during intense energetic particle events, and from the STEREO spacecraft, which are now on the far side of the Sun. Unfortunately, there is no magnetometer onboard SOHO (it was de-scoped very early during SOHO’s development), and hence no measurements of the solar wind plasma’s magnetic field. This is arguably the biggest shortcoming of SOHO’s in situ solar wind measurements and explains why ACE solar wind data are more widely used by the space weather community.

Conclusion SOHO is a robust solar observatory that has revolutionized both the understanding-driven science of solar physics and the application of heliophysics that is now known as space weather. During the first year of SOHO’s operation, it became clear that the significant improvements in image quality, combined with near-real-time return of LASCO and EIT images (almost 20 h per day), would define the “gold standard” for midrange (1–3 day) space weather forecasting. Researchers and forecasters have relied on LASCO and EIT data in various techniques, and combined with different auxiliary observations, to predict the arrival time of CMEs and interplanetary shocks at Earth.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_14-1 # Springer International Publishing Switzerland (outside the USA) 2014

Cross-References ▶ Advanced Composition Explorer (ACE) (1997) ▶ Cluster (2000) ▶ Solar and Cosmic Radiation and Hazards: The Basics ▶ Solar Dynamics Observatory (SDO) (2010) ▶ Solar Flares ▶ Solar Terrestrial Relations Observatory (STEREO) (2012)

References Bothmer V, Daglis IA (2007) Space weather – physics and effects. Springer-Praxis, Chichester Chen PF (2011) Coronal mass ejections: models and their observational basis. Living Rev Solar Phys 8:1 Fleck B, Domingo V, Poland AI (eds) (1995) The SOHO mission. Reprinted from Solar Phys 162(1–2). Kluwer Academic, Dodrecht. Fleck B, Brekke P, Haugan S, Sanchez Duarte L, Domingo V, Gurman JB, Poland AI (2000) Four years of SOHO discoveries – some highlights. ESA Bull 102:68. http://soho.nascom.nasa.gov/ publications/ESA_Bull102.pdf Fleck B, M€ uller D, Haugan S, Sanchez Duarte L, Siili T, Gurman JB (2006) 10 years of SOHO. ESA Bull 126:24. http://soho.nascom.nasa.gov/publications/ESA_Bull126.pdf Kunow H, Crooker NU, Linker JA, Schwenn R, Von Stieger R (eds) (2006) Coronal mass ejections. Space sciences series of ISSI, vol 21. Reprinted from Space Sci Rev J 123/1–4 Mackay D, Yeates A (2012) The Sun’s global photospheric and coronal magnetic fields: observations and models. Living Rev Solar Phys 9:6 Pauluhn A, Huber MCE, von Steiger R (eds) (2002) The radiometric calibration of SOHO, ISSI scientific report SR-002, ESA Publications Division, Noordwijk Posner A (2007) Up to 1-hour forecasting of radiation hazards from solar energetic ion events with relativistic electrons. Space Weather 5(5):05001 Schrijver CJ (2009) Driving major solar flares and eruptions: a review. Adv Space Res 43(5):739–755 Schrijver CJ, Siscoe GL (2009) Heliophysics – plasma physics of the local cosmos. Cambridge University Press, Cambridge Schwenn R (2006) Space weather: the solar perspective. Living Rev Solar Phys 3:2 Song P, Singer HJ, Siscoe GL (eds) (2001) Space weather, vol 125, Geophysical monograph. American Geophysical Union, Washington, DC St. Cyr C (2005) The last word: the definition of Halo Coronal mass ejections. EOS 86(30):281–282 Webb DF, Howard TA (2012) Coronal mass ejections: observations. Living Rev Solar Phys 9:3 Wiegelmann T, Sakurai T (2012) Solar force free magnetic fields. Living Rev Solar Phys 9:5

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Solar Dynamics Observatory (SDO) W. Dean Pesnell* NASA Goddard Space Flight Center, Greenbelt, MD, USA

Abstract NASA’s Solar Dynamics Observatory (SDO) stands sentinel for the cosmic hazards created by solar activity. The instruments on SDO provide immediate knowledge and understanding of solar eruptive events such as flares and coronal mass ejections. In the longer term SDO provides scientific understanding to better predict the trends of solar activity over the next few months to years. SDO comprehensively observes the magnetic field of the Sun. It measures the surface magnetic field and observes the response of the solar atmosphere to changes in the magnetic field. SDO also gathers helioseismic observations that are analyzed to look inside the Sun and deduce the workings of the solar convection zone – the roiling motions inside the Sun that create the magnetic field. SDO, the data it produces, and some of the science results that help with planetary defense will be described.

Keywords Solar Dynamics Observatory; SDO; HMI; AIA; EVE; Solar dynamo; Extreme ultraviolet; Magnetic field; Helioseismology; Solar activity; Space weather; Solar flares; CME

Introduction The environments of the Earth and planets are both affected by the energetic particles and photons that cause space weather. Two major cosmic hazards caused by the Sun are solar flares and coronal mass ejections. Both of these can affect near-Earth space and our technology in space and on the ground. Solar flares and CMEs come from the destruction and expulsion of the solar magnetic field. NASA’s Solar Dynamics Observatory (SDO) was designed to study that magnetic field and learn the causes of solar flares and CMEs. One science goal of SDO is to improve our understanding of solar activity to such a degree that we can predict the output of the Sun over next few hours, years, or longer. Solar flares are incredibly bright flashes of electromagnetic radiation with wavelengths spanning from g-rays to radio (Fig. 1). Flares occur when a part of the Sun’s magnetic field is rapidly converted into the kinetic energy of energetic particles, heat, and radiation. Because the most common emissions from solar flares are at short wavelengths that are completely absorbed by the atmosphere, they are best studied from space. If solar flares are the lightning of space weather, coronal mass ejections, or CMEs, are the storm clouds. They arise when a filament (an arch of solar plasma that is also called a prominence) is ejected from the Sun. If pushed away with sufficient force, the material leaves the Sun and moves out

*Email: [email protected] Page 1 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 1 An example of a solar flare. This X1.9 flare happened on the eastern limb of the Sun over Active Region 1302. This flare started at 1029 UTC, peaked at 1101 UTC, and ended by 1144 UTC. Illustrated here at 1157 UTC is the remaining bright region of the flare, sitting above post-flare loops that formed during the initial part of the flare. Background loops are behind the flare and survived the magnetic field changes that caused the flare. Foreground loops grew during the flare. They are darker (and hence cooler) than the material behind them

into interplanetary space. CMEs do not spread out to fill the solar system as they move away from the Sun. This leads to one of the fundamental differences between flares and CMEs. Photons from a flare will strike anything that can see the part of the Sun where the flare occurred. The particles and magnetic field of a CME can only strike an object that lies within its much narrower zone of influence. Understanding the impact of a solar flare or a CME requires different data sets and models. Individual solar flares are able to cause errors in radio communications and navigation systems, but they do not cause long-lasting changes in our natural environment. The cumulative effects of solar activity over millions of years, however, can change or even remove a planetary atmosphere (Catling and Zahnle 2009). Measuring the solar X-ray and EUV output over many solar cycles is necessary to determine how the Sun affected the evolution of planetary ionospheres and atmospheres. SDO’s observations guide the study of such effects and also help improve predictions of the Sun of both short and long timescales. One major assumption that has been made in the past is that solar output changes in a similar way each solar cycle. This flies in the face of the evidence from the sunspot number record. Each 11-year sunspot cycle differs from all others. It should not be surprising that the magnetic field or the X-ray and EUV spectral irradiances would also be different in each cycle. Solar Cycles 23 and 24 have been the best-studied sunspot cycles to date, with many satellites making measurements of different aspects of solar activity. Ground-based observatories, such as the National Solar Observatory, made visible-light measurements at the same time. We know what happened inside and outside of the Sun better than ever before. Even so, the predictions of the amplitude of Solar Cycle 24 spanned a wide range of values. This shows the limits of our knowledge of the solar dynamo inside the Sun that creates the solar magnetic field and the processes above the surface of the Sun that destroy or expel that field.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 2 An illustration of the SDO showing the positions of the instruments (AIA, EVE, and HMI), the deployed solar panels, and one of the high-gain antennas

The Solar Dynamics Observatory The Solar Dynamics Observatory (SDO, illustrated in Fig. 2) was launched on February 11, 2010, and began normal science operations on May 1, 2010. SDO flies in a geosynchronous orbit inclined at 28 near the longitude of the dedicated ground station in New Mexico. All three science instruments are returning excellent data. SDO is the first mission to be launched for NASA’s Living With a Star (LWS) Program, a program designed to understand the causes of solar variability and its impacts on Earth. SDO data will help us understand the Sun’s influence on Earth and near-Earth space by studying the solar atmosphere on small scales of space and time and at many wavelengths simultaneously. SDO’s goal is to understand the solar variations that influence life on Earth and our modern technological environment. The mission is designed to determine how the Sun’s magnetic field is generated, structured, and then converted into variations in the solar irradiance and the motion of energetic particles and the solar wind. One major aspect of SDO science is to develop the capability to predict when the solar magnetic field will change. That predictive capability would allow us to anticipate space weather hazards at all of the planets and the space in between. The cosmic hazards that SDO helps to defend against are produced by the energetic photons and particles emitted by the Sun: 1. Changes in planetary atmospheres that increase satellite drag and cause the loss of the atmosphere 2. Changes in planetary ionospheres that interfere with radio communications, GPS navigation, and power grids 3. Damage to satellites in space, especially the electronics 4. Harm to astronauts in space from increased radiation dose

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

SDO Measurements The instruments on SDO, which are pointed out in Fig. 2, provide data that continues to lead to a better understanding of the underlying physics of critical solar variations. Each instrument was built and is run by a Science Investigation Team (SIT). Each SIT receives their data from SDO, after which they process, analyze, archive, and serve the data. The instruments and their measurements are: HMI: The Helioseismic and Magnetic Imager (HMI) produces full-disk Dopplergrams, magnetograms, and visible-light images of the Sun with high spatial resolution (Schou et al. 2012). Dopplergrams are full-disk photospheric velocity maps that are created every 45 s with a pixel size of 730  730 km, a data recovery of 98 %, and a data completeness of 99 % for each Dopplergram (Fig. 3, left). One of the images used to create the Dopplergrams is available as a visible-light image of the Sun (Fig. 3, middle). HMI is also creating full-disk longitudinal magnetic field measurements every 45 s (Fig. 3, right) and full-disk vector magnetic field maps every 12 min. HMI data is available from the SDO JSOC (2014). AIA: The Atmospheric Imaging Assembly (AIA) takes eight images every 12 s. It images the solar atmosphere in multiple wavelengths to link changes above the surface of the Sun to changes inside the Sun (Lemen et al. 2012). The EUV channels measure the emissions of He II 304 Å, Fe XVIII at 94 Å, Fe VIII and XXI at 131 Å, Fe IX at 171 Å, Fe XII and XXIV at 193 Å, Fe XIV at 211 Å, and Fe XVI at 335 Å. The diversity of iron ions allows AIA to sample many temperatures in the corona and chromosphere, including hot flare channels. Every 12 s, AIA captures all seven EUV channels while alternating between chromospheric images of C IV (1,600 Å) and continuum at 1,700 Å from one 12 s cycle to the next. One image at 4,500 Å is included at low cadence to help align AIA with other imagers. Figure 4 shows three images from AIA, taken at the same time as the HMI images in Fig. 3. AIA data have a pixel size of 875  875 km and are available from the SDO JSOC (2014). EVE: The Extreme Ultraviolet Variability Experiment (EVE) measures the solar extreme ultraviolet (EUV) irradiance with unprecedented spectral resolution, temporal cadence, and precision (Woods et al. 2012). EVE EUV spectral irradiances allow us to understand variations on the timescales that influence the Earth’s climate and near-Earth space.

Fig. 3 Three views of the Sun at 2030 UTC on January 19, 2014. From left to right are a Dopplergram, intensity image, and LOS magnetogram from HMI. The Dopplergrams are displayed with red shifts in black and blue shifts in white. The color scale for the magnetogram uses white for field pointing toward the observer and black for field pointing away. Several active regions are identified in the intensity image. You can see several active regions in the Dopplergrams. You can also see several regions of strong magnetic field that cannot be seen in the other two images

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 4 Three views of the Sun at 2030 UTC on January 19, 2014. From left to right are the AIA 304 Å, AIA 171 Å, and AIA 193 Å images. You can see the active regions listed in Fig. 3 as bright regions, with coronal loops extending above the limb from ARs 11959 to 11960. Coronal loops are seen above the other active regions as well. There is also a coronal hole in the center of the northern hemisphere and several filaments

Fig. 5 A day-averaged EUV spectral irradiance for January 19, 2014, as measured by EVE, plotted against the wavelength in nm. The seven AIA passbands are identified with vertical dashed lines. The He II 304 Å line is the brightest in this wavelength range, with the C III 977 Å line the next brightest. Although the total radiant energy in this spectrum is 4.7 mW m 2, about 10 5 times the total solar irradiance, it is responsible for most of the ionization in the thermospheres of the Earth, Venus, and Mars. Such spectra, at a 10-s cadence, are the primary data produced by EVE

EVE produces spectra covering 0.1–105 nm with a 10-s cadence and a spectral resolution of 0.1 nm. This includes the He II 304 Å line. The accuracy of the spectra at the bright spectral lines is about 10 %. An example of an EVE EUV spectrum is shown in Fig. 5. EVE data is available from the EVE website (EVE 2014). Two SDO instruments return measurements of the Sun in EUV wavelengths. EUV radiation is a probe of the solar corona as well as a major source of ionization in planetary atmospheres. Energetic electrons in the solar corona produce solar EUV photons by a two-step process. First, the electrons must create highly ionized atomic ions in the corona; then they must excite the electrons that remain on those ions. The presence of different ions acts as a thermometer of the coronal plasma. For example, Fe XII ions, which are seen in the AIA 193 Å passband, are created by higher temperatures than the Fe IX ions seen in the AIA 171 Å passband. When EUV photons are absorbed by a planetary thermosphere, they create ions and electrons whose lifetime can exceed the length of a night. This Page 5 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 6 Six day-averaged EUV line irradiances from May 1, 2010, to January 20, 2014, as measured by EVE. The He II 304 Å line is the brightest, followed by the C III 977 Å line and H I 1,026 Å. The peak He II 304 Å irradiance was in late December 2013 and a horizontal line is drawn at that value. The peak H I 1,026 Å irradiance, also marked with a horizontal line, has been reached several times in Solar Cycle 24

results in a persistent layer of ionization that can interfere with radio-based technologies. The density of each planetary ionosphere and the temperature of the planetary thermosphere tend to track the solar cycle variation in the solar EUV output. The EUV output of the Sun increases during solar maximum, due to both flares and a slower varying background glow. Figure 6 shows that slower varying part, which is important in heating the thermosphere, causing it to expand and increase satellite drag (Odenwald et al. 2006). Each wavelength varies in its own way. At this point in Solar Cycle 24, the emissions of the chromosphere at He II 304 Å have increased 75 % to reach a local maximum, above their brightness in November 2011 when the highest sunspot number so far in Solar Cycle 24 was reached. By comparison, the coronal Fe XVI 335 Å line has increased a factor of ten since the launch of SDO, with larger rotation variations. Even with the utility of these measurements, the EUV spectral irradiance between 0.1 and 105 nm has been measured on only about 70 % of the days since 1967 (Fig. 7). Understanding these spectral irradiances is necessary to construct accurate models of their emission at the Sun and how they create the ionospheres and thermospheres of planetary atmospheres. HMI returns information about the surface magnetic field and surface velocity fields. The former is immediately useful as it provides the state of the magnetic field as well as the boundary conditions for extrapolating that field into the corona with magnetic field models. Flares and CMEs are a direct result of the buildup of the magnetic field above the surface. Most of that buildup can be tracked to what emerges through the surface. Models of the coronal magnetic field are an essential tool in understanding and forecasting space weather hazards. The HMI Dopplergrams are an integral part of our understanding of the solar convection zone, the seat of the solar dynamo. Just like seismic waves on the Earth can be inverted to tell us about the interior of the Earth, the solar p-modes can be inverted to measure conditions inside the Sun. Additional analyses can show when localized changes are present and can indicate a magnetic field about to erupt. Other wave patterns are seen in the Dopplergrams. These include the supergranulation pattern that tracks conditions in the outer part of the solar convection zone. SDO has a prime mission of 5 years. This allows us to make our measurements over a significant portion of a solar cycle. By capturing the solar variations that exist in different time periods of a solar Page 6 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 7 The history of measurements of the solar EUV spectral irradiance. The F10.7 solar irradiance, a widely used measure of solar activity, is plotted as a solid line. Appended to that curve is a prediction of the remainder of Solar Cycle 24 from Pesnell (2014). At the top of the figure are the satellites that have measured the EUV spectral irradiance since the launch of OSO-3 in March 1967. The spectral coverage is shown by the height of the colored box (from 1 to 150 nm) although some missions provide measurements to longer wavelengths. The temporal coverage of each mission, taken from the NSSDC mission summary pages, is shown by the horizontal extent of the colored boxes. The right sides of the SOHO, TIMED, and SDO boxes are drawn at the end of the currently funded missions

cycle, SDO can quantify the differences between the rising, maximum, and declining phases of Solar Cycle 24. If SDO continues into the extended mission phase, it will be able to make those comparisons over an even wider range of solar activity.

Data Volume and Completeness The raw data from all three instruments on SDO are CCD images. As a result, SDO produces about 3.4 million images every month. One of the design challenges for SDO mission was to ensure the timely delivery of that data to the SITs and on to other users. To reduce aliasing in the Fourier transforms used in the helioseismic data, the goal was that 95 % of the Dopplergrams must contain 99 % valid pixels. Because Dopplergrams are composed of 5–6 individual CCD images, or filtergrams, measured closely in time, a comprehensive data completeness budget was developed. An onboard recorder was determined to be too difficult to manage, so SDO uses a continuous downlink of the data to a dedicated ground station. This also means that near-real-time, rapid cadence, and low-latency SDO data is available for space weather forecasters.

SDO Science and Cosmic Hazards SDO is a science mission that produces data useful for space weather forecasters. But SDO also produces research into the causes of solar activity. Understanding those causes will help with predicting solar activity, the linchpin of LWS science and a primary science objective of SDO. Warnings of cosmic hazards coming from the Sun can be separated into categories according to how far in advance the warning is needed. Tactical awareness of the Sun comes from an assessment of the near-real-time data. Understanding begins when the analysis and correlation of that data produces short-term predictions and then tests those predictions. Long-term forecasts arise when the science analysis produces accurate and verifiable forecasts that are validated after ever-increasing forecast lead times. SDO produces data and science results in all of these categories:

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Knowledge: By releasing the near-real-time data as rapidly as possible, SDO provides a tactical awareness of when flares occur, the location on the Sun, duration, and spectral content. The filament liftoffs that can produce CMEs can also be quickly detected. The SDO data is also run through detection and classification software that determines what features are present. A database of discovered features is maintained at LMSAL’s Heliophysics Events Knowledgebase (HEK 2014). This near-real-time data is available at a variety of websites. Short term: Predictions of the timing and strength of solar flares, especially anticipating the next several hours to days, are critical for protecting space assets and astronauts. SDO provides line-ofsight magnetic fields that are used in empirical flare predictions. It also provides vector magnetic fields and spatially resolved temperature and radiance maps that should allow more accurate short-term predictions to be developed. Long term: Predicting solar activity at longer times in the future, weeks to years, is needed for mission planning and designing mitigation techniques for power systems, GPS, and other technologies threatened by space weather. The atmospheres of all of the planets are sensitive to the evolution of the photon and particle output of solar activity. SDO science results provide models of the solar interior, spectral irradiance, and magnetic field that can be adapted to these predictions. Here are a few examples of how SDO data is changing our view of solar activity.

Late-Phase Flares

Even after 100 years of solar flare research, the launch of SDO provided new information about the spectral content of long-lasting flares. Radiative energy from flares has been monitored in X-rays since 1976 by GOES. A great deal of work has been done to understand the association of X-rays with other measures of solar activity (Aschwanden and Freeland 2012). These analyses assumed that most, if not all, of the radiated energy was being captured by the GOES radiometers. Soon after EVE began regular observations of the solar EUV spectral irradiance, it was noticed that the spectral irradiance at longer wavelengths often increased long after the X-ray irradiance had faded. Because few flares had been occurring each day at this point in this solar cycle, and by verifying the source of the radiation in AIA images, it was determined that more energy can be emitted at the longer wavelengths than in X-rays as the loops over an active region return to a non-flaring condition (Woods et al. 2011). This additional energy is absorbed higher in the Earth’s atmosphere than are X-rays (Fig. 8), creating ions and electrons in the F-region ionosphere and heating the thermosphere. More energy and longer duration should mean a measurable change in the densities and temperatures within the ionosphere and thermosphere. Any increase in the density of the thermosphere increases the drag on satellites in low-Earth orbit. Unfortunately, the duration is so long that any effects are masked by the normal diurnal variation. Research continues to see if late-phase flares are an important component of space weather or simply an essential clue of how solar flares work.

Prominence and Filament Eruptions

Solar prominences and filaments are long arcs of relatively cool material suspended above the surface of the Sun by the solar magnetic field. Prominences are bright arcs at the solar limb while filaments are the same structures seen as dark arcs on the disk. Their presence and dynamics are often used as an early indicator of the eruptive events that drive space weather. When either erupts from the surface, they can form a coronal mass ejection (or CME). The energetic particles in a CME can disable spacecraft and interfere with radio communications. Page 8 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014 250

200 Thermosphere z (km)

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100 Mesosphere 50

Stratosphere Troposphere

0 0

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Fig. 8 An illustration of the absorption of ultraviolet radiation in the terrestrial atmosphere. Red colors denote unattenuated solar radiation at that altitude and wavelength. Black regions are altitudes where light at that wavelength was completely absorbed above that point. Contours are drawn at 25 %, 50 %, and 75 % absorption. Horizontal blue lines show the dividing lines for the named atmospheric layers. The absorption in the EUVoccurs above 150 km altitude, making the solar emissions at those wavelengths critical to understanding the density and temperature of the thermosphere

Compared with flares, the effects of CME take longer to arrive at a planet but can last several days as the magnetic field of a planet (the magnetosphere) relaxes from the impact of the CME. During the initial passage of the CME by a planet, the magnetosphere is distorted and then relaxes after the CME has left. Particles within the magnetosphere are energized by the relaxation of the magnetic field toward a quiet state. During the several days this relaxation takes, the energetic particle fluxes are higher and chances of harm to satellites or the built environment are increased. Predicting that a CME will strike a planet is the first step to mitigating this cosmic hazard. Knowing how filaments form and why they erupt is a crucial step toward making this prediction. Continuous, high-cadence SDO observations have enabled scientists to observe in detail how filaments are formed. Their work shows that filaments can be formed by hot gas cooling within a coiled magnetic field. Once cooled the material finds itself trapped in the magnetic field, which keeps it from falling back toward the solar surface or at least significantly slows that fall for some time. This means filaments are long-lived patterns where material cycles through them: cool material rains out, while new material is added as it descends from the hot corona above them. New, hot material bubbling up along pathways that thread through the descending cooler material refills the reservoir above the filament. The SDO observations also show how filaments may become unstable and how they subsequently erupt as part of a solar coronal mass ejection. The combined SDO and STEREO data reveal rolling motions that are signs of electrical currents and the cause of the filament material sloshing around within the coronal magnetic field. The observations are interpreted by measuring the twist or number of turns in the filament material. Figure 9 shows prominence material unrolling as it moves away from the solar surface. Once the buildup of twist exceeds a critical value, the magnetic configuration erupts, displaying a characteristic kinking and twisting motion (Sterling et al. 2012; Su and van Ballegooijen 2013). SDO data gives an unprecedented view of these eruptions, at a rapid cadence, excellent spatial resolution, and multiple temperatures.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 9 An example of how material in a prominence unwinds. This prominence eruption occurred February 24, 2011, between 0700 and 0930 UTC. These images were taken 36 s apart near 0730 UTC. The material in the hook has rotated counterclockwise between the two images. The multiple images radiating in an “X” from bright areas are caused by the diffraction pattern of the telescope. A movie of this event can be viewed at the SDO website (SDO 2014b, Item 60)

Fig. 10 An example of how filaments are coupled by the global magnetic field. White arrows point at two filaments in this AIA 304 Å image from 0600 UTC on August 1, 2010. Cyan arrows point at two active regions. A small flare in the upper active region (AR1) at 0300 UTC started a cascade of eruptions, first in the larger active region (AR2), then the upper filament (P1), and finally the lower filament (P2). In this image the upper filament has just begun to erupt. The lower prominence will erupt at 1000 UTC. A movie of this event can be viewed at the SDO website (SDO 2014a, Item 52)

Global Magnetic Fields SDO data has been used to observe and explain rapid changes in the solar corona under the control of the global magnetic field. Many examples have been seen where one part of the solar corona rapidly changes because of a change in another part far away. SDO observations have shown the entire corona can respond to an explosive eruption by a crowning of the magnetic field, much like a forest fire moving through the tops of trees. (An example from 01-AUG-2010 is described in Fig. 10.) A model of the sympathetic eruptions on this date shows how they are triggered and even how the order of eruption does not progress in distance from the first event (Titov et al. 2012). More Page 10 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

frequently, waves are seen to move across the disk of the Sun, covering a large area of the Sun as they pass. These EUV waves can be analyzed to measure the magnetic field in the corona (Liu et al. 2012). Global models of the solar magnetic field start from the surface of the Sun. SDO is providing the first measurements of the strength and direction of the vector magnetic field over the visible disk of the Sun. These data are available every 12 min. This data set is used as the boundary condition for coronal magnetic field models and for developing an understanding of how the field emerges from inside the Sun. One interesting area of study is whether projections of the vector field, summed over an active region and followed in time, can be used to predict when that active region will flare or erupt. This reduction in complexity of the data set is essential for assessing the hazard of an active region. If you combine the vector magnetic field with velocities derived by tracking features at the surface, you can calculate the electric field in the photosphere. The electric and magnetic fields determine how much electromagnetic energy flows into the corona and chromosphere. Although the solar magnetic field has been measured for over 100 years, the electric field has rarely been measured and this Poynting flux is poorly determined. The ohmic heating can also be determined from these calculations. In magnetically dominated plasma like the corona, the Poynting flux and ohmic dissipation join thermal conduction and radiative losses as important parts of the energy balance. SDO is also using two small-scale probes of the solar global magnetic field. The brightenings seen when a comet passes through the corona or when material from an eruption falls back onto the Sun may be very small in size but are important checks on our understanding of how the corona works. These observations help calibrate our models of the coronal magnetic field and add to our understanding of how the emissions are created. For example, the energy emitted by the material as it stops must be about the same as the kinetic energy of the material falling back onto the Sun (Innes et al. 2012). The multiple passbands of AIA can resolve the heating of this material as it falls onto the chromosphere. The atomic components of ice evaporated from Sun-grazing comets must be heated to 105–106 K to be seen in the AIA passbands. The motion of the ionized material tests our understanding of how the magnetic field deflects the material, and the emission tests how cooler material is excited to become visible in the SDO passbands (Schrijver et al. 2012). Models of the solar magnetic field were improved to explain the observations, and models of the emission of material in the corona were adjusted to allow for the input of new material (Bryans and Pesnell 2012). Results from these probes shed new light on the long-standing key question of what causes the heating of the solar corona and the solar wind.

Other Magnetic Features

Solar flares and CMEs are not the only cosmic hazards from the Sun that endanger the planets and our modern technological environment. High-speed streams emanating from coronal holes and the current sheet that forms throughout the solar system are two other cosmic hazards coming from the Sun. Coronal holes are dark areas of the corona with low densities (one can be seen in Fig. 4). These parts of the corona have open field lines, meaning a magnetic field line that leaves the Sun within a coronal hole will not trace back to the surface of the Sun. Any plasma that moves up a field line in a coronal hole can escape as the fast solar wind. Magnetic field measurements from SDO are used to calculate models that predict the magnetic field line connecting the Sun to the Earth. High-speed streams moving along that field line will often hit the Earth. When that happens the magnetosphere responds by creating a geomagnetic storm lasting several days. A geomagnetic storm produces high Page 11 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

fluxes of energetic electrons and protons. A similar magnetic connection can be found between the Sun and other planets. Coronal holes and high-speed streams are more common in the declining phase of a sunspot cycle. Long-lived coronal holes can survive for several solar rotations. That means if a high-speed stream from a coronal hole hits the Earth today, it probably will hit it again in 27 days. These are two simple predictions of solar activity. These same magnetic field models can calculate the position of the current sheet that modulates the flux of the cosmic rays as they enter the solar system and the Earth.

Helioseismology HMI Dopplergrams are maps of wave patterns that are used to probe the inside of the Sun, the location of the solar dynamo that generates the magnetic field. The raw Dopplergram in the left panel of Fig. 3 shows three different kinds of motions. The first is solar rotation, with the left side of the Sun moving toward the viewer and the right side moving away. Next is a set of large cells, looking much like craters on the Moon and visible better around the outer part of the image, called supergranulation. These cells are a motion of material and magnetic field in the top layers of the convection zone. The third motions are the 5-min oscillations or p-modes. These acoustic waves are best seen near the center of the Sun, where their line-of-sight (LOS) velocity is the highest. All of these motions provide clues about the solar dynamo, but the p-modes can be used to look deep inside the Sun. One example of how p-modes help to understand the solar dynamo is their use to determine the pattern of the bulk velocities of the plasma within the Sun. The main result is a profile of the meridional velocities within the solar convection zone. Meridional velocities move plasma and magnetic field from the equator to the pole, down inside the Sun, and back toward the equator, where they emerge to start a new cycle. They are similar to wind patterns seen in the Earth’s atmosphere. The first profile, obtained using data from SOHO and GONG in Solar Cycle 23, showed that the plasma moves upward at low latitudes, poleward near the surface, and then downward at high latitudes. To close the flow pattern, it was necessary to assume some pattern deep in the solar interior. Assuming the flows have a single cell means that an unseen equatorward flow takes place somewhere deep inside the Sun. We were not sure how deep in the Sun that return flow happened and why was there only one cell. If we look at the Earth’s atmosphere, there is a single cell of circulation in the thermosphere but three cells (Hadley, Ferrel, and polar) in the troposphere. Just ask any sailor who gets stuck in the calm winds of the horse latitudes whether a single cell would be better! Having three cells instead of one has profound effects on our weather patterns and climate. Why should the Sun be limited to only a single cell? HMI has extended the observations into Solar Cycle 24. New techniques in local helioseismology were developed by Zhao et al. (2013). to extend the view of the flows to greater depth and with better accuracy. This new result is illustrated in Fig. 11. It was determined that material circulated in two cells, one above the other, rather than the single cell that had been assumed from earlier work. Other work has determined that the shape of the cells changes as solar activity comes and goes. Sometimes it is a single cell from equator to pole and other times there are several upwelling and downwelling regions. The complexity of this circulation pattern means that predictions based on these motions are less certain. The variation of the torsional oscillations is examined for even longer-term predictions. Rings of slightly faster and slightly slower rotation gird the Sun and drift slowly from high latitudes toward the equator as the solar cycle progresses. The motion of these rings appears to indicate the timing of the solar cycle. Sunspots begin to appear as one ring passes by the 35 latitude line. These results Page 12 of 15

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_16-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 11 Schematic plot showing the double-cell meridional circulation structure inside the Sun. Meridional circulation, which transports solar materials between low and high latitudes inside the Sun, may be a fundamental property of the Sun but it was poorly known. It is thought that meridional circulation plays an important role in creating the 11-year solar activity cycle by redistributing solar angular momentum and transporting magnetic flux (Image courtesy of Zhao and Stanford University)

have only been known for two sunspot cycles, but they show that we are moving toward developing the models we need to predict the amplitude and timing of an upcoming sunspot cycle.

Conclusion The behavior of Solar Cycle 24 shows that even a below-average solar cycle can produce significant solar eruptive events. The first X-class flare of Solar Cycle 24 happened on February 14, 2011, and was accompanied by a halo CME, which means it was heading for Earth. SDO and other observatories have studied Active Region 11158, the site of the February 2011 flare, in great detail in many wavelengths. A series of filament eruptions on August 1, 2010, was a casebook study on sympathetic eruptions. Precipitated by the emergence of magnetic flux on the far side of the Sun, three filaments erupted as the magnetic field high above them changed (Fig. 10). A flare in July 2012 produced the fastest CME yet seen (Russell et al. 2013). If that CME had struck the Earth, it might have caused the largest geomagnetic storm since the Carrington Event in 1859. SDO is part of a research and operational system of observatories, both space- and ground-based, whose combined data is used to fill the holes in each individual part. An excellent example of combining data is the picture of the entire Sun produced by merging views from SDO and the twin STEREO spacecraft. Since February 6, 2011, the EUV images from these three spacecraft have produced a view of the complete EUV Sun. This means that scientists and space weather forecasters are able to watch the evolution of active regions from emergence to decay as they rotate around the Sun. Several cosmic hazards to whose mitigation SDO has contributed were described. The presence of late-phase flares may show that the X-ray irradiance is not sufficient to track the effect of solar activity on planetary atmosphere or stellar activity on planets in other solar systems. The formation and eruption of filaments to create coronal mass ejections has been well documented by SDO observations and analysis. Large eruptions in the global magnetic field of the Sun have been shown Page 13 of 15

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to come from modest changes in regions quite remote from the erupting region. This is an important consideration when predicting CMEs. SDO is producing the data and models needed to address the cosmic hazards of solar activity for Solar Cycle 24 and beyond. As of April 30, 2014, it has recorded over 166 million images with high spatial resolution, spanning multiple wavelengths in the corona and including measurements of the EUV spectral irradiance, Doppler velocity, and magnetic field at the solar surface. SDO provides the most accurate, continuous measurements of the EUV photon irradiances that are critical for understanding and predicting the hazards produced by solar activity at the Earth and planets. Research models available at the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center use SDO data to broaden the usefulness of the data to locations throughout the heliosphere. With almost two complete sunspot cycles (a whole solar cycle) measured by spaced-based assets carrying a wide range of instruments, the predictions of solar activity during Solar Cycle 25 should be the most accurate ever. This allows us to anticipate the cosmic hazards caused by the Sun in our planetary atmospheres and in our modern technological environment.

Acknowledgments This work was supported by NASA’s Solar Dynamics Observatory (SDO). The SDO data is courtesy of the NASA/SDO and the AIA, HMI, and EVE Science Investigation Teams.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ FlaresBasics of Solar and Cosmic Radiation and Hazards ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Medical Concerns with Ionizing Radiation and Radio-Biological Effects ▶ Nature of Coronal Mass Ejections and Historical Patterns of Their Occurrence ▶ Solar Flares ▶ Solar Flares and Impact on Earth ▶ Solar Radiation and Spacecraft Shielding

References Aschwanden MJ, Freeland SL (2012) Automated solar flare statistics in soft x-rays over 37 years of GOES observations: the invariance of self-organized criticality during three solar cycles. Astrophys J 754, eid: 112 Bryans P, Pesnell WD (2012) The EUV emission from sun-grazing comets. Astrophys J 760, eid: 8, 18 pp Catling DC, Zahnle K (2009) The planetary air leak. Sci Am 300:36–43 Extreme Ultraviolet Variability Experiment (EVE) (2014) Retrieved 1 June 2014 from http://lasp. colorado.edu/home/eve/

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Heliophysics Events Knowledgebase (HEK) (2014) Retrieved 1 June 2014 from http://www.lmsal. com/hek/ Innes DE, Cameron RH, Fletcher L, Inhester B, Solanki SK (2012) Break up of returning plasma after the 7 June 2011 filament eruption by Rayleigh-Taylor instabilities. Astron Astrophys 540, did: L10 Lemen JR, Title AM et al (2012) The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Sol Phys 275:17–40 Liu W, Ofman L, Nitta N, Aschwanden M, Schrijver C, Title A, Tarbell T (2012). Quasi-periodic fast-mode wave trains within a global EUV wave and sequential transverse oscillations detected by SDO/AIA. Astrophys J 753, eid: 52 Odenwald S, Green J, Taylor W (2006) Forecasting the impact of an 1859-calibre superstorm on satellite resources. Adv Space Res 38:280–297 Pesnell WD (2014) Predicting solar cycle 24 with geomagnetic precursor pairs. Sol Phys 289:2317–2331 Russell CT et al (2013) The very unusual interplanetary coronal mass ejection of 2012 July 23: a blast wave mediated by solar energetic particles. Astrophys J 770, eid: 38 Schou J, Scherrer PH et al (2012) Design and ground calibration of the Helioseismic and Magnetic Imager (HMI) instrument on the Solar Dynamics Observatory (SDO). Sol Phys 275:229–259 Schrijver CJ, Brown JC, Battams K, Saint-Hilaire P, Liu W, Hudson H, Pesnell WD (2012) Destruction of Sun-grazing comet C/2011 N3 (SOHO) within the low solar corona. Science 335:324–328 SDO (2014a) Item 52. Retrieved 1 June 2014 from http://sdo.gsfc.nasa.gov/gallery/main/item/52 SDO (2014b) Item 60. Retrieved 1 June 2014 from http://sdo.gsfc.nasa.gov/gallery/main/item/60 SDO Joint Science Operations Center (JSOC) (2014) Retrieved 1 June 2014 from http://jsoc. stanford.edu Sterling AC, Moore RL, Hara H (2012) Observations from SDO, Hinode, and STEREO of a twisting and writhing start to a solar-filament-eruption cascade. Astrophys J 761, eid: 69 Su Y, van Ballegooijen A (2013) Rotating motions and modeling of the erupting solar polar-crown prominence on 2010 December 6. Astrophys J 764, eid: 91 Titov VS, Mikic Z, Török T, Linker JA, Panasenco O (2012) 2010 August 1–2 sympathetic eruptions. I. Magnetic topology of the source-surface background field. Astrophys J 759, eid: 70, 17 pp Woods TN, Hock R et al (2011) New solar extreme-ultraviolet irradiance observations during flares. Astrophys J 739, eid: 59 Woods TN, Eparvier FG et al (2012) Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): overview of science objectives, instrument design, data products, and model developments. Sol Phys 275:115–143 Zhao J, Bogart RS, Kosovichev AG, Duvall TL Jr, Hartlep T (2013) Detection of equatorward meridional flow and evidence of double-cell meridional circulation inside the Sun. Astrophys J Lett 774, eid: L29

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STEREO as a “Planetary Hazards” Mission M. Guhathakurtaa* and B. J. Thompsonb a NASA Headquarters, Science Mission Directorate, Washingto, DC, USA b Heliophysics Science Division, NASA/GSFC, Greenbelt, MD, USA

Abstract NASA’s twin STEREO probes, launched in 2006, have advanced the art and science of space weather forecasting more than any other spacecraft or solar observatory. By surrounding the Sun, they provide previously impossible early warnings of threats approaching Earth as they develop on the solar far side. They have also revealed the 3D shape and inner structure of CMEs – massive solar storms that can trigger geomagnetic storms when they collide with Earth. This improves the ability of forecasters to anticipate the timing and severity of such events. Moreover, the unique capability of STEREO to track CMEs in three dimensions allows forecasters to make predictions for other planets, giving rise to the possibility of interplanetary space weather forecasting too. STEREO is one of those rare missions for which “planetary hazards” refers to more than one world. The STEREO probes also hold promise for the study of comets and potentially hazardous asteroids.

Keywords Sun; Heliosphere; CMEs; Space weather

Introduction As planetary hazards go, few perils eclipse the Sun. The iconic example is the Carrington Event of 1859. At 11:18 AM on the cloudless morning of Thursday, September 1, 1859, 33-year-old astronomer Richard Carrington was in his well-appointed private observatory. Just as usual on every sunny day, his telescope was projecting an 11-in.-wide image of the Sun on a screen, and Carrington skillfully drew the sunspots he saw. Suddenly, before his eyes, two brilliant beads of blinding white light appeared over an enormous sunspot group. Realizing that he was witnessing something unprecedented and “being somewhat flurried by the surprise,” Carrington later wrote, “I hastily ran to call someone to witness the exhibition with me. On returning within 60 s, I was mortified to find that it was already much changed and enfeebled.” He and his witness watched the white spots contract to mere pinpoints and disappear. Thus, solar flares were discovered. Before dawn the next day, skies all over Earth erupted in red, green, and purple auroras so brilliant that newspapers could be read by their light. Stunning auroras pulsated as far south as Cuba, the Bahamas, Jamaica, El Salvador, and Hawaii.

*Email: [email protected] Page 1 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Even more disconcerting, telegraph systems worldwide went haywire. Spark discharges shocked telegraph operators and set telegraph papers on fire. Even when telegraphers disconnected the batteries powering the lines, aurora-induced electric currents in the wires allowed messages to be transmitted. The “Victorian Internet” was simultaneously energized and brought to its knees. What would happen if such an event occurred today? The National Academy of Sciences has framed the problem in a landmark report entitled “Severe Space Weather Events – Societal and Economic Impacts” (National Research Council, 2008). It noted how people of the twenty-first century rely on high-tech systems for the basics of daily life. Smart power grids, GPS navigation, air travel, financial services, and emergency radio communications can all be knocked out by intense solar activity. A century-class solar storm could cause 20 times more economic damage than Hurricane Katrina. It was once thought that the Carrington Event was an extraordinarily rare thing, but that idea is beginning to change. The Carrington Event is indeed the undisputed champion of radiation storms: Energetic particles accelerated by the flares of September 1859 enveloped Earth, possibly leaving a record in the nitrates of ice cores. By this measure, the Carrington Event may be the biggest in 500 years and nearly twice as big as the runner-up. However, there is more to space weather than radiation storms. Another measure is geomagnetic activity – the shaking of Earth’s magnetic field due to the impact of a coronal mass ejection (CME) (a magnetized cloud of plasma from the Sun). In this respect, the Carrington Event has rivals in modern times. A geomagnetic storm at least half as strong as the Carrington Event erupted in May 1921. Researchers examined geomagnetic records from that storm and modeled its effect on the modern power grid (National Research Council 2008). In North America alone, he found more than 350 transformers at risk of permanent damage and 130 million people without power. The loss of electricity would ripple across the social infrastructure with water distribution affected within several hours; perishable foods and medications lost in 12–24 h and the loss of heating/air conditioning, sewage disposal, phone service, fuel resupply, and other services persisting for unknown periods of time. A more recent example occurred in March 13, 1989, when a strong flare provoked geomagnetic storms that disrupted electric power transmission from the Hydro-Québec generating station in Canada. More than six million people were plunged into darkness for 9 h. Aurora-induced power surges melted power transformers as far away as New Jersey. Much of the damage can be mitigated if managers know a storm is coming. Putting satellites in “safe mode” and disconnecting transformers can protect these assets from damaging electrical surges. Preventative action, however, requires accurate forecasting – a job that has been assigned to NOAA. Space weather forecasting is still in its infancy. Many observers liken it to terrestrial weather forecasting – 50 years ago. Nevertheless, researchers at NOAA’s Space Weather Prediction Center in Boulder, Colorado, are making rapid progress. Space weather forecasting is actually a collaboration between NASA and NOAA. NASA’s fleet of heliophysics research spacecraft provides NOAA with up-to-the-minute information about what is happening on the Sun. The NASA fleet complements NOAA’s homegrown GOES and POES satellites, which focus more on the near-Earth environment. Among many capable solar observatories operated by NASA, one stands out as particularly unique: the twin STEREO probes. STEREO, short for “Solar TErrestrial RElations Observatory” (Kaiser et al. 2008), is the third mission in NASA’s Solar Terrestrial Probes program. It consists of two nearly identical Page 2 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

3-axis-stabilized space-based observatories – one ahead of Earth in its orbit, the other trailing behind – which observe the Sun from multiple (and sometimes stereoscopic) points of view. The two solar-powered probes were launched on October 25, 2006, and they have been beaming back unprecedented data about the Sun ever since.

Mission Overview The original objective of the STEREO mission was not to provide planetary defense, but rather to conduct fundamental investigations in solar physics. Researchers wanted to investigate the 3D structure and internal magnetohydrodynamic physics of coronal mass ejections (CMEs). CMEs are key agents of planetary space weather. They are powerful eruptions that can blow up to 10 billion tons of the Sun’s atmosphere into interplanetary space. A typical CME has a speed of .5–2 million mph (~1–3 million kph), but extremely energetic eruptions have been observed exceeding 5 million mph (8 million kph). When CMEs sweep past Earth, their interaction with our planet’s magnetic can spark pronounced geomagnetic activity and storms. By observing CMEs from multiple points of view and tracking their progress across the Sun-Earth divide, researchers have been able to make progress on a number of previously intractable questions. The authors of the mission’s 1997 Science Definition Report wanted to know the following: • Are CMEs driven primarily by magnetic or nonmagnetic forces? • What initiates a CME? • What is the origin of waves, shocks, and particle radiation that often precede a CME’s arrival at Earth? “In order to understand and forecast CMEs,” they wrote, “we need 3D images of them and of the ambient solar corona and heliosphere.” It is notable that even in the earliest thought-pieces about the STEREO mission, forecasting CMEs appeared alongside understanding them. Planetary hazards were on the minds of mission planners from the very beginning. To accomplish these goals, two spacecraft would be required: one probe orbiting just inside the orbit of Earth and one probe orbiting just outside. STEREO-Ahead (inside) and STEREO-Behind (outside) would drift away from one another, STEREO-A moving ahead of Earth’s orbit and STEREO-B behind at a rate of ~22.5 /year, providing the necessary points of view (see Fig. 1). This scheme had another advantage. Within a few years of launch, the separating probes would gain an excellent view of the far side of the Sun. For the first time, NASA could monitor the entire 360 circumference of our star. The Sun has a vexing habit of surprising forecasters with sunspots that developed on the far side of the Sun, spitting flares and hurling CMEs when they rotated toward Earth. With STEREO, those days would be a thing of the past.

Mission Characteristics

As with many nascent space missions, one of the first challenges for STEREO was financial. The NASA budget allowed for a single rocket to launch the mission, yet the two probes needed to be placed in significantly different orbits. Mission planners called on the Moon for assistance. Mission designers realized that they could use the Moon’s gravity to redirect the probes to their appropriate orbits – something the launch vehicle alone could not do. For the first 3 months after launch, the two observatories flew in highly elliptical orbits extending from very close to Earth to Page 3 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 1 Diagram of STEREO spacecraft positions from 2007 through 2015 (Courtesy of NASA)

just beyond the Moon’s orbit. STEREO Mission Operations personnel at the Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, nudged the spacecraft’s orbits closer and closer to the Moon itself. About 2 months after launch, STEREO-B was close enough to use the Moon’s gravity to fling it to a position “behind” Earth. Approximately 1 month later, STEREO-A encountered the Moon again and was flung to its orbit “ahead” of Earth. This was the first time a “double lunar flyby” had been used to manipulate orbits of multiple spacecraft at the same time. After their encounters with the Moon, the two STEREO probes were in nearly 1-AU orbits with periods slightly less and slightly more than 1 year. From the point of view of Earth, STEREO-A would slowly drift ahead of our planet, gaining a view of solar “terrain” previously hidden on one side of the Sun, while STEREO-B would lag behind, providing a view of the other side. Early in the mission, when the spacecraft separation was small, the viewing angles were ideal for stereoscopic reconstruction of CMEs. In situ investigations were able to provide multipoint measurements of the same eruption, providing insight into the structural variation within a particular event. Later, as the separation increased, STEREO undertook different challenges, such as tracking eruptions all the way from the Sun to Earth. Also, the coronal imagers began to see more and more of the Sun that was hidden from Earth’s view, providing the first global observations of the atmosphere of a star. At first, the twin spacecraft saw only a fraction of the Sun’s far side, but as they continued to drift apart, the view improved. On February 6, 2011, STEREO reached “opposition.” The two probes were 180 apart, each looking down on a different hemisphere. Coincidentally, this occurred on Super Bowl Sunday in the USA, and NASA Public Affairs took advantage of the occasion to release a “first light” 3D movie of the Sun. For the first time in the history of astrophysics, researchers could see and study a star as a fully realized sphere as we regularly do with Earth (see Figs. 2 and 3).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 2 Left: 3D reprojection of STEREO EUVI and SDO AIA 304 Å images onto a solar sphere. Right: 360 maps of the full solar corona in September 2012, when the STEREO and SDO spacecraft achieved maximum average separation (120 ). From top to bottom, the EUVI/AIA wavelengths represented are 304 Å, 171 Å, and 193/195 Å (Courtesy of the STEREO/SECCHI consortium)

Fig. 3 Four of the SECCHI telescopes from both STEREO-A and STEREO-B were used to reconstruct the 3D propagation toward Earth. Not shown is the HI2 outer heliospheric imager (Figure reproduced from Byrne et al. 2010)

NASA’s Earth-orbiting Solar Dynamics Observatory is also monitoring the Sun from its location in Earth’s orbit. Working together, the STEREO-SDO fleet will be able to image the entire 3D Sun until May/June 2019 (apart from periods when the STEREO spacecraft are too close to the Sun-Earth line to allow communication).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Can STEREO last that long? Originally, STEREO was conceived as a 2 ½ year mission, but that idea was quickly scrapped. Such a short mission would never reveal the full expanse of the far side of the Sun. Also, in early designs, there had been a limit on the movement of the high-gain antenna which would have curtailed operations to approximately 2013. The Applied Physics Lab removed that limit at the request of the NASA project office, and now there is no impediment (other than funding) to continuing on for many more years. The spacecraft’s solar arrays can provide power for any reasonable extension of the program. Both spacecraft have passed the point of “infant mortality” – that is, systems failing early – but of course electronics can fail at any time in response to cosmic rays and, ironically, solar storms.

Scientific Investigations Getting the probes into their correct orbits and engineering them to last more than a decade were significant technical challenges. Even more challenging, however, are the mission’s scientific requirements. To fully understand the genesis, evolution, and planetary impacts of CMEs, the STEREO probes would have to have a dynamic range of sensitivity unlike any other observatory in NASA’s history. Researchers needed to see (1) intensely bright explosions near the Sun’s surface, (2) moderately bright CMEs ramrodding out of the Sun’s atmosphere, and (3) the vanishingly faint remains of CMEs expanding into the near-vacuum of interplanetary space. Moreover, to understand the environment of CMEs, STEREO would also need to image the solar wind itself, flowing almost transparently in and around the storm cloud. No single telescope could do the job alone. Designers therefore equipped STEREO with a package of five telescopes in the SECCHI investigation (Howard et al. 2008), each operating in a different range of brightness and observing events at different distances from the Sun. The first SECCHI telescope is the Extreme Ultraviolet Imager (EUVI) built at the Lockheed Solar and Astrophysics Laboratory in Palo Alto, California. EUVI is able to make high-resolution (2 k  2 k) images of the Sun and its lower atmosphere in four different extreme ultraviolet emission lines: 171, 193, 284, and 304 angstroms. The four wavelengths were selected to trace plasma temperatures and magnetic conditions of special interest to solar physicists who wish to study the onset of explosions such as flares and CMEs. The Extreme Ultraviolet Imager observes the Sun between 1 and 1.7 radii from disk center – in other words, it monitors the bright solar surface, the chromosphere, and the inner corona. Next is the inner coronagraph, known as COR1. Coronagraphs are devices that create an artificial eclipse using an opaque disk to block the glare of the Sun. Built at Goddard Space Flight Center, COR1 is a classic “Lyot internally occulting refractive coronagraph” adapted for the first time to be used in space. COR1’s field of view ranges from 1.4 to 4 solar radii, so there is some overlap with the Extreme Ultraviolet Imager. Unlike EUVI, however, COR1 is designed to observe fainter things – primarily the gossamer solar corona and CMEs which plow through it en route to Earth. Although the Sun is blocked by an occulting disk, scattered light in the optical path of COR1 can still be a problem. To mitigate this, COR1 is equipped with a linear polarizer to suppress scattered light and to extract the polarized brightness signal from the solar corona. When engineers have to build a telescope that spends all of its time staring into the Sun, special measures must be taken to handle thermal loads and protect sensitive components. COR1 is a good example of how STEREO engineers dealt with these problems. Because the two STEREO spacecraft are in elliptical orbits about the Sun, the COR1 instruments experience considerable variation in solar irradiance, from 1,264 to 1,769 W/m2 for STEREO-A and from 1,068 to 1,482 W/m2 for STEREO-B. When these loads are combined with expected changes Page 6 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

in the telescope’s material thermal properties from beginning to end of life, the worst-case temperature variation in the COR1 instrument is from 2.5 to 30  C. There is also an axial gradient in temperature from the front to the back of the telescope, ranging from 3 to 7  C. To deal with such gradients, designers placed software-controlled heaters with programmable set points at strategic locations throughout the instrument. They keep the instrument within the 0–40  C operational temperature range. There are also survival heaters controlled by mechanical thermostats to keep the instrument within the 20 to +55  C nonoperational range. Other measures also help the instrument deal with intense solar heat. For instance, specialized composite coatings of oxides over silver are deposited onto many exposed surfaces around the telescope’s aperture, such as the objective lens holder and door assemblies. These stable coatings absorb little sunlight and do a good job reradiating what they do absorb as infrared radiation. Another “hot spot” is the tip of the coronagraph’s occulting device. A majority of the solar load collected by the telescope’s main lens is concentrated there, raising its temperature as high as 125  C. This tip is made of titanium and is diamond-turned to direct the sunlight into a light trap. The tip is also coated with a composite silver coating for high reflectivity. To further cool things down, the shaft of the occulting device is coated with black nickel to radiate away even more heat. Managing heat is a challenge for any solar observatory. A detailed discussion of heat management techniques and the extensive thermal engineering required for all of STEREO’s telescopes is beyond the scope of this chapter. Suffice it to say that all five telescopes have employed an innovative array of tricks to keep things cool.

The third SECCHI telescope is the outer coronagraph, known as COR2. Unlike COR1, which blocks the Sun inside the telescope assembly, COR2 is an externally occulted Lyot coronagraph. Designed and built at the Naval Research Laboratory in Washington DC, COR2 is a descendant of the highly successful LASCO C2 and C3 coronagraphs onboard the Solar and Heliospheric Observatory (SOHO). COR2 has approximately the same field of view as the two SOHO coronagraphs combined and is able to take pictures with a much shorter exposure time to reveal faster dynamics of CMEs, all while fitting into a smaller space inside its spacecraft. COR2 can track CMEs out to 15 solar radii when they are exiting the Sun’s atmosphere and entering interplanetary space. SECCHI’s COR1 and COR2 observations are complementary to SOHO’s C2 and C3 coronagraphs, which provide observations from Earth’s point of view. With SOHO’s view from Earth and SECCHI’s additional views, the three comprise a powerful 3D viewing assembly for CMEs. Fourth and fifth are, arguably, the most amazing telescopes of all – STEREO’s Heliospheric Imagers. The Heliospheric Imagers monitor a vast realm of space extending from the Sun’s upper atmosphere all the way to the orbit of Earth. They can track CMEs uninterrupted over a gulf of more than 93 million miles. By the time these storm clouds travel so far from the Sun, they are very faint, 13–15 orders of magnitude fainter than the solar disk. The HI instruments must be able to see them against a busy background of stars, planets, and even comets that sometimes get in the way. The Heliospheric Imagers consist of two small wide-angle telescopes mounted on the side of the STEREO spacecraft. They are sheltered from the glare of the Sun by a series of linear occulters. Unlike the coronagraphs, which put an occulter directly in front of the Sun to reduce glare, HI operates in the shade of a more conventional baffle. The concept is not unlike observing the night sky after the Sun has gone below the horizon. One telescope (HI-1) sees a patch of sky about 20 wide; the other (HI-2) sees 70 , extending beyond the orbit of Earth. The fields of view overlap by about 5 , to allow continuous tracking from the inner heliosphere to beyond 1 AU. The greatest challenge for HI is the extreme faintness of CMEs. Background starlight from the Milky Way and the glow of sunlight scattered by interplanetary dust (zodiacal light) tend to overwhelm the gossamer clouds. In order to extract the CME signal, the signal-to-noise ratio must

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 4 Composite imagery from the five SECCHI telescopes showing three CMEs on January 9, 2009: one in the COR2 field of view, one in HI-1, and one reaching 1 AU in HI-2. Three planets are also shown: the blue dot represents Earth, pink indicates Venus, and yellow indicates Mercury (Courtesy of C. E. DeForest; see DeForest et al. 2011, 2013)

be increased over what is possible with a single exposure. Exposures are therefore summed onboard. This requires that the images be scrubbed for cosmic rays, which can make bright streaks and flashes in individual exposures, prior to summing. A 2  2 binning results in angular sizes of 70 arc second per pixel for HI-1 and 4 arcmin per pixel for HI-2. The combination of summing 50 images and 2  2 binning results in an increase in signal-to-noise ratio of about 14 times for HI-1. The effective exposures are 20 and 60 arc minutes for HI-1 and HI-2, respectively. Powerful image processing techniques, specifically developed for STEREO’s HI imagers, have further enabled the ability to view event faint eruptions. Figure 4 shows three different CMEs in the STEREO-A SECCHI combined field of view, tracking their transit over the course of several days. The result of this processing is a high dynamic range, wide-field image capable of recording stars as faint as 12th magnitude alongside planets orders of magnitude brighter. Indeed, Earth itself often appears in HI images. From their locations over the far side of the Sun, the STEREO probes can look back and see our home planet – a key requirement in tracking CMEs across the Sun-Earth divide. When all of its telescopes are operating nominally, STEREO can simultaneously observe objects as bright as the Sun (astronomical magnitude 27) and as dim as a 12th magnitude star. That gives the probes a dynamic range approximately ten billion times greater than the human eye. STEREO can detect flashes as intense as a solar flare and as faint as a charcoal-black asteroid approaching Earth from the direction of the Sun – and everything in between. No other astrophysics observatory has this kind of Olympic range. STEREO is also able to detect radio emissions from a variety of shock waves and plasma oscillations excited by flares and CME. It does this using the SWAVES instrument package: Three mutually orthogonal monopole antenna elements, each 6 m in length, jut out of the spacecraft to sample electrostatic and electromagnetic waves. The antennas are connected to five radio receivers variously sensitive to frequencies between 10 kHz and 50 MHz. Working together, these receivers can pick up type II, III, and IV “solar radio bursts” indicative of shocks and energetic particle interactions (see Fig. 5) as well as a variety of in situ plasma modes such as Langmuir, whistler, Z-mode, and electrostatic solitary waves (Bougeret et al. 2008). In situ measurements of particles and fields are provided by two STEREO investigations: IMPACT and PLASTIC. The IMPACT (In Situ Measurements of Particles and CME Transients; Luhmann et al. 2008) investigation is comprised of seven instruments: SWEA (Solar Wind Electron

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 5 Detection of radio bursts associated with a flare, CME, and post-eruptive loops on the Sun (shown in the upper left corner). CMEs do not propagate through a vacuum. On their way to Earth, they interact with shock waves, solar wind streams, and other gaseous “obstacles.” Indeed, the interaction of CMEs with the interplanetary medium can be a source of hazards to Earth and astronauts: Shock waves at the leading edge of CMEs can accelerate particles in the interplanetary medium to dangerous velocity. Studying the CME by itself is not enough. The structure of the medium it propagates through is equally important (Courtesy of N. Gopalswamy)

Analyzer), STE (Suprathermal Electron Telescope), MAG (Magnetometer), SEPT (Solar Electron Proton Telescope), SIT (Suprathermal Ion Telescope), LET (Low Energy Telescope), and HET (High Energy Telescope). SWEA measures solar wind electrons from below an eV to several keV, while STE covers 2–20 keVelectrons, SEPT covers 20–400 keV, and HET covers.7–6 MeV. Protons are measured by SIT, SEPT (20–7,000 keV), LET (2–30 MeV), and HET (13–100 MeV), while measurements of helium and heavier elements are provided by SIT, LET, and HET. The MAG system provides magnetic field measurements in three dimensions and is divided into eight ranges to allow the capability of measuring a wide variety of magnetic field strengths. The PLASTIC (Plasma and Suprathermal Ion Composition; Galvin et al. 2008) investigation consists of three main components. The Solar Wind Sector (SWS) Small Channel provides a 45 field of view of solar wind protons and alpha particles, while the SWS Main Channel measures elemental composition and charge state properties and velocities for heavier ions. The Wide-Angle Partition (WAP) Sector has a 225 field of view on STEREO-A (210 on STEREO-B), representing the remaining unobstructed directions not covered by the SWS components. All three components deliver measurements at a time resolution of 1 min. The PLASTIC entrance system is an energy-percharge analyzer, and the resulting energy ranges are .3–10.6 keV/e for SWS Small Channel, .3–80 keV/e for SWS Main Channel, and.3–80 keV/e for WAP. The IMPACT/PLASTIC in situ suite on STEREO has advanced our understanding of interplanetary hazards for several major reasons. Multipoint in situ measurements of major events have provided a dramatic improvement in our understanding of the 3D structure of space weather phenomena. The manifestations of hazard-causing phenomena are far from homogeneous in structure. When two spacecraft are able to sample the same event, the data frequently reveal great variations. Multipoint measurements have improved our ability to complete a 3D picture of these

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 6 3D flux rope reconstruction of a CME on March 7, 2011, using the Thernisien, Howard, and Vourlidas (2006) “croissant” model. The model allows an accurate determination of the spatial extent of a CME and can track the temporal evolution as the CME propagates in the inner corona (Courtesy of the STEREO/SECCHI consortium and A. Thernisien)

complex phenomena. Notably, both STEREO probes detected the historic radiation storm of July 2012, when a sunspot erupted and produced one of the most prolific streams of energetic protons in the history of the Space Age. Earth was not in the line of fire, and without STEREO, researchers might not have known the event occurred at all. By sampling the storm from points far from Earth, the STEREO probes replaced that cloud of ignorance with a wealth of IMPACT/PLASTIC data that researchers are still studying years later. The IMPACT/PLASTIC combination has also drastically improved our ability to understand the 3D structure of the heliosphere. It has long been known that the Sun is only the beginning of the story. CMEs, energetic particles, and shocks are strongly modulated by the solar wind through which they propagate. Heliospheric structure is capable of speeding up, slowing down, or even deflecting CMEs. It can also enhance or decrease the magnitude of the hazard; for example, extremely highenergy proton events, which pose the greatest risk to assets in space, are produced by the interaction of a CME and shocked solar wind. These protons then travel along the solar wind magnetic field; without knowledge of the magnetic structure of the heliosphere, it is impossible to determine where or how strongly an energetic particle event will manifest itself.

STEREO Space Weather Beacon Data In support of space weather forecasting capabilities, each of the investigations on the two STEREO spacecraft also generate a special low-rate telemetry stream known as the Space Weather Beacon. Outside of the regular Deep Space Network contacts, which deliver the full science data, this Space Weather Beacon stream consists of a low-rate subset of the data specifically designed to allow rapid assessment of the space environment. Various antenna partners around the world collect this telemetry and pass it on to the STEREO Science Center (SSC) in near real time via a socket connection over the open Internet. The Space Weather Beacon allows forecasters and other users to access critical data days before the high-rate science data becomes available.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 7 Sunspot AR1429 unleashed a powerful X5-class solar flare on March 7, 2012, commencing the “St. Patrick Day storms” of 2012. The blast also propelled a massive coronal mass ejection (CME) toward Earth. Left: NASA’s Solar Dynamics Observatory recorded the flare at multiple extreme ultraviolet wavelengths (Courtesy of the SDO/AIA consortium). Right: A 3D CME model run from CCMC/iSWA shows how the CME would propagate through the inner solar system (Courtesy of the Community Coordinated Modeling Center)

Key Findings and Results CME Topology

The STEREO mission has achieved its major goal – the three-dimensional modeling of CMEs. From our single vantage point on Earth, CMEs flying in all directions away from the Sun appear to have a confusing variety of forms. Indeed, researchers had spent years examining thousands of CMEs recorded by Earth-orbiting cameras without finding the answer. As soon as STEREO was added to the mix, however, a common form emerged: CMEs resemble croissants (Figs. 6 and 7). Actually, theoretical models had predicted this for some time. A croissant shape naturally results from coiled magnetic fields called “flux ropes” widely believed to thread through the hearts of CMEs. Three-dimensional STEREO observations removed any doubt that this was the case (Vourlidas et al. 2013). Follow-up observations by NASA’s Solar Dynamics Observatory have revealed flux ropes near the solar surface that twist and break away to form CMEs (Patsourakos et al. 2012). Although the structure of CMEs can evolve significantly as they propagate, the croissant/flux rope model is now on a very firm footing. This is crucial for two reasons. First, even with STEREO on duty, CMEs leaving the Sun are not always observed from multiple points of view. Knowing the common shape of a CME allows forecasters to model its speed and trajectory using less-than-complete data. This improves the precision of forecast CME impact times. Second, the ability of a CME to foment a magnetic storm on Earth depends critically on its inner magnetic structure. Knowing the form of the magnetic structure – it is a flux rope – helpfully narrows the options for modelers who try to anticipate what a CME will do when it arrives. In 2014, forecasters are still struggling to weave this information into their forecasts. It is just a matter of time, however, before flux rope models improve the fidelity of geomagnetic storm warnings.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

The Drivers of Solar Eruptions The full-sun view afforded by STEREO and supporting observatories does more than improve space weather forecasts. It has led to a whole new understanding of solar activity. For decades, astronomers have understood solar activity in terms of localized regions on the Sun. When the magnetic fields of individual sunspots crisscross and reconnect, powerful explosions ensue. This is how flares and CMEs happen. On August 1, 2010, this simple idea was upset. On that date the STEREO-SDO fleet observed a massive global series of explosions engulfing more than two-thirds of the Sun. Researchers catalogued more than a dozen significant shock waves, flares, filament eruptions, and CMEs spanning 180 of solar longitude and 28 h of time (Schrijver and Title 2011). At first it seemed to be a cacophony of disorder until they plotted the events on a map of the Sun’s magnetic field. The events were connected by magnetism, one explosion triggering another like a series of falling dominoes. Solar physicists had long suspected this kind of magnetic connection was possible. The notion of “sympathetic flares” goes back at least three quarters of a century. Sometimes observers would see flares going off one after another – like popcorn – but it was impossible to prove a link between them. Arguments in favor of cause and effect were statistical and often full of doubt. For this kind of work, STEREO and SDO are game changers. Together, the three spacecraft allow researchers to see connections that they could only guess at in the past. To wit, only a fraction of the August events were visible from Earth, yet all of them could be seen by the SDO-STEREO fleet. Moreover, SDO’s measurements of the Sun’s magnetic field revealed direct connections between the various components of the “Great Eruption” – no statistics required. Much remains to be done. Researchers are still unsure about the timing: Was the event one big chain reaction, in which one eruption triggered another – bang, bang, bang – in sequence? Or did everything go off together as a consequence of some greater change in the Sun’s global magnetic field? The next global eruption observed by STEREO – and, yes, there will be a next one – could answer these questions.

Sun-to-Earth Observations

For many years, a “holy grail” of space weather forecasting has been to track a CME all the way from the Sun to Earth. STEREO has accomplished this, too. In December 2008, STEREO-A was 65 million km from Earth when a CME sped away from the Sun. The cloud remained in STEREO-A’s field of view as it propagated all the way across the Sun-Earth divide. When CMEs first leave the Sun, they are bright and easy to see. Visibility is quickly reduced, however, as the clouds expand into the void. By the time a typical CME crosses the orbit of Venus, it is a billion times fainter than the surface of the full Moon and more than a thousand times fainter than the Milky Way. CMEs that reach Earth are almost as gossamer as vacuum itself and correspondingly transparent. Even with STEREO’s onboard image enhancements described earlier in this chapter, it was an enormous challenge to pull such a faint cloud out of the confusion of starlight and interplanetary dust. Indeed, it took almost 3 years for the researchers to learn how to do it. Footage of the 2008 storm was not released until 2011! Now that the technique has been perfected, it can be applied on a regular basis without such a long delay (DeForest et al. 2011). If Sun-to-Earth CME tracking can be sped up and perfected, it would lead to a revolution in space weather forecasting. For one thing, forecasters would know exactly when and where a CME is going to strike. Uncertainties could be narrowed to the point that forecasts of space weather effects on Page 12 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Earth could become regional, rather than merely global as they are now. Tracking a CME continuously from Sun to Earth also means that forecasters could watch the cloud’s magnetic evolution and accurately anticipate its degree of “coupling” with Earth’s own magnetic field. They would know exactly what kind of geomagnetic storm is in the offing. These dramatic improvements, however, are still in the future. They require processing times to be reduced from years to hours, so there are huge practical challenges yet to overcome. Nevertheless, STEREO has shown us the possibilities.

Interplanetary Space Weather

While one revolution waits, another is already under way – the revolution of interplanetary space weather forecasting (Guhathakurta 2013). Researchers working with STEREO’s 3D CME models quickly realized that they could make predictions not only for Earth but also for any other target in the solar system. The “planet” in “planetary hazards” could be any world from Mercury to Neptune. Tracking CMEs through the plasma-filled interplanetary medium takes more than a quick glance at data streaming in from the fleet. High-power computing is required. Around the time STEREO was launched, international researchers began to install their best physics-based models of the heliosphere on a bank of high-speed supercomputers at the Community Coordinated Modeling Center (CCMC), an interagency facility located at Goddard. NASA also established the Integrated Space Weather Analysis System (iSWA) to fetch space weather information from a wide array of spacecraft and sensors. Together, these programs can take raw data from the STEREO-SDO-SOHO fleet and turn them into meaningful space weather forecasts for any point in the solar system. Interplanetary space weather forecasting is important to NASA and other space agencies as probes are now orbiting or en route to Mercury, Venus, the Moon, Mars, Ceres, Saturn, Jupiter, and Pluto. Each mission has a unique need to know when a solar storm will pass through its corner of space. This is illustrated by the ironic example of MARIE on Mars Odyssey. The sensor, designed to measure space radiation in the vicinity of the Red Planet, was disabled by a fusillade of solar protons during the Halloween storms of 2003. Turning MARIE off during the storm might have saved it, but no one knew the protons were coming. Controllers of ongoing missions such as MAVEN and Curiosity would like Mars-specific warnings to help them safeguard their hardware. Earth’s satellite fleet is similarly exposed. A widely reported example is Galaxy 15: In April of 2010, a minor CME swept past Earth just as the massive telecommunications satellite was coming out of Earth’s shadow. What happened next is still controversial, but many researchers believe events unfolded as follows: Suddenly exposed to hot, energetic electrons stirred up by the CME, the satellite began to bristle with electricity. Electrons accumulated on the surface of Galaxy 15 until a sudden discharge turned the comsat into a “zombiesat.” It stopped accepting commands from Earth and spent the next 8 months drifting through the Clarke Belt broadcasting its own signals atop those of other satellites until it was recovered. Future episodes like this may be prevented if NOAA forecasters can pinpoint when CMEs will arrive and warn satellite operators to put their assets in safe mode at crucial moments. It might seem that Galaxy 15 hardly calls for an interplanetary forecast. However, the same 3D CME modeling that permits forecasts for Mercury, Venus, and Mars also offers substantially improved forecasts for our own planet.

Modern Superstorms As mentioned previously, the iconic example of space weather hazards is the Carrington Event of 1859. Because of STEREO, researchers were able to study a recent eruption that has been compared to the Carrington Event in terms of geoeffectiveness, and few events exemplify STEREO’s full Page 13 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 8 Three views of the July 23, 2012, CME: STEREO-B COR2, SOHO LASCO C3, and STEREO-A COR2 (Courtesy of the STEREO/SECCHI consortium)

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Fig. 9 Left: The measurements derived from the multiple viewing angles of the July 2012 CME were then used as input to simulations. 3D models forecast the propagation and evolution of the CME in the inner heliosphere. Although the CME had a dramatic impact on much of the inner heliosphere, fortunately the majority of inner heliospheric space assets were clustered in less impacted longitudes (Courtesy of the Community Coordinated Modeling Center). Right: Radio bursts from the CME shock front as measured by STEREO-A SWAVES (Courtesy of N. Gopalswamy)

capability better than the July 23, 2012, CME. The eruption was, for the most part, directed away from geospace; however, the STEREO spacecraft were able to record one of the fastest CMEs ever observed (Russell et al. 2013) and the most intense solar energetic particle event in decades (Mewaldt et al. 2014). Baker et al. (2013) demonstrated, by combining observations and state-ofthe art models, that if the CME had been directed toward Earth it likely would have had a much larger impact than the Carrington storm. Despite being launched into the weakest solar cycle of the space age, STEREO was able to capture what could have been the storm of the century, had it impacted Earth. Figure 8 shows three views of the coronal mass ejection on 23 July 2012 as observed by the SOHO C3 and STEREO C2 coronagraphs. The multiple viewpoints allowed for a clear determination of the speed and direction of the eruption, and detection in the STEREO heliospheric imagers and in situ extended the speed measurements to 1 AU. The CME’s initial speed was determined to be 2,500  500 km/s, with a width of 140  30 . These parameters were used to drive simulations to determine the CME’s propagation through the heliospheric medium. Figure 9 shows the density impact of the CME as determined by the Wang-Sheeley-Arge (WSA)-ENLIL (Arge and Pizzo 2000; Odstrcil et al. 2004) simulation. Page 14 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 10 The July 23, 2012, CME was detected at STEREO-A only 19 h after the eruption, the fastest transit ever measured. The bottom panel shows the local solar wind speed detected by STEREO-A PLASTIC, the middle panel shows the magnetic field measurements from STEREO-A IMPACT, and the upper panel shows the IMPACT SEPT, LET, and HET energetic proton measurements (Figure adapted from Russell et al. 2013)

SWAVES added valuable information about the leading edge of the shock of the CME, determining from type II drift frequencies that the leading edge of the shock was traveling at ~3,000 km/s (Fig. 9). The shock extended over 240 in longitude, as most of the inner heliosphere felt the impact of the eruption. The increased energetic particle fluxes were detected almost immediately, and the shock and CME were detected in situ later in the day (around 21:00 UT), when solar wind speeds spiked to over 2,000 km/s and the magnetic field strength increased to over 100 nT (see Fig. 10). The 19-h CME transit time from the Sun to 1 AU is the fastest ever measured directly, as the 17-h transit time of the Carrington Event was inferred from the flare and the geospace impacts (Figs. 11, 12, and 13). Although the transit time was slightly longer than the Carrington Event, the estimated geomagnetic impact based on models described in Baker et al. (2013) indicates that if the CME had impacted Earth, the storm would have been even greater than the famous 1859 Carrington storm. Without STEREO, little information would have been available on this “modern” Carrington Event, and we would have missed the opportunity to study what could have been the storm of the century. In addition, thanks to STEREO, we now know that huge potentially damaging events can occur at any phase of the solar cycle irrespective of the degree of sunspot activity.

Interplanetary “Nanodust” Another discovery by STEREO is not a hazard to planets, but it could be a hazard to spacecraft moving rapidly through interplanetary space. The discovery is “nanodust.”

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 11 Dust trails as detected by the STEREO-A HI1 imager on May 1, 2007. The image at the right shows the HI-1 image in the left image with a prior image subtracted from it, thereby enhancing the dust trails (Courtesy of the STEREO/ SECCHI consortium. See St. Cyr et al. 2009)

Fig. 12 These series of three still images were taken from a visualization of Comet Encke flying through the solar storm as witnessed by the STEREO satellite. Note Encke’s tail being torn off by the coronal mass ejection, highlighted by the red line, in the second and third frames (Courtesy of A. Vourlidas and R. A. Howard, see Vourlidas et al. 2007)

The solar system is choked full with dust. We see these particles disintegrating in the night sky as meteors, and we see them in even greater numbers scattering sunlight from the plane of the solar system. Observers call it the “zodiacal light.” Nanodust is much smaller than these ordinary forms of space dust. Nanodust particles lie at the frontier between macroscopic objects and atomic structures. Unlike regular dust, which is mainly

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

V837 Tau

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Fig. 13 NASA’s STEREO Spacecraft Discovers New Eclipsing Binary Stars: A STEREO Heliospheric Imager (HI-1A) image taken on March 7, 2010 (left), with two variable stars highlighted in the image. The varying brightness of the two stars V837 Tau and V1129 Tau are shown (right top and bottom, respectively) (Courtesy of D. Bewsher and the STEREO/SECCHI consortium)

controlled by the gravitational field of the Sun, nanodust grains have a high electric charge relative to their mass and therefore strongly interact with the solar wind’s magnetic field. The solar wind sweeps up grains of nanodust and accelerates them to velocities of hundreds of kilometers per second (a million mph) near Earth’s orbit. These microscopic bullets can create surface charges on the hulls of interplanetary spacecraft. Indeed, this is how STEREO found them, using SWAVES. Each of the twin probes has a long antenna for sensing radio waves generated by CMEs plowing through the Sun’s atmosphere and, later, through the interplanetary medium. When a grain of nanodust hits STEREO at high velocity, it “craters out” and ionizes some of the spacecraft’s surface material. Impacts close enough to an SWAVES antenna produce a voltage pulse. Researchers counted these pulses to determine the flux of grains in the 5–20 nm size range. They found, surprisingly, that the population of nanodust makes up a significant fraction of the total mass of dust in interplanetary space (Le Chat et al. 2013).

Comets Finally, the STEREO probes have made exciting new observations of comets. It started with Comet Encke in 2007. Amateur astronomers know Comet Encke is the source of the Taurid meteor shower, a slow display of midnight fireballs that occurs every year in early- to mid-November. Every 3.3 years, the comet dips inside the orbit of Mercury where it is exposed to solar activity at point blank range. In April 2007, only 6 months after the mission launched, STEREO-Ahead watched a CME strike the comet and rip off its tail. CMEs have surely collided with comets before, but this was the first time a spacecraft had witnessed the process. At first glance, it might seem surprising that a CME could rip off Encke’s tail. For all their mass and power, CMEs are spread over a large volume of space. The impact of a gossamer CME exerts little more than a few nanopascals of mechanical pressure – softer than a baby’s breath. Therefore, the ripping action must be due to something else. Researchers now believe the explanation is “magnetic reconnection.” Magnetic fields around the comet bumped into oppositely directed magnetic fields in the CME. Suddenly, these fields linked together – they Page 17 of 21

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“reconnected” – releasing a burst of energy that tore off the comet’s tail. A similar process takes place in Earth’s magnetosphere during geomagnetic storms powering, among other things, the aurora borealis. In a sense, the comet experienced a geomagnetic storm. It is the first time astronomers witnessed such an event on another cosmic body. Four years later, in December 2011, STEREO was joined by an armada of solar observatories in watching Comet Lovejoy plunge through the Sun’s atmosphere. In this case, it was the Solar Dynamics Observatory, not STEREO, which had the best view. Dramatic SDO movies showed the sungrazing comet’s tail veering back and forth as it was buffeted by magnetic structures in the solar corona. Movies of these interactions have sparked a number of studies on how comets can be used as “solar probes.” Just as you can learn about the hydrodynamics of a pond by tossing a stone into it and watching the ripples, you can learn about the magnetohydrodynamics of the solar corona by watching comets fly through. STEREO took center stage again when Comet ISON approached the Sun in 2013. The Heliospheric Imagers on STEREO-A tracked the comet from the orbit of Earth all the way to the doorstep of the Sun’s atmosphere. No other observatory in space or on Earth could match the quality of the movies STEREO obtained. Footage showed gusts of solar wind buffeting the comet, whirls, and eddies of plasma propagating down the comet’s tail and even a remarkable conjunction between Comet ISON and Comet Encke. When ISON entered the Sun’s atmosphere, STEREO’s coronagraphs followed the action as the comet, lamentably, broke apart. It turns out that Comet ISON was not as tough as its predecessor Comet Lovejoy, so it did not survive its brush with solar fire. STEREO’s coronagraphs and Heliospheric Imagers watched as a cloud of dust emerged where Comet ISON was supposed to be – and quickly faded into the black void of space. On the bright side, STEREO and other observatories such as SOHO had a ringside seat for the disruption of a comet, an event which researchers are enthusiastically studying even now.

“Sun as a Star” Studies Although STEREO is primarily a solar mission, the team realized that the stability of the Heliospheric Imagers (HI) aboard the twin spacecraft could be used to monitor variations in the brightness of stars (Wraight et al. 2012). Researchers have discovered 122 new eclipsing binary stars and observed hundreds more variable stars in an innovative survey using STEREO. STEREO’s ability to sample continuously for up to 20 days, coupled with repeat viewings from the spacecraft during the year, makes it an invaluable resource for researching variable stars. Observations from the HI cameras are enabling scientists to pin down the periods of known variables with much greater accuracy. In addition, HI measurements may be useful for exoplanet and asteroseismology research (Wraight et al. 2011). Very small changes to the brightness of stars can be detected, which could reveal the presence of transiting exoplanets or trace a star’s internal structure by measuring their seismic activity. One such case has been already identified using HI data. The twin STEREO probes have proven to be among the most versatile spacecraft ever launched. Nevertheless, there is still one area where they have not yet “spread their wings” – the search for potentially hazardous asteroids. Asteroids approaching Earth from the direction of the Sun are among the most difficult to detect by ground-based observatories. Detecting faint objects in the vicinity of the Sun, however, is STEREO’s specialty. The Heliospheric Imagers could prove to be useful tools for asteroid hunters, but this is not a capability that researchers are exploiting. This should be considered a small omission, though, given the scope of STEREO’s accomplishments so far.

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Conclusion When the words “planetary hazards” are spoken, most people (lay and scientist alike) probably think of asteroids. Yet when was the last time an asteroid did serious damage to human civilization? The Tunguska Event of 1918 leveled a forest, not a city, and the Chelyabinsk Meteor of 2013, which exploded over a populated area in the Urals of Russia did little more than break some windows. This is not to say that asteroids are safe; they most certainly are not. However, to find a recent example of substantial damage to human interests caused by a heavenly body, the place to look is the Sun. There are multiple examples in the last 25 years alone. During the great Quebec Blackout of 1989, for instance, more than nine million people spent a cold autumn night without lights or power. The same storm that blacked out Quebec damaged multiton transformers as far away as New Jersey and Great Britain and caused more than 200 power anomalies across the USA from the eastern seaboard to the Pacific Northwest. A similar series of “Halloween storms” in October 2003 triggered a regional blackout in southern Sweden and may have damaged transformers in South Africa. And eruptions like the July 23, 2012, CME demonstrate how even weak solar cycles have the ability to produce historic events. Strong solar storms are not far-fetched and improbable. They have happened in our lifetime. The problem we face is, ironically, progress. Since the beginning of the Space Age, the total length of high-voltage power lines crisscrossing North America has increased nearly tenfold. This has turned power grids into giant antennas for geomagnetically induced currents. With demand for power growing exponentially, modern networks are sprawling, interconnected, and stressed to the limit – a recipe for trouble, according to the 2008 report of the National Academy of Sciences: “The scale and speed of problems that could occur on [these modern grids] have the potential to impact the power system in ways not previously experienced.” Storms akin to the Carrington Event or the Quebec Blackout could cause lasting damage to these modern smart power grids, irreparably damaging transformers and knocking out power for months in areas hundreds to thousands of miles wide. Clean water supplies, financial services, telecommunications, and even some aspects of medical care could be crippled. These dangers are the reason why we can call STEREO a “planetary hazards mission.” Although the twin probes were dispatched to do research, they have quickly produced practical benefits, arguably advancing the art and science of space weather forecasting more than any other solar observatory. As humankind expands into the solar system, STEREO will be remembered as the mission that gave a new broader meaning to the term “planetary hazards.” Earth is not the only world in the crosshairs of the Sun. With STEREO, and follow-up missions like it, we may be able to protect them all.

Acknowledgments The authors would like to thank the STEREO SECCHI, SWAVES, IMPACT, and PLASTIC investigations for their support in the preparation of this manuscript. Additionally, the authors gratefully acknowledge contributions and editorial support from Nat Gopalswamy, Joseph Gurman, Russell Howard, Ian Richardson, William Thompson, and Angelos Vourlidas.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_17-1 # Springer International Publishing Switzerland (outside the USA) 2014

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Early Solar and Heliophysical Space Missions ▶ Fundamental Aspects of Coronal Mass Ejections ▶ Solar and Heliospheric Observatory ▶ Solar Dynamics Observatory

References Arge CN, Pizzo VJ (2000) Improvement in the prediction of solar wind conditions using near-real time solar magnetic field updates. J Geophys Res 105:10465 Baker DN et al (2013) A major solar eruptive event in July 2012: defining extreme space weather scenarios. Space Weather 11:585 Bougeret JL et al (2008) S/WAVES: the radio and plasma wave investigation on the STEREO mission. Space Sci Rev 136:1–4 Byrne JP, Maloney SA, McAteer RTJ, Refojo J, Gallagher PT (2010) Propagation of an Earthdirected coronal mass ejection in three dimensions. Nat Commun 1:74 DeForest CE, Howard TA, Tappin SJ (2011) Observations of detailed structure in the solar wind at 1 AU with STEREO/HI-2. Astrophys J 738:103 DeForest CE, Howard TA, McComas DJ (2013) Tracking coronal features from the low corona to earth: a quantitative analysis of the 2008 December 12 coronal mass ejection. Astrophys J 769:43, and references therein Galvin AB et al (2008) The Plasma and Suprathermal Ion Composition (PLASTIC) investigation on the STEREO observatories. Space Sci Rev 136:1–4 Guhathakurta M (2013) Interplanetary space weather: a new paradigm. EOS Trans Am Geophys Union 94(18):165 Howard RA et al (2008) Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI). Space Sci Rev 136:1–4 Kaiser ML et al (2008) The STEREO mission: an introduction. Space Sci Rev 136:1–4 Le Chat G et al (2013) Interplanetary nanodust detection by the solar terrestrial relations observatory/waves low frequency receiver. Sol Phys 286:549 Luhmann JG et al (2008) STEREO impact investigation goals, measurements, and data products overview. Space Sci Rev 136:1–4 Mewaldt RA et al (2014) A 360 view of solar energetic particle events, including one extreme event, submitted to the Proceedings of the International Cosmic Ray Conference 2014 National Research Council (2008) Severe space weather events – understanding societal and economic impacts, space studies board report. National Academic Press, Washington, DC, pp 3 and 77 Odstrcil D et al (2004) Initial coupling of coronal and heliospheric numerical magnetohydrodynamic codes. J Atmos Solar-Terrestrial Phys 66:1311 Patsourakos S, Vourlidas A, Stenborg G (2012) Direct evidence for a fast coronal mass ejection driven by the prior formation and subsequent destabilization of a magnetic flux rope. Astrophys J 764:125

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Russell CT et al (2013) The very unusual interplanetary coronal mass ejection of 2012 July 23: a blast wave mediated by solar energetic particles. Astrophys J 770:38 Schrijver CJ, Title AM (2011) Long-range magnetic couplings between solar flares and coronal mass ejections observed by SDO and STEREO. J Geophys Res 116:A4 St. Cyr OC et al (2009) STEREO SECCHI and S/WAVES observations of spacecraft debris caused by micron-size interplanetary dust impacts. Sol Phys 256:475–488 Thernisien A, Vourlidas A, Howard RA (2006) Modeling of flux rope coronal mass ejections. Astrophys J 652:763 Vourlidas A, Lynch BJ, Howard RA, Li Y (2013) How many CMEs have flux ropes? Deciphering the signatures of shocks, flux ropes, and prominences in coronagraph observations of CMEs. Sol Phys 284:179 Vourlidas A et al (2007) First direct observation of the interaction between a comet and a coronal mass ejection leading to a complete plasma tail disconnection. Astrophys J 668:L79 Wraight KT, White GJ, Bewsher D, Norton AJ (2011) STEREO observations of stars and the search for exoplanets. Mon Not R Astron Soc 416:2477 Wraight KT, Fossati L, White GJ, Norton AJ, Bewsher D (2012) Bright low mass eclipsing binary candidates observed by STEREO. Mon Not R Astron Soc 427:2298

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

The Earth’s Natural Protective System: Van Allen Radiation Belts Sayavur I. Bakhtiyarov* NMTech Socorro, Socorro, NM, USA

Abstract In this chapter the reviews of radiation electron anomalies and seismic activities, remediation of natural and artificial radiation belts, and feasibility of an electric generator converting kinetic energy of particles of the radiation belts into electric power are provided.

Keywords Space radiation; Van Allen radiation belts; Geomagnetic disturbance; Radiation remediation; Geomagnetic storm; Ring current; Corpuscular stream; Plasmapause; South Atlantic Anomaly; Radiation belt remediation; L-shells; MeV

Introduction Van Allen radiation belts consist of layers of plasma (charged particles) around the Earth. These belts extend 1,000–60,000 km above the Earth’s surface and are supported by its magnetic field. There are suggestions that the particles that form the Van Allen belts come from solar wind and cosmic rays. The belts are located in the inner section of the geomagnetosphere. The outer belt is formed mainly by energetic electrons and the inner belt by a combination of protons and electrons. Both radiation belts contain small amounts of other nuclei. These radiation belts are harmful to artificial space satellites orbiting a considerable time in the radiation belts. Therefore, an ample shielding is required to protect their electronic components. A third (transient) radiation belt was discovered by NASA’s Goddard Space Flight Center in 2013 using the Radiation Belt Storm Probes launched on August 30, 2012. The mission is expected to last from 2 to 4 years. This belt was observed for 4 weeks, and it was destroyed by a strong Sun’s shock wave (Fig. 1). The toroidal-shaped outer electron radiation belt is extended from 13,000–60,000 km above the Earth. Its maximum radiation intensity is at 24,000–30,000 km above the Earth. The outer belt is produced by the inward radial diffusion and local acceleration due to transfer of energy from plasma waves to radiation belt electrons. The outer belt consists of high-energy (up to 10 MeV) electrons ensnared by a magnetosphere of the Earth. The trapped particles of the outer belt consist of electrons and different ions such as energetic protons, alpha particles, and O+ oxygen ions. This mixture of ions suggests that ring current particles probably come from more than one source. The particles in the outer belt have higher fluctuation amplitudes than the inner belt. The inner belt contains high concentrations of electrons and energetic protons with energies more than 100 MeV. The inner electron belt extends from an altitude of 1,000–6,000 km above the Earth. During strong solar activities, the inner periphery can reach 200 km above the Earth. Also, the inner

*Email: [email protected] Page 1 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014 Rotational Axis Magnetic Axis

Outer Radiation Belt Inner Radiation Belt

Fig. 1 Van Allen radiation belts

Fig. 2 NASA’s Van Allen Probe (Credit: JHU/APL, NASA)

belt is closer to the South Atlantic Anomaly (SAA) area due to the offset of the belts relative to the Earth’s geometric center. The magnetic field and plasma disturbances produced by the Sun result in geomagnetic storms which consequently impact energetic (radiation) particle fluxes. It is suggested that injections and acceleration of particles from the tail of the magnetosphere would increase particle flux. The NASA’s Institute for Advanced Concepts developed a technique to collect natural antimatter existed in the Van Allen belts (Fig. 2). It is estimated that only several micrograms of antiprotons are present in the whole belt. It is believed that the radiation belts exist around other planets of the solar system. The NASA’s Voyager program discovered the existence of similar magnetic belts around other planets such as Neptune and Uranus. Two most important features of geomagnetic storms are (1) an initial increase in the horizontal magnetic force at the Earth’s surface and (2) a subsequent larger and more prolonged decrease (Akasofu and Chapman 1961). In 1917 Schmidt (1917) ascribed the decrease to the influence of a westward electric current (now called the geomagnetic ring current) that encircles the Earth. Schmidt concluded that it must wax and wane as magnetic disturbance increases or decreases. Page 2 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

From a study of the monthly means of the horizontal component, he suggested that the electric current never dies away completely but is a permanent companion of the Earth. Schmidt attributed magnetic storms to the influence of corpuscular streams or clouds from the Sun. The obvious proposition of his conclusions was that some of the solar matter remains near the Earth for a significant period. In other words, the solar material is partially trapped by the Earth’s magnetic field, and one consequence is the enhancement of the ring current and its geomagnetic effects. Schmidt did not consider the scale or the location of the current. Chapman and Ferraro (1931a, b, 1933, 1940) and Ferraro (1952) attempted to understand by mathematical deduction the consequences of the impact of a neutral ionized solar stream upon the Earth. Their theory discussed an idealized “model” which did not consider significant features of the real situation. Their idealized and simplified presumptions indicate the fundamental mechanism of the first phase of magnetic storms and the scale of the penetration of the solar gas. The deflection of the gas particles by the geomagnetic field, by which most of the gas is continuously reflected or scattered away from the Earth, produces the first phase of the storm. It was established that some of the gas found its way into the Earth’s atmosphere in high latitudes and there produced auroras. But some gas was retained in the field for a time in the form of a ring current. The authors were unable to explain or describe the motions of these two subgroups of the solar particles. However, they postulated the existence of the ring current, on the basis of the geomagnetic evidence, and discussed the equilibrium, stability, and decay of the current. They assumed a toroidal current ring model with protons and electrons circulating around the geomagnetic axis, with vaguely different speeds, the motion of the protons, at least, being westward. According to Alfven (1957), this type of ring current is unstable. Singer (1957) proposed a different model of the trapped component of the solar gas, based on the work of Stormer (1955) and Alfven (1957). Instead of a toroidal form and a simple circular motion for most of the particles of the gas, Singer indicated that the gas would have the form and motions proved by later satellite and cosmic rocket exploration (Van Allen and Frank 1959; Vernov et al. 1959). According to Singer, the particles oscillate rapidly between mirror points in fairly high northern and southern latitudes. At the same time, they circle round the magnetic field lines and also drift round the Earth – the protons westward and the electrons eastward. Singer concluded that these motions necessarily correspond to a ring current around the Earth. Later, the ring current and its field were discussed by Dessler and Parker (1959) and by Akasofu (1961). Dessler and Parker (1959), for example, developed a formula relating the total energy of the ring current to the magnetic field perturbation at the center of the Earth. Their analysis considered two particle distributions, isotropic and completely equatorial, and the validity of this formulation for all pitch angle distributions were extended by other researchers later. Dessler and Parker (1959) also extended the arguments that the main phase of the geomagnetic storm is caused principally by protons or electrons with kilovolt energies trapped in the geomagnetic field, and the authors concluded that the main contribution arises from protons trapped at a geocentric distance of 3–5 Re. For the time being, satellite observations bearing on these problems have been made during magnetically quiet and disturbed periods. The radiation belts have been much observed, and some magnetic measurements have been made by the USSR Mechta and the US Explorer VI. The Mechta found magnetic deviations that indicated a ring current in the outer Van Allen belts. The Explorer VI found evidence of a ring current much farther out, in a region beyond 5 Earth radii, and its presence was supposed from auroral and magnetic data. The large decrease in the horizontal component of the Earth’s field during the main phase of magnetic storms has been ascribed to the formation or enhancement of a geomagnetic ring current. Akasofu and Chapman (1961) discussed the motions of particles trapped in the Earth’s dipole field and the resulting ring current. These calculations deal only with a steady state, though during storms Page 3 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

the state is changing. The general equations for the current intensity, to obtain the total current and the magnetic field at the Earth’s center, were applied to the outer radiation belt (V2) and to a special “model” belt V3. The V3 belt had a particular type of pitch angle distribution and a number-intensity distribution of Gaussian type along an equatorial radius. The results are considered in connection with magnetic records for several storms and with satellite data. The authors suggested that during magnetic disturbance, protons of energy of the order of a few hundred keVare occasionally captured between 5 and 8 Earth radii and that they produce a transient belt V3. The variety of development of the ring current from one storm to another may be connected with irregularities in the distribution of particles in the solar stream, which may contain tangled magnetic fields. As was shown by Alfven (1950), the motion of a charged particle in a magnetic field can in certain circumstances be analyzed into the motion of a “guiding center” associated with the particle (this motion being partly along and partly across the lines of force) and virtually circular motion around the lines of force, relative to the guiding center. The motion of the guiding center across the lines of force is often called a drift. The guiding center approximation is valid (i) when the average radius R of the circular motion is much less than the scale length of the system considered and (ii) when the period T of the circular motion is much less than the other scale times associated with the phenomenon. According to Chapman (1961), in the Earth’s undisturbed dipole field, the scale length is of the order of 8000 km, and the scale time is of the order of 104 s in the ring current problem. It is generally assumed that the naked Earth bears a large negative electric charge, Qs, generating a vertical electric field at its surface. In the fair-weather area, the magnitude of this electric field is about 100 V/m, corresponding to a charge Qs ¼ 4pe0rs2E ¼ 4.5  105 C (rs ¼ 6371 km) at Earth’s surface (Uman, 1974). However, an almost equal amount of positive charge is distributed throughout the Earth’s nearest atmosphere. Apart from QE, it is assumed that the two Van Allen belts (Van Allen and Frank 1959) also bear a net electric charge: a positive charge Qi for the inner torus and a negative charge Qo for the outer torus. The two described belts are separated by a region with zero net charge, the so-called electron slot. The magnetic field around the Earth is important for the orientation of the Van Allen belts, and the electric interactions between the charges QE, Qi, and Qo were investigated by many researchers. Starting from the three tori model, recently developed for pulsars and black holes (Biemond 2007), equilibrium between the charges QE, Qi, and Qo appears to be possible. From the same model, three different expressions for the Coulomb electric field, depending on the distance from the Earth’s center, have been derived by Biemond (2007). The deduced Coulomb electric field at the plasmapause is put equal to the so-called corotation field. Values for the charges QE, Qi, and Qo were calculated for the solar maximum or minimum, respectively. The results of the idealized model were discussed, and the contributions to the Earth’s magnetic field caused by the proposed charges QE, Qi, and Qo were calculated. Since the latter contributions appear to be almost negligible, a previously proposed gravitational explanation of the Earth’s magnetic field was considered (Biemond 2007). Especially, the so-called Wilson–Blackett law was discussed. In order to obtain agreement between observed and predicted magnetic fields, the existence of a large toroidal current in the Earth was assumed. Stoffle et al. (2011) carried out FLUKA simulations of energy deposition within the silicon layer using models describing the particle flux within the Van Allen Radiation Belts as well as for Galactic Comic Ray particle interactions. The approach taken in the simulation of tracks for individual frames within the Timepix detector necessitates a time resolution on a scale sufficient to differentiate between points within the vehicle trajectory which are less than 1/10th of an orbit. This is necessary to differentiate between portions of the vehicle orbit that are well shielded and portions that traverse regions of the geomagnetic field open to the Van Allen belts and lower Page 4 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

energy Galactic Cosmic Rays. Timepix is a version of the technology developed by the Medipix2 Collaboration (Llopart et al. 2007), which is based at CERN. It is a pixel-based ASIC wherein the electronics for each of the individual 55 m m square pixels is contained within the footprint of that pixel. The Timepix version of the Medipix2 detector has a charge-sensitive preamp and an associated discriminator attached to a logic unit capable of being employed in one of the several different modes including as a simple counter for the number of times that the externally applied common threshold value has been exceeded (Medipix mode), as a time-to-digital converter (TDC), or for the application described here, as a Wilkinson-type analog-to-digital converter (ADC). Each pixel has a 14-bit pseudorandom shift register for data storage and transfer, and there is an adjustable global “shutter” that gates the data-taking active time. Current ground-based applications take advantage of the technology’s dynamic range and radiation hard design. These same characteristics make it an ideal candidate for use in space radiation environments. To that end, work toward simulation of tracks from individual particles has begun in order to understand both the detector response as well as provide initial input for design of hardware and software based on the Timepix technology for use aboard both manned and unmanned space vehicles. While the initial intent is simulation of the space radiation environment, the same approach can be utilized with other radiation sources, and the method can be adapted to simulations of medical diagnostics as well as larger scale experiments utilizing the Timepix technology. The fundamental approach for the simulation of tracks in a Timepix silicon detector is outlined and initial results are presented by Stoffle et al. (2011). In addition, several areas are identified that allow enhancement in the simulation fidelity. The Timepix readout chip is a hybrid pixel detector with over 65 k independent pixel elements. Each pixel contains its own circuitry for charge collection, counting logic, and readout. When coupled with a Silicon detector layer, the Timepix chip is capable of measuring the charge, and thus energy, deposited in the Silicon detector layer. Such simulations are useful in characterizing the Timepix Si detector response in a mixed radiation field with application to similar detectors’ future use as dosimeters and area monitors aboard manned spaceflight missions. The core technology is also applicable to purely scientific instrumentation. The ISS orbit inclination is high enough that it traverses both the South Atlantic Anomaly and low rigidity cutoff regions, and as a result sees both inner and outer Van Allen belt populations, as well as accessing locations in the geomagnetic field containing lower energy galactic cosmic rays (GCRs) populations. The Space Environment Information System (SPENVIS) trajectory generation tool was used to generate the trajectory of interest. Latitude, longitude, altitude, as well as B and L coordinates were generated for one-minute increments along the orbit trajectory. Additionally, the two-line element historical data was used to interrogate the trajectory to identify 1/10th of an orbit track lengths that traversed both the geomagnetic cusp regions and well-shielded regions of the vehicle orbit.

Radiation Electron Anomalies and Seismic Activities Inside the Van Allen belts, electrons and ions trail spiral trajectories around the field line of the Earth’s magnetic field, while drifting perpendicular to the magnetic field, in opposite direction to protons and electrons. Simultaneously, ions and electrons moving toward higher latitudes are reflected in the strong magnetic field and are trapped within the inner and the outer Van Allen belts. A considerable effort has been made to detect and interpret electromagnetic phenomena related to seismic activity, and, a number of characteristic physical changes have been confirmed as antecedent signals of preparing earthquakes. Several methodologies have been developed, which Page 5 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

use Earth-based instrumentation to detect electromagnetic variations occurring in the lithosphere (Kopytsenko et al. 1990; Hayakawa et al. 1996a; Varotsos et al. 1998). Other studies have shown that, before strong earthquakes, characteristic electromagnetic interactions occur in the ionosphere, which are observed as plasma variations or electromagnetic emissions, by either Earth-based (Hayakawa et al. 1996b; Pulinets and Boyarchuk 2004) or space-based (Parrot 2006; Li and Temerin 2000) instrumentation. In addition to the earthquake-related electromagnetic phenomena taking place in the lithosphere and ionosphere, electromagnetic processes related to seismic activity affect the trapped population of the radiation (Van Allen) belts, and several authors have reported satellite measurements suggesting radiation belt energetic particle flux variations during enhanced very-lowfrequency (VLF) electric field activity before earthquakes (Ginzburg et al. 1994; Galper et al. 1995; Aleksandrin et al. 2003; Pulinets and Boyarchuk 2004; Sgrigna et al. 2005). Research results based on DEMETER satellite measurements suggested no relationship between anomalous electron flow and seismic activity within 18 h from the earthquake incidence (Buzzi 2007), while more recent studies suggested that energetic electron precipitation occurs several days before strong earthquakes and that this phenomenon follow a distinct temporal pattern, at least for earthquakes in Japan, which were studied statistically (Anagnostopoulos et al. 2010). Consequently, the question whether radiation electron anomalous bursts are earthquake preliminary signals seems that it has not been obviously answered. As a result, the phenomenon of energetic electron rainfall in the upper ionosphere has not been critically considered as an important earthquake prediction instrument until now (European Space Agency).

Remediation of Natural and Artificial Radiation Belts The dipole structure of the Earth’s magnetic field has the ability to trap energetic charged particles in regions near the Earth (Hoyt and Minor 2005). Within these regions (Van Allen Radiation Belts) energetic electrons and ions generated through natural and man-made events can persevere for many years. These high-energy particles cause considerable hazard to missions in the Earth’s orbit, damaging electronics and materials in spacecraft systems and causing biological harm to people in space. The costs associated with hardening electronics and other systems to survive and perform reliably in the radiation environment are a major driver in the high costs of space systems (Hoyt and Minor 2005). The radiation belts could become more hazardous to space systems if a nuclear device is detonated at high altitude. Experiments conducted in the 1960s, such as the Starfish experiment, have shown that a high-altitude nuclear detonation (HAND) can produce an intense artificial radiation belt that can persist for several years (Hoyt and Minor 2005). Even a very-low-yield nuclear device could produce a radiation belt with a radiation flux several orders of magnitude greater than the natural environment. The intense artificial radiation belts created by a HAND event could cause rapid failure of many government and commercial space systems and could result in tremendous damage to both the global economy and national defense capabilities (Hoyt and Minor 2005). Radiation belts, both natural and artificial, tend to follow the contours of the geomagnetic field. The size and geometry of the region affected by a HAND can vary significantly depending upon the geographic location and altitude of the explosion, with high-altitude detonations generating wide, diffuse belts and low-altitude detonations creating very narrow, intense belts. A method for rapidly remediating a HAND-induced radiation belt could provide a means for preserving a significant portion of the operational lifetime of existing satellites (Hoyt and Minor 2005). It could also provide a means of reducing the threat posed by the natural Van Allen belts to manned space missions as well as the rate of degradation of Earth-orbit satellites. Numerous concepts have Page 6 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

been proposed for remediating natural and artificial radiation belts. One of the concepts proposes to place a dense material into orbit to absorb the radiation. Unfortunately, this method would necessitate a very large amount of mass and the high launch costs to place the mass in orbit. The other concepts that have been proposed do not require to absorb the radiation but rather to scatter the charged particles, reducing the “pitch angle” between their velocity vector and the geomagnetic field vector (Hoyt and Minor 2005). If their pitch angle is reduced below a certain value, called the “loss cone angle,” the particles are no longer trapped by the convergence of the Earth’s magnetic field lines at the poles and can follow the magnetic field lines down into the upper atmosphere, where they dissipate their energy through collisions with atmospheric particles. Among the scattering-based concepts that have been proposed are the use of very-low-frequency (VLF) waves to cause resonant scattering of high-energy electrons and the use of large current loops to create localized distortions in the geomagnetic field that will scatter charged particles (Hoyt and Minor 2005). Scattering of energetic charged particles by high-voltage electrostatic tether structures may present a technically and economically viable method of rapidly remediating radiation belts caused by both natural processes and man-made events. Hoyt and Minor (2005) described a concept for a system of electrostatic tether structures designed to rapidly remediate an artificial radiation belt caused by a high-altitude nuclear detonation. The authors investigated the scaling of the system size and power requirements with the tether voltage and other design parameters. These scaling analyses indicated that a conventional single-line tether design cannot provide sufficient performance to achieve a system design that is viable. The authors proposed the innovative multi-wire tether geometry and showed that this tether design can significantly improve the overall performance of the electrostatic system, enabling the requirements for total power and number of satellite systems to be reduced to levels that are both technically and economically viable. The behavior of high-energy electrons trapped in the Earth’s Van Allen radiation belts has been extensively studied both experimentally and theoretically. During quiet times, energetic radiation belt electrons are distributed into two belts divided by the “electron slot” at L ~ 2.5, near which there is relatively low energetic electron flux (Rodger et al. 2006). Since the discovery of the radiation belts (Van Allen et al. 1958; Van Allen 1997), it has proven difficult to confirm the principal source and loss mechanisms that control radiation belt particles (Walt 1996). The large-scale injections of relativistic particles into the inner radiation belts are associated with geomagnetic storms which can result in a 105-fold increase in the total trapped electron population of the radiation belts (Li and Temerin 2000). In some cases, the relativistic electron fluxes present in the radiation belts may increase by more than two orders of magnitude (Reeves et al. 2003). In most cases, however, these injections do not penetrate into the inner radiation belt. Only in the biggest storms, for example, November 2003, do the slot region fill and the inner belt gain a new population of energetic electrons (Baker et al. 2004). Even before the discovery of the radiation belts, high-altitude nuclear explosions (HANEs) were studied as a source for injecting electrons in the geomagnetic field. This was confirmed by the satellite Explorer IV in 1958, when three nuclear explosions conducted under Operation Argus took place in the South Atlantic, producing belts of trapped electrons from the b-decay of the fission fragments. The trapped particles remained stable for several weeks near L ¼ 2 and did not drift in L or broaden appreciably (Hess 1968). Both the USA and USSR conducted a small number of HANEs, all of which produced artificial belts of trapped energetic electrons in the Earth’s radiation belts. One of the most studied was the US “Starfish Prime” HANE, a 1.4 megaton detonation occurring at 400 km above Johnston Island in the central Pacific Ocean on July 9, 1962. Again, an artificial belt of trapped energetic electrons was injected, although over a wide range of L-shells from about L ¼ 1.25 out to perhaps L ¼ 3 (Hess, 1968). The detonation also caused artificial aurora observed as far away as New Zealand, and an electromagnetic pulse which shut down Page 7 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

communications and electrical supply in Hawaii, 1,300 km away (Dupont, 2004). The effect of the Starfish Prime HANE on the radiation belts was observed by multiple spacecrafts. However, the intense artificial belts injected by the HANE damaged three of the five satellites operating at the time. Within a small number of days, data transmissions from the Ariel, Transit IVB, and TRAAC satellites became intermittent or ceased altogether (Massey, 1964), primarily due to degrading solar cells. Other effects were also noted even in this early case; the transistors flown in the first active communications satellite, Telstar, failed due to radiation exposure, even though the satellite was launched after the Starfish Prime HANE. The artificial belts produced by this Starfish Prime HANE allowed some understanding of the loss of energetic electrons from the radiation belts, as demonstrated by the comparison of calculated decay rates with the observed loss of injected electrons (Walt 1994). Collisions with atmospheric constituents are the dominant loss process for energetic electrons (>100 keV) only in the innermost parts of the radiation belts (L < 1.3) (Walt, 1996). For higher L-shells, radiation belt particle lifetimes are typically many orders of magnitude shorter than those predicated due to atmospheric collisions, such that other loss processes are clearly dominant. Above L ~ 1.5 C collision-driven losses are generally less important than those driven by whistler mode waves, including plasmaspheric hiss, lightning-generated whistlers, and man-made transmissions (Abel and Thorne 1998, 1999; Rodger et al. 2003). It is recognized that HANEs would decrease the operational lifetime of low-Earth-orbit satellites (Parmentola 2001; US Congress 2001; Steer 2002), principally due to the population of HANE-injected >1 MeV trapped electrons. It has been suggested that even a “small” HANE (~10–20 kt) occurring at altitudes of 125–300 km would raise peak radiation fluxes in the inner radiation belt by 3–4 orders of magnitude and lead to the loss of 90 % of all low-Earth-orbit satellites within a month (Dupont, 2004). In 2004, there were approximately 250 satellites operating in low Earth orbit (LEO) (Satellite Industry Association, 2004). These satellites fulfill a large number of roles, including communications, navigation, meteorology, military, and science. In the event of a HANE, or an unusually intense natural injection, this large population of valuable satellites would be threatened. Due to the lifetime of the injected electrons, the manned space program would need to be placed on hold for a year or more. However, recent theoretical calculations have led to the rather surprising conclusion that wave–particle interactions caused by man-made very-low-frequency (VLF) transmissions may dominate non-storm time losses in the inner radiation belts (Abel and Thorne 1998, 1999). This discovery has attracted significant interest, suggesting practical human control of the radiation belts (Inan et al. 2003) to protect Earth-orbiting systems from natural and man-made injections of highenergy electrons. The man-made control of the Van Allen belts has been called “Radiation Belt Remediation” (RBR). An RBR system involved an assemblage of around ten satellites (Dupont, 2004), which would transmit VLF waves so as to enormously increase the loss rate of energetic electrons by precipitation into the upper atmosphere, basically dumping the HANE-produced artificial radiation belt. In order to be effective, an RBR system needs to flush the HANE-produced 1MeVelectrons in a short time scale, which has been suggested to be as low as ~1–2 days or perhaps as long as 10 days (Papadopoulos 2001). Rodger et al. (2006) consider the upper atmospheric consequences of an RBR system in operation. The dumping of high-energy relativistic electrons into the atmosphere would generate strong energetic particle precipitation, leading to large ionization changes in the ionosphere. This type of precipitation is expected to direct to large changes in atmospheric chemistry and communications interruption, mainly for the case of HANE injections. Particle precipitation results in augmentation of odd nitrogen (NOx) and odd hydrogen (HOx), which play a crucial role in the ozone balance of the middle atmosphere because they devastate odd oxygen through catalytic reactions (Brasseur and Solomon 1986). Ionization changes produced by a 1 MeV electron will have a Page 8 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

propensity to peak at ~55 km altitude (Rishbeth and Garriott 1969). Ionization enhances occurring at similar altitudes caused by solar proton events are known to lead to local perturbations in ozone levels (Verronen et al. 2005). Changes in NOx and O3 consistent with solar proton-driven modifications have been observed (Seppala et al. 2004; Verronen et al. 2005). It is well known that the precipitation of electrons at high latitudes produces additional ionization leading to increased HF absorption at high latitudes (MacNamara 1985), in extreme cases producing a complete blackout of HF communications in the polar regions. In order to estimate the importance of RBR-driven precipitation to the upper atmosphere, the authors consider two cases of an RBR system operating to flush the artificial radiation belt injected by a Starfish Prime-type HANE over either 1 or 10 days. In the first case, they consider the effect of a space-based system, while in the second case, they also consider a ground-based RBR system. This research work examines the range of practical prospective environmental and technological effects due to this man-made precipitation, including changes to the ozone balance in the middle atmosphere and disruption to HF communication. Although, nanomaterials have found broad applications in the exploration of space, however, the emerging new generation of carbon nanoparticles doped with different clusters is not well characterized for space radiation protection purposes. An experimental approach to design and develop nanostructured materials is one of the pivotal challenges facing the nanotechnology and modern space material science. The ability to control material properties at the nano-size level by using nanoparticles in order to create arrays, patterns, and networks is an important requirement in fabricating new multifunctional nanomaterials. A utilization of the magnetic field in manufacturing nanomaterials is quite new and has the promise of broadest applications. This method is quite effective in controlling the macro- and microstructures of synthesized materials with unique properties. Rukhadze et al. (2010a, b, c, 2011a, b, c, 2012, 2013a, b) and Kutelia et al. (2012) presented the results on the characterization of the newly developed carbon nanoparticles doped with clusters and synthesized via a novel technology for space radiation protection. The authors showed based on the obtained results the possibility of using nanocomposite for spacecrafts. The objective of their work was a development of the carbon nanoparticles doped with ferromagnetic iron oxide and clusters of cobalt atoms synthesized via a novel technology which combines the method of pyrolysis of ethanol vapors and the chemical vapor deposition (CVD) process in horizontal continuous reactor with certain temperature gradients and controlled partial oxygen pressure. Scanning electron microscope (SEM) and Auger electron spectroscopy (AES) studies of synthesized magnetic carbon nanopowders showed that under freely deposited state in the absence of the external magnetic field, the nanopowder consists of the randomly distributed carbon nanoparticles’ aggregates of 200 nm diameter doped with the magnetic clusters. Under the exposure to the low external magnetic field (~0.01 T), the nanoparticles were assembled into the large-scale linear nano-chain structures.

Feasibility of an Electric Generator Converting Kinetic Energy of Particles of the Radiation Belts into Electric Power A power plant providing for power supply of operation of onboard service devices and science and technology instrumentation is one of the foremost elements of any spacecraft (Kolesnikov and Yakovlev 2008). Currently, designing the power plants transforming the natural energy of space environment into power supply is the most promising technology of development of space power engineering. This type of power source includes firstly various converters of electromagnetic radiation of the Sun (semiconductor photoelectric cells, thermoelectron, thermionic, and Page 9 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

thermoelectric converters). Along with manufacturing the power plants that use the energy of electromagnetic radiation of the Sun, the scientists and engineers are developing fundamentally new space electric power generator concepts that are based on utilizing other types of energy available in space medium such as energy of the Earth’s magnetic field (Vignoli et al. 1987), energy of the solar wind plasma (Bolonkin 1992), etc. The viability of constructing a high-voltage electric generator (HEG) transforming kinetic energy of particles of the radiation belts into electric power is considered by Kolesnikov and Yakovlev (2008). The maximum specific power of a generator was theoretically evaluated for particular cases where a generator was positioned in the Earth’s polar region inside the Earth radiation belts (ERB). The authors demonstrated that from the viewpoint of weight parameters, the suggested design of HEG is quite competitive with power sources of low-thrust spacecraft operating on conventional principles. The estimations show that specific power of HEG inside the natural radiation belts of the Earth is no more than 3.3 W/kg, but inside the auroral zone, it can exceed 100 W/kg. In its weight characteristics, the HEG construction is quite competitive with the power plants for small spacecraft operating on conventional principles. Studying the influence of leakage currents through the highvoltage vacuum gap on functioning of HEG, the authors concluded that a further substantiation of the suggested concept of power supply should include investigations of the problem of maintenance of the stiffness and stability of the generator construction and calculations of its strength characteristics. It was indicated that the Earth is not the single planet in the solar system with radiation belts. The powerful radiation belts have been found in the vicinity of other planets, such as Jupiter, Saturn, and Uranus.

Conclusion The following reviews on the Earth’s natural protective system are provided: • Radiation electron anomalies and seismic activities • Remediation of natural and artificial radiation belts • Feasibility of an electric generator converting kinetic energy of particles of the radiation belts into electric power Further space missions and researches are required to achieve scientific understanding of origins of formation of relativistic electrons and ions in space and their dynamic change in response to solar activity and the solar wind changes. Further studies are required to estimate the flux levels in the inner and outer Van Allen belts and specifically the beta radiation levels which are dangerous to humans if they were exposed for an extended period of time during space missions.

Cross-References ▶ Goddard Space Flight Center ▶ High-Altitude Nuclear Detonation ▶ NASA Institute for Advanced Concepts ▶ NASA Voyager Program ▶ Radiation Electron Anomalies and Seismic Activities Page 10 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_19-1 # Springer International Publishing Switzerland 2014

▶ South Atlantic Anomalies ▶ Space Environment Information Systems ▶ The Earth’s Natural Protective System: Van Allen Radiation Belts ▶ Van Allen Probe

References Abel B, Thorne RM (1998) Electron scattering loss in earth’s inner magnetosphere-1. Dominant physical processes. J Geophys Res 103:2385–2396 Abel B, Thorne RM (1999) Correction to “Electron scattering loss in earth’s inner magnetosphere, 1. Dominant physical processes” and “Electron scattering loss in earth’s inner magnetosphere, 2. Sensitivity to model parameters”. J Geophys Res 104:4627–4628 Akasofu SI (1961) The ring current and the outer atmosphere. J Geophys Res 65:535–543 Akasofu SI, Chapman S (1961) The ring current, geomagnetic disturbance, and the Van Allen radiation belts. J Geophys Res 66(5):1321–1350 Aleksandrin SY, Galper AM, Grishantzeva LA, Koldashov SV, Maslennikov LV, Murashov AM, Picozza P, Sgrigna V, Voronov SA (2003) High-energy charged particles bursts in near-Earth space as earthquake precursors. Ann Geophys 21:597 Alfven H (1950) Cosmical electrodynamics. Oxford University Press, Oxford Alfven H (1957) On the theory of magnetic storms and aurorae. Tellus 10:104–116 Anagnostopoulos G, Rigas V, Athanasiou M, Iliopoulos A, Vassiliadis E, Iossifidis N (2010) Temporal evolution of energetic electron precipitation as a promising tool for earthquake prediction research: analysis of IDP / DEMETER observations, 9th Hellenic Astronomical Society Conference. Publ Astron Soc Pacific 424:67–74 Baker DN, Kanekal SG, Li X, Monk SP, Goldstein J, Burch JL (2004) An extreme distortion of the Van Allen belt arising from the “Halloween” solar storm in 2003. Nature 432(7019):878–880 Biemond J (2007) The origin of the magnetic field of pulsars and the gravitomagnetic theory. In: Lowry JA (ed) Trends in pulsar research. Nova, New York, Chapter 2 Bolonkin A (1992) Space electric generator run by solar wind. In: World apace congress: 43rd congress international astronaut federation (IAF) and 29th Plen. Meet. Comm. Space Res. COSPAR (28 Aug–5 Sept 1992, Washington, DC), pp 182–183 Brasseur G, Solomon S (1986) Aeronomy of the Middle Atmosphere. Second edition, D. Reidel Publishing Company, Dordrecht Buzzi A (2007) DEMETER satellite data analysis of seismo-electromagnetic signals. Doctorate thesis, University of Rome Chapman S (1961) Scale times and scale lengths of variables with geomagnetic and ionospheric illustrations. Proc Phys Soc London 77:424–432 Chapman S, Ferraro VCA (1931a) A new theory of magnetic storm. Terr Magn Atmos Electr 36:77–97 Chapman S, Ferraro VCA (1931b) A new theory of magnetic storm. Terr Magn Atmos Electr 36:171–186 Chapman S, Ferraro VCA (1933) A new theory of magnetic storms, II, The main phase. Terr Magn Atmos Electr 38:79–96 Chapman S, Ferraro VCA (1940) The theory of the first phase of a geomagnetic storm. Terr Magn Atmos Electr 45:245–268

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U.S. Congress (2001) Report of the commission to assess United States national security, space management and organization, public law 106–65, Chapter II: space: today and the future, 21–22, 11 January 2001 Dessler AJ, Parker EN (1959) Hydromagnetic theory of geomagnetic storms. J Geophys Res 64:2239–2252 Dupont DG (2004) Nuclear explosions in orbit. Sci Am 290:68–75 European Space Agency, Space Environment Information System, http://www.spenvis.oma.be/ Ferraro VCA (1952) On the theory of the first phase of a geomagnetic storm. J Geophys Res 57:14–49 Galper AM, Koldashov SV, Voronov SA (1995) High energy particle flux variations as earthquake predictors. Adv Space Res 15:131–134 Ginzburg EA, Malishev AB, Proshkina IP, Pustovetov VP (1994) Correlation of strong earthquakes with radiation belt particle flux variations. Geomagn Aeron 34:315–320 Hayakawa M, Kowate R, Molcanov OA, Yomoto K (1996a) Results of ultra-low-frequency magnetic measurements during the Guan earthquake of 8 August 1993. Geophys Res Lett 23:241 Hayakawa M, Molcanov OA, Ondoh T, Kawai E (1996b) The precursory signature effect of the Kobe on VLF subionospheric signals. J Comm Res Lab, Tokyo 43:160 Hess WN (1963) The artificial radiation belt made on July 9, 1962. J Geophys Res 68(3):667–683 Hess WN (1968) The radiation belt and magnetosphere. Blaisdell, London Hoyt RP, Minor BM (2005) Remediation of radiation belts using electrostatic tether structures. In: Proceedings of IEEE aerospace conference, Big Sky, pp 583–594 Inan US, Bell, TF, Bortnik J, Albert JM (2003) Controlled precipitation of radiation belt electrons. J Geophys Res 108:1186 Kolesnikov EK, Yakovlev AB (2008) Harnessing of the power of the solar wind particles captured in the Van Allen belts. In: ACT workshop on innovative concepts. ESA-ESTEC (28–29 January 2008), pp 1–9 Kopytsenko Y, Matiashvili TG, Voronov PM, Kopytsenko EA, Molchanov OA (1990) Ultra low frequency emission associated with Spitak earthquake and following after shock activity using geomagnetic observatories Dusheti and Vrtya. IZMIRAN 3:888 Kutelia ER, Rukhadze LN, Maisuradze NI, Kukhalashvili GV, Dzigrashvili TA, Kukava TG, Bakhtiyarov SI (2012) The mechanism of core-shell type magnetic carbon nano-particles formation on the surface of ferromagnetic metal plate substrates. Georgian Engg News 2 Li XL, Temerin MA (2000) The electron radiation belt. Space Sci Rev 95(1–2):569–580 Llopart X, Ballabriga R, Campbell M, Tlustos L, Wong W (2007) Timepix, a 65 k programmable pixel readout chip for arrival time, energy and/or photon counting measurements. Nucl Instrum Meth Phys Res A 581:485 Massey H (1964) Space physics. Cambridge University Press, UK MacNamara LF (1985) High frequency radio propagation, in Handbook of Geophysics and the Space Environment, edited by Jursa AS, Chapter 10, Air Force Geopys. Lab., US Air Force, 45–65 Papadopoulos D (2001) Threat to satellites of a high altitude nuclear detonation. Proc of 1st meeting of Future of Space, Washington, DC Parmentola J (2001) High altitude nuclear detonations (HAND) against low earth orbit satellites (“HALEOS”). In: Report of the defense threat reduction agency, Advanced systems and concepts office, Fort Belvoir Parrot M (2006) Special issue: first results of the DEMETER micro-satellite. Planet Space Sci 54(5):411–558 Page 12 of 14

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Pulinets S, Boyarchuk K (2004) Ionospheric precursors of earthquakes. Springer, Berlin Reeves GD, McAdams KL, Friedel RHW, O’Brien TP (2003) Acceleration and loss of relativistic electrons during geomagnetic storms. Geophys Res Lett 30(10):1529 Rishbeth H, Garriott O (1969) Introduction to ionospheric physics. New York, Academic Press Rodger CJ, Clilverd MA, McCormick RJ (2003) Significance of lightning generated whistlers to inner radiation belt electron lifetimes. J Geophys Res 108(12):1462 Rodger CJ, Clilverd MA, Ulich T, Verronen PT, Turunen E, Thomson NR (2006) The atmospheric implications of radiation belt remediation. Ann Geophys 24:2025–2041 Rukhadze LN, Kutelia ER, Maisuradze NI, Eristavi BG, Bakhtiyarov SI (2010a) Magnetic carbon nanopowders. J Mater Sci Eng 4(2):75–80 Rukhadze LN, Kutelia ER, Maisuradze NI, Eristavi BG, Bakhtiyarov SI (2010b) Development of Novel Magnetic Carbon Nanopowders. In: ASME international mechanical engineering congress and exposition, Vancouver, Nov 12–18 Rukhadze LN, Kutelia ER, Maisuradze NI, Eristavi BG, Bakhtiyarov SI (2010c) Magnetic carbon nanopowders i-manager’s. J Mech Eng 1(1):16–20 Rukhadze LN, Kutelia ER, Maisuradze NI, Eristavi BG, Bakhtiyarov SI (2011a) A novel technology of synthesizing carbon nanoparticle doped with ferromagnetic iron oxide and clusters of cobalt atoms. In: Proceedings, thermal and materials nanoscience and nanotechnology conference, Antalya, May 29–June 3, 2011 Rukhadze LN, Kutelia ER, Maisuradze N, Eristavi B, Firooz AA, Bakhtiyarov SI (2011b) A novel high temperature resistant electromagnetic/radiation shielding material for space exploration. In: Proceedings, the 5th international association for the advancement of space safety (IAASS) conference “A safer space for a safer World”, ESA communications, Versailles, Paris, 17–19 Oct 2011, pp. S6 (1–4) Rukhadze LN, Kutelia ER, Maisuradze N, Eristavi B, Firooz AA, Bakhtiyarov SI (2011c) A novel high temperature resistant electromagnetic/radiation shielding material for space exploration, the 5th international association for the advancement of space safety (IAASS) conference. “A safer space for a safer World,” Final program and abstract book, Versailles, Paris, 17–19 Oct 2011, pp 39–40 Rukhadze LN, Kutelia ER, Maisuradze NI, Eristavi BG, Bakhtiyarov SI (2012) A novel radiation shielding nano-composite material for space exploration (Paper # 3018), Nuclear and emerging technologies for space, The Woodlands, March 21–23 Rukhadze LN, Kutelia ER, Maisuradze NI, Eristavi BG, Bakhtiyarov SI (2013a) A nanocomposite material for space exploration, nuclear and emerging technologies for space 2013 (NETS 2013), Albuquerque, NM, 25–28 Feb (Paper # 6768) Rukhadze L, Kutelia ER, Maisuradze N, Eristavi B, Bakhtiyarov SI (2013b) A novel radiation shielding nano-composite material for space exploration. J Energy Power Eng 2(1):12–18 Satellite Industry Association (2004) Satellite industry overview, presentation to the U.S. Department of Commerce, 16 Dec 2004 Schmidt A (1917) Erdmagnetismus, enzyklopddie der mathematischen wissenschaften. Band VI, Leipzig Seppala A, Verronen PT, Kyrola A, Hassinen S, Backman L, Hauchecrne A, Bertaux JL, Fussen D (2004) Solar proton events of October–November 2003: Ozon depletion in the Northern hemisphere polar winter as seen by GOMOS/Envisat. Geophys Res Lett 31(9):107 Sgrigna V, Carota L, Conti L, Corsi M, Galper AM, Koldashov SV, Murashov AM, Picozza P, Scrimaglio R, Stagni L (2005) Correlations between earthquakes and anomalous particle bursts from SAMPEX/PET satellite observations. J Atm Solar- Ter Phys 67:1448 Page 13 of 14

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Singer SF (1957) A new model of magnetic storms and aurorae. Trans Am Geophys Union 38:175–190 Steer I (2002) Briefing: high-altitude nuclear explosions; blind, deaf and dumb. Janes Defense Weekly, pp 20–23 Stoffle N, Pinsky L, Empl A, Hoang SM, Pospisil S, Jakubek J, Turecek D, Vykydal Z (2011) Simulation of Van Allen belt and galactic cosmic ray ionized particle tracks in a Si Timepix detector. In: Proceedings of 32nd international cosmic ray conference, Beijing 11, pp 442–445 Stormer C (1955) The polar aurora. Oxford University Press, Oxford Uman MA (1974) The Earth and its atmosphere as a leaky spherical capacitor. Am J Phys 42:1033–1035 Van Allen JA (1997) Energetic particles in the Earth’s external magnetic field. In: Gillmor CS, Spreiter JR (eds) Discovery of the magnetosphere, history of geophysics, vol 7. AGU, Washington, DC, pp 235–251 Van Allen JA, Frank FA (1959) Survey of radiation around the earth to a radial distance of 107,400 kilometers. Nature 183:430–434 Van Allen JA, Ludwig GH, Ray EC, McIlwain CE (1958) Observation of high intensity radiation by satellites 1958 Alpha and Gamma. Jet Propulsion 28:588–592 Varotsos P, Sarlis N, Lazaridou M, Kapiris P (1998) Transmission of stressed induced electric signals in dielectric media. J Appl Phys 83:60–70 Vernov SN, Chudakov AE, Vakulov PV, Logachev YI (1959) Study of terrestrial corpuscular radiation and cosmic rays during flight of the cosmic rocket. Doklady Akad Nauk SSSR 125:304–307 Verronen PT, Seppala A, Clilverd MA, Rodger CJ, Kyrola E, Enell CF, Ulich T, Turunen E (2005) Diurnal variation of ozone depletion during the October–November 2003 solar proton event, J Geophys Res 110(A9):1029–1032 Vignoli M, Miller W, Matteoni M (1987) Power generation with electrodynamic tethers. Tethers in space: proceedings international conference, Arlington, 17–19 Sept 1986, San Diego, pp 473–481 Walt M (1994) Introduction to geomagnetically trapped radiation. Cambridge University Press, Cambridge, UK Walt M (1996) Source and loss processes for radiation belt particles. In: Lemaire JF, Heynderickx D, Baker DN (eds) Radiation belts: models and standards, vol 97, Geophysical monograph. AGU, Washington, DC, pp 1–13

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

International Sun-Earth Explorers 1 & 2 C. T. Russell* Department of Earth and Space Sciences, Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, USA

Abstract The ISEE-1&2 Explorers were a joint NASA-ESA program with instruments on both spacecraft from the USA and Europe with ISEE-1 built in the USA and ISEE-2 in Europe, launched on a single rocket into the same orbit. The interspacecraft distance was variable, allowing the velocities of the boundaries traversed by the spacecraft to be measured and hence their thickness to be determined and compared quantitatively with theory. The missions’ major discoveries included determining that magnetic reconnection controlled magnetospheric dynamics, what factors controlled the rate of reconnection, and which plasma physical processes provided the dissipation for collisionless shocks. Together with ISEE-3 stationed in orbit around the L-1 Lagrangian point, this was the first space weather mission.

Keywords Bow shock; Magnetopause; Magnetotail; Reconnection; Charged-particle acceleration

Introduction The Earth’s magnetosphere and its interaction with the supersonic flow of plasma from the Sun and the solar wind, are dynamic, constantly in motion and constantly changing. Initial studies of this region with high-altitude elliptical orbiters, especially on the Orbiting Geophysical Observatories 1, 3, and 5, had shown the rapid motion and oscillations of the bow shock and the magnetopause. Not knowing the speed of the motion meant that the temporal profiles could not be converted to spatial profiles. Hence, quantitative comparison with theory was difficult in the early days. Nevertheless, qualitative studies did point to the role of the southward magnetic field in magnetic flux transport from the dayside of the magnetosphere to its magnetotail (Aubry et al. 1970; Russell and McPherron 1973), and later reconnection in the tail returning this magnetic flux and stored energy to the nightside magnetosphere. These observations provided the context for the design of the ISEE-1 and 2 mission and its companion spacecraft ISEE-3 that was for the prime ISEE-1 and 2 mission period (with some delay due to its later launch), in orbit about the L-1 Lagrangian point, 237 Earth radii (RE) in front of the Earth. The ISEE-1 and 2 spacecraft would co-orbit the Earth at low latitudes in an elliptical orbit with sufficient distance to probe the magnetopause, bow shock, and near-Earth magnetic tail using a variable separation to measure the velocity of the boundaries and hence translate temporal profiles into spatial. The mission was conceived as a joint NASA-ESA program with instruments provided by both the USA and Europe, with the launch provided by the USA.

*Email: [email protected] Page 1 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

ISEE-1, the larger “mother” spacecraft, was built by NASA, while ISEE-2, the smaller daughter spacecraft, was built under contract to ESA. ISEE-1 and 2 were successfully launched from the Eastern Test Range at the Cape Canaveral Air Force Base in Florida in October 1997 and, after 10 years of operation, entered the Earth’s atmosphere in 1987. ISEE-3 was moved out of the forward Lagrangian point and used to probe the distant magnetotail and then sent to intercept comet Giacobini-Zinner in 1985, despite not being instrumented to optimally make either distant magnetotail or cometary measurements. Thus, most space weather studies could only be undertaken using the periods when Earth-orbiting spacecraft were in the solar wind until the launch of the Wind spacecraft in late 1995. The lack of continuous interplanetary field measurements throughout the 1970s, 1980s, and early 1990s also reduced the number of detections of interplanetary field enhancements that have been associated with collisions of small asteroids and meteorites in the solar wind, some of which could produce hazardous debris near 1 AU (Lai et al. 2013a, b).

The ISEE-1 and 2 Missions The ISEE 1 and 2 missions were launched into an elliptical orbit that penetrated the bow shock and magnetopause into the solar wind, centered in October of each year, and crossing through the center of the tail in March and April (Ogilvie 1982; Formisano 1982), as illustrated in Fig. 1. The separation of the two spacecraft was variable and was measured in terms of the time delay between the crossings of the same radial distance by the spacecraft. This time was varied through the mission, as shown in Fig. 2. One second delay is equivalent to 2 km separation at 15 RE. Since the separation time could exceed 5,000 s, the spatial separation could approach 2 RE at 15 RE. At apogee where the spacecraft traveled more slowly, the separation was less, but near perigee where the speeds were much faster, the spacecraft were separated by a very great distance. The large occasional separations meant that one antenna could not view both spacecraft, and the inability often to get a second antenna for the two spacecraft meant that the spacecraft went into single-spacecraft mode as they had

Fig. 1 The ISEE-1 and 2 orbit illustrating its annual “precession” through the magnetosphere due to its motion around the Sun (Russell 2000) Page 2 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Fig. 2 The separation strategy of the ISEE-1 and 2 spacecraft from launch to 1984. One second of separation is equivalent to 2 km at a distance of 15 RE (Russell 2000)

no memory devices, because of the technology of the time, and had decided not to use tape recorders. Eventually the project stopped using large separations. The use of time delay to obtain the speed of a boundary along the normal to the boundary depends on the ability of the spacecraft instruments to determine the direction of the normal in other ways. At times, the direction of the normal can be specified by the geometry of the boundary to the accuracy needed. At least on the large scale, it was possible to occasionally obtain four spacecraft measurements which provide an unambiguous velocity and normal direction, as shown in Fig. 3 for an interplanetary shock. Such four-spacecraft observation opportunities were used to calibrate singlespacecraft techniques such as shock co-planarity formulas (Russell et al. 1983). The ISEE-1 spacecraft carried 13 instruments led by different investigators. These covered the thermal plasma, the energetic particles up to cosmic ray energies, plasma waves, and the magnetic and electric fields. The ISEE-2 spacecraft had 8 instruments, each led by a different investigator providing a subset of the ISEE-1 measurements, not a duplicate set of measurements. These measurements are listed in Tables 1 and 2 (Ogilvie 1982; Formisano 1982).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Fig. 3 Four encounters with the same interplanetary shock on August 18, 1978, as seen in the magnitude of the magnetic field. Location of the measurement points shown by asterisks in the X-Y solar ecliptic plane (Russell 2000)

The ISEE-1 and 2 spacecraft continued to operate for 10 years with most instruments still functioning at the end of the mission. The re-entry into the atmosphere was caused by gravitational torques that increased the eccentricity of the orbit forcing perigee into the atmosphere. The mission achieved its objectives. The motions of the boundaries were measured and the physics of the processes involved were determined. Not all the problems of the magnetosphere were solved. In particular, it became clear that the magnetospheric system required simultaneous measurements in the solar wind, in the tail, in the equatorial plane, and at high latitudes in the polar cusp. Such a mission, International Solar Terrestrial Probes (ISTP), including Wind, Polar, and Geotail, was designed and launched in the mid-1990s, but a key element, the equatorial measurements, was descoped. The next major mission solar terrestrial mission was Cluster, a four-spacecraft mission to the polar cusp. The most recent major magnetospheric mission, Magnetospheric Multiscale (MMS) may recover some of these objectives. It is an equatorial four-spacecraft mission with simultaneous solar wind and magnetotail measurements made by other spacecraft not originally associated with MMS.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Table 1 ISEE-1 investigations Principal investigator K. Anderson L. Frank D. Gurnett C. Russell S. Bame C. Harvey R. Helliwell J. Heppner D. Hovestadt D. Williams F. Mozer K. Ogilvie R. Sharp

Measurement Electrons and protons Electrons and protons Plasma wave electric Magnetic Magnetic field Plasma ions Plasma electrons Plasma density/active/passive Wave receiver Plasma waves Cosmic rays Energetic protons Electrons Electric field Plasma electrons Ion composition

Range 8–380 keV 1–50 keV 5.6 Hz–2 M Hz 5.6 Hz–10 k Hz 256 nT; 8,192 nT 5 eV–40 keV 5 eV–20 keV

0.1–3,200 Hz 0.05–20 MeV/nucleon 25 keV–2 MeV 25 keV–1 MeV 0–12 Hz 7 eV–7 keV 0–40 keV/q; 1–138 AMU

Table 2 ISEE-2 investigations Principal Investigator K. Anderson L. Frank D. Gurnett C. Russell C. Harvey E. Keppler A. Egidi G. Paschmann

Measurement Electrons and protons Electrons and protons Magnetic and electric field Magnetic field Electron density/propagation Protons/electrons Solar wind ions Fast plasma, ions Electrons

Range 1.5–280 keV 1.0 eV–45 keV 5.6 Hz–31 kHz 256 nT; 8,192 nT 25–800 keV 50 eV/q–25 keV/q 50 eV–40 keV 5 eV–20 keV

Technical Challenges A mission always involves some design trades. One trade was made that reduced the useful data by about half, and that was the decision to obtain only real-time data. It apparently was not appreciated that on many occasions the separation of the two spacecraft would not allow data acquisition from both spacecraft. It should be noted that earlier missions did have tape recorders. The most serious instrumental problems involved electric field measurements and the spacecraft potential. The spacecraft potential affects the ability to obtain measurements of the cold and low-energy plasma. The electric field measurements are affected by this and also have their own design problems. Basically, on ISEE-1 and 2, it was difficult to understand the electric field surrounding the spacecraft, either DC or AC. For example, it is unknown whether many of the identified plasmapause boundaries were real density changes or whether the flow of the plasma just was in the direction away from the inlet to the instrument. This problem has been addressed on other spacecraft with electric potential control and better electric antenna design.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Key Findings The ISEE-1 and 2 missions were designed first and foremost to measure the speed of motion of plasma boundaries. This it was able to do very well in most instances. Figure 3 shows four measurements of the magnetic field measured by ISEE-1, 2, and 3 and IMP-8, all in the solar wind during the passage of an interplanetary shock. Measurements like this one could provide an accurate orientation of the shock normal and the speed of the shock. These were then compared with the normal derived at each location for the single-spacecraft techniques such as magnetic co-planarity. While some single-spacecraft techniques were found to be less accurate than expected, it was possible to develop good techniques based on the comparisons possible when four spacecraft were present. Some of these comparisons and improvements, especially at the magnetopause, have continued with the Cluster mission. Some of the key findings were in the area of plasma physics. Figure 4 shows a series of bow shock encounters as seen in the magnetic field strength and displayed versus the ion inertial length. One can see that at low Mach number (top panel), there are standing whistler-mode waves decaying over some distance and higher frequency waves (1 Hz) generated in the shock and moving upstream. At a higher Mach number (but still subcritical), the wavelength of the standing whistler shortens and the noise is more confined to the shock ramp and vicinity. As the shock strengthens further, the noise increases over the entire region around the shock. However, at even higher frequencies, the turbulence cannot be resolved well because the fast motion of the shock has interacted with the instrument’s anti-aliasing filter and smoothed the data.

Fig. 4 Evolution of the magnetic field profile of the Earth’s bow shock as the Mach number of the shock increases with respect to the critical Mach number. Distance is measured in terms of the ion inertial length (Russell 2000) Page 6 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Fig. 5 Plasma and magnetic field measurements across multiple crossings of the magnetopause when reconnection was taking place almost continually (Russell 2000)

The ISEE-1 and 2 spacecraft’s most important discovery was the proof that the process known as reconnection exists in a magnetized plasma as predicted, and it controls the behavior of the magnetosphere. This discovery had been presaged by the motion of the magnetopause controlled by the southward component of the magnetic field with OGO-5 observations, but until ISEE-1 and 2 observed the predicted accelerated flow in the magnetopause (Paschmann et al. 1979), it was not accepted by the scientific community. Figure 5 shows these critical data. Here the VZ component (seen by ISEE-1) is the northward flow predicted to occur within the magnetopause. Furthermore, the accelerated flow is present steadily. When the boundary rocks back and forth across the spacecraft, the flow is always seen at the magnetopause on this day with “antiparallel” magnetic fields in the magnetosheath and magnetosphere.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Fig. 6 The magnetic field in boundary-normal coordinates across the magnetopause in the presence of FTEs on November 29, 1977 (Russell 2000)

ISEE-1 and 2 also revealed the unexpected. One important discovery about reconnection that makes perfect sense in retrospect is that when the plasma pressure far exceeds the magnetic pressure (called high beta conditions), the magnetic reconnection rate is minimal. This occurs because the forces in the plasma are nonmagnetic under these conditions. Only when the plasma pressure is low can the magnetic stress control the plasma flow (Scurry et al. 1994). A totally unexpected discovery at the magnetopause was transient reconnection or what was called a flux transfer event. In this process, limited bundles of magnetic flux became reconnected about 10 k Webers at a time. Figure 6 shows the magnetic field observed on both ISEE-1 and ISEE-2 as the two spacecraft approach the magnetopause. Periodic disturbances then appear moving across the two spacecraft with field not parallel to the magnetospheric field (Elphic and Russell 1979). This phenomenon is common at the Earth’s magnetopause, present but rare at Jupiter (Walker and Russell 1985), and very frequent at Mercury (Russell and Walker 1985). One of the key findings from the ISEE-1, 2, and 3 data that was not fully appreciated at the time was the interplanetary field enhancement (IFE) which is a nearly pure magnetic compression that is traveling nearly at the solar wind speed (Arghavani et al. 1985). Because of the correlation with the phase of the asteroid 2201 Oljato with the appearance of IFEs at Venus (Russell 1987), and because of its evolution in rate of occurrence between the PVO and VEX missions, this phenomenon is now understood to be due to collisions between small bodies (meteoroids) with debris co-orbiting with Oljato (Lai et al. 2013a). The long-term record of data at 1 AU was not originally explored, but recently has been, and it has been found that IFEs at the same longitude as today were present 40 years ago. Thus, collisions with material orbiting the Sun near the Earth are occurring and archives of interplanetary magnetic records can provide insight to where these debris trails are.

Conclusion The ISEE-1 and 2 measurements were obtained over 30 years ago, but they are still providing insight to this day. It is fortunate that some of these records have been preserved. However, it is unfortunate that the data have not been better preserved. The data are difficult to access, many of them are Page 8 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

missing, and the documentation has become separated from the data in many cases. Thus, while with time some insight into the phenomena has been gained, often this later insight cannot be exploited. It must not be forgotten that data can become useful at future times for reasons not presently understood. Planetary defense is now an important issue, and old records aid in understanding processes whose time scale is measured in decades for which there is no way to get these long databases except to use historical records.

Acknowledgments We are grateful to NASA and the teams of scientists and engineers who staffed the ISEE-1 and 2 missions. ESA’s support was equally invaluable. Many of the data were preserved by the National Space Science Data Center and can be still accessed today.

References Arghavani MR, Russell CT, Luhmann JG, Elphic RC (1985) Interplanetary magnetic field enhancements in the solar wind: statistical properties at 1 AU. Icarus 62:230–243 Aubry MP, Russell CT, Kivelson MG (1970) Inward motion of the magnetopause before a substorm. J Geophys Res 75:7018–7031 Elphic RC, Russell CT (1979) ISEE-1 and -2 magnetometer observations of the magnetopause. In: Battrick B (ed) Magnetospheric boundary layers, volume ESA SP-148. European Space Agency, Paris, pp 43–50 Formisano V (1982) The International Sun-Earth Explorer mission – ISEE-2, data from ISEE-1 for the IMS period. In: Russell CT, Southwood DJ (eds) IMS source book. American Geophysical Union, Washington, DC, pp 27–36 Lai HR, Russell CT, Wei HY, Zhang TL (2013a) The evolution of co-orbiting material in the orbit of 2201 Oljato from 1980 to 2012 as deduced from Pioneer Venus Orbiter and Venus Express magnetic records. Met Planet Sci. doi:10.1111/maps.12102 Lai HR, Wei HY, Russell CT (2013b) Solar wind plasma profiles during interplanetary field enhancements (IFEs): consistent with charged-dust pickup. AIP Conf Proc 1539:402–405. doi:10.1063/1.4811070 Ogilvie KW (1982) Data from ISEE-1 for the IMS period. In: Russell CT, Southwood DJ (eds) IMS source book. American Geophysical Union, Washington, DC, pp 21–26 Paschmann G, Sonnerup BUÖ, Papamastorakis I, Sckopke N, Haerendel G, Bame SJ, Asbridge JR, Gosling JT, Russell CT, Elphic RC (1979) Plasma acceleration at the Earth’s magnetopause: evidence for reconnection. Nature 282:243–246 Russell CT (1987) Interplanetary magnetic field enhancements: further evidence for an association with asteroid 2201 Oljato. Geophys Res Lett 14:491–494 Russell CT (2000) ISEE lessons for Cluster. In: Harris RA (ed) Proceedings of the Cluster-II workshop: multiscale/multipoint plasma measurements, ESA SP-449. European Space Agency, Noordwijk, pp 11–23 Russell CT, McPherron RL (1973) The magnetotail and substorms. Space Sci Rev 15:205–266 Russell CT, Walker RJ (1985) Flux transfer events at Mercury. J Geophys Res 90:11,067–11,074

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_26-1 # Springer International Publishing Switzerland 2014

Russell CT, Mellott MM, Smith EJ, King JH (1983) Multiple spacecraft observations of interplanetary shocks: four spacecraft determinations of shock normal. J Geophys Res 88(A6):4739–4748 Scurry L, Russell CT, Gosling JT (1994) Geomagnetic activity and the beta dependence of the dayside reconnection rate. J Geophys Res 99:14,811–814,814 Walker RJ, Russell CT (1985) Flux transfer events at the Jovian magnetopause. J Geophys Res 90:7397–7404

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

ISAS-NASA GEOTAIL Satellite (1992) A. Nishidaa* and Toshifumi Mukaib a Institute of Space and Astronautical Science, Machida, Tokyo, Japan b Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Hino, Tokyo, Japan

Abstract GEOTAIL spacecraft launched on 24 July 1992 has explored the Earth’s magnetotail across the range of 10–210 RE from the Earth. GEOTAIL not only clarified the basic structure of the magnetotail both in quiet and active times, but it also revealed the kinetics of the plasma that underlies macroscopic dynamics. In the magnetotail magnetic reconnection is the key process which governs energy dissipation and acceleration of ions and electrons. GEOTAIL has addressed the relation between the reconnection and auroral phenomena and clarified the kinetics of the energy conversion process in the reconnection region that operates on the scale of the ion inertia length. Understandings have also been advanced on the entry of the solar wind plasma into the magnetotail due to turbulence generated on the magnetopause and the excitation of plasma waves on account of prevalent nonequilibrium velocity distributions of plasma particles. The processes addressed by in-situ observations by GEOTAIL in space should be common to collisionless plasmas that prevail in astrophysical objects.

Keywords Magnetotail; Plasma sheet; Plasmoid; Lobe; Solar wind; Aurora; Substorm; Acceleration; Heating; Reconnection; Neutral line; Convection; Kelvin-Helmholtz instability; Hall current; Ion-electron decoupling

Introduction Cosmic rays, that is, energetic ions and electrons having energies up to 1021 erg, pose the outstanding threat to life in the universe. However, the life on the Earth has been protected from the major part of the spectrum by the magnetic field generated by the dynamo action in the core region. Under the pressure of the solar wind that flows continually from the solar corona, the geomagnetic field is enclosed in a domain called magnetosphere which shields much of the cosmic rays. The magnetosphere is not quiet and static. Solar wind produces a complex structure and activates the magnetosphere. This is the subject of this chapter. Energy and momentum imparted from the solar wind generate global convection in the magnetosphere which circulates between the day and the night side. Geomagnetic field lines are stretched at the same time and form the magnetotail extending behind the Earth. The magnetic energy is converted to the kinetic energy in the magnetotail. This energy conversion occurs primarily through

A. Nishida and T. Mukai are retired *Email: [email protected] Page 1 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

the magnetic reconnection at the neutral sheet in the magnetotail. The collapse of extended field lines produces a variety of disturbances such as substorms on the earthward side of the reconnection region, while plasmoid is ejected on its anti-earthward side. Thus the magnetotail plays a key role in the dynamics of the magnetosphere. The GEOTAIL spacecraft was uniquely designed to address the physics of the Earth’s magnetotail. The prime target was the magnetic reconnection in the near-Earth magnetotail: its location and development, relation to substorms, and microscopic structure of the energy conversion process. Also studied are the solar wind entry into the magnetosphere, outflow of ionospheric ions to the magnetotail, and excitation of plasma waves in the tail plasma. These are the basic processes that make the foundation of the space weather phenomena. GEOTAIL was implemented as a joint mission between ISAS (Institute of Space and Astronautical Science) of Japan and NASA of USA. ISAS developed the spacecraft and NASA launched it. Responsibilities for onboard instruments were shared. It was launched on 24 July 1992 and has been working soundly for more than two solar cycles by now. Acquired data have been openly disseminated to the international space science community.

Spacecraft, Scientific Payload, and Orbit The configuration of the GEOTAIL spacecraft is shown in Fig. 1. It has a cylindrical shape with diameter of 2.2 m and height of 1.6 m. Two masts with 6-m length are deployed symmetrically to separate the magnetometers from the main body, and four 50-m wire antennas are deployed to measure the electric field from DC to 800 kHz. Particular attention was paid to make the spacecraft electromagnetically clean. The spacecraft attitude is spin stabilized with the rate of 20 rpm and with the axis being nominally perpendicular to the ecliptic plane; more exactly, the spin axis was

MST-S WANT-B PANT-B

HGA LGA-A

RCS THRUSTERS

WATN-A LGA-B

MGA

PANT-A MST-F

Fig. 1 Configuration of the GEOTAIL spacecraft (Nishida 1994)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

Table 1 Science instruments on board GEOTAIL (Nishida 1994) Item Electric field (EFD)

Magnetic field (MGF)

Plasma (LEP)

Plasma (CPI)

Energetic particles (HEP)

Energetic particles (EPIC)

Plasma waves (PWI)

Description Spherical probe and wire antenna Electron boomerang Ion emitter Fluxgate Search coil

Range dc – 32 Hz (2 comp) dc – 10 Hz (3 comp) dc – 16 Hz (3 comp) 1–50 Hz (3 comp)

Ion/electron 3-dim.velocity distributions Solar wind ions Ion mass/energy spectrum Ion/electron 3-dim velocity distributions Solar wind ions Ion mass/energy spectrum Low-energy particles Ion/electron burst Medium-energy ion isotope ratio High-energy ion isotope ratio Ion charge state/mass/energy Ion mass and energy Electron energy Frequency sweep Multichannel analyzer Waveform capture

10 eV–40 keV/q 150 eV–8 keV/q 0.1–25 keV/q 1 eV–50 keV/q 150 eV–7 keV/q 1 eV–50 keV/q 30 keV–1.5 MeV/n 0.7–3.5 MeV/n 5–50 MeV/n 10–230 MeV/n 30–230 keV/q > 50 keV–5 MeV > 30 keV E: 25 Hz–800 kHz H:25 Hz–12.5 kHz 10 Hz–4 kHz

PI, co-I K. Tsuruda F.S. Mozer R. Schmidt S. Kokubun M. Acuna D.H. Fairfield T. Mukai

L.A. Frank

T. Doke B. Wilken

D.J. Williams

H. Matsumoto R.R. Anderson

controlled to be inclined sunward and make an angle of 87  with respect to the solar ecliptic plane for 11.5 years after launch until the fuel was exhausted. Seven sets of science instruments are on board GEOTAIL, as listed in Table 1. Measured items constitute basic elements of space plasmas. Magnetic field represents the framework of the magnetosphere. Electric field reflects the plasma dynamics. Waves in these fields are essential ingredients of the collisionless plasma. A unique feature in the plasma wave instrument is the waveform capture (WFC), which was quite a new technique in those days (although it has become common to plasma wave instruments on board recent spacecraft). Plasma and particles are measured by four sets of experiments because of their vital importance in physics of the magnetosphere. Energy ranges for the ion measurements covered by these experiments are shown in Fig. 2. For detailed description of each instrument, refer to the special section “GEOTAIL Instruments and Initial Results” of the Journal of Geomagnetism and Geoelectricity (vol. 46, pp. 3–95 and 669–733, 1994). One of the plasma instruments, the low-energy plasma (LEP) experiment, became inoperative on 22 August 1992, when a latch-up occurred in the key part of the electronic circuit due to electrical arcing, but this instrument was revived on 1 September 1993, by turning off the spacecraft power in the lunar shadow which was created on purpose. No experiments were adversely affected by this special operation. The recovery of LEP was critical for the success of the GEOTAIL mission, since most of the results to be described in the subsequent sections have been brought forth by the LEP observations. A key feature of the LEP energy-per-charge analyzers is geometrical factors which are larger than the conventional ones in those days; the geometrical factor of the LEP ion analyzer is more than

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

Fig. 2 Energy coverage of plasma and particle experiments on board GEOTAIL

20 times larger than that of the CPI hot plasma analyzer. This large geometrical factor of LEP means high sensitivity so that high time resolution measurements can be made with sufficient counting statistics. This has proved to be vital especially for the studies of magnetic reconnection and plasma transport processes across boundary layers (i.e., magnetopause as well as internal boundaries such as the plasma sheet boundary layer). On the other hand, the detection efficiency of micro-channel plates (MCP), the particle detectors used along with the energy analyzers, generally degrades with the total counts integrated over the measurements when they are operated with a fixed bias voltage. Therefore, the degradation would be faster if the count rate is higher. The bias voltage is increased if the detector gain of LEP decreases in order to keep the detection efficiency at a reasonable value. The degradation rate, however, was much slower than had been anticipated, and as of 2014 after more than 20 years have elapsed, the LEP instrument is still providing useful observations of magnetospheric plasma. It is mandatory to calibrate the detection efficiency with in-flight data, since the efficiency varies with the instrument operation time. In LEP, the ion detectors are calibrated as follows. At first, after subtraction of background noise, relative efficiencies between different channels (detectors at different elevation angles) are examined. Fortunately the relative efficiencies of the ion detectors have not changed throughout the observation, so that those measured in the preflight calibration experiment in the laboratory have been used. Then, ion velocity moments are calculated, and the resultant ion density is compared with electron density estimated from the plasma wave data: cutoff frequency of the continuum radiation in various regions including plasma sheet, lobe, and magnetosheath. From this comparison, the absolute value of the ion detection efficiency can be obtained. Correction of the electron detection efficiency needs a more complicated procedure, since the electron data are sensitive to the spacecraft potential and contain spurious data due to photoelectrons and secondary electrons. In addition, the detector efficiency depends on the electron energy. The detail of the calibration method is described elsewhere (Saito and Mukai 2007; McFadden et al. 2007). Figure 3 shows an example of proton energy distribution measured by three different instruments, LEP-EA, EPIC-STICS, and EPIC-ICS. Although calibrations of the three instruments were carried out independently, agreement among data of these instruments is excellent, which demonstrates high reliability of the respective calibration procedures. Page 4 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

Fig. 3 Comparison of proton energy distributions measured by three different instruments, LEP-EA, EPIC-STICS, and EPIC-ICS, on board GEOTAIL (Courtesy of ISAS/JAXA)

Fig. 4 Orbits of the GEOTAIL spacecraft (Courtesy of ISAS/JAXA)

For the first 2 years, the spacecraft surveyed the distant magnetotail (with apogees on the nightside at 80–210 RE from the Earth) by executing double-lunar-swingbys orbits. The orbits in this distanttail phase are shown in Fig. 4 (left) with xy projection on top and xz projection at bottom. The apogee was lowered to 50 RE in mid-November 1994 and then further down to 30 RE in order to focus on the magnetic reconnection in the near-Earth magnetotail. The inclination was set at 7 in order that the apogee is to be on the tail midplane, which is hinged to the geomagnetic equatorial plane at about 10 RE at midnight, around the December solstice when the spacecraft is free from shadowing by the Earth. The perigee was about 10 RE so that the spacecraft skimmed the magnetopause on the

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

dayside; it was further reduced later to 9–9.5 RE to increase the chances of observing the low-latitude boundary layer of the magnetosphere. The orbits in 1999 are shown in Fig. 4 (right). After 2007 the orbit is no longer controlled and currently the inclination is about 30 .

Basic Structure of the Magnetotail Figure 5 shows the noon-midnight meridional section of the magnetotail in quiet (a) and active (b) conditions (Hones 1984, modified). The x direction is toward the sun, the z direction contains the Earth’s magnetic dipole, and the y direction is perpendicular to x and z. Magnetic field is directed earthward in the northern half of the tail and anti-earthward in the southern half. The “tail lobe” in high latitudes is filled by open field lines which have only one root on the Earth. In low latitudes field lines are closed, that is, they have both roots on the Earth. The interface where the sunward component Bx is zero is called the neutral sheet. Actually the neutral sheet is often inclined to the (x,y) plane. In the absence of the reconnection, Bz should be northward everywhere. However, magnetic field lines are reconnected in the magnetotail and hence Bz is southward beyond certain distance. In quiet times the magnetic neutral line, where Bz changes from northward to southward, is located in the distant tail (Fig. 5a). This neutral line, called “distant neutral line,” marks the demarcation between the closed field lines and the open field lines. The open field lines have been produced by reconnection on the dayside magnetopause, move from the lobe region toward the neutral sheet, and are closed by reconnection at the distant neutral line. Plasma which has been heated in the process flows earthward on the earthward side of the neutral line and antiearthward on the anti-earthward side. The earthward flow accompanies closed field lines, and the anti-earthward flow accompanies the field lines that are no longer rooted on the Earth and extended to the solar wind. The hot plasma deposited on the closed field lines constitutes the “plasma sheet.” Magnetic flux transported by the flow is represented by Ey = VxBz. To find the location of the distant neutral line, seven orbits of GEOTAIL are selected when the geomagnetic activity index Kp was higher than 3 for 24 h or more, and the sums of Ey are calculated separately for intervals of the tailward flow and the earthward flow. The ratio between them is plotted in Fig. 6. A sharp drop of the ratio is seen at a distance of about 130 RE from the Earth, suggesting that the neutral line tends to be

Fig. 5 Basic structure and terminology of the magnetotail in (a) quiet and (b) active states (After Hones (1984), modified) Page 6 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_27-1 # Springer International Publishing Switzerland 2014

Fig. 6 Ratio between magnetic fluxes transported tailward and earthward is plotted against the distance x from the Earth. The drop of this ratio from >1 to 10 keV) stream outward while low-energy electrons (M5 Event >M5 (R2) Event >X1 (R3) Event >X10 (R4) Event >X20 (R5) RADIO EVENTS Type-II Type-IV 10 cm PROTONS >10Mev >10 pfu (S1) >100 pfu (S2) >1K pfu (S3) >10K pfu (S4) >100K pfu (S5) PROTONS >100Mev >1pfu ELECTRON FLUX >2MeV >1Kpfu GEOMAGNETIC Sudden Impulse K=4 K=5 (G1) K=6 (G2) K>=7 (G3) K>=8 (G4) K>=9 (G5) WATCH G1 G2 G3 G4 or greoter STRATOSPHERIC Stratwarm

Feb 18

Legend Key:

Feb 19

Feb 20

Feb 21

Feb 22

Feb 23

Feb 24

ALERT cr Continuatiion

WATCH (G-based)

Extends Beyond

SUMMARY

WARNING (Onset) WARNING (Persistence)

Latest Update

Sudden Impulse Warning

Updated 2014 Feb 21 2354 UTC

All data in Universal Time

Feb 25

CANCELLATION

NOAA/SWPC Boulder, CO USA

Fig. 31 Space weather alerts and warnings timeline (http://www.swpc.noaa.gov/alerts/warnings_timeline. html – Accessed 21 Feb 2014)

Three categories of descriptive scales for space weather were developed, which are most relevant to possible adverse effects on satellite-based and other systems. These are (NOAA 2000): • Geomagnetic storms – disturbances in the geomagnetic field caused by gusts in the solar wind that blows by the Earth • Solar radiation storms – elevated levels of radiation that occur when the numbers of energetic particles increase • Radio blackouts – disturbances of the ionosphere caused by X-ray emissions from the Sun The NOAA Space Weather Scales are divided into categories, each of which is designated by a number and a single word descriptor. Each scale refers to a list of possible effects in each category of activity, the physical measure that determines the category of an event, and a climatological assessment that explains the probability of observing events of each magnitude during a solar cycle. Five levels of severity are used in each category, but the intervals between the categories are not always scaled uniformly with the physical measure’s value. For geomagnetic storms, the G-scale categories differ by equal steps of Kp, which itself is a quasi-logarithmic index that is currently the best estimate of global geomagnetic activity available in near real time (Table 1). For solar radiation storms, each successive S-scale category is reached when the flux of greater than 10 MeV particles increases by a factor of 10 (Table 2). For radio blackouts, R-scale categories increase based on quantitative (and historically used) flare X-ray brightness levels, rather than “regular” intervals Page 33 of 38

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_32-1 # Springer International Publishing Switzerland 2014

(Table 3). The R-scale is used for radio blackouts based on solar X-ray flux from GOES to characterize the level of interruption of communication in frequency ranges affected by the solar radio flux. The Space Weather Scales have worked their way into various SWPC products, forecasts, and alerts. As previously shown in Fig. 12, the Space Weather Scales are displayed on the default SWPC digital dashboard interface, indicating scales activity for the past 24 h and current conditions. These are assessed at specific threshold levels for each environmental disturbance or event type. This enables the general public, operational user, and decision-maker to assess potentially damaging space weather at first glance, before consulting more detailed data sources and model simulation output. Latest space weather alerts updated hourly are also issued based on these scale categories (http://www.swpc.noaa.gov/alerts/index.html). These are often used in conjunction with graphical timelines and data plots (Fig. 31). In summary, the NOAA Space Weather Scales have been successful in tying physical measures of solar phenomena to possible outcomes, at least in general terms. This enables easier and more intelligible understanding of the importance and consequences of space weather. Knowledge that a significant space weather event is occurring, as well as timely and accurate forecasts of the future state of the space environment, provides the means to take proactive measures to mitigate the negative impacts of potentially damaging space weather events.

Benefits and Challenges The previous sections have shown examples of the wide variety of digital dashboard and tools available for supporting monitoring and analyzing the space environment, as well as sending out timely space weather notifications. Such dashboard systems provide a way to consolidate, display, and access space weather data that is already being gathered by various ground- and space-based sources, institutions, and organizations. The functionality of these digital dashboards is going beyond just visualization and information management, but also serving as a decision support system for the user community and forecasters. Web-based interactive systems are user configurable, where input parameters and model settings can be adjusted on the fly. Sophisticated online visualization and analysis tools are also readily available. Such space weather tools and displays enable space weather information to be extracted from complex scientific models, making research simulation results operationally useful and ready to be used by forecasters. As previously discussed, a large number of online tools and widgets/ cygnets are available via the SWPC. Tool design has been developed in collaboration with NOAA, AFWA, and NASA users. Certain products have combined outputs from several models and datasets from various sources. Examples include real-time imagery, plots, text/notifications, and graphical displays. At the same time, users of space weather products and decision-makers must make decisions about how to apply such tools in practice. For examples, they must answer questions, such as how good are model predictions and at what level of confidence? What forecasting models should be installed next? How can model performance be traced over time? When should upgrades be installed? Challenges exist with adopting community-wide metrics for model validation. This relies not only on obtaining good quality observational data and model performance, but model evaluation ultimately depends on user requirements and user-defined thresholds. A key requirement is the facilitation of communications between research and operational communities. This is achieved to

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_32-1 # Springer International Publishing Switzerland 2014

a certain extent with CCMC dashboard systems, such as the iSWA web-based data dissemination solution and new initiatives such as DONKI and the StereoCAT analysis tool. Moreover, operational challenges still exist with updating and keeping dashboard links and pages current and up to date. Implementing a vision of free and worldwide public space weather data dissemination via dashboard displays and web-based platforms raises fundamental computational challenges at the intersection of computer science, engineering, operations research, information management, and even social sciences. Space weather response and data sharing requires optimization of interdependent infrastructures, collecting and aggregating data in real time, reducing uncertainty in predictions, and understanding decision-maker requirements for formulating effective response and management plans to space weather events. Leadership is required in community-wide model validation efforts for defining physical parameters and metrics formats relevant to dashboard applications and addressing uncertainties and challenges in model-data comparisons. Forecasting scores depend on a combination of probability of detection and probability of false detection. Space weather models themselves are evaluated on their strategic importance, operational significance, implementation readiness, and cost of operation, maintenance, and improvement. Empirical models also serve as a valuable baseline and possible independent product. Organizations such as the CCMC and SWPC have key roles in the independent validation of models and transitioning from research to weather operations. However, establishing standardized metrics for model and forecast evaluations remains a challenge. The development and evolution of digital dashboards and online reporting tools is in recognition that addressing space weather needs requires innovative, collaborative, and cost-effective ways (Kuznetsova 2012). Prior to such services, space weather models and data were first accessed and used exclusively by researchers and developers only. Models were later then used and validated by the entire community. Subsequent developments in real-time data flow monitoring and controlling systems meant that models could then continuously run in real time. Advantages were more robust processing and real-time data drivers. This led to the development of space weather displays that were customized for specific applications and missions. These had the benefits of being ready to be used by forecasters, while combining model output and data, but were still limited in availability to specific user groups. The advancement of current digital dashboards, such as the iSWA, has enabled flexible collection and dissemination of space weather information. This has revolutionized the transition from research to operations, addressing the custom needs of user communities. Tools are now available for forecasters worldwide via the Internet and mobile app platforms. Customized dashboard displays not only provide prototype innovative web-based forecasting and analysis tools but also serve to educate operators, students, and the general public. This has helped to lead joint operations and innovative partnership between space weather research, educational, and operational institutions worldwide. The International Space Environment Service (ISES) has engaged international coordination of space weather services since 1962. One of its mandates is to assist transition of research results into operations, with a commitment to free and open exchange of data and products, long-term data stewardship, and compliance with agreed-upon data standards and conventions. ISES provides mechanisms to facilitate and improve access to data and services, enhancing data availability, and information exchange. Such mandates are largely achieved by realtime imagery and data disseminated by dashboard services.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_32-1 # Springer International Publishing Switzerland 2014

Conclusion Knowledge that a significant space weather event is occurring, as well as timely and accurate forecasts of the future state of the space environment, provides the means to take proactive measures to mitigate the impacts of these potentially damaging space weather events. The dependencies and interconnectedness of key infrastructure reaffirms that solar weather phenomena are not only a concern to scientists and physicists, but are critical knowledge for supporting a multitude of planners and decision-makers. Such user groups require access to accurate and real-time data about space weather phenomena to assess risks and to plan mitigation, response, and recovery measures. To this end, dashboard displays offer robust and integrated systems that provide information about past, present, and future space weather conditions. Unlike many other systems, dashboards provide a web-based interface that the user can customize to suit a unique set of data requirements in real time. There is a unique level of customization and flexibility available, drawing together information from various data sources from ground- and space-based observations. Moreover, information is publicly available and accessible via the Internet and mobile systems, providing a valuable resource for educating the public about space weather. Dashboard displays for dissemination of space weather information are continuously evolving. There are new resources increasingly appearing from various agencies, institutions, and operators to provide real-time views of space weather. Access to such tools provides users with a personalized “first look” at space weather information, detailed insight into space weather conditions, as well as tools for historical analysis of solar events. Such initiatives will continually support the open free exchange of space weather data and products worldwide for real-time forecasting and monitoring of space weather. In turn, this will contribute to improving the prediction of damaging space hazards for reducing and mitigating space weather impacts on technology, critical infrastructure, and human activities.

Cross-References ▶ Advanced Composition Explorer (ACE) (1997) ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Coronal Mass Ejections ▶ Coronal Mass Ejections and Their Cause and Nature ▶ Cosmic Radiation Management ▶ Early Solar and Heliophysical Space Missions ▶ Introduction to the Handbook of Cosmic Hazards and Planetary Defense ▶ NASA Wind Satellite (1994) ▶ Nature of Coronal Mass Ejections and Historical Patterns of Their Occurrence ▶ Nature of the Threats and Historical Patterns of Occurrence ▶ New Information the Geomagnetosphere from Current Space Probes ▶ NOAA Satellites and Solar Backscatter Ultra Violet (SBUV) Subsystems ▶ Risk Management and Insurance Industry Perspective ▶ Solar and Heliospheric Observatory (SOHO) (1995) ▶ Solar Dynamics Observatory (SDO) ▶ Solar Flares ▶ Solar Flares and Impact on Earth ▶ Spaceguard Survey by NASA Page 36 of 38

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_32-1 # Springer International Publishing Switzerland 2014

▶ STEREO as a ‘Planetary Hazards’ Mission (1996) ▶ U.S. Ground Observatories

References CCMC (2002) Concept of operations for the Community Coordinated Modeling Center (Prepared by Interagency Consortium – AFOSR, AFRL, AF/XOW, NASA GSFC, NASA HQ, NOAA, NSF, ONR, SMC) DashboardInsight.com (2014) What is a dashboard? http://www.dashboardinsight.com/articles/ digital-dashboards/fundamentals/what-is-a-dashboard.aspx. Accessed 19 Feb 2014 ExcelDashboardWidgets (2014) What is dashboard reporting? http://www.exceldashboardwidgets. com/what-is-dashboard/what-is-dashboard.html. Accessed 18 Feb 2014 Gordon B (2013) State of the Space Weather Prediction Center 2013. Space Weather Workshop, 16 April 2013. http://www.swpc.noaa.gov/sww/SWW_2013_Presentations/Tuesday_Morning/ StateoftheSpaceWeatherPredictionCenter2013_BrentGordon_NOAASWPC.pptx Ideum.com (2011) Over 100K downloads for NASA Space Weather iPhone App in March. http:// www.ideum.com/blog/2011/03/100k-downloads-for-nasa-space-weather-iphone-app/. Accessed 19 Feb 2014 ISES (2014) http://www.ises-spaceweather.org Kuznetsova M (2012) CCMC: models, tools and systems for operational space weather forecasting and analysis. Space Weather Workshop, 16–19 April 2012 Lloyd’s (2013) Solar storm risk to the North American electric grid. http://www.lloyds.com/~/ media/lloyds/reports/emerging%20risk%20reports/solar%20storm%20risk%20to%20the% 20north%20american%20electric%20grid.pdf. Accessed 19 Feb 2014 NASA (2011) http://www.nasa.gov/mission_pages/sdo/multimedia/20110907_briefing_materials_prt.htm. Accessed 19 Feb 2014 NASA (2014) http://www.nasa.gov/mission_pages/hinode/solar_004.html. Accessed 19 Feb 2014 NASA CCMC (2014) http://ccmc.gsfc.nasa.gov. Accessed 19 Feb 2014 NASA Goddard Space Flight Center (2013) iSWA Wiki. http://iswa.ccmc.gsfc.nasa.gov/wiki/index. php/Main_Page. Accessed 19 Feb 2014 NASA SDO – Solar Dynamics Observatory (2014) http://sdo.gsfc.nasa.gov. Accessed 19 Feb 2014 NASA Sun-Earth Connection Program (2014) http://sec.gsfc.nasa.gov. Accessed 19 Feb 2014 National Research Council (2008) Severe space weather events – understanding societal and economic impacts: a workshop report. The National Academies Press, Washington, DC NOAA (2000) New scales help public, technicians understand space weather. http://www.swpc. noaa.gov/NOAAscales/EosNewScales.html. Accessed 19 Feb 2014 NOAA SWPC (2000) SWPC Center review presentation materials http://www.swpc.noaa.gov/ AboutUs/Review2000/index.html. Accessed 19 Feb 2014 Space Science Division (2014) Compact coronagraph http://www.nrl.navy.mil/ssd/branches/7680/ CCOR. Accessed 19 Feb 2014 U.S. Department of Homeland Security (2011a) National infrastructure protection plan. Department of Homeland Security U.S. Department of Homeland Security (2011b) http://www.dhs.gov/xlibrary/assets/rmageomagnetic-storms.pdf. Accessed 19 Feb 2014

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_32-1 # Springer International Publishing Switzerland 2014

University Corporation for Atmospheric Research (2009) 2009 Community review of the NCEP Space Weather Prediction Center http://www.ncep.noaa.gov/director/ucar_reports/ SWPC_Report_UCAR_Final.pdf. Accessed 19 Feb 2014 White House (2013) Report on space weather observing systems: current capabilities and requirements for the next decade. http://www.whitehouse.gov/sites/default/files/microsites/ostp/ spaceweather_2013_report.pdf. Accessed 19 Feb 2014

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_35-1 # Springer International Publishing Switzerland 2014

Comet Shoemaker-Levy 9 Frederick M. Jonasa* and Firooz Allahdadib a Gallup, NM, USA b Space Science and Environmental Research, Albuquerque, NM, USA

Abstract In 1994 comet Shoemaker-Levy 9 captured the world’s attention. Discovered quite by accident, this comet was to provide the world the first direct observational evidence of an impact by one body on another body in the solar system. Comet Shoemaker-Levy 9 put on a spectacular display. The comet Shoemaker-Levy 9 fragments collided with Jupiter from July 16 through July 22, 1994. The glorious show put on by comet Shoemaker-Levy 9 in July 1994 should continually remind us that the threat of impact from above is very real. We must be continually vigilant.

Keywords Comet; Shoemaker; Levy; Shoemaker-Levy 9; Near-Earth object; NEO; Jupiter; Earth; Impact; Fragments; Observatory

Introduction In 1994 comet Shoemaker-Levy 9 captured the world’s attention. Discovered quite by accident, this comet was to provide the world the first direct observational evidence of an impact by one body on another body in the solar system, in this case comet Shoemaker-Levy 9 impacting Jupiter. A composite image of Jupiter from the Cassini spacecraft is shown in Fig. 1 (the dark spot is the moon Europa).

The Discovery On the night of March 24, 1994, while perusing photographs taken by the Palomar Observatory 16-in Schmidt telescope, amateur astronomers Carolyn and Eugene Shoemaker and David Levy discovered a comet that had been previously overlooked. It was the ninth periodic comet (orbital period of 200 years or less) discovered by the Shoemakers and Levy, thus the name Shoemaker-Levy 9, and their eleventh comet found overall. They had been looking to uncover more near-Earth objects (NEOs) and came upon an image that appeared to show an unusual comet with multiple nuclei in an elongated region of space, 21 discernible fragments in all (Fig. 2). It lay near Jupiter and its apparent motion suggested that it was close to Jupiter. Once noted and announced, observations came pouring in and orbital calculations were performed. Not only was it near Jupiter, it was orbiting Jupiter with a period of about 2 years. The orbit was highly eccentric (e ¼ 0.9986) and it appeared this comet had been orbiting Jupiter for 20–30 years prior to this observation.

*Email: [email protected] Page 1 of 6

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_35-1 # Springer International Publishing Switzerland 2014

Fig. 1 Majestic Jupiter

Fig. 2 Shoemaker-Levy 9 fragments

Jupiter Capture Due to its immense size, mass, and resulting gravitational pull, massive Jupiter plays a vital role in cleaning up and reducing space debris within the inner solar system. Containing more mass than all the remaining planets combined, Jupiter really does rule the solar system through its gravitational reach. Because of its deep gravitational well, the rate of comet impacts on Jupiter is thought to be between two to eight thousand times higher than the rate on Earth. And the impact rate on Earth is less overall due to Jupiter capturing or perturbing the orbits of such potential Earth-bound objects enough to miss Earth. Because Jupiter does have significantly more impacts than other objects in our solar system, it is not surprising that our first visible proof of such impacts on other bodies in the solar system was provided by Jupiter. The object, comet Shoemaker-Levy 9, had already been captured by Jupiter and in fact had been pulled apart into 21 visible fragments by the time we found it. In its final orbit, comet Shoemaker-Levy was to visibly demonstrate the ultimate fate of such objects captured by Jupiter’s unforgiving gravitational pull. Based on the observations and calculations, comet Shoemaker-Levy 9 was thought to originally have been a periodic comet orbiting the Sun inside Jupiter’s orbit. Sometime in the 1960s or 1970s, the comet passed too close to Jupiter and was captured by Jupiter’s massive gravitational pull. In this capture the comet acquired a highly eccentric orbit, nearly a flattened ellipse. This capture and resulting orbit was later confirmed by calculations showing that on July 7, 1992, comet ShoemakerLevy 9 came within 40,000 km of Jupiter’s cloud top, an altitude well within the planet’s Roche limit. The Roche limit or radius is the distance at which one celestial body, held together by its own gravity, will come apart due to the tidal forces of a second body overcoming the first body’s Page 2 of 6

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_35-1 # Springer International Publishing Switzerland 2014

gravitational self-attraction. That close encounter, closer than others, is thought to have essentially pulled the comet apart resulting in the fragments observed by the Shoemakers and Levy in 1994. No other prediscovery images prior to March 1993 have been found, but computational simulations and the visible evidence seemed to indicate the recent capture and disruption by Jupiter of this cometary body. The visible fragments were estimated to range in size from a few hundred meters to two-plus kilometers suggesting the original comet may have been up to five kilometers in diameter. Each fragment was designated alphabetically from A to W. (Fragments were designated A, B, C, D, E, F, G, H, J, K, L, M, N, P2, P1, Q2, Q1, R, S, T, U, V, and W.) Fragment G, with an estimated diameter of 3–4 km, was likely the largest and heaviest. Impact Is Predicted More exciting than the discovery of comet Shoemaker-Levy 9 was the fact that with a 2-year orbital period, Shoemaker-Levy 9 would again approach Jupiter in a close encounter in 1994. The estimate for this next close encounter would put the comet within 45,000 km of Jupiter’s center sometime in July 1994. Jupiter’s radius is approximately 70,000 km. It definitely appeared that comet Shoemaker-Levy 9 was going to impact Jupiter. That put comet Shoemaker-Levy 9 on the front pages around the world. Observers everywhere geared up to observe this first ever impact or collision of one body on another body within the solar system. Any and all ground-based, space-based, and any other-based assets that could be dedicated to observing this event turned their sensors in the direction of Jupiter. The accidental discovery of this comet was made at exactly the right time for if the impact did occur as predicted, comet Shoemaker-Levy 9 would be no more, never to be seen again. We would have undoubtedly seen the results and may have even been fortunate to record some impacts . . . but now we were ready to see, observe, and record the entire event, start to finish. Impact predictions varied in the magnitude and effects but generally concluded that the comet Shoemaker-Levy 9 fragments would start colliding with Jupiter around mid-July and last for about 5 days. The impacts would be at 60 km per second (km/s) and at an angle of 45 relative to the surface (or the cloud tops in the case of Jupiter). It would not be a glancing blow. Regarding the impact speed, Earth orbital speeds (low Earth orbit [LEO]) are on the order of 7–10 km/s. Relative meteoroid speeds in Earth’s vicinity (LEO) are on the order of 20 km/s. These fragments were moving much faster, and there was a lot of mass. The impacts had the potential to be spectacular. But astronomy has had a lot of spectacular events fizzle, most recently comet Ison. Plus, the impacts would occur on the back side of Jupiter (relative to Earth). We might not see anything, especially given the relative mass of the comet to Jupiter. Most expected to see no long-lasting results. Astronomers cautiously announced the coming event given their doubts and previous experiences. The whole world was captivated by the real-time event occurring right before our eyes and was watching intently. And we were watching across a variety of wavelengths in the electromagnetic spectrum, not just visible light. There were no measuring instruments and/or sensors spared in recording such a galactic phenomenon. Impacts Comet Shoemaker-Levy 9 in fact put on a spectacular display. The comet Shoemaker-Levy 9 fragments collided with Jupiter from July 16 through July 22, 1994. At a press conference (Space Telescope Science Institute in Baltimore) prior to the anticipated impacts, discoverers Eugene and Carolyn Shoemaker and David Levy were being cautious and trying to lower expectations. In the midst of this press conference, an observer rushed in with the first results, an image from the Hubble Space Telescope. The image clearly showed an impact had indeed occurred. Page 3 of 6

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_35-1 # Springer International Publishing Switzerland 2014

Fig. 3 First impact as recorded by the Hubble Space Telescope

A picture of that first impact which occurred at 20:13 Universal Time (UT), on July 16, 1994, is shown in Fig. 3. A plume could clearly be seen emerging as the impact site rotated into view. The results were spectacular. And this was only the beginning. Clearly anticipated was the impact of the largest fragment, fragment G. At least 21 observable fragments impacted the planet Jupiter. The impacts occurred on average every 7 h. The fragments impacted Jupiter just out of view of the Earth. It then took the impact site 11 min to rotate into view for Earth-based observers. The impacts caused plumes to extend thousands of kilometers high and were clearly seen before the impact site rotated into view. The impacting fragments left hot bubbles of gas in the atmosphere and great dark scars (streaks) which lasted for months after the collision. The impact scars and streaks become a planet-wide chain of smoldering impact sites. These impact plumes and scars were clearly visible as shown in Figs. 4 and 5. The ferocity of these impacts and their interactions is a reminder of their devastating consequences. However, because of the oblique trajectory of comets, the impacting fragments did not go very deep into the atmosphere of Jupiter and the scars have since been erased. The fragment G impact (07:33 UT, July 18, 1994) created a fireball that was at least 30,000 km high. The multi-ringed impact scar, once in view, was estimated to be over 12,000 km across or about the size of Earth’s diameter. The explosion energy of that impact was estimated to be six million megatons of TNT equivalent. Earth’s largest nuclear detonation was Tsar Bomba, detonated by the Soviet Union in 1961, and estimated to be on the order of 60 megatons. The fragment G impact was significantly more powerful. If the impact had occurred on Earth, it would have left a crater at least 60 km in diameter potentially ending the human race, or at least civilization, as we know it.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_35-1 # Springer International Publishing Switzerland 2014

Fig. 4 Impact images (near infrared)

Comet Shoemaker-Levy 9 Impact Photos Photo CD Images - 14th Schmidt Cassegrain Texas A&M Observatory

July 20, 1994 1:29UT Impacts G/D and L

July 20, 1994 2:25UT Impacts H G/D and L

July 27, 1994 1:25UT Impacts G/D/S/R L and K/W

Fig. 5 Impact images (visible)

Conclusion The comet Shoemaker-Levy 9 impact with Jupiter was spectacular. It far exceeded our expectations. The data continues to be analyzed and assessed regarding what the impact uncovered about Jupiter. Further, it reminds us that the process of mass accretion continues in the solar system. There are no safe zones free from the threat of impact. While the comet Shoemaker-Levy 9 impacts were entertaining to observe from afar, such impacts on Earth would most likely end civilization and perhaps us as well. We, the citizens of the Earth, are on this path and must be prepared for such eventuality however remote. National and international efforts have started and are continuing in an effort to identify, categorize, catalogue, and characterize all NEOs and other extraterrestrial threats to Earth. This includes the vast pool of amateur astronomers like the Shoemakers and Levy who all continue to make significant contribution in finding and identifying NEOs. Finally, NASA and other like-minded organizations around the world are developing realistic concepts to defend the Earth Page 5 of 6

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_35-1 # Springer International Publishing Switzerland 2014

once we should ever find a definite threat. The glorious show put on by comet Shoemaker-Levy 9 in July 1994 should continually remind us that the threat of impact from above is very real. We must be continually vigilant.

Cross-References ▶ Deep Impact and Related Mission ▶ Hypervelocity Impact ▶ NEO Discovery and follow up Surveys ▶ Planetary Defense, Global Cooperation and World Peace

References Beatty KJ, Goldman SJ (1994) The great crash of 1994: a first report. Sky Telescope 88(4):18–23

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_36-1 # Springer International Publishing Switzerland 2014

Key Reports on Cosmic Hazards and Planetary Defense Issues and Initiatives Joseph N. Pelton* Executive Board, International Association for the Advancement of Space Safety, Arlington, VA, USA

Abstract As we become more aware of cosmic risks to human existence, there have been more and more efforts to identify the nature of these risks, share information as to the nature and types of these risks on a global scale, and even initiate and execute programs to carry out some form of planetary defense. The most obvious of these threats are potentially hazardous asteroids, comets, and bolides that we know can result in planetary disaster and mass exterminations. Increasing efforts have been undertaken to identify the nature of cosmic risks and to devise programs that can assist with planetary defense. This chapter seeks to identify some of the most important reports and programs that have been prepared to address planetary risks and possible defense and mitigation activities. Some of the activities are well advanced, while others are just beginning. Although the bulk of national, regional, and international efforts related to planetary defense around the world, as addressed in the Chapter on Planetary Defense, Global Cooperation and World Peace, is indeed to identify, catalog, respond, and mitigate harmful objects that could crash into Earth, this is starting to change. The world community is clearly alerted to the mounting risks of orbital debris. Further research by a number of space-faring nations is increasingly identifying the serious risks associated with solar and cosmic radiation, coronal mass ejections, and orbital debris and even beginning to address external or alien viruses and cosmic radiation. Therefore, some of the important reports and initiatives with respect to these other threat areas, particularly with regard to the efforts of the World Meteorological Organization, are also noted at the end of this chapter. Nevertheless, the major portions of this chapter are directed to key reports such as those of the Working Group on Near-Earth Objects (WGNEO) of the International Astronomical Union and the annual report by NASA to Congress with regard to the Safeguard program, the work of the Association of Space Explorers, the Panel on Asteroid Threat Mitigation, the Action Team-14, and the work of the UN Committee on the Peaceful Uses of Outer Space. Today most of these reports and efforts are directed at “detection” and achieving a better scientific understanding of the level of cosmic threats as well as a wider sharing of threat information on a global basis. Increasingly, in the last few years, these efforts have also transitioned to the development of preventive programs that actually begin to see viable ways to “implement” global defenses against cosmic threats. Today, the International Astronomical Union, the International Academy of Astronautics, the United Nations (as discussed in the earlier chapter), the Association of Space Explorers, the Action Team-14, as well as NASA, ESA, and other national and regional space agencies support the abovementioned efforts. All of these efforts play a prime role in publishing critical information about cosmic hazards and planetary defense in various locations but with prime focus on the Minor Planet Center in Cambridge, Massachusetts, in the USA. In the future, however, a growing number of institutions will be involved. Organizations playing a key role today range from the Association of Space Explorers, the Planetary Society, the Safeguard Foundation, and the *Email: [email protected] Page 1 of 13

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_36-1 # Springer International Publishing Switzerland 2014

B612 Foundation (which is implementing the new Sentinel infrared telescope). Key roles are also played by academic institutions such as the Minor Planet Center (at the Harvard University and Smithsonian Astrophysical Observatory) as well as observatories around the world. Even commercial space programs are involved since micrometeoroids are a threat to commercial satellite programs. These entities and more will thus play an increasing and positive role in informing the public as well as implementing defensive programs.

Keywords Association of space explorers; B612 Foundation; International Academy of Astronautics (IAA); International Asteroid Warning Network (IAWN); International Astronomical Union (IAU); Impact Disaster Planning Advisory Group (IDPAG); Interprogramme Coordination Team on Space Weather (ICTSW) Minor Planet Center; NASA; Near-Earth objects (NEOs); Planetary society; Spaceguard Foundation; Spaceguard Program; Space Missions Planning Advisory Group (SMPAG); Space weather; United Nations Office of Outer Space Affairs; World Meteorological Organization; Working Group on Near-Earth Objects (WGNEO) of the Science and Technology Committee of the IAU

Introduction There is a growing global awareness that our fragile planet and the life that exists on it are at risk. We, humans, and all forms of life live under a modest biosphere that on a relative scale is thinner than the outer skin of an apple and is clearly at peril with regard to cosmic hazards. The most obvious devastating risk is that could be caused by a near-Earth object such as a large-scale comet or asteroid or bolide.

1996 Report of the International Astronomical Union Science and Technology Committee It was the draft resolution in the report of the International Astronomical Union Science and Technology Committee on “The Detection of Asteroids and Comets Potentially Harmful to Mankind” of 1996 that helped to form a global consensus that near-Earth objects represented a true threat to global civilization (IAU, Science and Technology Committee, Doc. 7480). This report and the draft resolution provided a clear scientific summary of the type and nature of the threat to humanity. This draft resolution, in part, stated the following: 1. There are two broad categories of extraterrestrial objects which have the potential to impact our planet: comets and asteroids. They are generally known among planetary scientists as Near-Earth Objects (NEOs). Their total number is unknown, but the number of Earth-crossing asteroids with sizes larger than 1 km is estimated to be about 2 000. These objects are the most dangerous and only a tiny fraction of them have been detected to date. 2. Considering that the explosion close to the Earth's surface of even an object with a diameter of 50 metres can have the effect of a 10 megaton nuclear weapon, the consequences of larger impacts would be disastrous on a global scale. The best known recent examples are the Tunguska explosion of an NEO about 60 metres in size (over Siberia) in 1908, resulting in the destruction of over

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2 000 km2 of largely-unpopulated forest, and the violent impacts into Jupiter of the fragments of comet Shoemaker-Levy 9 (in July 1994); those fragments were only about 0,5 km in size, but caused devastation over a larger area than that of the Earth. Traces of other smaller impacts on our planet are frequently being discovered, as well as fossil records of cataclysmic impact events in the past. 3. The significant amount of information gathered over the last few years on asteroid and comet collisions indicates how they can trigger large-scale and large-standing ecological catastrophes, sometimes leading to mass extinctions of species. Such impacts therefore represent a significant threat to human civilisations. (IAU, Science and Technology Committee, Doc. 7480)

This report went on to call on nations to organize to address this threat in a number of ways that included the following points: to establish an inventory of NEOs as complete as possible with an emphasis on objects larger than 0.5 km in size as well as to contribute to a long-term global strategy for remedies against possible impacts. (IAU, Science and Technology Committee, Doc. 7480)

Other elements of the resolution asked for these various activities to be globally coordinated with regard to collection and dissemination within a Spaceguard Program that had begun by NASA in the early 1990s and continues under the 2005 George Brown, Jr. Near-Earth Object Survey Act by the US Congress. This Act sets current goals for NEO identification for the USA. Since the 1996 IAU report, efforts have increased around the world. The results of these more recent efforts are that the number of potentially hazardous NEOs has been discovered to be of a much greater number than estimated in 1996 and the inventory effort has been refined to seek to identify such objects down from 0.5 km to 140 m, and if the Sentinel IR telescope is deployed, even smaller disaster asteroids can be identified (George E. Brown Jr. Near-Earth Object Survey Act). The 1996 IAU report was particularly effective in capturing world attention to this issue and has led to a series of important consequential actions. Although this is certainly not the only report on this subject nor the earliest, it is a useful place to start a global review of key reports and actions related to planetary defense. Since this report of 1996, there have been a number of key reports and supporting efforts relating to cosmic hazards and planetary defense. Virtually all of these reports and activities relate to the issue of potentially hazardous near-Earth objects (NEOs) with little cooperative global activities or reports about other forms of cosmic hazards such as solar flares, coronal mass ejections, or cosmic radiation. The only real exception has been global cooperation and collaboration with regard to orbital space debris mitigation. It is hoped that in the future years other cosmic hazards related to coronal mass ejections, solar flares, weakening of the Earth’s magnetosphere, cosmic radiation, and orbital debris will also be addressed in key international forums as the need for systematic approach to such issues on a global scale is also widely recognized.

Unispace and Action Team-14 UNISPACE III met in Vienna, Austria, in 1999. The final resolutions adopted at UNISPACE III established Action Teams in a number of areas. These Action Teams were tasked with creating terms of reference for new global coordinative mechanisms in such areas as global satellite navigation and with regard to the threat of near-Earth objects. The NEO group was created as Action Team-14 since this subject was the 14th resolution adopted by UNISPACE III (Report of the Third UNISPACE Conference).

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This Action Team-14 formally set up in 2001. It is currently composed of Australia, Brazil, China, Czech Republic, Finland, Germany, Iran, Japan, Kazakhstan, Lebanon, Malaysia, Nigeria, Pakistan, Poland, the Russian Federation, Saudi Arabia, the Syrian Arab Republic, the UK, and the USA. It also has the support and participation of the following organizations: Association of Space Explorers (ASE), European Space Agency (ESA), Committee on Space Research (COSPAR), International Astronomical Union (IAU), National Space Society, Space Generation Advisory Council, European Space Science Committee, European Science Foundation, and Spaceguard Foundation (Action Team-14). It has now adopted a formal report structure that is to address the following areas: • • • • • •

NEO detection and remote characterization Orbit determination and cataloging Consequence In situ characterization Mitigation Policy

(AIAA Planetary Defense Conference of 2007) The first four areas have advanced significantly within the AT-14 and the Working Group on NEOs since the UNISPACE resolution 14 was adopted. These activities are now coordinated within the UN COPUOS as well as the WGNEO of the International Astronomical Union. The coordinative work is primarily carried out within the domain of the Minor Planet Center and the Safeguard Project. These networks allow easy global access to information about all NEOS that are detected through ground and space observation. Although much work on detection remains to be done, the coordinative structure on a global basis is in place. The key areas where the greatest amount of effort needs to be undertaken are with respect to mitigation techniques and the development of policy processes to characterize threats to the global community (such as through the Torino and Palermo Hazard Scale). In short, there is still that remains to be done in terms of deciding and implementing the who, what, and how elements of any mitigation efforts that might be undertaken as part of any planetary defense efforts.

US Initiatives Involving NASA and Actions Taken Pursuant to US Law NASA had been tracking asteroids, comets, and potentially hazardous objects during the 1990s, and its efforts contributed to the report of the IAU’s Science and Technology Committee’s Working Group on Near-Earth Objects in 1996. Subsequently this activity by NASA has increased through the use of infrared telescopes. Especially, observations to detect asteroids have been using the Widefield Infrared Surveyor Explorer under a program known as NEOWISE. In 2005 the US Congress passed a bill known as the George E. Brown, Jr. Near-Earth Object Survey Act. This legislation that was signed into law set specific objectives for NASA (NASA Authorization Act of 2005). These objectives included defining a program, involving both space- and ground-based observation equipment, for the identification and mapping of potentially harmful NEOs that would be quickly presented for Congressional approval. This law called for NASA to provide Congress with annual reports on progress toward these objectives with the first such report being developed a year after the legislation went into effect and objectives established. It also asked for updates with regard to possible strategies for deflecting potentially harmful objects. NASA produced the first such report Page 4 of 13

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Table 1 Short-term impulsive techniques to address near-term threats Short-term impulsive technique Conventional explosive (surface) Conventional explosive (subsurface) Nuclear explosive (standoff) Nuclear explosive (surface) Nuclear explosive (delayed) Nuclear explosive (subsurface)

Description of process Denote on impact Drive explosive device into PHO, detonate Detonate on flyby via proximity fuse Impact, detonate via contact fuse Land on surface, detonate at optimal time Drive explosive device into PHO, detonate

Table 2 Longer-term impulse techniques to address longer-term threats Longer-term impulsive technique Focused solar Pulsed laser Mass driver Gravity tractor Asteroid tug Enhanced Yarkovsky effect

Description of process Use large mirror to focus solar energy on a spot, heat surface, “boil off” material Rendezvous, position spacecraft near PHO, focus laser on surface, material “boiled off” surface provides small force Rendezvous, land, attach, mine material, eject material from PHO at high velocity Rendezvous with PHO, fly in close proximity for extended period, gravitational attraction provides small force Rendezvous with PHO, attach to PHO, push Change albedo of a rotating PHO; radiation from sun-heated material will provide small force as body rotates

in March 2007 that set forth the objectives for a program for identifying NEOs. It also provided a detailed analysis of possible strategies for deflecting an asteroid or comet and evaluated their ability to accomplish this feat both for shorter term responses as well as responses that could be implemented over a longer-term period. The initially identified goal in this report was to identify “by the end of 2020, 90 percent of all Potentially Hazardous Objects (PHOs) greater than 140 meters whose orbits pass within 0.05 Astronomical Units (AUs) of the Earth’s orbit (as opposed to surveying for all NEOs)” (NASA Report to Congress). This report also reflected NASA’s original assessment of feasible methods for deflection of potentially hazardous NEOs. NASA analysis was divided into strategies for short-term deflections where it was suggested that an impulsive technique using either conventional explosives or nuclear devices would be necessary. This NASA analysis suggested that if there were longer-term warning available, then a so-called soft push technique that would gradually divert the potentially hazardous object into a safe orbit or an orbit that would steer the NEO into the Sun’s gravity field (or that of another planet) would represent the best and most viable solution in terms of cost and simplicity. The techniques presented in the March 2007 NASA report are reflected in the two tables below (Tables 1 and 2). More recently in 2013 the Action Team-14 has recommended the formation of a warning network and two advisory groups. These would be an International Asteroid Warning Network (IAWN), a Space Missions Planning Advisory Group (SMPAG – pronounce “same page”), and an Impact Disaster Planning Advisory Group (IDPAG). In effect all of these groups would assist with Page 5 of 13

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international coordination of efforts to identify and response to NEO threats. This would not create new bodies or entities but rather allow effective communications and coordination among all of the people working in this area around the world (Recommendations of the Action Team on Near-Earth Objects). On the basis of this recommendation, the UN General Assembly during its session in 2013 formally approved the creation of the IAWN and the two advisory groups.

The Third IAA and Planetary Society Planetary Defense Conference of 2013 In April 2009 the first Planetary Defense Conference was held under the sponsorship of the International Academy of Astronautics followed by the second such conference in May 2011 and the third in April 2013. The International Academy of Astronautics together with the Planetary Society has organized these conferences to gather the world’s best researchers and scientists to compare notes on what is known about asteroid and comet threats to Earth and the latest information about mitigation techniques that could be deployed against known threats. There has been increasingly wide attendance with experts in the field from all over the world to address every aspect of this issue. Papers at the latest conference were presented on every aspect of this issue from NEO discovery and orbit determination, NEO characterization, mitigation techniques, potential asteroid intercept missions, and also papers that address warning, disaster recovery and management, and costs. The proceedings from these conferences represent some of the most up-to-date information on what is known and not known about asteroid threats. What is clear from the latest proceedings is the following: Locating and Tracking NEOs to Determine Their Orbits: About 90 % of asteroids that are 1 km in diameter or larger have been discovered and their orbits determined. Although this sounds reassuring, this still leaves hundreds of potential asteroids that are “planetary threats” to be found. Asteroids that are on the order of 17 m (the Siberian asteroid of February 15, 2013) are another matter entirely. The number of asteroids of this size could be a huge number (i.e., over a million). This relatively small asteroid contained the kinetic energy equivalent to a 330 kt bomb, injured 1,000 people, and did millions of dollars of damage while impacting a largely rural and not heavily populated area. Physical Characterization: The truth is the reports and papers from the third conference indicate that space scientists and astronomers are still early in the process of getting physical data about NEOs, but things are improving. There is now useful data with regard to rotation rates to learning if a given asteroid is really a binary pair or cluster to the more challenging determination as to whether a given asteroid is a solid rock or a porous much lesser threat. Mitigation: This involves strategies or techniques leading to deflection or disruption or breaking apart of hazardous NEOs. At this time such techniques are not well tested. Certainly no strategy could be instantly implemented on short notice. A few techniques have been added to the list that NASA first developed in 2007. These new techniques involve use of lasers to create “propulsive jets” out of the asteroid material itself, directed beam systems, etc. Impact Destruction and Public Safety: The problem with impact destruction is that there are quite different models if the asteroid bursts in the sky, impacts the ground, or impacts the ocean and creates a tidal wave. The recent events in February 2013 and new discoveries of asteroids that could impact in the foreseeable future has increased public awareness but has not released

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significant funds to cope with asteroids mitigation or public safety measure such as “informed evacuations” to prepare for a global or regional disaster. Disaster Management: We may have little warning of impending impact, making evacuation something that must be considered, or no warning – in which case it becomes disaster relief. This conference has really helped jump-start discussions with the disaster management community.

Association of Space Explorers Panel on Threat Mitigation (PATM) The Association of Space Explorers has been actively engaged in developing a strategy for addressing cosmic hazards and planetary defense for over 20 years. In October 2013 the Association of Space Explorers hosted a conference in New York City at the Rose Planetarium. This conference was planned to coincide with the UN General Assembly and was designed to use the persona of well-known astronauts to capture the attention of global leaders. The Association of Space Explorers first of all applauded the action of the General Assembly to adopt the recommendations of the UN-backed Action Team-14 by agreeing to create the International Asteroid Warning Network (IAWN) and to create the two advisory groups noted above. The assembled leaders of the ASE, however, advocated a further plan that asked the UN General Assembly to take the following additional steps: 1. Brief their respective national policymakers on the asteroid hazard and the latest General Assembly actions taken to prevent a NEO impact. 2. Call for national policymakers to address impact hazards in their disaster response plans and budgets. 3. Call for national governments to explicitly assign lead responsibility for asteroid hazard response to their space or disaster response agency, creating clear lines of responsibility. 4. Maintain that in order to find the approximately one million NEOs capable of threatening Earth, it was necessary for national policymakers to commit the modest funds necessary to support the launch of a space-based search telescope by 2020. 5. Call for policymakers to direct their national space agencies to launch within 10 years an international deflection demonstration, to alter the path of a small near-Earth asteroid. The UN COPUOS Working Group on NEOs as well and IAU’s Working Group on NEOs will continue to report on global efforts at discovery and mitigation. The challenge of asteroids represents a significant global threat, but the ability to find and travel to these objects is a largely understood activity that can employ conventional rocket systems. Comets, however, which can travel at much greater velocities and in much different orbital planes represent a different type of challenge that largely exceeds current capabilities (Association of Space Explorers Calls for Global Cooperation to Confront Asteroid Threat 2008, 2013).

Orbital Space Debris Just as the issue of asteroid and comet impact on Earth has been recognized and addressed over the past few decades, so too has the international community become increasingly aware of the problem

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Fig. 1 The mounting space debris problem particularly in low-Earth orbit (Image courtesy of NASA)

of orbital debris and has begun to cooperate to address this problem as well. In the 1980s Donald Kessler, who was a scientist working for NASA, did an analysis of increasing space activities and launches. He suggested that over time space debris could increase to the level that there could be a runaway cascade of debris that would be difficult to control. This prediction was discounted at the time, but is today broadly seen as a real threat to future space activity and is known as the Kessler syndrome. Today’s reality is that more than 300,000 space debris elements in the 1–10 cm size are now in the Earth’s orbit and some 22,000 larger elements are being constantly tracked. Some 6000 tons of space junk, with over 40% in low earth orbit, now circle Earth, and the problem continues to worsen despite new controls. In the 1990s this problem was increasingly recognized as real (Fig. 1). As of 1994 the UN Committee on the Peaceful Uses of Outer Space formed a subcommittee to address the issue of orbital debris (UN COPUOS Sub-Committee on Orbital Debris A/AC.105/571). The process of achieving consensus within COPUOS, however, is quite difficult. This committee with some 70 members with sharply divided interests and political agendas does not quickly come to unanimous agreement. When there was a lack of substantial progress within the UN-based discussions after several years, an attempt to address this problem in more technical forums was considered a logical thing to do. The space agencies recognized that the mounting level of orbital space debris could be a threat to future space activities, and thus it was agreed to form the Inter-Agency space Debris Coordination (IADC) Committee. The IADC proceeded to develop mitigation guidelines which they first developed in the form of an initial and comprehensive set of proposals as of October 2002 (IADC 02-01). In developing these proposals they drew on a wide range of previous reports, proposed standards and background documents. These included the following previous works from 1995 through 2001: – Technical Report on Space Debris, text of the report adopted by the Scientific and Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space, 1999 – Interagency Report on Orbital Debris 1995, the National Science and Technology Council Committee on Transportation Research and Development, November 1995 – US Government Orbital Debris Mitigation Standard Practices, December 2000 – Space Debris Mitigation Standard, NASDA-STD-18, March 28, 1996 – CNES Standards Collection, Method and Procedure Space Debris – Safety Requirements, RNC-CNES-Q-40-512, Issue 1- Rev. 0, April 19, 1999

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– Policy to Limit Orbital Debris Generation, NASA Program Directive 8710.3, May 29, 1997 – Guidelines and Assessment Procedures for Limiting Orbital Debris, NASA Safety Standard 1740.14, August 1995 – Space Technology Items. General Requirements. Mitigation of Space Debris Population. Russian Aviation and Space Agency Standard OCT 134-1023-2000 – ESA Space Debris Mitigation Handbook, Release 1.0, April 7 1999 – IAA Position Paper on Orbital Debris – Edition 2001, International Academy of Astronautics, 2001 – European Space Debris Safety and Mitigation Standard, Issue 1, Revision 0, September 27 2000 Over the next 5 years, these IADC Space Debris Mitigation Guidelines were revised and perfected through additional research and discussion. This led to a new document (IADC 02-01 revision 1) that achieved a wide level of global consensus and helped to achieve a consensus within COPUOS even though the UN-backed guidelines were “voluntary” rather than mandatory (Inter-Agency space Debris Coordination Committee (IADC) Orbital Debris Mitigation Procedures (IADC 02-01 and IADC 02-01 Revised)). The UN General Assembly in 2008 adopted resolution 62/217, endorsing the Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space. These voluntary guidelines outlined space debris mitigation measures for the planning, design, manufacture, and operational phases of spacecraft and launch vehicles (UN General Assembly). The guidelines call for limiting the long-term presence of spacecraft in low-Earth orbit (LEO), up to some 1,600 km (1,000 miles) above Earth’s surface, after the end of their mission. The guidelines call for the removal of such spacecraft from orbit or for their disposal in other orbits that avoid their long-term presence in the LEO region, where the majority of satellites are placed and where they are in greatest danger of collision. This is not to say that other orbits such as medium-Earth orbit and geosynchronous orbit do not constitute problem. Thus after 14 years of consideration, consensus was achieved. Yet despite this progress the reality is that orbital debris continues to increase and active mitigation procedures to reduce debris is still largely conceptual.

International Space Weather Coordination: Solar Space Hazards and Other Cosmic Threats Perhaps the largest and certainly the most unnoticed threat to global society is that represented by extreme “space weather” in terms of massive coronal mass ejections or extremely high energy solar flares or cosmic radiation. We truly do not know what would be the impact if something like the Carrington Event of 1859 were to recur, but the results in terms of massive power outages could be catastrophic. Further there are new concerns that recent changes to the Earth’s magnetosphere could be greatly increasing global vulnerabilities (Fig. 2). The effects of space weather, especially in cases of extreme eruptions, could disable vital infrastructure on which our planet with some seven billion people, largely concentrated in cities, now greatly depends. The damage from solar flares and coronal mass ejections can come in a variety of forms. There could be massive damage to communications, navigation, remote sensing, and weather satellites due to charged ions from a solar flare or cosmic radiation. There could widespread power outages due to a wide number of transformers being “fried” due to a large-scale coronal mass ejection. It is sometimes not recognized how dependent we are on our power grids and communications, navigation and remote sensing, and weather satellites. The exercise called “a day without Page 9 of 13

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_36-1 # Springer International Publishing Switzerland 2014

Fig. 2 False color images of solar flare and coronal mass ejection (Image courtesy of NASA)

satellites” suggests that much of our economy, defense systems, and safety nets could come to a halt with a massive hit on our space infrastructure. If one adds to that a loss of electrical power, the vulnerability spreads to almost all people and all business systems. Every day it becomes more important to monitor, understand, and explore protective actions with regard to extreme space weather events because almost every aspect of our lives could be impacted by a large hit. At the international level most of the coordinative actions with regard to space weather and solar hazards and cosmic radiation have been coordinated through the World Meteorological Organization. During the past 5 years, this activity has increased considerably. One of the more important actions was taken by the Executive Council of the World Meteorological Organization (EC-LX).in June 2008. It formally noted in a report the potential of extreme space weather events having a negative impact on meteorological satellites and forecasting equipment. Of greater significance the report continued to note that a big solar weather event could actually have a wide spread negative impact around the world on many important human activities and commercial systems including airline and transportation systems, banking, electrical power grids, and telecommunications and IT systems. This could ultimately impact more than 90 % of the world’s commercial services. Thus the Executive Council agreed that WMO should support international coordination of space weather activities and help to raise funds to carry out such international coordinative actions needed to defend against such extreme space weather events. In May 2010, WMO as a whole established the Interprogramme Coordination Team on Space Weather (ICTSW). This new coordination team was provided a mandate on a global basis to support space weather observation, data exchange, product and services delivery, and operational applications. ICTSW as of late 2013 has recruited space weather experts from 21 different countries and seven international organizations to work in this area and to assist with rapid and effective data transfers (World Meteorological Organization, Inter-Programme Coordination Team on Space Weather (ICTSW)). The World Meteorological Congress (Cg-XVI), which meets every 4 years, convened in Geneva, Switzerland, during the period 23 May to 16 June 2011. The Congress, as a follow-up to the actions taken by the Executive Council, formally affirmed the need for a coordinated effort by WMO Members to address the need for improved global preparedness related to space weather hazards.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_36-1 # Springer International Publishing Switzerland 2014

Annex IV of its report provided the following statement on this subject that had been drafted the group tasked with addressing space weather hazards:

Global Preparedness for Space Weather Hazards The Congress in its final report noted:

• The increasing risks of space weather events to all WMO members due to the increasing reliance on advanced technologies • The diversity of sectors impacted by space weather, including: navigation, communication, electric power, pipelines, satellites, and aviation, as well as the impacts on core meteorological observations • The actions being taken today by industries and governments to prepare for, and respond to, space weather storms and related indirect hazards • The progress already achieved in establishing ground-based and space-based observing networks • The progress already achieved in establishing a framework of space weather prediction and service centers • The need for coordinated near-term and far-term actions in order to plan and implement capabilities that will meet regional and global space weather requirements, as identified in the WMO Rolling Review of Requirements (RRR) in a sustained, comprehensive, robust, efficient, and integrated fashion • The capacity of WMO members to contribute to a globally coordinated system of observations and services, relying on their national R&D and operational assets, as well as on international partnerships • The benefits that can accrue to all WMO members from increased WMO coordination of space weather activities • The need to raise awareness, advocate the benefits, and provide training so that WMO members can take advantage of coordinated space weather activities The participants in the Cg-XVI Side Event on Space Weather therefore recommended: • To develop and implement near-term and far-term action plans that will enable members to determine needs and requirements and to benefit from existing services • That WMO members will contribute, where possible, to enhance regional and global capabilities, including observation collection and information delivery • That Cg-XVI requests the development of action plans, including training and education, and the implementation of a coordinated strategy for space weather hazards (Global Preparedness for Space Weather Hazards) Although this adopted statement by the WMO and the efforts of the Interprogramme Coordination Team on Space Weather (ICTSW).to organize efforts in this area are a plus, it is clear that there is much more to be done here. The needed level of international research and coordination to address the space weather dangers is lacking. The efforts here are far less well organized and funded than in other sectors. COPUOS has working groups on near-Earth objects and on orbital debris and the sustainability of space, but none directly related to space weather. Although there is cooperation between some of the space agencies in this field – notably NASA, ESA, JAXA, and the UK Space Authority – far more collaborative efforts are possible. Recent new solar research efforts on the part of the Russian Space Agency (Roscosmos) is particularly welcome, but more needs to be done. Page 11 of 13

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_36-1 # Springer International Publishing Switzerland 2014

This conclusion is drawn simply because in the next 100 years, the odds weigh heavily in the direction that the most likely cosmic danger to actually occur is an extreme space weather event. This could have huge negative consequences in terms of global infrastructure and potentially massive areas of commercial losses. To be more precise a massive coronal mass ejection could lead to the loss of vital applications satellites, the crash of airlines, massive power grid failures, and other horrific events for which we are totally not prepared. In order to respond to these threats, more involvement by space agencies and those involved with homeland security will be needed, more resources need to be dedicated to identifying vulnerabilities and protective actions, and international agencies beyond the WMO need to become directly involved in consideration of these hazards.

Conclusion There are literally thousands of reports, records of legislative hearings, proposed standards and guidelines, and national, regional, and international agreements that relate to cosmic hazards and potential methods to identify and record those threats, reduce those risks, or mitigate the various problems associated with cosmic hazards. We have moved forward from simply recognizing threats to actively coping with them and in a coordinated way within the international scientific community. This chapter has focused on the problems related to near-Earth objects, orbital space debris, space weather, and cosmic radiation and key reports and national and international actions to cope with these various threats in outer space. This brief chapter cannot completely cover all of the vast literature now available regarding cosmic hazards, but it does seek to identify some of the major milestones over the last two decades and indicate the status of these efforts within the processes of the United Nations (including COPUOS, the Action Team-14, and the World Meteorological Organization, the International Astronomical Union, the International Academy of Astronautics, the Spaceguard Program and the Spaceguard Foundation, the Inter-Agency space Debris Coordination (IADC) Committee), plus the actions of relevant nongovernmental organizations such as the Association of Space Explorers, the Planetary Society, the B612 Foundation, as well as many others, including key national and regional space agencies. The references in this section can be used to explore more details about the particulars of key reports and United Nations agreements and processes.

Cross-References ▶ ESA’s Potentially Hazardous Asteroid program ▶ NEO Shield Program of the European Space Agency ▶ Planetary Defense, Global Cooperation and World Peace ▶ United Nations Activities ▶ Working Group on Near Earth Objects (WGNEO) of the International Astronomical Union

References Action Team-14 (AT-14) AT14 report 2006/7 (A/AC.105/C.1/L.290). 12 December 2006 AIAA Planetary Defense Conference of 2007, Washington, DC. www.aero.org/conferences/planetary/defense Page 12 of 13

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_36-1 # Springer International Publishing Switzerland 2014

Association of Space Explorers (2008) Asteroid threats: a call for global response, Houston. Text available at http://www.spaceexplorers.org/index.html Association of Space Explorers Calls for Global Cooperation to Confront Asteroid Threat (2013) Space daily, 30 Oct 2013. http://www.spacedaily.com/reports/Association_of_Space_Explorers_Calls_for_Global_Cooperation_to_Confront_Asteroid_Threats_999.html Brown GE Jr. Near-Earth Object Survey Act. NASA Authorization Act of 2005 (Public Law No. 109-155) Global Preparedness for Space Weather Hazards Abridged Final Report of the Sixteenth World Meteorological Congress, Annex 4. http://www.wmo.int/pages/prog/sat/documents/SATGEN_ST-14-Space-Weather-statement-Cg16-Annex4.pdf, p 404 IAU, Science and Technology Committee, Doc. 7480, 9 Feb 1996 Inter-Agency space Debris Coordination Committee, Terms Of Reference for the Inter-Agency Space Debris Coordination Committee (IADC) IADC-93-01 (rev.11.2, public version), Status: 11 July 2011; text at http://www.iadc-online.org/index.cgi?item¼docs_pub, cited as IADC TOR Inter-Agency space Debris Coordination Committee (IADC) Orbital debris mitigation procedures (IADC 02-01 and IADC 02-01 revised) International Asteroid Warning Network (IAWN) NASA Authorization Act of 2005 (Public Law No. 109-155) NASA Report to Congress, Near-Earth Object Survey and Deflection Analysis of Alternatives March 2007 Recommendations of the Action Team on Near-Earth Objects for an international response to the near-Earth object impact threat, 20 Feb 2013 http://www.oosa.unvienna.org/pdf/misc/2013/at-14/ at14-handoutE.pdf Report of the Third UNISPACE Conference, The United Nations Conference on the Exploration and Peaceful Uses of Outer Space (A/CONF.184/6) http://www.unoosa.org/oosa/en/unisp-3/index. html UN Committee on the Peaceful Uses of Outer Space, Sub-Committee on orbital debris. (A/AC.105/ 571, paras. 63–74) United Nations General Assembly, Report of Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space (Vienna, 19–30 July 1999), A/conf.184/6, 157 pp, cited as (UNISPACE III) Working Group on Near Earth Objects (WGNEO) of the International Astronomical Union World Meteorological Organization, Inter-Programme Coordination Team on Space Weather (ICTSW) www.suparco.gov.pk/pages/ictsw.asp

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE A. Mainzera*, J. Bauera, T. Gravb, R. Cutric, J. Masieroa, R. S. McMilland, C. Nugenta, S. Sonnetta, R. Stevensona, R. Walkere and E. Wrightf a JPL, Pasadena, CA, USA b Planetary Science Institute, Tucson, AZ, USA c California Institute of Technology, Pasadena, USA d University of Arizona, Tucson, AZ, USA e Monterey Institute for Research in Astronomy, Monterey, CA, USA f UCLA, Los Angeles, CA, USA

Abstract NASA’s Wide-field Infrared Survey Explorer (WISE) mission, designed to survey the entire sky at infrared wavelengths, has proven a valuable means of discovering and characterizing the small bodies in our solar system. Modifications to the mission’s science data processing system, collectively known as NEOWISE, have allowed new minor planets to be discovered using this spacebased infrared telescope. Using radiometric thermal models, physical properties such as diameter and albedo have been derived for more than 158,000 asteroids, including approximately 700 nearEarth objects and 160 comets. Following the conclusion of its primary mission, the WISE spacecraft was placed into hibernation in February 2011. Now renamed NEOWISE, the spacecraft was brought out of hibernation in 2013 to continue the search for near-Earth objects.

Keywords Asteroids; Comets; Impact; Infrared telescope; Main belt asteroid; Minor planet; Near-Earth object; NEOCAM; NEOWISE; PanSTARRS; Spatial resolution; Surveys; Wide-range infrared survey explorer (WISE); WISE moving object processing system (WMOPS)

Introduction Asteroids and comets have interacted with the Earth since the dawn of the solar system. Examples of collisions exist throughout history and evidence for these events can be found around the globe. Approximately four billion years ago, a massive number of asteroids and comets collided with the nascent Earth, possibly delivering much of our oceans (see, e.g., Chyba 1990). The formation of a large impact crater on the Yucatan peninsula in Mexico 65 million years ago is thought to be associated with the mass extinction of non-avian dinosaurs (Alvarez et al. 1980). Most recently on February 15, 2013, a 20 m asteroid entered the atmosphere over Chelyabinsk, Russia, bursting into pieces and causing widespread damage to persons and property. Quantifying the impact hazard posed by these objects to the Earth requires discovering and characterizing as many as possible. Significant strides have been made in this area in the last two decades. However, much work remains *Email: [email protected] Page 1 of 24

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

Fig. 1 The WISE flight system during the process of assembly into the launch vehicle shroud at Vandenberg Air Force Base, with protective aperture cover still installed

to be done, particularly for sub-kilometer-sized near-Earth objects (NEOs), both in terms of discovering the majority of potential impactors and determining basic physical properties such as size, albedo, composition, rotational state, etc. While spacecraft in situ missions allow for the most detailed investigations of asteroid physical properties, the expense of such missions means that only about a dozen asteroids have been visited. Terrestrial radar observations, which are capable of improving orbits and in some cases determining shapes and spin states, have observed several hundred NEOs to date. With infrared radiometry, it is possible to discover objects as well as obtain information on objects’ sizes, albedos, and thermophysical properties for a large number of minor planets.

Mission Objectives NASA’s Wide-field Infrared Survey Explorer (WISE, Fig. 1) mission obtained thermal infrared observations for more than 158,000 minor planets (Wright et al. 2010; Mainzer et al. 2011a). As a Medium Explorer mission funded by NASA’s Astrophysics Division, WISE was competitively selected and was completed on cost and on schedule. Led by Principal Investigator Dr. Edward Wright of UCLA, the WISE mission’s primary scientific objective was to map the entire sky in four infrared wavelengths (3.4, 4.6, 12, and 22 mm). Scientific goals included the discovery of extremely nearby cool stars and distant, ultraluminous infrared galaxies. In the 3 years since the first public data release, the mission has resulted in more than 700 peer-reviewed journal articles across a broad range of topics in astronomy and planetary science.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

Fig. 2 The WISE Sun-synchronous orbit results in continuous observing near 90 solar elongation and provides an average of 10–12 exposures over all parts of the sky. Coverage increases to hundreds of exposures near the ecliptic poles. Full sky coverage was achieved after 6 months

WISE’s original science requirements were driven by the need to produce the all-sky images and source catalogs. Nevertheless, it was recognized that the mission would also be well suited for observing asteroids and comets. However, the baseline mission provided only for producing an image atlas and catalogs based on coadding all exposures collected at a given part of the sky together. While these coadded images are adequate for study of sources that do not move, minor planets are removed by outlier rejection schemes designed to eliminate cosmic rays and other transient sources. To facilitate study of small bodies in our solar system, NASA’s Planetary Science Division provided the resources to archive the individual exposures and extracted single-frame source lists and to discover new moving objects from the data in near real time. These two tasks were collectively named NEOWISE.

Technical Characteristics WISE. WISE was launched on December 14, 2009, into a 525 km 6 am/6 pm Sun-synchronous polar orbit. Formal survey operations began on January 14, 2010, following in-orbit checkout. In order to maximize survey efficiency, the telescope scanned continuously, while images were frozen onto the 4747 arcmin field of view using a small mirror moving in the opposite speed and direction of the telescope boresight. The 11-s exposure cycle allowed sufficient time for images to be collected in all four wavelengths; images were read out, while the scan mirror reset to the starting position. The survey was designed to provide significant overlaps over the entire sky by offsetting the telescope’s pointing by 10 % of a frame width each orbit, ensuring 90 % frame overlap with each successive orbit. In the in-scan direction, a frame-to-frame overlap region of 10 % allowed for accurate registration of images. All four wavelengths were imaged simultaneously through the use of three beamsplitters. This survey design allowed the mission to complete its first survey of the entire sky in all four wavelengths after 6 months. The average region of the sky received more than 12 exposures, rising to hundreds at the ecliptic poles (Fig. 2). The spacecraft always observed near 90 solar elongation. To minimize loss of sky coverage, data downlinks and momentum dumps via magnetic torque rods were executed over the ecliptic poles. As an infrared space telescope, WISE is millions of times more sensitive than an observatory operating at similar wavelengths on the ground, as ground-based telescopes must observe through the infrared background produced by self-emission and the atmosphere. WISE’s two shortest wavelengths, 3.4 and 4.6 mm, were collected using HgCdTe detectors that were cooled to 32 K during the first 8.5 months of the mission. The two longer wavelengths, 12 and 22 mm, used Si:As arrays that required cooling to 7.8 K. The telescope optics and structure were kept below 17 K to allow for background-limited sensitivity.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

To achieve these temperatures, the mission employed a two-stage solid hydrogen cryostat. The cryostat exceeded its required lifetime of 7 months by 3 weeks. The first tank was depleted on August 5, 2010, causing the immediate loss of the 22 mm channel and gradually reducing the sensitivity of the 12 mm channel. On September 30, 2010, the remaining hydrogen was exhausted, and the instrument warmed to 73.5 K. The two shortest wavelengths, 3.4 and 4.6 mm, continued to operate with little change in performance. At this point, NASA approved a 4-month extension of the mission to complete a survey of the inner main belt and to continue the search for NEOs. On February 1, 2011, the mission was placed into hibernation; its solar arrays were left pointed at the Sun, but communications with it ceased. During its entire operational lifetime, the WISE spacecraft provided detections of 747 million sources extracted from more than three million images (Cutri et al. 2012). The sensitivity and spatial resolution were significantly improved over the previous generation of all-sky surveys at these wavelengths: the Cosmic Background Explorer and the Infrared Astronomical Satellite (IRAS). Despite having a smaller aperture than IRAS (40 vs. 60 cm), the WISE satellite returned images hundreds of times more sensitive at 12 and 22 mm because its four-megapixel infrared array images to be critically sampled. In contrast, IRAS had 62 pixels and consequently undersampled images at similar wavelengths, underscoring the profound impact of modern electronics on astronomy (Neugebauer et al. 1984). NEOWISE. To extract moving object candidates from the data, an algorithm known as the WISE Moving Object Processing System (WMOPS) was developed. This code was adapted from the PanSTARRS project to work with the WISE observing cadence (Kubica et al. 2007). WMOPS operates on extracted source lists, comparing them from exposure to exposure to remove stationary objects such as stars and galaxies and then linking the remaining transient detections to form position-time lists known as tracklets (Mainzer et al. 2011a). The WISE observing cadence allows a typical minor planet to be observed 10–12 times over a span of 36 h. This cadence was sufficient to allow many of the new candidates to be declared by the Minor Planet Center as “discovered.” However, to secure orbits such that objects can be recovered at the next apparition, it is necessary to obtain follow-up observations that span at least 20–30 days. A requirement was therefore levied on the NEOWISE project to deliver tracklets to the Minor Planet Center within 10 days of the midpoint of their observations on board the spacecraft. This requirement ensured that they could receive the prompt follow-up needed to avoid objects becoming lost, with orbits so uncertain that future positions cannot be predicted accurately. The WMOPS pipeline was run every 4–5 days during the prime mission, and the average lag time between observational midpoint and delivery to the MPC was 4.5 days. In order to distinguish real asteroids from spurious transients such as cosmic rays, noisy pixels, or other artifacts, WMOPS requires a minimum of five detections before a tracklet is assembled. Tracklets with observations that cannot be entirely associated with previously known objects are evaluated by scientists for validation prior to being submitted to the MPC (Fig. 3). At the beginning of the mission, WMOPS was operated with a conservative source signal-to-noise (SNR) threshold of 7 in place, while artifacts and distortion were precisely mapped. Once these calibrations were completed, the SNR threshold was successively lowered to 5, then 4.5, and finally 4. When searching for new objects, many are found at or near the survey’s detection threshold. Although increasing numbers of objects can be detected when the SNR is decreased, it becomes more difficult to distinguish between real objects and noise or artifacts. Moving object identification is particularly sensitive to the presence of transient artifacts such as latent images, cosmic rays, stray light, and noisy pixels. The WISE data’s artifacts were carefully and continuously monitored and flagged using the full-frame uncompressed images, allowing them to be excluded from the data. Page 4 of 24

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

Fig. 3 The WMOPS quality assurance (QA) process allowed for visual inspection of objects that could not be unambiguously associated with previously known minor planets. The QA system allows astronomers to reliably distinguish between real point sources (or extended objects such as 2009 WJ50, shown here and revealed to be cometary by NEOWISE) and artifacts such as latent images, cosmic rays, diffraction spikes, etc. The display shows repeated exposures at the same coordinates in different wavelengths (12 and 22 mm are shown in the top and second rows, respectively) as well as the immediately preceding exposures

Candidate NEOs detected by WMOPS were placed on the Minor Planet Center’s NEO Confirmation Page to make them widely available for the community to follow-up. Follow-up observations were obtained by observers all over the world, including both professional and amateur astronomers. The average equivalent visual magnitude of most NEOWISE NEO candidates was V  21.5; however, as an infrared telescope, NEOWISE frequently detected extremely low-albedo NEOs with visual magnitudes as faint as V  23. Furthermore, as an all-sky space-based survey making multiple passes over the ecliptic poles, detections frequently fell at extreme declinations in both hemispheres. Follow-up was also complicated by the fact that NEOWISE detected objects regardless of lunar phase or weather, unlike ground-based observers. In spite of these observational challenges, nearly all of the NEO candidates submitted to the NEO Confirmation Page during the prime mission were followed up. Out of 135 new discoveries, only 25 candidates never received optical follow-up, but 13 of these objects had WISE observational arcs sufficient to be declared discovered even without follow-up. Of the more than 300,000 tracklets submitted to the Minor Planet Center, fewer than a dozen were rejected as spurious associations. In 2010, the NEOWISE survey submitted more observations of minor planets than all other surveys by a factor of two. An advantage of the WMOPS system is that previously known and newly discovered objects’ tracklets were constructed in an identical fashion. Furthermore, the survey’s sensitivity and pointings were well known, and as a space-based survey, weather and atmospheric seeing were not factors. Because the four WISE bands are primarily sensitive to thermal emission from asteroids, they are equally sensitive to both low and high-albedo objects. These properties made it possible to compute the observational biases and selection effects that govern the observed sample. Once these biases in orbital elements, size, and albedo were determined, it was possible to extrapolate the properties of the observed sample to the population as a whole. This debiasing work has allowed the project to estimate the numbers, orbital characteristics, and physical properties of a number of minor planet populations to date. In total, the NEOWISE project detected more than 158,000 minor planets, including >34,000 new discoveries (Fig. 4). Of these, most are main belt asteroids (MBAs). The spacecraft observed 700 NEOs, including 135 new discoveries, and 160 comets, of which 21 were discovered by NEOWISE. The project is currently engaged in mining the dataset for new detections by rerunning

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

Fig. 4 NEOWISE detected >158,000 minor planets, mostly in the main belt (black dots). Red and green circles represent NEOs discovered and detected by NEOWISE, respectively. Yellow and cyan squares indicate comets discovered and detected by NEOWISE. The red dashed line indicates the position the WISE spacecraft was observing when the cryogen was completely exhausted and the 4-month post-cryogenic phase of the prime mission began. Planet orbits are shown in gray, with the largest orbit belonging to Jupiter

WMOPS with lower SNR thresholds (applied in a uniform manner over the entire survey) and by stacking all available detections of all 600,000 known minor planets. Because WISE collected an average of 10–12 detections per object, stacking frames should result in the recovery of many additional objects that fell just below the single-frame detection threshold. The NEOWISE project delivered its data products, including single-frame images and extracted source lists, on schedule to NASA’s Infrared Science Archive (IRSA), hosted at the California Institute of Technology’s Infrared Processing and Analysis Center (IPAC). All data products from the prime mission are publicly available and accessible through IRSA. During the fully cryogenic portion of the mission, the 3-band cryogenic, and post-cryogenic phases, respectively, the project delivered 9.5 billion, 3.7 billion, and 7.3 billion extracted sources taken from a total of 2.7 million exposures. The NEOWISE project also supported the development of solar system science-friendly query tools that allow users to enter an object’s name or orbital elements and search through all available images and extracted sources. These tools support the “precovery” of objects discovered by other surveys in the future (Cutri et al. 2012). In addition to providing a well-determined set of survey biases, the NEOWISE survey offered the opportunity to derive physical properties for a large number of minor planets. Because asteroid thermal emission is a weak function of albedo, infrared observations allow for the derivation of radiometric diameters. Furthermore, the WISE observational cadence of 10–12 observations spaced uniformly over 36 h usually resulted in reasonable coverage of each object’s rotational light curve. Comparison of radiometrically derived diameters and albedos of objects with independently derived diameters from radar observations, spacecraft visits, and stellar occultations revealed

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

Fig. 5 The albedo distribution as a function of size for NEOs selected by WMOPS based on their 12 mm fluxes is roughly uniform (blue line), whereas the albedos for small NEOs discovered by visible light surveys and subsequently recovered from the NEOWISE data show a marked increase with decreasing size (black line)

agreement to within 10 % and 25 %, respectively, for models using WISE 12 mm observations (Mainzer et al. 2011b, c). Using only the 3.4 and 4.6 mm observations available during the postcryogenic mission phase, radiometric diameters and albedos reproduced those derived from 12 mm data to within 25 % and 40 %, respectively (Mainzer et al. 2012c; Masiero et al. 2012a). By comparison, diameters derived from visible light data alone are uncertain by factors of 2–3, and albedos cannot be computed. Prior to NEOWISE, robust physical properties were only known for several thousand minor planets, including IRAS, AKARI, radar, and ground-based infrared observations. With infrared observations of >158,000 objects, physical properties are now available for many more small bodies.

Key Findings and Results WISE data are being used at a rate of roughly one peer-reviewed journal article per day. NEOWISE data have resulted in >100 peer-reviewed journal articles since the first public data release of singleframe images and source lists in 2010 (Wright et al. 2010). Because NEOWISE represents a timedomain infrared survey, the data have been used for a wide range of topics in astronomy and planetary science, including cosmic distance ladder determinations, galactic structure, variable star studies, proper motion and parallax measurements, compact objects, and a plethora of solar system studies. NEOs. For NEOs, NEOWISE data have been used to constrain their numbers, sizes, albedos, and orbital characteristics. The sample of 429 NEOs detected by WMOPS during the fully cryogenic phase of the mission at 12 mm reveals the NEO albedo distribution to be roughly independent of size for objects ranging from more than 1 km in effective spherical diameter to 100 m (Fig. 5). This result contradicts previous findings that suggested that smaller NEOs became brighter; however, previous studies were based on optically selected samples, i.e., the objects were discovered by visible light surveys that are less sensitive to smaller, darker objects. Computing and accounting for Page 7 of 24

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

the observational biases of the fully cryogenic sample suggest that there are 20,500  3,000 nearEarth asteroids (NEAs; near-Earth comets were not included in the study) larger than 100 m, a somewhat smaller number than prior estimates, which ranged from 36,000 to 100,000. Furthermore, the NEOWISE study concluded that the so-called Spaceguard goal of discovering >90 % of near-Earth asteroids larger than 1 km had been met. However, the study found that only 25 % of objects larger than 100 m have been discovered to date. The study was inconclusive for NEAs smaller than 100 m as only a handful were detected by WMOPS (Mainzer et al. 2011e). The debiased NEO orbital element distribution showed reasonably good agreement with previous model predictions (e.g., Bottke et al. 2002). However, a notable exception was found when the sample was narrowed only to those NEOs considered potentially hazardous asteroids (PHAs; the subset of NEOs with minimum orbit intersection distances 90 % over a range of temperatures achievable via passive cooling

performance pre-launch indicate that the Earth-Sun L1 location offers the best means for efficient and reliable NEO discovery, characterization, and tracking. The mission architecture combines elements from the WISE, NEOWISE, and Spitzer missions. As with the WISE project, the science data processing center is at IPAC, and image atlases and source catalogs will be released annually through IRSA. Industrial partners include Teledyne Imaging Sensors and the Space Dynamics Laboratory, producers of the WISE payload. At present, the new detectors are undergoing detailed characterization to evaluate their performance and ensure that they are space qualified. Comparison with Sentinel. The B612 Foundation has proposed to build a very similar mission to NEOCam in 2012 named Sentinel using only private donations instead of NASA funding and project management. Like NEOCam, Sentinel proposes to use an infrared telescope with a central wavelength near 8 mm to search for NEOs. The major architectural differences between NEOCam and Sentinel are (1) orbit, (2) detectors, (3) cryogenic system, and (4) science data processing techniques. Instead of the Earth-Sun L1 Lagrange point, the B612 Foundation proposes to send Sentinel to a Venus-like orbit. The detectors they propose to use employ a different readout architecture: a capacitive transimpedance amplifier that is traditionally used in high-background applications, such as Earth science and defense, as opposed to the source follower per detector readout circuit that is standard for space-based astronomy that NEOCam uses. Because a spacecraft in Venus-trailing orbit is typically located 0.3–1.7 AU away from Earth, compared with 0.01 AU from the L1 Lagrange point, the data rate is reduced by a factor of 900–30,000. This necessitates a radically different approach to science data processing than the techniques employed by NEOWISE to detect moving objects. Lossless data compression only yields factors of 2–3 compression, so at this distance from the Earth, lossy compression is necessary and will result in loss of sensitivity. The desire to use standard scientific data reduction techniques inherited from WISE, NEOWISE, and Spitzer that allow for accurate subtraction of instrumental and sky background signatures, along with identification of artifacts and undesirable transient sources such as cosmic rays, diffraction spikes, latent images, and other stray light partially, motivates the choice of the Earth-Sun L1 Lagrange point for NEOCam. In a survey, most new objects are discovered near the sensitivity threshold, so it is preferable to avoid any destructive data compression that reduces sensitivity. Maintaining the low temperatures necessary for natural backgroundPage 20 of 24

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

limited performance for a cryogenic telescope is also more difficult at 0.7 AU from the Sun instead of 1 AU. Passive cooling is insufficient to drive the telescope structure and detectors to the necessary temperatures, so Sentinel must therefore employ mechanical cryocoolers. Finally, survey simulations show that there is no substantial benefit to a Venus-trailing orbit compared to the L1 Lagrange point for objects larger than 100 m. It is most likely significantly more challenging when accounting for data compression losses.

Conclusion Asteroids and comets have interacted with the Earth since its formation and continue to pose an impact hazard. Understanding the orbital distributions and physical properties of these objects is crucial to gauge the present risk. With this in mind, the NEOWISE project and the proposed NEOCam mission seek to fill this knowledge gap through the detection and characterization of NEOs using space-based infrared detectors. The NEOWISE project has significantly expanded the number of minor planets that have well-determined physical properties. The archiving and serving of the individual exposures from the WISE project has resulted in a significant number of scientific investigations covering a wide range of topics in planetary science and astrophysics. The total cost of the NEOWISE augmentations to the WISE science data processing pipeline, including operating the spacecraft for 4 months during the post-cryogenic mission phase, was $8.5 million, compared to the $320 million cost of designing, building, launching, and operating WISE. In the 3 years since launch, NEOWISE single-exposure images, source lists, and derived minor planet physical properties have been used in over 200 peer-reviewed publications. As with the WISE mission, the NEOWISE project delivered its data on cost and on schedule, providing a legacy for current and future solar system science. As new asteroids and comets are discovered, researchers can search the archival NEOWISE datasets for them, and the restarted NEOWISE mission is collecting new observations. By continuing to discover and characterize minor planets throughout the solar system, NEOWISE data will help to refine our understanding of how often and with what energy these bodies encounter Earth.

Cross-References ▶ Deep Impact and Related Missions ▶ European Operational Initiative on NEO Hazard Monitoring ▶ European Space Agency’s Program on Potentially Harmful Asteroid ▶ Hayabusa Missions ▶ Key Reports on Cosmic Hazards and Planetary Defense Issues and Initiatives ▶ NASA’s Asteroid Redirect Mission ▶ OSIRIS-REx Asteroid Sample Return Mission ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_41-1 # Springer International Publishing Switzerland 2014

References Alí-Lagoa V, Lionni L, Delbo M, Gundlach B, Blum J, Licandro J (2014) Thermophysical properties of near-Earth asteroid (341843) 2008 EV5 from WISE data. Astron Astrophys 561:45 Alvarez L, Alvarez W, Asaro F, Helen V (1980) Extraterrestrial cause for the cretaceous-tertiary extinction. Science 208:1095 Bauer JM, Walker RG, Mainzer AK, Masiero JR, Grav T et al (2011) WISE/NEOWISE observations of comet 103P/Hartley 2. Astrophys J 738:171 Bauer JM, Mainzer AK, Grav T, Walker RG, Masiero JR et al (2012a) WISE/NEOWISE observations of active bodies in the main belt. Astrophys J 747:49 Bauer JM, Kramer E, Mainzer AK, Stevenson R, Grav T et al (2012b) WISE/NEOWISE preliminary analysis and highlights of the 67p/Churyumov-Gerasimenko near nucleus environs. Astrophys J 758:18 Bauer JM, Grav T, Blauvelt E, Mainzer AK, Masiero JR et al (2013) Centaurs and scattered disk objects in the thermal infrared: analysis of WISE/NEOWISE observations. Astrophys J 773:22 Bottke WF, Morbidelli A, Jedicke R, Petit J-M, Levison HF, Michel P, Metcalfe TS (2002) Debiased orbital and absolute magnitude distribution of the near-earth objects. Icarus 156:399 Busch MW, Giorgini JD, Ostro SJ, Benner LAM, Jurgens RF et al (2007) Physical modeling of nearEarth Asteroid (29075) 1950 DA. Icarus 186:581 Carruba V, Domingos RC, Nesvorný D, Roig F, Huaman ME, Souami D (2013a) A multidomain approach to asteroid families’ identification. Mon Not R Astron Soc 433:2075 Carruba V (2013b) An analysis of the Hygiea asteroid family orbital region. Mon Not R Astron Soc 431:3557 Carruba V, Domingos RC, Huaman ME, dos Santos CR, Souami D (2014) Dynamical evolution and chronology of the Hygiea asteroid family. Mon Not R Astron Soc 437:2279 Christou A, Asher D (2011) A long-lived horseshoe companion to the earth. Mon Not R Astron Soc 414:2965 Chyba CF (1990) Impact delivery and erosion of planetary oceans in the early inner solar system. Nature 343:129 Connors M, Weigert P, Veillet C (2011) Earth’s Trojan asteroid. Nature 475:481 Cutri RM, Wright EL, Conrow T, Bauer J, Benford D et al (2012) Explanatory supplement to the WISE all-sky data release products Delbo M, Tanga P (2009) Thermal inertia of main belt asteroids smaller than 100 km from IRAS data. Planet Space Sci 57:259 Fernández YR, Jewitt DC, Sheppard SS (2002) Thermal properties of Centaurs Asbolus and Chiron. Astron J 123:1050 Fernández YR, Jewitt D, Ziffer JE (2009) Albedos of small Jovian Trojans. Astron J 138:240 Fernández YR, Kelley MS, Lamy PL, Toth I, Groussin O et al (2013) Thermal properties, sizes, and size distribution of Jupiter-family cometary nuclei. Icarus 226:1138 Giorgini JD, Ostro SJ, Benner LAM, Chodas PW, Chesley SR et al (2002) Asteroid 1950 DA’s encounter with earth in 2880: physical limits of collision probability prediction. Science 196:132 Grav T, Mainzer AK, Bauer J, Masiero J, Spahr T et al (2011) WISE/NEOWISE observations of the Jovian Trojans: preliminary results. Astrophys J 742:40 Grav T, Mainzer AK, Bauer J, Masiero J, Spahr T et al (2012a) WISE/NEOWISE observations of the Hilda population: preliminary results. Astrophys J 744:197 Grav T, Mainzer AK, Bauer JM, Masiero JR, Nugent CR (2012b) WISE/NEOWISE observations of the Jovian Trojan population: taxonomy. Astrophys J 759:49 Page 22 of 24

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Greenstreet S, Gladman B (2013) High-inclination Atens are indeed rare. Astrophys J Lett 767:18 Hirayama K (1918) Groups of asteroids probably of common origin. Astron J 31:743 Holman MJ, Wisdom J (1993) Dynamical stability in the outer solar system and the delivery of short period comets. Astron J 105:1987 Horner J, Evans NW, Bailey ME (2004) Simulations of the population of Centaurs – I. The bulk statistics. Mon Not R Astron Soc 354:798 Kramer EA, Fernandez YR, Lisse CM, Kelley MSP, Woodney LM (2014) A dynamical analysis of the dust tail of Comet C/1995 O1 (Hale-Bopp) at high heliocentric distances. Icarus 236:136 Kubica J, Denneau L, Grav T, Heasley J, Jedicke R, Masiero J, Milani A, Moore A, Tholen D, Wainscoat RJ (2007) Efficient intra- and inter-night linking of asteroid detections using kd-trees. Icarus 189:151 Mainzer A, Bauer J, Grav T, Masiero J, Cutri RM et al (2011a) Preliminary results from NEOWISE: an enhancement to the wide-field infrared survey explorer for solar system science. Astrophys J 731:53 Mainzer A, Grav T, Masiero J, Bauer J, Wright E, Cutri RM, McMillan RS, Cohen M, Ressler M, Eisenhardt P (2011b) Thermal model calibration for minor planets observed with wide-field infrared survey explorer/NEOWISE. Astrophys J 736:100 Mainzer A, Grav T, Masiero J, Bauer J, Wright E, Cutri RM, Walker R, McMillan RS (2011c) Thermal model calibration for minor planets observed with WISE/NEOWISE: comparison with infrared astronomical satellite. Astrophys J Lett 737:9 Mainzer A, Grav T, Masiero J, Hand E, Bauer J et al (2011d) NEOWISE studies of spectrophotometrically classified asteroids: preliminary results. Astrophys J 741:90 Mainzer A, Grav T, Bauer J, Masiero J, McMillan RS et al (2011e) NEOWISE observations of nearearth objects: preliminary results. Astrophys J 743:156 Mainzer A, Masiero J, Grav T, Bauer J, Tholen DJ et al (2012a) NEOWISE studies of asteroids with Sloan photometry: preliminary results. Astrophys J 745:7 Mainzer A, Grav T, Masiero J, Bauer J, McMillan RS et al (2012b) Characterizing subpopulations within the near-earth objects with NEOWISE: preliminary results. Astrophys J 752:110 Mainzer A, Grav T, Masiero J, Bauer J, Cutri RM, McMillan RS, Nugent CR, Tholen D, Walker R, Wright EL (2012c) Physical parameters of asteroids estimated from the WISE 3-band data and NEOWISE post-cryogenic survey. Astrophys J Lett 760:12 Mainzer A, Bauer J, Grav T, Masiero J, Cutri RM et al (2014a) The population of tiny near-earth objects observed by NEOWISE. Astrophys J 784:110 Mainzer A, Bauer J, Cutri RM Grav T, Masiero J et al (2014b) Initial performance of the NEOWISE reactivation mission. Astrophys J (submitted) Masiero Joseph R, Mainzer AK, Bauer JM, Grav T, Nugent CR, Stevenson R (2013) Asteroid family identification using the hierarchical clustering method and WISE/NEOWISE physical properties. Astrophys J 770:7 Masiero JR, Mainzer AK, Grav T, Bauer JM, Cutri RM et al (2011) Main belt asteroids with WISE/ NEOWISE. I. Preliminary albedos and diameters. Astrophys J 741:68 Masiero JR, Mainzer AK, Grav T, Bauer JM, Cutri RM, Nugent C, Cabrera MS (2012a) Preliminary analysis of WISE/NEOWISE 3-band cryogenic and post-cryogenic observations of main belt asteroids. Astrophys J 759:14 Masiero JR, Mainzer AK, Grav T, Bauer JM, Jedicke R (2012b) Revising the age for the Baptistina asteroid family using WISE/NEOWISE data. Astrophys J 759:14 McMurtry C, Lee D, Beletic J, Chen C-YA, Demers RT, Dorn M et al (2013) Development of sensitive long-wave infrared detector arrays for passively cooled space missions. Opt Eng 52:9 Page 23 of 24

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Nesvorný D (2012) HCM asteroid families V2.0. EAR-A-VARGBDET-5-NESVORNYFAM-V2.0. NASA Planetary Data System Neugebauer G, Habing HJ, van Duinen R, Aumann HH, Baud B, Beichman CA, Beintema DA, Boggess N, Clegg PE, de Jong T, Emerson JP, Gautier TN, Gillett FC, Harris S, Hauser MG, Houck JR, Jennings RE, Low FJ, Marsden PL, Miley G, Olnon FM, Pottasch SR, Raimond E, Rowan-Robinson M, Soifer BT, Walker RG, Wesselius PR, Young E (1984) The infrared astronomical satellite (IRAS) mission. Astrophys J Lett 278:1 Opeil CP, Consolmagno GJ, Britt DT (2010) The thermal conductivity of meteorites: new measurements and analysis. Icarus 208:449 Ryan E, Woodward C (2011) Albedos of small Hilda group asteroids as revealed by Spitzer. Astron J 141:186 Spitale J, Greenberg R (2001) Numerical evaluation of the general Yarkovsky effect: effects on semimajor axis. Icarus 149:222 Stevenson R, Kramer EA, Bauer JM, Masiero JR, Mainzer AK (2012) Characterization of active main belt object P/2012 F5 (Gibbs): a possible impacted asteroid. Astrophys J 759:142 Vokrouhlický D, Milani A (2000) Direct solar radiation pressure on the orbits of small near-earth asteroids: observable effects? Astron Astrophys 362:746 Walsh KJ, Delbó M, Bottke WF, Vokrouhlický D, Lauretta DS (2013) Introducing the Eulalia and new Polana asteroid families: re-assessing primitive asteroid families in the inner main belt. Icarus 225:283 Wright EL, Eisenhardt PRM, Mainzer AK et al (2010) The wide-field infrared survey explorer (WISE): mission description and initial on-orbit performance. Astron J 140:1868 Zappalà V, Cellino A, Farinella P, Knezevic Z (1990) Asteroid families. I – Identification by hierarchical clustering and reliability assessment. Astron J 100:2030 Zappalà V, Cellino A, Dell’Oro A, Paolicchi P (2002) Physical and dynamical properties of asteroid families. In: Bottke WF Jr, Cellino A, Paolicchi P, Binzel RP (eds) Asteroids III. University of Arizona Press, Tucson, pp 619–631

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning Harold J. Reitsemaa* and Edward T. Lub a Reitsema Enterprises Inc., Holland, USA b The B612 Foundation, Mill-Valley, CA, USA

Abstract The nonprofit B612 Foundation is building a space observatory called Sentinel. Its goal is to find a much larger number of smaller-scale asteroids than previous ground-based and space-based surveys because of its improved capabilities. Sentinel will be able to detect potentially harmful asteroids that may impact Earth with sufficiently early warning to permit the deflection of the threat. The Sentinel mission will position a 0.5-m infrared telescope in an orbit around the Sun’s interior to the Earth’s orbit and will scan space in the region near the Earth’s orbit for at least 6.5 years. There are an estimated one million asteroids near the Earth that are larger than 40 m that can destroy a city-sized area if they impact the Earth, and only about 10,000 of these have been found to date since smallersize asteroids are difficult to observe. Sentinel is designed to find over 100,000 near-Earth asteroids per year. The data collected by Sentinel will allow the orbital path of these detected objects to be determined with sufficient accuracy that it will be possible to map the asteroid’s future path for up to 100 years and assess whether there is a potential for an impact with Earth. Sentinel will be built by Ball Aerospace & Technologies Corp. under an innovative contracting approach that enables substantial cost savings. Sentinel will be privately funded by the B612 Foundation with philanthropic support. Launch is planned for 2018.

Keywords Asteroid; Ball Aerospace & Technologies Corp; B612 Foundation; Comet; Falcon 9 space mission vehicle; Field of regard (FOR); Hubble Space Telescope (HST); Kepler Space Telescope; Keplerian orbital motion; Minor Planet Center; NASA; NASA Deep Space Network (DSN); Near-Earth asteroids (NEA); Near-Earth objects (NEOs); Sentinel Space Telescope; Spaceguard Survey program; Spitzer Space Telescope; Torino hazard scale; Tunguska asteroid event

Introduction The threat to Earth posed by asteroids has been known since at least 1963, when Gene Shoemaker of the US Geological Survey convincingly demonstrated that many impressive craters on Earth were formed by asteroid impacts. The asteroids that cause these impacts are members of a group of asteroids known as near-Earth objects (NEOs). The potentially hazardous objects are primarily asteroids but there are also a small number of comets. NEOs are asteroids that originated in the main

*Email: [email protected] *Email: [email protected] Page 1 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

asteroid belt between the orbits of Mars and Jupiter. These asteroid NEOs (near-Earth asteroids or NEAs) have been gravitationally or collisionally perturbed into orbits which now bring them closer to Earth. NASA initiated the Spaceguard Survey program in 1998 as noted in Chapter ▶ NEOSHIELD - A Global Approach to Near-earth Object Impact Threat Mitigation. The objective established at that time was to locate within 10 years at least 90 % of the near-Earth objects that are larger than 1-km diameter. As substantial progress was being made by 2003, NASA commissioned a Science Definition Team (SDT) (Stokes et al. 2003) to study the threat posed by even smaller NEOs. The SDT determined that the most efficient observations of NEOs were to be obtained in thermal infrared (~5 to ~10 mm), where they reemit sunlight absorbed on their dark surfaces. Following the SDT report, in 2005 the United States Congress gave NASA the goal of compiling a catalog complete to 90 % by 2020 of all NEOs larger than 140 m in diameter (US Congress 2005) as the next step in reducing the possibility that an impact can occur without advance warning. The Spaceguard Survey program created by NASA, together with other ground-based activities, has produced the discovery of over 10,000 NEOs. Current detection rates are about 1,000 NEOs per year, with the expectation that this rate could double with the maturing of the Pan-STARRS search program (Denneau 2013). From statistical analysis of discoveries, it is estimated that there are somewhat less than 1,000 NEOs with diameters greater than 1 km, of which over 90 % are known (Harris 2008). The detection rate for smaller NEOs, however, is a much greater problem. This is because these smaller asteroids are both much more numerous and much more difficult to detect because their small size makes them quite faint. There are perhaps one million NEOs larger than 40 m, the size of the object that exploded over Tunguska in Siberia in 1908 with a force of a several megaton atomic bomb. The force of that airburst flattened over 1,000 km2 of forest. The total number of NEOs within this size range is uncertain to at least a factor of two, and possibly as much as 10 (Brown et al. 2013). Thus predictions of the risk of impact by a Tunguska-like object (or worse) are also uncertain by as much as a factor of ten, but the current expectation is that Earth will experience a Tunguska-like event every 200–300 years. This is generally consistent with the Torino hazard scale discussed in Chapter ▶ Advanced Composition Explorer (ACE) (1997). The recent fireball event near Chelyabinsk, Russia, was produced by an asteroid estimated to have had a size of 19 m and released an explosive energy equivalent to 500 kt of TNT. Multiple such events occur every century. This threat of an asteroid impact is the reason that the B612 Foundation was established. After showing the feasibility of deflection of a potential asteroid impact by either a gravity tractor (Lu and Love 2005) or a kinetic energy impactor (Hall and Ross 1997), the foundation decided in 2010 to address the problem of identifying impact risks. The detection rate of 1,000/year is wholly inadequate to address the problem, given the estimated number of potentially hazardous asteroids that might destroy a city (i.e., 40 m in size). It is very difficult to improve on this rate from the surface of the Earth because of the diurnal cycle, weather, lunar stray light, and the transmission properties of the Earth’s atmosphere which blur images and block infrared radiation. Thus, the B612 Foundation decided to develop a space observatory along the concept studied by the NASA SDT a decade ago. Since the time of the SDT report, substantial progress has been made in developing infrared astronomical technologies for space, demonstrated by NASA’s Spitzer and WISE missions (Mainzer 2011). It is now possible to implement a space infrared mission that will provide a catalog of the majority of the Earth-threatening NEOs (National Research Council 2010). The B612 Foundation is developing such a mission, raising money through private sources to build a half-meter infrared telescope that will operate in space and detect and track over a half-million NEOs. This IR space telescope is named Sentinel. It will couple the heritage of these prior infrared missions with technologies from the Kepler planet-finding telescope that demonstrated a wide field-of-view Page 2 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

Fig. 1 The Sentinel observatory is designed for long-term operations in deep space, drawing technology and design from previous successful missions including Spitzer and Kepler. The abbreviations refer to the low-gain antenna (LGA), medium-gain antenna (MGA), and high-gain antenna (HGA) (Figure courtesy Ball Aerospace)

telescope in deep space (i.e., not Earth orbit) with a large-format camera and substantial on-board data processing (see Fig. 1). As Ball Aerospace & Technologies Corp. developed both the Kepler mission and the Spitzer telescope, the B612 Foundation selected Ball as the contractor to build Sentinel.

Mission Objectives The Sentinel mission objective is to maximize the number of NEOs for which orbits are sufficiently accurate to permit accurate prediction of future impact threats. Based on the 2003 NASA SDT report, and consistent with the George E. Brown Act, B612 has defined the top-level mission requirement to be to find 90 % of all NEOs larger than 140 m in diameter. The time required to meet that goal is dependent on models of the NEO population and its orbital characteristics, but studies have shown that excellent progress can be made toward this goal in 6.5 years, taken as the minimum mission design lifetime. Sentinel will have the capability to find much smaller asteroids than 140-m NEOs. At closer range, smaller NEOs will be recorded with the same accuracy. This will permit Sentinel to track objects that are 30 m in diameter or even smaller. Sentinel will be able to see 30-m objects that are at the Earth’s orbital distance from the Sun (a range from Sentinel of 30 million miles) and can see 140-m NEOs at a range of 70 million miles. Data processing for all discoveries will be conducted without initial knowledge of NEO size. Size will be determined only much later once an orbit has

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

been determined and therefore the distance to the NEO at the time of observation. The observed brightness is corrected for distance to determine the intrinsic brightness and hence the size of the NEO. The size distribution of NEOs generally follows a power law, increasing by more than 200 % for every decrease in size of 50 %. Smaller NEOs have less surface area emitting infrared radiation. In the case of the smallest detectable NEOs, their proximity to the telescope gives them high apparent motion that smears their images and makes them less detectable. Consequently, Sentinel will discover the highest number of NEOs in a size range of 25–50 m, where Sentinel expects to find over 200,000 objects during the mission. At larger sizes, there will be fewer discoveries because of the decreasing population of objects. Sentinel will find nearly all of the roughly 1,000 objects larger than 1 km in size during the mission. The mission will also identify and catalog perhaps 40,000 asteroids larger than 140 m (>90 %) and a total of about 500,000 NEOs of all sizes. The actual population of NEOs in the 10–100-m size range is poorly known at this time as earlier noted. For this reason the above predictions are uncertain by perhaps 50 %. Thus one of the important scientific outcomes from the Sentinel mission will be a far better understanding of the population statistics for smaller NEOs. The good news might be that they are less numerous than currently projected. There is also the possibility that they are actually more numerous. The data obtained on new discoveries will be used to project the orbits forward to search for Earth impact threats. Accurate orbit prediction requires that each discovered object be followed for at least a month to give the desired accuracy. Even then, orbits will have substantial uncertainty associated with forward projections. Reduction in the predicted position uncertainty will be obtained by repeated observation from Sentinel whenever the NEO is within the field of view of the telescope and sufficiently bright to be recorded. Further orbit refinement will be achieved through follow-up observations from ground-based observatories. These observations of known objects can reach much fainter objects than can search programs. Follow-up observations from both ground and space (Sentinel and other missions such as Hubble) are important for objects whose orbits show a high potential for impact: most objects that draw attention because of moderate impact potential will be shown to come close to, but not impact, the Earth once more accurate orbits are known. The Sentinel mission is somewhat larger in scope and complexity than missions that have flown in the NASA Discovery mission line (such as Kepler). Those missions have been budgeted at roughly $650 M including launch and mission operations. The B612 Foundation will implement the Sentinel mission using a different programmatic approach than that employed for US Federal Government and NASA missions. B612 will put the selected contractor, Ball Aerospace, under a fixed-price contract with specific payment milestones and detailed performance requirements. This is an approach frequently used by commercial organizations with space-based activities such Intelsat, Inmarsat, etc. The burden of proof of mission suitability will be on Ball. The B612 Foundation has convened a review board of highly competent people that have experience on nearly every NASA deep space mission, both within the US government and from private industry. This Sentinel Special Review Team (SSRT) will be convened at key milestones during the mission. Thus, the Foundation will have input and advice on mission risk and progress from people with deep understanding of space mission implementation. Ball Aerospace will function as a traditional prime contractor, responsible for manufacturing and testing the observatory as well as launching it and performing mission operations. Sentinel can be launched on the Space Exploration Falcon 9, a lower-cost launch alternative for deep space missions. Mission operations, both command and control and data handling, will be performed for Ball by the University of Colorado Laboratory for Atmospheric and Space Physics (LASP). Ball has used LASP extensively in this role, but for Sentinel, LASP will also be processing the returned data into Page 4 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

useable track information for each NEO that is discovered. This data will then be forwarded to the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics where it will be incorporated into their already large database of NEO orbits. The Foundation has established a Space Act Agreement (B612 Foundation Space Act Agreement 2012) with NASA to cooperatively conduct the Sentinel mission, with no exchange of funds. In exchange for all of the mission data for the MPC, NASA will provide assistance through use of the Deep Space Network for spacecraft communications as well as tracking information. NASA is also providing technical consultants in a NASA Technical Consulting Team that will supplement the SSRT.

Technical Characteristics Figure 2 shows the Sentinel observatory’s orbit which is interior to the Earth’s orbit so that the survey can include a large region surrounding the Earth. Sentinel can view all of the sky within a 100 half-angle cone that is centered on the anti-sun point, covering over half of the sky. This field of regard (FOR) includes over ¼ of the Earth’s orbit and is ideal for searching space near the Earth. A further advantage of an orbit interior to Earth is that the observatory will have an orbital period of only ~206 days, permitting it to lap the Earth every ~514 days and enabling observations of objects whose orbital periods are near 1 year and therefore seldom come close enough to be observed from Earth or space observatories close to Earth. Thus the interior orbit is an important design element of the Sentinel mission that provides excellent discovery performance. The final orbit for Sentinel is to be established through a gravitational encounter with Venus that slows the spacecraft and reduces its aphelion below 1 AU. The final orbit is determined by the flyby

Fig. 2 Sentinel orbit. The Venus flyby reduces the orbital energy of Sentinel resulting in an elliptical orbit that ranges from 0.6 to 0.8 AU from the Sun (Figure courtesy Ball Aerospace) Page 5 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

geometry, but since there are no tight requirements on the orbit, the encounter geometry is not tightly constrained. The simple requirement is that Sentinel be slowed sufficiently to result in a semimajor axis that permits the desired observing opportunities. The nominal eccentric orbit ranges from 0.6 to 0.8 AU. No propulsive maneuvers are required to establish or maintain the orbit with only trajectory correction thrusts required to establish the Venus encounter parameters. Survey observations can begin once observatory checkout has been completed, well before the final orbit is established. NEOs are identified in images by their changing position caused by Keplerian orbital motion. While a NEO may show a streaked image in a single exposure, it is much easier to identify them by comparison of two images taken at different times, allowing the NEO to move relative to the background star field. Comparison of the two images reveals a detection of an object in one image of the pair that is not reproduced in the second because it has moved elsewhere. With crowded fields having multiple moving objects (as is expected for Sentinel), unique correlation of one observation on an object with another requires confirmation from a second image pair. Sentinel’s nominal design obtains these image pairs with 1 h of separation between them. Analysis of the expected NEO population shows that over 1 h, a typical NEO will move roughly one arc minute, easily revealing its motion but not moving so far as to increase confusion. Once a moving object has been identified on this series of four images (taken at times 0 h, 1 h, 48 h, and 49 h), data analysis can produce a vector called a track that allows the calculation of a range of potential orbits. An object is not considered to be “found” with the observation of a single track. Sentinel scans its entire FOR in an observing cycle (lasting roughly 1 month) and then repeats the FOR scan during the following observing cycle. An object has been “found” if Sentinel can provide a track for the object in at least two observing cycles (or if observations from ground-based observatories give a similar second observation epoch). This gives a reasonable orbit that permits the NEO to be uniquely identified whenever it is seen again. More importantly, the orbit has sufficiently small errors that the future location of the NEO can be determined to identify potential threats to Earth. An orbit derived from only two observing cycles will have uncertainties that will need to be reduced for objects whose motions will bring them close to Earth. By design, Sentinel will provide many more than the minimum two observing cycles of observations for the great majority of NEOs. With its 200 FOR, most NEOs will be observable during five successive observing cycles, and many will be seen during subsequent orbits providing observations spanning several years and leading to very good orbits with reliable predictions for roughly 100 years. The Sentinel team has developed two models for evaluating the expected performance of the observatory, one at Ball Aerospace and the other within the B612 team. These models are used in design studies that evaluate the potential of various design alternatives. The models show that Sentinel will reach the 90 % completion level on 140-m NEOs in roughly 7.5 years (Fig. 3). This number further reduces to 6.5 years when the ongoing and anticipated ground-based efforts are included in the calculation. The model is also useful for a number of other comparisons such as alternative cadences for the pairs of images that are currently baselined at 1 h and 2 days. To help with the analysis of that issue and others, the Foundation has established a Sentinel Operations and Data Architecture working group chaired by Dr. Marc Buie, the Sentinel Mission Scientist. This working group has members with deep experience in ground-based NEO detection and is able to identify and address many issues that arise in planning Sentinel observations. Infrared detector technology has been developed for previous space missions such as Hubble, Spitzer, and the James Webb Space Telescope, and B612 will take advantage of these efforts in developing the focal plane detector for Sentinel. While these prior astronomy missions have had very low background signals, Sentinel must address a significantly different problem. The thermal blackbody emission from NEOs in the inner solar system is strongest in the 5–10.2 mm spectral Page 6 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

Fig. 3 Modeled completeness prediction showing that Sentinel will detect and track nearly 90 % of all NEOs larger than 140 m in diameter and will catalog 63 % of 60-m NEOs in 7 years. When combined with continuing ground-based searches, this will achieve the goals of the George E. Brown Act (Figure courtesy Ball Aerospace)

region where the NEO is bright. In this spectral range, zodiacal light, arising from dust derived from solar system formation and erosion of comets and asteroids, is the dominant source of background noise. Thus, while previous space IR detectors have focused on very low detector noise, Sentinel is working with a different, higher background signal level, design requirement. Following investigations of the Sentinel mission parameters by detector manufacturers, B612 and Ball have made the selection of a readout scheme that will perform well in the high background noise situation that Sentinel faces. Thus the Sentinel detectors will employ a Capacitive Trans-Impedance Amplifier readout circuit rather than the more common source follower readout. The detector unit cell contains a capacitor which can accumulate the expected large signal levels without saturation while maintaining its linear signal response. Also necessary is good gain stability over the 1-h period between a pair of measurements of a single star field so that any detected changes in signal level will clearly be due to object motion and not due to gain changes. A demonstration detector has been built for Sentinel that has shown good performance in important parameters including self-emission. The next step is the development of a prototype detector that will demonstrate all of the key performance requirements for the device. The Sentinel focal plane will consist of a mosaic of 16 individual infrared detectors arranged in a 2  8 array of detectors each having 1,640  1,120 pixels with 32-mm pitch. The photosensitive material is mercury cadmium telluride. This will have detection sensitivity extending to 10.2 mm. The detectors have minimal structure on three sides, permitting a close-packed array with minimumsize gaps of approximately 1 mm, giving a fill factor of 95 %. The active area is 54  294 cm, covering a field of view on the sky that is 2.5  11 . The focal plane will be cooled to 40 K to lower thermal charge generation well below the zodiacal light background. Sentinel will use an off-axis three-mirror anastigmat telescope to achieve the wide field of view with low obscuration, low emissivity, and high rejection of stray light. The telescope mirrors and structure will be made of aluminum to control cost, mass, and thermal distortion. This approach is possible with the lower optical tolerances of infrared systems relative to the familiar visible-light telescopes. The telescope includes a flat fold mirror that moves the focal plane to a readily accessible position. This design will facilitate detector integration and thermal control. The telescope line of sight is offset from the observatory symmetry axis by 40 to allow the observatory to scan the entire anti-sun hemisphere while keeping the sun within 50 of normal to the solar arrays. This arrangement will allow adequate power production to be maintained in all positions. Page 7 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

Thermal control of Sentinel is very similar to the scheme successfully employed on the Spitzer Space Telescope. The heat load from the Sun is intercepted by a series of three thermal shields. The solar array provides the first layer of shielding, being populated by a combination of the required area of solar array and filled out with silvered surface to reject solar heat. Two additional shields are positioned between the back of the solar array and the telescope, each having a good view of space toward which they reject heat that they intercept. Following the Spitzer design, and using the Spitzer-calibrated thermal model, the Sentinel telescope is expected to achieve a temperature of 70 K even at 0.7 AU where the solar insolation is twice that received by Spitzer. To achieve the required 40 K for the focal plane, Sentinel will use a mechanical Stirling cycle cryocooler similar to the one built by Ball Aerospace for the Landsat Imagery mission (Bertele et al. 2012). In addition to providing 3 W of cooling at 40 K for the detectors, the cooler also will be able to provide additional cooling to the telescope. This will enhance performance margin to ensure that thermal emission from the optics is not detectable. The spacecraft for Sentinel will be based on Ball’s highly successful Kepler spacecraft bus design. While the Kepler reaction control system experienced a failure after the mission design lifetime, Sentinel will use different reaction control wheels that have demonstrated highly reliable performance on other missions. Spacecraft mechanical, thermal, power, and control systems will be very similar to Kepler’s. The largest modification to the Kepler design will come in the telecommunication area. Even though Kepler was deployed in deep space and sent data back over a range of 0.7 AU, Sentinel’s orbit will take it to a range of 1.7 AU. At this range, a more powerful transmitter is required. The Kepler-type transmitter is capable of this range but, since it will need to be operated at higher power, it will require additional qualification testing. Kepler performed on-board data co-adding and editing, a data-compression approach that will also be used on Sentinel. Six successive 30-s exposures of a given field will be co-added to achieve the 3-min integration. Intercomparison of each sub-exposure will allow on-board software to identify and reject cosmic ray signals. The co-added 3-min image will be stored in memory until the companion image of the same field of view is obtained 1 h later. At that point, the on-board computer examines both images to identify pixels that show changes that exceed the noise threshold by a factor of five (signal-to-noise ratio SNR > 5). Moving objects that are sufficiently bright will produce differences that exceed this value at both the location it had in the first image and in the second. The on-board computer will extract the 4  4 region centered on the change and copy those pixels into the telemetry memory. This approach reduces the data volume by more than a factor of 1,000 and sends all of the image data on moving objects to the ground in only 4 h of telemetry per week. Sentinel will employ the NASA Deep Space Network 34-m antennas operating in the Ka-band for this purpose. Telemetry data volume will be controlled through selection of the SNR threshold. Additional image pixels are put into telemetry for pre-planned astrometric reference stars to establish the precise pointing of the images. Sentinel will have the capability to transmit entire images for quality inspection or other engineering or scientific purposes. Ground operations and data processing will be performed at the Laboratory for Atmospheric and Space Physics at the University of Colorado under contract to Ball Aerospace. There, received telemetry will be reconstructed into images that will have no data (zeroes) in regions that experienced no change (SNR > 5) in the 1-h interval separating the image pair. These images will then be examined to reject spurious signals from noise spikes, residual cosmic rays, variable stars, and other sources of variability not related to moving objects. The remaining objects will be examined for potential linkages indicating motion. Such so-called tracklet linkages are considered to be preliminary and are stored for reconsideration when the second pair of images of the region is obtained 2 days later. Once the second of the 1-h pairs is available, with their associated tracklet Page 8 of 10

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identifications, further analysis looks for pairs of tracklets that can be linked by a Keplerian orbit. This level of linkage produces a track from which a very preliminary identification of a moving object is possible. Comparison with the database of known objects will show if this is a previously known object or a possible new discovery. New discoveries are only confirmed when this process produces a second linkage during a second observing cycle. This might occur as soon as 1 month later. Once a second track is associated with an object, the object is a confirmed discovery. These are forwarded to the Minor Planet Center at the Smithsonian Astrophysical Observatory. There they are confirmed and added to a comprehensive database of NEOs and other solar system objects.

Mission Status Sentinel is being financed through philanthropic donations to the B612 Foundation. A Program Concept and Implementation Review has been conducted and reviewed by the Sentinel Special Review Team, whose suggestions and findings have been incorporated into the program plan. B612 and Ball are preparing for the Mission Requirements Definition work that will culminate in the Sentinel System Architecture Approval review. Launch will be in 2018 for the nominal 6.5-year mission. The only consumable commodity on the spacecraft is fuel for the reaction control system. Sentinel will launch with a minimum of 10 years of fuel so that the mission can continue at least that long if desired.

Conclusion Only with Sentinel will the census of NEOs be extended to sizes small enough to fully assess the hazard to Earth from asteroid impact. The prime objective is to detect a half-million objects down to a size of less than 20 m; Sentinel will greatly increase the scientific understanding of this important population of objects. There will be much better statistics regarding how many objects exist, and the high-quality orbits that will be determined will help quantify the threat that they pose. While today the number of objects in the city-killer size range of 40–100 m is known with an accuracy of less than a factor of 5, Sentinel will determine the population statistics with much, much higher accuracy. Even more importantly, Sentinel will determine accurate orbits for the objects that it detects, permitting the forward propagation of their orbits and the identification of potential threats of impact on Earth. Early identification of potential threats is extremely important so that sufficient time will exist to deal with any identified risks. It will take time to get additional information on the orbit and characteristics of a NEO before any deflection efforts are initiated. Ground-based follow-up will provide better orbit determinations that will assist in assessing the impact probability. Spectroscopic observations will reveal the composition of the asteroid. Photometric studies can establish the rotation rate, shape, and pole orientation of an asteroid, which are important factors for future mitigation missions. It may also prove desirable to fly a reconnaissance mission to rendezvous with a potentially threatening NEO to obtain even better information. One attractive feature of such a mission would be the capability to determine a very precise orbit for the object, allowing an improvement in the prediction of the future location of the NEO and potentially demonstrating that the NEO will miss the Earth without deflection.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_42-1 # Springer International Publishing Switzerland 2014

Cross-References ▶ Asteroid Redirect Mission by NASA ▶ Deep Impact and Related Missions ▶ Defending Against Asteroids and Comets ▶ European Operational Initiative on NEO Hazard Monitoring ▶ European Space Agency’s Program on Potentially Harmful Asteroid ▶ International Astronomical Union and the NEO Hazard ▶ Keyholes ▶ Minor Planet Center ▶ Nature of the Threat/Historical Occurrence ▶ NEOSHIELD - A Global Approach to Near-earth Object Impact Threat Mitigation ▶ Potentially Hazardous Asteroids and Comets ▶ Risk Management and Insurance Industry Perspective ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE ▶ The NASA Sentry Risk Table ▶ The Palermo and Torino Scales (Risk Assessment of NEO Collisions and Magnitude of Impact) ▶ U.S. Ground Observatories ▶ Water Impacts

References B612 Foundation Space Act Agreement (2012) The B612 Foundation. http://b612foundation.org/ wp-content/uploads/2012/06/SAA-redacted.pdf. Retrieved 28 Dec 2013 Bertele T, Aerospace B et al (2012) Test results for a high capacity cryocooler with internal thermal storage. AIP Conf Proc 1434:154–160 Brown PG et al (2013) A 500-kiloton airburst over Chelyabinsk and an enhanced hazard from small impactors. Nature 503:238–241 Denneau L (2013) The Pan-STARRS moving object processing system. Pub Astr Soc Pac 125:357–395 Hall CD, Ross M (1997) Dynamics and control problems in the deflection of near-Earth objects. Adve Astrol Sci: Astrodyn 97(Part I):613–631 Harris AW (2008) What spaceguard did. Nature 453:1178–1179 Lu ET, Love SG (2005) Gravitational tractor for towing asteroids. Nature 438:177–178 Mainzer A (2011) NEOWISE observations of near-Earth objects: preliminary results. Astrophys J 743:156–172 National Research Council (2010) Defending planet Earth: near-Earth object surveys and hazard. National Academies Press, Washington, DC Stokes G et al (2003) The study to determine the feasibility of extending the search for near-Earth objects to smaller limiting diameters. NASA Office of Space Sciences, Solar System Division U.S. Congress (2005) National Aeronautics and Space Administration Authorization Act of 2005. Retrieved 28 Dec 2013, from Public Law 109–155 – 30 Dec 2005. www.gpo.gov/fdsys/pkg/ PLAW-109publ155/pdf/PLAW-109publ155.pdf

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Deep Impact and Related Missions Michael F. A’Hearna* and Lindley N. Johnsonb a Department of Astronomy, University of Maryland, College Park, MD, USA b Planetary Science, NASA Headquarters, Science Mission Directorate, Washington, DC, USA

Abstract This chapter reviews the history of and the results from the Deep Impact mission, its extension as the EPOXI mission, and its further extension as a remote observatory for cometary studies. The mission has had a major impact on the understanding of comets and on their role in solar system formation. It has also provided considerable information needed for planetary defense against Near-Earth Objects (NEOs).

Keywords Comets; Impacts; NEO Hazard; Experiments

Introduction The concept of using a large impact to study the interior of small bodies in the solar system dates back at least to 1968, when Arthur C. Clarke (1968) wrote the novel, 2001, A Space Odyssey, although the more detailed studies date to the ill-fated Comet Rendezvous Asteroid Flyby (CRAF) mission that was started in the wake of the flybys of comet Halley by every space agency except NASA. During the early development phases of that mission, the project scientist, Marcia Neugebauer, led a small team that looked into using the CRAF spacecraft as an impactor at the end of the mission (private communication). Unfortunately, as costs grew for the CRAF-Cassini combination (they were to share a common spacecraft), the CRAF mission was cancelled before any significant hardware development. Deep Impact (hereafter DI) was developed as a cost-effective way of exploring far below the surface of a cometary nucleus to test theories of volatile segregation and depletion in the outer layers of a cometary nucleus. To fit into NASA’s Discovery Program, a program that was then still proving itself as a cost-effective way to do scientific exploration, the mission was kept as simple as possible while still being consistent with the technical needs of excavating a large crater and observing the outcome. It was first proposed to NASA in response to an AO (Announcement of Opportunity) issued in 1996, at which time it was rejected with significant issues pointed out by the review panel. The mission was redesigned and was then proposed to a subsequent AO issued in 1998, which led ultimately to selection by NASA as Discovery Mission 8, confirmed in 2000 (Belton and A’Hearn 1999; A’Hearn and Belton 2005).

*Email: [email protected] Page 1 of 18

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It had been noted in the proposal (two sentences out of a 25-page science section) that the spinoff from the mission would be valuable for defense against NEOs, but it was clear that this was not the goal of the mission or the primary basis on which it should be selected.

Deep Impact Development and Execution Design Approach The institutional partners in developing the mission were the University of Maryland, home of the Principal Investigator (PI), Michael A’Hearn; Ball Aerospace and Technology Corp. (BATC), which developed all the hardware and assisted in operations; and the Jet Propulsion Laboratory (JPL), which had management responsibility for the hardware and the operations. As a Discovery Mission, the PI was responsible for the overall success of the mission. It is notable that neither the PI (or his institution) nor BATC had any direct experience with deep-space missions (other than the cancelled CRAF for A’Hearn), so the learning curve was steep. Fortunately, the PI had available on his science team both Michael Belton, the Deputy PI, and Joseph Veverka, a coinvestigator, both of whom had extensive experience with deep-space missions. The target had been chosen in the proposal phase to be comet 9P/Tempel 1 based on the criteria (a) that it have a reasonably large nucleus (R >2 km) to simplify targeting; (b) that it be a predictable comet, active at previous apparitions; and (c) that it allow for a launch in the window specified in the AO. The trajectory (Fig. 1) was designed to launch in January 2004 into a slightly elliptical orbit that would encounter the Earth again in January 2005, at which point the Earth’s gravity would divert the spacecraft into a much more elliptical orbit that would encounter the comet near its perihelion and near its crossing of the ecliptic, both of which occurred within a week of 4 July 2005, the chosen date for the encounter. Additional details are available from Blume (2005). It was clear from the outset that, in order to excavate a deep, large crater and allow sufficient time after excavation to observe the results, the mission would require two coupled but independent, fully functional, intercommunicating spacecraft – an impactor and a flyby spacecraft. It was also clear (and emphasized by the panel review of the proposal in 1996) that the impactor would need to be

Fig. 1 Orbital trajectory. This shows the direct orbit trajectory as actually flown. The original mission design included a 1-year loop around the sun with a gravitational boost from Earth to put the spacecraft into essentially the same trajectory that is shown here (Credit: NASA/JPL)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

released early and carry out autonomous navigation to ensure an impact with enough time to observe the results before the flyby spacecraft flew past the comet. To keep things simple, moving parts were limited to four items – the separation mechanisms between the flyby and the impactor, filter wheels in the two cameras on the flyby spacecraft, and a gimbal on the high-gain antenna of the flyby spacecraft with sufficient range to keep it pointed at Earth during the attitude changes expected between release of the impactor and closest approach to comet Tempel 1. Since the backup mission was just to launch 1 year later to reach the same comet with similar geometry, there was no requirement for communication with Earth at all attitudes. Similarly, thermal stability at low operating temperatures was ensured by keeping the instrument bench thermally isolated from the rest of the spacecraft and designing the combination of instruments and solar panels so that the entire instrument suite was shielded from direct sunlight at all attitudes expected during the encounter with comet Tempel 1. The impactor was designed to operate on battery power for a day (with significant margin), since release a day prior to impact would allow the flyby to decelerate sufficiently (by 100 m/s) to view the entire impact event. The trajectory design yielded an encounter at 10.3 km/s, the impactor having a mass of 370 kg including estimated residual hydrazine fuel, of which roughly 50 % was copper, chosen to minimize oxidation reactions with the cometary water that would lead to contaminating bright emission lines. The instruments were also developed, assembled, and integrated with the spacecraft at BATC based on specifications from the science team (see Hampton et al. 2005 for full details). The instruments on the flyby spacecraft included a Medium Resolution Instrument (MRI), which consisted of a 12.1-cm aperture, Cassegrain telescope with a 2.1-m focal length feeding a CCD camera through a filter wheel. Filters in this camera were chosen to isolate emission bands and continuum in the coma of the comet from the OH band in the near UV (305 nm) to a near-IR filter for the continuum at 850 nm. An identical system, but with the filter wheel omitted, constituted the Impactor Targeting Sensor (ITS), the camera used for navigation and for science on the impactor. The High Resolution Instrument (HRI) on the flyby spacecraft was much more complex. The Cassegrain telescope had a 35-cm aperture and a focal length of 10.5 m. This made it, at least for a short time, the largest telescope on any deep-space mission. The telescope fed a dichroic beam splitter, which sent the infrared to a spectrometer for the 1.05–4.80 mm band and the visible to a CCD camera (300–1,000 nm) with a filter wheel. Filters in the camera were chosen to measure colors on the nucleus, a series of medium-band filters spanning the near UV to the CCD sensitivity cutoff near 1 mm. The spectrometer was a two-prism design to avoid order separation problems with a grating (since the spectral range was more than a factor two in wavelength). The IR detector was HgCdTe, bonded to Rockwell’s model Hawai’i-1R multiplexer, part of their development of detectors for the HST Wide Field Planetary Camera 3. Figure 2 shows the final system, with the flyby spacecraft being lowered onto the impactor spacecraft in the clean room at BATC. The system was launched with the impactor attached to the launch vehicle and the flyby spacecraft riding on top of the impactor in their mated positions. The figure shows the compact size of the two spacecraft, including the solar panels that power the flyby, compared to the large size of the instruments, particularly the HRI.

Development Challenges As with any planetary mission, there were numerous challenges in development. Perhaps one of the most surprising, and one which was not discovered early enough, was that each of the three partners used the same words to refer to different things. This derived from the three organizations having very different cultures and fundamentally different approaches to the mission, but it was Page 3 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 2 Spacecraft system. The white stand simulates the adapter ring on the launch rocket, to which the impactor is attached. The flyby is being lowered to mate with the impactor, much of which was encased by the flyby during flight. The very long tube pointing at the engineer on the left is the HRI telescope, with the infrared spectrometer at the upper right (Credit: Ball Aerospace)

ultimately due to the fact that two of the three partners had minimal experience with deep-space planetary exploration. This led to misunderstandings of requirements and assumptions among the partners. At a very early stage after selection, both spacecraft were redesigned from what had been proposed. The flyby spacecraft was redesigned due in large part to accommodation issues. The impactor was redesigned on the basis of numerical simulations of impacts, which showed that the original design (a cylindrical can) would be very inefficient in excavating a crater. The redesign emphasized an inert copper spherical cap forward in the impactor, constituting roughly one third of the total mass of the impactor and hollowed out in order to better impedance-match the impactor to the low-density cometary nucleus. This significantly increased costs but led to a much better scientific result. The impactor’s attitude control system was also changed from a cold nitrogen system to a more complicated hydrazine system, in which the experienced engineers had more confidence. The most common challenge of course continued to be cost, despite what appeared at project start to be nominally sufficient reserves. The original design of the spacecraft computer, based on a wellestablished RAD600 chip, turned out to have inadequate capacity for the complex software being developed. This required switching to the newly developed RAD750 chip as the CPU and, although at the time of the switch it was understood that other missions would fly the chip before DI, it turned out that DI became the first civilian space mission to fly the newly developed chip as the CPU. Development of the entire computer system presented major challenges. Ultimately, late Page 4 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

delivery of the spacecraft (not the instruments), due in part to the delays in delivery and testing of the computer system, led to a 1-year launch delay. The HRI presented challenges also. The first primary mirror broke from one of its mounts during vibration testing, but fortunately a spare had been purchased. The instructions for preparing the mirror bonding surfaces were revised after consultation with the mirror provider. Ultimately, the HRI was also out of focus when launched (focus mechanisms had not been included in any of the instruments, partly for cost reasons but, in the case of HRI, also because of the difficulty of designing one with sufficient mechanical range). There had been two independent focus tests in cold vacuum, both of which gave the same result for the focus position. These gave a different result than did a theoretical model of the structure of the telescope. In order to maintain schedule (before it was known that a launch delay would be required), the decision was made to accept two independent experimental measurements of the focus. Ultimately, it turned out that there was one piece of optics in common between the two tests, a flat used to measure the curvature of the window in the vacuum chamber. That flat had been inherited from the Spitzer program, and it had not been realized that the flat developed curvature when cold. Fortunately, the PSF of an out-of-focus Cassegrain telescope retains considerable high-frequency information, so that deconvolution worked well on all images and the resultant images were invaluable in understanding the structure of the nucleus (Busko et al. 2007; Lindler et al. 2013). The short flight time of the mission (6 months from launch to encounter), coupled with a lack of complete flight sequences before launch, resulted in a very heavy workload to learn all the quirks to flying the spacecraft while simultaneously developing all the observational and pointing sequences. Intensive interactions between the activity leads from JPL and the science team led to success despite the issues. But this resulted in the inability to get flat-fields on the moon, particularly for the IR spectrometer, before the spacecraft left the Earth-moon system. Failure to communicate with the spacecraft immediately after separation from the launch vehicle caused a temporary panic, until it was realized that the spacecraft was in safe mode. This was caused by the fault protection software, which had been set with too restrictive limits for some parameters, in this case the catalyst-bed heater temperature in the hydrazine thruster system. Fortunately, those limits were easily resettable. The area that led to the most tension was the targeting software. This had been a major challenge because the shape of the nucleus was unknown except for its average radius, close to 3 km. The flyby of comet Borrelly by Deep Space 1 had revealed a very elongated nucleus with a bend in the middle. This led to the realization that certain shapes for the nucleus could lead to the center of light not always being on the nucleus (such as an extreme banana shape for the nucleus). Thus more sophisticated algorithms were required and developed by Mastrodemos et al. (2005). This allowed inclusion of a “bias” to push the impact site toward the side of the nucleus from which the flyby spacecraft would observe the impact. The challenge in the more complicated algorithms was ensuring that the flyby spacecraft would choose the same impact point that the impactor chose, despite seeing the nucleus from a different direction. In the end this worked exactly as desired.

Encounter Spacecraft observations of the comet began 2 months before encounter with a regular monitoring program of images both for science and for navigation. Due to the narrow range of solar elongations over which the spectrometer would remain cold and due to anticipated limited sensitivity, spectra were obtained regularly beginning only 2 weeks before encounter. On 3 July 2005, with the combined spacecraft targeted to impact the nucleus, the impactor spacecraft was released from the flyby via spring mechanisms, turned on for autonomous operation, Page 5 of 18

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and allowed to separate gently from the flyby spacecraft. When the impactor had separated by a safe distance, the flyby spacecraft used its thrusters to divert by 5 m/s laterally in order to miss the nucleus by 500 km and then to slow down by 100 m/s, from 10.3 to 10.2 km/s. This provided a window of 800 s to view the impact and its effects before the flyby spacecraft passed the nucleus. As the impactor approached the nucleus, it made three trajectory correction maneuvers to optimize the targeting. When it got very close (within about 22 s to impact or 230 km), four cometary grains impacted the spacecraft with sufficient effect that the attitude control system had to respond to them and images showed the spacecraft attitude displacement. Three of the particles had masses of 1–10 mg, while the fourth (the last in time at a distance of 30 km or 2.5 s from the nucleus) had a mass of order 0.5 g. Buffering delays in telemetry from the impactor to the flyby resulted in the last transmitted data having been taken roughly 2 s (24 km) prior to impact. The smallest surface features resolved in the last images from the impactor had sizes of 2–4 m. The impactor delivered 19 GJ (5 t of TNT equivalent) of kinetic energy to the nucleus, more than the energy possible if the entire mass of the impactor had been only the most efficient chemical explosives known, a totally unrealistic scenario. In addition to being offset significantly toward the side of the nucleus facing the flyby spacecraft at closest approach, the final trajectory of the impactor at impact was only 30 above the local horizontal, thus providing a valuable separation of up-range and down-range phenomena, altogether a most successful targeting. Because all instruments were body mounted, the flyby spacecraft rotated to track the nucleus. At 500 km (41 s) before its closest approach, the spacecraft rotation was halted to remain in an orientation with maximum shielding against cometary dust. This had been chosen to be somewhat less than the spacecraft’s maximum attitude rate. After passing through the densest parts of the comet’s coma, the flyby spacecraft turned and looked back at the comet to obtain further data on the ejecta over 2 days (additional data beyond 2 days were not obtained due to memory management issues). All data, raw and calibrated, were delivered to NASA’s Planetary Data System (PDS) before the end of the calendar year and they are available at the Small Bodies Node of PDS (2014), many of them in recalibrated versions delivered at later times as the calibration of the instruments was better understood. Since the limited instruments that could be carried on a Discovery-class mission could not possibly probe all aspects of the phenomena, a significant effort was devoted to organizing a campaign of Earth-based observing using telescopes both on the surface of the Earth and in space. Nearly every major astronomical facility on Earth observed comet Tempel 1 at or near the time of the DI encounter. These data proved invaluable in understanding the larger picture of cometary behavior in response to an impact.

Deep Impact Results This section will address only the results obtained directly from the Deep Impact prime mission. Other results that came from more of a synthesis of the prime mission and the extended mission will be addressed after discussing the extended mission. It is particularly important to point out at the start what has become a truism of science, which might be called the Harwit principle after his book on this topic (Harwit 1984): Whenever one enters a new measurement regime, the most interesting results and the ones for which the experiment/mission will be remembered are likely to be the unanticipated results. The results for which the mission was designed may be important but they are likely to be less interesting than the totally new phenomena that are discovered. This has been particularly true of DI and its extensions. Page 6 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 3 Impact site combination. The yellow arrows indicate the impact site in the successive images, the times of which (prior to impact) are given in red. The images are successively smaller subframes of the camera to allow transmission to the flyby spacecraft at a rapidly increasing rate (Credit: NASA/UMD)

The key event, of course, was the impact and its resultant ejecta, events that were quickly summarized in the literature by A’Hearn et al. (2005). Figure 3 shows successive images from the ITS with the ultimate impact site shown in each. The three white spots nearest the impact site are each no more than 2–3 m in diameter. Figure 4 shows a pseudo-color image derived from blue, green, and red images with the HRI visible imager (deconvolved). The bluish regions on the upper part of the nucleus are actually as dark as charcoal but brighter than the rest of the nucleus. The bluish color is a clue to the fact that they are 3 % ice-covered (Sunshine et al. 2006). The ejecta are by far the brightest features in the image. They also are slightly bluish since they include a large amount of ice.

Physical Properties of the Nucleus

Two independent approaches were used to estimate the density of the nucleus. The first method uses the flash that occurs immediately after the impact and is due to the hydrodynamically ejected hot material. This flash was unusually faint, and comparison with laboratory experiments using the Ames Vertical Gun Range showed that the outer layers at the impact site, within a few meters (a few impactor diameters) of the surface, had a porosity of at least 75 % (Ernst and Schultz 2007). The other approach used the fallback of ejecta onto the surface on ballistic trajectories after being excavated. This approach used the look-back images of the plume and led to a surface gravity and thus an estimate of the bulk density of the nucleus of 0.4 g/cm3 (Richardson et al. 2007). For any reasonable mix of dust and ice, this also implies a porosity for the bulk nucleus of order 75 % or higher, consistent with the result for the surface layer. Both results are consistent with previous models of the nongravitational acceleration of cometary orbits due to outgassing that suggest bulk densities less than 1 g/cm3, but these new approaches are less sensitive to model assumptions.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 4 Impact ejecta (HRI 937–1). A color-composite image from the HRI Vis imager shows the very bright ejecta and the less bright icy patches on the morning portions of the nucleus (the upper left portion in this picture). The sun is to the right (Credit: NASA/JPL/UMD)

The analysis of the ejecta plume also leads to an estimate of the tensile strength of the cometary material. Since the ejecta plume was “over the limb” when the spacecraft looked back at it, only upper limits can be set on whether the plume separated from the surface. Thus only upper limits can be set on the strength, of order 10 kPa, but the data are consistent with zero strength (Holsapple and Housen 2007; Richardson et al. 2007; Richardson and Melosh 2013). An examination of the nucleus in Fig. 4 (and in pre-impact images) shows extensive layering of materials, some of which may be primordial while other layers may have been more recent flows. There are also two large features that appear to be the eroded bases of large (200–300 m) impact craters that have been exhumed. These craters may date back to the formation era. The combination of obvious layering together with large bulk porosity suggests that the accretion of cometary nuclei does not proceed quite as models of asteroid and TNO (trans-Neptunian object) formation would have it. They also suggest that cometary nuclei are not fragments of TNOs as had been widely thought to be the case. Moderately gentle accretion of porous bodies can lead to spreading of the impactor, thus forming layers on the nucleus. These layers are generally orthogonal to the radius, but they are totally unrelated to the onion-skin layering that might be expected from evolutionary models of the nucleus due to a variety of processes. Building a nucleus in this way was discussed by Belton et al. (2007).

Volatiles in the Comet The primary goal of DI was to look inside a cometary nucleus and search for differences between the surface and the interior, particularly in the volatiles, as had been predicted by numerous theoretical models of the nucleus. Observations of the volatiles released in the impact were made by DI itself using the HRI, by numerous ground-based observatories, by space observatories including HST and Spitzer, and even by ESA’s Rosetta mission. From the vaporization and dissociation to OH of the excavated ice, it is known from at least three different independent observatories that roughly 7  2  104 kg of water ice was excavated (Schleicher et al. 2006; Biver et al. 2007; Keller et al. 2007) and that it was mostly in the form of micron-sized grains of ice rather than large chunks

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

of ice (A’Hearn et al. 2005). Adding a comparable amount for refractory grains and using a density of 0.4 g/cm3 for a cometary nucleus, this yields a minimum radius for the crater of 20 m. The biggest unknown is in estimating what fraction of the excavated ice fell back to the surface and was buried cold enough to remain as ice. Typically most of the excavated material returns to the surface, but some of the returned ice might have been warm enough to sublimate even buried under the refractory ejecta. Nevertheless it seems safe to assert that material was excavated from depths of 20 m or more. More interestingly, observations at ultraviolet, visible, and infrared wavelengths were all consistent in showing that the relative abundances of ALL volatiles excavated in the impact (numerous individual papers on different species) were the same, to within a factor two, as the relative abundances in the ambient outgassing prior to the impact. This includes organic species and simple, very volatile ices such as CO. Thus the principal conclusion is that the surface of a cometary nucleus erodes away fast enough in active areas to keep up with the progress of the differentiation front into the nucleus and that primitive material is always therefore near the surface. On the other hand, it was also clear that the relative abundance of different volatiles in the ambient outgassing varied considerably from place to place on the nucleus. The ratio of CO2 to H2O was much higher above the south polar region (the pole itself had just entered winter night 2 months earlier) than along the subsolar meridian. There appeared to be a deficit of CO2 relative to H2O above the pole that had recently entered summer day (Feaga et al. 2007). Whether this is a seasonal effect or an effect due to the nucleus being formed of cometesimals formed with different primordial abundances is not yet resolved (Fig. 5). The ease with which CO2 could be observed and its relative abundance (5–10 % relative to H2O) implied that CO2 might be an important volatile in many comets. Furthermore, the visible-light monitoring on approach showed that the comet had frequent outbursts, typically occurring at

a NP

Dust

>0.030 0.025 0.020 0.015 0.010 6.75e−4 5.40e−4 4.05e−4 2.70e−4 1.35e−4 0.00e−4

c

CO2

>1.5e−4 1.2e−4 0.9e−4 0.6e−4 0.3e−4 0.0e−4

Fig. 5 Volatile maps of Tempel 1. The upper panel shows a map of the continuum at 2 mm (dominated by reflected light from solid grains) of the innermost cometary coma. The middle panel shows the distribution of gaseous H2O around the nucleus and the bottom panel shows the distribution of CO2, all from the HRI infrared spectrometer. The distributions of the gaseous species are very different from each other and the grains (seen in the top panel) are better correlated with the CO2 than with the H2O (Credit: NASA/UMD)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

particular rotational phases. Analysis of these outbursts has shown the presence of CO2 in these outbursts (Moretto and Feaga, private communication). Ice was also observed on the surface of the nucleus but only in a few locations in the early morning regions of the surface and typically associated with depressions (Sunshine et al. 2006). This ice was coarser (grains many tens of micrometers in diameter) than the ice excavated in the impact, as was also true for the refractory grains in the ambient outgassing versus those excavated by the impact. Even in the icy patches, the ice coverage is only about 3 % of the surface, making those parts of the surface slightly brighter than charcoal while the rest of the surface is darker than charcoal. An interesting question is whether those ices are morning frost deposits that disappear every day or topographically shaded regions of bulk ice that only outgas slowly until much later in the day. We note that the icy patches on the surface were not the source of prominent jets in the coma. There was enhanced activity above these areas but it was so weak that it was only observable when the icy patch was almost precisely on the limb as seen from the spacecraft, so that the activity could be seen against the darkness of deep space. These plumes, which may have been composed of either icy grains or dirt grains, driven by sublimation of water from the icy patches, were visible for only a small fraction of a nuclear radius above the limb. A collection of all the results available in mid-2007 is contained in the special issue published as volume 191 of the journal Icarus.

Extended Mission Development and Execution As the prime mission was being developed and safety margins were being considered on lifetimes and expendables, there had been preliminary examination of possible extended missions to other comets. Margins were decided with these possibilities in mind, particularly the margin on hydrazine fuel. One of the targets identified at that time was comet 103P/Hartley 2, which had been considered a backup target for the prime mission. After the flyby of Tempel 1, the flyby spacecraft was on a heliocentric trajectory with a period very close to 3 years. Thus the spacecraft would return to its perihelion near Earth in December 2007, and this close approach could then be used for a gravity assist to redirect the spacecraft to a new target. After the prime mission was completed, it was nearly 2 years before there was an opportunity to propose an extended mission. A combined mission was proposed, carrying out a flyby of comet Boethin (DIXI = Deep Impact extended Investigation), with comet Hartley 2 as a backup, and studying extrasolar planets (EPOCh = Extrasolar Planet Observation and Characterization). The combination of two scientific missions, which was essential to ensuring an experienced operations team throughout the years of cruise prior to Boethin encounter, was selected for funding by NASA (with the EPOCh project mostly funded outside the Planetary Science Division and not discussed in this chapter). Since approval for the extended mission arrived only months before the Earth-flyby to redirect the spacecraft, an intensive campaign was organized to recover comet Boethin. Ultimately this campaign showed that the comet had disintegrated and that no remaining fragments could be larger than 200 m in radius (Meech et al. 2013). This triggered a change to the backup target, Hartley 2, which had always been foreseen as a scientifically more interesting target, albeit one for which the mission would be more expensive due to a very long cruise phase. The flyby of Earth on 31 December 2007 was therefore targeted for comet Hartley 2. There were several technical problems but also some scientific breakthroughs during the cruise phase. The most significant technical problem was discovered shortly after the flyby of Earth, when Page 10 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

it was realized that RF power was being reflected back into the transmitters. This was attributed to a problem with the waveguide switch. It was only discovered after many flips of that switch, and ultimately it was concluded that the problem was most likely caused by thermal issues in the communications package due to the perihelion of the post-Tempel 1 orbit bringing the spacecraft closer to the sun than ever before. This had cost some observing time for EPOCh, but the switch to Hartley 2 as a target provided the opportunity for EPOCh to more than make up for the lost observations. The spacecraft trajectory in the EPOCh phase brought the spacecraft back to Earth roughly every 6 months with either close or distant encounters depending on the orbital geometry. This allowed numerous observations of Earth as an archetypical exoplanet. It also allowed numerous calibration observations of the moon in order to obtain flat-fields for the IR spectrometer. This is one of the most challenging tasks in calibrating spectrometers and the process worked very well. Fortuitously, it also put DI in a position to be the conclusive factor in favor of the discovery of lunar OH radicals by the Moon Mineralogy Mapper (M3) team on Chandrayaan (Pieters et al. 2009; Sunshine et al. 2009). The data taken with DI covered the OH absorption much better in wavelength than did the spectra from M3, and they were more extensive, allowing demonstration that the OH abundance on the lunar surface was stronger at high latitudes than near the equator and that it varied diurnally. The encounter with Hartley 2, on 4 November 2010, was executed almost perfectly. A slight pointing error due to a numerical value stored deep in the software during the encounter with Tempel 1 led to an unplanned off-pointing that helped in the discovery of the chunks of ice surrounding the nucleus of Hartley 2. In real time, surprising phenomena were observed as discussed below. As in the prime mission, an extensive program of Earth-based observations was also organized by the team, taking particular advantage of the very close approach of the comet to Earth less than 2 weeks prior to the flyby.

Extended Mission Results The most immediate surprise during the flyby of comet Hartley 2 was the presence of tens of thousands of large grains in the vicinity of the nucleus (Fig. 6). Grains ranged in size up to order 10–20 cm, assuming they had the reflectivity of ice (A’Hearn et al. 2011; Kelley et al. 2013). The many images of the coma from very different directions allowed reconstruction of the 3-D velocity vectors, showing that the grains were moving at speeds of only a few meters per second relative to the nucleus and that a significant fraction (10–30 %) was moving at less than escape velocity (Hermalyn et al. 2013). Such grains had been anticipated at previous encounters but never seen, so finding them at Hartley 2 was surprising. However, Hartley 2 had been known for some time to be hyperactive, i.e., it produced more water vapor than should be possible from a nucleus of its size if the whole surface were active and these grains are likely the source of the excess water vapor. This process probably also explains the hyperactivity of a small number of other cometary nuclei. Some of the best data on the size distribution of the icy grains were obtained using deconvolved images from the out-of-focus HRI visible imager. Furthermore, the grains were clearly being released from the nucleus in the immediate vicinity of a strong jet of CO2 gas (A’Hearn et al. 2011). Thus CO2 is likely the driving gas for the activity, unlike the situation in most comets, for which H2O is the driving gas. Organics also are concentrated in the major jet with the CO2 (Fig. 7). Interestingly, CO was not detected with DI, but contemporaneous observations with HST showed that Hartley 2 has the lowest CO fractional abundance ever measured, 0.003 relative to H2O (Weaver et al. 2011). Page 11 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 6 Icy grains. A deconvolved image from the HRI visible camera showing the individual chunks of ice near one end of the nucleus of Hartley 2 (Credit: NASA/JPL/UMD)

Fig. 7 Coma spectral maps of Hartley 2. The gases in the innermost coma are shown, together with the distribution of icy grains (as measured by an absorption feature of H2O-ice). The icy grains and the organics and even the refractory grains are much better correlated with CO2 than with H2O (Credit: NASA/UMD)

Another surprise is that the nucleus appeared as though it might have once been a contact binary, with the “waist” between the two lobes filled in with extremely fine material (Figs. 7, 8). The smaller lobe is clearly more active than the larger one throughout the rotation of the nucleus. The only large feature in the coma when imaged in H2O emission is a straight feature (cylindrical or fan-shaped)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 8 Nucleus. This deconvolved HRI image of the nucleus of Hartley 2 (sun at right) shows the very clear distinction between the smooth waist and the two lobes, which might once have been the components of a contact binary (Credit: NASA/JPL/UMD)

immediately above the smooth neck between the two nuclei. The dynamics of the gas are not yet well understood. The nucleus also appeared to be in an excited state of rotation with periods that changed by tens of % over the 2 months of approach to the comet (Belton et al. 2013). Simple models show that torques from the jets could provide enough angular acceleration. If the smooth waist is assumed to be an equipotential (as it might be if composed of very fine, loose grains), then the bulk density of the nucleus is 0.2–0.4 g/cm3, even more porous than Tempel 1. Note that for Hartley 2, the centrifugal force due to rotation must be taken into account in estimating the equipotential. Water ice was found on the surface of the nucleus, much more widespread than on Tempel 1 but following the same pattern of being confined to morning areas with very rough topography. A collection of the detailed results from the encounter available in late 2011 appeared in volume 222 of the journal Icarus. After the flyby of Hartley 2, operations were continued using divisional reserve funds at NASA HQ. These allowed significant observations of C/Garradd (2009 P1) and limited observations of C/ISON (2012 S1). However, the project was clearly understaffed and contact was lost with the spacecraft between the two observing windows for comet ISON. This was traced to an overflow of a time-conversion calculation in the fault protection software. Nevertheless, the data collected on C/Garradd led to a surprising result (at 2 AU post-perihelion, the highest CO relative abundance ever measured inside 3 AU) that required rethinking all the observations by other groups and showed that, unlike the normal behavior of water-outgassing (peaking near perihelion), the release of CO increased monotonically from more than 2 AU pre-perihelion to approximately 2 AU postperihelion (Feaga et al. 2014). This result calls into question any measurements of relative abundance at only a single point in a comet’s orbit and clearly requires rethinking the key features of cometary outgassing.

Stardust NExT The extended mission of the Stardust spacecraft, called the New Exploration of Tempel (NExT), was also a direct consequence of Deep Impact in that it was targeted to fly past Tempel 1 a full orbital Page 13 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

period (5½ years) after the DI encounter. It had three goals – to search for evolutionary changes over an orbital period in terrain that had first been seen by DI, to observe terrain that had not been seen with DI, and to examine the impact site. The key challenges for this mission were twofold. The first was to predict the rotational phase of the comet accurately enough a year prior to encounter that the time of encounter could be adjusted so that the impact site would be on the observable side of the nucleus. Two independent studies disagreed on the prediction by a large amount, but the compromise solution averaging the two resulted in an ideal encounter that included visibility of the impact site, visibility of a lot of previously observed terrain, and visibility of considerable previously unseen terrain. The other key challenge was to predict the amount of hydrazine fuel remaining after the expected maneuvers. This set a maximum of about 8 h on the time period over which the arrival could be varied, and it turned out that the spacecraft was actually “running on vapor” by the end of the Tempel 1 encounter. Results from this mission have been summarized by Veverka et al. (2013), and only selected results are discussed here. Examination of the region of the impact by DI’s impactor spacecraft shows a depression consistent with diameter 50 m, consistent with the 40 m inferred above from adding up the estimated excavated ice that sublimed in the coma (Schultz et al. 2013). However, the terrain has been covered out to much larger distances, and there is a bright circular arc with diameter 120–180 m, which is a likely candidate for the raised rim of the crater. This would be consistent with the excavated ice and the observation that, at least in higher gravity environments, most of the ejecta, of order 90 %, falls back to the surface (Richardson and Melosh 2013; Schultz et al. 2013). There is not yet a consensus on the interpretation of all aspects of the resultant crater, but all interpretations imply very weak, low-density material and widespread ejecta. There were two other key results from Stardust NExT mission regarding the evolution of comets that will help to separate evolutionary effects from primordial properties on comets. There is reasonably strong evidence that the jets commonly seen in cometary comae likely arise, in most cases, from very steep surfaces (scarps, cliffs, crater walls) rather than from horizontal surfaces (Farnham et al. 2013) and comparisons of surface features seen both by DI and by Stardust NExT show that the average loss of material from the surface (estimated at 1/3 m) is episodic at least spatially and plausibly temporally. Changes observed, all in the sense of loss of material, had spatial scales of tens of meters (Veverka et al. 2013).

Conclusions Importance of Cometary Missions for Solar System Origins

Nuclei of five comets have now been imaged in varying degrees of detail (Fig. 9). They are remarkably diverse in overall shape and in surface topography, without obvious signs of different processes being important. This makes it difficult to interpret the differences and/or to separate evolutionary processes from primordial properties. The Stardust NExT mission helped considerably in identifying clearly defined evolutionary changes. Deep Impact’s most significant contributions to the larger picture were twofold. The DI mission and its follow-on activity have played a key role in rethinking the origin of comets and helped to bring comets back as a viable source of the Earth’s water. Hartogh et al. (2011) showed that the D/H ratio in the water from comet Hartley 2 was equal to that in terrestrial mean ocean water (contrary to what had been previously measured only for long-period comets). A’Hearn (2008) discussed the developments prior to the encounter with Hartley 2, but the understanding has evolved considerably since then. The studies of CO2 by DI coupled with the publication of measurements of Page 14 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 9 Five comets. Images of all cometary nuclei visited in situ show dramatic differences in gross shape and also in the nature of the topographic features. Although all comets have jets in the coma, only for Halley and Hartley 2 is it possible to see the jets without using special image enhancements. Given the results at Hartley 2, it seems likely that jets (normally seen in white light reflected by solid particles) are only seen easily when the jets contain many nearly pure icy grains (Credit: NASA/JPL/UMD)

CO2 from the Japanese AKARI satellite (Ootsubo et al. 2012) led the team to reexamine the whole question of relative abundances of volatiles in different dynamical classes of comets. This was coupled with the new studies of migration of the giant planets by Walsh et al. (2011) and led A’Hearn et al. (2012) to argue that short-period comets did not form in the classical Kuiper belt, but rather formed in a region that significantly overlapped the formation of the Oort cloud comets, but which on average was closer to the sun than the region in which the Oort cloud comets formed, the opposite of previous understanding. They were then ejected, by migration of the giant planets, to the Scattered Disk. This also explained several other aspects of comets, such as the D/H ratios in short-period and long-period comets. Contemporaneously, Belton (2014) studied a variety of properties of cometary nuclei and the size distribution of TNOs (Trans-Neptunian Objects) to argue strongly that cometary nuclei are not fragments of large TNOs, but rather primitive bodies of small size from the Scattered Disk. Formation in the classical Kuiper belt, based on size distributions there, had predicted that most cometary nuclei would be fragments.

Cosmic Hazards and NEO Defense

One of the advantages of scientifically driven missions is that they collect enough data to find surprising results of relevance to practical issues. DI made significant contributions to understanding the hazard from NEOs and the required planning for mitigation campaigns. Although Tempel 1 is not an NEO, roughly 10–15 % of NEOs are either fragments of cometary nuclei (a large number of them are independently orbiting fragments of comet Schwassmann-Wachmann 3!) or asteroids with many of the dynamical and physical characteristics of cometary nuclei. In fact, a recent paper Page 15 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_43-1 # Springer International Publishing Switzerland (outside the USA) 2014

(Mommert et al. 2014) argues that (3552) Don Quixote, the third largest known NEO, does exhibit cometary activity. The properties deduced for Tempel 1 are therefore very likely representative for cometary NEOs. First and foremost, DI emphasized the wide variation in many properties among cometary nuclei, this contrasting with a few properties that are common. Many nuclei appear, from indirect measurements, to be very porous, as more directly measured by DI for comet Tempel 1 and inferred indirectly by DI for comet Hartley 2. Unpublished results from the numerical modeling of the ejecta plume of Tempel 1 (J. Richardson, private communication) imply that the momentum transfer efficiency, the so-called beta factor, would be only about 2, provided the geometry of the impact was on a line through the center of mass. This is relatively low compared to the value expected for competent, rocky bodies. Shape is one of the most variable properties among comets, and the experience of DI is that rotational light curves are not reliable indicators of the shape of the nucleus, at least with the limited (but typical) range of observational geometries that were available for the targets of DI. DI’s algorithms for targeting a small body of unknown shape are a major step forward in targeting hazardous NEOs for mitigation. However, it is clear that targeting an impactor (or even an explosive device) to impact on a line through the center of mass is still a difficult challenge to our present capabilities. Fortunately, the average radius, and thus a crude volume, appears to be reliably determined from remote sensing, thus enabling early estimates of the mass of a hazardous NEO using a bulk density of 0.5 g/cm3. This in turn allows a more reliable estimation of the energy that would be delivered by an impacting NEO. A totally unanticipated result was an ability to deduce the mass of impacting cometary grains from the attitude fluctuations that they induced in the impactor. At hypervelocity, milligram grains had a large effect on the attitude of a 1/3 t impactor. Although these impacts would not significantly affect the trajectory of an impactor, they could have serious effects on, e.g., proximity fusing for an explosive device or the effectiveness of any device shaped for penetration. These results all suggest fertile areas requiring further study for development of effective mitigation of hazardous NEOs.

Cross-References ▶ Defending Against Asteroids and Comets ▶ International Astronomical Union and the NEO Hazard ▶ Micrometeoroid Hazards ▶ Potentially Hazardous Asteroids and Comets ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE

References A’Hearn MF (2008) Deep impact and the origin and evolution of cometary nuclei. Space Sci Rev 138:237–246 A’Hearn MF, Belton MJS (2005) Deep impact: a large-scale active experiment on a cometary nucleus. Space Sci Rev 117:1–21 A’Hearn MF, Belton MJS, Delamere WA, Kissel J, Klaasen KP et al (2005) Deep impact: excavating comet temple 1. Science 310:258–264

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A’Hearn MF, Belton MJS, Delamere WA, Feaga LM, Hampton D et al (2011) EPOXI at Comet Hartley 2. Science 332:1396–1400 A’Hearn MF, Feaga LM, Keller HU, Kawakita H, Hampton DL et al (2012) Cometary volatiles and the origin of comets. Astrophys J 758:29 (8 pp) Belton MJS (2014) The size-distribution of scattered disk TNOs from that of JFCs between 0.2 and 15 km effective radius. Icarus 231:168–182 Belton MJS, A’Hearn MF (1999) Deep sub-surface exploration of cometary nuclei. Adv Space Res 24:1167–1173 Belton MJS, Thomas P, Veverka J, Schultz P, Hearn A et al (2007) The internal structure of Jupiter family cometary nuclei from deep impact observations: the “Talps” or “Layered Pile” model. Icarus 187:332–344 Belton MJS, Thomas P, Li J-Y, Williams J, Carcich B et al (2013) The complex spin state of 103P/ Hartley 2: kinematics and orientation in space. Icarus 222:595–609 Biver N, Bockelée-Morvan D, Boissier J, Crovisier J, Colom P et al (2007) Radio observations of Comet 9P/Tempel 1 before and after deep impact. Icarus 187:253–271 Blume WH (2005) Deep impact mission design. Space Sci Rev 117:23–42 Busko I, Lindler D, A’Hearn MF, White RL (2007) Searching for the deep impact crater on Comet 9P/Tempel 1 using image processing techniques. Icarus 187:56–68 Clarke AC (1968) 2001, A space Odyssey. Signet Books, New York (Chap 18) Ernst CM, Schultz PH (2007) Evolution of the deep impact flash: implications for the nucleus surface based on laboratory experiments. Icarus 190:334–344 Farnham TL, Bodewits D, Li J-Y, Veverka J, Thomas P et al (2013) Connections between the jet activity and surface features on Comet 9P/ Tempel 1. Icarus 222:540–549 Feaga LM, A’Hearn MF, Sunshine JM, Groussin O, Farnham TL (2007) Asymmetries in the distribution of H2O and CO2 in the inner Coma of Comet 9P/Tempel 1 as observed by deep impact. Icarus 190:345–356 Feaga LM, A’Hearn MF, Farnham TL, Bodewits D, Sunshine JM et al (2014) Uncorrelated volatile behavior during the 2011 apparition of Comet C/2009 P1 Garradd. Astron J 147:24 Hampton DL, Baer JW, Huisjen MA, Varner CC, Delamere A et al (2005) An overview of the instrument suite for the deep impact mission. Space Sci Rev 117:43–93 Harwit M (1984) Cosmic discovery: the search, scope, and heritage of astronomy. MIT Press, Cambridge, MA Hermalyn B, Farnham TL, Collins SM, Kelley MS, A’Hearn MF et al (2013) The detection, localization, and dynamics of large Icy particles surrounding Comet 103P/Hartley 2. Icarus 222:625–633 Holsapple KA, Housen KR (2007) A crater and its Ejecta: an interpretation of deep impact. Icarus 187:345–356 Keller HU, K€ uppers M, Fornasier S, Gutiérrez PJ, Hviid SF et al (2007) Observations of Comet 9P/Tempel 1 around the deep Impact event by the OSIRIS cameras onboard Rosetta. Icarus 187:87–103 Kelley MS, Lindler DJ, Bodewits D, A’Hearn MF, Lisse CM et al (2013) A distribution of large particles in the Coma of Comet 103P/Hartley 2. Icarus 222:634–652 Lindler DJ, A’Hearn MF, Besse S, Carcich B, Hermalyn B et al (2013) Interpretation of results of deconvolved images from the deep impact spacecraft high resolution instrument. Icarus 222:571–579 Mastrodemos N, Kubitschek DG, Synnott SP (2005) Autonomous navigation for the deep impact mission encounter with Comet Tempel 1. Space Sci Rev 117:95–121 Page 17 of 18

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Meech KJ, Kleyna J, Hainaut OR, Lowry SC, Fuse T et al (2013) The demise of Comet 85P/Boethin, the first EPOXI mission target. Icarus 222:662–678 Mommert M, Hora JL, Harris AW, Reach WT, Emery JP et al (2014) The discovery of cometary activity in Near-Earth asteroid (3552) Don Quixote. Astrophys J 781:25 NASA’s Planetary Data System (PDS). http://pds.nasa.gov/. Accessed July 2014 Ootsubo T, Kawakita H, Hamada S, Kobayashi H, Yamaguchi M et al (2012) AAKARI nearinfrared spectroscopic survey for CO2 in 18 Comets. Astrophys J 752:15 (12pp) Pieters CM, Goswami JN, Clark RN, Annadurai M, Boardman J et al (2009) Character and spatial distribution of OH/H2O on the surface of the moon seen by M3 on Chandrayaan-1. Science 326:568–572 Richardson JE, Melosh HJ (2013) An examination of the deep impact Collision site on Comet Tempel 1 via Stardust-NExT: placing further constraints on cometary surface properties. Icarus 222:492–501 Richardson JE, Melosh HJ, Lisse CM, Carcich B (2007) A ballistics analysis of the deep impact Ejecta plume: determining Comet Tempel 1’s gravity, mass, and density. Icarus 190:357–390 Schleicher DG, Barnes KL, Baugh NF (2006) Photometry and imaging results for Comet 9P/Tempel 1 and deep impact: gas production rates, Postimpact Light Curves, and Ejecta Plume Morphology. Astron J 131:1130–1137 Schultz PH, Hermalyn B, Veverka J (2013) The deep impact crater on 9P/Tempel-1 from StardustNExT. Icarus 222:502–515 Small Bodies Node of PDS. http://pdssbn.astro.umd.edu/. Accessed July 2014 Sunshine JM, A’Hearn MF, Groussin O, Li J-Y, Belton MJS et al (2006) Exposed water ice deposits on the surface of Comet 9P/Tempel 1. Science 311:1453–1455 Sunshine JM, Farnham TL, Feaga LM, Groussin O, Merlin F et al (2009) Temporal and spatial variability of lunar hydration as observed by the deep impact spacecraft. Science 326:565–568 Veverka J, Klaasen K, A’Hearn M, Belton M, Brownlee D et al (2013) Return to Comet Tempel 1: overview of Stardust-NExT results. Icarus 222:424–435 Walsh KJ, Morbidelli A, Raymond SN, O’Brien DP, Mandell AM (2011) A low mass for Mars from Jupiter’s early gas-driven migration. Nature 475:206–209 Weaver HA, Feldman PD, A’Hearn MF, Dello Russo N, Stern SA (2011) The carbon monoxide abundance in Comet 103P/Hartley 2 During the EPOXI Flyby. Astrophys J Lett 734:L5

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

OSIRIS-REx Asteroid Sample-Return Mission Dante S. Lauretta* Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

Abstract The primary objective of the Origins, Spectral Interpretation, Resource Identification, and SecurityRegolith Explorer (OSIRIS-REx) mission is to return pristine samples of carbonaceous material from the surface of a primitive asteroid. The target asteroid, near-Earth object (101955) Bennu, is the most exciting, accessible, and volatile- and organic-rich remnant from the early Solar System. OSIRIS-REx returns a minimum of 60 g of bulk regolith and a separate 26 cm2 of fine-grained surface material from this body. Analyses of these samples provide unprecedented knowledge about presolar history, from the initial stages of planet formation to the origin of life. Prior to sample acquisition, OSIRIS-REx performs comprehensive global mapping of the texture, mineralogy, and chemistry of Bennu, resolving geological features, revealing its geologic and dynamic history, and providing context for the returned samples. The instruments also document the regolith at the sampling site in situ at scales down to the sub-centimeter. In addition, OSIRIS-REx studies the Yarkovsky effect, a non-Keplerian force affecting the orbit of this potentially hazardous asteroid (PHA), and provides the first ground truth for telescopic observations of carbonaceous asteroids.

Keywords OSIRIS-REx; Asteroids; Sample return; Spacecraft; New Frontiers Program; Carbon; Water; Volatiles; Yarkovsky effect; Potentially hazardous asteroid; Telescopes; 101955 Bennu; Resources; Spectroscopy

Introduction OSIRIS-REx provides exceptional science return. For the first time in US space-exploration history, a mission will return a pristine sample of a carbonaceous asteroid. Maintaining geological context is critical to linking the chemical and physical nature of the sample to the bulk properties of Bennu and the broader asteroid population. Since high-priority NASA science objectives are to understand the initial stages of planet formation and sources of organics delivered to Earth that may have ultimately led to the development of life, samples of a primitive carbonaceous object such as Bennu are highly desirable. A major advantage of the OSIRIS-REx mission is that the evolving capabilities of state-of-the-art laboratory analytical instrumentation, which is impossible to duplicate on a spacecraft, can repeatedly be brought to bear on OSIRIS-REx samples to advance NASA science objectives by many future generations. OSIRIS-REx ushers in a new era of planetary exploration by developing unprecedented operational capabilities in small-body proximity operations. OSIRIS-REx executes precise

*Email: [email protected] Page 1 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

spacecraft navigation to “kiss” the surface and acquire samples of Bennu. These operational capabilities (and the hardware/software inherent to them) are essential as humanity explores nearEarth space to increase our understanding of Solar System bodies and develop in situ resource utilization processes. OSIRIS-REx also serves as a demonstration of what has been termed a “transponder mission,” a type of mission to a potentially hazardous asteroid (PHA) with the dual objectives of refining the orbit to ascertain whether an impact is impending and characterizing the object to facilitate a possible deflection mission. OSIRIS-REx thus seeks to understand the Solar System scientifically, prepare for human exploration, and assess the risk of one of the most threatening PHAs.

The OSIRIS-REx Target: Asteroid Bennu The first step in achieving the mission objectives was selection of the optimum target asteroid. OSIRIS-REx seeks to return samples from a primitive body that represents the objects that may have brought prebiotic seeds of life and volatiles to Earth. The most plausible sources of these compounds are primitive asteroids and comets. Geochemical and dynamic constraints suggest that 200 m (estimated by selecting those brighter than 21.5 absolute magnitude) reduced the list of accessible asteroids to 26. Of these, a dozen had been spectrally characterized and taxonomically classified, and five were known to be carbonaceous. Bennu rose to the top of the list of potential sample-return targets based on both its high science value and its extensive characterization by ground- and space-based telescopes, which greatly reduce the risk for proximity operations planning. Bennu was discovered in September 1999 and is an Apollo NEO with a semimajor axis of 1.126 astronomical units (AU) (Williams 1999). It is a B-type asteroid characterized by a linear, featureless spectrum with bluish to neutral slope (Bus and Binze 2002; Clark et al. 2010; Lantz et al. 2013). Near-infrared spectroscopic data show evidence of a thermal tail longward of 2 mm, suggesting a very low albedo (3.5
1.5 %) that is consistent with a carbonaceous surface. Thermal infrared data show that there is no observable dust or gas in the proximity of Bennu (Emery et al. 2014). Lightcurve observations give a rotational period of 4.2834 (
0.0065) hours (Hergenrother et al. 2013). The light curve displays no evidence of satellites in orbit about Bennu. Bennu is a PHA that comes within 0.002 AU of the Earth and has one of the highest probabilities of impacting the Earth of any known asteroid (Milani et al. 2009; Chesley et al. 2014). Bennu is therefore an extremely high science-value sample-return mission target (Fig. 2).

Fig. 2 Bennu’s orbit crosses the Earth every revolution – making a close approach every 6 years

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

Fig. 3 The planetary radar system provided high-resolution shape information for Bennu – facilitating mission planning

Members of the OSIRIS-REx Science Team observed Bennu with the Arecibo Planetary Radar System in 1999, 2005, and 2011 and with the Goldstone Planetary Radar System in 1999 (Nolan et al. 2013). Because of these observations, Bennu has formal uncertainty of 6 m in the semimajor axis, the lowest of any asteroid (Chesley et al. 2014). This knowledge ensures accurate navigation for rendezvous. Delay-Doppler imaging provides shape information at a spatial resolution of 7.5 m/ pixel. These data reveal a 492-m (
20 m, mean diameter) asteroid undergoing retrograde rotation. The pole orientation is nearly perpendicular to the ecliptic plane, resulting in favorable lighting conditions for the entire asteroid during rendezvous. Radar observations also display no evidence of satellites. The radar polarization ratio (0.18) suggests a smooth surface of fine-grained material. These data provide high confidence in the presence of regolith on the surface of Bennu (Lauretta et al. 2012, 2014; Fig. 3). Members of the OSIRIS-REx team observed Bennu with the Spitzer Space Telescope in May 2007 (Emery et al. 2014; Muller et al. 2012). These observations provide additional information about the nature and distribution of regolith on the surface of Bennu. The Spitzer observations confirm that Bennu is extremely dark and further constrain the albedo to 4.3
0.3 %. The Spitzer data yield a thermal inertia of Bennu of 310
70 J m2 s0.5 K1, suggesting that the regolith is comprised of fine gravel (sub-cm). These data strongly support the concept that there is abundant regolith on the surface of Bennu available for sampling (Lauretta et al. 2012). Thus, Bennu is the ideal mission target: our knowledge allows for detailed mission operations planning with minimal risk and exceptional science return.

Science Implementation Touch-and-Go Sample-Acquisition Mechanism (TAGSAM) TAGSAM is an elegantly simple device that satisfies all sample-acquisition requirements. TAGSAM consists of two major components: a sampler head and an articulated positioning arm. The head acquires the bulk sample by releasing a jet of high-purity N2 gas that “fluidizes” the Page 4 of 21

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

regolith into the collection chamber. The articulated arm, which is similar to, but longer than, the Stardust aerogel deployment arm, positions the head for collection, brings it back for visual documentation, and places it in the Stardust-heritage SRC. The team has performed extensive hardware development and testing combined with dynamics simulations. Using a series of Engineering Development Units (EDUs), TAGSAM has been tested separately in vacuum and microgravity conditions. In every case, these tests resulted in acquisition of sample mass substantially above the baseline requirement of 60 g.

OSIRIS-REx Camera Suite (OCAMS) OCAMS is composed of three cameras: PolyCam, MapCam, and SamCam (Hancock et al. 2013; Smith et al. 2013). PolyCam, an F/3.2 Ritchey-Chretien telescope, acquires Bennu from 1 M-km range, refines its ephemeris, and performs high-resolution imaging of the surface. Its focal length is 625 mm. At 0.8 its FOV is five times smaller than MapCam. It uses a 1,024  1,024-pixel CCD array and it is equipped with a focus mechanism that translates one of its field-flattening lens to allow it to focus anywhere within a 200-m to infinity object range. The mechanism includes a shutter that, on every one of its 25 rotations over the focus range, allows it to assume three nominal focal positions while still being able to be safe (if necessary) (Fig. 4). MapCam searches for plumes and satellites, provides narrow-angle optical navigation, performs filter photometry, maps the surface, and images the sample site. MapCam uses the same 1,024  1,024-pixel CCD array as the PolyCam. Optically, it is a five-element refracting telephoto lens with the aperture set to f/3.3. The focal length is 125 mm, with a 4.0 field of view and a 68 mrad IFOV. It is also equipped with a filter wheel populated with four filters consistent with the Eight Color Asteroid Survey (ECAS) photometric system, as well as two panchromatic filters, one allowing imaging from 100 m to infinity and the other allowing imaging around 30 m range. The filters are the v, w, x filters (550, 770, 860 nm) from the ECAS standard set in addition to a blue filter shifted from the ECAS b from 437 to 470 nm to allow better camera performance. Each of the filters can be sequenced and images taken on 5 s centers so that it takes 20 s to collect the 5 images needed (4 colors + 1 panchromatic). SamCam is a 22 -FOV camera that documents the sample-acquisition event from a range of 3–30 m. It uses the same detector as the other two imagers and is also equipped with a filter wheel;

Fig. 4 The OSIRIS-REx Camera Suite (OCAMS) will characterize Bennu from 1 M km to 2-m range – and all distances in between (Figure from Smith et al. (2013))

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this one contains three identical panchromatic filters that allow backup imaging if one or more filters get contaminated by the sampling event. It also contains a diopter, similar to that mounted within the MapCam’s filter wheel, that allows it to refocus at a range of 2 m, in order to achieve higherresolution imaging of the TAGSAM head after the sampling event. All three cameras are able to back up each other’s functions to a significant degree. The alternate imaging campaigns would occur from different ranges and at different stages of the mission but represent a reliable functional redundancy to guard against failures resulting in the loss of a single camera’s functionality.

OSIRIS-REx Laser Altimeter (OLA) OLA provides ranging data out to 7 km and maps the shape and topography (Barnouin et al. 2012; Dickinson et al. 2012). OLA is an advanced lidar (Light Detection and Ranging) system that is a hybrid of the lidar on the Phoenix Mars Lander’s Canadian weather station and an instrument flown on the 2005 US Air Force Experimental Satellite System-11 (XSS-11). OLA will scan the entire surface of the asteroid to create a highly accurate, 3D model of Bennu, which will provide the team with fundamental and unprecedented information on the asteroid’s shape, topography, surface processes, and evolution. OLA uses a receiver and two complementary lasers to provide the information about the asteroid surface. OLA’s high-energy laser transmitter will be used for scanning from further distances (from 1 to 7.5 km from the surface of Bennu). The low-energy laser will be used for rapid imaging at shorter distances (500 m to 1 km) to contribute to a global topographic map of the asteroid as well as local maps to assist the team in selecting the best site for sample collection. OLA will deliver high-density 3D point cloud data, enabling reconstruction of an asteroid shape model at the highest density yet recorded on any small body and providing much needed slope information at the sample site leading up to acquisition. These data will be important for determining the geological context of the samples obtained by the OSIRIS-REx mission as well as for minimizing the risk of encountering hazards during sampling. In addition, OLA will be important for the accurate determination of the gravity field of Bennu by providing an accurate measure of the distance between the spacecraft and asteroid in support of Radio Science. Finally, OLA will provide ranging in support of other instruments and navigation.

OSIRIS-REx Visible and Infrared Spectrometer (OVIRS)

OVIRS is a point spectrometer (4-mrad FOV) with a spectral range of 0.4–4.3 mm, providing fulldisk Bennu spectral data, global spectral maps, and local spectral information of the sample site (Reuter and Simon-Miller 2012; Simon-Miller and Reuter 2013). OVIRS spectra will be used to identify volatile- and organic-rich regions of Bennu’s surface and guide sample-site selection. OVIRS obtains a full spectrum over all wavelengths simultaneously using linear variable filter segments. OVIRS has three broad filter strips with sufficient resolution to resolve key spectral features across its entire wavelength range. In addition, OVIRS contains a fourth narrow filter strip to measure key spectral signatures of organic functional groups with higher spectral resolution (Fig. 5). The OVIRS signal-to-noise ratio is dependent upon detector sensitivity, the wavelength region of interest, and phase angle of the observation. Thermal emission will fill in spectral features in the near-IR for higher surface temperatures. To obtain full compositional information about Bennu, observations will be obtained at multiple stations during the detailed survey, each optimized for different portions of the spectrum and different science objectives.

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Fig. 5 The OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) provides high-resolution spectral data – helping us find the optimum site for sampling (Figure from Simon-Miller and Reuter (2013))

For absolute spectral and radiometric calibration, OVIRS utilizes two internal calibration sources, filaments and blackbodies, and a solar calibration port. Throughout the mission, occasional solar observations will allow an absolute calibration check of the entire system, while more frequent internal lamp calibrations will be used for an instantaneous relative check of calibration.

OSIRIS-REx Thermal Emission Spectrometer (OTES)

OTES is an uncooled, FTIR point spectrometer that maps the thermal flux and spectral properties of Bennu from ~5 to 50 mm with a signal-to-noise ratio (SNR) of >325 between 7.4 and 33.3 mm for a 325 K target (Fig. 6). The design of the spectrometer is heritage from the Mars Global Surveyor TES and the Mars Exploration Rovers Mini-TES instruments. The heart of the instrument is a Michelson interferometer that collects one interferogram every 2 s (where each 2-s data acquisition is called an ICK, for Incremental Counter Keeper). OTES’s spectral resolution is 10 cm1 and its field of view is 8 mrad, achieved with a 15.2-cm f/3.91 Ritchey-Chretien telescope. At Bennu, OTES will have an accuracy of better than 3 % and a precision (noise equivalent spectral radiance, NESR) of 2.3  108 W cm2 sr1/cm1 between 300 and 1,350 cm1. OTES calibration in flight is achieved via a two-point calibration that uses space and an internal, conical blackbody calibration target. To map the compositional variation of Bennu at global and site-specific scales, OTES collects data at multiple times of day during the Detailed Survey and Reconnaissance phases, respectively. The data for thermal mapping are collected during the Orbital B, Detailed Survey, and Reconnaissance phases.

Radio Science Radio Science plays several key roles in determining the environment on, within, and about the asteroid (Scheeres et al. 2012). Radio Science reveals the mass, gravity field, internal structure, and surface acceleration distribution. These analyses provide information on the dynamic environment about the nominal asteroid model, the gravity field down to the surface of the asteroid, and the internal structure and mass distribution within the body. The asteroid mass and gravity field coefficients will be determined during two main mission periods. First, upon arrival the spacecraft will undertake a few slow hyperbolic flybys of the asteroid

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Fig. 6 The OSIRIS-REx Thermal Emission Spectrometer (OTES) provides information on the temperature, mineralogy, and grain size of the asteroid surface

to determine the total mass and detect the lower degree and order gravity coefficients. Then later in the mission there is a period of low, near-polar orbits dedicated to determining the asteroid spherical harmonic gravity field coefficients. Analysis shows that these should be detectable up to fourth degree and order, at least.

Regolith X-ray Imaging Spectrometer (REXIS) The REXIS Student Collaboration Experiment is a joint venture of the Massachusetts Institute of Technology and Harvard-Smithsonian Center for Astrophysics (Fig. 7; Allen et al. 2013). REXIS significantly enhances OSIRIS-REx by obtaining a global X-ray map of elemental abundance on Bennu. REXIS was conceived as a student-led project whose primary goal is the education of science and engineering students who will participate in the development of flight hardware in future space missions. Additionally REXIS also augments the observation capabilities of the OSIRIS-REx mission at the high end of the electromagnetic spectrum, which will enable characterization of the asteroid elemental abundances from a global scale down to 50 m, a capability unique to REXIS among instruments of this type that have previously flown. REXIS is designed to observe induced X-ray fluorescence lines emitted from the asteroid surface that arise as a result of exposure to solar X-rays as well as the cosmic X-ray background.

Sample-Return Capsule (SRC) OSIRIS-REx safely returns the samples to Earth in a Stardust mission-heritage SRC (Brownlee et al. 2003). The SRC lands at the Utah Test and Training Range (UTTR), following protocols established during recovery of the Stardust SRC. The SRC recovery team follows Stardust-heritage procedures to transport the SRC to Johnson Space Center (JSC), where the samples are removed and delivered to the dedicated OSIRIS-REx curation facility (Fig. 8).

Flight System

The OSIRIS-REx flight system builds on proven Lockheed Martin experience and uses established hardware, software, technology, and processes from Stardust, Odyssey, and MRO, as well as Juno, GRAIL, and MAVEN. The flight system architecture was developed in concert with science, instruments, subsystems, mission operations, navigation, and management. The resulting construct

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

Fig. 7 The Regolith X-ray Imaging Spectrometer (REXIS) combines education with enhanced science at Bennu (Figure from Allen et al. (2013))

Fig. 8 OSIRIS-REx is reflying the successful sample-return capsule from the Stardust mission

was populated with heritage subsystems and components. The OSIRIS-REx flight system pulls from previous spacecraft designs to create a flight system that is fully capable of achieving the mission at a low level of risk. This ability to select the “best of the best” enabled the team to select heritage components and designs without over-constraining the mission. OSIRIS-REx is single-fault tolerant with block, functional, and subsystem internal redundancies with appropriate cross-strapping, autonomous fault detection, isolation, and recovery. Instrument Page 9 of 21

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accommodations meet all pointing, power, thermal, and data handling requirements with significant margins. The flight system design was evaluated for its ability to execute the design reference mission (DRM) within the context of launch vehicle, trajectory, communications, and ground systems.

Contamination Control and Knowledge The pristine nature of the sample is preserved using stringent cleaning protocols during fabrication and careful mission design during spacecraft operations. Any contamination is thoroughly documented. The OSIRIS-REx team defined pristine to mean that no foreign material introduced into the sample hampers scientific analysis of the sample. This requires that contamination sources of astrochemically relevant compounds are low and that sufficient knowledge of the low levels of contamination introduced by the flight system and sample handling can be understood and corrected for. Amino acids are a compound class of high scientific interest with low meteorite abundances (~1 mg/g) and high industrial and biological backgrounds. With the exception of contamination originating from the aerogel itself and nylon bags initially used for curation, there were no contamination issues discovered during scientific investigations of the Stardust material. Analyses of Stardust foils showed a maximum amino acid contamination level of 186 ng/cm2 (sample C2092S,0), which still resulted in significant amino acid results (Elsila et al. 2009). This demonstrates that Stardust’s assembly, launch, return, and curation procedures provided sufficiently stringent contamination control procedures. The Stardust mission collected samples on aluminum foils and in aerogel, which made for much more challenging contamination control compared to cleaning the metal and Mylar surfaces inside TAGSAM. Thus, the pristine nature of the OSIRISREx sample will be preserved by starting with the Stardust contamination control plan and then incorporating technology improvements and applying the lessons learned from that mission, including ten lessons explicitly stated by the Stardust contamination science team (Sandford et al. 2010). In addition, the OSIRIS-REx team requires contamination levels from the high-purity aniline-free hydrazine (N2H4) used in the spacecraft propulsion system be no greater than the total carbon requirement of 180 ng/cm2. These requirements are placed on the TAGSAM surface since that can be quantitated directly and no assumptions about the properties of Bennu regolith are required. In addition to contamination control, OSIRIS-REx implements a detailed contamination knowledge plan, driven by the level-1 requirement to “Document the contamination of the sample acquired from collection, transport, curation, and distribution.” Documentation of possible sources of sample contamination throughout collection, return, and curation and stringent contamination control procedures is essential for understanding the pristine nature of samples returned by OSIRIS-REx. The contamination knowledge group sets the methods of implementation of the contamination control as well as performs the contamination science of studying hardware, witness material, and analogs to characterize and document the trace levels of contamination that will be present. The mission has also developed and implemented detailed contamination control plans for construction and testing of the spacecraft, recovery, and curation. The team scrutinizes materials lists for substances to archive or be wary of and provides detailed knowledge of the trace contaminants that are acceptable, monitors spacecraft contamination control, and ensures that the documentation and contamination information collected is available to the OSIRIS-REx science team and international science community. For example, the team has worked to limit the number of different organic materials used in construction and ensure that those used are carefully selected to minimize organic contamination of the sample. TAGSAM construction materials and witness plates exposed during flight system construction will be periodically tested and archived. Page 10 of 21

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Baseline Science Mission OSIRIS-REx will usher in a new era of planetary exploration. The mission executes precise navigation to the surface of a carbonaceous asteroid, thoroughly characterizes the asteroid and the sample site, acquires a significant quantity of pristine regolith, and returns these samples safely to Earth for detailed analyses (Lauretta and OSIRIS-REx Team 2012). To ensure mission success, the OSIRIS-REx system engineering team developed a comprehensive design reference mission (DRM). The team uses the DRM to validate all top-level mission requirements and systematically flow requirements down to the flight system and ground system. The DRM schedule provides ample time to conduct and plan asteroid proximity operations and properly develop comprehensive global knowledge of Bennu prior to sampling. The OSIRIS-REx mission employs a methodical, phased approach to ensure success in meeting the mission’s science requirements. OSIRIS-REx launches in September 2016 on an Atlas V 411 launch vehicle. The spacecraft will arrive at Bennu in August 2018. Sampling is nominally scheduled to occur in 2019, but the DRM timeline provides substantial operational margin beyond this point. The departure burn from Bennu occurs between March and June 2021. On September 24, 2023, the SRC lands at the Utah Test and Training Range (UTTR). Stardust-heritage procedures are followed to transport the SRC to JSC, where the samples are removed and delivered to the OSIRIS-REx curation facility. After a 6-month preliminary examination period, the mission will produce a catalog of the returned sample, allowing the worldwide community to request samples for detailed analysis.

Science Objectives Objective 1: Return and Analyze a Sample of Pristine Carbonaceous Asteroid Regolith in an Amount Sufficient to Study the Nature, History, and Distribution of Its Constituent Minerals and Organic Material Primitive asteroids are the remnant building blocks of the terrestrial planets (Bottke et al. 2002). Laboratory investigations of meteorites and interplanetary dust particles from asteroids reveal the nature of early Solar System processes responsible for planet formation (Lauretta and McSween 2006). The presence in primitive meteorites of complex organic compounds with terrestrial counterparts has led to speculation that meteorites could have seeded early Earth with prebiotic elements and molecules. However, meteorite samples are altered by the processes of ejection from their parent body and by atmospheric entry. In addition, these materials are very quickly contaminated, colonized, and consumed by terrestrial microbes. For example, the possible presence of extraterrestrial RNA nucleobases in the Murchison meteorite has been controversial for 30 years because of likely contamination from terrestrial DNA and RNA (Stoks and Schwartz 1979, 1982; Martins et al. 2008; Martins 2011; Callahan et al. 2011). Only by studying the organic chemistry and geochemistry of a pristine carbonaceous asteroid sample can the nature of extraterrestrial organic compounds be understood. Primordial organic compounds are preserved in the interiors of grains and freshly exposed surfaces on Bennu. However, extended exposure to the space environment modifies these compounds. These processes include micrometeorite impact and reworking, implantation of solar wind and flare particles, radiation damage and chemical effects from solar particles and cosmic rays, and sputtering erosion and deposition (Sasaki et al. 2001). Carbonaceous asteroids contain minerals and

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organic matter potentially modified by space weathering. However, the effect of space weathering on carbonaceous material is essentially unknown. Large carbon-based polymers may be produced. These polymers would darken asteroidal surfaces, redden the visible and near-IR spectral slope, and produce a dark and featureless spectrum such as that of Bennu. OSIRIS-REx offers the first opportunity to study the distribution of organic molecules and the effects of space weathering processes on an organic-rich body both in situ and through detailed analysis of a returned sample. After Earth return, samples are available to the worldwide scientific community, who perform precise analyses in terrestrial laboratories that cannot be duplicated by spacecraft-based instruments. Ongoing sample analysis by generations of scientists using cutting-edge tools and methods guarantees an enduring scientific treasure that only sample return can provide. Combining true exploration and laboratory-based science, OSIRIS-REx leaves a multigenerational legacy for the science community and people of the world. Just as Apollo lunar samples are still being analyzed in new and previously unpredictable ways more than 40 years after their collection, OSIRIS-REx samples will be available for the future of humankind (Fig. 9).

Objective 2: Map the Global Properties, Chemistry, and Mineralogy of a Primitive Carbonaceous Asteroid to Characterize Its Geologic and Dynamic History and Provide Context for the Returned Samples OSIRIS-REx provides insight into the geologic and dynamic history of Bennu (Lauretta et al. 2014). According to the current paradigm of asteroid dynamics, Bennu formed in the main asteroid belt, where most B-type objects currently reside (Bus and Binzel 2002; Walsh et al. 2013). Its parent body was a primitive asteroid that formed ~4.5 billion years ago. A collision shattered this parent body. Bennu then migrated due to the Yarkovsky effect into a dynamic resonance capable of placing it into an Earth-crossing orbit (Delbo and Michel 2011). This history is recorded in the shape, surface texture, spectral properties, mass, rotation state, and composition of Bennu. OSIRIS-REx will thoroughly map the global properties, chemistry, and mineralogy of Bennu and develop globalscale knowledge of Bennu at a spatial resolution that provides a well-defined context for the returned samples (Fig. 10). OCAMS characterizes the shape, rotation state, and surface texture of Bennu. MapCam captures global images at a spatial resolution of 1-m per pixel of the physical dimensions and orientations of all surface geological features, including craters, boulders, grooves, faults, and regolith distribution. Bennu’s crater distribution will help determine the timing of the last major resurfacing event on the body. Bennu has a prominent equatorial ridge, which may be a region of regolith pileup and provide evidence that Bennu was the primary object in a binary system (Bottke 2008). However, extensive ground-based characterization shows that Bennu has since lost any major companion. Furthermore, its rotation period is now far too slow for it to be actively shedding mass. The origin of the equatorial ridge on Bennu will be inferred from geologic analysis of surface morphology and mineral distribution. Spectral mapping of the surface of Bennu is performed using the four spectral filters (470, 550, 770, 860 nm) on MapCam. These wavelength regions characterize the broad spectral features observed on a wide variety of carbonaceous asteroids and provide direct comparison with groundbased observations. These images provide context for the high-spectral-resolution data from OVIRS and OTES and guide sample-site selection. Though the Spitzer Telescope observations the team has analyzed show no thermal-excess evidence for a dust belt around Bennu, it is possible that a few particles remain. For science and

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

Fig. 9 Coordinated sample analysis exponentially increases science return

mission safety, PolyCam and MapCam will determine the orbit and nature of any particles >10 cm in the vicinity of Bennu in the Hill Sphere (the region of space where orbits are stable). OLA provides an independent means to determine shape and surface texture and provides an absolute range for all other remote-sensing data. OLA will generate global topographic maps with 1-m spatial and vertical resolution. OLA will also provide precise data of surface slopes. The synergy between OCAMS and OLA significantly enhances and accelerates the characterization of large- and small-scale topography. These surface topographic data will also constrain Bennu’s internal structure. OSIRIS-REx performs extensive global mapping of the surface spectral characteristics with comprehensive spectral coverage (0.4–50 mm) and global spatial resolution of 5 % in this wavelength range. This data set provides information on the distribution and composition of minerals and organic material across the surface of Bennu. It allows the first analysis of surface processing of carbonaceous material and guides sample-site selection, ensuring maximum science value from the samples. In addition, any spectral

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

Fig. 10 OSIRIS-REx develops complete global knowledge of Bennu, which is necessary to understand its geologic history and its impact probability

diversity will be used to understand how material is being displaced on the surface, providing important clues to the geological and geophysical evolution of Bennu. Radio Science will determine the mass of Bennu and estimate the mass distribution to second degree and order, with limits on the fourth degree and order distribution. Knowing the mass estimate and shape model, the team will compute the bulk density and apparent porosity of Bennu. Together, this information constrains the internal structure. Most importantly, the gravity field knowledge provides information on regolith mobility and identifies areas of significant regolith pooling.

Objective 3: Document the Texture, Morphology, Volatile Chemistry, and Spectral Properties of the Regolith at the Sampling Site In Situ at Scales Down to the Sub-centimeter The value of the sample increases enormously with the amount of knowledge captured about the site from which it was obtained. The OSIRIS-REx spacecraft is highly maneuverable and capable of investigating any region on Bennu at scales down to the sub-cm. The OSIRIS-REx instruments are

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

used to characterize the spectral properties, micro-texture, and geochemistry of the regolith at the sampling site in exquisite detail. Sample-site characterization is performed over several phases of the DRM at increasing resolution. During the Orbital Phase, PolyCam is used to map up to a dozen candidate sample sites using stereo imaging with 5-cm resolution. Concurrently, OLA performs detailed topographic mapping of the entire asteroid. These data sets enable the team to assess the safety and sampling potential of each candidate site. The PI prioritizes four of these sites for detailed reconnaissance. The Reconnaissance phase consists of four 225-m altitude flyovers over the sunlit side of Bennu, out of the 1-km terminator orbit plane, for collecting data needed to assess the sampleability of up to four candidate sites, followed by two 525-m flyovers, one over each of the highest priority sites to characterize their science value. These six sorties to low altitude are separated by a period of 2 weeks back in the 1-km Safe-Home orbit to determine the orbit of the spacecraft, design and perform an orbit phasing maneuver to ensure the spacecraft departs the orbit at the right place and time to target flyover of the candidate site, and perform additional tracking to upload final maneuver adjustments to the spacecraft prior to orbit departure. Between sorties the science data is being processed, analyzed, and interpreted to select the prime and backup sites. After the prime site is selected, a methodical and incremental series of approach events is executed to safely prepare for the touch-and-go (TAG) sample collection (Berry et al. 2013; Sanchez et al. 2013). During this phase, each step in the sampling maneuver is practiced sequentially, followed by a return to Safe-Home orbit. The TAG dynamics are driven by the ability of the Flight Dynamics team and the Guidance, Navigation, and Control (GN&C) subsystem to deliver the spacecraft to the ground with an accurate touchdown velocity and minimum attitude and rate errors. MapCam images are collected to provide additional verification of the trajectory and provide additional photo documentation of the sample site. OVIRS and OTES continuously acquire data during this phase. Before leaving the Rehearsal phase, newly identified surface hazards (slopes, rocks that exceed safety limits) must be analyzed before a decision to proceed with the TAG can be made. The TAG maneuver follows the transfer orbit, approach, and velocity-matching maneuvers as previously rehearsed. Following the MatchPoint maneuver, OSIRIS-REx approaches the surface along the vector normal to the sampling plane under reaction wheel attitude control, as OCAMS (MapCam or SamCam), OVIRS, and OTES continuously collect data to characterize the surface. The result of these extensive efforts is complete documentation of the texture, morphology, geochemistry, and spectral properties of the regolith at the sampling site, greatly enhancing the science value of the returned samples.

Objective 4: Measure the Yarkovsky Effect on a Potentially Hazardous Asteroid and Constrain the Asteroid Properties that Contribute to This Effect

Bennu is a potential Earth impactor. The highest individual impact probability is 9.5  105 in 2,196, and the cumulative impact probability is 3.7  104, leading to a cumulative Palermo Scale of 1.70 (Milani et al. 2009; Chesley et al. 2014), one of the highest for any known asteroid. The primary source of uncertainty is the dynamic model of its orbital evolution. The main nongravitational orbit perturbation expected over a time span of centuries is due to the Yarkovsky effect, which results from the way the asteroid rotation affects the surface temperature distribution and therefore the anisotropic thermal reemission (Chesley et al. 2003). When thermal forces align with orbital vectors, the Yarkovsky effect can cause a steady drift in semimajor axis. OSIRIS-REx dramatically extends the time horizon for reliable position predictions for Bennu, not only by

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

Fig. 11 OSIRIS-REx provides an unprecedented level of understanding about the Yarkovsky effect – in which the thermal reemission of absorbed sunlight changes Bennu’s orbits

measuring spin state, surface area, albedo distribution, and thermal emission, but also by directly measuring the Yarkovsky acceleration (Fig. 11). A close approach of Bennu to Earth in September 2011 permitted the OSIRIS-REx team to use the Arecibo Planetary Radar System to acquire radar astrometry and detect the Yarkovsky effect. The signal-to-noise ratio in this detection was sufficient to measure the range to within one asteroid diameter. During encounter, precision tracking of the OSIRIS-REx spacecraft, in combination with modeling of the spacecraft motion relative to Bennu, will improve the signal-to-noise ratio, providing the most accurate determination of the Yarkovsky effect. This increase in position knowledge leads to better understanding of the possible threat, allowing ample time for policy makers to approve appropriate mitigation efforts. The Yarkovsky effect on Bennu accumulates quadratically with time (Milani et al. 2009), reaching approximately 200 km by the time of the OSIRIS-REx rendezvous relative to the ballistic ephemeris. The OSIRIS-REx navigation plan results in high-quality range measurements over 2 years. Radio ranging to the spacecraft fixes its position in the heliocentric frame, while the Doppler tracking, optical navigation, and OLA measurements constrain the position of the spacecraft with respect to Bennu. Combining the Earth- and Bennu-relative spacecraft solutions into a global fit with all data determines the location of Bennu to within 10 m. This precision exceeds that of the best ground-based asteroid radar measurements, and continuous measurements made over the course of the mission, rather than only for a few days near-Earth approach, result in an extremely precise measurement of the extent of Yarkovsky drift.

Objective 5: Characterize the Integrated Global Properties of a Primitive Carbonaceous Asteroid to Enable Direct Comparison with Ground-Based Telescopic Data of the Entire Asteroid Population The diversity of the asteroid population is reflected in both the large variation in their spectral properties and the large compositional range of meteorites. Although the silicate mineralogy of asteroids can be inferred by spectral matching between asteroids and meteorites (e.g., Hiroi et al. 2001), the detailed mineralogy of most asteroids is still unknown. This record is obscured by the fact that astronomy (telescopic measurements) and cosmochemistry (laboratory measurements) study inherently different samples. Telescopic reflectance spectra sample the top few mm of an object’s surface while meteorites represent subsurface material. OSIRIS-REx’s separate collection of bulk and surface material, combined with spectral characterization of Bennu, enables detailed

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

understanding of the connection between the spectral properties of asteroid surfaces and the bulk composition and mineralogy of the returned samples. The possible parent asteroid associated with a meteorite class can be constrained with reflectance spectroscopy and is helped when a dynamic mechanism can be identified to deliver meteorite samples. Success in connecting meteorites to asteroids began with the identification of Vesta as the source of the HED meteorites (Drake 2001) and confirmed by the Dawn mission (McSween et al. 2012). However, there are several spectral classes of asteroids whose meteorite counterparts have been difficult to locate. As a result, the compositional distribution of planetary building blocks is essentially unknown. This fact is highlighted by the recovery of fragments from the F-class asteroid 2008 TC3, which shocked the meteorite world by linking this class of asteroids to the ureilite meteorites (Jenniskens et al. 2009). The spectral characteristics of the extremely dark B-class asteroids are unlike any measured meteorites, though the extremely rare and friable CM1 chondrites provide the closest spectral match (Clark et al. 2011). Only sample return allows definitive identification of the mineralogy of such complex and important asteroids and provides the first ground-truth calibration for asteroid remote-sensing data. The team will perform high-precision astrometry to refine the ephemeris of Bennu as the spacecraft approaches Bennu. MapCam will measure photometric properties, obtain a light curve, determine color indices, and characterize the phase function. From this data set, the team will perform the same type of reduction used with telescopic data to predict asteroid properties. During the approach to Bennu, OVIRS and OTES will acquire high-spectral-resolution full-disk coverage until Bennu fills the entire field of view for each instrument. The combination of these observations, ground-based telescopic spectral measurements, and detailed spectroscopic and mineralogical characterization of the returned samples will provide ground truth for the Bennu reflectance spectrum. These results will be extrapolated to the global B-type asteroid and comet populations to estimate the distribution of volatile and organic compounds across the Solar System.

Conclusion OSIRIS-REx will characterize and return samples from Bennu, the most accessible, organic-rich body from the early Solar System. OSIRIS-REx explores the past through detailed characterization of the B-type carbonaceous asteroid Bennu. Bennu is a time capsule from the birth of our Solar System that records presolar history, the initial stages of planet formation, and the sources of prebiotic organic compounds available for the origin of life. OSIRIS-REx returns extraterrestrial samples from an extremely dark (albedo ¼ 4.3 %), B-type carbonaceous asteroid, with extraordinary context from a thoroughly documented sample site. OSIRIS-REx also explores the hazards and resources in near-Earth space that are important for securing Earth’s future, since Bennu is an accessible near-Earth asteroid and potential impactor. Detailed knowledge of Bennu can be extrapolated to thousands of carbonaceous asteroids in the main belt, revealing the distribution of volatile and organic compounds across the Solar System.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_44-1 # Springer International Publishing Switzerland 2014

Cross-References ▶ Air Bursting Modeling ▶ Asteroid Redirect Mission by NASA ▶ Defending Against Asteroids and Comets ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ European Space Agency's Program on Potentially Harmful Asteroid ▶ Hayabusa Missions ▶ International Astronomical Union and the NEO Hazard ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Introduction to the Handbook of Cosmic Hazards and Planetary Defense ▶ Keyholes ▶ Micrometeoroid Hazards ▶ Minor Planet Center ▶ Nature of the Threat/Historical Occurrence ▶ NEOSHIELD - A Global Approach to Near-earth Object Impact Threat Mitigation ▶ Planetary Defense, Global Cooperation and World Peace ▶ Potentially Hazardous Asteroids and Comets ▶ Risk Management and Insurance Industry Perspective ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning ▶ Space-Based Infrared Discovery and Characterization of Minor Planets with NEOWISE ▶ Strategic Issues Involved with Planetary Defensive Systems and Active Debris Removal Systems ▶ The NASA Sentry Risk Table ▶ The Palermo and Torino Scales (Risk Assessment of NEO Collisions and Magnitude of Impact) ▶ The Yarkovsky Effect

References Alí-Lagoa V, de Leon J, Licandro J, Delbo M, Campins H, Pinilla-Alonso N, Kelley MS (2013) Physical properties of B-type asteroids from WISE data. Astron Astrophys 554:A71 Allen B, Grindlay J, Hong J, Binzel RP, Masterson R, Inamdar NK, Chodas M, Smith MW, Bautz MW, Kissel SE, Villasenor J, Oprescu M, Induni N (2013) The REgolith X-ray imaging spectrometer (REXIS) for OSIRIS-REx: identifying regional elemental enrichment on asteroids, conference on optical modeling and performance predictions VI, San Diego Barnouin O, Daly M, Bierhaus B, Dickenson C, Gaudreau D, Tripp J, Ilnicki M, Garvin J, Hildebrand A (2012) The OSIRIS-REx laser altimeter. LPI Contrib 1667:6198 Berry K, Sutter B, May A, Williams K, Barbee BW, Beckman M, Williams B (2013) OSIRIS-REx Touch-And-Go (TAG) mission design and analysis. In: 36th annual AAS guidance and control conference, Breckenridge, 1–6 Feb 2013 Binzel RP, Perozzi E, Rivkin AS, Rossi A, Harris AW, Bus SJ, Valsecchi GB, Slivan SM (2004) Dynamical and compositional assessment of near-Earth object mission targets. Meteorit Planet Sci 39:351–366 Bottke WF (2008) Asteroids – how to make a flying saucer. Nature 454:173–174 Bottke WF, Morbidelli A, Jedicke R, Petit JM, Levison HF, Michel P, Metcalfe TS (2002) Debiased orbital and absolute magnitude distribution of the near-Earth objects. Icarus 156:399–433 Page 18 of 21

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Brownlee DE, Tsou P, Anderson JD, Hanner MS, Newburn RL, Sekanina Z, Clark BC, Horz F, Zolensky ME, Kissel J, McDonnell JAM, Sandford SA, Tuzzolino AJ (2003) Stardust: comet and interstellar dust sample return mission. J Geophys Res Planet 108(E10):8111 Bus SJ, Binzel RP (2002) Phase II of the small main-belt asteroid spectroscopic survey: A featurebased taxonomy. Icarus 158(1):146–177 Callahan MP, Smith KE, Cleaves HJ, Ruzicka J, Stern JC, Glavin DP, House CH, Dworkin JP (2011) Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases. Proc Natl Acad Sci U S A 108:13995–13998 Chesley SR, Ostro SJ, Vokrouhlicky D, Capek D, Giorgini JD, Nolan MC, Margot JL, Hine AA, Benner LAM, Chamberlin AB (2003) Direct detection of the Yarkovsky effect by radar ranging to asteroid 6489 Golevka. Science 302:1739–1742 Chesley SR, Farnocchia D, Nolan MC, Vokrouhlicky D, Chodas PW, Milani A, Spoto F, Rozitis B, Benner LAM, Bottke WF, Busch MW, Emery JP, Howell ES, Lauretta DS, Margot J-L, Taylor PA (2014) Orbit and bulk density of the OSIRIS-REx target asteroid (101955) Bennu. Icarus 235:5–22 Clark BE, Ziffer J, Nesvorny D, Campins H, Rivkin AS, Hiroi T, Barucci MA, Fulchignoni M, Binzel RP, Fornasier S, DeMeo F, Ockert-Bell ME, Licandro J, Mothe-Diniz T (2010) Spectroscopy of B-type asteroids: subgroups and meteorite analogs. J Geophys Res Planet 115 E06005 Clark BE, Binzel RP, Howell ES, Cloutis EA, Ockert-Bell M, Christensen P, Barucci MA, DeMeo F, Lauretta DS, Connolly H Jr, Soderberg A, Hergenrother C, Lim L, Emery J, Mueller M (2011) Asteroid (101955) 1999 RQ36: spectroscopy from 0.4 to 2.4 mu m and meteorite analogs. Icarus 216:462–475 Delbo M, Michel P (2011) Temperature history and dynamical evolution of (101955) 1999 RQ36: a potential target for sample return from a primitive asteroid. Astrophys J Lett 728:L42 Dickinson C, Daly M, Barnouin O, Bierhaus B, Gaudreau D, Tripp J, Ilnicki M, Hildebrand A (2012) An overview of the OSIRIS REx Laser Altimeter (OLA), Lunar And Planetary Institute Science conference abstracts, p 1447 Drake MJ (2001) The eucrite/Vesta story. Meteorit Planet Sci 36:501–513 Elsila JE, Glavin DP, Dworkin JP (2009) Cometary glycine detected in samples returned by Stardust. Meteorit Planet Sci 44:1323–1330 Emery JP, Fernández YR, Kelley MSP, Warden KT, Hergenrother C, Lauretta DS, Drake MJ, Campins H, Ziffer J (2014) Thermal infrared observations and thermophysical characterization of OSIRIS-REx target asteroid (101955) Bennu. Icarus 234:17–35 Gomes R, Levison HF, Tsiganis K, Morbidelli A (2005) Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets. Nature 435:466–469 Hancock J, Crowther B, Whiteley M, Burt R, Watson M, Nelson J, Fellows C, Rizk B, KinneySpano E, Perry M (2013) OSIRIS-REx OCAMS detector assembly characterization, In SPIE Optical Engineering+ Applications (pp. 88600J–88600J). International Society for Optics and Photonics Hergenrother CW, Nolan MC, Binzel RP, Cloutis EA, Barucci MA, Michel P, Scheeres DJ, Drouet d’Aubigny C, Lazzaroh D, Pinilla-Alonsoi N, Campins H, Licandro J, Clark BE, Rizk B, Beshore EC, Lauretta DS (2013) Lightcurve, color and phase function photometry of the OSIRIS-REx target asteroid (101955) Bennu. Icarus 226:663–670 Hiroi T, Zolensky ME, Pieters CM (2001) The Tagish Lake meteorite: a possible sample from a D-type asteroid. Science 293:2234–2236 Hsieh HH, Jewitt D (2006) A population of comets in the main asteroid belt. Science 312:561–563

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Jenniskens P, Shaddad MH, Numan D, Elsir S, Kudoda AM, Zolensky ME, Le L, Robinson GA, Friedrich JM, Rumble D, Steele A, Chesley SR, Fitzsimmons A, Duddy S, Hsieh HH, Ramsay G, Brown PG, Edwards WN, Tagliaferri E, Boslough MB, Spalding RE, Dantowitz R, Kozubal M, Pravec P, Borovicka J, Charvat Z, Vaubaillon J, Kuiper J, Albers J, Bishop JL, Mancinelli RL, Sandford SA, Milam SN, Nuevo M, Worden SP (2009) The impact and recovery of asteroid 2008 TC3. Nature 458:485–488 Lantz C, Clark BE, Barucci MA, Lauretta DS (2013) Evidence for the effects of space weathering spectral signatures on low albedo asteroids. Astron Astrophys 554:A138 Larson HP, Feierberg MA, Lebofsky LA (1983) The composition of asteroid-2-Pallas and its relation to primitive meteorites. Icarus 56:398–408 Lauretta DS, McSween HY Jr (2006) Meteorites and the early solar system II. University of Arizona Press, Tucson Lauretta D, OSIRIS-REx Team (2012). An overview of the OSIRIS-REx asteroid sample return mission, Lunar And Planetary Institute science conference abstracts, p 2491 Lauretta D, Barucci M, Bierhaus E, Brucato J, Campins H, Christensen P, Clark B, Connolly H, Dotto E, Dworkin J (2012) The OSIRIS-REx mission-sample acquisitions strategy and evidence for the nature of regolith on asteroid (101955) 1999 RQ36. LPI Contrib 1667:6291 Lauretta DS, Bartels AE, Barucci MA, Bierhaus EB, Binzel RP, Bottke WF, Campins H, Chesley SR, Clark BC, Clark BE, Cloutis EA, Connolly HC, Crombie MK, Delbó M, Dworkin JP, Emery JP, Glavin DP, Hamilton VE, Hergenrother CW, Johnson CL, Keller LP, Michel P, Nolan MC, Sandford SA, Scheeres DJ, Simon AA, Sutter BM, Vokrouhlický D, Walsh KJ (2014) The OSIRIS-REx target asteroid 101955 Bennu: constraints on its physical, geological, and dynamical nature from astronomical observations. Meteorit Planet Sci Martins Z (2011) Organic chemistry of carbonaceous meteorites. Elements 7:35–40 Martins Z, Botta O, Fogel ML, Sephton MA, Glavin DP, Watson JS, Dworkin JP, Schwartz AW, Ehrenfreund P (2008) Extraterrestrial nucleobases in the Murchison meteorite. Earth Planet Sci Lett 270:130–136 McSween HY Jr, Mittlefehldt DW, Beck AW, Mayne RG, McCoy TJ (2012) HED meteorites and their relationship to the geology of Vesta and the Dawn mission. In: The Dawn mission to minor planets 4 Vesta and 1 Ceres. Springer, New York, pp 141–174 Milani A, Chesley SR, Sansaturio ME, Bernardi F, Valsecchi GB, Arratia O (2009) Long term impact risk for (101955) 1999 RQ(36). Icarus 203:460–471 Morbidelli A, Chambers J, Lunine JI, Petit JM, Robert F, Valsecchi GB, Cyr KE (2000) Source regions and timescales for the delivery of water to the Earth. Meteorit Planet Sci 35:1309–1320 Muller TG, O’Rourke L, Barucci AM, Pal A, Kiss C, Zeidler P, Altieri B, Gonzalez-Garcia BM, Kuppers M (2012) Physical properties of OSIRIS-REx target asteroid (101955) 1999 RQ(36). Astron Astrophys 548:A36 Nolan MC, Magri C, Howell ES, Benner LAM, Giorgini JD, Hergenrother CW, Hudson RS, Lauretta DS, Margot J-L, Ostro SJ, Scheeres DJ (2013) Shape model and surface properties of the OSIRIS-REx target asteroid (101955) Bennu from Radar and Lightcurve observations. Icarus 226:629–640 Pravec P, Harris AW (2000) Fast and slow rotation of asteroids. Icarus 148:12–20 Reuter D, Simon-Miller A (2012) The OVIRS visible/IR spectrometer on the OSIRIS-Rex mission. LPI Contrib 1683:1074 Sanchez P, Scheeres D, Bierhaus E, Clark B (2013) Simulations of regolith interactions in microgravity. LPI Contrib 1719:2271

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Sandford SA, Bajt S, Clemett SJ, Cody GD, Cooper G, Degregorio BT, de Vera V, Dworkin JP, Elsila JE, Flynn GJ, Glavin DP, Lanzirotti A, Limero T, Martin MP, Snead CJ, Spencer MK, Stephan T, Westphal A, Wirick S, Zare RN, Zolensky ME (2010) Assessment and control of organic and other contaminants associated with the Stardust sample return from comet 81P/Wild 2. Meteorit Planet Sci 45:406–433 Sasaki S, Nakamura K, Hamabe Y, Kurahashi E, Hiroi T (2001) Production of iron nanoparticles by laser irradiation in a simulation of lunar-like space weathering. Nature 410:555–557 Scheeres D, McMahon J, Takahashi Y, Chesley S, Nolan M (2012) Radio science at 1999 RQ36 for OSIRIS-REx. LPI Contrib 1667:6191 Simon-Miller A, Reuter D (2013) OSIRIS-REx OVIRS: a scalable visible to near-IR spectrometer for planetary study. LPI Contrib 1719:1100 Smith P, Rizk B, Kinney-Spano E, Fellows C, d’Aubigny C, Merrill C (2013) The OSIRIS-REx camera suite (OCAMS). LPI Contrib 1719:1690 Stoks PG, Schwartz AW (1979) Uracil in carbonaceous meteorites. Nature 282:709–710 Stoks PG, Schwartz AW (1982) Basic nitrogen-heterocyclic compounds in the Murchison meteorite. Geochim Cosmochim Acta 46:309–315 Walsh KJ, Delbó M, Bottke WF, Vokrouhlický D, Lauretta DS (2013) Introducing the Eulalia and new Polana asteroid families: re-assessing primitive asteroid families in the inner main belt. Icarus 225:283–297 Williams GV (1999) 1999 RQ36. Minor planet electronic circular 1999-R44

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_46-1 # Springer International Publishing Switzerland (outside the USA) 2014

NASA’s Asteroid Redirect Mission Michele Gates* and Lindley Johnson NASA Headquarters, Human Exploration and Operations Directorate, Washington, DC, USA

Abstract NASA is examining concepts for the Asteroid Redirect Mission, in which the agency would launch a robotic spacecraft to capture and redirect an asteroid into a stable orbit in the Earth-Moon system. This would be followed by an early use of the powerful Space Launch System (SLS) launch vehicle and Orion crew spacecraft to ferry astronauts to retrieve samples and return to Earth. NASA is examining two options for the robotic segment: one to redirect a small asteroid to a lunar distant retrograde orbit (LDRO) and another to extract a cohesive mass from a larger asteroid and return it to this same orbit. A preliminary set of mission objectives includes opportunities for planetary defense deflection demonstrations. This brief chapter describes the mission concepts currently under examination in preformulation, including aspects and potential applications to planetary defense.

Keywords Asteroid redirect mission; Asteroid redirect mission robotic concepts; Asteroid initiative

Introduction NASA’s Asteroid Initiative was announced in April 2013 and consists of two separate but related activities: the Asteroid Redirect Mission (ARM) and the Asteroid Grand Challenge (AGC). The Asteroid Redirect Mission comprises of three segments: the detection and characterization of candidate near-Earth asteroids for the robotic redirect mission; the robotic rendezvous, capture, and redirection of the whole or part of a selected target asteroid to the Earth-Moon system; and the crewed mission to explore and sample the captured asteroid mass using the SLS and Orion. The Asteroid Grand Challenge is an enhanced and accelerated effort to find all asteroid threats to human populations and to know how to protect our planet against these threats. As of January 1, 2014, 10,576 near-Earth objects (NEOs) have been found, including 94 comets (Chamberlain 2014). Current systems in NASA’s NEO Program include two data processing and analysis nodes: the Minor Planet Center hosted at the Smithsonian Astrophysical Observatory Center for Astrophysics, Cambridge, MA, and the NEO Program office at the Jet Propulsion Laboratory (JPL), Pasadena, CA. Four dedicated NEO search teams support NASA’s observation efforts: the Catalina Sky Survey of the University of Arizona; the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) of the University of Hawaii; the Lincoln Near-Earth Asteroid Research (LINEAR) team at the Massachusetts Institute of Technology Lincoln Laboratory; and the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) space observatory operated for NASA by JPL. The discovery of NEOs in general has slowly increased in rate in

*Email: [email protected] Page 1 of 7

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_46-1 # Springer International Publishing Switzerland (outside the USA) 2014

the last few years. NASA also uses planetary radar from its own Goldstone Deep Space Network facility in California and the Arecibo Radio Telescope Facility in Puerto Rico to provide additional information about NEOs, such as high-precision orbit data, size and shape to within ~2 m, spin rate, and surface roughness. Seventy to 80 NEOs are observed with radar every year. Both aspects of the initiative will utilize enhancements to NASA’s NEO observation activities to accelerate the search for potentially hazardous asteroids and characterize NEOs. The ARM concept was proposed in 2011 during a feasibility study at the Keck Institute for Space Studies (Brophy 2014). Important ongoing activities across NASA’s Human Exploration and Operations, Space Technology, and Science Mission Directorates will be leveraged for the mission, including searching for potentially hazardous asteroids, advancing high-power solar electric propulsion, and developing the high-capacity SLS rocket and the Orion multipurpose crew vehicle. The robotic segment will demonstrate interaction with low-gravity, noncooperative targets along with high-power and lifelong solar electric propulsion (SEP) for cargo delivery and extensibility to human missions. The human part of the mission planned for the mid-2020s will also utilize advanced technologies and systems for rendezvous and extravehicular activities (EVA), the International Docking System, and integrated vehicle stack operations. The ARM involves sending a high-efficiency (ISP 3000 s), high-power (40 kW) SEP robotic vehicle that leverages advanced space technology development to rendezvous with a near-Earth asteroid (NEA) and returns asteroidal material to a stable lunar distant retrograde orbit (LDRO) (Strange et al. 2013). Once the retrieved asteroidal material is placed into the LDRO, a two-person crew would launch aboard an Orion capsule to rendezvous and dock with the robotic SEP vehicle at its LDRO position. After docking, the crew would conduct two EVAs to collect asteroid samples and potentially deploy instruments prior to Earth return. The crewed mission will use a lunar gravity assist for both the outbound and inbound trajectories and is anticipated to be about 27–28 days in duration. There are two options for asteroid capture currently under examination: one that captures an entire 2–10-m-mean diameter NEA (Muirhead and Brophy 2014) and another that retrieves a 2–4-m-mean diameter boulder from a 100+-meter class NEA (Mazenek et al. 2014). Both robotic segment options include potential slow-push planetary defense demonstrations of NEA deflection techniques, which could include ion beam deflection, gravity tractor, and/or enhanced gravity tractor (in the case of the boulder retrieval).

NEA Observations NASA’s NEA discovery enhancements include plans to bring into operation a second colocated 1.8-m Pan-STARRS telescope and to increase the time devoted to NEO searches. NASA is also working to utilize for observing time the Defense Advanced Research Projects Agency Space Surveillance Telescope for NEO detection. The Asteroid Terrestrial-impact Last Alert System (ATLAS) will be an extremely wide-field new survey capability, covering the entire night sky every night, but not as deeply as other systems (Johnson 2013) (see Figs. 1 and 2). In addition to the reactivation of NEOWISE, NASA’s NEO characterization enhancements include increased time on the Goldstone and Arecibo radars for NEO observations, as well as streamlining rapid response capabilities. At the InfraRed Telescope Facility (IRTF), increased on-call time is improving the rapid response capability and instrumentation modifications will be installed for spectroscopy and thermal signatures (Johnson 2013).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_46-1 # Springer International Publishing Switzerland (outside the USA) 2014

Total Discovered

Near-Earth Asteroids Total Discovered per Size Bin 3000

3000

2500

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1500

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500

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0 30

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Fig. 1 Known NEA population by size bins as of January 1, 2014 (Credit: Chamberlain 2014)

Near-Earth Asteroid Discoveries All Asteroids

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LINEAR NEAT Spacewatch LONEOS Catalina Pan-STARRS NEOWISE all others

600 500 400

300

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0 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 19 19 19 19 19 20 20 20 20 20 20 20 20 20 20 20 20 20 20

Half Year Intervals

Fig. 2 NEAs discovered by observation sites as of January 1, 2014 (Credit: Chamberlain 2014)

The defined nomenclature for asteroid target selection for the ARM includes four tiers. A “potential candidate” is one for which orbit parameters satisfy the rough constraints on launch and return dates, and absolute magnitude indicates the size lies roughly in the right range. A candidate is “characterizable” when it approaches the Earth (or the Spitzer Space Telescope) close enough and with suitable enough observing geometry that it can be adequately characterized. A “valid candidate” is one for which detailed mission design has been performed for feasible launch and return dates, yielding a maximum returnable mass, and physical properties have been

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_46-1 # Springer International Publishing Switzerland (outside the USA) 2014

Fig. 3 Conceptual drawing of the robotic flight system (Credit: NASA)

characterized and lie within acceptable ranges to achieve mission goals. A “selectable target” meets programmatic constraints (e.g., on achievable schedule and minimum return size) and has identified but manageable risks.

Asteroid Redirect Mission Robotic Capture Concept Summary NASA has examined two robotic mission concepts for the ARM, both of which utilize a highefficiency (Isp 3000 s), high-power (40 kW) SEP-based robotic spacecraft to return a cohesive asteroid mass to a stable LDRO. The flight system is largely common to both mission concepts and several permutations of these two concepts exist. The SEP module consists of large solar arrays, xenon propellant tanks, and power processing units. The mission module contains the spacecraft attitude control system, the communication and data handling system, the communications system, the power system, and the thermal control system. The capture system could be a deployable structure that is either an inflatable bag that captures an entire small asteroid or robotic manipulators that remove a boulder from an asteroid’s surface. Integrated navigational sensors used during asteroid rendezvous, proximity operations, and capture could be located on the mission module or capture system. A docking mechanism attached to the aft end of the robotic spacecraft will allow it to dock with the Orion spacecraft. Figure 3 presents a concept drawing of the robotic flight system (Dr. Paul Chodas, Jet Propulsion Laboratory, personal communication). The robotic spacecraft will demonstrate high-power, long-life SEP technology in deep space. The mission concepts call for at least 6 years of deep-space flight. The flight system concept includes four Hall thrusters operating at approximately 10 kW each, 50 kW advanced high-power solar arrays, and approximately 10 tons of xenon propellant. This flight system is envisioned to serve as a building block for future exploration, i.e., it will have a design scalable up to 150 kW, enabling future versions to maneuver larger masses into interplanetary space, such as habitation modules or consumable cargo. The component and system capabilities emerging from this development effort could become standard for the SEP industry.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_46-1 # Springer International Publishing Switzerland (outside the USA) 2014

Asteroid Redirect Mission Robotic Capture Concept A One asteroid capture option, “concept A,” for the robotic capture segment involves a small single NEA, which has a mean diameter of 10 m or less and a mass of less than 1,000 tons. Here, the SEP-based robotic spacecraft will rendezvous with the small rotating NEA and match its motion and then deploy an inflatable system to envelop and “capture” the asteroid, provided that it is not spinning too fast or composed of materials that prohibit capture. The orbits of the potential asteroid targets are such that the robotic spacecraft would nudge them over time spans on the order of 2–4 years into the desired capture orbit around the Moon. After capture, the spacecraft will despin the small asteroid using the reaction control systems and maneuvers it using SEP to a stable, crew-accessible LDRO. For concept A, the NEA used for the reference mission concept design is 2009 BD, which is estimated to be less than 145 tons. There are seven other small asteroids identified as potential candidates for this option: 2007 UN12, 2008 EA9, 2010 UE51, 2013 LE7, 2009 BD, 2013 PZ6, and 2011 MD (Dr. Paul Chodas, Jet Propulsion Laboratory, personal communication). These asteroids could be put into NASA’s desired LDRO between 2020 and 2024. Mission concept A is reliant on the NEO Program to identify a selectable target. A demonstration of ion beam deflection can be accomplished through mission concept A by using the SEP system to impart thrust directly onto the asteroid. The spacecraft would use its reaction control system or flip-turns to maintain position. Current calculations indicate that for an asteroid less than 500 t, the concept flight system will impact 1 mm/s change in velocity in less than an hour (Mr. Brian Muirhead, Jet Propulsion Laboratory, personal communication).

Asteroid Redirect Mission Robotic Capture Concept B Another capture option, “concept B,” for the robotic segment involves a larger NEA, which is 50–100 m in diameter or larger, and acquisition of a 2–4-m-diameter coherent boulder with mass approximately 10–70 tons (Mr. Dan Mazanek, NASA Langley Research Center, personal communication). This concept utilizes the SEP-based spacecraft and robotic arms to capture a boulder and return it to the same stable, crew-accessible LDRO. This mission leverages data from previous robotic asteroid missions and is enhanced by the NEO Program. Here, the SEP-based robotic spacecraft will perform approach and flyby operations and in situ characterization of the asteroid. This capture concept assumes 44 days to verify and refine the shape, spin, and gravity models of the asteroid and obtain centimeter-scale imagery of the majority of the surface. Rendezvous with the larger rotating NEA includes two dry-run operations for up to three sites to refine local gravity, verify navigation, and obtain sub-centimeter-scale imagery prior to a collection attempt. The concept allows for up to five boulder-collection attempts to provide contingency against surface and boulder anomalies. Larger asteroids from which boulder-sized samples could be collected and redirected are: Itokawa, a sample of which was returned to Earth in 2010 under Japan’s Hayabusa mission; Bennu, from which NASA’s Osiris-REx mission, launching in 2016, plans to study and return a small sample to Earth in 2023; 1999 JU3; 2008 EV5; 2011 UW158; and 2009 DL46 (Dr. Paul Chodas, Jet Propulsion Laboratory, personal communication). The candidate object used for the conceptual design of mission concept B is Itokawa. A 2019 launch of the concept spacecraft could return a 19-ton boulder to the LDRO in 2025.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_46-1 # Springer International Publishing Switzerland (outside the USA) 2014

A demonstration of gravity-tractor deflection can be accomplished through the mission concept B by using the gravity attraction of the robotic spacecraft to change the velocity vector of the asteroid. This concept of operations provides 260 days for operations and proper Earth-Itokawa alignment to verify deflection. This concept could also accommodate an enhanced gravity-tractor demonstration using the acquired boulder to significantly increase the robotic spacecraft’s mass, which would be planned for an estimated 180 days of mission operations, with 60 days required for measurable deflection (Mr. Dan Mazanek, NASA Langley Research Center, personal communication).

Asteroid Redirect Crewed Mission Concept Once the asteroid is returned to the stable LDRO in cislunar space, NASA will send two crew members in the Orion vehicle, launched atop the SLS, to study, explore, and sample it. The versatile Orion spacecraft will serve as the in-space crew transportation vehicle, habitat, and airlock for this mission. It will rendezvous and dock with the asteroid-carrying spacecraft to demonstrate early human exploration capabilities including longer duration operations in deep space, rendezvous and proximity operations, life support, and EVA capabilities. Two four-hour EVAs are planned to explore, select, and obtain samples using a variety of sample collection techniques such as core drilling into the asteroid and using sample containers to collect loose material. Once the samples are obtained, the crew will ingress Orion, repressurize the spacecraft, and return the samples to Earth with an entry into the Pacific Ocean off the coast of California.

Conclusion NASA is in the early stages of formulation for the Asteroid Redirect Mission, which will draw upon key ongoing activities across the agency. One of the primary objectives of the Asteroid Redirect Mission is to enhance the detection and observation of near-Earth asteroids. These enhancements are designed to increase the search for potentially hazardous asteroids for planetary defense and characterization of all potential mission candidates possible within the range of the assets. Substantial progress has been made to examine two approaches to the Asteroid Redirect Robotic Mission: one to redirect a small asteroid to a lunar distant retrograde orbit and another to extract a coherent mass from a larger asteroid and return it to this same orbit. NASA is examining opportunities for planetary defense deflection demonstrations in both approaches.

References Brophy J (2012) Asteroid retrieval feasibility study. Keck Institute for Space studies report Chamberlain A (2014) Near earth asteroid discovery statistics. Near Earth Object Program website. www.neo.jpl.nasa.gov/stats/ Johnson L (2013) NASA near earth object observation program. Presented at the asteroid initiative ideas synthesis Mazenek D et al (2014) Asteroid redirect robotic mission: alternate concept overview. American Institute of Aeronautics and Astronautics, Space 2014 conference, San Diego

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Muirhead B, Brophy J (2014) Asteroid redirect robotic mission feasibility study. Presented at IEEE aerospace conference, Big Sky Strange N et al (2013) Overview of mission design for NASA asteroid redirect robotic mission concept. Presented at the 33rd international electric propulsion conference, The George Washington University, Washington, DC

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_49-1 # Springer International Publishing Switzerland 2014

NEO Discovery and Follow-Up Surveys Donald K. Yeomans* Jet Propulsion Laboratory, Pasadena, CA, USA

Abstract The search for near-Earth objects (NEOs) has been ongoing since the 1970s, but sophisticated search efforts, using modern CCD detectors and computer-aided search efforts, have only been in place since the 1990s. While there are a number of important international contributors to the NEO observational program, including the European Space Agency, NASA provides the primary support for the NEO discovery surveys, the follow-up observational activities, and the NEO physical characterizations observations. NASA also provides support for the Minor Planet Center in Cambridge, MA, and the NEO Program Office at JPL. Currently, the primary ground-based discovery surveys are the Catalina Sky Survey operation near Tucson, Arizona, and the Pan-STARRS group operating on Haleakala on Maui, Hawaii. NEOWISE, an Earth orbital 0.4-m telescope operating in the near infrared, plans to continue NEO discoveries and physical characterizations through 2015.

Keywords Near-Earth objects; Asteroids; Comets; NEOWISE; Pan-STARRS; Catalina Sky Survey; LINEAR; Spacewatch; NEAT; LONEOS

Introduction There are a number of NASA-supported near-Earth object (NEO) discovery teams currently in operation. The early efforts to discover NEOs relied upon the comparison of photographic films of the same region of the sky taken several minutes apart. Early discovery techniques included blink comparators and stereomicroscopes to examine the photographic images. The vast majority of the objects recorded upon these films were stars and galaxies, and their images were located in the same relative position on these films. Because a moving NEO would be in a slightly different position on each photograph and the background stars and galaxies were not, the NEOs appeared to jump back and forth when each image, in turn, was quickly viewed through a so-called blink comparator. Alternately, the NEO’s image appeared to “rise” above the background stars when two different and slightly offset images were viewed with a special stereo-viewing microscope. A number of pioneering photographic efforts were carried out led by Eleanor Helin, Gene and Carolyn Shoemaker, Bob McMillan, and Tom Gehrels. Beginning in 1973, Helin and Gene Shoemaker began using the 18-in. Palomar Schmidt telescope in southern California for finding NEOs. Carolyn Shoemaker then joined this team in the early 1980s. In 1983, McMillan and Gehrels began using the 0.9-m aperture Steward Observatory telescope near Tucson, Arizona, for NEO

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searches. By 1984, this so-called Spacewatch telescope was being used full time for NEO searches, and it employed, for the first time, a charge-coupled device (CCD). For more details concerning these pioneering NEO search efforts, see Yeomans (2013, Chapter 5). All of the current NEO discovery teams use the so-called charge-coupled devices (CCDs) rather than photographic images. These CCD cameras are similar in design to those used in cell phones and they record images digitally in many electronic picture elements (pixels). The length and width of a CCD detector is usually given in terms of pixel elements. A fairly common astronomical CCD detector might have dimensions of about 2,000
2,000 pixels (2k
2k). While the CCD technology allows today’s detectors to be more sensitive and accurate than the older photographic images, the modern discovery technique itself is rather similar. Separated by several minutes, three or more CCD images are taken of the same region of the sky. These images are then compared to see if any NEOs have systematically moved to different positions from one image to the next. For a newly discovered NEO, the separation of the object’s location from one image to the next, the direction it appears to be traveling, and its brightness are helpful in identifying how close the object was to the Earth, its size and general orbital characteristics. For example, an object that appears to be moving very rapidly from one image to the next is almost certainly very close to the Earth. Sophisticated computer-aided analyses of the CCD images have replaced the older, manual detection techniques, but oftentimes, a new NEO discovery is still verified using the human eye. Not surprisingly, discovery teams who search the largest volume of sky each month will have the most success in finding new NEOs. How much sky each telescope covers per month will depend upon a number of factors including the number of clear nights available for observing, the telescope aperture, the sensitivity and efficiency of the CCD detector, and the field of view of the telescope. As well as searching wide areas of sky each night, it is important for search teams to extend their searches to greater and greater distances from the Earth or, in other words, go to fainter limiting magnitudes. In 1998, NASA established a goal to discover 90 % of the NEOs larger than 1 km in diameter, and in 2005, Congress extended that goal to include 90 % of the NEOs larger than 140 m. There are thought to be about 1,000 NEAs larger than 1 km and roughly 15,000 larger than 140 m. The progress toward meeting these goals can be monitored on the NEO Discovery Statistics page (neo. jpl.nasa.gov/stats/). Since NASA’s initiation of the NEO observations program in 1998, near-Earth object (NEO) surveys have been extremely successful finding more than 90 % of the near-Earth asteroids (NEAs) larger than 1 km and a good fraction of the NEOs larger than 140 m. The vast majority of NEO discoveries have been due to NASA-supported ground-based telescopic surveys including the Catalina Sky Survey (CSS) and Spacewatch near Tucson, Arizona; the LINEAR project near Socorro, New Mexico; the Pan-STARRS on Haleakala, Maui, Hawaii; the LONEOS near Flagstaff, Arizona; and the NEAT project run by the Jet Propulsion Laboratory (JPL) in La Canada, California. The NEAT and LONEOS surveys terminated operations in 2007 and 2008, respectively, and the Spacewatch effort has transitioned from a discovery and follow-up facility to one that concentrates upon follow-up observations. NEO discovery and physical characterization observations are also being successfully carried out by the so-called NEOWISE program, which employs a 0.4-m telescope on the Wide-field Infrared Survey Explorer (WISE) spacecraft in the Earth orbit.

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NEAT Beginning in 1995 and continuing for several years, the JPL Near-Earth Asteroid Tracking (NEAT) program, in cooperation with the Air Force, ran a 1-m then a 1.2-m Air Force telescope on Hawaii’s Mt. Haleakala for survey purposes. In 2001, the NEAT program began a transition to using the 1.2-m Schmidt telescope at Palomar Mountain in southern California. Begun under the direction of Eleanor Helin, the Principal Investigator, and David Rabinowitz, the NEAT program was led successively by Steve Pravdo and Ray Bambery at JPL and then by Caltech’s Mike Brown before ceasing operations in 2007. JPL’s Ken Lawrence was active in the data reduction process throughout the 12-year NEAT survey. The combined NEAT program found 442 NEOs with about 63 being 1 km or larger.

LONEOS Ted Bowell and Larry Wasserman ran the Lowell Observatory NEO Survey (LONEOS) from 1993 through 2008 using a Lowell Observatory 0.6-m Schmidt telescope at Anderson Mesa observing station. Brian Skiff and Bruce Koehn were also instrumental in the LONEOS effort. LONEOS also collected four images of each field to search for moving objects. Due to competition with other observing facilities with larger telescopes, LONEOS saw their productivity decline and first switched their primary objective to making photometric observations of NEOs and then ceased operations in 2008. During its operational period, LONEOS discovered 288 NEOs, including about 42 that are 1 km or larger.

Spacewatch Beginning in 1980, and initially under the leadership of Tom Gehrels and Bob McMillan, the 0.9-m, Newtonian f/3 Steward Observatory Spacewatch telescope has been used full time for surveying comets and asteroids. First installed on the University of Arizona campus in 1923, this telescope was moved to Kitt Peak, Arizona, in 1963. In 1983, this instrument was donated to the Spacewatch team, and in 1984 it then became the first telescope to detect and discover asteroids and comets with electronic CCD detectors, as opposed to photographic plates or film. The initial 320
512 CCD detector used from 1984 to 1988 was replaced with a large-format 2,048
2,048 CCD detector used during the interval 1989–1992. This system had a field width of 38 arc minutes and a limiting visual magnitude (V) of 20.5. The sensitivity of the CCD (quantum efficiency) was doubled to 70 % in 1992 when a thinned 2,048
2,048 CCD was installed. The 0.9m telescope was used about 23 nights per month to search for near-Earth objects. By locking the right ascension axis in place and allowing the star fields to drift through its field of view (“driftscan”) while the CCD detector was constantly read out, this telescope covered about 200 degrees of sky each month down to V ¼ 21. Each region of sky was scanned three times, about 30 min apart, to examine which objects had moved relative to the background stars. In 2001, the Spacewatch group began observing with a newly built 1.8-m aperture telescope designed for follow-up of asteroids as they fade from view following discovery. In late 2002, a largemosaic CCD camera (four 4,608
2,048 CCDs) was added to the 0.9 m, and the optical system was replaced to allow a wider field of view (2.9 square degrees). The 0.9-m design now operates in the “stare” mode rather than in the previous “drift-scan” mode, whereas the 1.8-m telescope continued to be operated in the “drift-scan” mode until 2011. From 2005 through 2008 the Spacewatch group Page 3 of 10

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gradually shifted their emphasis from NEO discoveries to the follow-up observations that are critical for securing accurate orbits. In October 2011 the imaging detector on the 1.8-m telescope was replaced with a “staring” CCD with finer pixel resolution, fast readout, and flatter focus. With it, 54 % more observations of NEOs are being made, with astrometric residuals half the size as before. The Spacewatch 1.8-m telescope is currently among the world’s leaders in faint object follow-up, especially in terms of the critical follow-up of the most important and under-observed objects. The Spacewatch team was a pioneer in digital detection of NEOs. They discovered the first NEO on digital frames in 1989 and had the first automatic (computer) discovery in 1990. They led the efforts to modernize and automate the discovery and follow-up of NEOs. The Spacewatch team has automated the usage of both the 0.9- and 1.8-m telescopes for faint object follow-up observations; both telescopes can be run from a single control room by a single observer.

The Current Discovery Surveys The Catalina Sky Survey (CSS), based at the University of Arizona, is a very successful discovery program, an achievement that is due, in large part, to their comprehensive sky coverage, continuing improvement and human attention to potential discovery images, and on-site follow-up observation capabilities. In 2013 alone, CSS discovered more than 603 NEOs. Some 20 % of CSS observing time is devoted to the post-discovery, follow-up observations that allow the object’s orbit to become secure. The Catalina Sky Survey (CSS) has a long history of NEO discovery and minor planet surveying. The original telescope configuration was a 0.41-m f/3 Schmidt design, with film loading and telescope positioning and pointing all done by human effort. Due to tracking errors, all exposures longer than 30 s necessitated manual guiding. During 1993–1996, CSS was operated by T. Spahr and C. Hergenrother as a photographic survey. During 1997–1998, S. Larson procured a large-format CCD, built and installed a camera, and funded a small pilot study using this instrument. During the fall of 1998, the observing team discovered a handful of NEOs, indicating that the telescope had the potential to contribute to the survey for NEOs. Because of the large data volume, moving-object detection software was required and was created during the winter of 1998 and the spring of 1999. This software utilized the SExtractor (Bertin and Arnouts 1996) object detection package, as well as custom-written software. The software took the novel approach of requiring four detections of a moving object to confirm the detection. The CSS team also took a careful approach dithering the telescope (offsetting from the exact pointing by a small fraction between successive exposures) in such a way that bad pixels or image defects could never have linear motion and mimic real detections. CSS also followed the Spacewatch team’s approach of having trained observers validate detections before submitting them to the MPC. The combination of these techniques allowed the CSS team to push much deeper into the background noise and allowed a relatively small telescope to be competitive with their much larger brethren. The original CSS telescope and optical system could cover 500 square degrees per night with 2.5 arc seconds pixels to visual magnitude V  19.5 During 2003–2004, the Catalina Schmidt was upgraded to a f/1.8, 0.7-m telescope, resulting in a faint limit of V  20.0. The resulting field of view is 8.2 square degrees, which allows a nightly coverage of 1,000–1,500 square degrees. The change to this telescope vaulted the CSS program into the lead in terms of annual discoveries. In 2004–2005, the CSS team procured a 4k
4k CCD that delivers a 1.2 sq. deg. field of view, built a prime focus camera, and installed this on the Mount Lemmon 1.5-m telescope owned by the Page 4 of 10

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University of Arizona. Under good conditions, the faint limit is V  21.5, and on an average night 200 square degrees can be surveyed. This survey excels at finding very small objects that are very close to the Earth and demonstrates the need to shift to larger and larger optical systems in order to complete the inventory of smaller, yet still threatening, NEOs. The CSS found the only two Earth impactors discovered in advance of their impacts (i.e., 2008 TC3 and 2014 AA) as well as the 5-m sized mini moon that was in a temporary Earth orbit between September 2006 and June 2007. The 0.5-m Uppsala Schmidt telescope at Siding Spring, Australia, was operated by the CSS for several years when it was the only NEO survey in the southern hemisphere. However, a number of unavoidable factors resulted in support for this survey site being dropped in 2013. The Australian dollar became much stronger against the US dollar when compared to when the survey was established, and the modest aperture size and moderate field of view restricted the number of discoveries compared to the northern hemisphere assets run by the Catalina Sky Survey. The spiraling costs and relatively modest discovery rate forced a tough, but necessary, decision to drop support to the Siding Spring survey. Each of the cameras from Catalina, Mt. Lemmon, and Siding Spring is identical thinned 4 k backilluminated detectors packaged by Spectral Instruments, Inc. of Tucson, AZ, and cooled with a closed-cycle cryocooler. Keeping all of these cameras the same has minimized development, maintenance, and operations costs. In 2014, the Catalina Schmidt will be upgraded to a larger CCD array that will increase its field of view from 8.2 to 19.6 square degrees, and the Mt. Lemmon 1.5-m telescope will be upgraded to a larger CCD array that will increase its field of view from 1.2 to 5 square degrees. The Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) discovery telescope, run by the University of Hawaii’s Institute for Astronomy, is a 1.8-m telescope on Haleakala in Maui, Hawaii. It has a very large camera with a 7 square degree field of view. The first NEO discoveries by Pan-STARRS were recorded in the second half of 2010, but only about 5 % of the observing time was devoted to NEO discoveries. Beginning in November 2012, the time dedicated to NEO discovery was increased to 11 %. In addition, 56 % of the observing time was used for a 3-pi survey observing a wide variety of astrophysical transient objects using three color filters. This survey is also executed in a manner that leads to the discovery of NEOs. Beginning in April 2014, and due to the demise of the science consortium support to Pan-STARRS, the time devoted to NEO searches was increased to 100 %. A strength of Pan-STARRS (PS) lies in having the highest faint limit of any active survey, detecting objects routinely to V  21.5–22 in good conditions. This allows the team to detect NEOs, particularly larger objects, moving slowly and detectable but too faint for all other systems. PS has had considerable success observing areas of sky near the sun where sizable potential impactors would be expected (Chesley and Spahr 2004) or observing at fairly small solar elongations (10 mm 45,919 4.12e + 09 1.13e + 09 22,241 30,162 4.98e + 12 1.18e + 13 1.62e + 12 2.70e + 13 4.53e + 13

>100 mm 45,919 3.84e + 08 1.17e + 08 22,241 30,162 2.33e + 12 – 2.28e + 11 1.08e + 12 3.64e + 12

>1 mm 31,139 1.53e + 4.46e + 22,241 30,162 1.39e + – – 8.00e + 1.67e +

07 06

08

06 08

>1 cm 5,827 433,466 92,677 15,790 18,410 177,914 – – – 744,084

>10 cm 5,814 14,719 2,927 5,750 – – – – – 29,210

>1 m 4,174 432 63 773 – – – – – 5,442

debris population down to the cm-size regime (see Table 4). The most significant breakup-related, relative increase of the catalog population occurred in 1961, when the first accidental explosion in space of an Ablestar injection stage more than tripled the catalog population from 110 to almost 400. The most significant absolute growth of the catalog so far occurred in January 2007, when the Feng Yun 1C kinetic ASAT test produced some 3,400 trackable fragments (+34 %), and in February 2009, when the accidental collision between Cosmos 2251 and Iridium 33 generated another 2,200 fragments (+22 %). At sub-catalog sizes residues from solid rocket motor (SRM) firings become important. The number of on-orbit solid rocket motor firings up to 2013 was on the order of 1,100, with peak rates of up to 47 events per year and a mean annual rate of 23.5. The injection orbits where SRMs were applied are to 80 % associated with US missions. The size of the solid motors, in terms of propellant capacity, covers a wide range. The most frequently used SRMs are the Star 37 motors, with a propellant mass of 1,067 kg, used, for instance, as final stage of Delta launchers to deploy GPS/Navstar payloads; the Payload Assist Module PAM-D, with 2,011 kg, also used as Delta Page 9 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

final stage, for instance, for GTO injections; and the Inert Upper Stage (IUS), deployed from Titan IV or Space Shuttle, for instance, to inject payloads into GTO with a first stage of 9,709 kg and subsequently deliver the payload into a circular GEO by a second stage of 2,722 kg. Another powerful SRM engine, HS-601 with 4,267 kg, is used by Long March LM-2E launchers both for LEO and GTO payload injections. SRM combustion residues are mainly composed of aluminum oxide and residues of motor liner material. Aluminum powder is added to most solid fuels, typically with a mass fraction of 18 %, to stabilize the combustion process and improve the motor performance. It is assumed that about 99 % thereof is continuously ejected with the exhaust stream during the main thrust phase in the form of Al2O3 dust of diameters largely within 1 mm  d  50 mm. Due to design constraints, many solid motors have nozzles protruding into the burn chamber, causing cavities around the nozzle throats. During the burn phase, trapped Al2O3, molten aluminum droplets, and parts of released thermal insulation liner material can cumulate in this pool and form slag particles which can grow to sizes of typically 0.1 mm  d  30 mm. These slag particles are released at the end of the main thrust phase, as the internal motor pressure decreases. It can be assumed that during more than 1,100 SRM firings, more than 1,000 tons of propellant were released into space of which approximately 320 tons were Al2O3 dust particles and 4 tons were slag particles formed of Al2O3, metallic aluminum, and motor liner material. Due to orbital perturbations and their different effects on mm-size dust and cm-size slag, merely 1 ton of Al2O3 dust and 3 tons of SRM slag particles are believed to be still on orbit. Apart from more than 1,000 orbit insertion burns, there were also several hundred SRM burns to deorbit objects in a controlled fashion. These deorbit burns were almost exclusively performed for Russian reconnaissance satellites at very low altitudes, and the resulting SRM combustion products had a correspondingly low orbit lifetime. However, some in situ measurements (mainly from returned space hardware) show temporal increases in small-particle impact rates due to these events. At sizes of 1 mm  d 1 cm, SRM combustion residues dominate the space debris environment (see Table 4). Apart from intact objects, fragmentation debris, and SRM residues, there are other contributors to the space debris population: (1) sodium-potassium (NaK) coolant released from 16 Russian RORSATs as they ejected their reactor cores in the 1980s, (2) multilayer insulation (MLI) material that is unintentionally released by spacecraft or rocket stages, (3) ejecta material that is released by small-particle impacts on surfaces of spacecraft and orbital stages, and (4) degradation products that are released by aging surfaces of spacecraft and orbital stages. The debris mass contribution from these sources is much less than 1 % of the overall on-orbit mass, and they are either too small in numbers (NaK, MLI) or too small in size (surface ejecta and degradation products) to constitute a significant risk for space missions. Today’s population of trackable and non-trackable objects can be reproduced by space debris environment models, such as ESA’s MASTER-2009 model (Flegel 2010). Such models consider historic launch and release events, known in-orbit fragmentations, known solid rocket motor-firing events, intentional releases of NaK coolant liquid from Buk reactors of Russian RORSAT satellites, unintentional releases of surface degradation products (MLI and paint flakes), and the generation of ejecta and spall by surface impacts. Table 4 lists the resulting debris sources and their contributions to the MASTER-2009 population at the reference epoch of May 2009 for the applicable size regime larger than 1 mm. From the risk point of view, more than 160 million particles larger than 1 mm, at typical LEO collision velocities of 10–14 km s1, can disable sensitive satellite subsystems, more than 740,000 particles larger than 1 cm can render a spacecraft dysfunctional, and almost 30,000 objects larger than 10 cm are likely to cause a catastrophic breakup of a satellite or orbital stage.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

Fig. 6 Spatial density distribution of MASTER-2009 objects of d > 10 cm, in LEO to GEO altitudes, discriminated by sources (Flegel 2010)

Figure 6 shows the altitude distribution of MASTER-2009 objects larger than 10 cm in terms of resulting spatial densities (in objects/km3). The contributing debris sources at these sizes are explosion and collision fragments, intact objects, and lightweight sheets of MLI. Highest concentrations are in the LEO regime, between 750 and 900 km, with almost equal contributions from explosion fragments, collision fragments, and intact objects. In general, however, explosion fragments dominate the LEO and GEO regions, with GEO object concentrations about three orders of magnitude below the LEO maximum. When going to a 1 cm-size threshold, additional source terms come in, including NaK droplets and solid rocket motor slag, while launch and mission-related objects start playing a minor role. Figure 7 shows the individual contributions as a function of altitude. Reducing the size threshold further to 1 mm leads to the addition of ejecta particles, as shown in Fig. 8. With the decrease of the debris sizes from 10 cm to 1 mm, the enveloping curve of spatial densities tends to flatten, due to an increasing share of particles on eccentric orbits with a wider distribution over altitudes. As a consequence, the relative magnitude of the GEO concentration peak with respect to the LEO maximum reduces from 3 to less than 2 magnitudes. One cause of the increase of orbit eccentricities with decreasing object sizes lies in the area-to-mass ratio that drives solar radiation pressure and airdrag forces and is inversely proportional to the object diameter. This effect leads to a decay of small-size objects that have extended dwell times at altitudes within the denser Earth atmosphere. Spatial object densities are an essential input to debris collision risk assessments. The statistical behavior of the orbital debris population can be well represented by the laws of kinetic gas theory. Hence, the number of collisions c encountered by an object of collision cross section Ac, moving through a stationary debris medium of uniform particle density D, at a constant relative velocity Dv, during a propagation time interval Dt is given by c ¼ Dv D Ac Dt

(1)

where F ¼ Dv D is the impact flux (in units of m2 s1) and F ¼ F Dt is the impact fluence (in units

Page 11 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

Fig. 7 Spatial density distribution of MASTER-2009 objects of d > 1 cm, in LEO to GEO altitudes, discriminated by sources (Flegel 2010)

Fig. 8 Spatial density distribution of MASTER-2009 objects of d > 1 mm, in LEO to GEO altitudes, discriminated by sources (Flegel 2010)

of m2). The collision probability follows a binomial law which can be well approximated by a Poisson distribution, generating the following probability Pi¼n of n impacts and Pi¼0 of no impact: Pi¼n ¼

cn expðcÞ 7! Pi¼0 ¼ expðcÞ n!

(2)

The probability of one or more impacts is hence the complement of no impact, given by

Page 12 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

Pin ¼ P ¼ 1  expðcÞ  c 7! P  Dv D Ac Dt

(3)

The challenging part in the evaluation of this equation is the particle flux F ¼ Dv D. In the MASTER-2009 model 3-dimensional, time-dependent spatial object density distributions are established for a grid of spherical volume elements covering the entire Earth environment from LEO to GEO altitudes. Contributions from each member of the orbital debris population go into this distribution. For each of these objects, the velocity magnitude and direction is retained for each volume element passage. This information is later retrieved to determine relative impact velocities with respect to a target object passing through individual cells of the volume grid (Klinkrad 2006). The resulting impact flux is then determined from a summation over all volume cells that are passed by the target object, with contributions from all debris objects that passed the individual cells. When considering relative velocities between two objects on circular orbits at the same altitude, with the same orbital velocities v, but on different inclinations, then Eq. 4 yields the resulting collision velocity as a function of the impact azimuth A within the local horizontal plane (where A ¼ 0
denotes impacts from the flight direction): Dv  2 v cos ðAÞ

(4)

Since near-circular orbits are dominant for debris of critical sizes, Eq. 4 provides a good approximation of the correlation of impact velocity with impact geometry. It also states that the maximum relative velocity can be twice the orbit velocity, for an approach from the flight direction, and that the minimum relative velocity can be close to zero, for a sideways approach from 90
. Impacts from the rear quadrants can only occur for impactors that travel on eccentric orbits, during their perigee passes. Likewise, impacts from 0
can only occur if the impactor has an orbit with a “complementary inclination” of 180
minus the inclination of the target object. Only in that case can both objects be in the same orbit plane, on counter-rotating orbits, if their ascending orbit nodes are separated by 180
. For typical target orbits defined in Table 5, the mean times between impacts by orbital debris of different sizes are listed in Table 6 for a common reference cross section of 1 m2, assuming a spherical target object. In accordance with spatial densities shown in Figs. 6, 7, and 8, the highest collision risk for any of the selected sample orbits is encountered for ERS-2 on a sun-synchronous orbit of 774 km  789 km at an inclination of 98.5
. Apart from the debris concentration at this altitude, the collision frequency is also driven by the collision velocity (see Eq. 1). For ERS-2 it attains a most probable value of about 14 km s1, which is close to the maximum for two circular orbits at this altitude. Objects that could impact at such velocities are originating from the complimentary inclination band close to 81.4
(¼180
 98.6
; see Figs. 3 and 4). Since all major flux contributions are from inclinations i  65
, the resulting collision velocities are mostly within Table 5 Sample orbits for analyzing space debris collision flux ISS ERS-2 Globalstar GPS GTO GEO

Hp [km] 356 774 1,399 19,997 560 35,782

Ha [km] 364 789 1,401 20,003 35,786 35,790

i [deg] 51.6 98.6 52 55 7 0.1

a [km] 6,738 7,159 7,778 26,378 24,551 42,164

e [–] 0.0006 0.0010 0.0001 0.0001 0.7174 0.0001

o [deg] 0 90 0 0 178 0

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

Table 6 Mean time between impacts of a given debris size for a spherical target of 1 m2 cross section, on sample orbits as defined in Table 5, for a space debris environment according to ESA’s MASTER-2009 model (Flegel 2010) Diameter ISS ERS Globalstar GPS GTO GEO

>0.1 mm 9.0 d 0.7 d 1.7 d 244.8 d 36.8 d 676.3 d

>1 mm 636 y 42.5 y 102 y 10,794 y 2,627 y 18,674 y

>1 cm 41,102 y 1,252 y 9,208 y 1.1e+ 7 y 241,546 y 6.5e+ 6 y

>10 cm 942,507 y 43,783 y 126,550 y 7.2e+ 8 y 4.4e+ 6 y 1.4e+ 8 y

14  2 km s1 at impact azimuth angles –30
 A  +30
(see Eq. 4), with particles mainly originating from breakup events for the size regime larger than 1 cm. The situation changes for the ISS orbit. Its lower altitude goes along with a reduction of the debris flux by about one order of magnitude, and its lower inclination of 51.5
results in a gap of complementary inclination bands at 180
 51.6
¼ 128.4
. The populated inclination bands only start at about 100
. As a consequence, there are no impacts from azimuth angles –15
 A  +15
, and most probable collision velocities are at 10  1 km s1, resulting in approximately 50 % of the impact energy as compared to ERS-2. In contrast to ERS-2, slag residues from SRM firings are dominating the 1 cm debris population for ISS. They mostly reside on highly eccentric orbits of low inclinations, with perigee velocities that allow low-velocity impacts also from rear quadrants of ISS azimuth angles. When looking at a typical geostationary target orbit, then the spatial density of the debris environment as compared to the LEO peak drops by about three orders of magnitude for the 10 cm population and by about two orders of magnitude for the 1 cm population. For the GEO orbit velocity of about 3 km s1, the predicted collision velocities are in the range of 0  v  1 km s1, with a most probable value of 0.8 km s1, caused by old GEO objects that reached a maximum inclination excursion of 15
due to long-periodic orbit perturbations with a period of 53 years. Due to the low relative velocities, the impact azimuth angles are mostly at 80
. There are minor flux contributions from objects on GEO transfer orbits (GTO) and on 12 h Molniya orbits. They have apogee velocities of about 1.5 km s1, causing frontal impacts on the faster GEO objects. There are different ways to mitigate the risk and/or consequences of a collision of an operational spacecraft with a space debris object. For large-size catalog objects, the concept of conjunction event analysis and collision avoidance can be pursued. For sub-catalog debris that cannot be tracked, passive protection measures can be taken. To avoid catastrophic collisions with catalog-size objects of d 10 cm, the ISS operators perform a conjunction event screening on the basis of the US Space Surveillance Network (SSN) catalog. This screening is performed at least three times a day, for 72 hours ahead, in five steps: 1. SSN catalog-based identification of ISS approaches that fall within a 60 km radius (based on limited-accuracy orbit data in two-line element format) 2. Use of more accurate, osculating orbital elements, if the approach falls within 10 km   40 km   40 km (radial  along-track  out-of-plane) 3. Consideration of orbit uncertainties, if the approach falls within 2 km   25 km   25 km 4. Determination of collision probabilities, if the approach falls within 0.75 km   25 km   25 km 5. Decision on an evasive maneuver, if an accepted risk threshold is exceeded (e.g., 1 in 10,000) Page 14 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

In the first 4.5 years of operation, the ISS performed seven debris avoidance maneuvers, with three of them executed by the visiting Space Shuttle. Due to improved procedures, based on more reliable orbit data, the subsequent avoidance maneuver was only 5.5 years later, executed by the attached ATV-1 on August 27, 2008, to avoid a fragment of Cosmos 2421. This fragment was one of approximately 500 cataloged objects generated during three main breakup events in early 2008, just 60 km above the ISS altitude (Johnson 2009). A year of peak ISS collision avoidance activity was noted between April 2011 and April 2012, when ISS performed four evasive maneuvers. Two more conjunction events would have led to a maneuver. However, due to an insufficient reaction time span for a maneuver, the crew had to retreat into the attached Soyuz vehicle, to prepare for an emergency departure in the event of a collision. As is done by NASA for the ISS, ESA has maintained a conjunction event analysis service for their operational satellites (e.g., for ERS-2, Envisat, CryoSat-2, Cluster-2, etc.). Once a day the entire TLE catalog of the US SSN is screened for close conjunctions with the accurately known ESA satellite orbits for 7 days ahead. If the predicted collision probability exceeds a level of 1 in 3,000, then more precise orbit data are obtained for the conjunctor object through the processing of radar data from tasked observations. In most cases, the more accurately know conjunctor orbit with its much reduced error dispersion leads to a maneuver suppression, even if the flyby geometry is unchanged. If, however, the collision probability remains at a level above 1 in 1,000, then a collision avoidance maneuver is initiated by the relevant project team. Envisat, launched in 2002, had to perform five avoidance maneuvers up to December 2009. Due to the Chinese Feng Yun 1C ASAT test in January 2007, and as a result of the collision between Cosmos 2251 and Iridium 33 in February 2009, the debris environment at the Envisat and ERS-2 orbit altitude significantly deteriorated. As a consequence, the overall avoidance maneuver frequency in the year 2010 increased to 9 (4 each for Envisat and ERS-2 and 1 for CryoSat-2). The risk of catastrophic collisions of Envisat with a 10 cm fragment from the Feng Yun 1C and Cosmos 2251/ Iridium 33 breakup events alone increased by +58 % as compared to the rest of the US SSN catalog. The risk of a mission-terminating impact by a 1 cm class debris object even grew by +86 %, as compared with a modeled space debris population prior to these events. In total, ESA satellites performed 22 collision avoidance maneuvers between 2004 and 2012. To protect against non-trackable debris and meteoroids, the ISS has its manned modules covered by stuffed Whipple shields. For ESA’s Columbus module, for instance, they consist of a 2.5 mm bumper and a 4.8 mm back wall, separated by an 11 cm standoff distance. Between the bumper and the back wall, fabric layers of 4 mm Kevlar and 6 mm Nextel sheets are embedded as a “bulletproof vest.” The shields of the ISS manned modules can withstand impacts by objects up to 1.4 cm in size, at velocities on the order of 10 km s1. The related kinetic energy corresponds to a 1.5 ton midsize car hitting at 50 km h1 or to the energy released by an exploding hand grenade. An ISS module of 100 m2 cross section is expected to have impacts from debris objects of d 1 cm at a rate of 1 in 410 years. Meteoroid impacts are negligible in this size regime. For the same module cross section, impacts from objects of d 1 mm will occur at a rate of 1 in 6 months, with a 90 % probability that they originate from meteoroids. Whipple shields rely on impact velocities that are larger than about 6 km s1, in order to break up the impacting object into a cloud of solid, liquid, and gaseous matter that can more easily be withheld by the back wall and intermediate fabrics, due to a wider spreading and time-distributed arrival of the fragment cloud, with a resulting reduction of the pressure peak. While the volume and mass requirements of such shields are prohibitive for normal spacecraft, there are still ways of reducing their impact risk. The Canadian Radarsat, for instance, used lightweight Nextel fabric covers as external protection and rearrangements of sensitive spacecraft subsystems to

Page 15 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

improve the survivability of its 5-year mission by 50–87 %. This gain was achieved for a mass penalty of 0.6 % (+17 kg). In order to increase the safety of US space assets, the US Space Command is upgrading its operational surveillance network. In particular, the replacement of the UHF-based surveillance fence that extends along the 33rd parallel across the USA to an S-band system is expected to allow a catalog maintenance down to 2 cm sizes at the ISS altitude. This could increase the SSN catalog size to more than 100,000 objects. With the full orbit knowledge of these objects, one would be in a position to close the gap between avoidable and shieldable objects for ISS and hence significantly improve the on-orbit safety for manned space flight. The space debris environment at critical sizes above 10 cm has in the past been dominated by explosion fragments and by dysfunctional but intact remnants of previous missions. Collisions played a minor role until the Feng Yun 1C ASAT test in 2007 and the accidental collision between Cosmos 2251 and Iridium 33 in 2009. By 2010 these two events alone accounted for almost 40 % of the US SSN catalog. In order to curtail the growth rate of hazardous space debris, particularly in the LEO regime, the international space community has identified and adopted a set of space debris mitigation measures. The main categories of recommendations can be summarized as follows: • • • • •

Reduction of mission-related objects Prevention of on-orbit explosions (passivation) Limitation of nonexplosive release events Collision avoidance between trackable objects and operational assets Post-mission disposal of space systems

Mission-related objects (MROs) contribute 6 % to the trackable catalog population, with 72 % of these related to launch systems and 28 % related to payloads. MROs, also referred to as operational debris, are defined as objects released during nominal operations by both spacecraft and rocket bodies. This includes debris from launcher staging and payload separation (such as adapters, shrouds, and clamp bands) and objects released during spacecraft deployment and commissioning (such as parts of explosive bolts, solar array latches, and lens covers). Most of these objects are released with low relative velocities, and so they remain in close proximity to the operational orbit of the source object. The release of MROs can be limited by system design. The best method of reducing the population of MROs is not to produce the objects in the first instance. This is reflected in most debris mitigation standards through recommendations to minimize or to avoid the use of debris-generating systems (e.g., yo-yo despinners, nozzle closures of propulsion systems, protective lens covers, etc.). System design is also encouraged to ensure that released parts (e.g., antenna deployment mechanisms, protective covers, explosive bolts, ullage motors, heat shields, etc.) are retained with the primary object. This can be achieved through the use of lanyards, sliding or hinged covers, and special catchment devices. Moreover, materials and basic system technologies (e.g., tanks, surface materials, structures, etc.) should be selected such that they are resistant to environmental degradation (e.g., aging by radiation, atomic oxygen and microparticle impact erosion, and thermal cycling). Explosions of spacecraft and upper stages in orbit have been the major source of debris in the past, with some 250 events up to 2013, at a mean annual rate of about 5. These failures, which caused at least 4,000 cataloged fragments, might have been avoided, if onboard passivation techniques had been employed. Such procedures are a standard on many of today’s launchers, and so far there are no recorded explosions of successfully passivated orbital stages. End-of-life (EOL) passivation was first considered as a design requirement at the beginning of the 1980s. All upper stages and Page 16 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

spacecraft which were launched before then, and which are still in orbit, continue to pose an explosion hazard (a Titan III-C Transtage launched in 1967 exploded after 27 years in orbit). Hence, there is a significant number of latent explosion sources still on orbit. Space debris mitigation standards recommend that all onboard reservoirs of stored energy (e.g., propellants, pressurants, batteries, momentum control gyros) should be permanently depleted when they are no longer required for any nominal or post-mission operations. The following passivation aspects should be considered: • Idle burn or venting of residual propellants, with valves left open • Venting of all pressure systems and/or activation of pressure relief mechanisms to avoid explosions due to external heating • Discharge of batteries, shutdown of charging lines, and maintenance of a permanent discharge state • Deactivation of range safety systems • Dissipation of energy contained in momentum control gyros Fuel depletion or “idle” burns of orbital stages may be performed such that the resulting thrust leads to a braking maneuver, leaving the stage in a reduced-lifetime orbit. The residual lifetime should be less than 25 years to be compliant with international recommendations for space debris mitigation. The class of non-breakup release events includes residues from SRM firings (slag and dust), sodium-potassium droplets that were generated during RORSAT reactor core ejections, or surface degradation products that are caused by aging paint coatings or multilayer insulations (MLI). All of these debris sources can be reduced or even suppressed in total through design measures. Collision avoidance, as another debris mitigation measure, is nowadays implemented by many space operators for their operational payloads. This concept, however, can only be applied to about 5 % of the catalog population, assuming that about 1,000 of the on-orbit payloads in 2013 were operational, of which about 80 % could be maneuvered. Hence, future collisions will most often occur between uncontrollable debris objects. To reduce the number of catastrophic collisions between large, intact, but nonoperational objects, the use of ground-based lasers is investigated. If a close conjunction is predicted, then a radar-guided laser beam could ablate material from one of the objects to impart a momentum that could sufficiently alter the flyby distance to a safe level. In 2013 the mean time between two catastrophic collisions in the LEO region was on the order of 5 years. One way of reducing future collision rates is through post-mission disposal measures, i.e., through mass removal of (still) active space assets. International guidelines recommend removing spacecraft and orbital stages after their mission completion, in particular from the densely populated LEO regime and from the unique GEO ring. For GEO spacecraft disposals, an orbit raise to a graveyard region at approximately 300 km above GEO is recommended. The magnitude of the altitude raised to a near-circular disposal orbit is determined by the area-to-mass ratio of the spacecraft. It is defined such that long-term orbit perturbation effects will not lead to a return of the orbit into a “GEO protected region” that extends 200 km around the GEO ring (which is at 35,786 km altitude). Table 7 shows a summary of GEO post-mission disposals over a 13-year time span. It is evident that the degree of compliance with international guidelines has gradually improved and has reached a mean level of almost 50 % by 2012 and a 64 % compliance in 2012 itself (Flohrer 2014). End-of-life mitigation measures for the “LEO protected zone” (i.e., below 2,000 km altitude) recommend an active deorbiting or a natural decay of payloads and orbital stages into a destructive Page 17 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

Table 7 History of post-mission disposal activities of geostationary spacecraft through December 2012 (L1 ¼ 75
E, L2 ¼ 105
W, “too low” and “compliant” refer to the IADC orbit raising recommendation in Anonymous (2002)) EoL disposal Left at L1 Left at L2 Left at L1/L2 Drift orbit (too low) Drift orbit (compliant) Annual total

‘99 5 1 – 4

‘00 3 1 2 2

‘01 5 1 – 6

‘02 1 1 – 5

‘03 – 1 – 7

‘04 2 1 – 5

‘05 1 1 1 5

‘06 2 1 – 7

‘07 1 – – 1

‘08 2 1 1 1

‘09 3 – – 6

‘10 1 – – 4

‘11 – – – 3

‘12 1 – – 4

Total 27 9 4 60

(15.5 %) (5.0 %) (2.2 %) (29.3 %)

5

3

2

4

8

5

11

9

11

6

12

11

12

9

108

(48.0 %)

15

11

14

11

16

13

19

19

13

11

21

16

15

14

208

(100 %)

reentry within 25 years after mission completion. For typical area-to-mass ratios of such objects, a timely natural decay requires an end-of-mission altitude below 600 km. Alternatively, chemical or electrical propulsion can be used to induce a direct reentry. A monopropellant hydrazine system would need about 8.8 % of the spacecraft mass for a controlled deorbit from 800 km (6.3 % for a bipropellant system). Electrical propulsion systems, due to their higher ejection velocities, can be more mass efficient by a factor of about 10. Their lower thrust levels, however, will lead to an uncontrolled reentry. An accelerated uncontrolled reentry can also be induced by thin, conductive tethers of several kilometers length that orientate themselves along the local vertical through gravitygradient forces. As they cut through the magnetic field lines, they induce a tether current that is closed through the ambient plasma and that leads to a retarding Lorentz force, acting opposite to the direction of motion of the spacecraft, with best performance for low-inclination orbits. For a mass penalty of less than 3 %, such systems are able to reduce orbital lifetimes of Globalstar satellites (at 1,400 km and 52
inclination) from 9,000 years to less than 2 months, and they can reduce orbital lifetimes of Iridium satellites (at 780 km and 86
inclination) from 100 years to less than 8 months. Space debris mitigation guidelines, standards, and requirements have been developed by several space agencies since the early 1990s. In parallel, the knowledge on space debris sources increased, and the understanding of effective remedial actions improved. A first step to a wider, international application of debris mitigation measures was taken by the InterAgency Space Debris Coordination Committee (IADC) in 2002, with the publication of their space debris mitigation guidelines (Anonymous 2002). This document, which was first presented at the UN COPUOS Scientific and Technical Subcommittee in 2003, serves as a basis for the development of space debris mitigation principles in two directions: towards a nonbinding policy document and towards applicable implementation standards. The former route was followed by a UN COPUOS working group, while the latter direction was pursued by an Orbital Debris Coordination Working Group (ODCWG) within the Technical Committee 20 and its Sub-Committee 14 of the International Organization for Standardization (ISO TC20/SC14). To a large extent these UN and ISO working groups recruit their experts from IADC member organizations. International space debris mitigation policies and standards, based on the consensus of the IADC guidelines, could in the future facilitate and harmonize the implementation of space debris mitigation measures at a global scale. Internationally agreed standards could enforce appropriate debris mitigation measures on spacecraft operators and launch service providers through the mechanisms of conditional launch license issuance and insurance coverage, depending on the acceptance of a space debris mitigation plan by the launch authority. Fifty years after the beginning of space flight, Page 18 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

Fig. 9 Long-term prediction of the LEO debris environment of critical-size objects of d > 10 cm, discriminated by source terms, for a “no future launch” scenario according to Liou (2011)

the voluntary implementation of debris mitigation and disposal measures by many space operators has become common practice. For several launching nations, the compliance with national regulations, or with a national space law, makes debris mitigation measures even mandatory. While debris mitigation is a necessary condition to maintain an orbital environment within a tolerable risk level for space missions, long-term forecasts of the debris environment indicate that some orbit regions may still become unstable within a few decades. Figure 9 illustrates the evolution of the LEO debris population larger than 10 cm for a hypothetical case of no future launches. The case corresponds to an extreme, hypothetical mitigation scenario, with immediate deorbiting of payload(s) and insertion stage(s) after orbit injection and with no intermediate release of mission-related objects. Predictions with NASA’s LEGEND model (Liou and Johnson 2008a, b) demonstrate that even for such optimistic assumptions, the LEO environment will become unstable. Within 20 years collision fragments will start to outnumber explosion fragments, and within 70 years, an initially stabilizing effect from naturally reentering objects will be superseded, and the 10 cm population growth will follow the slope of the collision-induced fragment increase. In the course of the 200-year projection, more and more collision fragments will collide with other collision fragments. This so-called Kessler syndrome is a self-maintained collisional cascading process that is fed by the LEO mass reservoir of 2,500 tons in 2013. Its natural termination would be reached in the very far future when all LEO crossing objects are ground to subcritical sizes that can no more reach the specific impact energy threshold of 40 kJ kg1 for causing a catastrophic breakup. As a consequence, space debris mitigation is a necessary but insufficient condition to maintain a stable orbital environment. In order to sustain an acceptable debris risk level for future space missions, debris mitigation measures must be augmented by space debris environment remediation measures that actively remove mass from orbit, with priority on the LEO regime (Klinkrad and Johnson 2009, 2013). The effectiveness of space debris environment remediation measures is governed by their capability to reduce the short- and long-term risk of catastrophic collisions. An initial indicator of the debris environment deterioration is the concentration of critical-size objects of 10 cm and larger that have the capability to cause catastrophic breakups. Figure 4 shows the distribution of the catalog objects in LEO. Highest Page 19 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

concentrations are at 800  200 km, spread over inclination bands at 65  2
, 72  2
, 82  1
, and 97  3
, with an almost equal share of intact objects, explosion fragments, and collision fragments. There are a lower, secondary LEO peak at 1,400  100 km and minor local peaks for MEO navigation satellite constellations and for GEO objects, both of which are about three orders of magnitude lower. In 2013, the orbit environment consisted of almost 12,200 cataloged LEO objects, larger than 10 cm, of a total mass of almost 2,500 metric tons. The corresponding rate of catastrophic collisions was 0.19 per year, resulting in one such event every 5–6 years. About 45 % of these collisions would have a rocket body, while 55 % would have a spacecraft as their main object. As many as 22 % of all catastrophic collisions will be attributed to a single 2
 50 km bin at 86.5  0.5
inclination and 780 km altitude, covering 72 large, intact objects, most of which are spent upper stages (Tsyklon 3rd stages, each with 1.4 tons and 6.2 m2; Vostok 3rd stages, each with 1.4 tons and 10 m2; and Delta II 2nd stages, each with 0.9 tons and 12 m2; Klinkrad and Johnson 2013). These 72 objects are facing fragments from the Iridium 33/Cosmos 2251 collision and from the Chinese Feng Yun 1C ASAT test as the main causes of their 10 cm collision flux. A secondary maximum of catastrophic collision rates at 11 % is due to a cluster of Cosmos satellites at 82
inclination and 920 km altitude. The short-term risk to the orbital debris environment can be expressed by the product of (collision flux)  (colliding mass), where the dominant target object masses drive the number of critical-size collision fragments, which determine the short-term level of debris environment deterioration. Using the same assumptions for determining catastrophic collision rates as above, the massweighted short-term environment risk is governed to 61 % by rocket bodies and to 39 % by spacecraft. Approximately 28 % of the overall short-term risk is due to objects in a single bin of 2
 50 km, centered at 71  0.5
inclination and 825  20 km altitude. Most of the corresponding mass is related to Russian Zenit 2 2nd stages with dry masses of 8.2 metric tons each. Of the 20 top-ranking objects according to metric #2, 19 are Zenit 2 rocket bodies, all of which are located in the above defined bin. The long-term risk to the environment can be expressed by the product (collision flux)  (colliding mass)  (orbit lifetime of fragments). As a simplifying, conservative assumption, the same orbital lifetimes shall be considered for the target object and its resulting fragments. The resulting aggregate of the individual products of catastrophic collision rate, target mass, and target orbit lifetime, over all intact LEO objects, leads to a long-term debris environment risk indicator that is governed to 72 % by rocket bodies and to 28 % by spacecraft. Approximately 42 % of the overall long-term risk is due to the same objects that dominate the risk metric #2, stemming from a single bin of 2
 50 km, centered at 71  0.5
inclination and 825  20 km altitude. Again, most of the related mass is due to Russian Zenit 2 2nd stages with an empty weight of 8.2 metric tons each, with a cross section of 33 m2, and with orbit lifetimes on the order of 700 years. Long-term debris environment projections (Liou and Johnson 2008a, b; Bastida and Krag 2009; Liou 2011; Klinkrad and Johnson 2013), based on an extreme scenario with no future launches and 90 % success rates of LEO post-mission disposals, indicate that the current environment could lead to a net increase of the long-lived 10 cm debris population by about 30 % in the next 200 years (see Fig. 9). This result confirms the onset of collisional cascading in some LEO orbit regions, also known as the “Kessler syndrome.” In the case of continued launch activities at today’s rates, the 10 cm debris population will even grow by 60 %, fueled by 24 catastrophic collisions (Bastida and Krag 2009). These collisions will almost exclusively occur between members of the previously identified, densely populated LEO inclination bands and between orbits of low to moderate eccentricities. Further parametric studies of the long-term debris environment evolution predict that active mass removal, focusing on inclination and altitude bands with high mass concentrations in a few large objects, can reduce the number of catastrophic collisions to 14 within 200 years and Page 20 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

lead to a stable 10 cm object population, if 5–10 removals per year are performed (Bastida and Krag 2009; Liou 2011; Klinkrad and Johnson 2013). Several research groups, with different backgrounds and application targets, have devised techniques that could be used for the removal of mass from orbit and hence for orbital debris environment remediation. In order to qualify as a remediation measure (as opposed to a mitigation measure), all techniques must be applicable to dysfunctional target objects. Mass removal from orbit has a technical, a financial, and a legal dimension. As of today, many of the suggested solution concepts are not yet sufficiently advanced in their technology readiness, and even the most mature concepts would incur significant costs if they were realized. Moreover, the removal of on-orbit mass that belongs to another launch authority and/or space operator requires mutual agreement on the procedure, on the cost sharing, and on possible liabilities, particularly for an uncontrolled reentry.

Conclusion Out of 16,316 objects that were contained in the US Space Surveillance Network catalog in November 2013, slightly more than 1,000 were operational spacecraft, of which roughly 80 % could be maneuvered. More than 420 of these were in the GEO ring, and more than 300 were in the LEO regime. Since LEO and GEO are of particular interest for space operators, these orbit regimes were denoted as “protected regions” by IADC and UN COPUOS. In order to safeguard a sustainable longterm usability of the LEO and GEO regions, space debris mitigation measures must be applied rigorously by all space-faring nations and supernational organizations. The necessary mitigation measures have been identified, e.g., by the 12 IADC members, and cast into international guidelines and standards, into agency-specific sets of requirements, and into national space laws. Analyses of the long-term evolution of the space debris environment indicate that such agreed mitigation measures are a necessary but insufficient condition to maintain the space object population at a stable level. Even an extreme mitigation scenario with no future launches will result in a long-term collisional cascading (the so-called Kessler syndrome) at some LEO altitudes. This runaway process is fueled by existing mass on orbit, and the only way to stabilize the environment is through active mass removal from particularly densely populated altitude and inclination bands. This is a challenging task from a technical, economical, and legal point of view that can only be successfully implemented if an international consensus is reached among space-faring nations. In the past the Scientific and Technical Subcommittee (STSC) of UN COPUOS, with guidance from IADC members and contributions from COPUOS members, installed a working group that developed the UN COPUOS Debris Mitigation Guidelines (Anonymous 2009) in the course of a multiyear work plan. Likewise, in 2010, UN COPUOS STSC established a working group on the “sustainable use of outer space.” This initiative could be a starting point for the development of an international framework that could include space debris environment remediation as one of its main objectives. Following the publication of previous reports on “space traffic management” and “space debris mitigation,” the International Academy of Astronautics (IAA) published a report on “space debris environment remediation” in 2013 (Klinkrad and Johnson 2013). Its authorship, with more than 20 contributors from 11 different countries and many different disciplines, could further consolidate the basis for international deliberations on the technical, economical, and legal aspects of mass removal from critical orbit regions. Such joint initiatives could prepare the ground for a sustainable and safe use of outer space.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_67-1 # Springer International Publishing Switzerland 2014

The overarching principle of a responsible and sustainable use of space was formulated back in the 1990s by the late Joseph P. Loftus, former assistant director of NASA/JSC: “Space operations should comply with a general rule of the National Park Service: ‘What you take in you must take out’.”

Cross-References ▶ Micrometeoroid Hazards ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris

References Anonymous (2002) IADC space debris mitigation guidelines. IADC-02-01, rev.1 Anonymous (2009) UNCOPUOS space debris mitigation guidelines. A/RES/62/217, UNCOPUOS Scientific & Technical Sub-Committee Bastida B, Krag H (2009) Strategies for active removal of space debris. In: Proceedings of the 5th European conference on space debris, ESA-SP-672 Flegel S (2010) Maintenance of the ESA MASTER model, final report of ESA contract 21705/08/D/ HK Flohrer T (2014) Classification of geosynchronous orbits – issue 16. European Space Agency, GEN-DB-LOG-00126-OPS-GR, 2014 Johnson NL (2009) The International Space Station and the space debris environment 10 years on. In: Proceedings of the 5th European conference on space debris, ESA-SP-672 Klinkrad H (2006) Space debris – models and risk analysis. Springer-Praxis, Berlin Klinkrad H, Johnson NL (2009) Space debris environment remediation concepts. In: Proceedings of the 5th European conference on space debris, ESA-SP-672 Klinkrad H, Johnson NL (2013) Space debris environment remediation. International Academy of Astronautics (IAA), ISBN 978-2-917761-30-4 Liou JC (2011) An active debris removal parametric study for LEO environment remediation. Adv Space Res 47(11):1865–1876 Liou JC, Johnson NL (2008a) Instability of the present LEO satellite populations. Adv Space Res 41:1046–1053 Liou JC, Johnson NL (2008b) A sensitivity study of the effectiveness of active debris removal in LEO. Acta Astronautica 64:236–243 Oswald M, Wegener P, Stabroth S, Wiedemann C, Rosebrock J, Martin C, Klinkrad H, Vörsmann P (2005) The MASTER 2005 model. In: Proceedings of the 4th European conference on space debris, ESA-SP-587

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

Strategies to Prevent Radiological Damage from Debris Curt Botts* Launch Safety, Air Force Space Command, 45th Space Wing Safety Office, Patrick Air Force Base, FL, USA

Abstract Discussion of the potential threats to population from accidents involving satellite payloads utilizing radioisotopes for power generation or heating. Accidents include launch aborts and on-orbit failures that subsequently lead to Earth impact and possible release of radioactive materials. Understanding risks and acceptance prior to launch and contingency operations used to mitigate impact or release.

Keywords Radiological payload; Debris impact; Launch abort; Exposure; Acceptable risk; Launch criteria; INSRP; Range safety

Introduction The threat from cosmic space objects is not the only lurking danger our planet can face. Man-made satellites abound in various orbits and exist from launch until they exit our neighborhood or decay and impact the Earth. This transitory “life” means there are ample opportunities for accidents to occur. Anomalous events can happen during the difficult initial climb from the surface, while orbiting, or during a planned entry and landing or disposal. Encountering other space objects or reaching their end of life can lead to loss of a stable orbit and unplanned entry and impact of debris. These scenarios carry increased hazards and challenges when the involved spacecraft carries radioisotope materials. The benefits of the reliable radioactive components for generating necessary heat or power must be carefully weighed against the exposure risks should an accident occur.

The Threat Launch Abort Since the discovery of rocket propulsion, there have been launch accidents. Since 1957 there have been approximately 845 orbital rocket launches from the US Air Force Eastern Range (including Cape Canaveral Air Force Station and Kennedy Space Center). Sixty-nine of these launches ended in failure leading, in most cases, to a suborbital trajectory and ground or ocean impact. Because a successful launch and ascent to orbit cannot be guaranteed, the Range evaluates the potential for failure and calculates the risk to the public, personnel, and assets from the three basic hazards of launch abort – debris impact, toxic effluent exposure, and distant focusing overpressure (DFO) effects.

*Email: [email protected] Page 1 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

On Orbit Once the challenge of achieving a stable orbit is met, spacecraft can enjoy a rather benign life, performing a primary task, making station keeping adjustments, and basically taking up residence at its assigned spot in space. Events that can disturb this condition include onboard system failures, encounters with other space objects, and final expenditure of critical “fuel” to defend against the interminable pull of gravity. A sufficient disturbance can lead to rapid or slow decay until the space vehicle or remaining debris encounter atmospheric entry and terminal descent toward final impact. Some satellite missions are designed for space exploration and do not maintain a standard orbit around Earth. These transfer trajectories can take advantage of gravity assist maneuvers to increase velocity and may utilize an Earth flyby. Anomalies during transit could lead to atmospheric entry and subsequent impact.

The Risk Each launch from the Eastern Range is evaluated to verify the risk is within acceptable limits. Criteria for the three standard launch abort hazards are dictated in Air Force Space Command Manual (AFSPCMAN) 91-710, Range Safety User Requirements, volume 1, Air Force Space Command Range Safety Policies and Procedures: 2.3.5. Range Safety Offices. . . .The responsibilities of the Chiefs of Safety or their designated representatives apply throughout all phases of a launch program (planning, generation, execution, and recovery) and include, but are not limited to, the following:

2.3.5.8. Determining criteria for flight termination action; assessing risks to protect the general public, launch area, and launch complex personnel and property; developing and using mathematical models to increase the effectiveness of errant vehicle control while minimizing restrictions on launch vehicle flight; establishing mission rules and criteria for flight termination action in conjunction with the Range User. 2.3.5.16. Ensuring public safety up until the time of flight at which the launch vehicle/spacecraft achieves a sustainable orbit or escape velocity for space vehicles, or through final impact for vehicles with suborbital trajectories and can be shown to pose no statistically significant additional safety risk. 2.5.3.5. Performing risk analyses and implementing design and mission plans consistent with acceptable risk to the general public for deorbiting launch vehicles, upper stages and spacecraft.

Calculated risk values are in the form of collective expectation of casualty, EC, and individual probability of casualty, PC, based on each hazard’s influence on human survivability or probability of impact, PI, for asset damage assessments. The consolidated EC risk (from debris, toxics, and DFO) to persons unassociated with launch processing activities (i.e., the general public) must be below 100 in a million (100  10 6 or 1 chance in 10,000). The Launch Decision Authority (i.e., the Space Wing Commander or designee) approves launch and under certain circumstances may accept a higher risk (usually based upon national need) according to Fig. 1. Additionally, the individual risk, PC, must be below one in a million (1  10 6). These criteria were developed early in the space program when Public Law 60, establishing the Joint Long-Range Proving Ground for guided missiles, was approved in May of 1949. In the Legislative History the need for a test range was discussed and the then undisclosed location’s ideal placement in a remote area was promoted. The following excerpt described the basic safety philosophy that led to present day risk criteria:

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

Fig. 1 Air force launch risk criteria For reasons of military security, the location of the proposed long-range guided-missile proving ground cannot now be disclosed. However, it has been ascertained that there will be no serious likelihood of hazard to persons or property, or of interference with private and commercial interests in connection with the test flying of missiles on the proposed range. The danger will be very small because every possible precaution will be taken. Means will be provided to dispose of missiles in the air, over a safe area, should they deviate too far off course. Normally they will fly so high as to be impossible of detection except with special instruments. From a safety standpoint they will be no more dangerous than conventional airplanes flying overhead, and from a nuisance standpoint they will be less objectionable. Most important of all, the test range will be located in a region so sparsely inhabited in the areas where there might be any danger that the hazard will be wholly negligible.

This suggestion made good sense, to be no more dangerous than an aircraft flying overhead, and studies at the time provided reasonable estimation of that aircraft risk thus establishing a benchmark for rocket flights. Launch constraints evacuate the launch pad and surrounding Flight Hazard Area on CCAFS/KSC and the immediate ocean downrange. Additional requirements prevent purposeful overflight of landmasses during the early phase of ascent. Autonomous and commanded Range Safety Systems can detect anomalous flight behavior that violates predetermined rules and appropriate action can terminate thrust or destroy the vehicle’s propellant tank integrity to control fallback and impact within acceptable risk zones. Launches of spacecraft payloads which utilize radioisotope materials require additional risk evaluation to understand the potential long-term effects of accidental exposure should a failure lead to release.

Nuclear Risk The use of radioisotope material in spacecraft is well established providing reliable heat to maintain electronics or generate electricity. Since 1961 there have been approximately 70 launches from the USA, USSR/Russia, and China of payloads which utilize radioisotope materials. Thirty-one of those originated from the USA. Ten of the 70 international payloads had failures at launch or during the mission. Table 1 provides a description of these failures and their outcomes, some speculative since

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

Table 1 Nuclear payload reentries Date launched Spacecraft 04/21/1964 Transit 5B-N3 USA 05/18/1968 Nimbus B-1 USA

02/23/1969 Alternate 02/19/1969

Luna Ye-8-5 USSR

23 September Cosmos 300 1969 Luna Ye-8-5 USSR 10/22/1969 Cosmos 305 Luna Ye-8-5 USSR 04/11/1970 Apollo 13

04/25/1973

09/18/1977

08/30/1982

11/16/1996

ALSEP USA Unnamed RORSAT USSR Cosmos 954 RORSAT USSR Cosmos 1402 RORSAT USSR Mars 96 Russia

Launch vehicle ThorAblestar

Radioisotope system 2 SNAP 9A RTGs (238Pu)

Thor 1 SNAP 19B2 Agena-D RTG (238Pu) PuO2 Mo Cermet Proton 1 210Po RHU 8K82K

Date of impact/burn up Impact/burnup area 04/21/1964 Atmospheric burnup over West Indian Ocean north of Madagascar 05/18/1968

02/23/1969

Santa Barbara Channel ~5 km north of San Miguel Island. Recovered at ~90 m depth 5 months later. No detrimental effects to fuel 1st Stage engine failure caused rocket to crash 15 km from pad. Rumor is sentries downrange found source and used it as a hand warmer Failed to leave low Earth orbit due to stage 4 failure. Reenters and is destroyed by frictional heating

Proton 8K82K

1 210Po RHU

09/27/1969

Proton 8K82K

1 210Po RHU

10/24/1969

Still attached to 4th Stage, reenters and is destroyed by frictional heating

Saturn V 1 SNAP 04/17/1970 27 RTG (238Pu) PuO2 microspheres

ALSEP RTG impacted in Tonga Trench, Pacific Ocean. No release detected

Tsiklon-2 Buk Reactor (235U) 1st flight of BES-5

05/07/1973

Launch failure led to reactor fallback into the Pacific Ocean north of Japan. Radiation was detected by US air sampling aircraft

Tsiklon-2 Buk Reactor (235U)

01/24/1978

Tsiklon-2 Buk Reactor (235U)

02/07/1983

Atmospheric breakup and impact in Northwest Territory, Canada. Major recovery effort, Operation Morning Light Atmospheric burnup over South Atlantic, east of Brazil. No release detected

Proton K/D-2

4 RTGs (238Pu) 11/17/1996 PuO2 pellets

Atmospheric burnup over South Pacific Ocean off the coast of Chile and Bolivia. No release detected. May have impacted land

RTG radioisotope thermoelectric generator, RHU radioisotope heater unit, ALSEP Apollo Lunar Surface Experiment Package

they have not been registered in the United Nations Office for Outer Space Affairs Register of Space Objects (UNOOSA). Design features of spacecraft utilizing radioisotope material normally include either survivable protection or the ability to deposit the space nuclear subsystem into a long-duration, safe orbit. In the case of Cosmos 954, the nuclear reactor was successfully separated from the spacecraft, but the system intended to boost it into a safe orbit failed. Failure of that mitigating device can lead to release upon reentry and land impact. The Soviet safety philosophy provides for a backup mode that disperses the reactor core designed to limit radiation dose to people living in a potentially

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

Fig. 2 RORSAT with Buk (Бук) reactor

contaminated area to less than 0.5 rem (5 mSv) during the first year after reentry (Angelo 1985). Following this accident, the reactor safing system was redesigned to improve reliability and safety.

Demise of Cosmos 954 The most intensive recovery operation to date following the reentry and impact of a man-made nuclear powered spacecraft was initiated early in December of 1977 (Heaps 1978). Technicians at the North American Air Defense (NORAD) Space Defense Center had been monitoring the Russian Cosmos 954 Radar Ocean Reconnaissance Satellite (RORSAT) for 88 days since its launch on September 18, 1977. Known in Russia as the Upravlyaemy Sputnik Aktivny (Управляемый Спутник Активный), or US-A, this satellite was powered by a Buk (Бук) nuclear reactor utilizing 30 kg of uranium-235 (see Fig. 2). Concerns were rising as the spacecraft’s orbit showed signs of instability and ever decreasing velocity. The US Department of Energy’s Nuclear Emergency Search Team (NEST) was alerted of Cosmos 954’s impending reentry. Given the chaotic nature of the spacecraft’s trajectory, it was extremely difficult to predict when the final entry point would occur and where the debris would impact. Without sufficient information the risk of exposure to the radioactive materials was unknown. Impact in a high population area meant high risk of exposure and long-term effects. Ocean impact meant low concern of public exposure. Land impact in a low population area meant the risk might be manageable if the hazardous debris could be safely recovered. Throughout January of 1978 Cosmos continued to orbit erratically with each ground track moving westward. International governments were notified of the potential disaster, and by the 21st of January, reentry was narrowed to within a few days. However, an accurate impact footprint could not be completed until the debris entered the atmosphere. A consensus of aerospace engineers examining the reentry formed a solution that made the likely impact in the northern part of North America. By the night of the 23rd, the impact location was becoming more focused and the final orbits of Cosmos 954 were bringing it over the North American continent more and more frequently. At 2:00 AM on January 24 Cosmos appeared to be on its last orbit and NORAD predicted a 3:56 AM Pacific Standard Time reentry with impact at 4:17 AM. At 4:30 AM Cosmos reentered the atmosphere and in a fiery death trailed debris toward the Northwest Territories of Canada. There were few eyewitnesses on January 24 in Yellowknife, a small town situated on the western end of Great Slave Lake. Jimmy Doctor, a Dog Rib Indian observed a big flame going northeast and thought it might be a plane on fire. Marie Ruman, also of the Dog Rib tribe worked at the Canadian Page 5 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

Broadcasting Corporation cleaning offices at night. She had arrived home early that morning and saw what she thought was a plane on fire with a flaming jet stream heading northeast. Peter Pagonis was delivering tanks of water to the military aircraft hangar at the Yellowknife airport. He noticed three bluish red UFOs streaking across the dark morning sky. The streaks trailed fiery tails and dove beyond the town in a northeasterly direction. In this early instance of nuclear powered spacecraft use, there was no pre-approved risk assessment. There certainly was an understanding that the space nuclear power reactor provided a threat. and thus, a reliable means to “dispose” of the hazard was designed into the system. But once this disposal mechanism failed to transport the reactor core to a sufficiently high orbit, the risk event was inevitable. The Soviet-designed backup system allowed for reentry burnup of the reactor core but admittedly would deliver some remaining material to impact leaving a purported low-level contamination area. Perhaps too high of a guarantee was afforded to that critical system; perhaps any remaining failure probability was acceptable to the designers and launch agency. This event would drive fundamental changes in the way the world would accept these types of launches. For this disaster, however, the mitigation had failed; only reaction, response, and recovery could be employed to lower the risk of exposure.

The Mitigation Operation Morning Light (Heaps 1978) With the reentry and impact assured, NEST had begun to assemble the necessary manpower and equipment needed to conduct a recovery operation. On January 22 the NEST team began assembling their final members and equipment at Andrews Air Force Base in Maryland. By January 23 a small team had deployed to the Canadian Forces Base near Edmonton, 600 miles south of Yellowknife. While many breathed sighs of relief that Cosmos 954 had landed in a remote area of northern Canada, locals at Yellowknife became concerned for the nearly 47,000 people, scattered over approximately 1.5 million square miles. Certainly this population consisted of small communities of trappers and hunters, but the extent of the debris coverage was as yet unknown. The chosen headquarters for Operation Morning Light was the second floor of Hangar 5 at the Canadian Armed Forces Base at Namao north of Edmonton. Military personnel, scientists, and equipment began assembling there to determine the nature of the incident and the appropriate response. This was made especially difficult considering the time of year and the extreme temperatures ( 60  F at night) that would be faced on the Great Slave Lake. Colonel David Garland, Commander of Base Edmonton, acted as the on-scene commander of the mission directing Canadian and American personnel from Canada’s Department of National Defense and Atomic Energy Control Board and the US Department of Energy. DOE efforts were under the control of Mahlon Gates through scientific advisors and equipment managers. The Department of National Defense objective was to locate, secure, and identify risk. The Atomic Energy Control Board was to recover, store, and dispose of the hazardous materials found. Public relations were controlled through DOE representative Dave Jackson, tasked with communicating details of the accident and recovery operations to a growing crowd of media agents arriving from the USA, Japan, Australia, Europe, and, of course, Canada. Initial surveys on January 25 at high altitude detected no radiation, and the search began in earnest on the ground. Twelve aircraft flew over the predicted debris footprint (see Fig. 3) searching for indications of radiation from specialized instrumentation. On January 28 the gamma ray spectrometer flying Page 6 of 22

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_69-1 # Springer International Publishing Switzerland 2014

Fig. 3 Cosmos 954 debris footprint and search areas

aboard a Canadian Hercules aircraft gave the first indication that a radiation source was below in the McLeod Bay region at the northeast end of Great Slave Lake. Finding the debris that caused the reading would be the next difficult task. On that same day, Mike Mobley and John Mordhurst were traveling over the Thelon River via dog sled tracing the route of John Hornby an explorer who had died in the area in 1927. Headed to Hornby’s final camp, they came around the river bend and discovered a small, shallow, pock-marked crater, about 8 ft across, containing pieces of metal. Several charred, twisted metal tubes were disconnected from a squashed canister. What looked perhaps like an abandoned snowmobile had dug into the snow and burned an irregular pattern, forming a patch of smooth black ice. Mordhurst touched the metal with his gloved hand. Other smaller pieces of metal were scattered along a path to the crater. They left after about 5 min and continued on to Hornby Point. Later, when they returned to their base camp at Warden’s Grove, rejoining their larger group, they made contact via radio with Yellowknife and reported what they had seen. That was followed with a transmission warning them to stay a thousand feet from the objects and by morning a plane picked them up and took them to Yellowknife for examination and interviews. A NEST geophysicist departed for the site just hours after the discovery was reported and suspected the metal pieces were part of the satellite’s propulsion unit. His radiation detector registered only 15 Roentgens, a hazard, but this indicated the debris was not part of the reactor core. By January 30 two large fragments and several dozen smaller pieces had been found making it possible to refine the footprint and predict the most likely areas where debris might be located. As hits were made from the airborne instrumentation, their location would be transmitted to helicopter teams who would try to locate the site and survey with handheld detectors. Debris or snow containing very small particles were deposited in bags and sealed in specially lined steel drums for transport to Namao and onward to the Whiteshell Atomic Energy Labs at Pinawa, Manitoba, for analysis. The slow progress and difficult logistics involved led to building an intermediary supply camp named Camp Garland on “Cosmos” Lake very near Warden’s Grove and Hornby Point in the Thelon Wildlife Sanctuary.

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The search continued into February with only small “pepper flake” pieces being found in the snow. Results from the Whiteshell analyses were withheld from the public which caused increased concern. On February 8 a small, flat fragment, 10 in. by 3 in., was found on the ice near McLeod Bay which had a reading of 500 roentgens per hour. Two other “hot” fragments were also located. Cosmos 954’s reactor core assembly was estimated to weigh about 117 lb (53 kg). The reactor assembly (with fuel) weighed approximately 298 lb (135 kg) (Grahn). By the end of March, searchers had accumulated 100 lb (45.4 kg) of material of which only a fraction was from the uranium core. Some of the material would have been vaporized on reentry. Since the core had been ejected, the reentry of the spacecraft would have a separate trajectory than the reactor core. Radioactive particles were being found south of the footprint meaning the wind may have dispersed the material over a larger area. In April particles of enriched uranium from the core were discovered hundreds of miles from Yellowknife as far west as Buffalo Lake and Hay River. Cleanup efforts began in the towns of Snowdrift, Pine Point, and Fort Resolution. The distribution of particles was sparse; in Snowdrift six particles were found roughly 200 ft apart. As the spring thaw began, particles would no longer be dormant on the ice surface. Summer teams, mostly Canadian Geological Survey personnel, continued the search as the US teams returned home. Camp Garland had been disbanded by the end of March since the lake ice could no longer hold the 78,000 lb Hercules aircraft. On April 3 40 fishing lodges had been searched and cleared of fallout. It was concluded that the core did not completely burn up in the atmosphere as many scientists suggested. There may have been millions of the tiny particles on the ice which sank to the lakebed when the spring thaw arrived. The data obtained during Operation Morning Light was reviewed for months after the end of the effort. An analysis by Lawrence Livermore Lab (Hanafee 1978) provided information on debris recovered much of which consisted of beryllium parts. Perhaps a more thorough examination of the potential failures and a rigorous assessment of the consequences could have revealed the need for higher reliability systems or alternative methods of preventing release of these hazardous components. Depending on pure chance that reentry might occur at such a time and location to assure impact in a less populated zone is not a recommended practice. Designing in protective devices or other reaction systems that prevent release under any failure circumstances provides a much better assurance that the benefits of radioisotope power systems are worth the risk.

Design Changes Cosmos 954 prompted design changes to the Buk reactor. The modifications would trigger the safing sequence by active command from the ground, or if the spacecraft lost pressurization or became unstable, or if reactor power anomalies occurred (Siddiqi 1999). The systems would separate as before into three components: the nuclear reactor with a self-contained booster rocket, the satellite’s propulsion stage, and the satellite bus. If the reactor boosting maneuver failed, a backup mechanism would trigger due to natural orbital decay. At 114–120 km altitude, the aerodynamic heating would activate ejection of the fuel core from the reactor. In 1983 this system was operated for Cosmos 1402.

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International Policy United Nations Reaction Following the Cosmos 954 accident, the UN pushed for increased notification of hazardous satellite launches. In November 1978 the General Assembly authorized its existing Committee on the Peaceful Uses of Outer Space (UNCOPUOS) to establish a technical working group to evaluate space nuclear systems and their risks. Beginning as an ad hoc committee in 1958, UNCOPUOS was made a permanent body by 1959, and in 1961 requested that a public registry of launchings be maintained. The Convention on Registration of Objects Launched into Outer Space in 1974 provided that Member States declare launchings to the UN. As of 1 January 2012, 56 States have acceded or ratified, four have signed, and two international intergovernmental organizations have declared their acceptance of the rights and obligations provided for in the Registration Convention. Approximately 93.5 % of all functional space objects have been registered with the SecretaryGeneral (UNOOSA). The Scientific and Technical Subcommittee debated implications of Cosmos 954. A moratorium on launches of nuclear reactors was proposed but a consensus was not reached to support this. In 1979, the Subcommittee established a Working Group on the Use of NPS in Outer Space which deliberated use of, reentry prediction, and possible safety measures for these devices (Benko et al. 1985). Their report provided agreements including: 1. Appropriate measures for radiation protection should be derived principally from the existing, and internationally accepted, basic standards recommended by the International Commission on Radiological Protection (ICRP). These measures should be taken for protection during all phases of an orbital mission of a spacecraft with nuclear power sources: launch, parking orbit, operational orbit, or reentry. 2. The safety of radioisotope systems is being assured by designing them to contain the radioisotope for all normal and abnormal conditions. The design should ensure minimal leakage of the radioactive contents and must at least meet the limits recommended by the ICRP in all circumstances including launch accidents, reentry into the atmosphere, impact, and prolonged water immersion. 3. Reactor systems should be started and operated in orbits sufficiently high to give time for radioactive materials to decay to a safe level in space after the end of mission. In this way the dose equivalents at the time of reentry could be guaranteed in all circumstances to be within the limits recommended by the ICRP for non-accident conditions. If reactors are intended for use in low orbits where the radioactive materials do not have sufficient time to decay to an acceptable level, safety depends on the start of the operation in orbit, and the success of boosting nuclear power sources to a higher orbit after operation is completed. In the event of an unsuccessful boost into higher orbit, the system must in all circumstances be capable of dispersing the radioactive material so that when the material reaches the Earth, the radiological hazard conforms to the recommendations of the ICRP. They concluded that Space Nuclear Systems can be safely used provided the above considerations were addressed and the decision to use such a system should be based on technical considerations provided safety requirements can be met. In 1992, Principles Relevant to the Use of Nuclear Power Sources in Outer Space, provided 11 guidelines to ensure the safe use of space nuclear systems. Principle 3 restricted the use of nuclear systems to missions which could not otherwise be powered (e.g., solar, nonnuclear) and described Page 9 of 22

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general goals and specific criteria for nuclear reactors and radioisotope generators. Principle 4 ensures that a thorough and comprehensive safety assessment is conducted prior to launch and is made publicly available. Principle 5 requires notification of reentry “in a timely fashion” and Principle 6 that the launching State promptly respond to requests for further information on a reentry event. In 2007, the Subcommittee and the International Atomic Energy Agency (IAEA) agreed to jointly draft a safety framework for space nuclear systems. This Safety Framework for Nuclear Power Source Applications in Outer Space represents technical consensus of both bodies (UN and IAEA 2009). It provides guidance for governments on safety policy, requirements, and processes, justification for use of nuclear systems, launch authorization, and emergency preparedness and response. The framework describes assignment of responsibilities for safety and leadership goals in maintaining a safety culture. Technical guidance is provided for maintaining competency in nuclear safety, incorporating safety in design and development, appropriate risk assessment methods, and mitigation of accident consequences.

US National Space Policy The latest update of US National Space Policy (Pres. B. Obama 2010) reminds readers of the growing orbital debris issue and challenges departments and agencies to “strengthen measures to mitigate orbital debris.” It encourages international cooperation in identifying improvements and innovations toward space surveillance and debris monitoring capabilities as well as advances in space nuclear power to support science and exploration. To preserve “the space environment for the responsible, peaceful, and safe use of all users,” the Policy directs that the USA must: • Lead the continued development and adoption of international and industry standards and policies to minimize debris, such as the United Nations Space Debris Mitigation Guidelines; • Develop, maintain, and use space situational awareness (SSA) information from commercial, civil, and national security sources to detect, identify, and attribute actions in space that are contrary to responsible use and the long-term sustainability of the space environment; • Continue to follow the United States Government Orbital Debris Mitigation Standard Practices, consistent with mission requirements and cost effectiveness, in the procurement and operation of spacecraft, launch services, and the conduct of tests and experiments in space; • Pursue research and development of technologies and techniques, through the Administrator of the National Aeronautics and Space Administration (NASA) and the Secretary of Defense, to mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment; and • Require the head of the sponsoring department or agency to approve exceptions to the United States Government Orbital Debris Mitigation Standard Practices and notify the Secretary of State.

This focus on debris mitigation enhances the statements provided in previous editions of National Space Policy by Presidents Bush (Pres. G. H. W. Bush 1988) and Clinton (Pres. W. Clinton 1989); (Pres. W. Clinton 1996). In 1997 a US interagency working group created a set of orbital debris reporting standard practices. These were based on NASA’s standard (NASA 1996) for limiting debris and intended for government-operated or government-procured systems. Approved for implementation by all US Government agencies in February 2001 (SecDef 2001), these guidelines have been shared with international aerospace agencies to encourage adoption of similar practices. The Inter-Agency Space Debris Coordination Committee (IADC) promotes information exchange and development of space debris research and mitigation methods.

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Cosmos 1402 On 23 January 1983 these policies were tested as another Russian Cosmos spacecraft failed to boost the separated nuclear reactor into a higher, safe, 400-year orbit. As designed, the reactor components were separated and burned up on reentry. Remaining particles dispersed over the South Atlantic Ocean east of Brazil.

Demise of Other Russian Reactors Of 39 RORSAT satellite launches from 1965 to 1998, 31 carried nuclear material. Of these 31, three failed to properly achieve relocation to a safe orbit and the radioisotope burned on reentry with any remaining debris or particles impacting in the ocean or, in the case of Cosmos 954, the Northwest Territory of Canada.

US Nuclear Launch Approval Since the Space Age began with Sputnik’s debut, the USA has developed the use of space nuclear systems and the accompanying space policies to safely utilize them. In November 1957 President Eisenhower reconstituted President Truman’s little used Science Advisory Committee (United States 1986) as the President’s Science Advisory Committee (PSAC). Prompted by the launch of Sputnik, Eisenhower ushered in a new era of collaboration between President and scientists. On advice of the PSAC, he proposed to the Congress that the country’s civilian space program should be led through the existing National Advisory Committee for Aeronautics (NACA), the precursor to NASA which was later established in 1958. The National Aeronautics and Space Council (NASC) was also created in 1958 and consisted of the President, as chairman, the Secretaries of State and Defense, the NASA Administrator, the Chairman of the Atomic Energy Commission (AEC), and any additional members that the President chose to appoint. In January 1959, the advent of space nuclear power was christened when AEC officials showed a polonium thermoelectric demonstration device to President Eisenhower in the oval office! In reaction to complaints that a highly lethal item had been placed on the President’s desk, a safety evaluation was developed in a matter of days. This first Safety Evaluation Report (SER) covered handling procedures and other matters regarding the safety of RTGs and accompanied the demonstration device as it toured other foreign capitals. Criteria were developed in June 1960 at a meeting of the AEC’s Aerospace Nuclear Safety Board and included: • The isotope material should be contained and the capsule present no hazard in the event of a launch abort. • This condition should be maintained in the event of failure to reach orbit, and in addition the capsule should fall in broad ocean areas. • In the event of failure to obtain a stable orbit, or in reentry from a successful orbit for any planned time, the capsule and contents should be burned and dispersed in the upper atmosphere. By the end of 1959, the AEC had established an Aerospace Nuclear Safety Board “to analyze and project the possible effects of nuclear space devices upon the health of the peoples of the world. . .and recommend standards of safe practice for the employment of nuclear powered space devices proposed by the U.S.” (DOE 1987). In 1960, Keith Glennan, the first NASA Administrator, suggested that the AEC should begin to define the conditions for safe use of nuclear auxiliary power Page 11 of 22

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systems in space missions and propose safeguards which would have to be provided. In August a memorandum of understanding was signed between the AEC and NASA assigning Harold Finger as manager of a joint project office. This new AEC-NASA Nuclear Propulsion Office reported to the Director of the Division of Reactor Development in the AEC and to the Director of Launch Vehicle Programs in NASA. Safety concerns and the organizational effort to bring the AEC and NASA together led to new mechanisms for handling and anticipating safety problems.

Kennedy Era (20 Jan 1961–22 Nov 1963) By March 1961 a comprehensive safety analysis of the Transit spacecraft to be launched aboard a Thor-Ablestar rocket was completed. The Transit-4A spacecraft utilized a SNAP-3B radioisotope thermoelectric generator (RTG). This early RTG was one of the many Systems for Nuclear Auxiliary Power which were developed and flown. The analysis focused on potential hazards that might result if launch or reentry failures were to occur. It was shared at a joint meeting of Navy, Air Force, DoD, and AEC personnel, and responsibilities of the various agencies were defined. In May of this same year, a National Security Action Memorandum (NSAM) was issued by then President John F. Kennedy’s Special Assistant for National Security Affairs, McGeorge Bundy. NSAM-50, Official Announcements of Launching Into Space of Systems Involving Nuclear Power In Any Form, provided in three short sentences that: The President desires to reserve to himself all first official announcements covering the launching into space of systems involving nuclear power in any form. The President is especially concerned with announcements relating to the planned use of SNAP devices aboard TRANSIT satellites which are tentatively scheduled for launching in June and July of 1961. Will you please advise members of the Space Council of the President’s interest.

Seventeen years before the Cosmos 954 accident, the importance of appropriate decision authority was evident. Vice President Lyndon Johnson was made the head of the NASC per the National Aeronautics and Space Act of 1961. This Act provided that presidential approval of nuclear power system launches be coordinated by the NASC. Initially denied approval by the NASC due primarily to objections from the Department of State, the Transit 4-A launch received approval on 23 June for a scheduled launch on the 27th. Two days delayed, the first launch of a US satellite carrying radioisotope material occurred on 29 June 1961. In 1962, concerns that a single launch failure might shut down the SNAP program led the Joint Space Nuclear Propulsion Office to expand the review group (DOE 1987). NASA was invited to participate in the reviews of DoD’s Transit spacecraft. These early reviews solidified procedures for launch approval. While most assessments showed little safety risk from a launch abort accident, it was pointed out that the potential for political repercussions was great, especially if foreign territories were affected. Establishing a review group to assess safety issues required some choices in the organizational structure. An ad hoc panel representative of concerned agencies was preferred over a standing committee, since it was thought that a committee would require public participation, a difficult prospect given the confidential nature of the information. As early as January 1963, a model charter had been developed for a possible interagency review group, eventually dubbed the Interagency Nuclear Safety Review Panel (INSRP). On 17 April 1963, following the second Transit launch with more launches scheduled, President Kennedy signed a more definitive policy via NSAM-235, Large-Scale Scientific or Technological Experiments with Possible Adverse Environmental Effects. This policy governed conduct of

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“experiments that might have significant or protracted effects on the physical or biological environment” and provided the following guidelines (paraphrased): 1. The head of an agency proposing such an experiment must notify the Special Assistant to the President for Science and Technology sufficiently in advance. 2. The sponsoring agency must prepare a detailed evaluation of the importance of the experiment and possible direct or indirect effects associated with it. 3. The Special Asst. for Science and Technology reviews this evaluation to assure that the need has been properly weighed against possible adverse environmental effects. 4. The Special Asst. recommends to the President what action should be taken. He may request additional sponsoring agency studies or undertake independent study if the provided information is deemed inadequate. 5. Experiments involving significant or protracted adverse effects will not be conducted without President Kennedy’s prior approval. 6. Experiments with major national security implications require notification of the Special Asst. for National Security Affairs and Special Asst. for Science and Technology. The Special Asst. for Nat’l Security Affairs determines the procedure for review of these experiments to assure the need has been properly weighed against possible adverse environmental effects. 7. Consistent with national security and subsequent to approval, there should be early and widespread dissemination of public information explaining experiments of this type. 8. The final decision to conduct such experiments resides with the government. The National Academy of Sciences and where appropriate international scientific bodies or intergovernmental organizations may be consulted in the case of those experiments that might have effects beyond the USA. This course of action requires consultation with the Special Asst. for Science and Technology, the sponsoring agency, and the State Department. This then specified review and approval authority for launches of nuclear materials but left out any details of the required evaluation.

Johnson Era (22 Nov 1963–20 Jan 1969) On 10 April 1965, President Johnson, once again through McGeorge Bundy, revised the original NSAM-50 with a re-titled subject of Launching into Space of Systems Involving Nuclear Power. It reiterated that presidential approval was required for all launches of nuclear power devices into space and exempted “minor radioactive calibration and heat sources.” More specific criteria for the required evaluation were provided including probability of mission success, health and safety factors, and international political considerations. It required that the Secretary of State be consulted as to the timing of tests, that official announcements be made by the White House Press Secretary, and that the Executive Secretary of the NASC be responsible for coordinating requests for launch approval. This update directly followed the successful launch of SNAPSHOT on 3 April 1965, 1 year after the Transit 5B-N3 launch failure that caused 2 SNAP-9A RTGs to reenter and burn up over the West Indian Ocean north of Madagascar. There had been four successful launches of Transit spacecraft using RTGs prior to that event. SNAPSHOT carried the first Uranium-based space reactor power system designated SNAP-10A. After mission objectives were met, the reactor was placed in a high orbit (presently at approximately 832 miles altitude). No US reactor system has been launched since.

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Nixon Era (20 Jan 1960–9 Aug 1974) Even with four more failures (five total) involving space nuclear systems (i.e., Nimbus B-1, Cosmos 300, Apollo 13, Cosmos 469) during the years from issuance of the new NSAM-50 until the end of 1977, there were no changes to this policy. Evaluations followed the prescribed process laid down by the Aerospace Safety Review Board. The Interagency Safety Review Panel (ISRP 1969) wrote in their SER that the evaluation provided “Agency Heads of NASA, AEC and DoD with a common nuclear safety basis for their recommendations regarding flight approval.” The Apollo missions that involved deployment of the Apollo Lunar Surface Experiments Package (ALSEP) in 1968, which utilized the SNAP-27 RTG, shows how the ISRP established a protocol for conducting and reporting their findings. This ISRP consisted of five discipline-oriented working groups: Range Safety, Reentry, Meteorology, Oceanography, and Biomedical. For the SNAP-27/ALSEP review, approximately 100 varied scientific and engineering specialists from a number of government agencies, laboratories, and universities brought the best available expertise to bear. Each working group produced a final report of their analyses and conclusions which were used as a basis for the SER. In July 1973, President Nixon abolished the NASC and PSAC and shifted responsibility for nuclear power source launch approval to the National Security Council (NSC).

Ford Era (9 Aug 1974–20 Jan 1977)

President Ford instructed the Congress, in the first week after his inauguration in 1974, to reinstate the Science and Technology advisory function in the Executive Office of the President. The Office of Science and Technology Policy (OSTP) was formally established in May 1976 and given responsibility for nuclear power source launch approval (Frederick 1989).

Carter Era (20 Jan 1977–20 Jan 1981) Cosmos 954 had launched in September 1977 and began to threaten reentry by the end of November. Perhaps prompted by this pending accident, President Carter issued a new policy rescinding all previous NSAMs relating to nuclear payload launch approval. The first version of the Presidential Directive, National Security Memorandum-25 (PD/NSC-25) was signed on 14 December 1977 by the President’s National Security Advisor, Zbigniew Brzezinski. It reiterated the continued previous policy of providing the President with approval opportunity but also created limits on approval levels for radioactive source material. PD/NSC-25 established that: 9. A separate procedure will be followed for launching space nuclear systems. An environmental impact statement or a nuclear safety evaluation report, as appropriate, will be prepared. In addition, the President’s approval is required for launches of spacecraft utilizing radioactive sources con-taining more than 20 curies of material in Radiotoxicity Groups I and II and for more than 200 curies of material in Radiotoxicity Groups III and IV (as given in Table I of the NASC report of June 16, 1970 on “Nuclear Safety Review and Approval Procedures.” An ad hoc Interagency Nuclear Safety Review Panel consisting of members from the Department of Defense, Department of Energy, and National Aeronautics and Space Administration will evaluate the risks associated with the mission and prepare a Nuclear Safety Evaluation Report. The Nuclear Regulatory Commission should be requested to participate as an observer when appropriate. The head of the sponsoring agency will request the President’s approval for the flight through the Office of Science and Technology Policy. The Director is authorized to render approval for such launchings, unless he considers it advisable to forward the matter to the President for decision.

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In his first year as President, Jimmy Carter faced a unique challenge dealing with the reentry of a Russian nuclear reactor. The impact of Cosmos 954 debris on Canada drove changes at the United Nations level, but did not prompt changes to US nuclear payload launch approval policy. Seventeen years would pass before PD/NSC-25 was revised.

Reagan (20 Jan 1981–20 Jan 1989) and Bush, Sr. (20 Jan 1989–20 Jan 1993), Eras During this period between 1981 and 1993, there were 20 launches of nuclear payloads with one incident involving reentry of the Cosmos 1402 spacecraft in 1983.

Clinton Era (20 Jan 1993–20 Jan 2001) In May 1995 President Clinton’s Assistant for National Security Affairs, Anthony Lake, signed a revised PD/NSC-25 providing an update to the standard used to determine radioactivity limits associated with approval authority. This was prompted by an interagency review led by OSTP. The older NASC report of 1970, Nuclear Safety Review and Approval Procedures for Minor Radioactive Sources in Space Operations, was replaced with a more global specification in the International Atomic Energy Association’s (IAEA’s) Safety Series Number 6, Regulations for the Safe Transport of Radioactive Materials, written in 1985 and amended in 1990. Paragraph 9 changed to: 9. A separate procedure will be followed for launching nuclear systems. An environmental impact analysis or nuclear safety evaluation report, as appropriate, will be prepared. The President’s approval is required for launches of spacecraft utilizing reactors and other devices with a potential for criticality and radioactive sources containing total quantities greater than 1,000 times the A2 value listed in Table I of the International Atomic Energy Agency’s Safety Series No. 6, Regulations for the Safe Transport of Radioactive materials, 1985 Edition (as amended 1990). Launch of sources containing quantities greater than 0.1 percent of the A2 value from this table will be forecasted quarterly to the Office of Science and Technology Policy (OSTP). This report is for information and is not intended to introduce a new approval procedure. An Interagency Nuclear Safety Review Panel consisting of members from the Department of Defense, Department of Energy, National Aeronautics and Space Administration and the Environmental Protection Agency, will evaluate the risks associated with missions requiring the President’s approval and prepare a Nuclear Safety Evaluation Report. The Nuclear Regulatory Commission will participate as a technical advisor to the panel as appropriate. The head of the sponsoring agency will request the President’s approval for the flight through the Office of Science and Technology Policy. The Director is authorized to render approval for such launchings, unless he considers it advisable to forward the matter to the President for a decision.

The term “reactors” was added, likely to accent the previous accidents, and inclusion of the NRC was no longer a recommendation, but a requirement. The phrase ad hoc was removed as pertains to the INSRP and that had the potential to change their process. Ad hoc (Latin: for this) was previously applied in the initial version of PD/NSC-25 to show preference to use of empanelment for a single mission or system only. This was mainly since use of a committee had connotations of requiring public inclusion in the review, a difficult prospect given the confidential or classified nature of the information at the time. Legislative rules of the Congress provide that (Sullivan 2007): All meetings for the transaction of business of standing committees or subcommittees, except the Committee on Standards of Official Conduct, must be open to the public, except when the committee or subcommittee, in open session with a majority present, determines by record vote that all or part of the remainder of the meeting on that day shall be closed to the public.

There are some advantages to a standing committee as might be applied to the INSRP. The existing ad hoc nature of the panel means that constituting membership for a particular mission is done through a direct empanelment action. Upon completion of review and delivery of the SER to OSTP (or following launch in some cases) the INSRP is disbanded. Given the unique disciplines Page 15 of 22

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Fig. 4 Launch approval process

needed to conduct this type of review, often under limited schedule, there are benefits to having access to a more permanent membership. Often, during hiatus, there are opportunities for testing or model development used for nuclear risk assessment. These are not easily accomplished while preparing for a mission. Additionally, the maturity of INSRP members, necessary for the requisite experience level, makes it difficult to accommodate long-term developments of space nuclear systems. An allowance for an apprenticeship in the INSRP could boost the abilities of the panel to support any increase in nuclear payload missions or advancing technologies. However, allowing for the rather sparse number of these missions can provide for long gaps between empanelment. PD/NSC-25 was revised 1 year later in May 1996, returning the phrase ad hoc to the INSRP. The apparent importance of the phrase was reinforced since this was the only revision.

Bush, Jr. (20 Jan 2001–20 Jan 2009), and Obama (20 Jan 2009–today) Eras

Since 2001 there have been only five nuclear payload launches including the two Mars Exploration Rovers, Pluto New Horizons, Mars Science Laboratory, and China’s Chang’e 3 Yutu Moon Rover. They have all successfully left Earth’s orbit.

Safety Analysis Process Program Safety Analysis Process

The “Program” wishing to launch a nuclear payload, for example, NASA’s Mars Science Laboratory, initiates the process years before a launch date is finalized (Ref. Fig. 4). Normally, the Program will initially work on the requirements of the National Environmental Policy Act (NEPA) since the approval of the Environmental Impact Statement (EIS) is needed early in the mission planning Page 16 of 22

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phase. The EIS describes accident scenarios using the best available information on spacecraft and space nuclear systems providing environmental consequences of launch or mission failures. In this early phase, a launch vehicle may not yet have been chosen due to the lengthy acquisition process. Unique aspects of candidate launch vehicles and their response to accidents must then be included in the environmental assessment. The proposed, preferred design of the nuclear power system is compared to alternative methods (e.g., solar power) explaining benefits or disadvantages of each. The affected environments are described as well as any adverse, damaging short-term or long-term effects. A response to public comments is included that addresses questions or statements derived from a review of a Draft EIS as required by NEPA. Contingency plans are also provided describing what actions would be taken in the event of an accidental release of the radioisotope. The Mars Science Laboratory EIS (NASA 2006) included the following sections and appendices: 1. Purpose and Need for the Action 2. Description and Comparison of Alternatives 2.1. Description of Proposed Action (Alternative 1) 2.1.1. Mission Description 2.1.2. Spacecraft Description 2.1.3. Rover Electrical Power 2.1.4. Spacecraft Processing 2.1.5. Representative Launch Vehicle Configurations for the MSL Mission 2.1.6. Radiological Emergency Response Planning 2.2. Description of Alternative 2 (Solar Power) 2.3. Description of the No Action Alternative (if this mission isn’t accomplished) 2.4. Alternatives Considered But Not Evaluated Further 2.4.1. Alternative Power Sources (Other RTGs, Power Systems with Less PuO2) 2.5. Comparison of Alternatives Including the Proposed Action 3. Description of the Affected Environment 3.1. Land, Air, Noise, Geology, Hydrology, Biology, Socioeconomics 3.2. The Global Environment 4. Environmental Consequences 5. List of Preparers 6. Agencies, Organizations and Individuals Consulted 7. Index 8. References

Appendix A: Glossary of Terms Appendix B: Effects of Plutonium on the Environment Appendix C: Environmental Justice Analysis Appendix D: Responses to Public Review Comments Appendix E: Public Review and Comment Meetings Following submittal of the EIS to the US Environmental Protection Agency (EPA) for review, the development of a Launch Vehicle Databook begins. This documents the details of a particular launch vehicle’s characteristics, failure modes, reliability, and launch abort environments. MSL launched

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aboard an Atlas V 541 (5 m payload fairing, 4 augment solid rocket booster, 1 Centaur upper stage motor). The MSL Atlas V 541 Final SAR Databook had the following outline structure: 1. 2. 3. 4. 5. 6. 7. 8.

Introduction Mission Overview Launch Vehicle Description Spacecraft Description Launch Complex Description (LC-41, Cape Canaveral Air Force Station, Florida) Flight Safety System Trajectory Data Accident Probabilities 8.1. Introduction 8.2. Technical Approach 8.3. Prelaunch Accidents (Launch Processing to T-0) 8.4. Post Engine Health Check Accidents (T-0 through Earth escape) 8.5. Sensitivity and Uncertainty Analyses 9. Accident Environments 9.1. Liquid Propellant Explosions 9.2. Solid Propellant Explosions 9.3. Liquid and Solid Propellant Fires 9.4. Launch Vehicle Debris 9.5. Accidental Earth Reentry The data produced in Sections 8 and 9 especially are important for the development of the SAR. Section 8 applies the basic principles of Probabilistic Risk Assessment (PRA) logic models to compile and evaluate accident scenarios and sequences that lead to adverse environments being applied to the space nuclear system. All known and speculated failure modes of the launch vehicle subsystems and spacecraft are evaluated for their potential to damage the nuclear system. Each subsystem’s reliability values can be assessed by comparing to similar launch vehicle subsystems (nationally or internationally) and adjusted via Bayesian Update methodologies to provide a more accurate prediction of failures. These subsystem failures initiate the potential cascade of failures that may lead to damage of the nuclear system. Scenarios progress from a Basic Initiating Event (BIE), which may involve a single subsystem of the launch vehicle, but has the potential to subsequently affect other subsystems or directly affect the nuclear system. Event Sequence Diagrams (ESDs) visually and mathematically map the branch points along each failure scenario. At each branch a probability is assigned indicating the likelihood that one path or the other is potentially followed (Ref. Fig. 5). The assignment of branch point probabilities can be accomplished by analysis, use of empirical data, or by expert elicitation. Expert elicitation relies on individual judgment on the particular system’s failure mode to progress along one or another branch. Subjectivity in these judgments can be tempered by using multiple experts to gather a range of probabilities and selecting appropriate values. A BIE can lead to an Accident Initiating Condition (AIC) which will affect the nuclear system at varying levels of damage. The effects of the AICs are evaluated based on environmental threats such as explosive overpressure, fragment impingement, fire and thermal exposure, and impact energy. Mapping the AIC probabilities through the potential damaging effects provides an end state Accident Outcome Condition (AOC). As all accidents are mapped, an understanding of the AICs which can lead to high-risk AOCs is revealed, and mitigation techniques may be applied to reduce Page 18 of 22

Fig. 5 Branch point probabilities and event sequence diagrams

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Fig. 6 INSRP working groups

that risk. The probabilities assigned or calculated for these scenarios are then used as input values for the nuclear risk analysis. Section 9 details the assessment of adverse environments produced from accidents involving explosive yield of solid propellant, liquid propellant mixtures, fires involving propellants or other components, overpressure blast, and impact energy. Potential for damaging the space nuclear system from impacts of explosively propelled fragments in the near field is evaluated. Damage from accidental reentry and ground impact is also assessed. These defined environments are then applied in the nuclear risk analysis to determine the potential for release of radioisotope material and possible dispersion in the environment. Results of the nuclear risk analysis are documented in the Safety Analysis Report (SAR).

INSRP Process The procedure used by the INSRP (Ref. Fig. 4) follows the original AEC methodology. The “Program” initiates the process by requesting empanelment of an INSRP per PD/NSC-25 sending letters to each of the participating agencies (i.e., NASA, DoD, DOE, NRC, EPA). Each agency responds assigning an INSRP Coordinator (NASA, DoD, DOE) or Technical Advisor (NRC, EPA). Coordinators then select Chairmen of the necessary Working Groups. Traditionally, NASA has assigned Chairmen of the Reentry and Risk Integration and Uncertainty Working Groups, DoD the Launch Abort and Power Systems Working Group Chairs, and DOE the Biomedical and Environmental Effects Working Group Chairs. Each Working Group Chairman then gathers the necessary expertise to evaluate their particular technical area (Ref. Fig. 6). The Program normally introduces the INSRP to the mission shortly after completion of the EIS. The INSRP then follows the Program’s progress in developing the LV Databook, any ongoing or planned testing or analysis, results of risk modeling, and writing of the safety analysis reports. The INSRP has the opportunity to provide questions or inputs to the Program, and responses are returned to alleviate concerns or address issues. As the Program completes the Final SAR, the INSRP will

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produce a Safety Evaluation Report (SER) documenting their evaluation of the Program’s SAR and any related information. The SER can evaluate alternative probabilities of accidents, and thus consequences; provide risk assessments via alternate software; or document areas of concern (e.g., inadequate conservatism, overly conservative assumptions, improved or alternative methodologies) and recommendations for evaluating uncertainties for future missions.

Final Launch Approval The Program’s FSAR and INSRP’s SER are provided to OSTP for review, requesting approval to launch the nuclear source. Addressing the risk, probabilities of occurrence, mitigation techniques, and contingency operation plans provides OSTP necessary information to make a decision or elevate the decision up to the President. Once any concerns are addressed, OSTP issues their final approval to the Program. Air Force Safety requirements dictate that once all necessary launch constraints are met (normal processes for a launch that does not involve radioisotopes), the final launch can proceed after receipt of OSTP’s approval. Contingency operations commence when the space nuclear system is integrated with the spacecraft, normally as late in the processing flow as possible. Should a prelaunch accident occur that could lead to release of the radioisotope material, the contingency operations personnel can respond accordingly to mitigate any risk. Emergency teams are on station during the final countdown and remain ready to respond until the spacecraft with its nuclear source has reached a mission phase where it cannot return to Earth. If a mission includes a later flyby of Earth, contingency teams are available during that maneuver to monitor and respond as necessary if an accident occurs.

Conclusion Careful use of space nuclear power systems is necessary in the distant realms of space exploration. By understanding the risks involved and applying reliable mitigation techniques, these benefits can be enjoyed.

Cross-References ▶ Section 6 – Interaction of Radiation with Matter and Means of Protection ▶ Section 15 – Institutional and Financial Arrangements for Orbital Debris Mitigation ▶ Section 15 – Mounting Hazards of Man-Made Orbital Debris ▶ Section 15 – Nature of the Threats and Historical Patterns of Occurrence ▶ There May Be Others

References Angelo JA (1985) Space nuclear power (original edition ed.). Orbit Book Company, Malabar Benko M, De Graaff W, Reijnen G (1985) Space law in the United Nations. Marinus Niijhoff Publishers, Dordrecht DOE (1987) Atomic power in space: a history. Office of Nuclear Energy, Washington DC Page 21 of 22

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Frederick S (1989) The Evolution of the Space Nuclear Safety Review Process, NASA Jet Propulsion Laboratory, Appendix A of unpublished INSRP report, Interagency Nuclear Safety Review Panel Launch Approval Process Guidelines, Oct 1994 Grahn S (nd) The US-A Program (RORSAT) and radio observations thereof. Retrieved 2 19, 2014, from Kosmos-951 & Kosmos-954, a near-disaster: http://www.svengrahn.pp.se/trackind/ RORSAT/RORSAT.html Hanafee JE (1978) Analysis of beryllium parts for Cosmos 954. Lawrence Livermore Lab for US Department of Energy, Livermore Heaps L (1978) Operation morning light, terror in our skies, the true story of Cosmos 954. Paddington Press, New York ISRP (1969) SNAP 27/ALSEP safety evaluation report NASA (2006) Final environmental impact statement for the mars science laboratory mission. Science Mission Directorate, NASA, Washington DC NASA (1996, Mar 28) Space debris mitigation standard. NASA Pres. B. Obama (2010, Jun 28) National Space Policy. Washington DC: U.S. Govt. Pres. G. H. W. Bush (1988, May 5) National Space Policy. Washington DC: U.S. Govt. Pres. W. Clinton (1989, Nov 2) National Space Policy. Washington DC: US Govt. Pres. W. Clinton (1996, Sep 14) National Space Policy. Washington DC: US Govt. SecDef (2001, Feb) US government orbital debris mitigation standard practices Siddiqi A (1999, Nov/Dec) Staring at the sea: the Soviet RORSAT and EORSAT programmes. Br Interplanet Soc 397–416 Sullivan, JV (2007, July 24) How our laws are made. Retrieved 5 Mar 2014, from The Library of Congress: http://thomas.loc.gov/home/lawsmade.toc.html UN, IAEA (2009) Safety framework for nuclear power source applications in outer space. IAEA, Austria United States (1986) The papers of the president’s science advisory committee, 1957–1961. University Publications of America UNOOSA (nd) United Nations office for outer space affairs register of space objects. Retrieved 1 Feb 2014, from http://www.oosa.unvienna.org/oosa/en/SORegister/index.html

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris Joseph N. Pelton* Executive Board, International Association for the Advancement of Space Safety, Arlington, VA, USA

Abstract The topic of cosmic hazards is most closely associated with comets and asteroids that might crash into Earth with devastating effect. The truth is that in the nearer term adverse solar events might threaten Earth with powerful coronal mass ejections that could also result in a number of disaster scenarios. When these catastrophic events are the focus, the more modest issue of orbital debris is clearly seen as far less threatening. But the truth is that orbital debris also constitutes serious hazards to future human progress and safety in many different ways. Orbital debris will have an increasing chance of disabling critical satellite infrastructure – particularly in low Earth orbit – that can jeopardize critical services and in the case of major collision escalate the buildup of orbital debris even further. Orbital debris is nothing like the threat to life on Earth of say a category 10 asteroid on the Torino Scale colliding with Earth (“the Torino Impact Hazard Scale”), yet this hazard represents a serious problem to the long-term sustainability of space operations that will only get worse unless an active program to undertake debris removal is initiated. Most of what is written about space debris focuses on their characterization in terms of size number and orbital mechanics, the space technology needed to remove debris from orbit, or relevant regulatory issues. Technical papers such as the chapter written by Dr. Heiner Klinkrad describe such aspects as the growing extent of the problem and the factors that are contributing to the rate of buildup of debris. Other chapters of a technical nature often address the very important issue of the best approaches that can be used for debris removal and remediation. Regulatory papers, such as the chapter by Dr. Ram Jakhu and Dr. Fabio Tronchetti, on the other hand, address the current “due-diligence procedures” that are aimed at preventing or minimizing the creation of new debris. They also consider the questions of liability and legal responsibility and efforts aimed to create new regulatory processes within the UN system to control debris and/or remove debris from orbit. The focus of this chapter, however, is on examining the merits of establishing national, regional, and in time perhaps universal agreements to establish economic funds or entirely new international cooperative mechanisms to oversee the removal and mitigation process. The purpose of such a new international entity or international fund would be manyfold. Such mechanisms or economic processes would create financial incentives both to prevent new debris from occurring and for the removal of existing debris. It would create a recognized international process for active debris removal that would be consistent with existing UN treaties and to which all countries would be able to respond. Such an active response would be in recognition of the incentives for active debris removal as well as penalties associated with either the creation of new debris or not supporting the removal of debris. The ability to create universally accepted new international mechanisms to undertake such tasks as active debris removal is more difficult than it was several decades ago. This is due to the ever*Email: [email protected] Page 1 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

increasing number of nations who are now within the UN system and that now participate in COPUOS, the lack of a cohesive support for coordinated world initiatives – such as existed immediately after World War 2 – and the divergence of world economic, political, and strategic interests in outer space. This divergence of views is particularly noticeable in the outer space arena since this sector is often associated with military and strategic applications on the part of many spacefaring nations. This divergence of views suggests that any new international arrangements related to the active removal of orbital debris will most likely follow an evolutionary path. In short, any longer-term international consensus to address the orbital debris problem will most likely be developed slowly over time. Since the key UN space treaties were developed in the 1960s and early 1970s, no major new space conventions have been agreed since. This chapter thus discusses possible evolutionary processes – lead by economic mechanisms or active mitigation and removal techniques that directly reduce the orbital debris buildup. These processes are most likely to start – at the national and regional level and ultimately transition to the global level as time goes by. This might lead to longer-term efforts to create an international mechanism or organizational mechanism to address not only the space debris problem but perhaps other space operations issues such as commercial space flight safety, space traffic management, space and improvement in the near-Earth space environment, etc. (Jakhu et al. (2011) The need for an integrated regulatory regime for aviation and space: an ICAO for space? Springer Wien, New York).

Keywords China; Debris mitigation; Debris removal Europe; France; GEO orbit; Inter-Agency Space Debris Coordinating Committee (IADC); International Telecommunication Union; Intelsat; Japan; Kessler syndrome; LEO orbit; MEO orbit; Office of Outer Space Affairs (OOSA); Russian Federation; Space debris; Space debris mitigation; United Nations Committee on the Peaceful Uses of Outer Space (COPUOS); United States; Upper stage rockets

Introduction Space applications have become a very diverse and increasingly important aspect of modern global society. Over time-space applications have expanded in scope, divided into many submarkets, and have evolved into a series of many different “space actors.” These include civil governmental space agencies, defense-related space agencies, commercial launch operators, operators of various commercial spacecraft organization, and even public service space operators that are operated by both commercial and nonprofit organizations. The various governmental, defense, and commercial space markets are today quite large with all related annual space applications, expenditures, and revenues totaling perhaps $400 billion (US). The true impact of space activities is not simply a function of their economic size, however, but rather their overall impact on society. Space-related activities today relates to national security; the monitoring of possible attacks via nuclear-armed missiles; the use of space navigation to control transportation (including the takeoff and landing of aircraft); the deployment of satellites for voice, data, and television communications; and the use of satellites to forecast weather and avert the impact of hurricanes, typhoons, and other violent weather. There are many remote sensing operations that observe the Earth to detect natural resources, conduct fishing operations, monitor oil spills, and chart the impacts of climate change. Page 2 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

These remote sensing have a variety of public service and commercial goals as is the case with telecommunications satellites, remote sensing, meteorological, navigation satellites, and other types of application satellites. In recent years the proliferation of orbital debris associated with space activities has raised serious questions about the sustainability of human space activities going forward. In 1980 there were just under 5,400 sizeable objects in space being tracked; by 2010 this number of large space debris objects had increased to 15, 639 and currently it is over 22,000. There is also substantial buildup of microelements too small to track (under 4 cm in diameter). There are perhaps 750,000 space objects the size of 1 cm or larger and millimeter-sized space debris now numbers in the millions. The threat of the so-called Kessler syndrome whereby space debris collides in a cascading manner to create more and more debris has now become a truly serious concern (“New Debris Tracking..” 2012). Despite the guidelines developed within the Inter-Agency Space Debris Coordinating Committee (IADC) and the UN COPUOS to limit new debris, the reality is that there is, in fact, a continuing formation of additional space debris. This continued creation space debris is due to many factors. These factors include, among others: (i) hardware degradation; (ii) collisions involving existing debris and various space objects; (iii) continued deployment of all types of satellites that by a certain percentage fail to be disposed or safely removed when they become defunct; (iv) large, medium, and small upper stage rockets that remain in orbit; and (v) explosions of pressurized tanks and batteries. Mitigation of space debris creation is a condition necessary but no longer sufficient to stabilize the orbital debris environment. Major junks, like defunct satellites and spent upper stages, are those that in a way or the other will generate in time a multitude of smaller debris. They must be therefore the primary target of active removal efforts. If the buildup of space debris is not curtailed and instead continues to increase, then all future space activities could eventually become impossible, and all future space applications, scientific missions, and space exploration could quite simply become unsustainable. When most people think about cosmic threats, they perhaps first think about threats from comets, asteroids, or powerful space weather eruptions from the sun, but orbital debris increasingly poses a risk to the continued successful operation of the world’s extensive satellite infrastructure. Uncontrolled falling space debris poses real threats to air and land safety as well.

Key Concerns and Threshold Questions There are a number of key threshold questions that world leadership must consider with regard to orbital debris and its removal from Earth orbit. Threshold Question Number 1: Can better design and engineering for spacecraft and launch vehicles plus new due-diligence procedures as developed by the UN COPUOS, the International Telecommunication Union (ITU), and the Inter-Agency Space Debris Coordinating Committee (IADC) sufficiently mitigate the spread of space debris going forward with enough effectiveness that new regulations are not needed and active removal of space debris will not be required? Response Number 1: The short answer clearly appears to be no. The truth is much more needs to be done! Despite guidelines and due diligence the rise of space debris continues to rise. Computer modeling that forecasts future amounts of space debris projects a continuing buildup of orbital space debris especially in polar and low Earth orbits that are crucial to remote sensing, meteorological, and other satellite applications. Such projections may, in fact, underestimate the threat. This is because these models may not fully take into account battery explosions, fuel tank explosions, buildup due to natural causes such as mini-meteoroids striking satellites, etc. Procedures to mitigate debris need to Page 3 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

be made mandatory and backed by financial incentives (or penalties) to ensure compliance, plus concerted efforts made to finance active debris removal. Otherwise orbital debris buildup will continue to increase and become ever more difficult to deal with in future years. The choice is to pay now or pay much more at a later date. This applies to pollution on the Earth and it applies to pollution in space. Threshold Question Number 2: Is there a cost-effective and reliable method to ensure the effective deorbit of space debris from Earth orbit in the years ahead. Response Number 2: Again the answer is no, but progress is being made. Today the processes are generally fairly expensive and often unreliable. Current processes and technology need to be improved and/or new capabilities developed. Passive systems that can be deployed at end of life like balloon or kitelike devices can create drag to bring satellites down earlier than would otherwise be the case. Active plasma jet systems now in development seem promising as a reliable system to deorbit smaller satellites in low Earth orbit. One of the larger problems is constituted by medium Earth orbit that need large amounts of fuel to be successfully deorbited at end of life. (Typically medium Earth orbit satellites require a 40 % add-on of fuel just to deorbit at end of life.) Active removal systems for larger derelict satellites or rocket upper stages represent the largest technical challenge. Removal systems of this nature are today unproven, expensive, and in need of extensive further research and development. Threshold Question Number 3: If better processes for active removal of space debris objectives from Earth orbit could be developed, who would be authorized to undertake such deorbit operations and who can designate orbit debris as appropriate for removal from Earth orbit? Response Number 3: Today there is much discussion about the fact that no entity exists with the authority to designate satellites for removal. Even if a nation designates a “space object” as debris without maneuverability, that nation still remains liable for any damage associated with deorbit. Further, much concern is expressed that many of the processes designed to achieve removal could be considered equivalent to the deployment or use of space weaponry. The use of such processes, is argued, that could have possible military applications is thus likely to be opposed in the international community. The discussion should be approached by a completely different angle. The nationality of each major piece of debris currently orbiting Earth is known with absolute certainty. Therefore, the countries with major debris now in orbit should have a primary concern, and indeed responsibility, for the gradual removal of their own debris. This sounds straightforward, but, in fact, it is not. Under the current liability convention as adopted by the United Nations, it is the launching country of record that is responsible, even though commercial organizations, international consortia, or a joint effort of several space agencies or research institutes may have been the ones who designed and arranged for the launch and operation of the derelict satellites. In other words, a number of other organizations, other than the launching states, may actually been involved with improper action such as not deorbiting a satellite or not degassing a hydrazine tank in a timely manner or some other critical operation that would have lessened the debris problem (Wired 2010). Clearly a removal mission can be made cost-effective by removing in sequence a number of space debris which may belong to different countries. In such case realizing missions as international cooperation, bilateral or multilateral, can effectively address the legal concerns, while reducing procurement costs. Furthermore, the development of capture systems through international cooperation, possibly on commercial basis, would eliminate, or at least minimize, the military concern of technological advantage in a dual-use technology.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

This point remains as a major issue to be addressed and as such will be discussed later. The key objective still remains as to how a market for such removal services could be created and how to provide incentives for voluntary removal within such a market.

Threshold Question Number 4 A number of coordinated actions are needed to move ahead with active debris removal. Liability provisions for “space objects” may need to be updated and modified. Indeed space debris needs to be defined so that there is a widely shared understanding of what this term actually means. Different regulatory provisions with regard to launch and deorbit for low, medium, and geosynchronous orbits need to be made with regard to removal activities. Certainly it would best if such provisions could be made mandatory rather than merely voluntary. If mandatory provisions could not be devised and implemented, then perhaps these could be achieved through a system of incentives and/or financial penalties forming the enforcement process. The problem is that various types of solutions and corrective actions are today entirely hypothetical. The establishment of a “fund to support debris removal is just one approach. It may be that spacefaring nations or a spacefaring region such as Europe may chose direct action through their national space agency to remove debris and not seek to create specialized financial mechanisms such as a fund to relate removal to all types of forwardlooking space activities. The United States is already paying through national taxes for advanced space situational awareness tracking capability. Although the new “S-band radar Space Fence” that would have cost many billions of dollars more has been cancelled due to budget cuts imposed by the so-called sequester process, its expenditures on already elaborate space- and ground-based tracking capabilities remain quite high. Thus, spacefaring nations may decide that financial mechanisms involving the commercial users of outer space and creating incentives for contractors to remove orbital debris is too complicated or unnecessary to address the orbital debris problem. This direct action approach on a governmental space agency basis would also presumably be premised on the idea that due-diligence prelaunch activities would be sufficient to ensure that future debris will be removed. At this time, however, some form of financial mechanism or direct action by national governments seems more likely than the creation of an international space debris removal entity. In the following sections the way ahead to support the removal of the space debris by various means will be discussed. One possible solution would involve the so-called space debris removal fund which would provide the financial resources for removing space debris.

Space Debris Removal Fund One of the possible solutions that could help address active space debris efforts might involve as initial step the creation of a space debris removal fund. This might be done first at a national or regional level and might occur in parallel with technical demonstrations of space debris removal capabilities. Such an economic mechanism or fund should be brought into place as soon as possible. This is simply because the problem continues to worsen. The fund (or series of national/regional funds) could be established over time in an “organic manner” with countries forming such a fund on a national basis – or perhaps for Europe as a region. This type of national, regional – and in time ultimately universal – fund would be formed by space actors for the specific purpose of addressing the space debris issue. The creation of such funds could represent a proactive “forward-looking” approach to financing a solution to the problem rather than seeking a “backward-looking” approach to addressing space debris formed in the past wherein no financing mechanism was in place.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

The money to capitalize this type of space debris fund would be collected prior to all launches and would capitalized in an amount equivalent to perhaps 5 % of the total cost of various space-related missions. This fund would be collected for a period of perhaps 25 years but would have a sunset provision on the premise that re-mitigation of orbital debris could perhaps be successfully accomplished over this length of time. Such a fund (or network of funds) would be formed by means of a specific assessment paid into a designated bank account (or space insurance company or some other designated entity/entities) prior to launch. This fund would apply to all those deploying spacecraft into Earth orbit or if on a national or regional basis, would apply to all launches from that country or region. Organizations launching satellites beyond Earth orbit would also pay into the fund but at lesser rate. After each launch there would be a partial rebate assuming it was a certified as a clean “debris-free” launch as independently verified. Such a clean launch would require that the upper stage rocket would be actively deorbited and no residual debris created. When a spacecraft reaches its end of life and is then actively deorbited or successfully placed in a graveyard orbit, there would be a further rebate. The size of the rebate for a “clean launch” and “successful disposal” would be specified at the time the fund(s) were established. The rebate formulas could be updated over time at suitable intervals. Approximately half of the payments into the fund, however, would also be retained to compensate those entities involved in removing “officially designated” debris from orbit or moving defunct space objects to a graveyard orbit. The prime purpose of the national, regional (or hopefully universal global) space debris fund would be to compensate those entities “licensed under an appropriate regulatory framework” to remove debris from Earth orbit. It is possible that small fractional part of the fund could also help fund activities related to operating systems to avoid collisions (Pelton 2012). This licensing process for entities designated to undertake orbit debris removal or collision avoidance activities might, for example, be formally assigned to the UN Office of Outer Space Affairs or in time spelled out in a new international space convention. Other entities might also be “licensed” by the UN Office of Outer Space Affairs to undertake activities associated with the prevention of space debris or space debris mediation or collision avoidance activities separate from the active removal of space debris from orbit. Such activities, however, would be limited to no more than a set percentage of the available funds – such as no more than 5 % of the total available funds after rebates were paid. Payment into this fund would “seem and feel” to satellite operators and governmental space agencies conducting space operations very much like buying launch insurance for a spacecraft mission. Indeed the fund could possibly be administered by launch insurance companies. These payments would be different in that it would only represent about a third of the cost associated with purchasing launch insurance and rebates would eventually return half of the money paid into the fund. Further, the projected end date for the fund would establish a very real goal for accomplishing “a largely space debris-free world.” The creation of this fund and the rebate payments would reverse the current incentives that actually “encourage” the increase of orbital debris. Under current space law the owners and operators of space objects not only lack an incentive to remove their space debris from orbit; they actually face substantial financial penalties if the removal process somehow adversely affects another space object and create liabilities for which they are compelled to pay (Listner 2011). The payments into the fund are considered to be modest in comparison to the costs of postponing the removal process, since the cost of removal will only spiral upward. If the Kessler syndrome stage is ultimately reached and debris continues to cascade out of control, the cost of active debris removal might truly soar into levels that might involve trillions of dollars (US) (“Space Junk Problem”). Page 6 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Payments for launch insurance operations over the last three decades have widely varied from a low of about 6 % of total mission costs to as much as 20 % of total costs. If one considers this wide range of payments for launch insurance, the threat that orbital debris represents to all future space activities, and the cost of debris removal, it can be reasonably argued that a 5 % payment into an orbital debris fund is not excessive. This seems even for reasonable when consideration is given to the process of rebates after a clean launch and a further rebate when spacecraft is deorbited. One of the issues for particular further consideration is whether there should be a minimum payment related to small or nano-satellites. It is hoped that in time there would be a new international agreement reached concerning small satellites. This might provide for one of three provisions to be made for such small satellite launches. Option one would be for a passive deorbit capability at end of life. Option two would be an active deorbit capability at end of life. Option three would be for the small satellite to fly as a multi-mission vehicle with deorbit or on board a space station with subsequent controlled return or deorbit (Jakhu and Pelton 2014). If one considers the problem of orbital debris as akin to dangerous shoals on which ships are wrecked, then the logic of a fund to remove orbital debris becomes quite clear. No one ship owner wants to pay for a lighthouse and no one space mission wants to pay for all debris removal. A collection of funds associated with all future missions that is developed in a manner so that is seems quite the same as paying for launch insurance can thus be viewed as much like all ship owners contributing to the building of a lighthouse network. Another analogy that might be even closer would be for tax payers to pay for the cost of a super fund to clean up a toxic waste site (Schons 2011). The challenge would be to get this started in a serious way so that it gains traction and coincides with the development of suitable and cost-effective technology that can achieve active debris removal. The further advantage of the fund approach is that there could be a number “licensed entities” authorized under UN guidelines and approvals to be designated to undertake the removal process. Overall it is believed that the “economic fund” mechanism could help to create all the right incentives in the following ways: (a) reward to launching entities for a clean launch; (b) a further reward to operators for removing debris properly at end of life; (c) the “sunset provision” would establish a specific goal to get the job done; and (d) the “fund approach” (or alternatively even a prize approach) would allow the competitive development of the best and most cost efficient technology. Not everyone believes that this financial mechanism would work based on skepticism of the economics. One estimate has been made that ten major deorbit of large debris elements need to be undertaken each year to have a positive impact on debris buildup. If one were to estimate that the cost of each deorbit operation would be $200 million (US), then this would require $2 billion (US) a year of revenues and that such a fund would generate less than the needed finances to be viable. Such an assumption is based on a conventional fetch-and-retrieve robotic operation. There are many new concepts based on “electrodynamic” operations that, if they could be proved, could carry out multiple removal operations with a single in-orbit craft. The long and short of it is that new technology driven by economic incentives would be key to making such a funded approach viable in terms of achieving its mission. What is clear at this point is that there is no agreed plan – whether a fund for debris removal, national governmental debris removal missions, or any other approach – that is a viable solution to a problem that is growing worse each year. Another large-scale event such as collision of large craft or another missile shoot down could be catastrophic in threatening long-term safe access to space. The scenario vividly portrayed in the 2013 movie “Gravity” would ultimately lead to a “space debris winter” that would seal off longer-term safe access to space for humankind. Page 7 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Next Steps Forward Several countries have discussed the feasibility of direct action to demonstrate the feasibility of active debris removal. But one or two demonstration projects may help prove the viability of various techniques, but this is not sufficient to solve this problem. If the United States, France, China, Japan, or perhaps the Russian Federation, or perhaps Europe would blaze a trail by creating such a fund, this could be a key first step. This could test the viability of various provisions of how such a fund would be established, payments paid in, and generally administered. Such an initial effort could serve as a very useful test case for how this might be undertaken on a larger scale. This test case approach might also be useful in terms of addressing the liability issues, whether passive or active removal systems would somehow be supported and finally with the country or region assuming liability responsibility for any “accidents” that might occur during the removal process. The other option is for several countries – again the same countries as above – embarking on experimental missions to bring down the most dangerous space debris elements on a proof of concept basis. If several countries could join together to undertake such trial missions and prove that it could be safe and effective, this would be a very desirable step forward. The main element to stress here is that the idea of creating an orbital debris removal incentive fund and individual missions to deorbit space debris are not mutually exclusive. If well-coordinated, they could become, in time, a part of a globally agreed strategy.

Economic Considerations Currently the cost of removal of debris from orbit is very high and the technology is unproven. If an active remediation program is to be undertaken to remove space debris from certain orbits, the central issue that is clearly posed is how will the cost of these operations be funded and would this activity be under taken via national governments, an authorized international organization, or perhaps by commercial entities? What is clear is that there is today no established and ongoing mechanism to fund space debris removal either at the national, regional, or global level. The current situation is that one or more countries might be willing to fund a test case to prove the possibility to the viability of one or more technique. A one-off test case would certainly be of potential value, but still does not offer a longer-term solution. Establishment of an “orbital debris removal fund” to which all future launch entities would contribute has the advantage of letting all space activities (i.e., those of civil space agencies, defenserelated space entities, as well as commercial entities) contribute to the cost of removal. Such a fund could also be adapted so that commercial entities might be able to participate in the removal process. The major problem is that the technology needed to accomplish such removal is yet to be demonstrated and proven and currently is seen to be very expensive. Thus, no one can accurately project how much money would need to be collected to fund active fund removal. Currently the only specific concept that might be carried out on an “economic basis” is the proposal that laser pulses might be directed toward orbital debris that is seen as a collision risk with other space objects so as to change the debris orbit sufficiently to avoid collision. This approach has the negative feature as potentially being seen as a space weapon. The suggestion has been made that the registered country for the space object concerned could be asked to control the laser pulse emissions directly themselves and thus avoid the perception that such actions represent in any way a hostile action. From an economic viewpoint such an avoidance of a space-based collision by Page 8 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

a space debris object is currently the most cost-effective way to proceed since ground-based systems are less costly to build and operate.

Legal Concerns What legal or regulatory processes could be agreed to ensure that active or operational satellites were not intentionally – or even unintentionally – removed from the orbit? There is no effective mechanism to protect satellite operators from loss of their operational spacecraft that is foolproof or even demonstrated in practice. Nevertheless, reasonable precautions are possible. The first step is a universal machine-readable system that indicates the orbital characteristics of all trackable space objects. The Space Data Association is the first step in this direction but much more needs to be done. And if such removal of an operating space system should occur, how would the operational entity that deployed the satellite be fairly compensated? No clear-cut compensation process is currently in practice. There are nevertheless reasonable ways to proceed. A demonstration project that concentrated on removing upper stage rockets would clearly be one logical way to start to show how precise methods could be utilized to deorbit debris while avoiding adverse effects on currently operating space systems.

Bounding the Size of Space Activities in Terms of Their Economic Import A useful first step might be to try to calibrate the economic size and importance of space-related activities as they exist today – and to project these forward. The purpose of this exercise would be to have a reasonable “yardstick” for considering what the size of the “global fund” might be without it being overly onerous to the various participants. Contributions to the “orbital debris remediation fund” itself would be in fact indexed to only two factors: (a) the orbits that various space operators utilized and (b) the size and value of the various space missions (that presumably relate to their size and thus their potential future orbital debris risk factor). There might be a cap on “assessed value” for the very largest missions.

Various Space Activities and Their Economic Size The largest single identifiable space-related market is that of satellite communications. The annual studies by the Satellite Industry Association and the Futron Corporation put the combined satellite services revenues, satellite manufacturing, associated launch services, and ground equipment market for 2010 at just over $180 billion (US) (Futron 2012). This does not take into account insurance and regulatory/consulting costs nor does it quantify defense satellite communications systems into these figures. Another very sizable amount of spacerelated activities relates to satellite-based defense communications, strategic space surveillance, navigation and targeting, meteorological observation, and space weather observation. Worldwide this could add over $150 billion in annual space activities if one takes into account the programs of the United States, Europe, Japan, China, Russia, and a growing number of other spacefaring nations. There is now a great deal of commercial activities and operations related to satellite navigation that is not related to defense activities. The annual sales of consumer devices and related software for Page 9 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

satellite navigation are estimated to be as high as $30 billion. The deployment of next-generation GPS systems, Galileo, and satellite navigation systems by Japan, China, Russia, and India has a host of commercial applications, but the shift to the guidance of aircraft (including takeoff and landing), ships at sea, and trucking and bus operations adds a whole layer of economic importance and significance to satellite navigation. The quantification of the economic importance and economic product associated with remote sensing, Earth observation, and meteorological satellites (for weather forecasting and monitoring of climate change) becomes even more difficult. Each year meteorological satellites lead to more accurate forecasts that save perhaps tens of thousands of lives. One cannot easily quantify the value of spotting forest fires, crop diseases, natural resources, or schools of fish. It seems quite safe to say that a synoptic figure for all types of directly quantifiable space applications that provide commercial, defense, and governmental services plus scientific missions in Earth orbit is easily equivalent to some $400 billion a year and perhaps $500 billion a year. But if one considers the indirect benefits of all space-related activities to humankind and global security and safety that the actual “value” soars into the trillions of dollars. The threshold question of relevance is whether those engaged in all forms of space activities and applications and spacecraft launches into LEO, MEO, polar, or GEO orbits could be “enrolled” in a system whereby a very small percentage of their cost of their space operational costs could be marshaled toward the active removal of space debris. Today commercial satellite operators routinely spend 15 % of their satellite mission budgets on obtaining launch insurance. The payment of something like 5 % of their total mission expenses toward a space debris mitigation and remediation fund is in many ways a very parallel concept, except that it would be much cheaper, and if these undertakings were done in an efficient way, this “sustainability of space” fund might be necessary for only a relatively short period of 20–25 years. There are obviously many practical questions that are involved here that would need to be answered over time, but for now this is just an intellectual exercise – or thought experiment.

Users of Different Orbits: Why They Would Pay Differing Amounts in the Fund? The key initial question perhaps would revolve around the fact that the most profitable satellite commercial operations (i.e., satellite communications) for the most part use the geosynchronous (or Clarke orbit) where the space debris problem is now clearly the least severe. Conversely, the satellite operations in low Earth orbit and polar orbit, where the problem of space debris is the most severe, involve the types of operations that produce the least amount of revenue per satellite and involve all sorts of what might be called “extraneous markets” such as student experimenters, researchers, and developing countries wanting to launch microsatellites, CubeSats, and other instruments that have high space debris potential but low or no commercial value. This raises a major space policy question as to whether such experiments and small satellite projects should be required to have active or passive deorbit systems or be consolidated into larger integrated packages that can actively be deorbited. Quite simply, the dilemma associated with active space debris removal is the following. Those organizations with the greatest potential to help finance space debris removal are generally not those most significantly now contributing to the space debris problem. Further, there is no global entity such as the United Nations or the ITU that has the current authority to “tax” satellite operators or those who launch satellites in order to apply these revenues to active space debris mitigation. In Page 10 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

many ways the economic issues here is like the classic issue of who pays for a lighthouse from among all the owners of ships at sea. The most salient facts to be considered by the satellite communications industry and others that use the GEO orbit are the following: (i) Should the Kessler syndrome develop, it would in time seriously jeopardize the ability to launch satellites to GEO orbit; and (ii) the problem of orbital debris and possible collision between satellites in GEO orbit, as recorded in the space situational and satellite conjunction reporting of the Space Data Association (that currently reports on 60 % of the GEO orbit satellites), is worsening each year (Space Data Association 2011). In short, unless efforts are undertaken sooner rather than later, the problem of space debris and dangerous conjunction of spacecraft for GEO and LEO orbits, and indeed all Earth orbits, will continue to worsen over time. New measures are needed. The longer this remediation process is delayed, the worse the problem will become and the more expensive mitigation measures will become.

The Costs of Space Situational Awareness Versus the Costs of Orbital Debris Removal Another difficult issue is that of what is called space situational awareness and the cost of knowing about the current status of space debris. The United States and other countries spend billions of dollars to track space debris and maintain what is called “space situational awareness” as part of their missile defense programs. The United States shares the information obtained from the current US Surveillance System and likewise will share information derived from any other new capability such as the almost funded – but now cancelled – S-band radar Space Fence. This new installation would have cost at least $6 billion in capital investment. The problem is that the United States is not willing to surrender the operation of its tracking capability to an international agency because it considers the function of the facility to be vital to the protection of the US homeland from attack. The most significant thing to note here is that the cost of active debris removal and the cost of current and planned space situational awareness systems are roughly comparable (“New Debris-Tracking..” 2012). A number of satellite operators have begun sharing data concerning the orbits of their operational satellites via an organization already identified above as the Space Data Association, but at this stage this sharing of data is almost exclusively among operators who deploy satellites in GEO orbit and thus does not, to date, include any significant sharing of data in the LEO or polar orbits. The extension of the data sharing to all near-Earth orbits, and in a consistent machine-to-machine manner, is a most desirable next step forward (Space Data Association 2011) (Fig. 1).

Key Steps Forward Concerns Orbital Debris Reduction In summary, all the users of space for commercial, strategic, governmental or even educational, research, and humanitarian purposes have a stake in being able to access space reliably and “sustainably” into the future. A variety of steps are thus needed. These include: (i) improved space situational awareness; (ii) prelaunch due diligence enforced by governments in accord with international standards that would prevent the creation of further space debris; (iii) active deorbit of spacecraft at the end of their useful life, again in accord with international standards (as noted above the further issue of improved practices concerning the deorbit of small and nano-satellites must be Page 11 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Fig. 1 Scale representation of orbital debris in low Earth and polar orbit (Graphics courtesy of ESA)

addressed and resolved as soon as possible); and (iv) in the absence of active space debris deorbit capabilities, passive systems that assist with debris removal represent a fall back alternative. It is believed that there is merit in the creation of national, regional, and, in time, an international fund for debris removal and mitigation. This fund could be administered by one or more international banks or launch insurance companies or any other approved international mechanism. The purpose of the fund would be to pay out to “international licensed” entities which competently remove space debris from orbit according to a set schedule of payments for such debris cleanup activities. A small percentage of the fund could also be used to carry out internationally sanctioned debris mitigation and remediation-related activities. It might also be used to fund activities related to changing the orbit of debris that might also immanently crash into satellites or other large debris objects. The clarification of how such a fund might work and to what activities it would apply is one of the reasons that a national or regional fund – prior to a global fund – might be a useful preliminary step. The conceptual purpose of the fund in general terms, however, would be to finance (a) the mitigation of the future buildup of space debris, (b) the active removal of the most dangerous space debris elements from Earth orbit, and (c) the movement of derelict space objects in to a graveyard orbit or a safer location for the purpose of collision avoidance.

Feasibility of Establishing a New International Entity for Active Debris Removal Many might suggest that instead of creation of a fund that a new international entity might be created to undertake this purpose and that of course is certainly an option if only it were achievable. This could be an alternative and effective solution, but the currently fragmented international conditions that relate outer space make this an unlikely solution at this time as noted below. Page 12 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Difficulty of Obtaining International Consensus: The UN Committee on the Peaceful Uses of Outer Space is now comprised of some 70 countries where consensus is very difficult to reach. It is possible that various space agencies of the world that have formed the Inter-Agency Space Debris Coordination Committee (IADC) might create a new entity to undertake coordinated international action in this area or the Space Data Association’s role might be expanded to take on this task, but currently no such actions are seriously pending. Other Pending Space-Related Issues that Might Require an International Space Agency: The issue of orbital debris is not the only pending international issue involving space. Other serious issues such as planetary defense, atmospheric and stratospheric pollution, the regulation of the flight of space planes and the possible need for oversight of private space platforms, and possible military uses of outer space are other pending issues that might be considered higher priorities related to international space regulation. It is not clear whether an organization such as the International Civil Aviation Organization (ICAO) or the World Meteorological Organization (WMO) might, for instance, be assigned additional international regulatory authority regarding both “Protospace” and outer space, and if this were to occur, it might be assigned responsibility for addressing such issues. At this time the International Telecommunication Union (ITU) comes the closest to having regulatory authority in this area, and currently it has not been in a position to exert much authority to control the buildup of orbital debris. Certainly it lacks the power to exert sanctions over nations responsible for the creation of new debris. Costs and Organizational Complexity: Creation of a new international agency, whether within the UN system or under expanded versions of the IADC or the SDA would all be costly, involves much greater organizational complexity. Certainly there would clearly be difficulty in obtain agreement to given regulatory oversight authority to any new international entity and a further difficulty in raising the funds and agreeing to the staffing of this entity to operate. Incentives to Create New and More Cost-Effective Technology for Debris Removal: Aside from the other practical and political considerations, it is also likely that a fund approach – as opposed to creating a debris removal agencies – would create an economic incentive to create new technology to remove debris more efficiently and at lower cost than conventional ideas of robotic “fetch-and-retrieve” concepts that are enormously expensive. It is for the above reasons that an incremental approach to addressing orbital debris issues seems most prudent. In time a new international space regulatory agency that could be empowered to address all of the space-related issues noted above may be necessary. Indeed one might begin now to identify the various important space-related activities that an international space regulatory agency needs to address and document the nature and the importance of these needs to help work toward such an important global milestone (Jakhu et al. 2011). In the nearer term the creation of a funding mechanism to address space debris may represent a more achievable objective. It would seem to be more economically efficient to make payments – perhaps most likely collected by national governments – into a bank or insurance company-administered-and-invoiced fund. The funds would then subsequently be to pay out to “licensed entities” after they have removed debris elements from orbit. The fund would also serve a further function of creating financial incentives for “clean launches” and for “active removal” of satellites at end of life. If the fund were established on the basis of a 5 % of mission cost (i.e., a third of normal launch insurance costs), the rebate system might work as follows. After it is certified that the launch has been “clean” and created no new orbital debris – including the upper stage rocket – the entity posting the bond to the fund would be remitted 1.5 % of the 5 % payment. If at the end of life the satellite is reentered successfully or deployed in a prescribed graveyard orbit, there would be a further 1.5 % rebate. The residual amounts as well as the interest accrued on the funds would be used to “clean up” near-Earth orbits. Page 13 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Licensed entities deemed qualified to remove orbital debris or place an officially designated defunct satellite in a graveyard orbit would be required to work under appropriate international regulations and safety standards. Those who undertake the removal would only be compensated after the removal had been accomplished and clearly documented as to the size, mass, and orbit of the debris element. An international bank (or perhaps several banks or launch insurance companies) could be designated to undertake the investment and disbursement of the funds. Government administrations as designated by the ITU or UN COPUOS would be responsible for collecting the funds and depositing them in the bank prior to actual launch. The fund would be created by a two-tiered system that includes a “performance bond payment” against actual performance in terms of not creating debris at launch and in terms of removal from orbit at end of life. This performance bond payment would in each instance be equivalent to 1.5 % of the mission cost. The performance bond would certify that the mission would not release any space debris in the process of their launch and deployment, and when verified (e.g., by onboard cameras), they would receive a certification check. There would also be a performance bond against active removal of spacecraft from orbit at end of life or redeployment to a graveyard orbit. These provisions would be specifically designated for the cases of low, polar, medium, or GEO Earth orbit. They would have to provide for sufficient propellant systems and fuel (i.e., hydrazine, bipropellant, ion engine, etc.) to guarantee return of the satellite to Earth in a controlled fashion or in the case of GEO orbit to raise the satellite at least 1,000 km above GEO orbit or move the satellite into an orbit that would intersect with the sun. The entity would be refunded 1.5 % of the bond after a successful launch creating no orbital debris. After the removal of the satellite from orbit without creating debris, another 1.5 % of the bond would be returned. The size of the performance bond would be for a set amount of the overall cost of the mission (such as 5 %). The mission cost would become part of the filing with the ITU by the responsible administration at the time of the spacecraft filing. There could also be a tiered funding of the space debris removal fund. This might set the fund charge to be 5 % of the cost of the mission if in GEO orbit, 6 % of the cost of the mission if launched into MEO orbit, and 7 % of the cost of the mission if launched into LEO or polar orbit. In the case of MEO orbit missions, if there were insufficient fuel associated with the mission to maintain stationkeeping and active removal at end of life, the fee would be set at a much higher rate. This process for establishing and sustaining the fund would in effect raise the net cost of all satellite launches by about 3–4 % percent for the next 25 years (assuming that most launches were indeed clean and most end-of-life disposal operations were successful.) The funds raised should be sufficient to reduce the amount of space debris substantially within a two decade to 25-year period. The cost of paying into the fund would create large economic incentives to eliminate the formation of new space debris due to new satellite launches and also pay to remove significant elements from orbit by means of the licensed entities. There could be a mechanism to adjust the collection rates, if, for instance, the removal process turned out to be less costly than currently envisioned. Such an orbital debris removal fund concept would put economic incentives front and center. Operators and all types of space agencies would have a direct economic incentive to eliminate existing and future space debris. Those entities developing technologies and systems to remove space debris would have maximum economic incentive to actually remove existing material from orbit. Government regulators would be charged with identifying “prime targets” for removal of space debris. Launching states and space system operators would have strong incentives to create less space debris, not leave derelict space objects in orbit. Operators would likewise be financially motivated. The exact formula for payments into such a fund can obviously be crafted more carefully and precisely by those that might come together to negotiate the exact terms of building the funds. If the Page 14 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

funds are first established on a national basis, there should be a “model charter” for the fund so that national and regional funds could subsequently be merged into a global or universal fund. The challenge of course would be to convince all those launching satellite systems that a 5–7 % increase in their overall costs is a wise investment against avoiding a future condition in which all space operations would be impossible – i.e., the onset of the Kessler syndrome. In this case national governments may need to be the “grown-up in the room” that first act to create the initial funds. In this regard, there is a marked similarity in these proposals to various other economic strategies to stop speeding on highways, to maintain safe naval navigation, to stop environmental littering or pending strategies, and to stop runaway climate change. In all cases one is simply creating significant economic incentives to keep everyone on their best behavior and to take needed preventive action. The universal economic fund strategy would separate the fund from a number of “licensed actors” that would be free to develop multiple technologies and systems to carry out remedial actions. Today many technical approaches are currently under consideration to address this problem. These approaches are outlined in the preceding chapter. The fund would avoid trying to pick a winner and would let a market system decide which technology or system was actually best.

The Value of Earth Orbit to Humanity and Future Space Commerce Some might argue that such a fund for removal of orbital debris is premature. Others would argue that since the problem now is largely concentrated in the low Earth and polar orbits, the fund, if created, should collect only for launches into these orbits. These short-sighted views of the problem do not account for the fact that as the debris problem grows and cascade, debris from larger debris elements will eventually endanger all space launches – even those launches of payloads beyond Earth orbit. The most important thing to focus on is that the value of all Earth orbits is tremendous. If one concedes that the value of a GEO slot is today perhaps $1–3 million per year and access to a safe LEO environment is also worth millions per year, then the combined value of “safe access to Earth orbit” is worth perhaps a billion per year and that mounting orbital debris is constantly serving to depreciate the value and usability of this global commons resource. Indeed these valuations are perhaps quite low. Fairly recently two companies, out of a total seven bidders, won the rights to use satellite orbital positions auctioned in 2011 by Anatel of Brazil. Hughes Communications will pay $95 million for two Ka and Ku slots in GEO. Star One (owned by Embratel) will pay $39 million for two slots in the X, Ku, and Ka bands (“Slim Owned..” 2011). The value of the GEO, MEO, and LEO orbits is by any reasonable calculation now worth billions of dollars (US) over just a 10-year period. Investing several hundred millions to clean it up for all space users seems not only logical but cost-effective as well. These valuations would tend to put the annual worth of many orbital positions to be $4–10 million per year. The bottom line is that there are “costs” associated with not cleaning up Earth orbit from orbital debris, and the sooner this challenging task is undertaken, the lower the cost of removal will be and the safer access to space will be for the longer term. Economic analysis suggests that delay in the attacking serious common global problems – whether it be climate change, ozone layer depreciation, or orbital debris buildup – will only become more difficult, more technically challenging, and certainly more expensive.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

Micro- and Nano-satellites and Orbital Debris One may also suggest that this approach, however, could also serve to limit the launch of microsatellites and smaller projects of developing countries. Certainly, this new system could well serve to create economic disincentives for smaller educational and research space projects and for projects of developing countries. Yet at the same time, it could also create “incentives” to consolidate their efforts within larger platforms or to fly experiments on the International Space Station or other space stations. A number of “CubeSats” can be joined together and efficiently flown as an integrated system. It is certainly the case that small or microsatellites are indeed one of the key complicating factors in the development of space debris. Small satellites, especially when launched into low Earth orbits, are currently a small amount of the orbital debris problem, and it is the largest satellites (and derelict larger space objects) that are the most significant concern. Nevertheless better ways to mitigate debris caused by small satellites need to be addressed. The three options that might be internationally agreed with regard to the deorbit of small satellites have been briefly outlined above in “Key Steps Forward” (Jakhu and Pelton 2014).

Analysis of Different Means and Ways for Solving the Space Debris Problem Regulatory Approaches: Clearly any of the various ways forward will include a regulatory component. The UN COPUOS has developed voluntary guidelines for orbital debris control and minimization in conjunction with the Inter-Agency Space Debris Coordination Committee (IADC). The Space Data Association (SDA) has contributed quasi-regulatory concepts to the control of space debris. There is a need for more than guidelines to control formation of debris and the removal of space debris has technical and economic challenges that are not likely to be solved by regulations alone. An international agreement on linking the granting of launch and operations licenses to a credible plan for the removal of a space system at the end of its mission, and to levy high penalties equal or higher than the cost of the system in case successful removal is not achieved, would be a key step to create a market for removal services. Technical Approaches: The current wide diversity of ideas about how to remove space debris suggests several things. It suggests that at this stage at least there is no clear “winning idea” about how this could be done. All of the technical options now available are unproven, are expensive, and also give rise to a variety of concerns. It has been proposed that the best place to start is to undertake several demonstration projects to start the removal of the largest derelict objects. This makes a great deal of sense. Nevertheless, the idea of a fund would likely create major incentives to develop newer, lower cost, and more efficient technology. Organizational Approaches: The creation of a single international agency to carry out this task gives rise to a host of concerns. These concerns include (i) high likelihood of focusing on a single technology; (ii) high overheads; and (iii) the problem of international agencies not necessarily being the best source of innovation, not likely to produce cost-effective solutions, and often can be selfsustaining even if their mission has been fulfilled. Instead a mixed government-private consortium similar to the early INTELSAT that launched international telecommunication services via satellite 50 years ago may be an interesting model to follow, in particular if transition in due time to a fully private company is pre-agreed. An even more important consideration is that there may need to be a new organization to address other such issues as space traffic management, stratospheric pollution and climate change, etc. Such a new space-related organization would need to consider these issues Page 16 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_70-1 # Springer International Publishing Switzerland 2014

as well as orbital debris. In short, a synoptic overview is needed as to which existing international organization could best address these complex of issues or if a new international entity is indeed required. Economic and Incentive Prize Approaches: The best way to alter human and state behavior on a global scale today seems most often to involve the creation of clear market incentives. If there is a price to pay for NOT removing space debris and there were also strong economic incentives to create the best technology to remove debris from Earth orbit, then the likelihood of success seems to increase considerably. If there were a strict process for controlling the “licensing” of entities to remove elements from space and there were the equivalent of a major prize that would go to the entity that could develop the best and most efficient way to remove space debris, then the most rapid and effective progress might well be achieved. This would be in some ways equivalent to the “XPrize” approach to developing commercial space travel or fuel-efficient cars or low-cost ways to explore or create permanent settlements on the Moon. The international “licensing” of international entities that were “authorized” to develop the technology and then to remove space debris under guidelines developed by the UN COPUOS or a consortium of governmental space agencies (organized like the IADC) poses a number of tricky issues to be solved. But such challenges are not an impossible goal to achieve.

Conclusion If one creates economic incentives for prevention of space debris and high penalties for its creation, this will prove to be a powerful tool to stop this growing problem. A focus on economic solutions can allow a diversity of new and more cost-effective technology to be developed. Performance bond incentives based on actual results (i.e., rebates against no new debris and payouts for deorbiting at end of life or placing satellites into graveyard orbits) should be a part of the solution. The ideas outlined in this paper are analytic and conceptual. The details of actually implementation would need to be worked out through detailed international negotiation. The basic concepts are, however, quite clear: • A new space convention that allows the right incentives and penalties for “clean launches” and system disposal at end of life and allows derelict space objects to be designated as space debris would certainly be a step forward. Such new space convention would link the granting of launch and operations licenses to credible plans for removal of space systems at the end of their mission and would levy high penalties perhaps equal or higher than the cost of the system itself in case successful removal is not achieved. Creation of a fund that would compensate “licensed entities” after they had performed debris removal would create a powerful market force to get the greatest amount of debris down in the most efficient way. This solution would let economic market forces drive technical innovation. • The fund should have a beginning and end of life with a clear objective to accomplish the “cleaning up” of Earth orbit by the time space operators would stop paying into the fund. • The funds may well start at the national or regional level and this could work out a number of problems about the funds’ efficient operation. The desire would be for the fund to eventually be “universal” among all space launching entities. A “model charter” for such a fund would facilitate the “evolution” of the funds to become universal. There should be technical, regulatory, and economic incentives for small satellites, microsatellites, and nano-sats to be combined and consolidated. These smaller missions should where practical and possible be carried out on the Page 17 of 19

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• •

•

•

International Space Station or consolidated so that active disposal is possible. The three options for addressing orbital debris and small satellite proliferation as outlined above under “Key Steps Forward” should become a part of the international discussion. Creating a “wise, effective, and strategically effective way” to license entities to perform space debris removal is one of the top challenges to this approach but this is not an impossible task. International banks or launch insurance companies or some other entity could administer such a fund or funds. Limited new mechanisms would be necessary for proceeding in this manner and if the arrangement looked, felt, and essentially acted as if it were a new form of launch insurance, then its implementation could certainly be advanced more quickly. None of the ideas provided with regard to creation of a Fund for Orbital Debris Mitigation should be considered to be opposition to or against the parallel efforts for national space agencies to undertake trial programs to undertake “fetch and retrieve” programs to deorbit major space debris elements. Such efforts should be carried out in concert with each other and not in competition. Finally it should be noted that there are several key issues of global governance involving near Earth that are currently pending. These include (i) frequency management, interference, and future spectrum demand; (ii) stratospheric pollution and climate change; (iii) space traffic management and regulation of the use of the “Protozone” (i.e., 21–100 km in altitude); and (iv) increasing levels of orbital debris. It is really not logical or even possible to consider these issues in isolation of each other. A systematic solution to appropriate regulatory action in all of these areas is needed. In the interim if economic incentives could be created to minimize the creation of new debris and also actively move to deorbit debris elements, this would be a very positive step forward.

Cross-References ▶ Active Orbital Debris Removal and the Sustainability of Space ▶ Hazard of Orbital Debris ▶ Nature of the Threat/Historical Occurrence ▶ Regulatory Aspects Associated with Response to Cosmic Hazards

References Futron Corporation (2012) Annual assessment of satellite communications enterprise for the Satellite Industry Association. Bethesda Jakhu R, Pelton J (2014) Small satellites and their regulation. Springer Press, New York Jakhu R, Sgobba T, Dempsey P (2011) The need for an integrated regulatory regime for aviation and space: an ICAO for space? Springer Wien, New York Latin American Herald Tribune (2011) Slim-owned satellite company wins orbital slots in Brazil. www.laht.com/article.asp?CategoryId¼14090&ArticleId¼421247. Accessed 1 Sept 2011 Listner M (2011) Revisiting the liability convention: reflections on ROSAT, orbital space debris, and the future of space law. The Space Review, 17 Oct 2011 Pelton JN (2012) A global fund for space debris remediation: a new way forward to address the mounting space debris problem. International Space University symposium, Strasbourg, March 2012

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Schons M (2011) Superfund: how one government program helps clean up toxic-waste sites. National Geographic Education. http://education.nationalgeographic.com/education/news/ superfund/?ar_a¼1. Accessed 21 Jan 2011 Space junk problem is more threatening than ever—report warns. www.space.com/12801-spacejunk-threat-orbital-debris-report.html Space.com (2012) New debris-tracking ‘space fence’ passes key test. http://www.space.com/14867space-fence-orbital-debris.html. Accessed 12 March 2012 The Space Data Association (2011) Space Data Association now performs conjunction screening for more than 300 satellites. http://www.space-data.org/sda/wpcontent/uploads/downloads/2011/01/ SDA_press_release_21_Jan_2011_RELEASED.pdf The Torino impact hazard scale. neo.jpl.nasa.gov/torino_scale.html Wired Magazine (2010) The looming space junk crisis: it’s time to take out the trash. www.wired. com/magazine/2010/05/ff_space_junk/all/1. Accessed 24 June 2014

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Nature of the Threat/Historical Occurrence Frederick Jonas* Amateur Cosmologist, Gallup, NM, USA

Abstract The threat of a comet or meteor Earth impact exists and is evidenced by the geologic record of impacts on Earth. More recently is the well-publicized Chelyabinsk meteor airburst that occurred in Russia on February 15, 2013. Explosion was estimated to be on the order of 4–500 kt (TNT equivalent). The resulting airburst explosion resulted in numerous injuries and building damage. Chelyabinsk showed us that the threat to Earth is real. It is also natural. The evolution of the solar system began with mass lumping together, and it is still doing so today. Mass accretion. The Earth is still growing. It will continue to do so in the future. However, this natural order can be hazardous depending on the size of the impactor continuing the mass accretion process. This threat to Earth regarding potentially dangerous impactors must be mitigated. There is a growing international effort and concern, heightened by the Chelyabinsk meteor, to find, characterize, and defend against threatening solar system bodies. The good news is these efforts have begun. They must continue.

Keywords Accretion; Solar nebula; TNT equivalent; Late Heavy Bombardment (LHB); Astronomical unit (AU); Shoemaker-Levy 9; Earth impact data; Earth-Crossing Objects (ECOs); Near-Earth Objects (NEO); Potential Hazard Asteroid (PHA); NASA; NOAA

Introduction Clearly, the threat of a comet or meteor Earth impact exists as is evidenced by the geologic and recent record of impacts on Earth. Meteor (Barringer) Crater (Fig. 1) in Arizona offers visible evidence of a relatively recent impact that occurred a mere 50,000 years ago. The impactor is estimated to have been a nickel-iron meteorite about 50 m in diameter. This impact resulted in a crater about 1,200 m wide and 170 m deep. To give a broader context, such a crater would have been created from a 10-Megaton (TNT equivalent) nuclear explosion. It should be noted that 10-Megaton TNT equivalent nuclear device is in the range of the largest yield hydrogen bombs developed during the Cold War. Other evidences regarding large impacts on Earth of course include the event that may have contributed to the final demise of the dinosaurs 65 million years ago (the Chicxulub crater). Analysis of the geologic record seems to indicate that the dinosaurs may have already gone extinct by the time of this impact; regardless, this impact sealed the deal and significantly altered the Earth’s environment and weather for many years after. Finally and most recently is the Chelyabinsk meteor airburst that occurred in Russia on February 15, 2013. The latter was estimated to be on the order of 4–500 kt

*Email: [email protected] Page 1 of 12

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 1 Meteor (Barringer) Crater in Arizona

Fig. 2 The backside of the moon gives visible evidence of impacts across the entire surface

(TNT equivalent). The resulting airburst explosion resulted in numerous injuries and building damage evidenced by the numerous broken windows due to the air-blast shock wave. And if the scant yet convincing Earth impact record is not enough, then all we need to do to convince ourselves that impacts due to meteors and comets occur is to look to the heavens. Most notably, our closest neighbor, the moon, especially the back side, is excessively pockmarked by impacts as shown in Fig. 2. Visible eye evidence shows the scars of multiple impacts. Other airless bodies we have observed in the solar system all bear the same evidence regarding the nature of the threat due to impacts. Their surfaces are literally covered with impact craters of all sizes, preserving a record of impacts over the course of our solar system’s four-and-a-half-billion-year history. And that history appears to be very violent. More importantly, it appears that impacts are but a natural evolution of the solar system development, growth, and maturity built on the premise of “mass accretion.” That is how the solar system is believed to have evolved, mass accreting and clumping together growing into the Sun, planets, moons, comets, and asteroids, all that we see. And, this is

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 3 A solar/disk around Beta Pictoris representative of our early solar system

how the solar system will continue to evolve. The threat will remain as long as the solar system exists. It represents the natural order.

Solar System Evolution The solar system is believed to have been borne from a swirling shrinking disk of gas and dust called the solar nebula some 4.5 billion years ago. Now, thanks to the Hubble Space Telescope, there are many recorded and archived evidences of creation and transmutation of nebulas into solar disks (Fig. 3). Ultimately, out of this swirling chaotic mass is borne the solar system. It all began with the process of mass accretion which then was ultimately dominated by gravity as the clumps grew larger. As it is today. As it will continue to be. That mass which clumps together naturally in this environment was vividly demonstrated in space by astronaut Donald Pettit onboard the International Space Station in 2004. His experiment demonstrated that matter ranging in size from 1 mm to 6 mm naturally clumps together in the microgravity environment perhaps due to electrostatic forces, but nevertheless clumps together. This process was also shown to be fast and repeatable. This presented clear evidence of the mechanism that initiated the growth of these “lumps” of matter before gravity begins to take over. The Sun, planets, and all bodies in the solar system then grew based on attracting and accreting the mass around them in the solar disk. A picture of such a solar disk around Beta Pictoris is shown in Fig. 3. This European Southern Observatory (ESO) photograph shows not only the solar disk but a planet (white dot) as well that is most likely suffering numerous impacts in its accretion process. That “accretion” process and gravitational attraction result in what we call impacts today and are occurring in Beta Pictoris as well. And, this process of accretion is never ending. The Sun, planets, and moons continue to gain mass today, albeit slowly. Recent evidence was seen by the entire world in Jupiter’s capture and resulting impacts of comet Shoemaker-Levy 9 in July 1994 (more information on this event is presented elsewhere). Accretion and impacts, with the potential for Earth impacts, will continue indefinitely which is the natural order. In order to estimate the threat, we need to understand the historical record of impacts and when they occurred. From this we can perhaps better predict the future probability of impacts here on Earth and determine if the rate of impacts with time is decreasing as we might expect. In that process, it was discovered that a significant and surprising increase in the impact record occurred some 3.9 million years, well into the solar system development some 600,000 years after the formation. That period of

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

time has come to be called the Late Heavy Bombardment (LHB). Understanding why that occurred is important to our ability to predict and understand the nature of future impacts.

Late Heavy Bombardment

All was proceeding in an orderly “chaotic” fashion in those first few hundreds of millions of years of formation in the early solar system. The first clues that this orderly “infinitely chaotic” process was interrupted about 3.9 million years ago came from the moon. The clues seemed to indicate that during a relatively short period of time, there was a huge increase and spike in the number of surface impacts. Examinations of Apollo moon rocks showed evidence that nearly all the craters in the lunar highlands formed during a brief period of time, approximately 100 million years long. Based on their age, this appeared to be 3.9 million years ago. During this period of massive impacts, it is estimated that nearly 2,000 impacts (resurfacing 80 % of the moon’s face) were larger than the Chicxulub meteor impact that coincided with the end of the dinosaurs. The resulting crater in the Gulf of Mexico near the Yucatan Peninsula centered near the town of Chicxulub is approximately 110 miles in diameter that resulted from a meteoroid estimated to have been 6 miles in diameter. The Earth, being a bigger target than the moon, is estimated to have suffered impacts 10 times more severe covering every square inch of the Earth during this same period. That qualitative increase in the number of impacts during this period is graphically depicted in Fig. 4 and is called the Late Heavy Bombardment (LHB). Up until the evidence began to accumulate in favor of the LHB, the solar system was thought to have operated with clockwork precision once the planets were formed. There were however other clues that this picture was not as it seemed. Pluto exists in an oddball elliptical orbit that is inclined almost 12 to the solar equator. Further, it is locked in a curious resonance with Neptune, orbiting the Sun twice for every three orbits of Neptune. Uranus has been knocked on its side with its north and south poles nearly aligned with the solar system’s orbital plane, an axial tilt of nearly 98 . Saturn orbits the Sun once for every two orbits of Jupiter. And, in the Kuiper Belt, numerous rocks and frozen objects have been found with wildly different orbits. Remnants of the solar system development, the Kuiper Belt is a defined region beyond the planets of the solar system starting at Neptune (30 astronomical units (AU)) out to 50 AU from the Sun. This belt consists mainly of small bodies composed of frozen volatiles and includes bodies like the planet Pluto. Emerging theories of solar system formation had planets like Neptune and Uranus forming closer to the Sun. From this evidence, it appeared that something very disruptive had happened in the early solar system.

Fig. 4 The Late Heavy Bombardment (LHB) Page 4 of 12

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Making matters more disconcerting, discoveries of planets around other stars were showing wildly different planetary systems with Jupiter- and Neptune-like planets racing around their Sun in scorching orbits with observed orbits of other planets being wildly eccentric. The “orderly” chaos is evident in these numerous observed systems. Perhaps our view of a clockwise system was simplistically reflecting our view then of the assumed stability and infinite unchanging universe. However, the evidence was piling up in favor of the LHB. The mounting evidence showed that some type of chaotic event occurred during this time period resulting in the solar system we see today. What had happened during this time period? One way to perhaps answer such questions is to employ computational models and simulations that obey the laws of physics as we understand them. That approach bore fruit in this case. A sophisticated computational model, called the Nice Model, developed in 2004 provided results that began to shed light on these mysteries. Hal Levison (Southwest Research Institute) (Reference) and three coworkers, R. Gomes, Alessandro Morbidelli, and Kleomenis Tsiganis, were the principal developers of the Nice Model. The developers were motivated by trying to understand the orbital eccentricities of Saturn and Jupiter and how Uranus and Neptune could have formed so far from the Sun in a theorized region of space that did not support their development. The culprit behind the LHB appeared ultimately to be Jupiter. The model begins with the assumption that Neptune, Uranus, and Saturn had formed closer to the Sun in nearly circular orbits as confirmed by many other theories. The computational results of their simulation showed that as Jupiter and Saturn locked into their 2:1 resonance about 500–700 million years into the solar system development, once linked, Neptune and Uranus were hurled violently outward to their present locations. Neptune then locked into the resonance with Pluto as we see today. In about half of the simulations, Neptune and Uranus swap places. Regardless, the violent sudden motions of these giant planets and resulting gravitational disturbances throughout the solar system caused chaos in the asteroid and Kuiper Belts, extending even into the Oort cloud. Named after Dutch astronomer Jan Oort, the Oort cloud is a hypothesized spherical cloud of icy bodies 5,000 A.U. to 100,000 A.U. from the Sun. 50,000 A.U. is approximately one light year. As noted earlier, Pluto at its farthest is slightly less than 50 A.U. from the Sun. The Oort cloud is estimated to contain 100–200 billion icy bodies and is believed to be the source of long-period comets. The entire solar system felt the effects of these massive gravitational disturbances. While sending bodies in all directions, many headed towards the inner solar system. The resulting violet bombardment of the inner planets (and moon) was brief on geologic time scales, lasting an estimated 100 million years according to the model. Since then, we have returned to a “clockwork” solar system, and impacts have decreased with time as one might expect. However, what we have learned from this model prediction and observations of other solar systems is that the clockwork system can be disrupted with catastrophic results.

Earth Impact History The majority of impact craters on Earth have long been erased with time due to tectonic shifts, geological surface activities, wind, and rain erosion. However, there are enough remaining Earth impact traces such as the Barringer Crater in Arizona to conclude that mother Earth is quite vulnerable to impacts. We are not immune. The Earth Impact Database (http://www.passc.net/EarthImpactDatabase/) provides a list of confirmed impact craters such as Meteor Crater. It is maintained by The Planetary and Space Science Centre (PASSC) located at the University of New Brunswick (Canada). From their web page: “The Earth Impact Database (EID) is a collection of images, publications and abstracts from around the world (compiled over the last 25 years) that provides information about confirmed impact structures Page 5 of 12

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 5 Vredefort Dome

for the scientific community and space enthusiasts.” And, “The Earth Impact Database (EID) comprises a list of confirmed impact structures from around the world. To date, there are 184 confirmed impact structures in the database.” The following is a review of a few of the more interesting Earth impact craters: • Suavj€arvi Crater (Fig. 5): The oldest known crater is estimated to be approximately 2.4 billion years old. Definitely formed well after the LHB. Estimated to be 16 km in diameter, it contains the Suavj€arvi lake at its center (approximately 3 km in diameter). The crater is located about 50 km north of Medvezhyegorsk in the Republic of Karelia, Russia. Not much of the crater survives today, and it was identified principally through the resulting impact shock formations in the surrounding geology. • Vredefort Crater: The largest Earth impact crater with an estimated diameter of 160 km just edges out the Chicxulub crater at 150 km. The Vredefort crater is located in South Africa and is estimated to be just over two million years old. It is also the second oldest crater known. The town of Vredefort is located near the center of the crater. Evidence of impact (shock formations) was again noted in the surrounding geology confirming the crater as due to impact and not volcanic as originally thought. The body creating the crater is estimated to have been somewhere between 5 and 10 km in diameter. While common throughout the solar system, Vredefort is one of the few multiple-ringed impact craters on Earth. • Chesapeake Bay Crater (Fig. 6): The largest known impact crater in the United States. With a diameter of 40 km, it is the sixth largest in the world. Estimated to have occurred about 35 million years ago, the site was confirmed as an impact crater in the 1990s again based on evidence of a layer of fused glass beads (shock heating). While buried with time, the crater created a longlasting topographic depression ultimately determining the eventual location of Chesapeake Bay. The size of the body that created the crater is estimated to have been between 3 and 5 km. • Wolfe Creek Crater (Fig. 7): Another crater as well preserved as Barringer (Meteor) Crater. Barringer Crater is located in the desert of Arizona. This crater is also located in a desert. The lesser known Wolfe Creek Crater is located in the north-central desert of Australia. It is also the second largest rimmed crater in the world, second again to the Barringer Crater. Estimated to be

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 6 Chesapeake Bay crater

Fig. 7 Wolfe Creek Crater

about 300,000 years old, the crater is 870 m in diameter and 60 m deep. It is located 150 km south of Halls Creek in Western Australia. While most of the preceding has assumed solid impactors, we must not forget about the threat due to comets. Visible evidence of the reality of that threat was seen by the world in July 1994 with the impacts of the remnants of comet Shoemaker-Levy 9 with Jupiter (more is presented elsewhere on this comet). Comet Shoemaker-Levy 9 presented to the world the first direct visible observation and proof of extraterrestrial impacts with other solar system bodies. Another highly suspected and highly controversial impact perhaps due to a comet is the Tunguska event that occurred over remote areas of Siberia in 1908. The best theories regarding this event pose an airburst at 5–10 km altitude due to

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

either a small asteroid or comet about 60–190 m in diameter. If so, it is the largest impact on Earth in recorded history. Fragments have been found at the site that may be of meteoric origin. The blast is estimated to have been in the range of 10–15 megatons of TNT based on the level of destruction that occurred over 2,000 km2 of the forested area (over 80 million trees were estimated to have been toppled). Following the event, while unknown to most of the world at that time, glowing sunsets were reported. Natives and Russian settlers near the burst reported a bright bluish light moving across the sky, a flash, than artillery-like sounds rumbling in the distance. Those closer to the blast were knocked over by the blast wave. Seismic stations across Eurasia recorded the event, and atmospheric fluctuations were recorded in Great Britain. The first recorded expedition to the site was in 1921, years after the event, but the evidence for an airburst was and is overwhelming. No crater has been found. A similar well-publicized but much smaller airburst occurred in February 2013 over Chelyabinsk (Russia) resulting in numerous injuries from the air blast and resulting blast (shock) waves. Thus, whether a comet or a meteor, impacts have occurred on Earth. Being the natural order of how this solar system grew and evolved, the threat of Earth impact remains and will continue indefinitely.

Meteor Hazards In order to understand and assess the impact hazard accurately, one must be able to characterize and quantify attributes including size, distribution, and orbits of these near-Earth objects (NEOs) or those objects with orbits that regularly come close to the Earth orbit (those that intersect Earth’s orbit are called Earth-crossing objects (ECOs)). There is a significant effort by NASA and other institutions around the world, including an international effort led by the U.N. to identify and catalogue such heavenly bodies. It is a tedious skywatching activity and understood to underscore the survivability of human race as we know it and cannot be taken seriously enough. As might be expected, amateur astronomers play a huge role in this vigil. The results of this international community effort have shown to date that as expected, there exist many more small NEOs than large ones. Figure 8 is a NASA graphic showing potentially hazard asteroid (PHA) orbits numbering over 1,400 objects. We are of course interested in finding the most dangerous bigger NEOs first. It is estimated that there exist approximately 1,000 NEOs larger than 1 km in diameter and a 1,000 times that number, one million, greater than 40 m in diameter. While there may be many more comets, they are generally in orbits where they spend great distances from the Sun and are estimated to only contribute 1 % to the Earth-impact hazard. By 2013, more than 10,000 NEOs have been discovered, and as our ability to observe these objects improves, that number will only increase. Overall, it is estimated that over one million NEOs exist that could cause damage to the Earth from impact. None yet have been found that poses an immediate threat. The latest numbers, known sightings, and predicted orbits of these objects can be found at http://neo.jpl.nasa.gov. Small meteors, rocks and ice, and bits of space dust are striking the Earth daily. The Earth’s atmosphere protects us from most of these impacts creating colorful displays in the sky as “falling stars” with an occasional fireball. The Earth’s atmosphere protects us from most objects up to 40 m in diameter. Beyond that, the actual likelihood of a dangerous impact is small and much less than the risk from natural terrestrial hazards such as earthquakes or storms. Regardless, if large enough, impacting meteors or comets have the potential to end life as we know it and could perhaps lead to the extinction of the human race. Bodies with a diameter greater than 40 m and up to a kilometer in Page 8 of 12

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 8 Dangerous asteroid orbits visualized near Earth

diameter entering the atmosphere can cause severe local damage (e.g., the Tunguska event). Those 2 km in diameter and up, like the Chicxulub meteor, can result in mass extinctions and worldwide disturbances to the environment and weather. More importantly, massive impacts by objects such as the Chicxulub meteor, impacting in water, will create massive tsunamis. Wave heights created in such impacts would be hundreds of meters, compared with tens of meters for some of our recent worst tsunamis (Indian Ocean and Japan). Imagine the devastation such impacts would wreak. Most of civilization lives near the shore. Waves this immense would continue inland for significant distances. And the Earth is 70 % water. Chances of a water impact are much greater. Thus, while large impacts may be rare, the consequences can be severe. The lunar record of impacts shows that the frequency of impacts decreases with roughly the cube of the crater diameter, which in turn is related to the impactor size or diameter. It is estimated that for meteors 2 km in diameter or larger, impacts occur once every 100 million years and those 1 km in diameter every 500,000 years. The risk due to airbursts, however, may be higher than previously thought. The recent Chelyabinsk meteor, a suspect blast near the Prince Edward Islands off the coast of South Africa in 1963 (an estimated 1.1 megaton TNT equivalent blast), and the 1908 Tunguska event suggest that the risk due to incoming small space rocks is much higher than the risk assumed based on astronomical observations. Further, computer simulations of these events suggest that they are more damaging than equivalent nuclear explosions of the same yield. And, the frequency of these events is more difficult to estimate since they leave little or no impact evidence on the ground. Based on these recent airburst impacts, it is believed by many that the next destructive impact will be an airburst. Finally, an associated man-made risk associated with such an airburst may be that such an event is actually misinterpreted as a nuclear attack. The Chelyabinsk meteor came out of the Sun, undetected. If it had been a cloudy day, the bright explosion, blast wave, and artillery-like sounds in a different part of the world where nuclear tensions might be high might be interpreted as such. Even if on a clear day, the streaking meteor could have been seen to be an entering nuclear armed reentry vehicle. The Prince Edwards Islands blast could also be interpreted as a nuclear blast and was in fact detected by

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 9 Known near-Earth asteroids

networks designed to detect nuclear blasts during the height of the Cold War. While perhaps extreme examples of playing the “what-if” game, this simply illustrates the need to better track and characterize objects near the Earth that potentially pose a hazard due to impact. Without knowing the source, the blasts themselves can be easily misinterpreted and perhaps lead to greater catastrophe.

Mitigating the Hazard

There is a growing international effort and concern, heightened by the Chelyabinsk meteor, to find, characterize, and defend against these threatening solar system bodies to include the recent formation of an International Asteroid Warning Group by the United Nations General Assembly. And, there is information now posted on the Internet concerning NEOs. Notable sites include the NASA Near-Earth Object Program site at http://neo.jpl.nasa.gov/, the NOAA Space Weather Prediction Center site at http://www.swpc.noaa.gov/, and the spaceweather.com site at http://spaceweather. com/ (Tony Phillips, a NASA astronomer, runs the unaffiliated spaceweather.com website). Information concerning the latest on the NEO threats to Earth is presented at these sites. For example: • Information on the numbers of NEOs are presented at the NASA NEO Program site as shown in Figs. 9 and 10. It is believed that over 90 % of NEOs larger than 1 km in diameter have already been discovered (shown in red in Fig. 9). Those NEOs of course pose a significant threat to our civilization if they were to impact the Earth. Thankfully to date, there are none to worry about in the immediate future. The effort is now focused on finding 90 % of the population larger than 140 m. Figure 10 shows the numbers discovered by estimated diameter. Still a ways to go yet before we get to 40 m in diameter (where the Earth’s atmosphere takes over), but we are getting there as our observational capabilities improve. The dramatic improvement in our capabilities is graphically illustrated in Fig. 9 starting about the year 2000. Significant to this activity are the world’s amateur astronomers who provide daily input on the numbers and orbits of these potentially threatening objects. • Daily updated information on potentially hazardous asteroids (PHAs) is presented at the spaceweather.com site. PHAs are defined as objects larger than 100 m in diameter that come Page 10 of 12

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

Fig. 10 Known near-Earth asteroids by size Table 1 Recent and upcoming Earth-asteroid encounters (spaceweather.com). LD is lunar distance=384,401 km (0.00256 AU), the distance between the Earth and the moon Asteroid 2013 XH17 2013 XYB 2013 XS21 2013 XT21 2013 XU21 2011 YD29 2007 SJ 2012 BX34 2006 DP14 2000 EM26 2000 EE14

Date (UT) Dec 11 Dec 11 Dec 11 Dec 11 Dec 14 Dec 28 Jan 21 Jan 28 Feb 10 Feb 18 Mar 6

Miss distance (LD) 7.1 2 0.2 1.1 6.2 6.1 18.9 9.6 6.2 8.8 64.6

Size (m) 37 50 6 15 26 24 1,900 13 730 195 1,800

within 0.05 astronomical units (AU) of the Earth. The good news is that no known PHA is on a collision course with Earth, but new ones are being found all the time. As of 15 December, 2013, there are 1446 PHA encounters. Recent and upcoming Earth-asteroid encounters are listed daily as duplicated in the following table (Table 1): Finally, numerous innovative ideas are being developed throughout the world to defend the planet Earth against such catastrophic threat. The key to successfully defend Earth is to identify the threat, i.e., the heavenly body with an Earth-crossing orbit, well before it gets near the Earth orbit. After that, the threat can be mitigated by imparting an infinitesimal delta velocity so that the net momentum of body is altered ever so slightly and hence its trajectory would veer-off away from the Earth orbit. There are several proposals on imparting a delta velocity to a fast-moving asteroid; using space mirror to blow off mass from the asteroid or detonate a device in its path where the detonation product would nudge it away, run right into it hence perturbing its trajectory. More

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_71-1 # Springer International Publishing Switzerland 2014

elegant solutions include the use of gravity, the great nemesis causing the problem, to work for us instead of against us. Such concepts involve using a satellite and its mass to perturb the objects orbit enough to miss Earth. Given sufficient time, this gradual tugging could be used to shape the orbit so that it comfortably misses the Earth now and into the future.

Conclusion The more warning time the better, and thus, the international effort and collaborative activities amongst the world’s astronomers, including the ever-important amateur astronomers, are crucial to making sure we identify any potential threat as soon as possible. As the former New York Yankee Hall of Fame (baseball) player Yogi Berra once said, “you can observe a lot by just watching.” That is just what we are doing, watching, and we are getting better at it. The solar system is not a static environment as we have seen. Disturbances to orbiting bodies can and do occur on a continuous basis, and we must be continually observing the heavens to make sure these bodies do not pose a hazard to Earth. If they do, then we must be ready to deal with and mitigate that threat. It is after all ultimately a matter of survival.

Cross-References ▶ Defending Against Asteroids and Comet ▶ Directed Energy for Planetary Defense ▶ Micrometeoroid Hazards

References Irion R (2013) It all began in chaos. Nat Geosci 224(1):42–59 Lakdavalla E (2011) Pummeling the Planets. Sky Telesc 122(2):20–27

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

International Cooperation and Collaboration in Planetary Defense Efforts Joseph N. Pelton* International Association for the Advancement of Space Safety (IAASS) and Director Emeritus, Space and Advanced Communications Research Institute, George Washington University, Arlington, Virginia, USA

Abstract This chapter seeks to highlight the various activities that are now ongoing around the world in the planetary defense arena – broadly defined. This chapter also seeks to address key problems and challenges related to future planetary defense and how emerging patterns of collaboration in these areas are evolving in a positive way. In some cases entirely new models of cooperation across a number of diverse technical fields are emerging. Some of these levels of cooperation involve colleges, universities, foundations, and research institutes. Other collaborative links involve corporations, governmental agencies, and even concerned nongovernmental organizations and foundations such as the Association of Space Explorers (ASE), the Safeguard Foundation, and the B612 Foundation. The United Nations has also begun to build effective new collaborative programs. These UN programs are addressed in a separate chapter. In short, much, much more remains to be done, but serious new efforts to collaborate in this daunting field are indeed underway. In addition to reviewing patterns of international cooperation, this chapter also examines some of the national and regional programs of countries that are most active in this area.

Keywords Action Team-14 (AT-14); Association of Space Explorers (ASE); Asteroid; B612 Foundation Sentinel Project; Canadian Space Agency; Canadian Office of Critical Infrastructure Protection; Chinese National Space Agency (CNSA); Coronal mass ejection; DLR; European Space Agency; ESA Near-Earth Object Coordination Centre; European Union; Global space observatories; InterAgency Space Debris Committee; International Academy of Astronautics Conferences on Planetary Defense; International Astronomical Union (IAU); Japanese Space Agency (JAXA); Jet Propulsion Lab (JPL) Sentry Risk Table; Meteoroid; Minor Planet Center; NASA; National Science Foundation; NEOShield; NEOWISE; Near-Earth Object Dynamic Site (NEODyS) system; The Planetary Society; Panel on Asteroid Threat Minimization (PATM); Russian Space Agency (Roscosmos); Safeguard Foundation; Solar flare; Solar max; Solar observatories; Space debris; Space situational awareness; UN Committee on the Peaceful Uses of Outer Space; UN Working Group on Near-Earth Objects; US Department of Homeland Security; Wide-Field Infrared Survey Explorer (WISE)

*Email: [email protected] Page 1 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

Introduction There are a great many institutions around the world that are currently addressing the issue of cosmic hazards and planetary defense. At the international level, there is one organization, the Near-Earth Object Dynamic Site (NEODyS) system in Pisa, Italy (with a mirror site in Spain), that monitors and provides worldwide alerts with regard to potentially hazardous near-Earth objects. This system provided an alert with regard to the TC3 asteroid that resulted in an airburst over Sudan in 2008. Yet the air burst explosion of the 17 m meteorite over Siberia caught the world by surprise. The NEODyS system, the United Nations Near-Earth Committee and the Minor Planet Center, and the Safeguard Foundation provide useful services, but their focus is on NEOs and not other types of cosmic threats that could also create major damage and loss of life. The Safeguard Foundation is a joint effort of the United States, the European Union, Japan, and other countries. This nonprofit foundation was created to coordinate NEO detection and studies. It is currently located at the European Space Agency’s (ESA’s) Centre for Earth Observation (ESRIN) in Frascati, Italy, and this foundation works in close cooperation with NEODyS and the Minor Planet Center and also links to the United Nations NEO Committee. All of these activities represent progress toward international cooperative action (“Defending Planet Earth”). Yet, what is truly needed is a global cosmic hazards and planetary defense system that can help provide well in advance effectively communicated global warning of specific cosmic threats as well as serve as a hub to carry out research and test program to achieve an effective planetary defense. The degree of international cooperation and collaboration in the various areas of cosmic threats continues to grow and expand around the world. There are several complicating factors that make collaboration and cooperation in these areas difficult. First of all there are so many different types of actors in this field. Thus, one finds research institutes, colleges and universities, foundations, space agencies, and other affected governmental agencies in many diverse areas that are involved. These governmental agencies cover such areas as homeland defense, emergency management, economic development, transportation, environmental protection, energy, national defense, and related scientific and space research. In addition there are also private corporations, a number of regional and international agencies (both intergovernmental and nongovernmental), and of course the relevant United Nations entities. It is difficult for so many disparate groups to find the means and methods to share data and engage in cooperative programs and, of course, to find the necessary levels of funding. Secondly there are a sizable number of cosmic hazards which need to be taken seriously and addressed by a wide diversity of protective measures. Near-Earth objects and potentially hazardous asteroids and comets receive perhaps the greatest amount of attention. Yet a variety of hazards from solar and cosmic radiation and coronal mass ejections, changes in the Earth’s natural protective systems such as its geomagnetosphere and atmosphere, and other threats such as orbital space debris represent very serious concerns in terms of dangers to human life, air traffic, as well as credible threats to critical infrastructure on which a world of some seven billion people now depend. Each of these types of threat involve different types of scientific research and involve different types of technologies and observational equipment (on the ground and in space) to address these issues. Protective measures and defensive actions are likewise widely different. In short collaborative actions related to cosmic hazards involves finding ways to get many different types of players around the world to share data and work effectively together. It also involves a perhaps even larger challenge of finding ways for research scientists and engineers who work in many different fields (astronomy, celestial mechanics, radiation, nuclear physics, atmospheric sciences, radar systems, satellite systems engineering, chemical and electronic propulsion Page 2 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

systems, computer modeling, etc.) to find effective ways to share knowledge and develop effective planetary defense systems and technology across these very diverse areas of technical expertise. The truth of the matter is that a concerted effort on the scale of the Manhattan Project or the Apollo Program is likely needed to take on true planetary defense in a meaningful way. Unfortunately the political will to devote such a huge amount of resources is not there, because the perceived level of threat is simply not there. Currently activities such as the Safeguard Foundation, the Minor Planet Center, NEOShield, NEODyS system, etc. represent an expenditure level at the level of tens of millions of dollars – not tens of billions. And even if there was a clear recognition of a massive threat, the ability to marshal all of the resources needed to accomplish the many acts of economic and technical coordination on a global scale is clearly lacking. Another chapter addresses the leadership and global cooperative challenges that planetary defense, but the clear conclusion is that neither the political will nor dedicated highlevel leadership is now present. The first obvious step is to explore what cooperative processes are now underway and to develop preliminary strategies to build meaningful relationships that can make true planetary defense feasible in future years. The starting point for effective regional and international cooperation and collaboration in the area of planetary defense is to have a clear understanding of what cosmic hazards are concerned and what is meant by planetary defense. Unfortunately neither of these clear definitions now exists. Substantial risks to plant and animal life, humans, and critical infrastructure can originate from near-Earth objects (i.e., potentially hazardous asteroids, comets, bolides, and meteors) and from solar flares and coronal mass ejections, cosmic radiation, antimatter, and collisions, and space debris now threatens vital infrastructure. A deterioration of Earth’s natural protective shielding systems such as the geomagnetosphere and the atmosphere must be considered a key part of planetary risk assessment and protection. Global radiation management measures will increasingly be recognized as a part of planetary defense as the seriousness of climate change becomes clear in coming decades. All of these risks need to be considered in a holistic way and relevant data and information shared as widely as possible through systems that have proved effective in such areas as weather forecasting and other forms of disaster prediction and recovery. All legitimate agencies and entities (both private and public) conducting research, collecting data, or working on protective or recovery systems should be integrated into systematic information sharing arrangements. Steps that have already been taken such as the creation of the Minor Planet Center; the Near-Earth Object Dynamic Site (NEODyS) System in Pisa, Italy; the Safeguard Foundation, the JPL Sentry Risk Table, the ESRIN Near-Earth Object Coordination Centre; the Inter-Agency Space Debris Coordination (IADC) Committee; the various solar observatories around the world; the NOAA Online Solar Weather Dashboard; the IAA Conferences on Planetary Defense; the United Nations COPUOS Working Group on Near-Earth Objects, the NEOShield Project of the European Union; and other initiatives reported on and discussed in this chapter and elsewhere in the handbook are important efforts to be commended and their efforts are documented in this handbook. Nevertheless, the current system of collaboration needs to be strengthened and improved in a number of ways. The space agencies need to do more, and national governments (especially those with active space programs) also need to extend their research and discovery programs to detect space hazards as well as their efforts to mount improved measures to provide for planetary defense. The most important first step that needs to be done is to put the various types of risks into some sort of systematic process as to their nature, relative likelihood of doing damage to human life and infrastructure, as well as to plant and animal life. The good news is that there has been substantial

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

progress in this regard. If one takes the example of near-Earth objects that are a potential threat to humans, we can chart this progress in fairly start forward terms. The number of known potentially hazardous near-Earth asteroids with traceable orbits that could constitute major threats to life on Earth as of the end of September 2013 was 10,232 (JPL 2012). The following map as produced by NASA that charts the orbits of the “top 1400” asteroids that could collide with Earth is shown in Fig. 1 below (“NASA Reveals. . .”). In 1898 the first near-Earth object was detected with an orbit that could be considered threatening to Earth. This NEO is known as 433 Eros. In the next hundred years, i.e., from 1898 to 1998, only about 500 additional NEO were detected. Since that time, however, additional emphasis has been given to these NEO-detection efforts through ground observations and space-based infrared telescope efforts. There is even now in place a congressionally enacted mandate (i.e., under the so-called George Brown Act) to set a deadline for NASA to detect all Near-Earth Asteroids 1 km or more in diameter. Thus, the current NEA discovery rate is about 1,000 per year (NEO Coordination Centre). Out of the 10,000 discoveries, roughly 10 % are larger than 1 km in size, while the vast majority of NEAs are smaller than that, with the number of objects of a given size quickly increasing as the size decreases. It is thought that perhaps 90 % of all NEOs that are 1 km or more in size have been detected. Although this is clear progress, one should be aware that NEOs in the range of 140 m up to 1 km in size can have very considerable damage whether in an airburst, land impact, or water impact mode. The fact that all of this detection data is recorded with the Minor Planet Center and is systematically available to the world community represents great progress. The further fact that the Torino Scale has been globally accepted as a useful measure to help calibrate the impact damage of various-sized NEOs and their likely impact with Earth is also a key step forward. The parallel acceptance of the so-called Palermo Scale that assigns to detected NEOs the probability of their impacting Earth represents a further positive step in terms of global cooperation. Despite this progress, much more needs to be done. We now see private initiatives such as those of the Planetary Society and the B612 Foundation to assist with the detection and recording process. We see quite helpful efforts to coordinate efforts of universities in various countries to study how to mitigate or prevent the threat of detected NEOS from actually impacting Earth. One such effort is that spearheaded and funded – albeit at modest

Fig. 1 NASA hazardous asteroid map with Earth orbit shown in bright white (Graphic courtesy of NASA)

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

level – by the European Union, known as NEOShield. This program is coordinated by DLR, the German Space Agency that provides the funds to universities and research institutes to study how to prevent major damage and life-threatening events from NEOs. But this is but only one type of space threat. There are both naturally occurring space dangers as well as man-made dangers to space infrastructure and these dangers now number over a dozen. These include collisions involving asteroids, comets, and bolides, solar flares, coronal mass ejections, cosmic radiation, biological hazards from space, antimatter collisions, orbital space debris, electromagnetic pulses from space (that could be caused by a nuclear explosion in space), solar radiation and micrometeoroids that damage critical satellite infrastructure, and possible collapse or deterioration of natural Earth-protective systems such as the geomagnetosphere, the upper stratosphere, and ozone layer. What is needed and what is now lacking is an effective global process to address all of these forms of space-related risks; assess their threat level; undertake detection, measurement, and recording of relevant data; and carry out research to see out, minimize, mitigate, or eliminate these threats that could result in the loss of life at the level of millions to billions of people; create major harms to animals, plant life, and vital crops;, and create economic and infrastructure losses that could run in the many trillions of dollars (US). The first place for this to start would be in coordinative actions among the world’s space agencies.

Space Agency Coordination Today there are a dozen spacefaring nations with the ability to launch satellites into orbit. Beyond these countries with launch capabilities, there are some 50 countries with active space research or space applications agencies or commissions. At the annual International Astronautical Congress, many of these national and regional space agencies plus organizations such as EUMETSAT, the International Space University, etc. hold coordination meetings and exchange information. Beyond these rather space-focused nations, there are now some 90 nations that participate as members of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). Virtually every country and territory in the world actively utilizes space for telecommunications, remote sensing, meteorological forecasting, and space navigation. In short there is a wide spectrum of countries that range from intensive space activities and major space research, exploration, and applications programs with large annual budgets down to those that only use space facilities for services. It would seem reasonable for space agency coordination with regard to cosmic hazards and planetary defense to start by building on the positive experience of the established Inter-Agency Space Debris Coordination (IADC) committee that includes a critical mass of space agencies with the depth of resources and technical expertise to assist with this demanding field. The current IADC member agencies include the following: • • • • • • • • •

ASI (Agenzia Spaziale Italiana) CNES (Centre National d’Etudes Spatiales) CNSA (China National Space Administration) CSA (Canadian Space Agency) DLR (German Aerospace Center) ESA (European Space Agency) ISRO (Indian Space Research Organisation) JAXA (Japan Aerospace Exploration Agency) NASA (National Aeronautics and Space Administration) Page 5 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

• NSAU (National Space Agency of Ukraine) • ROSCOSMOS (Russian Federal Space Agency) • UK Space (UK Space Agency) Indeed the positive experience that has come from the IADC is clearly part of the inspiration for the formation of the so-called Action Team-14 that includes the 14 countries and their space agencies that agreed coming out of UNISPACE III to work together to coordinate the tracking of asteroids and comets and to explore means to deflect potentially hazards near-Earth objects from impact with our planet. The IADC as currently organized includes a Steering Group plus four Working Groups. These Working Groups include (i) Working Group 1 on Measurements, (ii) Working Group 2 on Environment and Database, (iii) Working Group 3 on Protection, and (iv) Working Group 4 on Mitigation. The IADC has been an effective international coordination process and has worked very effectively to develop orbital debris mitigation guidelines and has worked very effectively with the UN Committee on the Peaceful Uses of Outer Space (COPUOS) to provide key technical and scientific information (Pelton 2012). The AT-14 is indeed structured in a similar manner to work in such areas as (i) detection and measurements; (ii) collaborative space research and investigation programs; (iii) theory and analysis; (iv) strategies and capabilities for threat detection, reduction, and mitigation; and (v) public awareness and education. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) has also already established Working Groups of its Scientific and Technical Subcommittee that are relevant to this international coordination process. These are the Working Groups on Space Debris Mitigation (established in 2004), on Sustainability of Space (established in 2012), and on Near-Earth Objects (established in 2007) (United Nations Office of Outer Space Affairs 2013). The chapters later in this handbook, especially the one related to the work of the United Nations as provided by Sergio Camacho-Lara, report on the status of the UN COPUOS efforts and especially on the Working Group on Near-Earth Objects. It is clearly important for the space agencies’ coordinative efforts to develop specific methods of data exchange and systematic information collection and to help initiate joint space missions to be undertaken by specific spacecraft. The work as carried out by Action Team-14, the Association of Space Explorers, the Planetary Society, the B612 Foundation, the Safeguard Foundation, the Minor Planet Center, and others with technical space expertise can be undertaken in such a way so as not to duplicate the “global space policy” development process undertaken by the UN COPUOS. Perhaps most importantly this interagency committee might help to begin actual efforts to mitigate and reduce a variety of space hazards including not only with regard to near-Earth objects but also concerning radiation- and solar-related concerns. Perhaps it is useful to provide analogy here with regard to defining the respective roles of the InterAgency Space Committee and the UN policy concerns. It is likely that the work of the UN COPUOS will develop new broad space policy for the “overall forest” in this technically complex area. The interagency’s coordinative efforts, among the various space agencies, would be to develop detailed and specific collaborative space-related efforts at the level of “the trees, branches, and leaves” which would carry out the broad policies. In short the UN COPUOS efforts would involve process and procedure. The space agencies would carry out the research programs, launch the spacecraft programs, and perhaps even carry out steps to divert the orbits of threatening asteroids and comets or seek ways to divert the most dangerous ionic bombardments of the sun’s coronal mass ejections or better shield the Earth from solar radiation. Page 6 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

United States and NASA, NOAA, DHS, DoD, and the NSF Currently the United States, NASA, and NOAA, in partnership with a number of academic and independent research programs, carry out the most ambitious space threat inventorying, data collection, and threat mitigation programs. NASA is charged by the US Congress to create a complete inventory of large near-Earth objects. NASA was first charged to identify all NEOs of 1 km or more in size by 2008. Subsequently under the George Brown Jr. Near-Earth Object Survey mandate NASA was charged with identifying 90 % of all potentially hazardous objects that were 140 m in diameter or larger. NASA is required to prepare a formal report entitled the Near-Earth Object Search Report each year. Unfortunately this inventory is behind schedule and not complete. This activity has been largely carried out in space with the NEOWISE Space Infrared Survey (WISE is an acronym standing for the Wide-Field Infrared Survey Explorer). The NEOWISE project that was inactive for the last nearly 3 years was reactivated for another 2.5 years of NEO detection as of September 1, 2013 (“NASA Spacecraft Reactivated. . .”). To extend the capabilities for space-based infrared imaging to detect hazardous NEOs, the B612 Foundation is proposing to build and launch a highly capable Sentinel infrared telescope that could complete an inventory for smaller potentially hazardous NEOs and provide improved warning capabilities. Of course not all NEOs are detected by space-based systems. There are many efforts underway using ground-based observatories. The Lincoln Near-Earth Asteroid Research (LINEAR), Near-Earth Asteroid Tracking (NEAT), Spacewatch, Lowell Observatory Near-Earth Object Search (LONEOS), Catalina Sky Survey, and the Harvard, Smithsonian Astronomical Observatory are among the US-based observatories that collect and inventory information on NEOs as well as on solar activity. In addition, the Minor Planet Center, located at the HarvardSmithsonian Observatory, collects data from US sources, but from all over the world to create a complete inventory of data related to observed NEO threats. While NASA activities related to NEOS, including activities at JPL and the Minor Planet Center (which is 90 % funded by NASA), represent the prime US governmental agency actor with regard to asteroid and potential hazardous NEO detection, there are many other governmental agencies that play and active role with regard to cosmic threats. The National Oceanic and Atmospheric Administration (NOAA) provides warnings – a near-real-time dashboard display – with regard to space weather and solar flare and coronal mass ejections. The Department of Homeland Security that is responsible for civil defense and the National Response Framework has a potential major role to play in the case of a major threat and need for mass evacuation, but it has limited capabilities and guidelines deployed with regard to cosmic threats. This indeed is the case around the world. The Torino Scale helps to explain the potential threat level of NEOs based on their size, and the Palermo Scale assigns a threat level based on known objects of NEOs, but most civil defense agencies around the world lack clear procedures of what to do in case of detected threats due to NEOs, solar flares, coronal mass ejections, or other types of cosmic threats. The National Research Council report has also identified other agencies such as the Department of Defense, the National Science Foundation, as well as the Department of Agriculture. The US Department of Defense, which maintains the so-called space fence using S-band radar to carry out space situational awareness and has responsibility for the deployment of nuclear weapons that might be required for deflecting the orbits of hazardous NEOs, obviously has international capabilities in addition to national responsibilities. Other governmental units that were identified in the report included the Environmental Protection Agency, the Department of Health and Human Services, Department of Transportation, and even the Department of Agriculture as having some form of role in responding to cosmic threats. The bottom Page 7 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

line is that the United States, nor virtually all other countries, has clearly developed an actionable plans to address various types of cosmic threats that may be possible. The NEO survey as mandated by George Brown Jr. Act would seem to provide some level of reassurance as to being well protected against NEO impacts, but the recent discovery of a nearly 3 km asteroid in retrograde orbit after NASA’s survey of larger NEOs was thought to be essentially complete and serves as a reminder that much more still needs to be done. It is the contention of the B612 Foundation that only with the deployment of an especially designed infrared telescope optimally designed for potentially hazardous NEOs can hope to detect all serious threats on a comprehensive basis.

European Union and European Space Agency After the United States, it is the European Union and the European Space Agency that have devoted the most resources to the study of cosmic hazards and planetary defense. The Near-Earth Object Dynamic Site (NEODyS) system is a service sponsored by ESA operated in Italy and Spain. The most valuable service provided by NEODyS is the projection of all asteroid, meteoroid, and comet impacts with all of the planets in the solar system through the year 2100. This facility which is primarily supported by faculty from universities in Pisa and Rome with backup support from faculty in Spain uses specially developed computer software to calculate orbits from data supplied from the Minor Planet Center and other sources. Many believe that the most important feature of the NEODyS system is the so-called Risk Page that provides information for all NEOs with probabilities of hitting the Earth that are greater of 10
11 and from now until 2100. This Risk Page provides information on objects that are divided into five categories sorted into “Special,” “Observable,” “Possible Recovery for Observation,” “Lost,” and “Small.” Each object recorded in the “Risk Table” has its own so-called Impactor Table (IT). This table shows information such as size, type of orbit, albedo, thermal qualities, and calculated likelihood of impact that would be useful in assessing the level of risk of Earth impact. The center also served as the focus point for scientific studies needed to improve NEO warning services and provide near-real-time data to European and international customers (The Near-Earth Orbit Dynamic Site (NEODyS)). Closely associated with Near-Earth Object Dynamic Site is the ESA-sponsored Space Situational Awareness-Near-Earth Orbit Coordination Centre which is operated by the Space Dynamics Services S.r.l. (SpaceDys) under a contract with Elecnor Deimos, Spain, on behalf of the Agency’s Space Situational Awareness Programme Office. It serves as the central access point to a network of European NEO data sources and information providers being established under ESA’s Space Situational Awareness (SSA) Programme. The center supports experts in the field to carry out space situational awareness and detection and monitoring of near-Earth objects. The objective of the center is to create a cooperative federation of new and existing European assets, systems, and sensors to support an increasingly capable future NEO system. It supports the integration and initial operation of ESA’s NEO information distribution network. The network within the federation will supply information to scientific bodies, international organizations, and decision-makers (ESA Space Situational Awareness-NEO Centre). ESA has also launched infrared space telescopes to help chart the heavens and to detect near-Earth objects. The first of these missions was the ESA Infrared Space Observatory (ISO) mission which was launched in 1995 and remained active collecting data through 1998, and data from this mission was archived and analyzed through 2006 (The ISO Infrared Space Observatory).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

In May 2009 ESA launched the largest infrared telescope ever, the 3.5 m mirror system that was designed primarily to map the universe but with the additional capability to detect near-Earth objects. This highly capable Herschel Space Observatory has almost depleted its helium coolant and thus is nearing the end of its life. It might be repurposed as was the case with the NASA WISE (Wide-Field Infrared Survey Explorer) to target NEOs in the last stages of its operation (ESA “Herschel Space Observatory”; NASA “NEOWISE”). The European Union has sought to take a step beyond the collection of NEO impact risk data and to consider what types of countermeasures might be possible. This EU initiative called NEOShield is coordinated by the German Space Agency DLR. Currently this effort is funded at a modest level of about 4 million Euros. The NEOShield activity promotes relevant research at European universities to study the nature and composition of NEOs such as asteroids, bolides, and meteoroids (and even comets such as 3552 Don Quixote) and to consider means and methods by which their orbits, if detected as being on a collision course with Earth, might be deflected (“NEOShield”).

CNES France is one of the major funders of the European Space Agency and thus helps fund the abovementioned activities. France has some research capabilities with regard to asteroid threats and has maintained certain capabilities to following the orbits of so-called co-orbiting asteroids, meteoroids, and comets (“Co-orbital Asteroid Leaves Earth’s Orbit”). The French Space Agency CNES has actually paid a more active role with regard to other types of cosmic threats. Thus, CNES played a key role in developing experiments (in cooperation with NASA and ESA) of the SOHO satellite to explore the nature of solar flares and coronal mass ejections. It has been a key participant in the multi-satellite Swarm research satellite program to understand the nature of the Earth’s protective magnetosphere with launch of the Swarm satellites in late 2013. It has also participated in the earlier Oersted and Champ research satellite programs that have sought to explore changes to the Earth’s magnetic field and to discover a better understand in changes to the Earth’s ozone layer (Champ, Oersted, and Swarm Satellite Research Programs).

DLR The German Space Agency has for some years played a key role in asteroid and near-Earth orbit survey activities. DLR and its Institute of Planetary Research has been assigned the key role of coordinating research efforts associated with the NEOShield effort that is funded by the European Union cited earlier. Using EU funding, DLR works with universities and research institutes to undertake efforts to describe the composition of asteroids and to consider viable ways to divert threatening NEOs from Earth impact. These partners are listed below: • • • • • •

DLR Institute of Planetary Research The Paris Observatory The Open University of the UK The Fraunhofer Institute for High-Speed Dynamics/Ernst Mach Institute (EMI) Queen’s University of Belfast Astrium Page 9 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

• Deimos Space • SETI Institute, Carl Sagan Center • Russian Federal Space Agency (Roscosmos)/Central Research Institute of Machine Building (TsNllMash) • Surrey Space Center, Ltd./University of Surrey NEOShield was established in January 2012 under DLR direction with these 13 partners from research institutions and industry that are largely from Europe but with Russian and US participation. The first 4 years of activity began with 4 million Euros of funding from the EU plus 1.8 million in funding from the research partners. The objective is to investigate on a joint basis the prevention of impacts by asteroids and comets. The investigations will include the impact of a space probe with the asteroids to deflect them from their threatening courses, the use of long-term gravitational effects using adjacent probes, and other methods. Another German effort is the so-called Asiago DLR Asteroid Survey (ADAS). ADAS is a dedicated program to search for and follow-up on the orbits of asteroids and comets using ground-based observatories. This activity utilizes the 67/92 Schmidt telescope in Asiago/Padua, Italy, as well as the DLR Institute of Space Sensor Technology and Planetary Exploration in Berlin, Germany. This activity places a special focus on the discovery of NEO. It represents a part of the International Astronomical Union’s efforts under its Working Group on NEO and is also supported by the Spaceguard Foundation (Asiago DLR Asteroid Survey (ADAS)). In addition to the ADAS activities, there is a parallel effort called the Uppsala Astronomical Observatory-DLR Asteroid Survey (UDAS) as well as the DLR-Archenhold NEO Precovery Survey (DANEOPS). Each of these efforts uses ground-based astronomical observatories to detect NEO asteroids (Daneops Home Page).

JAXA-ISAS The Japanese Aerospace eXploration Agency (JAXA) was formed in 2003 by the combination of the NASDA (the National Space Development Agency of Japan) with the Institute of Space and Astronautical Science (ISAS) and the National Aerospace Laboratory (NAL). ISAS as a part of JAXA continues to be focused on planetary and space research including solar phenomena, cosmic radiation, and asteroids and near-Earth objects (NEOs). JAXA has been active in several programs to learn more about cosmic hazards. On May 9, 2003, the Hayabusa satellite mission was launched with the objective of the goal of collecting samples from a small asteroid near Earth that is name 25143 Itokawa. The Hayabusa satellite (that translated to Peregrine falcon in English) successfully landed on this small asteroid and gather samples in the fall of 2005. Hayabusa returned to Earth orbit and then released a small capsule that was able to return to Earth as of June 13, 2010, as pictured below. This was the first capture and return of a sample from an asteroid ever accomplished as is depicted in the graphic in Fig. 2 (JAXA “Hayabusa Project”). JAXA has also been quite active in the field of infrared telescope missions to map the skies and to assist in the identification of NEOs. JAXA infrared telescope missions have included the IRTS telescope (in 1995) and the Akari mission (in 2006). A planned infrared telescope mission for 2015 named SPICA is also planned with the possibility of contributed instruments from NASA and ESA. In addition JAXA provided support to ESA with regard to its ESA Infrared Space Observatory (ISO) mission that was carried out in the 1990s (JAXA “ISO Mission..”). Page 10 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

Fig. 2 Hayabusa satellite releasing the capsule with samples from Asteroid 25143 Itokawa (Graphic courtesy of JAXA)

Finally Japan has been quite active in the area of solar research. Japan’s solar astronomy started in the early 1980s with the launch of the Hinotori (ASTRO-A) x-ray mission. The next launch, also an ISAS mission was the so-called Hinode satellite (also known as the Solar-B) spacecraft. Next came the follow-on which was a joint Japan/US/UK mission with the Japanese name of Yohkoh but the international designation of this satellite is known as Solar-A. This spacecraft was launched on 23 September 2006. A Solar-C mission that would be a joint Japanese (JAXA), US (NASA), and European (ESA) project is contemplated for 2018 (Solar C Working Group).

ROSCOSMOS Russia and in particular the Russian Federal Space Agency (Roscosmos) has been active in various aspects of solar research, cosmic radiation hazards, and near-Earth object (NEO) research for many decades. In its recent future space research projects ROSCOSMOS has developed over a quarter of a billion dollars (US) to a total of ten solar and Sun-Earth research projects. Not only is Roscosmos an active member of the NEOShield research consortium, but it has contributed very innovative ideas to the process. The latest idea is to capture nearby smaller asteroids and tow them to locations so that they could collide with an incoming dangerous asteroid so as to deflect the orbit so as to protect Earth from impact. This so-called “space billiards” concept has been examined in computer modeling analysis and shown to be a possibly viable protective strategy (Eremenko 2013).

Other Space Agency Efforts to Address Cosmic Hazards There are a great number of additional space agency efforts that are directed toward detecting potentially hazardous near-Earth objects (NEOs) or to monitor space weather and cosmic radiation. Page 11 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

A large number of space agencies around the world, for instance, operate ground-based observatories that report sightings of NEOs that are discovered and report these to the Minor Planet Center, the ESA-sponsored Space Situational Awareness-NEO Coordination Centre, etc. Many of the space agency observatories of China, India, Brazil, Israel, Pakistan, South Africa, etc. have active programs to observe solar events, space weather, and cosmic radiation that are shared with the global space community at scientific conferences and through processes of the International Astronomical Union. Some of these space agencies have even begun space-based efforts in this regard. The Canadian Space Agency (CSA) in partnership with the Defence Research and Development Canada (DRDC) has sponsored the design and launch of the NEOSSat (Near-Earth Object Surveillance Satellite). This satellite now in an 800 km high orbit with a 100 min periodicity is searching in the infrared spectra for previously undetected NEOs. This satellite was built by Microsat Systems Canada and launched in February 2013. This small $15 million suitcase-sized satellite is the first space telescope developed by Canada to search for asteroids. In partnership with the India Space Research Organization, this small satellite was one of seven satellites launched on the Indian Polar Satellite Launch Vehicle-C20 (PSLV-C20) rocket (“Indian Space Launch to Deploy Canadian Satellite”).

University, Research Institute, and Ground Observatory Coordination Perhaps more than a thousand universities, research institutes, and ground observatories constitute a part of the global resources that are available around the world to monitor and identify potentially hazardous NEOs. These research efforts also contribute useful information with regard to solar events, cosmic radiation, comets, asteroids, bolides, meteoroids, and cosmic hazards. There are sophisticated processes by which observations and findings from these institutions can be widely shared. Most national space agencies have cooperative arrangements with national universities and often provide research grants or have research contracts with national research universities. The earlier section with regard to the German Space Agency (DLR) and the European Space Agency indicated just some of those types of programs. In Europe there are not only many national arrangements but regional programs as well. Three international types of coordinative programs with regard to cosmic hazards and planetary defense are of particular note. These are the Working Group on NEOs of the International Astronomical Union (IAU), the B612 Foundation that is sponsoring the Sentinel space telescope and other initiatives with regard to potentially hazardous asteroids, and the Planetary Society that also plays an important role in this field.

WGNEO of the IAU The Executive Committee of the IAU, shortly after its May 2010 meeting, formally proposed to reactivate its Working Group on Near Earth Objects. The charge that was provided for the WGNEO was to investigate and formulate requirements for an international ground- and space-based NEO survey, to detect, track, and characterize, through the use of optical, infrared, and radar sensing, the location of 90 % of all NEOs with a diameter greater than 40 m. It was also proposed to establish a permanent International NEO Early Warning System. The IAU has continued since that time to work toward this objective in cooperation with the United Nations Committee on the Peaceful Uses of Outer Space (UN COPUOS) and the International Council for Science (ICSU). The IAU also Page 12 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

continues to play a key role in this arena by its sponsorship at the Minor Planet Center, at the Harvard-Smithsonian Astronomical Observatory that is the universal location for all reported detections of NEOs. As of the February 2013 meeting of the UN Committee on the Peaceful Uses of Outer Space (COPUOS), the IAU presented a formal report of its current concerns about NEOs. This report stated: It is clear that, in order to be prepared for NEO impacts, the world needs a permanent international NEO Early Warning System, combining all efforts of ground-based NEO surveys and space-based NEO surveys. The UN COPUOS STSC Action Team 14 is working on protocols to coordinate this important issue. (“Statement by the IAU to the 50th Session of the UN COPUOS”)

In light of the need for the UN COPUOS which now includes some 90 international members, to achieve consensus, the ability to agree and implement such a NEO Early Warning System will take time. In the meantime the IAU Minor Planet Center represents the closest approximation of such a system. The problem is not so much on the detection of potentially hazardous NEOs, but a process to decide what to do against potential threats and how to communicate warnings effectively to the world community. As noted in the IAUs, most recent report, a near-Earth asteroid of about 45 m in diameter flew inside the Earth’s geosynchronous orbit at about 5 miles per second (7.8 km/s) on February 15, 2013. This potentially destructive NEO had the power of thousands of atomic bombs of the Hiroshima size and could have done tremendous damage and was detected only 1 year before its flyby. As noted earlier, the Russian Space Agency Roscosmos actually proposed in 2009 sending up a mission to crash into 99942 Apophis a PHA that has a diameter of some 325 m and thus capable of considerable lethal damage if it should hit a city or trigger a tidal wave near a major inhabited coastline.

The B612 Foundation The B612 project, a reference to the mythical asteroid of “The Little Prince” children’s book, originated from a workshop on asteroid organized at the NASA Houston Johnson Space Center on October 20, 2001. The nonprofit nongovernmental organization was officially established a year later. Although the original discussions at the workshop in 2001 focused prevention techniques such as a nuclear power spacecraft to tug a threatening asteroid into a harmless orbit, the B612 Foundation has developed new goals. These goals are the early detection of hazardous NEOs. The prime objective at this time is to deploy the so-called Sentinel infrared telescope spacecraft in a Venuslike orbit to provide an early warning capability. This spacecraft is designed in partnership with Ball Aerospace. This high-resolution telescope is designed to detect comets and asteroids of 140 m (or less) diameter and early enough that deflection missions could be successfully mounted. The cost of this spacecraft with a projected 6.5 year lifetime, a 50 cm telescope aperture, 95 gigabytes of memory, and 2 kW of power that is designed for launch on a Falcon 9 launcher would involve a total mission cost of nearly $400 million. It is thus the most ambitious private space initiative for space exploration ever attempted. The fact that this spacecraft has no backup and a limited lifetime of less than 7 years – driven by loss of coolant for the IR telescope – is a major element of risk concern (“The B612 Foundation”).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

The Planetary Society The Planetary Society that was founded in 1989 was initially spearheaded by the noted astronomer Carl Sagan and his colleagues Bruce Murray and Louis Friedman. The Planetary Society that is a worldwide alliance of scientists and space enthusiast is closely aligned with the B612 Foundation, the International Astronomical Union, and the International Astronautical Federation. The goals of the Planetary Society are wide and far-reaching. These goals include hunting for Earth-like planets, searching for life in the universe, advocating for science funding, and Science, Technology, Engineering, and Mathematics (STEM) education. It does strongly support the search for dangerous asteroids by its members and the efforts of B612 Foundation and the IAU. The Planetary Society can accurately claim to be the largest and most influential public space organization around the world with a global membership. Among the Planetary Society’s many activities are the Shoemaker awards to support asteroid tracking and identification. These grants provide funding to support the efforts of amateur observers as well as trained observers in developing countries and even professional astronomers to chart near-Earth objects. These efforts seek to identify previously unknown NEOs and especially to flag those that might potentially collide with Earth.

The Action Team-14 Effort The Action Team-14 efforts are coordinated through the UN Office of Outer Space Affairs (OOSA). This initiative was undertaken as one of the outcomes of the UNISPACE Conference III. The 14 member countries, subsequent members, as well as regional groups are as follows: National Members Australia, Brazil, China, the Czech Republic, Finland, German, Iran, Japan, Kazakhstan, Lebanon, Malaysia, Nigeria, Pakistan, Poland, Russian Federation, Saudi Arabia, Syrian Arab Republic, United Kingdom, and the United States Organization Members Association of Space Explorers (ASE), European Space Agency (ESA), Committee of Space Research (CoSpar), International Astronomical Union (IAU), National Space Society, Space Generation Advisory Council, European Space Science Committee, European Science Foundation, and the Spaceguard Foundation. The way the Action Team-14 is now configured is that it has efforts in the following areas: • • • • • •

NEO detection and characterization Orbit determination and cataloguing Consequence determination In situ characterization Mitigation Policy

The broad spectrum of participants in this AT-14 effort helps to ensure that if there is agreement with regard to mitigation and policy within this unit, that broader consensus within COPUOS can also likely be achieved. Page 14 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_74-1 # Springer International Publishing Switzerland 2014

These and other initiatives and their programs are discussed in greater detail elsewhere in the handbook.

Conclusion What should be clear from this chapter is that there not only are many activities around the world to track and identify NEOs of various types but also efforts to develop systematic early warning system SMF mitigation systems as advocated by the IAU to the UN Committee on the Peaceful Uses of Outer Space. Part of this ongoing process will be to put in place a more systematic way of assessing relative levels of risk and prioritization of effort consistent with the best understanding of overall levels of risk, immanence of occurrence, and interdisciplinary tools and instrumentation to study various forms of cosmic hazards. Perhaps even more important is to also recognize the need for greater coordination of effort with regard to space weather, cosmic hazards, solar flares, and coronal mass ejections as well as changes in the Earth’s natural protection systems in terms of its geomagnetosphere and the ozone layer in the upper atmosphere. While the efforts to track and defend against NEOs is being addressed by a wellcoordinated group of national, regional, and international units, the same sophistication of effort is lacking with regard to radiation and ionic dangers related to highly threatening and potentially destructive space weather.

Cross-References ▶ Defending Against Asteroids and Comets ▶ Directed Energy for Planetary Defense ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ NEOSHEILD-A Global Approach to Near-Earth Object Threat Mitigation ▶ Planetary Defense, Global Cooperation and World Peace ▶ Potentially Hazardous Asteroids and Comets ▶ Regulatory Aspects of Associated with Response to Cosmic Hazards ▶ Sentinel: A Space Telescope Program to Create a 100-Year Asteroid Impact Warning

References Asiago DLR Asteroid Survey (ADAS). http://dipastro.pd.astro.it/planets/adas/ Champ, Oersted, and Swarm Satellite Research Programs. http://www.cnes.fr/web/CNES-en/5922swarm.php Co-orbital asteroid leaves earth’s orbit leaves earth’s orbit. http://www.cnes.fr/web/CNES-en/5259co-orbital-asteroid-leaves-earths-orbit.php Daneops Home Page. http://earn.dlr.de/daneops/. 10 Jul 2013 Defending planet earth: near-earth object surveys and hazard mitigation strategies, section 7: National and International Coordination. http://www.nap.edu/openbook.php?record_id¼12842&page¼92 Eremenko A (2013) Russians propose space billiards for planetary defense. http://en.rian.ru/analysis/20130531/181439126.html. 31 May 2013

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ESA Space Situational Awareness-NEO Centre. http://www.esa.int/Our_Activities/Operations/ Space_Situational_Awareness/About_SSA-NEO_Coordination_Centre http://www.cnes.fr/web/CNES-en/1394-champ.php and http://www.cnes.fr/web/CNES-en/1452oersted.php Indian space launch to deploy Canadian satellite. http://www.redorbit.com/news/space/1112790403/ india-rocket-launch-polar-satellite-launch-vehicle-c20-canada-satellite-022513/. Apr 2013 JAXA (2012) The Hayabusa Project. http://jaxa.jp. Jul 2012 JAXA. ISO mission. http://en.Japan_Aerospace_Exploration_Agency Jet Propulsion Lab (JPL) (2012) Near earth object program. neo.jpl.nasa.gov./faq/. Dec 2012 NASA. NEOWISE. http://solarsystem.nasa.gov/missions/profile.cfm?Sort¼Chron&StartYear¼2010 &EndYear¼2019&MCode¼WISE NASA spacecraft reactivated to hunt for asteroids. http://rt.com/news/nasa-hazardous-asteroidmap-575/. 16 Aug 2013 NEOShield Preparing to protect the planet. http://www.neoshield.net/en/index.htm NEO Coordination Centre (2013) http://neo.ssa.esa.int/. 13 Oct 2013 Pelton JN (2012) Orbital debris and other space hazards. Springer Press, New York, p 32 Solar C Working Group. http://hinode.nao.ac.jp/SOLAR-C/index_e.html. Apr 2004 The Herschel Space Observatory—The largest infrared space telescope. http://www.space.com/ 20120-herschel-space-telescope-mission-ending.html. 10 Nov 2013 The ISO Infrared Space Observatory. http://iso.esac.esa.int/ The Near Earth Orbit Dynamic Site (NEODyS). http://newton.dm.unipi.it/neodys/ UAO-DLR Asteroid Survey. http://earn.dlr.de/udas. Apr 2013 United Nations Office of Outer Space Affairs (2013) Working group on near-earth objects. http:// www.oosa.unvienna.org/oosa/en/COPUOS/stsc/wgneo/index.html. Apr 2013

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

Active Orbital Debris Removal and the Sustainability of Space Joyeeta Chatterjeea*, Joseph N. Peltonb and Firooz Allahdadic a Institute of Air & Space Law, McGill University, Montreal, QC, Canada b International Association for the Advancement of Space Safety, Arlington, VA, USA c Space Science & Environmental Research, Applied Research Associates, Albuquerque, NM, USA

Abstract In the 1980s Donald Kessler of NASA noted the continuing buildup of space debris and projected that if not mitigated, it would severely limit future safe access to space. In particular, he noted that at some stage the accumulation of orbital space debris would begin to create new debris due to collisions and that this cascading process would threaten the long-term sustainability of human activities in space, including key space applications for communications, navigation, remote sensing, and weather monitoring. This concern, which today is quite real, has become known as the Kessler syndrome. Today there are international guidelines to control the debris population by deorbiting the upper stages of launch vehicles and other preventive measures. These include the 25 year rule for active or passive deorbiting of debris and the degassing of excess fuel that can lead to explosions in space. But these guidelines are insufficient to prevent the buildup of additional debris, particularly in low earth orbit and polar orbits, where the problem is more severe. There is increasing international agreement that a process for active removal of orbital debris elements – once they are clearly defined – will become necessary to address this problem that continues to grow worse over time despite the guidelines to minimize new debris. This orbital debris problem is a difficult one for many reasons. The cost of active debris removal is very high and the appropriate technology that would be ideal for this purpose remains elusive. Nevertheless, many proposals regarding various debris mitigation methodologies are being pursued. The launch of many small satellites with many of them lacking either an active or passive deorbit capability complicates the orbital debris problem even further. In addition to the technical and prohibitive cost associated with active orbital debris mitigation, there are legal issues as well. The current space law regime has no formal definition of space debris in that all elements in space are simply known as “space objects” despite whether they are functional or not. Current legal liability provisions that place all liability with the launching State do not help to facilitate any active removal activity. In short there are no incentives to remove debris from space at this time. This chapter addresses the threats to the long-term sustainability of space posed by the continuing buildup of space debris. In particular, it addresses current efforts and plans around the world to address the space debris problem with active removal and mitigation techniques and possible international legal changes or agreements that might facilitate these actions.

*Email: [email protected] *Email: [email protected] Page 1 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

Keywords Active orbital debris removal; Committee on the Peaceful Uses of Outer Space (COPUOS), electrodynamic propulsion; Inter-Agency Space Debris Coordination Committee (IADC); Liability convention; Kessler syndrome; Mitigation techniques; Outer space treaty; Robotic systems; Space weapons; Space data association; Space debris; Space object; Sustainability of space; United Nations

Introduction In the early 1980s when the problem of orbital space debris was first a subject of analysis and discussion, natural debris in the form of micrometeorites represented a much larger issue and concern. At that time spacecraft were more than a hundred times more likely to be hit by cosmic particles and interplanetary dust than human-created debris; thus, this issue was considered only a tangential area of concern. Over time, more and more launches, explosion of fuel tanks in orbit, upper stage launch vehicles remaining in orbit, derelict spacecraft not being deorbited, and a host of other activities over the past three decades have worsened the situation dramatically. Several key events such as the collision of the Iridium and Russian Kosmos satellite and the Chinese in-orbit targeting of an out-of-service weather satellite with a missile have sharply increased orbital debris and engendered an international discussion of what can be done about the increasing accumulation of space debris and a growing cascade effect that is worsening the problem. The Inter-Agency Space Debris Coordination Committee (IADC) and the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) have developed voluntary guidelines that launching nations are now systematically using to prevent or lessen the buildup of new space debris. The Space Data Association (SDA) has also developed procedures to help avoid the conjunction (i.e., collision) of operational satellites by sharing of orbital data (Space Data Association). Yet even with all these measures in effect, debris population still continues to rise. Also there are a rising number of small satellite launches that also continue apace. A large number of these diminutive craft have no active capability to deorbit after their mission is completed and are thus left to naturally deorbit over time due to atmospheric drag. In addition a large number of these small crafts are not formally registered with the International Telecommunication Union as formally required under existing international regulations that apply to all ITU members. This may seem harmless for very small satellites, but if the same practice were followed along our highways, all of our roadways would be littered with debris. Today, however, the most major problem with space debris involves the very largest debris. International discussions on the long-term sustainability of space are thus now focused on how to actively remove the largest derelict objects from space since collision of these objects can give rise to the largest amount of new debris. There are also many other topics that are being addressed, which include (i) How can it be ensured that there is sufficient fuel to deorbit spacecraft or put them at the end of life into a “safe parking orbit” that is sometimes referred to as the “junkyard orbit”? (ii) How can it best be ensured that the upper stage of launch vehicles actually descend from orbit immediately after launch? (iii) How can truly cost-effective and reliable means be developed to remove derelict spacecraft from orbit? (iv) How can “space debris” be clearly defined under international law and how can current liability provisions be amended so there is an incentive to deorbit spacecraft that have become derelict? (v) How can active debris removal be accomplished by either active space debris mitigation vehicles or via ground-based systems (i.e., laser beam or ion beam Page 2 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

projection) without violating bans on the deployment and use of “space weapons”? (vi) If active deorbit capacities are not available, are there appropriate ways to systematically employ “passive systems” to accelerate the deorbit process without becoming space debris themselves? (vii) Are new registration procedures needed or applicable to small satellites, given that many are not now being registered under UN procedures? (viii) Are there internationally acceptable new ways to use groundbased systems to avoid collisions? and (ix) Are there new international institutional, financial, and legal arrangements that can assist with orbital debris reduction activities that need to be implemented as a matter of priority? (Pelton 2012). Other chapters in this handbook address the nature and the causes of orbital debris buildup, as well as the financial and institutional arrangements that might be employed to encourage new solutions to the pervasive orbital debris problem. The focus of this chapter is on the means – both passive and active – that can be employed in space or on the ground to lessen the risk of orbital collision and hence lead to the decrease of the orbital debris population over time. The discussion of alternative technical means that might be employed to remove space debris from orbit will be followed by a listing of various initiatives that are underway or planned to remove debris from orbit. These projects are covered in subsequent sections. Finally, there will be a discussion on the legal issues and concerns that limit or serve to prevent the active mitigation of orbital debris under existing international laws and conventions.

Technical Approaches to Active and Passive Debris Removal as well as Collision Avoidance There is a high degree of agreement as to the need to lessen the buildup of orbital debris. Yet despite this general international consensus, it is far from clear as to what should be and even what can be done. Some believe that orbital debris are a menace and should be “entirely eliminated,” while others believe that the reasonable goal is to simply keep it largely in check as a form of homeostasis (Finkleman). The actual technology to be employed is another area of contention. There are a number of different ideas as to how orbital debris removal should be accomplished. One view is to use groundbased laser systems to create a pressure gradient by illuminating a large target, e.g., an upper stage rocket body, to alter its trajectory thus eliminating the risk of impending collision. Others propose the use of high-powered particle beam or laser systems to steer derelict space objects so that they would rapidly deorbit. The critics of this approach believe that such ground-based systems are, in fact, space weapons and thus cannot be used under international law. Others fear that the technology is not sufficiently mature and could lead to space collisions rather than prevent them. Then there are a wide range of possible space-based technologies that will be discussed briefly below that might be deployed once developed to bring space debris down. It is important to ensure that these space-borne debris-mitigating systems would not become debris themselves. Some techniques such as those employing robots that would latch on to an out-of-service satellite and then bring them down would work quite rapidly. Other systems that would “squirt” glueball balloons or mists to attach a tape onto derelict satellites would only hasten deorbit over time. Then there are advocates of passive systems that would at the end of life deploy a balloon or sail to create atmosphere drag to bring satellites (particularly small, low earth orbit) down at a more accelerated pace. This approach would involve putting a passive system on the satellite before launch. Some concepts such as the glueball balloon would be “stuck” on by an in-orbit maneuverable spacecraft (The Looming Space Junk Crisis). Page 3 of 16

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Finally, there are those that contend that none of these technologies can be used until the issues of legal liability and what constitutes a space weapon are resolved – except putting passive deorbit systems, i.e., inflating a balloon at end of life. Meanwhile, billions of dollars are being invested in radar systems in space, as well as the so-called S-band radar system (i.e., the “space fence”) just to track space debris. Currently some 22,000 space debris elements the size of a baseball or larger are being actively tracked. New radar systems will be able to track even smaller-size debris.

Technologies to Address Space Debris Mitigation Under Development Passive Deorbiting Systems A number of projects have been designed or are under development to create inflatable balloons, inflatable tube membranes (ITMs), tethers, solar sails, or deployable drag systems to accelerate the deorbiting process. Most of these are for small satellite programs in low earth orbit that do not have active thrusters to allow a controlled deorbit at end of life. Satellites that have used this type of passive deorbit technology include the NASA FASTRAC satellite with a large deployable solar sail, the Canadian-funded CANX-Drag Sail (Bonin et al. 2013), the European Union Protec 1-2015 program (“Passive Means..”), and a large number of university programs in the United States, Europe, and other parts of the world. These are typically designed for low earth orbit and quite small satellites. When these passive systems are deployed, the cross section that creates atmospheric drag can be significantly increased and thus accelerate the deorbit time and thus make deorbit two to three times more rapid.

Ground-Based Systems to Divert Orbits to Avoid Collisions Relatively low-powered laser systems can be used to illuminate a derelict satellite or a large debris element such as a rocket body that is projected to be on a collision course with another space body. If the collision trajectory can be predicted well in advance, then a small change in the linear momentum of the target debris either due to a change in velocity vector or mass removal (ablation) caused by laser illumination or both would prevent the collision. In this case the heat from the low-powered laser would create a small jet from the material of the satellite that would slowly push the space debris object into a new orbit (Ablative Laser Propulsion).

Ground-Based Laser Systems to Trigger Deorbiting A much high-powered laser beam could provide sufficient ablation of the satellite’s mass so as to push (i.e., momentum change principle) the satellite into a new orbit; the satellite would then lose altitude and reenter the Earth’s atmosphere (Buccino). This technique has also been suggested by the Planetary Society as a means of diverting the orbit of a threatening asteroid by sending a number of such ablative laser systems to create multiple jets from the surface of the threatening cosmic hazard.

Ion Beam Shepherd There are several techniques that might use ion beam projection systems. One of these approaches would utilize a precisely focused hypervelocity ion beam. This beam would be directed against a piece of space debris. This beam would then “shepherd” the space debris to a controlled deorbit. This approach could utilize a spacecraft-based ion beam, or with higher-powered mechanisms this could potentially be a ground-based system. This technique is being studied by the European Space Agency, NASA, and the Japanese Space Agency (JAXA) (Bombardelli et al.).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

A high-powered laser or particle beam system would be considered by most nations as a space weapon. A number of countries strongly object to such use of ground-based lasers or particle beam systems since they are seen as antisatellite weapons and as such are considered to be contrary to Article 4 of the Outer Space Treaty. One solution to this issue that has been recently proposed is that the country that is recorded as the launching State would be given control of the laser or particle beam ionic stream for the deorbit operation.

Electrodynamic Propulsion Systems for Space Debris Removal

This concept would utilize the Earth’s magnetic field to generate electric propulsion. This approach has the distinct advantage of not having to burn up rocket fuel to carry out its operation. These systems would use the Earth’s natural geomagnetic energy as its “fuel supply.” Two variations of this approach would be possible. The least ambitious means would be to have a conventional satellite with a chemical propellant that would maneuver in low earth orbit to simply attach tethers to satellites to help deorbit derelict space objects. This may or may not include an electric ion thrust motor with the tether to accelerate deorbit with the tether therefore being used to generate electric power. A much more ambitious technological approach has been proposed. This would be to create a large-scale electromagnetically driver device. In this case the in-orbit mechanism would seek to remove hundreds of orbital debris pieces over time (Pearson et al. 2011) and see (Hoyt).

Tether-Deployed Nets

This system would deploy “nets” around smaller elements of space debris and speed up their deorbit. (This system has been called “Rustler” for “Round Up of Space Trash – Low Earth orbit Remediation.”) The so-called GRASP approach (i.e., Grapple, Retrieve, and Secure Payload) represents a relatively low technology in principle. The derelict satellite would simply be enveloped by a net that would greatly increase atmospheric drag (Hoyt).

Adhesives A less complicated version of the deployed nets would be to deploy a satellite that would be capable of shooting at close range on to the surface of the debris object what might be called very sticky adhesive balls. These balls would be composed of substances such as resins or aerogels. The precise method of extruding the adhesive has not been precisely defined at this time. Once these adhesives are attached to space debris objects, they would in time alter their debris objects so they would degrade over time (Kushner 2010).

Terminator Tape This approach attaches a so-called terminator tape to the debris element, and this would by the pull of the Earth’s gravity be deployed like a gravity gradient antenna to create the maximum drag. This approach would assist small satellites to meet the 25-year deorbit objective (Hoyt).

Space Mist Systems The least sophisticated type system of this nature that would be for the smallest of debris elements would be a spacecraft that would shoot out “space mists” onto targeted space objects. In this case chemically propelled rockets would deploy especially equipped satellites in low earth orbit. These satellites would maneuver close to derelict space objects and then would spray gas mists, and the frozen gas mist would serve to help deorbit smaller orbital debris (Kushner 2010).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

Space Harpoon System

Astrium UK has proposed to develop a system that could fly in close proximity to a defunct satellite or upper stage rocket motor that had become space debris and then shoot it with a harpoon device. There would be a propulsion pack linked by a tether to the projectile. This propulsive system would then pull the targeted space debris downward so that it then burns up as it reenters the atmosphere. The harpoon system, as proposed by Astrium, will include about 30 cm long barbed spear. It would be possible to mount several harpoons and propulsive deorbiting systems on a “chaser satellite” that would advance to within 100 m of a junk object (Fishing Space Debris).

Space Debris Cleanup Robotic Systems The most commonly planned cleanup programs for space debris are robotic systems. This spacecraft would simply find and then clamp on to targeted space debris. Some systems would then just fire rockets to bring the robotic spacecraft and the debris element down in a controlled manner. Other designs would use the robotic spacecraft to deflect, using a detachable propellant motor, the space debris object and push it into a new orbit that would rapidly degrade. At the most ambitious level there have been thoughts of creating a large nuclear-powered robotically controlled “space pod.” This “space roaming spacecraft” might be able to operate over a period as long as 15 years. It would be able to propel large space debris into new orbits that would quickly degrade. This type of technology has been conceived as being able to capture and deflect a dangerous asteroid or bolide that is threatening Earth (Proceedings of the International Interdisciplinary Congress on Space Debris).

What Is the Optimal Technology for Debris Removal? Currently there is no clear-cut indication as to what can be considered the “best” or the “right” technology to undertake the task of orbital debris mitigation. In the chapter on the financial and institutional arrangements to remove space debris from orbit, there is currently a concern that if a single international agency is formed to remove orbital debris, it could focus on a single and perhaps ultimately the wrong technology. This could perhaps needlessly drive up the cost of this activity. This has led to thoughts that a new international fund to support the development of competitive technology to remove orbital debris should be established. This fund might even support a contest based on the XPrize model to develop such new technology.

The Importance of Space Situational Awareness to Debris Minimization Finally it is important to maintain spacecraft and debris tracking as part of an accurate space situational awareness capability. Obviously, it is not possible to remove debris unless there is a clear awareness of what orbit it is traveling in. Today the most “competent” space agencies to deal with space situational awareness and space debris removal technologies are most probably military entities. This concentration of technological expertise for tracking and active removal technologies naturally gives rise to concerns about space weapons and military uses of systems developed to remove space debris from orbit. The new S-band radar system known as the Space Fence will be able to track debris elements in low earth orbit as small as a golf ball. Page 6 of 16

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Current Initiatives Related to Space Debris Mitigation This section provides a survey of current international space debris remediation initiatives around the globe undertaken both by government actors and private industry. Many governmental programs see active debris remediation and satellite servicing as parallel and overlapping activities involving robotic mission capabilities, and thus these technical capabilities are treated as if they are one and the same in this review of active programs. In fact in-orbit servicing and repair, active orbital debris repair, and strategic defense capabilities in space are all interlinked, and thus one often sees an overlap of civilian and defense activities in this area. One of the reasons that the UN Committee on the Peaceful Uses of Outer Space (COPUOS) has often not been able to make progress in this area is because of the perceived overlap of strategic, defense, and civilian space considerations in this area. The National Aeronautics and Space Administration (NASA) and the Defense Advanced Research Projects Agency (DARPA) in the United States have sponsored several conferences on space debris remediation to encourage expert dialog among the international space community (NASA and DARPA) and (Barnhart). There has also been consensus among international experts in the form of a key finding at a conference organized by the European Space Agency (ESA) in 2009 that “active space debris remediation measures will need to be devised and implemented . . . there is no alternative to protect space as a valuable resource” (“Key Findings”). In a motion for a resolution on the European Space Policy – Green Paper in 2003, the Committee on Industry, External Trade, Research, and Energy of the European Parliament underlined the significance “to establish the necessary international cooperation to develop in-orbit servicing” and called upon ESA “to establish a research, development and demonstration programme on in-orbit servicing as a matter of priority, given its potential strategic advantage for the European space sector” (Report on European Space Policy). In the United States, the NASA Satellite Servicing Capabilities Office was established in 2009 to inter alia, “advance the State of robotic servicing technology” and “help to enable a future U.S. industry for the servicing of satellites” (Satellite Servicing Capabilities). Further, the United States Air Force and the National Reconnaissance Office have jointly established a space protection program office to advise the military and intelligence community on the safeguarding of space assets (Singer).

Phoenix Program, DARPA The Phoenix program under the aegis of the Unites States Defense Advanced Research Projects Agency (DARPA) has the stated goal of recycling space assets – usable antennas, solar arrays, and other components – from defunct or inactive satellites in orbit. Its goal is to “develop and demonstrate technologies to cooperatively harvest and re-use valuable components from retired, nonworking satellites in GEO and demonstrate the ability to create new space systems at greatly reduced cost” (DARPA Phoenix Satellite Servicing). It aims to secure “around-the-clock, globally persistent communication capability. . .by robotically removing and re-using GEO-based space apertures and antennas from de-commissioned satellites in the graveyard or disposal orbit” (DARPA Phoenix Satellite Servicing). The Phoenix program will develop miniature satellites which could be transported to the GEO region through a “piggyback” ride on a commercial satellite launch and then be used to create a new space system by robotically attaching it to the antenna of a nonfunctional cooperating satellite. It has set its first keystone mission in 2015 to “demonstrate harvesting an existing, cooperative, retired satellite aperture, by physically separating it from the host non-working satellite using on-orbit grappling tools controlled remotely from earth,” which will then be “reconfigured into Page 7 of 16

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

Fig. 1 Concept image of German DEOS active deorbit systems (Image Courtesy of DRL)

a ‘new’ free-flying space system and operated independently” to boost the notion of space recycling (DARPA Phoenix Satellite Servicing). DARPA has selected Honeybee Robotics Spacecraft Mechanisms Corporation to develop new tele-robotic end-effector prototypes designed to enable a servicing satellite to dock with and manipulate communications satellites in GEO (Honeybee).

Deutsche Orbital Servicing Mission (DEOS) The German Space Agency (DLR) also has an active space servicing mission currently in the works (Wolf). When the program was announced in 2010, the stated goal for the DEOS project is to “demonstrate the availability of technology and verify procedures and techniques for rendezvous, capture, maintenance and removal of an uncontrollable satellite from its operational orbit through a demonstration mission” (Sommer and Landzettel). This project entails two satellites, the robotic retriever and the “target” for recovery. This target satellite represents a noncooperative, unstable drifting, and tumbling satellite that has to be captured by a servicing satellite for repair, refueling, or disposal (DEOS). One might question why a new target satellite would be needed when so many defunct satellites are in orbit. Unfortunately, there are legal issues yet to be resolved as who can recover, service, or dispose derelict spacecraft in orbit. This DLR German Aerospace Center project is funded by the German Federal Ministry of Economics and Technology (BMWi). The aerospace company Astrium has been selected to carry out the definition phase of this project (Astrium wins; Fig. 1).

Orbital Express Space Operations Architecture, DARPA Another DARPA project in this area is known as the Orbital Express Space Operations Architecture program. This project was designed as a 3-month mission in 2007. The stated goal of this DARPA project was to “validate the technical feasibility of robotic, autonomous on-orbit refueling and reconfiguration of satellites” (Espero) and (Hastings 2006). The program, just as in the plans for DEOS, involves the deployment of two satellites – one that is the target for servicing and the other is the robotic capturing satellite. In this case the satellite designed to be serviced is called NextSat. The name for the satellite designed for capture is NextSat while the servicing vehicle is called ASTRO. This pair of satellites has been optimized to carry out a series of experiments to demonstrate autonomous rendezvous and docking capability. It is also designed to carry out tests to achieve unassisted on-orbit refueling as well as to replace batteries and other parts that might naturally fail on an extended mission (Orbital Express Space Operations). A compact state-of-the-art automated guidance system known as Advanced Video Guidance Sensor

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(AVGS) is considered critical to the docking operations. This sensor allowed ASTRO to capture NextSat and provide refueling with difficult to manage hydrazine hypergolic propellant. The mission design includes the ability to insert a new battery as well as an additional component (Smith 2007). Clearly, the capabilities demonstrated in this mission could also be applied to active debris remediation.

NASA Robotic Refueling Mission (RRM) The Robotic Refueling Mission (RRM) represents a collaboration between the Canadian Space Agency (CSA) and NASA and as such is also relevant. This experiment was carried out at the International Space Station (ISS) to “demonstrate and test the tools, technologies, and techniques needed to robotically refuel satellites in space—especially satellites not designed to be serviced” (NASA Robotic Refueling). The critical element in this experiment was in the use of the ISS’s “Canada Arm.” This device is formally known by the more complicated name of the Special Purpose Dexterous Manipulator. This is usually referred to as simply Dextre. This robotic device has now often been used for the capture and ad hoc docking of spacecrafts such as the SpaceX Dragon capsule and the Orbital Science Cygnus vehicle. The experience with these spacecraft captures has helped to add to the knowledge associated with spacecraft servicing and capture that should assist with future active debris mitigation missions. Dextre has been key to the capture of arriving spacecraft when conventional docking was not an option (Active Debris Removal). Shuttle-based Canada Arm was utilized by the crew members of STS-49 when they had to capture and repair the stranded Intelsat-VI satellite and then reequipping it with a new kick motor so that it could be lifted from low earth orbit to geo orbit. This was a particularly difficult operation because the spinner of the spacecraft had to be slowed down to attach this large rocket motor (Flight History of Canada Arm).

CleanSpace One Swiss Space Agency and the commercial company Swiss Space Systems (S3) are actively supporting the CleanSpace One project. This project is designed to recover and deorbit a small spacecraft from low earth orbit. The plan is to develop and build the first installment of a fleet of satellites designed to deorbit space debris. This initial low-cost demonstration project planned for 2017–2018 has an estimated cost of only about 10 million Swiss francs. This project is also being carried out in cooperation with the Swiss University EPFL or Ecole Polytechnique Federale Lausanne. The plan is to eject a small “capture” satellite from a suborbital space plane being developed by Swiss Space System. The CleanSpace One spacecraft will be traveling in a very high velocity trajectory at the point of ejection. This will allow the spacecraft to burn sufficient fuel to go into orbit and to be in proximity to one of the two Swiss nanosatellites selected for the deorbiting mission. This small spacecraft with robotic arms would be able to capture the small satellite and then in a controlled burn safely deorbit (Orbital Cleanup Satellite; Fig. 2).

Space Infrastructure Servicing (SIS), MacDonald Dettwiler and Associates MacDonald, Dettwiler and Associates (MDA), the Canadian space company has developed its Space Infrastructure Servicing (SIS) vehicle to assist with in-orbit servicing as well as potentially a deorbiting mechanism. This spacecraft with a specially designed robotic arm is capable of performing space-based maintenance and repair tasks, refueling, and servicing of a spacecraft. It could alternatively also be used to capture and assist with the deorbiting of a defunct spacecraft or upper stage rocket (Oldham). MDA, as a result of this work, has recently been chosen to support the

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

Fig. 2 CleanSpace One capturing a small satellite (Graphic Courtesy of Swiss Space Systems)

DARPA Phoenix program (MDA to be Key Supplier). In 2011, it had entered into an agreement with Intelsat as its anchor tenant to provide on-orbit servicing to the latter’s future generation of communications satellites. This agreement, however, has now been terminated (Space Infrastructure Servicing).

ViviSat ViviSat is a project that is jointly owned by the US Space LLC and ATK Aerospace Systems. This company is offering on-orbit life extension and fleet management services but could also be utilized as means to deorbit space debris. These services would be provided by ViviSat. Mission Extension Vehicle (MEV) is a robotic spacecraft that would allow long-term stationkeeping and attitude control for spacecraft that have exhausted their fuel or batteries but were otherwise functional. This service could also be used to relocate spacecraft in Geo orbit to alternative orbital slots. This same type satellite could also be used for the deorbiting satellites in cases where permissions had been granted and legal liability issues resolved (Vivisat) and (McGuirk).

Electrodynamic Debris Eliminator (EDDE) This project is signally different than the other active projects in that it would create a device that rather than relying on rocket fuel would utilize the Earth’s magnetic field to maneuver in low earth orbit. As envisioned by the EDDE enterprise, it would consist of wires several kilometers in length to generate electrical power with units along the wire that could manipulate space junk that the EDDE device would encounter. As currently envisioned, the EDDE device would consist of a thin cable several kilometers in length that would serve to generate electrical power as it moves through the Earth's magnetic field. There would be devices at the end to push device into a new orbit to accelerate decay. This type of approach would be used to assist with the deorbiting of a large number of defunct satellites and upper stage vehicles – as opposed to missions that would deorbit one satellite or piece of space debris at a time – would pose a much different type of issue in terms of international legal and liability issues that would arise with this comprehensive as opposed to a “single shot” operation. A claim is made that a configuration of 12 such EDDE vehicles could remove essentially all debris elements in excess of two kilograms–or about 2,500 large units of space junk–within a 7-year time frame (EDDE).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

International Demonstrator Project There are a wide range of international initiatives that have been presented and discussed within such forums as the International Astronomical Federation and the International Academy of Astronomy, the International Group of Experts on Space Debris, the International Space Debris Workshops, the Inter-Agency Space Debris Coordination Committee (especially within its working group on active debris mitigation), and the UN Committee on the Peaceful Uses of Outer Space. There have been specific proposals for an international demonstrator project that would involve a number of active space nations including Russia, Japan, Europe, the United States, and other space-faring nations. At this stage although there have been a number of proposed projects, such initiatives are still in the discussion stage (Activity on Space Debris Problem).

Legal and Policy Concerns Related to Active Space Debris Removal The preventive measures in the form of debris mitigation taken during the last decade through voluntary nonbinding guidelines have clearly not been able to effectively address the impending catastrophic situation. The only way to ensure secure and sustained access to the long-term utilization of space is through space debris remediation in the form of active removal of debris and on-orbit satellite servicing. However, the technology involved in this endeavor gives rise to a plethora of regulatory complexities and unanswered legal questions (Liou 2011). The current regime of international space law consisting of the five United Nations Treaties and five Declarations does not contain any specific definition of what is considered space debris. The operative terminology used in these Treaties, Conventions, and Declarations is a simply “space object.” This rather vague and ill-defined term apparently, covers any tangible human or even robotic-crafted matter or instrumentality in outer space. The concern over the absence of a proper definition of this term is underlined by the fact that “the basis of liability is that the damages or injury is caused by a space object” (UN Outer Space Treaty, Art. VII and Convention on Legal Liability, Art. II-III). The definition of “space objects” is broad enough to include objects constructed or assembled in outer space under the regime of the Liability Convention. This breadth of concept is to ensure that States do not ignore or contravene the provisions of applicable Treaties, Conventions, or Declarations by constructing or assembling said space objects in outer space. Thus, it is also important to address the status of satellites whose components have been derived from functional parts of “space debris” salvaged or serviced in outer space. This is certainly pertinent given the objective of the Phoenix program to retrieve and reutilize space assets from inactive satellites by 2015, as discussed in the preceding section. The consideration as to when a space object might be considered to be space debris seems to weigh heavily on the ability of said object being capable of being commanded to move. The key phrase that is cited in this context is “the ability of the man-made instrumentality to traverse in outer space.” Hence, the lack of maneuverability or functionality of the space object is frequently seen as key to determining its status as space debris so that it can be classified as a candidate element of “space debris” that is suitable for remediation (Hurwitz 1992). The Outer Space Treaty grants jurisdiction and control over a space object to the State of registry, that is, the State on whose registry an object launched into outer space is carried. The State of registry is further required to retain its jurisdiction and control over the space object, even after the expiry of its functional phase. Hence, it is certainly deemed to be quite clear that space objects include space debris. Page 11 of 16

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It is interesting to note that the international definition of “ownership” of space objects is not the same as the jurisdiction and control over them. While “jurisdiction and control” can be retained “while in outer space or on a celestial body,” “ownership” is “not affected by their presence in outer space or on a celestial body or by their return to Earth” (Outer Space Treaty, Art. VIII and Moon Treaty). The various UN Treaties and Conventions are silent about the legal possibility of renouncing de jure jurisdiction and control by a State of a space object. This means that there is considerable legal uncertainty about the status of possible legal liabilities that apply while a State or a private entity might undertake remediation activities for a space object. Legal liability and de jure ownership of a space object remain with the State of registry even if it has lost de facto control due to a variety of technological or contractual means. Legitimate exercise of jurisdiction by a State is marked by the presence of a genuine link between itself and the object in question (Nottebohm Case). Scholarly discourse identifies registration of space objects as sufficient nexus between the State and the space object (Hobe 2012). In the absence of registration, ownership over the object can be used to determine which State could lawfully exercise jurisdiction and control. Some States are currently not registering small satellites in all instances. This is particularly true of nanosats that are released as secondary or even tertiary parts of a larger mission. The status of such space objects has never been firmly established in a specific legal action, but the lack of registration is not likely a means of escaping legal liability (Hobe 2012). It is clear that public international space law is silent about the legality of remediation when it relates to the transfer of jurisdiction and control of a space object. In the event of a remediation performed by a State or a State-licensed actor, it will be considered legitimate if the State retains de jure jurisdiction and control of that space object or obtains explicit authorization from the State of registry. Thus, no legal complications are anticipated when a State seeks to remediate its own space objects. However, when a State or State-licensed actor seeks to remediate a space object that it did not carry its registry, the question will arise whether there can be an exception to this general rule of jurisdiction and control on grounds of the public policy goal of facilitating the long-term sustainability of outer space. Although international space law does not contain explicit provisions for the transfer of registry, public international law jurisprudence coupled with contemporary State practice have circumvented such a gap through the conclusion of bilateral or multilateral agreements. Actual practice will likely clarify the situation in the coming days as actual active remediation of defunct space objects takes place in the future. The implementation of advanced technology to perform remediation activities poses a number of legal and regulatory challenges. This is the result of the fact that the current regime of international space law is silent or ambiguous on what can and cannot be done and what legal liabilities do or do not apply. The primary concerns arise from definitional issues, registration processes, jurisdiction and control of space objects, and related liability considerations. These have been extensively examined in a theoretical sense to try to determine what public international law jurisprudence developed over the years does or does not apply. Actual practice and specific legal determinations are most likely to resolve these issues. Given the lack of any major new agreements, conventions, or declarations, it seems unlikely that a new space law to clarify these issues will be forthcoming any time soon.

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Conclusion The issue of active remediation of space debris is currently one of great interest around the world for many reasons. The problem of increasing buildup of orbital debris is of great concern because new collisions of larger space debris objects can generate thousands of smaller debris pieces. Two events in the past decade have particularly accentuated concerns about the long-term sustainability of space and particularly focused attention on low earth orbits and polar orbits where the debris accumulation has become most severe. In the 1980s natural debris such as micrometeorites outnumbered man-made debris by much more than ten to one. Today the situation in low earth orbit has reversed itself. Voluntary procedures to reduce the buildup of new orbital debris, as agreed by the Inter-Agency Space Debris Coordination Committee (IADC) and the United Nations Committee on the Peaceful Uses of Outer Space have served to ameliorate the situation, but the number of debris pieces larger than a baseball currently being tracked exceed 22,000 objects. The cost of satellite-based and ground tracking systems (such as the proposed S-band radar Space Fence) that maintain space situational awareness of orbital debris and now allow maneuvering to avoid major collisions in orbit now requires investments costing billions of dollars (US). The increasing consensus is that active orbital debris removal is necessary to sustain long-term access to and effective use of space for the future. Some have suggested that just the active removal of 5 to 10 large objects a year could represent major progress to address this problem. This chapter has indicated the various types of technologies that might be deployed to assist with active and passive debris remediation technologies – both in the near and longer term. Much more research is needed to find the best, most efficient, least costly, and environmental friendly way to proceed to make the use of outer space sustainable for the long run. A number of demonstration projects are now underway and new ideas about how active debris removal might be undertaken abound. In the shorter term positive steps are possible. These include active collision avoidance techniques, sharing of data about possible conjunctions such as what the Space Data Association (SDA) is doing, and use of passive technologies to assist with the deorbit of low earth orbit satellites (particularly small satellites). These steps represent good progress. The IADC and UNCOPUOS guidelines to prevent debris from being created in the first place are clearly major steps forward. Eventually active debris removal (especially for larger defunct satellites and upper stage rocket motors) will be needed. As technical progress is made to develop the best techniques to make this possible is achieved, the legal and regulatory community needs to develop practical methods and guidelines to be followed to limit liabilities, minimize the potential for accidents, and to ensure that only defunct and unusable space objects are removed from orbit. The starting point would be a widely agreed definition of space debris. The next steps would be methods for space debris removal that are safe, reliable, and do not represent a threat to anyone’s current or future civil or defense space operations.

Cross-References ▶ Hazard of Orbital Debris ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_75-1 # Springer International Publishing Switzerland 2014

References Activity on Space Debris Problem IAF symposium on space debris problem at COPUOS/STSC, Vienna, 11 Febr 2013. http://www.oosa.unvienna.org/pdf/pres/stsc2013/2013iaf-04E.pdf. Last accessed June 2014 Astrium wins DEOS contract to demonstrate in-orbit servicing. 13 Sept 2012. Online: Astrium http://www.astrium.eads.net/en/press_centre/-kx9.html. Last accessed June 2014 Barnhart D, Program manager, DARPA TTO (2012) Overview on DARPA’s ‘Fostering sustainable satellite servicing conference’. Presented at the European conference on on-orbit satellite servicing and active debris removal, Brussels, 30 Oct 2012 Bombardelli C et al Dynamics of ion-beam propelled space debris. http://web.fmetsia.upm.es/ep2/ docs/publicaciones/ahed11a.pdf. Last accessed June 2014 Bonin G et al (2013) The CanX-7 drag sail demonstration mission: enabling environment stewardship for nano and microsatellites http://utias-sfl.net/wp-content/uploads/Small-SatelliteConference-2013-SSC13-XI-9.pdf. Last acessed May 2014 Buccino D (2011) Ablative laser propulsion for space debris removal. Colorado Center for Astrodynamics Research, University of Colorado http://ccar.colorado.edu/asen5050/projects/ projects_2011/buccino/. Last accessed 16 May 2014 Committee on the Peaceful Uses of Outer Space (COPUOS) Active debris removal — an essential mechanism for ensuring the safety and sustainability of outer space: a report of the International Interdisciplinary Congress on Space Debris Remediation and On-Orbit Satellite Servicing. UNCOPUOS OR, 49th Session, UNCOPUOS A/AC.105/C.1/2012/CRP.16. 27 Jan 2012 at 18 DARPA Phoenix Satellite Servicing, Tactical Technology Office. Online: http://www.darpa.mil/ Our_Work/TTO/Programs/Phoenix.aspx. Last accessed June 2014 DEOS: A Robot serves Defective Satellites to prevent space debris, Research in Germany,. Online: http://www.research-in-germany.de/main/research-areas/space-technologies/2-nr-2-research-project s/43000/3-nr-3-deos,print¼true,slc¼dachportal_2Fen.html. Last accessed June 2014 Electro Dynamic Debris Eliminator (EDDE) vehicle. http://www.star-tech-inc.com/id121.html. Last accessed June 2014 Espero TM, Boeing Corporation Future space robotics and large optical systems: a picture of orbital express. Presented at the NASA workshop on “Astronomy Enabled by Ares V,” NASA Ames Research Centre, 27 April 2008. Online: http://event.arc.nasa.gov/aresv/ppt/Sunday/1Espero/ 1Espero.pdf. Last accessed June 2014 Evan I. Schwartz. The looming space junk crisis: it’s time to take out the trash. Wired Magazine. 24 May 2010. www.wired.com/magazine/2010/05/ff_space_junk/all/1. Last accessed June 2014 Finkleman D The intersections among policy, science, and engineering for sustainable space activity. International Academy of Astronautics. Last accessed May 2014 Fishing Space Debris from Orbit. http://www.sstl.co.uk/Blog/July-2013/Fishing-Space-Debrisfrom-orbit. Last accessed June 2014 Flight History of Canadarm. Online: Canadian Space Agency, http://www.asc-csa.gc.ca/eng/ canadarm/flight.asp. Last accessed June 2014 Hastings D (2006) Studies to enable a paradigm shift in the space enterprise: atro/orbital express, Department of Aeronautics and Astronautics, Massachusetts Institute of Technology . Online: http://www.dtic.mil/dtic/tr/fulltext/u2/a455064.pdf. Last accessed June 2014 Hobe S (2012) Environmental protection in outer space: where we stand and what is needed to make progress with regard to the problem of space debris. Indiana Journal of Law 8

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Honeybee Robotics selected for DARPA Phoenix program for on-orbit satellite servicing. Online: http://www.honeybeerobotics.com/about/honeybee-news/130-darpa-phoenix-selection. Last accessed June 2014 Hoyt R, Tethers Unlimited The rustler deorbit systems. www.tethers.com/papers/Tethers_RUSTLER_Presentation.pdf. Last accessed June 2014 Hurwitz BA (1992) State liability for outer space activities in accordance with the 1972 convention on international liability for damage caused by space activities. Martinus Nijhoff, Amsterdam, Netherlands, p 23 Key findings from the 5th European conference on space debris. 2 Apr 2009. Online: European Space Agency, http://www.esa.int/esaMI/Space_Debris/SEMYN9LTYRF_0.html. Last accessed June 2014 Kushner D (2010) The future of space: orbital cleanup of cluttered space. Popular Science 60–64. http://www.popsci.com/technology/article/2010-07/cluttered-space. Last accessed 6 October 2014 Liou JC (2011) A note on active debris removal. Orbital Debris Quarterly News 15:7–8. Online: http://www.orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv15i3.pdf. Last accessed June 2014 MDA to be key supplier in satellite servicing demonstration for US Government. 18 October 2012. Online: MDA http://www.mdacorporation.com/corporate/news/pr/pr2012101801.cfm. Last accessed June 2014 (2010) NASA and DARPA sponsor international debris removal conference . Orbital Debris Quarterly News 14:1. http://orbitaldebris.jsc.nasa.gov/newsletter/pdfs/ODQNv14i1.pdf. Last accessed June 2014 NASA Robotic Refueling Mission fact sheet. Online: http://ssco.gsfc.nasa.gov/images/ RRM_Factsheet.pdf. Last accessed June 2014 Nottebohm Case, International Court of Justice ICJ reports, 1955, p 4; 22 ILR, p 349 Oldham S, Vice-President MDA (2012) What the future holds: near-term servicing plans. Presented at the NASA second international workshop on on-orbit satellite servicing, May 2012. Online: http://ssco.gsfc.nasa.gov/workshop_2012/Oldham_final_%20presentation_2012_workshop.pdf. Last accessed June 2014 Orbital ceanup satellite to be launched in partnership with S3. http://space.epfl.ch/page-87472-en. html. Last accessed June 2014 “Passive means to reduce the impact of space debris” Protection of European assets in and from space-2015-LEIT SPACE Protec-1 2015. 11 Dec 2013. http://ec.europa.eu/research/participants/ portal/desktop/en/opportunities/h2020/topics/2453-protec-1-2015.html. Last accessed May 2014 Pearson J, Levin E, Carroll J (2011) Commercial space debris removal. Space Safety Magazine (1):21–22 Pelton JN (2012) The problem of space debris. In: Satellite communications. Springer Press, New York, pp 29–33 Proceedings of the international interdisciplinary congress on space debris, 7–9 May 2009. http:// www.mcgill.ca/channels/events/item/?item_id¼104375. Last accessed June 2014 Report on European space policy – green paper (2003/2092(INI)), 10 Sep 2003. Online: European parliament, http://www.europarl.europa.eu/sides/getDoc.do?type¼REPORT&reference¼A52003-0294&language¼EN#title2. Last accessed June 2014 Satellite Servicing Capabilities Office, NASA Goddard Space Flight Centre. Online: http://ssco. gsfc.nasa.gov/about.html. Last accessed June 2014 Singer J U.S. Air Force, Spy Agency Team up for Space Protection, 9 Apr 2008. Online: Space. Com http://www.space.com/5224-air-force-spy-agency-team-space-protection.html. For further Page 15 of 16

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details, see Budget Justification for the Space Protection Program, Feb 2012, online: http://www. dtic.mil/descriptivesum/Y2013/AirForce/stamped/0603830F_4_PB_2013.pdf. Last accessed June 2014 SmithR (2007) Orbital express scheduled to launch March 8: Marshall-developed automated rendezvous and docking technology to be tested in space. NASA Marshall Star 47:3. Online: http://marshallstar.msfc.nasa.gov/3-1-07.pdf. Last accessed June 2014 Sommer B Landzettel K DLR (2012) DEOS Deutsche Orbitale Servicing mission: the in-flight technology demonstration of Germany’s Robotics approach to service satellites. Presented at the NASA second international workshop on on-orbit satellite servicing, May 2012. Online: http:// ssco.gsfc.nasa.gov/workshop. Last accessed June 2014 Space Infrastructure Servicing Update, 11 Jan 2012. Online: MDA, http://www.mdacorporation. com/corporate/news/pr/pr2012011101.cfm. Also see, de Selding P Canadas MDA sees business case for in-orbit satellite servicing, 6 May 2010. Online: Space News. http://www.spacenews. com/satellite_telecom/100506-mda-in-orbit-servicing.html. CJune 2014). Last accessed June 2014 The Space Data Association Space Data Association now performs conjunction screening for more than 300 satellites. http://www.space-data.org/sda/wpcontent/uploads/downloads/2011/01/ SDA_press_release_21_Jan_ 2011_RELEASED.pdf. Last accessed June 2014 In-Orbit Servicing, A Corporate Overview of ViviSat, US Space. http://www.usspacellc.com/inorbit-servicing/vivisat. Last accessed 6 October 2014 Wolf T, DLR Deutsche orbitale servicing mission: the in-flight technology demonstration of German’s robotics approach to dispose malfunctioned satellites. Online: http://robotics.estec. esa.int/ASTRA/Astra2011/Presentations/Plenary%202/04_wolf.pdf. Last accessed June 2014

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Directed Energy for Planetary Defense Philip Lubina* and Gary B. Hughesb a Physics Department, University of California, Santa Barbara, CA, USA b Statistics Department, California Polytechnic State University, San Luis Obispo, CA, USA

Abstract Directed energy in the form of photons plays an increasingly important role in everyday life, in areas ranging from communications to industrial machining. Recent advances in laser photonics now allow very large-scale modular and scalable systems that are suitable for planetary defense. The fundamental requirements of directed energy planetary defense systems are described here, along with the current state of technological readiness. A detailed design is presented for an orbital planetary defense scheme, called DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation. DE-STAR is a modular phased array of kilowatt class laser amplifiers fed by a common seed and powered by photovoltaics. The main objective of DE-STAR is to use focused directed energy to raise the surface spot temperature of an asteroid to ~3,000 K, sufficient to vaporize all known substances. Ejection of evaporated material creates a large reaction force that alters the asteroid’s orbit. Both standoff (DE-STAR) and stand-on (DE-STARLITE) systems are discussed. The baseline standoff system is a DE-STAR 3 or 4 (1–10 km array) depending on the degree of protection desired. A DE-STAR 4 allows initial engagement beyond 1 AU with a spot temperature sufficient to completely evaporate up to 500 m diameter asteroids in 1 year. Small objects can be diverted with a DE-STAR 2 (100 m), while space debris is vaporized with a DE-STAR 1 (10 m). Modular design allows for incremental development, minimizing risk, and allowing for technological co-development. Larger arrays would be developed in stages, leading to an orbiting structure. The smaller stand-on systems (DE-STARLITE) are appropriate for targets with very long lead times to impact so that a dedicated mission can be implemented.

Keywords Asteroid impact; Directed energy; Laser phased array; Planetary defense

Introduction Recent advances in photonics make a scientific discussion of directed energy planetary defense feasible, whereas even 10 years ago it was close to science fiction. High-power lasers are capable of delivering sufficient energy density on a target to melt and vaporize any known material. Laser machining and welding are commonplace in industry, where even refractory metals are directly machined or joined with lasers. Scaling of laser technology has spurred the development of directed energy systems that are capable of delivering high energy density on distant targets. Recent developments have resulted in conversion efficiencies of electrical to photon energy of close to

*Email: [email protected] Page 1 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

50 % with powers in excess of 1 kW per (handheld) unit. Additionally, and critical for any phasedarray program, such devices can be phase locked. Laser design is rapidly changing and even more efficient devices with higher power density will be available in the near future. High power density allows the contemplation of directed energy systems for large-scale deployment. Inside the Earth’s atmosphere, directed energy systems are hindered by atmospheric fluctuations of the coherent beam. A directed energy system deployed above the atmosphere could project a beam through space unfettered by atmospheric interference and thus allows the design of systems that are essentially diffraction limited as the interplanetary medium (IPM) is extremely tenuous and does not affect the laser beam significantly. This chapter describes a feasible design for a future orbiting standoff directed energy system, which is called DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation (Lubin et al. 2013, 2014; Hughes et al. 2013). The system consists of an array of phase-locked modest power laser amplifiers. By controlling the relative phases of individual laser elements, the combined beam can be directed to a distant target. Lasers are powered by solar photovoltaics of essentially the same area as the laser array. By increasing the array size, it is possible to both reduce the spot size due to diffraction and increase the power. This dual effect allows the system to vaporize elements on the surface of asteroids at distances that are significant compared to the solar system. By raising the flux (W/m2) on the target asteroid to a sufficiently high level, direct evaporation of the asteroid occurs within the beam. This has two basic effects. First, direct evaporation of the asteroid begins, and given sufficient time, a threatening asteroid could be totally vaporized before hitting the Earth. Second, evaporation at the spot causes a back reaction on the asteroid from the vaporization plume which acts as a rocket, and thus the asteroid can be deflected to miss the Earth. This chapter explores the potential capabilities of the system for mitigating the threat of asteroid impact. Since DE-STAR is a phased array consisting of a very large number of elements, it can simultaneously be used for multiple purposes and is intrinsically a multitasking system. Figure 1 depicts an orbiting DE-STAR system simultaneously engaged in both evaporating and deflecting a large asteroid as well as powering and propelling a spacecraft. As this is a modular system, each DE-STAR is classified by the log of its linear size; thus, a DE-STAR 1 is 10 m, DE-STAR 2 is 100 m, etc. A DE-STAR 4 system will produce a reaction thrust comparable to the Shuttle Solid Rocket Booster (SRB) on the asteroid due to mass ejection and thus allow for orbital diversion of even larger asteroids, beyond several km in diameter, thus allowing for protection from every known asteroid threat. Smaller systems are also extremely useful. For example, a DE-STAR 2 (100 m size array) would be capable of diverting volatile-laden objects 100 m in diameter by initiating engagement at ~0.01–0.5 AU (AU ¼ astronomical unit ¼ mean distance from Earth to Sun ~1.5  1011 m). Smaller objects could be diverted on shorter notice. The phased-array configuration is capable of creating multiple beams, so a single DE-STAR of sufficient size could engage several threats simultaneously, such as a Shoemaker-Levy 9 scenario on Earth. An orbiting DE-STAR would also be capable a wide variety of other functions. Narrow bandwidth and precision beam control would aid narrow search and ephemeris refinement of objects identified with wide-field surveys. Propulsion of kinetic or nuclear tipped asteroid interceptors or other interplanetary spacecraft is possible using the “photon rail gun” mode from direct photon pressure on a spacecraft, propelling a 100 kg craft to 1 AU in 3 days and a 10,000 kg craft to 1 AU in 30 days. A DE-STAR could also provide power to ion propulsion systems, providing both a means of acceleration on the outbound leg and deceleration for orbit. Ideally two systems would provide the ability to “ping pong” spacecraft if this were needed, though this is vastly more challenging. Vaporization and deorbiting of debris in the Earth’s orbit could be accomplished with a DE-STAR 1 or 2 system. DE-STAR 3 and 4 arrays may allow standoff interrogation of asteroid composition by observing absorption lines in the blackbody spectrum of a vaporizing surface spot. There are a number of other Page 2 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 1 (a) Concept diagram of an orbiting DE-STAR engaged in multiple tasks including asteroid diversion, composition analysis, and long-range spacecraft power and propulsion. The system consists of an array of phase-locked lasers. By controlling the relative phases of individual laser elements, the combined beam can be directed to a distant target. Lasers are powered by a solar panel of effectively the same area as the laser array. A DE-STAR of sufficient size would be capable of vaporizing elements on the surface of asteroids. Given sufficient time, a threatening asteroid could be vaporized, deflected, or disintegrated prior to impacting Earth. The ability to direct energy onto a distant target renders DE-STAR capable of many functions. Asteroid interrogation may be possible by viewing absorption lines as the heated spot is viewed through the ejected vapor plume. Photon pressure can be used to accelerate (and decelerate) interplanetary spacecraft, among many other possibilities. (b) Visualization with relevant physical phenomenon included at a flux of about 10 MW/m2. For comparison, laboratory test setup is shown below in Fig. 24 where the bright high-temperature spot is also visible with about the same flux. The plume density is exaggerated to show ejecta. Asteroid diameter is about that of Apophis (325 m) relative to the laser beam diameter (30 m). Target is at 1 AU

applications as well, including downlink power via mm, microwave, or laser – the so-called Space Power System or SPS mode. The system is a standoff planetary defense system that is always ready when needed, and no dedicated mission is needed for each threat, as is the case with other proposed mitigation methods. The multipurpose aspect of the system allows it to be useful with very high “duty cycle.” The DE-STAR system is inherently modular and scalable, thus allowing a means to build and test smaller units in the lab, on the ground, and in suborbital test flights on balloons. Each module is modest in size and power and identical allowing for mass production. This is key to cost reduction. Each element uses only modest laser power, and thus the areal power density is low (0.2 kW/kg with near 40 % efficiency for the laser amplifier. Efficiency goals are comparable to current LEDs that are already about 50 % efficient. Coincidentally, on the space PV side, the power density is nearly identical at 0.1 kW/kg (ATK UltraFlex) with modest term possibilities for increasing this to 1 kW/kg. Recent work on Inverted Metamorphic Multijunction (IMM) cells promises >0.5 kW/kg. Schematic block diagram for a phased-array laser system based on individual kW-class fiber amplifiers is shown in Fig. 2. Long coherence length is critical and the existing fiber-based laser amplifiers are already good enough (depending on the mode in which they are operated), though new advances are becoming available to allow the SBS (stimulated Brillouin scattering) limit to be extended with even longer coherence lengths. With the current technology a DE-STAR 2 program could be started leading to launch and possibly a DE-STAR 3. A conservative and logical approach is possible, rapidly building smaller and much lower cost units (DE-STAR 0 and 1), testing on the ground, and then, as technology catches up and technological and system problems arise and are solved move to larger systems, eventually leading to orbital testing and scaling up to the full defensive goal. The system is not binary in that small systems have immediate applications (e.g., DE-STAR 1 space debris) as larger systems are being developed for comet and small asteroid protection (DE-STAR 2) leading eventually to a DE-STAR 3 or 4. As a goal, studies have been performed to assess the feasibility of a system possessing the capability to evaporate, prior to impact, asteroids in the size range 150 m to 1 km, and with typical orbital closing speeds. These stated capabilities drive system requirements into the multi-km-class array size for both the diffraction limit of the optics and the power required. As a specific example, one objective might be seeking to evaporate an Apophis-class asteroid (325 m diameter) with a worst-case assumption of complete chemical binding and less than 1 year to evaporate the entire boloid, with a desired interdiction starting at 1 AU. A 10 km DE-STAR system would be capable of meeting the stated goal as shown in the calculations presented below. It is also fortuitous that the same size system required to form a small spot on the distant asteroid from the diffraction limit, assuming a wavelength near 1 mm, is also about the same size as needed to power the laser amplifiers

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

in order to raise the flux to the evaporation point from converting sunlight that falls on the DE-STAR into electricity. At the Earth’s orbit, the “solar constant” is about 1,400 W/m2 or 1.4 (140) GW of sunlight on a 1 (10) km-sized solar array. This is sufficient to power the entire system and no additional power is needed. This also forms a very large potential for an SPS system to send excess power to the Earth. By utilizing a filled array of solar-powered phase-locked lasers, there is a nearideal convergence of size required both to power the system and to produce the diffraction-limited beam needed to begin vaporization. Baseline calculations are developed using a 1.06 mm wavelength, to produce sufficient flux at 1 AU that will sustain evaporation, which requires greater than approximately 5 MW/m2 flux at target. As stated existing Yb laser fiber amplifiers at 1.06 mm wavelength have efficiencies near 40 %. Space solar PV has efficiency of about 35 % in one Sun (not concentrated) with near 50 % when concentrated. Modest efficiency improvements are assumed for both laser and PV to 70 % which is not unreasonable in the realistic time scale of a full DE-STAR 4 system. Overall conversion efficiency of sunlight to laser power of about 50 % is assumed, resulting in approximately 0.7 GW/km2 of laser power. For a 1 km system, laser power would be 0.7 GW, while a 10 km system would have laser power of 70 GW, which is more than sufficient for meeting the stated goal of surface vaporization at 1 AU of all known materials. One major advantage of a phased array is that multiple independent beams can be produced, so multiple targets or efforts can be simultaneously engaged. For reference, 70 GW is the equivalent of about 1.4 MT (megatons TNT – 1 MT ~ 4.2  1015 J) per day or about 500 MT per year of potentially deliverable energy, a significant portion of the total currently active US nuclear arsenal. Note that in the process there is also 100 GW of electrical energy produced or the equivalent of about 100 large utility nuclear reactors. This would allow a very large SPS if needed. For DE-STAR, launch mass is critical in the costing analysis, so while the required efficiency is already effectively available, the power mass density must increase significantly. Solar PV cells can be extremely thin and low areal mass through focusing with thin film mirrors on solar PV may allow the lowest densities. For example, if 10 mm thick PV could be produced (this is more of a mechanical issue as thinner films already exist on plastic), a 104 m PV array would have a mass of about 3  106 kg. The current issue for many space solar cells is the charged particle degradation which is currently met with a “cover glass” on each size of about 100 mm. If laser power density of 10 kW/kg could be reached (50 higher than current), then 70 GW of fiber lasers would be 7  106 kg. This mass does not represent the entire DE-STAR system, but the scale is not outrageous. 10 kW/kg for laser mass density over 20 years is a goal, but even the existing 0.2 kW/kg density allows up to nearly a DE-STAR 3 using existing launcher capability. For reference, the International Space Station (ISS) mass is about 0.5  106 kg with much more than this being lifted into orbit as much of it was also returned in Shuttle missions. Conservatively, it is already possible to launch few  106 kg class space mission, an example being the ISS. Either heavy lift chemical launchers would be needed to loft DE-STAR 4 modules or a bootstrap ground-based DE-STAR-driven hybrid booster would be required. The modules are being designed around the existing heavy lift fairing size allowing for a 3–4 m diameter class module. The modules can be quite thin and stacked during launch and assembled in orbit. Since the system is a phased array, the structure does not need the structural integrity of a conventional mirror but rather must be stiff enough to have vibration modes that are below the metrology servo loop bandwidth as phase control is not handled by keeping the structure stiff but rather by measuring the relative position of each element adjusting the phase shifter in each amplifier to keep the beam on the target. While the baseline design is run in a continuous fashion (CW mode), it is also possible to run the system pulsed if needed, though short pulses are more problematic to phase properly. Extensive simulations and some laboratory testing indicate the debris field caused by the mass ejection should Page 6 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

not significantly interfere with the incoming laser as the ejecta density is quite low (maximum near the surface is estimated to be 102 kg/m3 and rapidly falling off due to the near isotropic ejecta emission into the space vacuum). Typical molecular ejecta speeds are 1–2 km/s. A reality check is to watch laboratory tests in one atmosphere at up to 40 MW/m2 or to view a video of a laser milling machine. The system is much like a laser-heated target in a semiconductor fabrication system. Thermal Dissipation: The average thermal load (to dissipate) of the system (independent of size) is about 500 W/m2 which is approximately that of a person (or the Earth). It is equivalent to a 300 K blackbody. The average thermal load is extremely low. The average laser power is also quite low, being about 700 W/m2 which is less than the solar “constant” on the surface of the Earth which is about 1,000 W/m2. You could literally walk in front of the system when operational and not be harmed (laser glasses are recommended however). Optical Design: The optical design of a phased array is different than that of a classic optical telescope in that the phasing to achieve constructive interference (which is what allows the image to form) is not done with mechanical alignment as it is in a mirror or lens (where every part of the mirror is essentially a part of the overall “phased array”), but rather the phasing is done by adjusting the phase at each sub-element to achieve constructive interference at the target. The design is an extremely narrow field of view system, and thus many of the constraints of a classical optical system do not apply. The array can be any shape, for example. The system is also extremely narrow bandwidth so thin film holographic grating diffractive “lenses” become viable. For simplicity the design will be roughly planar with each sub-element being either a small reflector or possibly a thin film holographic lens. The latter has been tried in some narrowband receiving mode systems, and extremely low areal densities have been achieved. This is an area where further work is needed to decide on the optimum approach. The design is a large number of identical low-power (700 W/m2) modules that lend themselves to mass production. Ultralow-mass holographic thin film large area “lenses” are particularly attractive, but SiC- or CFRP-replicated reflective optics may be suitable with refinement to lower the mass. In the current baseline, each element has a single fiber amplifier that feeds an optical element. A single 1 kW amplifier can feed a 1.5 m2 optic (mirror or lens). Coarse pointing could be accomplished using fiber tip position actuators behind the lens or mirror as appropriate. A fallback option would be to gimbal each element, though this is more complex. Fine pointing is done with electronic phase adjusters at each amplifier input. The phase is also compared at the output and between elements. The metrology of the entire structure becomes a key part of the servo system. There have been a number of orbital programs looking at extremely highprecision laser metrology over long baselines. The most extreme is the LISA gravitational wave detector that sets a metric of 20 pm resolution over 5  109 m baseline. This is vastly better than required for DE-STAR. Metrology of about 0.1 mm (l/10) is required over 10 km for the full DE-STAR 4. Similarly the AMD-MOST program has achieved 1 nm resolution over roughly 10 m baselines (limited by the vacuum chamber for testing). At longer wavelengths the Event Horizon Telescope has phased locked 1.3 mm wavelength telescopes across the globe (107 m baseline) and achieved 0.1 nrad beam formation or the same as the current goal. The RadioAstron, a Russian and Earth long baseline interferometer, has produced fringes corresponding to 0.04 nrad. Note that since the optical F# is very large (~1.5  107 for a DE-STAR – 1 AU target), the asteroid is far away and hence the beam is nearly parallel at the target with a large “depth of focus” ~F#2 l ~ 2  108 m. The F# (F number) is the ratio of L/d, where L is the target distance and d is the DE-STAR size. There are a number of challenges to the optical design and the targeting servo system that need to be explored. Asteroids are dynamic, and while motion in angle may be small relative to a viewing angle from Earth, it can still be significant. Typical asteroid moves at 10–30 km/s, and with a 30 m beam, this is 300–1,000 beam diameters per second in the worst case. The system will be moving in Page 7 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014 184312

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Fig. 3 Coherent beam combining of a 2  2 laser array in Zemax. The four individual elements are shown on the left, and then when combined, the central peak is intensified and the sidelobes are suppressed. With additional elements, the peak will grow and the sidelobes will decrease. The baseline uses a filled close-packed array to minimize sidelobes and to maximize the central peak

its orbit, the Earth is moving, etc. There are a lot of issues to be worked out. The Hubble Space Telescope has about a 35 nrad pointing stability over 24 h as an example. Better than 0.1 nrad pointing is ideally required (the current experimental beam is 0.2 nrad full-width, half max (FWHM) for a DE-STAR 4), though, as shown below in the simulations, there is some latitude in this. Optical designs have been started; Fig. 3 shows a simple 2  2 array as an example using coherent beam combining in Zemax. A far-field beam pattern simulation, based on beam propagation equations, is shown in Fig. 4.

Laser Versus Mirror

In general, the DE-STAR system can be described as “laser machining” on a solar system scale. While laser machining is common in everyday life, from processing of clothes to cars, it is not common to think about systems that can machine on solar system scales. One of the first questions asked is, “why not use a mirror to form an intense spot rather than convert from sunlight to electricity to laser light?” The answer is simple. If the Sun were a point source, it would be possible to do precise beam formation and targeting, but the Sun is not a point source and the conservation of phase space (Liouville’s theorem) prevents beam formation without the use of a mirror about the size of the distance to the target. For an object at 1 AU, targeting with a mirror would require a reflector about the size of the solar system! Stated more precisely, the flux for a spot on the target Fsp when using a mirror of a given F# ¼ focal length/diameter focusing a source whose surface flux is Fs will give F sp ¼

ϵF s 4F 2#


ϵ 1=4 ϵ 1=2 ! T ¼ F# T s F sp ¼ sT 4sp ¼ T 4s F 2 sp # 4 4 where Tsp is the spot temperature assuming only radiation equilibrium (no mass ejection), Ts is the source surface temperature, and ϵ is the efficiency of coupling the photons to the target. An assumption of ϵ ¼ 1 is used for simplicity. The Sun is roughly equivalent to a 5,700 K blackbody with a surface flux of about 60 MW/m2. To achieve good efficiency for rocky materials typical of asteroids, flux at the target needs to be greater than about 10 MW/m2 which requires a mirror with an F# ~ 1 or the diameter about the same as the target distance as mentioned above. This is also one reason why bringing mirrors to an asteroid requires that mirrors also have an F# ~1 so that the mirror

Page 8 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 4 Simulation of 1,000  1,000 array of 1 m sub-apertures. (a) 1D cut and (b) the full 2D pattern. Simulation includes the effects of uncorrelated phase noise equal to a WFE of l/10 per element. For WFE phase noise less than about l/6, there is little effect on the final beam pattern with the primary effect being main beam power being spread into the sidelobes (Hughes et al. 2014)

must be very close to the asteroid which can be very problematic for a variety of technical reasons. Comets require much lower temperature and flux to evaporate, but since the target flux drops inversely with F# 2 and the spot temperature drops inversely as F#1/2, even an ice asteroid would require an F# < ~300, so standoff planetary defense against comets with mirrors is not feasible; mirrors brought to comets and asteroids with large percentages of volatile compounds are feasible if it is possible to bring the mirror to the target Laser Arrays: It is possible to analyze the case of a simple square array as an extension of a series of rectangular apertures. The circular case is very similar. More complex systems with realistic phase noise and pointing errors are analyzed in Lubin et al. (2014). For the simple case of a square array of

Page 9 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

side d and target distance L assuming only cooling by radiation transfer (the case of mass ejection is considered below), the following definitions and relations hold: d ¼ laser array size (m) PE ¼ electrical power (W) ϵ L ¼ laser efficiency (wall plug) PL ¼ laser power (W) PL ¼ ϵ L PE ðWÞ l ¼ laser wavelength (m) L ¼ target distance (m) D ¼ spot size (m) D ¼ 2Ll/d ¼ 2F#l ¼ spot diameter where F # ¼ Ld ϵ B ¼ beam power fraction in spot ¼ beam efficiency F ¼ flux at target (W/m2) F¼

ϵ B PL D2

eT ¼ Target Absorption coeficient ¼ 1  a at wavelength l of laser a ¼ albedo ðreflectionÞ which includes surface and melt=vapor reflection Solving for the target parameters gives the following relations (note the scaling laws): ϵ B PL ϵ B ϵ L PE ϵ B ϵ L PE d 2 ϵ B PL d 2 F¼ 2 ¼ ¼ ¼ D 4L2 l2 4L2 l2 ð2Ll=d Þ2 / PL , d 2 , L2 , l2 ϵ T F ¼ sT 4 ¼ target adsorbed flux from laser ¼ radiated flux Here we assume only radiation balance and no mass ejection The real case of mass ejection dominance is discussed below  1=4 T ¼ ϵ TsF  1=4    ϵ T ϵ B ϵ L PE d 2 ϵ T ϵ B PL 1=4 d 1=2 T¼ ¼ Ll 4s 4L2 l2 s / PL , d 1=2 , L1=2 , l1=2 1=4

Page 10 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

rffiffiffiffiffiffiffiffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ϵ T ϵ B ϵ L PE d ϵ T ϵ B PL d ¼ L¼ 2 4s 4s T 2 l T l / PL , d, T 2 , l1 1=2

4L2 l2 aT 4 PL ¼ ϵT ϵBd2 / L2 , l2 , T 4 , d 2 Solving for T and D for the general case of an arbitrary-sized array, power, and target distance gives T ðKÞ  8, 160ðϵ T ϵ B Þ1=4 PL ðkWÞd 1=2 ðmÞL1=2 ðkmÞl1=2 ðmÞ L where F # ¼ d DðmmÞ ¼ 2 LðkmÞlðmÞd 1 ðmÞ DðmÞ ¼ 2F # lðmÞ   1=2 LðkmÞ ¼ 66:4 ðϵ T ϵ B Þ1=2 PL ðkWÞd ðmÞT 2 103 K l1 ðmÞ  3  2 2 4 L ð km Þl ð m ÞT 10 K PL ðkWÞ ¼ 2:27  104 2 ϵ T ϵ B d ðmÞ  2 3 2 4 L ð km Þl ð m ÞT 10 K PL ðkWÞ ¼ 2:27  104 ϵ T ϵ B d 2 ðmÞ 1=4

For L ¼ 1AU : 3  105 DðmÞ ¼ lðmÞ d ðmÞ DE-STAR with PV Array Equal to Laser Array Size: For simplicity in designing the baseline system, the assumption is that the PV array would be the same size as the laser array. In practice this is not necessary, but it yields about the right amount of power needed to begin interdiction at 1 AU for a class 4 system. In the case of the PV array being the same size as the laser array, the previous equations can be simplified. It is possible to solve for the flux on target and equivalent radiation transfer temperature at the spot – again assuming only radiation equilibrium and no mass ejection: PL Kd 2 eP eL eB d 2 Kd 4 eP eL eB ¼ F¼ 2¼ D 4L2 l2 4L2 l2 ep ¼ PV conversion efficiency eT ¼ target absorption ¼ 1  a where a ¼ albedo eB ¼ the beam eff (frac in spot) eL ¼ the laser conversion efficiency (“wall plug” efficiency) K ¼ “solar constant” in space near Earth  1,361 W/m2 at solar minimum and about 1,362 W/m2 at solar maximum.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 5 DE-STAR laser power, diffraction-limited beam divergence, and spot size at target engagement of 1 AU

Radiated flux is set equal to absorbed laser flux: F ¼ sT 4 ¼ eT F  1=4  4 1=4   F Kd eP eL eB d KeP eL eB 1=4 ¼ ¼ pffiffiffiffiffiffiffiffi T¼ s s 4L2 l2 s 2Ll pffiffiffiffiffiffiffiffi d ¼ T 2LlðkeP eL eB =sÞ1=4 1 d2  L ¼ 2 Kep eL eB eT s 2 2T l As an example, a class 4 system has F# ¼ Ld  1:5  107 for a target at L ¼ 1 AU with d ¼ 104m and achieves a spot temperature, if radiation limited, in excess of 6,000 K and delivers more than 1 MT/day equivalent. Figure 5 summarizes the above calculations for various values of array size and target distance. Coherence Length Requirements: For a phased array to work properly, the light must be coherent over a time and thus length scale sufficient for all elements to be able to interfere. The coherence length required can be calculated by determining the length difference between the various elements with the most extreme case being the conservative limit. For a planar array of size d and a target of distance L away, the path length difference between the central beam and the outermost beam is d ~ d2/8 L ¼ d/8 F# for the case of a target that is normal to the plane of the phased array. Moving off normal, the path length difference is d ¼ 1/2 d sin(y), where y is the angle of the target off the normal. The worst case is at right angles (y ¼ p/2) where d ¼ d/2. If there are controllable optical delay lines, then these issues are drastically mitigated, but it is preferable to have long coherence length, so delay lines are needed. For a target at L ¼ 1 AU ~ 1.5 Page 12 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

 1011 m and a DE-STAR 4 with d ¼ 104 m that F# is ~ 1.5  107 - > d ~ 80 mm corresponding to a coherence time tc ¼ d/c ~ 0.3 ps. For the worst case of d ¼ d/2, the equivalent tc ¼ d/c ~ 17 ms. The laser coherence time must be greater than these times. The “coherence bandwidth” of the current Yb fiber amplifiers is intrinsically about 5–10 kHz (with corresponding coherence times tc ~ 100 ms or comfortably longer than the stated worst case. For amplifiers run at their highest power level, this “coherence bandwidth” is generally artificially broadened to about 10 GHz (100 ps) in order to overcome what is known as the stimulated Brillouin scattering (SBS) limit that limits the amplification power. This is well above the normal incidence case but allows extremely little pointing margin. For example, even a 1 pointing difference will give a path length difference of d ¼1/2 d sin (y) ~ 90 m with a corresponding coherence time tc ¼ d/c ~ 300 ns. When the amplifier is run at a few hundred watts versus kilowatts, the “coherence bandwidth” is about 5–10 kHz or less as above. The solution to this is to run at normal incidence (not really a good option), add path delay lines (also not a good option in general), or run the amplifiers well outside the SBS limit where the coherence time is longer. The latter is the preferred option. There is technology that has been developed that appears to allow the Yb amplifiers to run at both relatively high power and with long coherence time. This is one of the development items on the roadmap. Since volume (as opposed to mass) is not as much of an issue, there may be a trade space that can be exploited to allow for better performance. Note that the deviation of the planar array from a sphere with radius R ¼ L is x ¼ d2/8R ¼ d2/8 L ~ 80 mm and deviation of the array plane from a classic optic with focal length f ¼ L is x ¼ d2/16f ¼ d2/16 L ~ 40 mm. The array is indeed quite planar! Space Qualification Issues: The DE-STAR system is a complex system of both power conversion (solar to electrical to laser) and metrology, targeting among many others. Solar PV is a mature technology, and the space qualification and “rad hardening” issues are understood. The situation for fiber amplifiers needs to be addressed as a part of the roadmap. Much of this can be done on the ground in accelerator beam lines, and some early long-term space exposure will help with determining what issues, if any, are critical to address in this area. The long-term exposure to radiation is not well understood for fiber amplifiers and needs to be addressed. Rad hardening of thin film holographic lenses also needs to be addressed, as does lowering the areal mass of space PV which is often dominated by the glass used to reduce charged particle (mostly electron) damage.

System Requirements to Evaporate Asteroids It is possible to calculate the energy required to melt and vaporize the various materials that are common in S-type (Si-rich), C-type (carbon-rich), and M-type (metal-rich) asteroids. Comets are much easier to vaporize in that they do not require a high temperature to begin significant mass ejection. The gravitational binding energy of a molecule to a typical asteroid is very small and is negligible compared to the chemical binding energy. The chemical bonding energy that requires heating of the spot to high temperature can be expressed through the heat of vaporization. The heat of fusion (melting) is a small fraction of the heat of vaporization. Models have been developed to explore the thermal interaction between the laser and asteroid in three ways. The first is a simple analysis based on power only with a flux equivalent to about a 6,000 K blackbody. The second method uses detailed calculations of the vapor pressure versus temperature for every element and many of the estimated compounds that are thought to make up asteroids. This is a quasi 2D analysis in that it includes radiation emission and mass ejection but ignores thermal conduction. The third method uses all the calculations from the second method but uses a full 3D finite element analysis (FEA) of spherical (any shape is possible) asteroids with various thermal conductivities. All three methods give essentially the same answers, which the calculations confirm with increasingly sophisticated simulations. The final method is a laboratory test system that uses a 19-element laser Page 13 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 6 (a) Melting and vaporization energy per unit volume for S-type (Si-rich) asteroids. (b) Vapor pressure versus T for virtually all elements on the periodic table (93 are modeled). (c) Vapor pressure versus target flux for the same 93 elements. The upper outlier is Mercury

array to produce a spot flux similar to that of the full DE-STAR 4 at 1 AU, namely, about 40 MW/m2, and targets “rock” samples with similar compositions to asteroids. This testing has begun and will continue over the next year to cross-check the simulations for evaporation rates, mass ejection densities, and plume thrusts among other parameters. As expected, when the flux exceeds about 2 MW/m2, most materials begin to significantly vaporize. The energy required to melt an asteroid is given by the heat of fusion and required increase in temperature to bring it to the melting point from (assumed) initial low-temperature starting point. In practice this is small compared to the heat of fusion and heat of vaporization. The typical energy per m3 is of order 1010 J to vaporize most materials. This can be seen in Figs. 6 and 7, which show models of the vapor pressure in pascals (N/m2) versus T and versus target flux for 93 elements. In addition models are shown for four common asteroid molecular compounds. Even vapor pressures of 103 Pa (0.01 atmospheres) correspond to enormous reaction forces on the asteroid and large mass ejection rates. While an asteroid of solid tungsten is not expected, it would still be possible to mitigate it. Contrary to the small iron-rich meteorites that are found on the ground, a more typical asteroid looks more like the lunar surface and has quite low thermal conductivity and is thought to be a “rubble” pile in many cases, particularly for larger (greater than a few hundred meters) asteroids. The worst case of complete chemical binding (i.e., solid) is assumed. In many cases asteroids will have significant low-temperature volatile materials that may make mitigation much easier. Asteroids are also molecular rather than atomic in species in general, but the conclusion is the same; namely, at temperatures around 2,000–3,000 K or target fluxes of 106–108 W/m2, all known materials will undergo vigorous evaporation. What is critical is to increase the spot flux to the point where

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 7 (a) Vapor pressure versus T for four common high-temperature asteroid compounds. (b) Vapor pressure versus target flux for the same found compounds. Note that at temperatures of 2,000–3,000 K or fluxes of about 10 MW/m2, the vapor pressure and hence mass ejection rates are very high

Fig. 8 (a) Spot temperature versus DE-STAR array size for various target distances from 103 to 10 AU, including average solar illumination on asteroid (sets lower limit on asteroid or comet temperature). (b) Distance to target versus array size for various spot temperatures from 300 to 6,000 K. At 300 K, icy comets become targets, while at 6,000 K (hotter than Sun), no known material survives

evaporation becomes large. It is not sufficient to simply apply a large amount of total power; there has to be a large flux to initiate evaporation. Once the material properties of the targets are understood (Binzel et al. 2009), it is possible to design a system that is capable of evaporating them and in this process divert them due to the large plume thrust generated. Figure 8 illustrates at what distances it is possible to begin to engage targets of differing compositions. For example, a comet will begin evaporation at much lower flux than a rocky asteroid and thus engage them at much lower total power levels and hence smaller systems or at much larger distances. These simulations assume the Sun is also illuminating the targets which accounts for the lower-temperature limit. This is approximate as it depends on the target reflectivity and orbit. The Sun does not have a significant effect except in the case of comets.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Escape Speed and Temperature It is possible to calculate the gravitational binding energy and thus the escape speed and equivalent escape temperature as follows. The equivalent temperature for escape is 1 2 3 mv ¼ GMm=R ¼ kT 2 2 vescape ¼ ð2GM =RÞ1=2 T esc ¼ 2GMm 3kR , where m is the molecular/atomic mass (kg), M is the asteroid mass (kg), R is the asteroid radius. Assume constant density r (kg/m3): 4 M ¼ pR3 r 3  1=2

vesc ¼ ð2GM =RÞ

vesc

¼

4 2G pR3 r=R 3

1=2

rffiffiffiffiffiffiffiffiffiffiffiffi 8p Gr ðm=sÞ ¼R 3

pffiffiffi vesc ¼ 2:36  105 rR T esc ¼

8p GrmR2 ¼ 1:35  103 rmR2 9k

Detailed Thermal Modeling Thermal modeling is critical. Three approaches are presented here, and all yield consistent results. The basic equations are derived from energy conservation where we now also include the critical mass ejection term. Power in (laser) ¼ power out (radiation + mass ejection) + dU dt , where U ¼ asteroid internal energy dU dU and dt is effectively from conduction. In the steady state dt ¼ 0, Ð dU Pin ¼ Pout þ dt with U ¼ rcvdv, where cv ¼ specific heat (J/kg-K): F L ¼ Laser Flux-in F rad ¼ Radiation Flux-out F ejecta ¼ Ejecta Flux -out F cond ¼ Thermal Conduction-in

W=m2 W=m2 W=m2 W=m2

P þ in ¼ Prad þ PEjecta þ Pcond  ðF L  F rad  F Ejecta  F cond  n^ dA ¼ 0 ð   ¼ ∇  F L  F rad  F Ejecta  F cond dv ¼ 0

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Locally, F L ¼ F rad þ F Ejecta þ F cond F rad ¼ sT 4 n^ F Ejecta ¼ Ge Hv n^ ¼ M 1=2 ð2pRT Þ1=2 ae 10½AB=ðT þC Þ Hv n^   F rad  ¼ sT 4   F cond  ¼ K∇T   F Ejecta  ¼ Ge Hv where kT is the thermal conductivity (which can be position and temperature dependent) and Ge is the mass ejection flux (kg/m2-s) and Heff is the effective heat of vaporization (J/kg) (here the heat of ð Tv fusion and integrated specific heat are also included, H eff ¼ H v þ H f þ C v dT. In some cases the Ta

material will directly sublimate into the vacuum. Hf is typically a small fraction of Hv so for practical purposes it is a good approximation to use Heff  Hv : Ge ¼

M ae ðPv  Ph Þ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ M 1=2 ð2pRT Þ1=2 ae ðPv  Ph Þ 2pMRT

where M ¼ molar mass (kg/mol) Pv ¼ vapor pressure (Pa) Ph ¼ ambient vapor pressure (Pa) ¼ 0 in vacuum ae ¼ coef. of evaporation 0 a 1 Models are given for the vapor pressure for each element and compound using a semi-analytic form known as Antoine coefficients where the vapor pressure and temperature T are related by: Log Pv ¼ AB/(T + C), where A, B, and C are the Antoine coefficients and are unique to each element and compound. These form the basis for Figs. 6 and 7. Hence, Pv ¼ 10½AB=ðT þC Þ   F Ejecta  ¼ M 1=2 ð2pRT Þ1=2 ae 10½AB=ðTþC Þ Hv A Gaussian profile is assumed for the laser as an approximation. For a Gaussian laser of power PT,   F L  ¼ PT er3 =2r2 2ps2 where r ¼ distance from spot center. In the approximation where the spot is small compared to the asteroid, the equation becomes

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

FL ¼

PT r3 =2r2 n^ e 2ps2

In the dynamic case, it is possible to solve for transient heat flow by solving the following heat flow equation: d ∇  ðK∇T Þ þ ðrcv T Þ ¼ 0 dT dΤ ¼0 K∇2 T þ rcv dt In the last equation, it is assumed that kT (the thermal conductivity) is independent of position and r, cv are time independent. In the full 3D time-dependent solution, all of the above conditions are invoked, and the equations are solved simultaneously using a 3D numeric solver (COMSOL in this case). In the 2D steady-state solutions, the thermal conductivity is assumed to be small (this is shown in 3D simulations to be a valid assumption as well as from first-principle calculations), and a combination of radiation and mass ejection (phase change) is used:       F L  ¼ F rad  þ F Ejecta  ¼ F T F T ¼ sT 4 þ M 1=2 ð2pRT Þ1=2 10½AB=ðT þC Þ Hv Inversion is not analytically possible, so numerical inversion is used to get T(FT) which gives Pv(FT), Ge (FT), etc. In this inversion, a function fit is found for each relevant compound (to 10th order typically): N X an ðlog F T Þn . T¼ n¼1

A Gaussian approximation to the laser profile is used (this is not critical) to get T(r), Pv(r), Ge(r), where r is the distance from the center of the spot. Since radiation goes as the fourth power of T, while the mass ejection from evaporation is exponentially in T, at low flux levels, the outward flow is completely dominated by radiation (you heat the asteroid slightly and it radiates). As the spot flux level increases (spot size shrinks or power increases or both), evaporation (mass ejection) becomes increasingly dominant, and eventually at about T ~ 2,000–3,000 K or fluxes of 106–107 W/m2, mass ejection by evaporation becomes the dominant outward power flow and (just as water boiling on a stove) the temperature  stabilizes and increasing flux only increases the rate of mass ejection with small increases in temperature. To help illustrate this, the relationship between flux and temperature in the purely radiation-dominated mode is depicted in Fig. 9. Results from the three methods are briefly summarized below: • 1D – energetics alone. Use heat of vaporization and set spot flux to T ~ 6,000 K. No radiation or conduction included. • 2D – model elements and compound vapor pressure versus T. Include radiation emission. Ignore thermal conduction. • 3D – full 3D FEA. Include phase change, vapor pressure, mass ejection, radiation, and thermal conduction. Page 18 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 9 Relationship between flux and temperature in spot in the radiation-dominated case. In reality the temperature rarely gets above 3,000 K as the power is diverted from radiation to mass ejection Table 1 List of thermophysical properties of common high-temperature asteroid compounds Material SiO2 Al2O3 MgO ZnS

Hf (kJ/mol) 9.0 14.2 77.4 38.0

Hv (kJ/mol) 143 293 331 320

M (g/mol) 60.1 102.0 40.3 97.5

Hv (106 J/kg) 2.38 2.87 8.21 2.46

Cv (J/kg-K) 730 930 1,030 472

Veff (km/s) 1.54 1.69 2.87 1.57

Teff (104 K) 0.573 1.15 1.32 1.28

Here Hf is the heat of fusion and Hv is the heat of vaporization. Effective ejection speed Veff ¼ (Hv(J/kg))1/2 and Teff ¼ (M*Hv)/3R where R ¼ k*NA ~ 8.31

1D – Energetics Alone: The heat of vaporization of a compound is the energy (per mole or per kg) to remove it from the bulk. Removal energy is related to an effective speed and an effective temperature which are related to but somewhat different than the physical speed of ejection and the physical temperature of vaporization. To be more precise, the term evaporation refers to molecules or atoms escaping from the material (e.g., water evaporating), while boiling is the point at which the vapor pressure equals or exceeds the ambient pressure. At any nonzero temperature, there is a probability of escape from the surface, so evaporation happens at all temperatures and hence vapor pressure is a quantitative measure of the rate of evaporation. The heat of vaporization is also temperature and pressure dependent to some extent. Table 1 gives thermal properties for various materials in asteroids. Figure 9 shows a plot of vapor pressure versus T and flux. These materials have relatively high effective temperatures reflecting the fact that there is a probability distribution of energies and that the increase in vapor pressure versus T in Fig. 9 shows that the thermal probability distribution has a “tail” allowing for escape from the surface at lower temperatures that one would naively conclude from a mean analysis only. A similar analogy is the Saha equation that relates the ionization fraction versus temperature where a mean analysis would conclude that extremely high temperatures are required to ionize an atom, but in fact significant ionization occurs at much lower temperatures due to the probability distribution tails. If power PT from the laser impinges on the

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

asteroid in a small enough spot to heat to above the radiation-dominated point (typically 2,000–3,000 K for “rocky” asteroids (vs. 300–500 K for comets)), it is possible to compute the evaporation flux (mass ejection rate) as: Tv ð

Ge ¼ PT =H eff where H eff ¼ H v þ H f þ

Cv dT Ta

Heff is the energy required (for 1 kg) to raise the temperature to the vaporization point and to vaporize it and includes the heat of vaporization, heat of fusion and energy required to raise the temperature to the vaporization point from the ambient asteroid temperature. Tv is the temperature at which vaporization is occurring and Ta is the initial asteroid temperature. In general Cv (specific heat) is temperature dependent. For most materials Hf  Hv and the integrated specific heat T Ðv Cv dT is a small correction (ie 150 m) are largely gravitational-bound “rubble piles” and for these the maximum rotation is independent of diameter and only depends on density r with an angular speed o and rotation period t given by

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Table 2 Common material thermal properties for comparison to the asteroid thermal properties in Fig. 12 Material Nickel Iron Granite Ice (solid) SiO2 (solid) Water (liq 0 C) Snow (firm) Soil (sandy) Pumice Styrofoam Air Moon (regolith)

K (W/m-K) 91 81 2.9 2.3 1.04 (200  C) 0.56 0.46 0.27 0.15 0.03 0.026 0.0029

r (kg/m3) 8,850 7,860 2,750 917 2,200 1,000 560 1,650 800 50 1.2 1,400

C (J/kg-K) 448 452 890 2,000 1,000 4,200 2,100 800 900 (varies significantly) 1,500 1,000 640

Г (J/m2-K-s1/2) 19,000 17,000 2,600 2,040 1,510 1,500 740 600 330 47 5.6 51

Fig. 13 Measured rotation period of 6,000 asteroids. Notice the very sharp cutoff at just above 2 h for larger diameter asteroids (Data from Minor Planet Center. Warner et al. (2009))

sffiffiffiffiffiffiffi rffiffiffiffiffiffiffiffiffiffiffiffi 4 2p 3p pGr ¼ ,t ¼ o¼ 3 t Gr t  1.19  104r(g/cc) 1/2s  3.3r 1/2h – this is independent of diameter. As an example, assuming a typical average density of 2 g/cc gives r ¼ 2 ! t ¼ 2.3 h. There is indeed a remarkably sharp cutoff in rotation periods very close to 2 h (about 10 rotations per day) for asteroids greater than diameters of approximately 150 m. Some smaller asteroids can rotate faster as they can have a tighter binding than purely gravitational (such as an iron meteorite), but these are

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

relatively rare and even the fastest ones can be dealt with since the mass ejection begins so quickly (type < 1 s) after the laser is turned on. As is seen in the transient thermal simulations below, the mass ejection and hence thrust begin within about 1 s for a DE-STAR 4 at 1 AU. It is largely a flux issue so that for the same flux at any distance, the mass ejection remains at this rate. This is assuming solid SiO2 which is extremely conservative. Loss is included to mimic the absorption qualities of asteroids which are very absorptive having typical reflection coefficients around 5 %. Thus a rotating asteroid with this rate (1 h) poses little problem. More interesting perhaps would be an attempt to spin up (or down) an asteroid depending on beam placement. 3D Results: Hundreds of 3D model simulations have been run, and a few salient results are apparent. Perhaps the most interesting bottom line is that starting with the simplest assumptions, namely, energetics only and conservation spot flux were borne out as being valid, but more sophisticated tools are available with which to analyze and optimize the system. 4D Simulations: For the case of dynamic targeting and rotating objects, time evolution has been added to the 3D solver (Johansson et al. 2014). Some of this is motivated by the need to understand the time evolution of the mass ejection under dynamic situations. This is partially shown in Fig. 14 (right) where the time evolution of the temperature at the center of the spot is shown. It is now

Fig. 14 All cases refer to SiO2 as the equivalent material. (a) Steady-state surface temperature distribution for a 100 m diameter asteroid at 1 AU with a DE-STAR 4 Gaussian beam derated to 50 GW. Spot diameter is approximately 30 m. Temperatures rise to the point of being mass ejection limited, which is about 2,600 K in the center of the spot. Solar illumination is modeled with an isotropic average of 350 W/m2. (b) Temperature distribution versus theta (angle from beam axis). High-frequency substructure is due to numerical meshing. (c) Transient time solution of temperature in the spot center (K) versus time (seconds) after the laser is turned on at t ¼ 0. Initial temperature is 200 K. Mass ejection begins within 1 s

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 15 Comparison of 2D and 3D models: temperature versus theta (angle from beam axis on sphere) for SiO2 with 50 GW total power and sigma ¼ 5 m Gaussian beam illumination. Results are nearly identical in the critical central region

possible to simulate full dynamics and apply this to the case of rotating asteroids. The same techniques can be applied to pointing jitter and “laser machining of the asteroid or other target.” Comparison of 2D and 3D Simulations: While the 3D simulations give time transient solutions and include full thermal conduction, they lack the numerical flexibility of the 2D solutions. Results of the temperature distributions for a Gaussian laser illumination are compared and found to be very close in their predictions. This builds confidence that it is possible to do both 2D and 3D simulations with high fidelity. The ultimate test will come when comparing model results with laboratory tests. Figure 15 compares the temperature distribution for a 3D model (blue) with a 2D model (black). They have nearly identical results in the critical center of the spot and then differ in the wings. As laboratory tests are refined, the results will feed back into the models.

Orbital Diversion via Plume Thrust In general, it is not necessary to evaporate the asteroid to avoid an impact scenario. It is sufficient to change its orbit enough to miss the Earth. The ability to stand off and divert using the plume thrust that DE-STAR generates is an extremely attractive approach. Consider the example of Apophis. It is approximately 325 m in diameter with a mass of 4  1010 kg and has an orbital speed of 30.7 km/s with a 30 h rotation. A direct hit would have a yield approaching 1 GT (gigaton TNT). This would be a bad day. The momentum is approximately p ¼ mv ~ 1.2  1015 N-sec. If a theoretical thrust to power ratio of 1 mN/W can be achieved, then the thrust with a DE-STAR 4 would be 7  107 N. If it is possible to activate DE-STAR for 1 month, then a change in momentum of Apophis of dp ~ 1.7  1014 N-s is possible. The effect on the orbit depends on the details of when and where the interaction begins, but it is possible to estimate the deflection angle to be dy ~ dv/v ¼ dp/p ~0.14 radians or a dv ~ 0.14v ~ 4.2 km/s. This is enormous by standards the deflection community speaks of. A simplistic distance deflection is given by dr (miss distance) ~L dy (L ¼ 1 AU 1.5  1011 m) ~ 2  1010 m ~ 3,000  Earth radii. This is 50 times the Earth-Moon distance. This is obviously extremely

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

conservative and less extreme scenarios are possible. In addition when running actual orbital trajectories as shown below the simple calculation shown above is often pessimistic and the actual orbital modification can be much larger for the same thrust since the asteroid is in a gravitational bound orbit relative to the Earth’s orbit. See section on “DE-STARLITE” for a detailed example of this. The amplification factor is typically a factor of three times the naïve deflection calculation depending on the details of the asteroids orbit. Keyhole amplifications due to the earth-moon orbit are also very large. Targeting and LIDAR Mode: One of the difficulties with asteroid mitigation in general is knowing where the targets are. Generally asteroids are found by looking for them in the visible bands using their reflected sunlight or in the thermal IR using their heat signature or with radar. It is possible to use a DE-STAR system for active illumination of targets to aid in both their detection and orbital refinement. This is done in much the same way that a radar system works except the laser beams are much smaller, providing much finer target determination and much greater range. The general technique is sometimes referred to as Light Detection and Ranging (LIDAR). The same phased-array optical system is used for the reception of the return light, as is used for the transmission of the laser. In this case, the system is run in a gated or long-term pulsed mode. The light travel time to 1 AU is about 8 min or a round trip light travel time of 16 min. The laser could be turned on to scan potential targets and then turned off just before the photons that are scattered off the target are expected to return and switch to a receive mode. This then forms a complete LIDAR system with the same optics used for transmit and receive. The receive system could also be phased to form a full phased-array receiver or could be run in a mode where each element acts as an independent receiver with the sum of all sub-elements co-added before detection. There are advantages to this mode in both simplicity of operation and in that a much larger field of view is received eliminating scanning the field for reception. The disadvantage is the increased background from a larger field of view per sub-element. The return signal is computed for a variety of mission scenarios, as well as the equivalent mapping times for small error boxes to full sky blind surveys. Illustrated in Fig. 16 are the background levels relevant for survey times at the target illumination (the same as the mitigation) wavelength of 1 mm. The relevant backgrounds are the cosmic infrared background (CIB) and the zodiacal backgrounds, which include both scattered sunlight and thermal emission. This technique not only allows for an “in situ” and “co-aligned” determination of the target position but also gives ranging from time of flight (or phase modulation) as well as speed from measured Doppler. Here a heterodyne technique is assumed for detection, which is now feasible with at the baseline wavelength. This is another relatively new development in photonic technology. Backgrounds for Remote Targeting: In order to determine the signal to noise of the return signature, it is necessary to understand the nontargeting signal-related sources of photons. This is generically referred to as the background. There are a number of such backgrounds that are important. Going outward from the detector to the target and beyond, there are: • Dark current and “readout noise” associated with the detector. • Thermally generated photons in the optical system. It is assumed the optical system is mostly running near 300 K. • Solar system dust that both scatters sunlight and emits from its thermal signature. Dust in the solar system is typically at a temperature of about 200 K. This is generically called “zodiacal” scattering and emission, respectively, or “zodiacal light” or zodi for short. • Photon statistics noise from the laser hitting the target. This is due to both the counting statistics nature of the light and its detection and to its bosonic nature (spin 1 statistics). Page 27 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 16 Active illumination (LIDAR mode) scenarios showing photon return rate versus asteroid diameter and system parameters as well as blind survey integration time to detect target versus sky fraction searched, asteroid size, and system parameters (Riley et al. 2015)

• • • •

Scattering of sunlight from the target itself as it is illuminated by the Sun. Thermal emission of the target. Distant background stars that are in the field of view. Sunlight scattered into the field of view for targets that are near to the Sun in the field of view. This is generally only important for targets that are very close to the Sun along the line of sight, though off-axis response of the optical system can be an issue as well. • The far-IR background of the universe is known as the cosmic infrared background or CIB. This is the total sum of all galaxies (both seen and unseen) in the field of view in the laser band that are NOT blocked by the target. This is relevant IF the target is smaller than the receive beam. It is not relevant to first order IF the target is larger than the receive beam (or spot at the target distance). • The cosmic background radiation or remnant radiation from the early universe. This turns out to be negligible for laser-directed energy systems.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 17 Diffuse CIB component flux versus wavelength

In all of these cases, the fact that the laser linewidth (bandwidth) is extremely narrow (from kHz to GHz depending on the system design) and the field of view is extremely narrow mitigates these effects which would otherwise be overwhelming for a broadband photometric band survey. Heterodyning is possible at 1 mm and will greatly aid in detection. Cosmic IR Background: The CIB was first detected by the Diffuse IR Background Explorer (DIRBE) instrument on the Cosmic Background Explorer (COBE) satellite launched in 1989. It is an extremely faint background now thought to be due to the sum of all galaxies in the universe from both the stellar (fusion) component at short wavelengths near 1 mm and from the reradiated dust component near 100 mm. On large angular scales (degrees), it is largely isotropic though at very small angular scales (arcsec), individual sources can be detected. The diffuse CIB component is shown in Fig. 17. Zodiacal Light: Like the CIB, the zodiacal light has two components and both involve dust in the solar system and the Sun. The sunlight both scatters off the interplanetary dust grains giving a “streetlight in fog” effect and heats the dust grains which then reradiate in the mid- to far IR. The scattered component can be seen with the unaided eye in dark extreme latitudes and is sometimes known as the “Gegenschein” and traces the ecliptic plane. The dust grains are in rough equilibrium through heating by the Sun and cooling through their own radiation. This “background” is NOT isotropic but is highly anisotropic depending on the position and orientation of the observer in the ecliptic. This was studied in detail by the DIRBE instrument on COBE. As seen in Fig. 18, based on some of the DIRBE measurements, the brightness of both the scattered and emitted components varies dramatically with the observed line of sight relative to the ecliptic plane. In the plot the angle relative to the ecliptic plane is given by the ecliptic latitude (Elat) where Elat ¼ 0 is looking in the plane and Elat ¼ 90 is looking perpendicular. The situation is even more complex as the scattered and emitted components vary with the Earth’s position in its orbit around the Sun. By comparing the CIB and the zodi, it is clear that even in the best lines of sight (perpendicular to the ecliptic plane), the zodiacal light completely dominates over the CIB. For the JWST mission, the zodi light is typically the limiting factor for IR observations. When observing asteroids with active illumination (LIDAR mode), the zodi is also an important factor. However, since illumination occurs with an extremely

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 18 Zodi background flux versus wavelength

narrow laser bandwidth, and detection occurs with an extremely matched narrow bandwidth, it is possible to largely reduce the zodi and the CIB to negligible levels. This is NOT necessarily true in broadband photometric (typically 30 % bandwidth) surveys that search for asteroids using scattered sunlight or using the thermal IR signature of the asteroid. This is one significant advantage of active illumination. The baseline laser amplifiers can be run with bandwidths between less than 100 Hz and 10+ GHz. The advantage of smaller bandwidths is the larger coherence length and stability, while the advantage of the larger bandwidth is higher power levels when in a stimulated Brillouin scattering (SBS)-limited mode. The current generation of high power density (1–3 kW) Yb fiber amplifiers uses large bandwidth (typ ~10 GHz) in order to mitigate the SBS limit by broadening the bandwidth, while the lower-power units (few hundred watts) have intrinsic bandwidths that are much less (typ ~100 Hz). There is a path forward to high power and lower bandwidth that is preferred for DE-STAR. To compare to the CIB and zodi backgrounds, Figs. 18 and 19 show the wavelength bandwidth in mm versus the frequency bandwidth in Hz. Optical Emission: Since the plan is to use the same phased-array elements used to transmit the optical emission of the laser illuminator, it is necessary to compute the optical emission rate into the detector. The optics are assumed to be at roughly 300 K for simplicity (this could be changed in some scenarios), indicating a brightness or emission rate of about 1.1  107 g/s-m2-st-mm for unity emissivity (or for a blackbody emitter) at 1.06 m. This is clearly an overestimate but represents a worst case. Under the assumption of a diffraction-limited system, the etendue of the optics is such that A O ¼ l2 ~ 1012 m2-st. The bandwidth of reception must also be included. Here a matched filter spectrometer is assumed (to get Doppler) with a bandwidth equal to the laser linewidth. As explained above, this is typically104–1010 Hz or approximately 4  1011 to 4  105 mm. The total per sub-element is thus an emission of about 4  1016 to 4  1010 g/s again for an emissivity of 1. This is an extremely small rate compared to the return LIDAR flux (see Fig. 16). Compare the brightness of 1  107 g/s-m2-st-mm for unity emissivity to the CIB and zodiacal light which are both much larger. For comparison, note that when looking directly at the Sun, the brightness of the solar surface is ~5  1025 g/s-m2-st-mm at 1.06 mm. Assuming a diffraction-limited system, the resulting photon rate would be about 2  103 to 2  109 for laser (receiver) bandwidths from 104 to 1010 Hz as above. This is NOT small compared to the CIB and zodi (as was the optical thermal emission), but it Page 30 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 19 Laser wavelength bandwidth in mm versus the frequency bandwidth in Hz

is still small compared to the LIDAR photon return rate for a DE-STAR 4 illuminating a 100 m asteroid at 1 AU. It does, however, point out the need to be reasonably careful in rejecting direct solar illumination in the off-axis response.

Ground Versus Airborne Versus Space-Based Systems While the baseline for DE-STAR is an orbital approach, a ground-based approach offers many obvious advantages in terms of testing and deployment, while the severe impediment of the atmospheric perturbations may be insurmountable for the foreseeable future. In all initial “roadmaps” to DE planetary defense, ground deployment for the smaller systems during test and debugging is a crucial step. The great strides made in adaptive optics for astronomy and situational awareness allow sub-arcsecond beam formation. Based on the active laser guide star programs, micro-radian beam formation is feasible from the ground. The transmission on clear days from excellent ground-based sites allows for less than 10 % transmission loss near 1 mm from ground to space. On cloudy days the transmission will be essentially zero. However, it is not the transmission which is the critical issue. It is the atmospheric turbulence or “seeing” – phase perturbations in the beam formation that is the limiting factor. One great advantage of a phased-array approach is that every aperture element is part of an “adaptive optics system” by the very nature of the phased array. In addition, rather than mechanically adjusting the phase front across a sub-optic in a classical adaptive optic system, DE-STAR will have much higher servo phase control bandwidth. This will lead to greatly improved adaptive optics performance, the limits of which are still to be explored. The early and smaller versions of DE-STAR, such as a DE-STAR 1 (10 m aperture), can be used from the ground to explore not only system design and performance but also may allow for initial space debris mitigation. As illustrated in Fig. 5, the beam size u (nrad) for an aperture size d (m) system is u (nrad) ~ 2  103/d. For reference the “seeing” from an excellent ground-based mountain top site (e.g., Mauna Kea) is about 2 mrad RMS at 1 mm wavelength. Ground-based seeing is typically given in arcsecond where 1 arcsec ~5 mrad, while adaptive optics are often quotes in wavefront error (often in nm) or in milliarcsec (mas) where 1mas ~5 nrad. It is important to note that

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

seeing is usually much more stable at night due to thermally driven perturbations during the day and that the “seeing” quoted for ground-based systems is for nighttime operation. With adaptive optics and decent Strehl ratios (~ > 0.5), 50 mas or 250 nrad at 1 mm wavelength is expected when using multiple active laser guide stars being planned for the next generation of ELT (extremely large telescopes) such as the TMT (Thirty Meter Telescope) among others when operated at night (of course). This (250 nrad) is approximately the beam size for a DE-STAR 1. Extremely aggressive sites, such as being above the boundary layer at Dome A, may allow even better adaptive optics and would be a possibility for small DE-STAR deployments. The extremely high-speed phase control of DE-STAR may allow even better Strehl ratios. This territory needs to be explored. For systems capable of true planetary defense (DE-STAR 3 or 4), one would need to have 100–1,000 times smaller beams, and thus ground-based deployment, while not impossible to imagine someday, is not likely to be effective with currently understood technologies for atmospheric perturbation mitigation. However, this area should be explored. In order to perform a proper analysis, the issues of weather (cloud cover, and other atmospheric distortions) and day/night seeing would have to be factored in. Daytime adaptive optics is also a complicated issue that needs further study. Airborne platforms offer the advantages of reduced atmosphere but usually severe operational constraints. Fixed wing aircraft are particularly problematic due to high-speed turbulence and airframe microphonics. Airship- and balloon-borne platforms are another alternative as balloons operate at above 30 km with near-zero relative airspeed. Balloon-borne platforms are viable for the smaller DE-STAR systems for multiple uses, but one of the primary issues is power. Beamed power from the ground is one option that has been studied in some detail for other programs. One could imagine large fleets of airship- or balloon-borne platforms, but it does not seem feasible for all but the smallest systems. Space-based deployment offers many advantages with the severe disadvantage of launch cost. Much of the current focus is on ultralow areal mass systems with a goal of under 1 kg/m2 for overall areal density. With the exception of thin film holographic lenses, no current technology can meet this goal. This optical possibility is the subject of active research. The lowest launch energy solution is a LEO Sun synchronous orbit to allow constant (except for eclipses) solar illumination and a relatively constant thermal environment. More stable orbital environments such as at a Lagrange point or possibly at geosynchronous orbits are more costly to achieve and vastly more complex to service. A lunar surface deployment might be another choice but again is much more difficult logistically and much more costly to deploy but could be a future defensive position for the Earth.

Pointing Issues The pointing requirements of the DE-STAR system are one of the more difficult technical challenges. Ultimately, the requirements for achieving high flux on target drive the overall pointing and thus the sensing and servo feedback loops. Unlike a classic optical system, a phased array offers both advantages and challenges compared to the bulk rigid body requirements of a system like the Hubble Space Telescope. The sub-element sizes of even the largest DE-STAR units are currently baselined to be in the meter diameter class (shroud size limited). Experience with rigid body pointing from the HST and upcoming JWST as well as many other space-based telescopes can be leveraged. As mentioned, HST had a 24 h RMS of 35 nrad. If each sub-element is pointed to this level but with uncorrelated pointing errors to its neighbors (clearly there will be some cross talk), the question is “what will the overall effect be on the synthesized beam?” Simulations of these scenarios are occurring now, and this will be covered in a future optical design paper. Since the beam from a 1 m sub-element (as an example) has a beam size of approximately 2 mrad, the individual element pointing error can be much smaller than the individual element beam size. Correlated pointing errors Page 32 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 20 Orbital deflection versus thrust for an Apophis-class asteroid with a diameter of 325 m and a laser on time of 15 years. Private communication K. Walsh 2014. Note the relatively small amount of thrust needed to deflect the target (2N yields about a 2 Earth radii miss)

are a much more serious issue and one where the overall feedback loop needs to feed information to correct for the final beam pointing. This is a nontrivial problem and one where significant work needs to take place for the largest systems where sub-nanoradian final beams need to be synthesized. A related effect of phase errors has been simulated extensively. Here the effect is opposite of the effect of pointing errors. For phase errors, complete correlation of the phase errors (or overall shifts) is canceled out to first order since it is the phase differences and not the absolute phase that is important. Large-scale correlated phase errors are important however. For example, a linear phase shift across the array would be equivalent to a pointing error. Again, the servo loop must correct and control the phasing to make a phased array. The effects of random phase error as might arise from phase noise in the amplifiers or highfrequency (beyond the servo bandwidth) mechanical vibrations have also been simulated. A Monte Carlo simulation is used with RMS phase errors of 103 to 1 wave (2p equivalent phase) and from 2 to 104 elements of individual sizes from 0.01 m to beyond 1 m and finds that the initial assumption of maintaining 1/10 wavefront error is a reasonable one, though 1/20 would be significantly better. Results are shown in Fig. 20. Simulation results are compared to simple Ruze theory (which is technically not appropriate due to the assumptions of correlation sizes in Ruze theory). The relationship from D’Addario (2008) is used: hI i 1  es0 2 ¼ þ es0 Io N 2

where I0 is the flux with no phase perturbation, hIi is the expected value of flux with phase perturbations, s0 is the RMS phase perturbation with zero-mean Gaussian distribution, and N is the number of elements. Simulation results agree extremely well with the simple Ruze exponential roll of forward gain or flux on target wherein the limit of infinite number of aperture becomes I ¼ I0 eVar(j), where Var(j) is the variance of the phase per element, I is the flux on target with phase perturbations, and I0 is the flux on target with no phase perturbations.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

“Stand-on” Applications: DE-STARLITE

While the primary motivation for DE-STAR has been as a “standoff defense” system, it can be used in a variety of modes where much smaller systems can be used as “stand-on” systems. The use of the same system in miniature to get close to a target and then use the focused laser in the same mode but at much closer distances allows for applications where a high flux laser can be used for remote laser machine of targets in asteroid or even lunar or Martian mining as well as for asteroid deflection via the same “plume thrust” mechanism outlined above. An example of this is the DE-STARLITE mission where a small (1–1,000 kW) system is taken near to the asteroid and mass ejection is initiated. The advantage compared to a simple mirror focusing on the asteroid is that the mirror must have an F# < 2 to be effective on high-temperature rocky compounds which requires getting the mirror extremely close to the asteroid (typically 10–100 m away). The reason that the F# has to be so low, for a mirror, is that the Sun is not a point source and thus the flux on target IT (W/m2) is the flux at the surface of the Sun divided by 4 times the F#2; thus, IT ¼ Isun/4 F#2. The flux at the surface of the Sun is about 60 MW/m2, and thus with an F# ¼ 2 mirror, the spot flux on the target would be about 4 MW/m2 which is just barely enough to start significant evaporation of rocky materials unless there are significant volatiles present. An F# ¼ 1 mirror would be much preferred in this case. This is the same reason that a simple mirror at the Earth will not evaporate distant asteroids unless the mirror diameter is roughly the size of the distance to the target (i.e., 1 AU mirror diameter). While using mirrors close to an asteroid is not insurmountable, the close proximity can cause severe optical pitting and dust buildup on the mirror. DE-STARLITE can stand off some 1–100 km away from the target and does not require Sun-target alignment allowing much more flexible steering. DE-STARLITE can also run pulsed if needed for more flexible mission scenarios. In all of these cases, the asteroid material is converted into its own propellant offering a much more efficient and powerful thruster than an ion engine of equivalent power and needed no propellant other than the asteroid itself. Studies to date indicate that Apophis-class asteroids (325 m diameter) can be deflected with a dedicated mission using less than 100 kW of power for a mission that gives roughly a decade of active mission time on target. Since the asteroid itself is the “rocket fuel,” such a mission does not suffer from having to take up a very large fuel load as required by an approach that uses ion engines only. A combined mission with ion engines for transport of the laser to the target and use of the ion engines for station keeping looks feasible with the upcoming SLS (Space Launch System). As a specific example, the deflection of a 325 m diameter asteroid (like Apophis) is studied, assuming a DE-STARLITE stand-on mission with the laser on for 15 years with a reasonable Earth-crossing orbit. A force as small as 2 N is sufficient to cause a 2-Earth-radius miss distance. Results of an orbital propagation simulation are shown in Fig. 21. Assuming a 0.1 mN/W (optical), this implies a 20 kW laser would be sufficient. A more conservative approach would use a 100 kW-class laser. In either case this is an extremely efficient approach to the mitigation of large asteroids using lasers. One option currently being studied is to use a laser add-on to the ARM mission concept where ion engines are used to propel the spacecraft to the asteroid and the laser is used to deflect it. This hybrid approach (ion engines + laser) works extremely well. Figure 21 shows the latest design concept for DE-STARLITE with 100 kw of solar PV. Since the build time after warning that an impact is likely, is not trivial, a better approach would be to keep a system (or several) in LEO or GEO or another orbit ready for a threat. This greatly reduces the total time required for mitigation. In the next few figures, we show the current status of the designs for the DE-STARLITE stand-on system. As seen in Fig. 22, the total time for (laser on) deflection for even large targets like Apophis are quite small.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 21 Artistic rendering of a deployed DE-STARLITE spacecraft deflecting an asteroid (Kosmo et al. 2014). The spacecraft is outfitted with two 15 m diameter ATK MegaFlex PV Arrays that give a total of 100 kw electrical power, a zfolded radiator deployed up and down, a laser array mounted on a gimbal at the front, and ion engines at the back. The laser array can be either a phased array or a parallel non phased array. Larger systems up to a megawatt fit within the SLS Block 1 launch vehicle

Fig. 22 Laser deflection time needed to achieve 2 Earth radii miss distance vs electrical power available assuming 50% amplifier efficiency and 80 micro-N/wopt coupling efficiency. Note that this is the laser on time not the warning time. The warning time needs to include a build and travel time from LEO to target. The time shown here is the time the laser is actually on. The asteroid density is assumed to be 2000 kg/m3

Laboratory Testing A laboratory test system was constructed to check calculations and simulations. The test system consisted of 19-fiber CW lasers, each of which was homogenized in an 800 mm core fiber and then reimaged to simulate active phase control. Each fiber had a diameter of about 150 mm and was fed with 2.1 W diode laser at 808 nm. The beam diverges with a NA ~ 0.2 and reconverges with a

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 23 (a) Cross-sectional diagram showing laser (which is 19 individual fiber-fed lasers) and the re-collimating optics. (b) Rendering showing beam expansion and imaging as well as sample holder. (c) Laser firing at a target (basalt in this case)

roughly 1:1 ratio to produce a spot that was about 1 mm in diameter. Fluxes up to 40 MW/m2 are achieved which is close to the target of a DE-STAR 4 at 1 AU. For reference, the surface of the Sun (assuming a 5,800 K surface) has a flux of about 60 MW/m2. When the laser is fired at a target, an extremely intense white hot spot is created that lights up the room and vaporizes every material tested. So far, tests are done outside the vacuum chamber, but vacuum tests will begin shortly. Diagnostics include IR (out to 12 mm) and visible light cameras as well as a fiber-fed optical spectrometer. Optical coupling from fiber tip to target was measured at about 90 %. Mass ejection was definitely observed (holes were punched through), but quantitative comparison to mass ejection model will be done in vacuum as the vapor pressure would have to exceed 1 atmosphere for normal evaporation. For basalt, the measured mass ejection (in 1 atm air) was 0.42 mg/s, while the theoretical maximum for this test was 2.2 mg/s. One significant issue is the complex nature of the test materials that are being evaporated. Some standard targets will be used in the vacuum tests. Air convection is also a serious issue, so it is not surprising that the measured mass ejection is less than anticipated for a variety of reasons. Plain sand from the local beach was used as a target; the sand was placed in a small crucible and the laser energy melted it into a glass ball as well as vaporized some of it. The laboratory setup and associated simulation results are shown in Figs. 23 and 24.

Standoff Approach for Efficient and Cost-Effective Impact Risk Mitigation There is a fundamental difference between DE-STAR and previously described approaches to orbit deflection. All currently described concepts are “stand-on” systems, in that assets required for orbit alteration would need to be deployed onto, or at least very near, the threatening asteroid. DE-STAR is a standoff system that would be capable of altering an asteroid or comet’s orbit from afar. Costs associated with DE-STAR development would be amortized over multiple threats and over multiple applications beyond planetary defense, since a functioning system could be used repeatedly. Asteroid 2012 DA14 (~45 m) was discovered 1 year before its close approach; could a kinetic impact mission have been attempted, had the asteroid been on a collision course? If the object that struck near Chelyabinsk had been discovered 1 year (or 1 day) before impact, could (or would) any stand-on mission be deployed to nullify the threat? A single DE-STAR system of modest size and flexibility would have been capable of eliminating the threats from both 2012 DA14 (in about a day

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Fig. 24 (a) 2D simulation with laboratory test parameters. Similar to Fig. 14 but set for lab testing. Plot is of expected mass ejection versus sigma (Gaussian beam) for various power levels. Measured sigma based on hole size in targets is less than 330 mm. Sample is assumed to be SiO2. (b) Picture of test system. Small camera is an 8–12 mm FLIR IR microbolometer unit. Sample is sand

of targeting) and the Chelyabinsk impactor in less than 1 h of targeting (assuming prior detection by surveillance efforts). In particular, a functioning DE-STAR would be capable of mounting very rapid responses to newly discovered objects that have no chance of being mitigated by stand-on systems. As previously stated, a single orbiting DE-STAR of sufficient size could be designed to simultaneously engage multiple approaching objects. Unlike stand-on approaches, DE-STAR could be tested and validated at every stage of development, considerably increasing confidence that the system would succeed when needed the most. Since DE-STAR would be capable of addressing other scientific goals, development costs could also be spread across multiple scientific budgets. The standoff strategy of DE-STAR has many obvious and critical advantages over stand-on schemes currently being considered for asteroid impact avoidance. It is worth the effort to explore the many issues associated with designing, developing, and deploying an orbiting DE-STAR. In this chapter, baseline system requirements and architecture are considered; cost-benefit analysis will be addressed in future work.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

Other Uses for DE-STAR Summary of Other Uses DE-STAR is a standoff directed energy system and there a number of other uses that are possible. Some of these alternative uses are explored in detail. Clearly if it is possible to “laser machine” on solar system scales, this brings up some thought-provoking discussions. Some of the more mundane ideas are: • Space debris mitigation – a small unit (DE-STAR 1) is extremely effective against space debris. A unit attached to the ISS would be very useful in clearing out orbital debris. • A LIDAR mode for refining the orbital parameters of asteroid. DE-STAR is extremely bright and makes an excellent “flashlight” to target asteroids in order to detect and refine their positions (Riley et al. 2014). As an aid to existing efforts, active illumination can be quite useful. The narrow bandwidth allows for extremely low-background searches as well as Doppler velocity determination. • Standoff composition analysis – the bright heated spot might be used as a backlight to determine asteroid ejecta composition. An analysis is underway to see what is feasible. • Orbital capture – modifying the orbits of asteroids may allow for easier capture if desired. • Beam power to distant probes – the system can be used to beam power to very distant spacecraft. At 1 AU, the flux is 70 MW/m2 or about 50,000 times the flux of the Sun. At the edge of the solar system (30 AU), it is about 80 kW/m2. At 225 AU, the beam is about as bright as the Sun is above the Earth’s atmosphere. Similarly it could be used to provide power to distant outposts on Mars or the Moon or literally to machine on the lunar surface (or possibly Mars). The latter would be a complex sociological and geopolitical discussion no doubt. • Spacecraft rail gun mode – while photon pressure is modest, it is constant until the beam diverges to be larger than the reflector. In a companion paper, Bible et al. (2013) discuss using this mode to propel spacecraft at mildly relativistic speeds. For example, a 100, 1,000, and 10,000 kg spacecraft with a 30 m diameter (9 kg – 10 mm thick multilayer dielectric) reflector will reach 1 AU (~Mars) in 3,10,30 days. Stopping is an issue! The 100 kg craft will be going at 0.4 % c at a 1 AU and 0.6 % c at the edge of the solar system. This is 1,800 km/s at the edge of the solar system with just a 30 m reflector. This speed is far greater than the galactic escape speed and nearly 100 times faster than the Voyager spacecraft. If a reflector could be built to intercept the beam out to the edge of the solar system (900 m diameter), the same craft would be going 2 % at the edge of the solar system and 3 % if illumination stayed on for about 2 months. It is not currently known how to build km-class reflectors that have low enough mass, though it appears feasible to make 30 m and 100 m reflectors. There is work on graphene sheets that may allow for future extremely large- and extremely low-mass reflectors that may allow for fully relativistic speeds. Future generation may build even larger DE-STAR 5 and 6 units to allow highly relativistic probes. • Laser-driven launch and boosters – a high-power ground-based DE-STAR could be used for launch purposes when used as an ablation (Campbell et al. 2003) or plume thrust driver. Similarly for orbital boost from low Earth orbit (LEO) to geosynchronous Earth orbit (GEO) and beyond, a DE-STAR could be extremely useful. • SPS mode – beam power to the ground via microwave or mm wave. The system would produce about 100 GW (electrical). The US consumption is about 440 GW (electrical) average (1,400 W/ person – average).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

• Interstellar beacon – DE-STAR appears brighter than the brightest nighttime star at 1,000 ly (typical distance to Kepler-discovered exoplanets). Optical search for extraterrestrial intelligence (SETI) use is being explored for both transmit and receive modes. • Ultrahigh-speed IR communications – the calculated data rates for DE-STAR to long-range, even interstellar probes are enormous with Mb/s speeds back to Earth from probes at the nearest stars for relatively small spacecraft transmitters and reflectors.

Conclusion Directed energy systems represent a solution to planetary defense against asteroids and comets that threaten Earth. The same system can be used for a multitude of other purposes and thus is not a single-use system waiting for an asteroid. Its use in active illumination, remote composition analysis, spacecraft propulsion, space debris mitigation, and SPS (Space Power Satellite) could more than justify its cost let alone its ability to protect the Earth from catastrophe. Being modular and scalable, the DE-STAR can be built in stages as technology progresses. Small DE-STAR 0 (1 m) and DE-STAR 1 (10 m) class units can be built, tested, and even flown on suborbital platforms to test the basic concepts as small orbital versions are built. The technology is improving rapidly and already nearly “there” in terms of conversion efficiency. There are many other uses that are not discussed here for brevity. A logical progression is possible from the smaller DE-STAR ground and suborbital units to small orbital units as the technology improves and laser mass power density improves until it is possible to deploy a full-scale system such as a DE-STAR 4. As humanity becomes more technologically advanced, even larger systems can be envisioned including systems that will allow the first interstellar probes.

Acknowledgments The funding from the NASA California Space Grant NASA NNX10AT93H in support of this research is gratefully acknowledged. The assistance from the Zemax support team for the Zemax optical simulations is also appreciated.

Cross-References ▶ Asteroid Redirect Mission by NASA ▶ Comet Shoemaker-Levy 9 ▶ Deep Impact and Related Missions ▶ Deflecting or Disrupting a Threatening Object ▶ Economic Challenges of Financing Planetary Defense ▶ ESA’s PHA’s Program ▶ Global Leadership and Strategies for Planetary Defense ▶ Hazard of Orbital Debris ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Keyholes ▶ Minor Planet Center ▶ Nature of the Threats and Historical Patterns of Occurrence Page 39 of 42

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_77-1 # Springer International Publishing Switzerland 2014

▶ NEO Shield Program of the EU ▶ OSIRIS-REx Asteroid Sample Return Mission ▶ Planetary Defense, Global Cooperation and World Peace ▶ Possible Institutional and Financial Arrangements for Active Removal of Orbital Space Debris ▶ Potentially Hazardous Asteroids and Comets ▶ Private Initiatives: The Sentinel Project ▶ Spaceguard Survey by NASA: Behind Schedule and Seeking to Increase Mapping Capabilities ▶ Strategic Issues Involved with Planetary Defensive Systems and Active Debris Removal Systems ▶ The B612 Foundation’s Sentinel Space Telescope to Create a 100 Year Warning Program ▶ The NASA Sentry Risk Table ▶ The Yarkovsky Effect ▶ US Based Systems (MPC, Smithsonian, MIT Linear System, NEAT, Spacewatch, LONEOS, Catalina) ▶ Wide-Field Infrared Survey Explorer (WISE) and NEOWise

References Belton MJS, Morgan TH, Samarasinha NH, Yeomans DK (eds) (2004) Mitigation of hazardous comets and asteroids. Cambridge University Press, New York Bible J, Johansson I, Hughes GB, Lubin PM (2013) Relativistic propulsion using directed energy. In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VII. Proceedings of SPIE, vol 8876, 887605 Binzel RP, Rivkin AS, Thomas CA, Vernazza P, Burbine TH, DeMeo FE, Bus SJ, Tokunaga AT, Birlan M (2009) Spectral properties and composition of potentially hazardous asteroid (99942) Apophis. Icarus 200:480–485 Campbell JW, Phipps C, Smalley L, Reilly J, Boccio D (2003) The impact imperative: laser ablation for deflecting asteroids, meteoroids, and comets from impacting the earth. In: BEAMED ENERGY PROPULSION: first international symposium on beamed energy propulsion 664(1), AIP Publishing, Melville, pp 509–522 Colombo C, Vasile M, Radice G (2009) Semi-analytical solution for the optimal low-thrust deflection of near-earth objects. J Guid Control Dyn 32(3):796–809 Conway BA (2004) Optimal interception and deflection of Earth-approaching asteroids using low-thrust electric propulsion. In: Belton MJS, Morgan TH, Samarasinha N, Yeomans DK (eds) Mitigation of hazardous comets and asteroids. Cambridge University Press, New York, pp 292–312 Cuartielles JPS et al (2007) A multi-criteria assessment of deflection methods for dangerous NEOs. In: New trends in astrodynamics and applications III. AIP conference proceedings 886(1), American Institute of Physics/Springer, New York, pp 317–336 D’Addario LR (2008) Combining loss of a transmitting array due to phase errors. IPN Progress Report 42-175, Nov 2008 Delbò M, Cellino A, Tedesco EF (2007) Albedo and size determination of potentially hazardous asteroids: (99942) Apophis. Icarus 188:266–270 Fan TY (2005) Laser beam combining for high-power, high-radiance sources. IEEE J Sel Top Quantum Electron 11:567 Gibbings MA, Hopkins JM, Burns D, Vasile M (2011) On testing laser ablation processes for asteroid deflection, 2011 IAA planetary defense conference, Bucharest Page 40 of 42

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Gritzner C, Kahle R (2004) Mitigation technologies and their requirements. In: Belton MJS et al (eds) Mitigation of hazardous comets and asteroids, vol 1. Cambridge University Press, New York, p 167 Harris AW (1998) A thermal model for near-Earth asteroids. Icarus 131:291–301 Hughes GB, Lubin P, Bible J, Bublitz J, Arriola J, Motta C, Suen J, Johansson I, Riley J, Sarvian N, Wu J, Milich A, Oleson M, Pryor M (2013) DE-STAR: phased-array laser technology for planetary defense and other scientific purposes (Keynote Paper). In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VII. Proceedings of SPIE, vol 8876, 88760J Hughes GB, Lubin P, Griswold J, Bozinni D, O’Neill H, Meinhold P, Suen J, Bible J, Riley J, Johansson I, Pryor M, Kangas M (2014) Optical modeling for a laser phased-array directed energy system (Invited Paper). In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VIII. Proceedings of SPIE, vol 9226 Hyland DC, Altwaijry HA, Ge S, Margulieux R, Doyle J, Sandberg J, Young B, Bai X, Lopez J, Satak N (2010) A permanently-acting NEA damage mitigation technique via the Yarkovsky effect. Cosm Res 48(5):430–436 Johansson I, Tsareva T, Griswold J, Lubin P, Hughes GB, O’Neill H, Meinhold P, Suen J, Zhang Q, Riley J, Walsh K, Mellis C, Brashears T, Bollag J, Matthew S, Bible J (2014) Effects of asteroid rotation on directed energy deflection. In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VIII. Proceedings of SPIE, vol 9226 Kahle R, Hahn G, K€ uhrt E (2006) Optimal deflection of NEOs en route of collision with the Earth. Icarus 182(2):482–488 Koenig JD, Chyba CF (2007) Impact deflection of potentially hazardous asteroids using current launch vehicles. Sci Glob Secur 15(1):57–83 Kosmo K, Pryor M, Lubin P, Hughes GB, O’Neill H, Meinhold P, Suen JC, Riley J, Griswold J, Cook BV, Johansson IE, Zhang Q, Walsh K, Melis C, Kangas M, Bible J, Motta, Brashears, T., Mathew S, Bollag J (2014) DE-STARLITE – a practical planetary defense mission. In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VIII. Proceedings of SPIE, vol 9226 Lu ET, Love SG (2005) A gravitational tractor for towing asteroids. arXiv preprint astro-ph/ 0509595 Lubin P, Hughes GB, Bible J, Bublitz J, Arriola J, Motta C, Suen J, Johansson I, Riley J, Sarvian N, Clayton-Warwick D, Wu J, Milich A, Oleson M, Pryor M, Krogan P, Kangas M (2013) Directed energy planetary defense (Plenary Paper). In: Taylor EW, Cardimona DA (eds) Nanophotonics and macrophotonics for space environments VII. Proceedings of SPIE, vol 8876, 887602 Lubin P, Hughes GB, Bible J, Bublitz J, Arriola J, Motta C, Suen J, Johansson I, Riley J, Sarvian N, Clayton-Warwick D, Wu J, Milich A, Oleson M, Pryor M, Krogen P, Kangas M, O’Neill H (2014) Toward directed energy planetary defense. Opt Eng 53(2):025103-1–025103-18. doi:10.1117/1. OE.53.2.025103 Maddock C, Cuartielles JPS, Vasile M, Radice G (2007) Comparison of single and multi‐spacecraft configurations for NEA deflection by solar sublimation. In: AIP conference proceedings, vol 886. AIP Publishing, Melville, p 303 McInnes CR (2004) Deflection of near-Earth asteroids by kinetic energy impacts from retrograde orbits. Planet Space Sci 52(7):587–590 Melosh HJ, Ryan EV (1997) Asteroids: shattered but not dispersed. Icarus 129(2):562–564 Morrison D, Harris AW, Sommer G, Chapman CR, Carusi A (2002) Dealing with the impact hazard. In: Bottke W et al (eds) Asteroids III. University of Arizona Press, Tucson, pp 739–754 Page 41 of 42

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Mueller M (2007) Surface properties of asteroids from mid-infrared observations and thermophysical modeling. arXiv preprint arXiv:1208.3993 Mueller M, Harris AW, Fitzsimmons A (1989) Size, albedo, and taxonomic type of potential spacecraft target Asteroid (10302) 1989 ML. Icarus 187:611–615 Olds J, Charania A, Schaffer MG (2007) Multiple mass drivers as an option for asteroid deflection missions. In: 2007 Planetary defense conference, Washington, DC, Paper, pp S3–S7 Riley J, Lubin P, Hughes GB, O’Neill H, Meinhold P, Suen J, Bible J, Johansson I, Griswold J, Cook B (2015) Directed energy active illumination for near-Earth object detection. J Astron Telescopes Instrum Syst (accepted) Schweickart R, Chapman C, Durda D, Hut P (2006) Threat mitigation: the gravity tractor. arXiv preprint physics/0608157 Vasile M, Maddock CA (2010) On the deflection of asteroids with mirrors. Celestial Mech Dyn Astron 107(1):265–284 Vorontsov MA, Weyrauch T, Beresnev LA, Carhart GW, Liu L, Aschenback K (2009) Adaptive array of phase-locked fiber collimators: analysis and experimental demonstration. IEEE J Sel Top Quantum Electron 15:269 Walker R, Izzo D, de Negueruela C, Summerer L, Ayre M, Vasile M (2005) Concepts for near-Earth asteroid deflection using spacecraft with advanced nuclear and solar electric propulsion systems. J Br Interplanet Soc 58(7–8):268–278 Warner BD, Harris AW, Pravec P (2009) The asteroid lightcurve database. Icarus 202:134–146 Wie B (2007) Hovering control of a solar sail gravity tractor spacecraft for asteroid deflection. In: Proceedings of the 17th AAS/AIAA space flight mechanics meeting, AAS, Washington, DC, vol 7, p 145

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

Risk Management and Insurance Industry Perspective on Cosmic Hazards Scott Ross* Global Aerospace, Inc., Parsippany, NJ, USA

Abstract “A good rule of thumb is to assume that everything matters.” Richard Thaler

Quantifying risk is a survival mechanism innate to the human race. From the days cavemen built shelters to protect themselves from the elements, the goal has been to mitigate risk. In modern society, insurance, which spreads risk among many to protect the few who have losses, is the backbone of risk mitigation. The hazards addressed are those thought to have the highest probability of causing bodily injury or property damage. Fire, flood, hurricane, and earthquake are common perils covered by insurance. Cosmic hazards including meteors, coronal mass ejections, solar flares, and orbital debris-related accidents are rare events. Individuals, corporations, governments, and insurance companies do not believe the risk is relevant to them so they do not address it. Even the well-publicized recent meteor event over Chelyabinsk, Russia, causing $30 million in damages and wounding over 1,600 people certainly will not change this (Borenstein S, Russian meteor in chelyabinsk may mean space rocks pose bigger risk than we thought. Huff Post, Science. http://www.huffingtonpost.com/2013/11/06/ russia-meteor-chelyabinsk-space-rocks-risk-studies_n_4227270.html. Accessed Sept 2014, 2013). While cosmic hazards are off the radar, it does not mean that insurance is not available to cover the damage caused by them. The effects of cosmic hazards are similar to natural catastrophes and covered by insurance in the same way. Insurance policies are written covering all risks of loss with no specific exclusions for cosmic hazards. So, by default insurance companies are covering cosmic hazards. However, if the frequency or severity of hazards does reach consciousness, then insurers will limit coverage, charge a premium for it, or exclude it all together.

Keywords Asteroid; Carrington event; Catastrophic bond; Commercial Space Launch Act (CSLA); Comet; Coronal mass ejection (CME); Halloween storm; Insurance-linked security; Kessler syndrome; Montreal event; Near-earth object (NEO); Price-Anderson act; Reinsurance; Solar flare; Space debris; Ultrahazardous insurance

Introduction “Risk comes from not knowing what you’re doing.” Warren Buffet

*Email: [email protected] Page 1 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

The earth is spinning and orbiting the sun as it has since its creation. Earth is not alone and is constantly in harm’s way of activities on the sun, comets, asteroids, orbital debris, and unknown biological contagions. History has shown that near-earth objects have caused devastation to all living things on earth. Cosmic hazards from a risk management perspective follow the same process as all other risks. The exposures are analyzed on the basis of frequency and severity. Risk mitigation options are weighed as whether to retain, avoid, reduce, or transfer the risk through the use of insurance. If available, insurance is proven to be the best risk mitigation tool. It is beneficial to society by promoting safety prior to occurrences, indemnifying insureds, and kick starting local economies after catastrophes have struck. While large catastrophic events from cosmic hazards are rare, the possibility exists. Like natural catastrophes in recent decades, the losses they can cause will increase in the future due to worldwide population growth, increase in urbanization, and concentration of exposures in coastal areas. Today earth is home to well over seven billion people, double of what it was in 1970. By 2024, the population will likely reach 8 billion, and the United Nations projects it will reach 10–12 billion by the end of the century (UN 2012). Property values will continue to rise as well. As of 2012, in the United States, there is $65 trillion in insured property and $11 trillion of that is located in coastal counties (AIR 2013). As sophisticated as modern insurance companies are with actuarial models, history proves over and over that no one can accurately predict the future. Insurance has its limits and large catastrophes can lead them to fail. This not only affects the stockholders of the company but places a large burden on policy holders, local economies, and the government. This chapter is written from a US perspective. International treaties and worldwide insurance market figures are universal in scope, while more specific regulations are US centric such as CSLA and flood insurance. Similar regimes to those discussed are in place around the world, and it is recognized they may be more advantageous than the US versions.

Cosmic Hazards: Identified The initial step in the risk management process is to identify the risks. Cosmic hazards include anything outside the earth’s atmosphere that can cause harm to people or property. There are four categories of cosmic hazards based on the damage they each cause and as such the insurance that applies. Near-earth objects can damage satellites but the greatest concern is the catastrophic potential they can cause on the ground. Solar hazards can be very detrimental to satellites in orbit but could be devastating to the earth’s electrical grids as well. Orbital debris is primarily seen in terms of probability of occurrence as a concern for satellites in orbit. Biological hazards are a concern for all people on earth. Near-earth objects (NEO) include comets, asteroids, meteors, meteorites, and bolides that can cause damage to the earth by impact or explosion resulting in any combination of wind, fire, earthquake, or flood. These are covered perils under standard homeowners and commercial general liability insurance policies. Earthquake coverage is not standard but it can be purchased. Flood coverage is excluded from traditional insurance and in the United States must be purchased from the government-run National Flood Insurance Program (NFIP). A quick mention of the descriptions of NEO may be helpful. Most objects directed toward the earth will burn up in the earth’s atmosphere depending on size and velocity of the object. These are referred to as meteors. Objects that are larger than meteors and explode once hitting our atmosphere are referred Page 2 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

to as bolides. Objects that penetrate the atmosphere and strike the ground or oceans are meteorites. Asteroids orbit the sun and can be very large up to 1,000 km across and travel at very high speeds. Comets come from the farthest reaches of the solar system and have the highest velocity. The amount of damage caused by a near-earth object event can vary depending on many factors. The location of the event on the earth could mean the difference between no damage and a catastrophic event. As over 70 % of the planet is covered by water or ice, this would reduce exposure to people and property unless the force is great enough to create a tidal wave or tsunami. The Tunguska, Russia, event of 1908 was over land but in an uninhabited area so the only damage was to trees. Had such an event occurred over a large city, the outcome would have been much different. Such a scenario is described later. The power of a NEO occurrence depends on size, composition, velocity, and the angle at which it hits the atmosphere. Three levels of criticality can be discussed as to what is an insurable event. The first would be objects that burn up in the atmosphere or impact the ground or water with minimal damage. The maximum damage may be thought of as to a small area such as a single house. This is not a large concern to the insurance industry due to the low severity and low frequency of an occurrence. The second level is an area where insurance applies and encompasses objects that explode in the atmosphere or impact an area that can cause significant economic damage. Chelyabinsk is considered to be a 100-year event and would fall in the low end of this level. Tunguska incident of 1908 would be on the upper end of this level. The third level of damage would be a climate-altering event that would cause global destruction that would leave insurance to be inconsequential. Such an event would involve a 1 km or largerdiameter meteor. A meteorite this size could cause worldwide catastrophic climate change wiping out life and vegetation such as the K-T mass extinction event that occurred 65 years ago.

NEO Occurrences

• In Chelyabinsk, Russia, in 2013, a 17–19 m diameter meteor exploded over the city injuring over 1,600 people with estimated losses of over $30 million. This is an insurable event. • In Tunguska, Russia, in 1908, large air burst of a 50 m diameter comet or asteroid over Central Siberia. Trees were leveled over 2,000 km square. The area was uninhabited and remote with only trees damaged. • In Yucatan Peninsula (Chicxulub), 65 million years ago, a 5–6 km diameter asteroid caused huge tidal waves and severe worldwide climate change and led to the extinction of 70 % of all species on earth.

Solar flares and coronal mass ejections (CME) arise from eruptions of high-energy radiation and ions from the sun’s surface. Flares are associated with sunspots and they may or may not be accompanied by coronal mass ejections. When a flare occurs, plasma accelerates energy almost to the speed of light. This plasma of energy is highly charged radiation and can damage satellites and electric grids on earth. Coronal mass ejections contain billions or even trillions of tons of ions that can trigger a natural electromagnetic pulse (EMP). Damage to electric grids can cause widespread blackouts. As society becomes more dependent on electrical devices for communication and navigation (GPS), the loss of power grids or satellites becomes more detrimental. The space insurance market insures damage to insured satellites. The coverage is all risk and does not exclude damage from solar activity. Government satellites such as those in the Global Positioning System are not insured. As to the risks on the ground, standard homeowner’s policies exclude electrical outage caused away from the home so they are left in the dark. But, business interruption Page 3 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

insurance or contingent business interruption for companies would provide coverage. Should there be a prolonged widespread electrical outage, it would be very costly for the insurance industry indeed. There are ways to improve the infrastructure of electrical grids so they are better protected from geomagnetic storms. Transformers and transmission lines can be better constructed with insulation against the elements. The use of capacitors and heavy-duty circuit breakers designed to shut off and stop the spread of highly charged currents could reduce the spread of the loss of the grid and blackouts. The 1989 Canadian event could have propagated to a much larger portion of the United States had it not been for a few dozen capacitors. Thus, most of the damage in the United States was largely contained to the Chicago area.

Solar Flare and CME Occurrences

• Halloween Storm, 2003. Solar activity started in mid-October and lasted almost 5 weeks. The most powerful x-ray flare CME event recorded since satellites started measuring them in the 1970s occurred on November 4, 2003, and took only 19 h to reach earth from the sun. The storm caused power outages in Sweden, caused astronauts on the International Space Station to take cover, and damaged satellites. Twenty-eight satellites were damaged and two were destroyed. The Japanese Midori 2 satellite was one of the satellites destroyed and it was valued at $570 million (Satellite Digest 2003). Because it was a government-funded satellite, there was minimal insurance. • Montreal Event, Canada, 1989. The Canadian Hydro-Quebec power grid was brought down in two minutes by the strongest geomagnetic storm ever measured in recent times. Six million people lost power. The economic cost was $12.7 billion (ABC 2013). • Carrington Event, 1859. Carrington was a solar astronomer who recorded huge sunspots on the sun. The CME associated with the sunspots traveled to earth in 17 h. The solar eruption started fires in telegraph offices. Auroras were bright enough to read by. This event was before the era of satellites so there was no damage to be caused there. A similar storm today could cause more than $2 trillion to electrical infrastructure (Ferris 2012). Orbital debris is also called space junk. It is the debris field circling the earth created by man from sending objects into space since Sputnik in 1957. As of 2014, some 22,000 pieces of debris larger than 5 cm are being tracked. There are another 300,000 pieces about the size of a marble with a substantial amount of kinetic energy. The highest density of debris resides in the lower earth orbits (LEO) – about 45 % of the 6 t of debris in the earth orbit (NASA Orbital Debris Program Office 2014). A theory posited as the Kessler syndrome states that if the debris becomes dense enough, collisions between objects could cascade with each collision generating orbital debris, which increases the likelihood of further collisions. The damage we are most concerned about is that to orbiting objects in space that are operational including commercial and military satellites, the ISS, and the deorbit of any of this debris. Insurance is available for satellites in orbit. As regards bodily injury or property damage to those on the ground, insurance would be available concerning health, life, or property, but there could be liability on behalf of the “owner” or launching state of the object that caused a loss to a third party. The deorbit of large debris can be detrimental to people and property on earth. Large objects can include space stations or satellites that have reached the end of their useful life. Just as the deorbit of Skylab and Mir were of concern, the eventual deorbit of the ISS will be greater still. Deorbit events of such space stations, satellites, or spent rocket stages have been and are insurable for liability to third parties. Page 4 of 18

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Orbital Debris Occurrences

• Satellite collision, February 10, 2009. Iridium 33 and Cosmos 2251 collided at altitude of 789 km. Iridium was an operational communications satellite, while the Cosmos was deactivated as past end of life. Neither satellite was insured. In March 2011, the ISS made an avoidance maneuver due to debris from this collision. • Chinese anti-satellite missile test, January 11, 2007. A Chinese weather satellite, FY-1C, at an altitude of 865 km was intentionally destroyed by a Chinese missile. This was the largest recorded creation of orbital debris in history with 150,000 debris particles, of which over 2,500 are large enough for active tracking. • Space Shuttle Columbia, February 1, 2003. Seven astronauts were killed when the shuttle disintegrated. Over 80,000 pieces were recovered which were spread over 72,500 square km of Texas and Louisiana. Analysis by the US Federal Aviation Administration (FAA) estimated that there was on the order of a 1 % probability that an aircraft could have been hit by the falling debris. • Mir Russian Space Station, March 23, 2001. Above the Pacific Ocean near Fiji, the 130,000 kg station broke into 1,500 fragments. • Skylab US Space Station, July 11, 1979. The 70,000 kg station fell into the Indian Ocean and parts of Western Australia. Biological hazards could be introduced to our planet from anything that reenters our atmosphere from space. This could apply to astronauts or any material from moons, planets, asteroids, or other celestial objects. The concern is bodily injury caused by a contagious agent that could reach epidemic or pandemic scale. Dangers from the cosmos causing sickness or death to people would be covered by health and life insurance. The insurance implications are reviewed later in the chapter.

Insurance “The first step in the risk management process is to acknowledge the reality of risk. Denial is a common tactic that substitutes deliberate ignorance for thoughtful planning.” Charles Tremper

Modern insurance started as fire insurance to protect property in response to the 1666 Great Fire of London. The general principle of insurance is to pool the exposures of the many to pay for the misfortunes of a few. Insurance is a contract to pay should a covered event occur. Today there is an insurance market available for almost any risk that is viewed as measurable and not catastrophic for a price. Every organization must manage its risk including insurance companies. Insurance companies not only have a responsibility to society to provide coverage but as corporations to their stockholders as well. How do insurers evaluate the unique exposures of cosmic hazards? Insurance companies require that a group of exposures have the following characteristics in order to qualify as an insurable risk (Baranoff et al. 2014): 1. Large number of similar exposure units. Insurance operates through the pooling of risks, and the larger the number of similar risks insured, the more predictable the losses. Insurance companies can debate how large that number must be in order to make the risk predictable. Life insurance risk is very predictable as the number of units is very large. Space insurance that may have only

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2.

3.

4.

5.

6.

7.

30 satellites launched a year on various launch vehicles is very unpredictable. How one qualifies a one in 100 year meteor event is more difficult. Definite loss. The loss needs to be identifiable as to when it happens, where, and with a known cause. Meteor strikes would meet these criteria, but orbital debris damage to a satellite or a contagious biological hazard affecting a large number of people may not. Fortuitous or accidental loss. The loss must be outside the control of the insured. There must be an element of uncertainty as to the occurrence of risk or the time of the occurrence. Large loss. The insured must view the insurance to be of value based on the size of a loss. Losses that would not have any large financial effect on the insured would not be worth paying a premium to protect. Affordable premium. If the cost to insure is greater than the cost to the insured to retain the risk, then it makes little sense to purchase insurance. Cosmic hazards are not currently directly addressed by insurance. Should a market develop, it may be expected that due to the large catastrophic nature, a large premium would be charged. Calculable loss. The probability of the loss must be calculable, and the amount of the insurance payout must be well understood as to the value when a claim is made. A nuclear event could affect millions of people, but the standards for nuclear power stations require the probability of a major radioactive release be below 1 in 10,000. A tsunami hitting the United States could be devastating, but estimates suggest it would occur once every thousands of years. Lastly, the chance of a large meteorite hitting a large city is currently thought to have the probability of perhaps being less than 1 in a million per year. Recent data from the nuclear monitoring system indicates that meteor strikes are more common than previously thought and the growth of urban centers to cover much more land will likely alter these assessments. Limited risk of catastrophic losses. Insurable losses must have a low probability of affecting all insureds at once. Insurers must be able to spread their risk in order not to risk bankruptcy. Using the example of earthquake, hurricane, or flood insurance, the insurers limit their exposure in specific geographic areas to protect themselves should there be a large event. Reinsurance is a mechanism for insurance companies to further spread their risk and is available to all lines of insurance including aerospace and space markets.

Worldwide Insurance Worldwide insurance premiums in 2012 including life and nonlife were $4.61 trillion. Nonlife insurance includes accident, health, and property casualty insurance. Life insurance was $2.62 trillion and nonlife $1.99 trillion (Insurance Information Institute (iii) 2014). In looking at the largest buyers of insurance, the top 10 countries represent 75 % of the world insurance premiums while only 30 % of the population. See Table 1. The United States and Japan alone purchase 42 % of the premium while representing only 6.25 % of the world population. This disproportion leaves areas of the world with large populations with much lower levels of insurance (Insurance Information Institute (iii) 2014). Looking at the largest countries by population and the amount of insurance they purchase, it can be seen that cumulatively they represent 58 % of the world population. See Table 2. When the United States and Japan, who are the largest buyers of insurance, are removed from these figures, it is noted eight of the largest countries in the world representing 52 % of the world population purchase just 9.5 % of the worldwide insurance (Insurance Information Institute (iii) 2014a). Insurance has a positive effect on society. Countries with lower per capita income must overcome larger economic losses from natural catastrophes than wealthier countries. By having adequate Page 6 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

Table 1 Largest buyers of insurance by country Top ten countries by life and nonlife direct premiums written, 2012 Country Population Premium (US$mn) United States 316,668,567 $1,270,884 Japan 127,253,075 $654,112 United Kingdom 63,395,574 $311,418 China 1,349,585,838 $245,511 France 65,951,611 $242,459 Germany 81,147,265 $231,908 Italy 61,482,297 $144,218 South Korea 48,955,203 $139,296 Canada 34,568,211 $122,532 The Netherlands 16,805,037 $100,342 Total 2,165,812,678 $3,462,680

% premium 27.55 14.18 6.75 5.32 5.26 5.03 3.13 3.02 2.66 2.18 75.08

Source: 2014 International insurance fact book (Swiss Re, sigma, No. 3/2013) Table 2 Largest countries and insurance premiums Ten most populated countries (July 2013) Life and nonlife direct premiums written, 2012 Country Population % of world population China 1,349,585,838 19.00 India 1,220,800,359 17.20 United States 316,668,567 4.46 Indonesia 251,160,124 3.54 Brazil 201,009,622 2.83 Pakistan 193,238,868 2.72 Nigeria 174,507,539 2.46 Bangladesh 163,654,860 2.30 Russia 142,500,482 2.00 Japan 127,253,075 1.79 Total 4,140,379,334 58.32

Premium (US$mn) $245,511 $66,441 $1,270,884 $15,509 $82,267 $1,559 $1,828 $1,044 $26,027 $654,112 $2,365,182

% of world premium 5.32 1.44 27.55 0.34 1.78 0.03 0.04 0.02 0.56 14.18 51.26

Source: 2014 International insurance fact book (Swiss Re, sigma, No. 3/2013)

insurance, the effects of a catastrophe can be mitigated. Insurance provides incentives for people to reduce risk in order to reduce premiums. Insurers will require mandatory safety measures such as improved building codes that can save lives. Insurance pays losses promptly which can limit business interruption expense and help the local economy rebound. Poor countries bear the brunt of the damage. In 2013 two natural catastrophes had vastly different effects on local economies. Typhoon Haiyan in the Philippines caused $10 billion in total losses and 6,000 fatalities. Only 7 % of the losses were insured and the balance will burden the government for years. In contrast, Germany had hailstorms causing $4.8 billion in damage while 80 % of the losses were insured which had little effect on the economy. It is a compounded problem for poor countries because they not only do not purchase insurance but also unable to put safety measures in place to mitigate the losses when a catastrophe occurs (Munich 2014).

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

Insurance Market Insurance can be available from the private sector and government, and today there are new derivatives that can be used to access increased amounts of insurance. While coverage can be found for almost any risk, costs can be prohibitive and capacity can be an issue for certain lines of insurance. There is no specific coverage for meteorites, bolides, or even biological exposures. These cosmic hazards are treated in the same way natural catastrophes are by insurance. So a description of many lines of insurance is worth mention be it private, public, hybrid, or derivative.

Private Insurance Private insurance is what we think of as traditional insurance. It includes incorporated companies insuring life, health, and property casualty insurance. Property casualty insurance covers commercial general liability including business interruption, automobile, homeowners, marine, aviation, and space. Cosmic hazards are not excluded from any of these lines of insurance. Life and health coverages, with few exceptions, pay regardless of the cause of the loss. There are standard exclusions for flood and earthquake. Flood insurance can be purchased in the United States from the National Flood Insurance Program (NFIP) (see below). Earthquake coverage is available but is not often purchased except in susceptible areas.

Public Insurance Governments step in to provide insurance when it is unavailable or perceived to be cost prohibitive in the private sector. In the United States, the National Flood Insurance Program (NFIP) was created in 1968. There is no coverage for flood under standard homeowner, renters, or commercial property policies. Coverage is available from NFIP and some private insurers. The program was able to cover its losses until 2005 when Katrina required the program to borrow $16.8 billion from the treasury to cover the huge number of claims (GAO 2008). The program has been unable to charge adequate rates to cover losses which once again happened with the occurrence of super storm Sandy. There are no exclusions in the coverage for flood or tsunami caused by meteorites.

Hybrid Insurance Hybrid insurance is a combination of private and public programs. Nuclear facility insurance promulgated under the Price-Anderson Act and commercial launch liability insurance organized under the Commercial Space Launch Act (CSLA) in the United States are described later. These examples combine a layer of private insurance with excess layers of coverage provided by the government. Both programs came into effect to address the unavailability of insurance at the high limits of liability required to address what could be catastrophic events caused by ultrahazardous activities. Both programs were able to attract needed capacity and have been very successful. Similar programs have been developed in France and other countries.

Derivative Insurance Derivative insurance was started in the 1990s using insurance-linked securities (ILS) via catastrophe bonds. This was in response to the view that after hurricane Andrew and the Northridge earthquake, natural catastrophe exposures have grown. Because of population growth, rising real estate values, and development in coastal areas, the world is exposed to higher losses. In the United States, over 68 million people live in coastal areas susceptible to hurricanes, and 80 % of Californians live near active earthquake faults (GAO 2002). ILS provides a new way for insurance and reinsurance

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

companies to spread their risk to new risk takers. The increased capacity prevents insurers from having to limit coverage or raise premiums. The catastrophe bond market by the end of 2013 has grown to $20.3 billion. Insurance or reinsurance companies to bundle risks and attract new capital have always sponsored catastrophe bonds. The Metropolitan Transportation Authority in New York (MTA) in response to a reduction in available insurance after super storm Sandy completed a $200 million storm surge catastrophe bond offering. This was the first cat bond tied solely to storm surge and the first cat bond sponsored by a public entity that was not an insurance company (Mayer Brown 2013). Natural catastrophes will continue to generate higher losses in the future so new capacity of any kind is beneficial to the strength of the insurance market as a whole.

Space Insurance Space insurance covers the value of a satellite during launch and on-orbit operations until end of life. Commercial satellite owners or anyone who wants to protect their financial interest in a satellite purchases insurance. Government and science satellites such as GPS or weather satellites are typically not insured as they are public assets even though insurance could be available. Coverage includes the cost of the satellite, the launch, and insurance. Should a satellite become unusable, the reimbursement of each of these costs would be required to fully indemnify the satellite owner. Insurance is typically purchased in annual increments. The most exposed phase is the launch followed by the commissioning period, the time from final release from the launch vehicle until solar arrays deploy and it is fully operational. Satellite insurance is all-risk coverage with only a small set of exclusions. Due to the inaccessibility of space when a loss occurs, it may not be possible to find the cause of loss so all-risk coverage is the best approach. Exclusions cannot be enforced if the cause of loss is unknown. In part the standard exclusions include war, anti-satellite device, confiscation, nuclear reaction or radioactive contamination (except radiation naturally occurring in space), electromagnetic or radio frequency interference, willful acts of named insured, loss of revenue, and consequential damages. Insurance pays for any loss not excluded. The space insurance market currently insures approximately 205 satellites in orbit valued at $26 billion. On average there are about 30 insured satellites launched a year. The total space insurance market premium is currently about $750 million a year. Just two large satellite failures a year can wipe out an entire year’s premium (Global Aerospace 2014). Any increases in the frequency or severity of orbital debris, solar flares, launch vehicle failures, or generic product defects could lead to a capacity crunch. Insurance companies would take note and for their own survival would have to exclude coverage for such events or limit their exposure completely by exiting the space insurance market.

Space Market Capacity The capacity of a market is the amount of coverage it can provide if each insurer provides its maximum line of insurance. A space insurance policy is backed by multiple insurers each taking a quota-share amount of the value of the satellite. They may in turn resell the premium to yet other insurers. This process is known as reinsurance. In today’s market, the maximum sum insured that can be covered is around $600 million. So, if a satellite owner wants to insure their satellite for $700 million, they will find only $600 million will be available.

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Capacity can quickly become an issue when values exceed market capacity. Dual payloads on a single launch vehicle can exceed the capacity. As private industry gets more involved with space tourism or manned transports, they will look to insure their assets. The value of such spacecraft will likely exceed space market capacity and the search for new capacity will begin. Traditional property casualty markets will be looked to for capacity, but because this is property insurance and not liability, ILS or governmental options for additional capacity will not be available. The space insurance market is a subset of the overall aviation insurance market that includes airlines, aerospace manufacturers, general aviation, and war coverage. Space is just 15 % of the aviation market (Aon 2014). The aviation market worldwide is just a quarter of a percent of the world’s property casualty market. If space capacity is to increase, the effort will be to bring in non-aviation markets.

Solar Flares: Lloyd’s Realistic Disaster Scenarios Cosmic hazards pose risks to satellites in orbit while not of great concern during launch or deorbit. If orbital debris is large enough to be tracked or a solar event spotted soon enough, there may be time for loss mitigation. Satellites can be turned away from the oncoming debris or be placed in safe mode in case of a solar storm. Even the ISS has taken evasive action when debris has been detected in its path. These mitigation techniques are very limited and spacecraft remains at the mercy of the hostile space environment. Solar flares and CME can damage a large number of satellites simultaneously, which could overwhelm the space insurance market. Lloyd’s of London has established Realistic Disaster Scenarios (RDS), which address underwriters’ risk. This is a risk management procedure based on possible catastrophic events for the insurance company to test how robust their portfolio is. Due to the catastrophic nature of a solar flare event, a RDS addresses it. The proton flare RDS reads in part as follows: For the purposes of this RDS, it should be assumed that either a single anomalous large proton flare or a number of flares in quick succession results in a loss to all satellites in synchronous orbit. All live exposures in this orbit will be affected by the proton flare. Managing agents should assume a 5% insurance loss to all affected policies. (Lloyds 2014)

In answer to this, if 95 % of the $26 billion in insured satellites are GEO and there is a 5 % insurance loss to the GEO satellites, the loss is $1.2 billion. This is a rough overview of the RDS and this amount would represent a full market loss. Because the scenario is based on a 5 % loss of every risk, there is no differentiation on a specific portfolio. Underwriters may want to make further review as an actual event would likely damage some satellites more than others in which different underwriters would have different results based on the satellites they participate on and how large of a quota-share line they take on each.

Space Liability Insurance Third-party liability insurance is available for satellite launches for the launch provider, for owners of satellites in orbit, or owners when a deorbit event takes place like a space station or large satellite that may cause damage on earth. Product liability insurance is also available for components of launch vehicles or satellites. The insurance covers bodily injury as well as property damage. Bodily injury to astronauts has never been a focus as they have always been the responsibility of the

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

launching state. But, in the not too distant future, considerations must be made for bodily injury to spaceflight participants, the FAA nomenclature for space tourists. Cosmic hazards do not affect space liability insurance except as regards orbital debris. The exposure comes when a satellite has exceeded its operational life and it becomes another piece of orbital debris. The owner of the satellite will have a liability exposure as long as the satellite remains in orbit. In-orbit liability for satellites that are no longer operational is rarely purchased. Upper stages of launch vehicles can also create orbital debris. While launch liability is primarily focused on the losses that can be caused on earth, there can be this exposure in orbit. The space insurance market addressing satellites is very specialized and underwriters are knowledgeable about space and rocket science. Liability underwriters, on the other hand, may be found in the broader aviation market that addresses products liability or other aviation liabilities. Launch liability for US providers has always resided in the comprehensive product liability policy. The market capacity for liability is based on sub-limiting exposure by each market rather than the amount of worldwide capacity, as is the case for the space markets. Limits are based on appetite of insurers as well as dictated by laws in each country or international treaties. Governmental regimes and treaties are stated below. Launch liability primarily addressing bodily injury and property damage on earth has limits of liability based on the governing laws of the launching state. In the United States, it is based on the maximum probable loss under CSLA, and that limit varies depending on size of launch vehicle and location of launch but does not exceed $500 million. $500 million per occurrence is currently the maximum available limit for launch liability worldwide (CSLA 1984). In-orbit satellite liability covers damage to third party to satellites and space stations including inhabitants in orbit or on earth in the event of a deorbit. The limits purchased are at the option on the owner but may be dictated by the launching state. Required limits are usually $100 million or less. Property damage to satellites can be endorsed to product liability policies to cover component parts of launch vehicles or satellites. Currently, this coverage is limited by underwriters to $250 million for any one satellite.

Space Liability Occurrences

• Space Shuttle Columbia, 2003. Seven astronauts were lost on Space Shuttle Columbia when it exploded over Texas. Wreckage debris spread over 100 miles from which NASA collected 45,000 pieces. NASA issued claim forms to anyone wanting to make a bodily injury or property damage claim arising from the fallen debris. Few claims were made (Manikowski 2005). • Delta II 1997 launch failure damaged a few buildings and destroyed and damaged cars for which claims were made. • Space Shuttle Challenger, 1986. Seven astronauts died and product liability claims were paid by Morton Thiokol and the Federal Government. Apollo I, 1967. Three fatalities generated product liability claims against North American Rockwell. Space liability arises from treaties and regulations and significant ones are reviewed below. The most significant concept that is incorporated in the relevant legislations is that of cross waiver of liability. In an effort to reduce third-party claims, each party agrees not to make claims against the other while participating in the specific space activity. Additionally, the cross waivers flow down to related parties including contractors, subcontractors, and customers.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

The Outer Space Treaty The United Nations Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies came into force in October 1967. The Outer Space Treaty provides the basic framework on international space law, including the following principles: • States shall be responsible for national space activities whether carried out by governmental or non-governmental entities. • States shall be liable for damage caused by their space objects. • States shall avoid harmful contamination of space and celestial bodies (UN 1967).

The Liability Convention The United Nations Convention on International Liability for Damage Caused by Space Objects of 1972 provides that a launching state shall be absolutely liable to pay compensation for damage caused by its space objects on the surface of the earth or to aircraft and liable for damage due to its faults in space. The convention also provides for procedures for the settlement of claims for damages. The problem with placing all liability on the launching state has created a variety of problems with the rise of commercial space activities and the transfer of ownership of spacecraft (UN 1972).

The Intergovernmental Agreement The International Space Station Intergovernmental Agreement (1998), or IGA, is the treaty signed by the partners (Canada, Europe, Japan, Russia, and the United States) involved in the space station. The framework dictates that each of the partner countries shall be responsible for their nationals and the portions of the ISS they provide. The IGA recognizes the Liability Convention of 1972 and establishes cross waivers of liability between the partners, and each partner shall implement the cross waivers with any contractors or subcontractors (IGA 1998).

Ultrahazardous Insurance When in their infancy in the United States, the commercial launch and commercial nuclear industries faced the same issue of how to promote the privatization of an ultrahazardous activity. Insurance was just not available in the amounts required should an accident occur due to the large catastrophic nature.

The Price-Anderson Act The Price-Anderson Act became law in 1957, and its purpose was to ensure the availability of a large pool of funds to compensate the public in the event of a nuclear or radiological accident regardless of who is liable. The purpose of including this law is it provided the framework for CSLA. Also, it demonstrates needed cooperation between the private sector and government to address inadequate market capacity for liability limits of insurance. Coverage applied to a facility on an omnibus basis in that the same coverage provided to the owner/licensee is extended to anyone having exposure for design, construction, or operation of the facility. Three tiers of protection were put in place as stated below (Price-Anderson 1957):

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

1. Insurance with a limit of $375 million paid for by each facility and insured by a pool of 60 companies (American Nuclear Insurers). 2. Self-insurance that is a fund each facility contributes to and currently amounts to $12.6 billion. This is a mutual insurance where each facility is partnering with the others to create a pool of funds. 3. Congressional mandate. To date the ANI has paid out $151 million with $70 million of that related to the 1979 Three Mile Island accident and $65 million claims to the Department of Energy (NEI 2014). Outside the United States, the costliest nuclear accident was in Kiev, Ukraine, at Chernobyl in 1986 that cost $6.7 billion and killed 4,056 people. This excludes the meltdown in 2011 at Fukushima, Japan, which although a major nuclear accident did not directly kill people due to nuclear exposure. The payout from this event continues to produce major payout of claims (Insurance Information Institute (iii) 2014).

The Commercial Space Launch Act The Commercial Space Launch Act of 1984 (CSLA) was modeled after the Price-Anderson Act. The purpose of CSLA was to encourage commercial space launches by the private sector. Private companies required assurances from the government that they would be protected should catastrophe strike (CSLA 1984). The Federal Aviation Administration Office of Commercial Space Transportation (AST) licenses each launch provider. There are three tiers to the program: 1. Insurance. The launch provider is the licensee and they apply to FAA/AST for a launch license. The FAA calculates a maximum probable loss (MPL) based on the type of launch vehicle, the launch location, and the mission. The licensee must purchase insurance up to the amount of the MPL up to a maximum of $500 million ($100 million for government property). Importantly, cross waivers are to be in place for the government, contractors, subcontractors, and customers of the launch provider with a flow down requirement. 2. The second layer of CSLA provides that by congressional appropriation of funds up to $1.5 billion in 1984 dollars (As of 2012, the inflation adjusted amount $2.7 billion). 3. The third tier of coverage reverts back to the launch provider. Outside the United States, similar insurance structures have been implemented to protect the private launch industry. Most countries have used CSLA as a model but often improve on it. Russia, France, China, and Japan require insurance for the first tier but it is typically $300 million or less, and the second tier of government indemnification has no upper limit so there exists no third tier exposing once again the launch provider. The laws in these countries also do not contain a sunset clause as is the case in the United States. The presence of a sunset clause that could end the program leaves the future uncertain for launch providers and makes them less inclined to invest.

Spaceflight Participant Exposure Bodily injury to humans in space is now limited to travel on the Soyuz (post shuttle), International Space Station (ISS), and Chinese programs. Soon it appears the exposure shall increase with the onset of space tourism, a replacement shuttle, and projects underway to travel back to the moon and even Mars. While the IGA and the Space Treaties discussed address a legal framework for the ISS, Page 13 of 18

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the United States has yet to solidify a structure for space tourism. Initially, space tourism will be suborbital parabolic flights that will not reach orbit. The launch vehicles for spaceflight participants are new and have yet to accumulate proven performance. There is little to compare it with but one could look at the space shuttle experience as a guide. The Challenger and Columbia disasters represented the two failures over 135 shuttle missions and 14 astronauts perished of 848 (NASA 2014). It could be argued that the private sector will not be as disciplined as NASA and the failure rate could be greater than one failure every 68 missions or one in every 60 spaceflight participants is killed.

Near-Earth Object Insurance A near-earth object collides with the earth. The damage caused depends on many factors including size, composition, trajectory, speed, and most importantly point of impact. There is a 30 % chance it will hit land and perhaps a very small chance that a large meteorite would directly hit a large city. Damage from the smallest scale to the largest manageable catastrophe would trigger insurance coverage. An unmanageable event would be a catastrophe so large that damages would exceed the resources of insurance companies and they would default on coverage. What is the point that insurers would be unable to respond to a super catastrophe is hard to say. Depending on the insurance company, each will have very different concentrations of risk to specific geographic areas and their size of reserves will vary. The largest natural catastrophe to date based on total losses would be the 2011 earthquake/tsunami in Japan which had 15,840 fatalities, $210 billion in overall losses of which $40 billion of the losses were insured (Munich Re 2013a, b). The second largest overall loss would be the combined losses of hurricanes Katrina, Rita, and Wilma in 2005 which had overall losses of $176 billion of which $120 billion was insured losses (IAIS 2012). The amount of losses will be significantly larger in affluent areas of the world because of the value of the property and the ability and interest in purchasing insurance. As noted before, the United States and Japan account for 42 % of worldwide insurance premiums. While total losses in other areas of the world may have larger numbers of fatalities or larger overall losses, it is the more affluent that will have the highest insured losses. Table 3 shows the distribution of losses in respective continents over a 32-year period. For the period overall losses totaled $3.8 trillion worldwide with 37 % of them in North America. However, North America had 64 % of worldwide insured losses. Thus, all countries other than North America had 63 % of the overall losses or $2.25 trillion and of that amount only $344 billion was insured losses. The disproportion is staggering (NatCatSERVICE 2013). Table 3 Worldwide distribution of natural catastrophes fatalities and losses Natural catastrophes worldwide 1980–2012 Continent Fatalities % North America 290,000 12 South America 50,000 2 Europe 150,000 7 Africa 610,000 27 Asia 1,180,000 52 Australia/Oceania 5,900 1 Total 2,300,000

Overall losses (US$mn) $1,400,000 $100,000 $500,000 $45,000 $1,600,000 $105,000 $3,800,000

% 37 3 15 1 41 3

Insured losses (US$mn) $620,000 $10,000 $160,000 $2,100 $130,000 $42,000 $970,000

% 64 1 16 1 14 5

Source: NatCatSERVICE, January 2013 Page 14 of 18

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

Tunguska Event Over New York City On June 30, 1908, a comet or asteroid exploded over the Tunguska River, a remote area in Russia. The event leveled 80 million trees over an area of 2,000 km2. The object is estimated to have been 50 m in diameter and the explosion was equivalent to a 10 megaton TNT explosion. Fortunately, the Tunguska airburst was in a remote area so the only damage was to trees. But, what if that event had occurred over a major city? In 2009 Risk Management Solutions did a study of what the effect of the Tunguska event would be if it were to occur over the center of Manhattan. The study estimated property losses to be $1.19 trillion, fatalities of 3.2 million, and injuries to 3.76 million people (Mignan 2009). The RMS study did not estimate what the insured loss amount would be for this scenario but it would be significant. For discussions sake very rough assumptions can perhaps be made to arrive at an insured loss figure. By referring to Table 3 in North America, it is found that insured losses are 44.3 % of the overall losses. Applying that to this scenario gives us $527 billion in insured property losses. This is over four times that of the Katrina, Rita, and Wilma hurricanes combined. Insurance companies would be distressed and some would fail. The state of New York and the Federal Government would need to provide a staggering amount of additional funding. This would be the largest loss in modern history. As devastating as this would be to the US infrastructure and financial resources would be in place to help it recover. If this event happened in Delhi, India, with a population of 25 million, the fatalities would be much higher and financial burden would be placed on the government as they purchase little insurance on a per capita basis. In terms of people and infrastructure loss, the largest potential loss would be if the impact covered the Tokyo and Yokohama metropolitan area.

Biological Hazards Since the first time man traveled above our atmosphere, there has been concern with the unknown biological hazards that might be brought back to earth. It would appear these fears are unfounded, as nothing involving exploration to date has caused an issue. But, man will continue to travel further and bring back more objects of interest so there is no way of knowing what extraterrestrial contaminants exist. The exposure to humans from an insurance perspective can be equated to the exposure of an influenza pandemic. The losses would be from sickness and fatalities. Life, health, and worker’s compensation insurance would pay the losses. RMS did a study on what would cause the greatest losses as regards fatalities and injuries. The perils of most concern were earthquake, terrorist attack, industrial accident, and influenza pandemic. It was the influenza pandemic that generated the highest number of fatalities. Of the largest fatal events to have occurred in the United States, the top three are from influenza pandemic. See Table 4 (RMS 2004). The RMS pandemic scenario was based on nationwide spread only in the United States. The scenario describes the outbreak of a standard strain of human flu with a mortality rate of 0.5 %. The scenario results in 10,000,000 illnesses with 200,000 fatalities costing the industry a total of $39.9 billion. This size of a loss would be manageable by the insurance industry but put a strain on the economy, as so many people would be out of work. But, the fear would be that an extraterrestrial strain would have a higher mortality rate, and unlike this study the view would be a global one not just the United States. A more lethal flu strain such as avian strain A (H5N1) has a 30 % mortality rate or the Ebola virus has up to a 90 % mortality rate. This would be devastating worldwide.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_78-1 # Springer International Publishing Switzerland 2014

Table 4 Historical death tolls from different types of US catastrophes Year 1918 1957 1968 1900 2001 1889

Event Influenza pandemic Influenza pandemic Influenza pandemic Hurricane 9/11 terrorist attack Dam burst in rain

Location Nationwide Nationwide Nationwide Galveston, TX DC, NY, PA Johnstown, PA

Fatalities 500,000 70,000 40,000 6,000 3,031 2,209

Source: Risk management solutions: catastrophe, injury, and insurance

Conclusion One can only speculate about the catastrophic losses that can possibly come from cosmic hazards. Clearly the impacts and the nature of the catastrophe would be widely different depending on asteroid or comet impact, extreme solar events, orbital hazards, or biological infections from space. It seems clear that private insurance could not provide anywhere near complete and comprehensive coverage and that governmental assistance must be the prime element of a recovery process. As shown by the above statistics, the degree of insurance and “insurability” varies widely around the world. This makes it quite difficult to create any type of comprehensive multinational approach to insurance related to cosmic hazards. The strong conclusion that emerges from this analysis is that preventive actions to protect against cosmic hazards would seem to be the wisest way to invest resources. It has been noted by the president of the B612 that the Sentinel Infrared Telescope that could provide a hundred-year warning system for asteroids down to 30 m in size could be built and deployed for the cost of building a modern urban overpass system. Investment in million-dollar warning systems against cosmic hazards versus trying to insure against trillion-dollar cosmic hazard events would seem a wise overall strategy.

Cross-References ▶ Economic Challenges of Financing Planetary Defense ▶ Hazard of Orbital Debris ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Regulatory Aspects Associated with Response to Cosmic Hazards

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References AIR Worldwide Corporation (2013) The coastline at risk: 2013 update of the estimated insured value of U.S. coastal properties. http://www.air-worldwide.com/Facet-Search/Search-Results/. Accessed Sept 2014 Aircraft Builders Council, Inc. (2013) Space weather forecast: blackouts with a chance of business interruption. Property casualty 360 http://www.iwpubs.com/CustomPages/CAPreview.asp?p= 16&ispreview=1&articleid=114221&editionid=21214&memberid=0&letterid=40401788&_ g=890F66C1819146C6A7C1395C90B8979D&_s=DF5B351A. Accessed Sept 2014 Aon Risk Solutions Global Broking Centre, Aviation (2014) The airport casualty market overview. ACI-NA Annual risk management conference by John C. Geisen. http://www.aci-na.org/sites/ default/files/gs1_-airport_casualty_market_update_john_geisen.pdf. Accessed Sept 2014 Baranoff E, Brockett PL, Kahane Y (2014) Risk management for enterprises and individuals, v. 1.0. Flat World Education, Inc. http://catalog.flatworldknowledge.com/bookhub/1?e=baranoffch06_s03. Accessed Sept 2014 Commercial Space Launch Act (1984) Public law 98–575, 98th congress. 98 STAT. 3055. https:// www.govtrack.us/congress/bills/98/hr3942/text. Accessed Sept 2014 Ferris T (2012) Sun struck, the space-weather forecast for the next few years: solar storms, with a chance of catastrophic blackouts on Earth. Are we prepared? Natl Geogr 221(6):36–53 Global Aerospace Underwriting Managers, Inc (2014) Company data in response to Lloyd’s realistic disaster scenarios, scenario specification January 2014, 19. Satellite Risks 19.1 Insurance Information Institute (iii) (2014a) 2014 International insurance fact book world life and nonlife insurance premiums. Premium source: swiss Re, sigma, No. 3/2013. Population source: U.S. Central Intelligence Agency. http://www.iii.org/publications/insurance-fact-book-2014. Accessed Sept 2014 Insurance Information Institute (iii) (2014b) 2014 International insurance fact book 20 costliest nuclear disasters, source: Benjamin K. Sovacool, contesting the future of nuclear power: a critical global assessment of atomic energy. World Scientific, London, 2011 International Association of Insurance Supervisors (IAIS) (2012) Global insurance market report (GIMAR), 2012 edition. http://www.iaisweb.org/Global-Insurance-Market-Report-GIMAR-962. Accessed Sept 2014 International Space Station Intergovernmental Agreement (1998) http://www.esa.int/Our_Activi ties/Human_Spaceflight/International_Space_Station/International_Space_Station_legal_frame work. Accessed Sept 2014 Lloyds (2014) Realistic disaster scenarios, scenario specifications. EM 102V1.0 http://www.lloyds. com/~/media/Files/The%20Market/Tools%20and%20resources/Exposure%20management/2% 20%20RDS%20%20Scenario%20Specification%20%20January%202014.pdf. Accessed Sept 2014 Manikowski P (2005) The columbia space shuttle tragedy: third-party liability implications for the insurance of space losses. Risk Manage Insur Rev 8(1):141–150 Mignan A (2009) Comet and asteroid risk: an analysis of the 1908 tunguska event, RMS special report. Risk Management Solutions, Inc. http://www.collectionspace.it/WEB-DOCUMENTI/ 1908_Tunguska_Event.pdf. Accessed Sept 2014 Munich Re (2013a) Significant natural catastrophes 1980–2012, 10 costliest events worldwide ordered by overall losses. http://mrphillipsibgeog.wikispaces.com/file/view/NatCatSERVICE_ significant_eco_en.pdf. Accessed Sept 2014

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Munich Re (2013b) NatCatSERVICE Geophysical events worldwide 1980–2012. http://www. munichre.com/en/reinsurance/business/non-life/natcatservice/annual-statistics/index.html. Accessed Sept 2014 Munich Re (2014) TOPICS GEO Natural catastrophes 2013 analyses, assessments, positions. http:// www.munichreamerica.com/site/mram/get/documents_E236640509/mram/assetpool.mr_amer ica/PDFs/3_Publications/Topics_Geo_2013_us.pdf. Accessed Sept 2014 NASA (2014) Space shuttle, mission information. http://www.nasa.gov/mission_pages/shuttle/ shuttlemissions/index.html. Accessed Sept 2014 NASA Orbital Debris Program Office (2014) http://orbitaldebris.jsc.nasa.gov. Accessed Sept 2014 Nuclear Energy Institute (2014) Price-anderson act provides effective liability insurance for nuclear power plants at no cost to the public, fact sheet. http://www.nei.org/Master-Document-Folder/ Backgrounders/Fact-Sheets/Insurance-Price-Anderson-Act-Provides-Effective-Li. Accessed Sept 2014 Price-Anderson Act (1957) 42 U.S. code 2210 – Indemnification and limitation of liability. http:// www.law.cornell.edu/uscode/text/42/2210. Accessed Sept 2014 Risk Management Solutions, Inc (2004) Catastrophe, injury, and insurance: the impact of catastrophes on workers compensation, life, and health insurance. http://static.rms.com/email/documents/ liferisks/reports/catastrophe-injury-and-insurance.pdf. Accessed Sept 2014 Satellite News Digest (2003) Midori II (ADEOS II). http://www.sat-index.co.uk/failures/index. html?http://www.sat-index.co.uk/failures/midori2.html. Accessed Sept 2014 The Mayer Brown Global Insurance Group (2013) Trends and developments in mergers & acquisitions, corporate finance, insurance-linked securities, and regulatory matters. Global Insurance Industry Year in Review 2013. http://www.mayerbrown.com/Global-Insurance-Industry-Year-inReview-2013/. Accessed Sept 2014 United Nations Convention on International Liability for Damage Caused by Space Objects (1972) http://www.oosa.unvienna.org/oosa/SpaceLaw/liability.html. Accessed Sept 2014 United Nations Office for Outer Space Affairs (1967) Treaty on principles governing the activities of states in the exploration and use of outer space, including the Moon and other celestial bodies. http://www.unoosa.org/oosa/SpaceLaw/outerspt.html. Accessed Sept 2014 United Nations, Department of Economic and Social Affairs (2012) WORLD: total population. http://esa.un.org/unpd/ppp/Figures-Output/Population/PPP_Total-Population.htm. Accessed Sept 2014 United States General Accounting Office (2002) Testimony before the subcommittee on oversight and investigations, committee on financial services, house of representatives. By David M. D’Agostino. http://www.gao.gov/assets/110/109634.pdf. Accessed Sept 2014 United States Government Accountability Office (2008) FEMA’s rate-setting process warrants attention. GAO-09-12. http://www.gao.gov/assets/290/283035.pdf. Accessed Sept 2014

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_79-1 # Springer International Publishing Switzerland 2014

International Legal Consideration of Cosmic Hazards and Planetary Defense Fabio Tronchetti* School of Law, Harbin Institute of Technology, Harbin, Heilongjiang, People’s Republic of China School of Law, University of Mississippi, Oxford, MS, USA

Abstract The relevance and importance of law for the issue of planetary defense are, and should be seen as, instruments facilitating international cooperation for avoiding legal risks should they arise while carrying out planetary defense operations. Currently, there is a significant absence of a specific legal and regulatory framework governing planetary defense since the international community has for the most part not addressed this matter seriously in the past. There is one important exception in the form of the University of Nebraska study commissioned by the Secure World Foundation (Legal Aspects of NEO Threat Response). In short, there is little legal literature on this issue as the space law community has not yet conducted extensive research in this regard. The situation may be expected to change as the threats from cosmic hazards become more known broadly and processes within the United Nations and the Committee on the Peaceful Uses of Outer Space continue to work in this area particularly through the Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA). This chapter briefly addresses and highlighted the need for clarifying the main legal issues relevant to planetary defense; i.e., the authority and duty to intervene, the responsibility to undertake planetary defense initiatives, as well as possible liability for damage or injury caused during such operations. It will also identify the challenges to existing international legal rules and suggest possible amendments thereto for undertaking planetary defense. Legal issues related to international response to cosmic disasters will also be briefly addressed. International space law, as provided for in the United Nations (UN) space treaties and in a number of General Assembly resolutions, lacks specific as well as binding provisions dealing with the protection of the Earth from natural cosmic hazards. Nevertheless recent actions by the UN General Assembly have led to new efforts in these areas. This has been seen in the creation in 2010 and 2010 of UN COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA). This has even more recently seen in the actions of the UN General Assembly to activate the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG) (“International asteroid warning network: first meeting of the steering committee” http://www.minorplanetcenter.net/IAWN/ and “SMPAG: summary of the first meeting” http://blogs. esa.int/rocketscience/2014/02/12/smpag-summary-of-the-first-meeting/comment-page-1/). The prime objective of this analysis is to examine what recent activities have been undertaken by the United Nations General Assembly, the UN Committee on the Peaceful Uses of Outer Space (UN COPUOS), and the UN Committee on Defense Analysis to develop legal or regulatory mechanisms concerning cosmic hazards and planetary defense.

*Email: [email protected] Page 1 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_79-1 # Springer International Publishing Switzerland 2014

The parallel part of this analysis is to consider where principles of public international law can aid in the future development of relevant regulatory or legal concepts to address the major issues presented by cosmic threats.

Keywords Action group-14; Inter-Agency Space Debris Coordination Committee; International Asteroid Warning Network (IAWN); International Astronomical Union; Liability Convention; Minor Planet Center; Outer Space Treaty; Principles of public international law; Registration committee; Space Mission Planning Advisory Group (SMPAG); United Nations; UN Committee on Defense Analysis; UN Committee on the Peaceful Uses of Outer Space (UN COPUOS); Working Group on Near-Earth Objects (WGNEO); Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA)

Introduction The fact that efforts to address cosmic hazards took some time to occur is not surprising. The space treaties were formulated when the primary goal of their drafters was not to address hypothetical threats coming from outer space but to lay down basic rules enabling all States to participate in the exploration and use of outer space and prevent outer space from becoming an area of conflict. In the decades that followed, attention was paid to more urgent issues, such as the legal questions related to remote sensing from space, direct broadcasting with satellites, and the use of nuclear power sources. In order to fill in the gaps that international space law presents in relation to the organization of planetary defense the way forward appears to be two fold. On one hand various initiatives were being carried out through the United Nations, such as the UN General Assembly, the Committee on the Peaceful Uses of Outer Space, the Action Group 14, the COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities (LTSSA), the International Asteroid Warning Network (IAWN), the Space Mission Planning Advisory Group, and even the UN Committee on Defense Analysis. The other part of the process is to consider ways that it is possible to rely on principles of public international law that might be invoked in the case of planetary defense or in cases involving a response to an international cosmic disaster such as international peace-keeping operation. The relevance and applicability of public international law to outer space activities is clearly spelled out in Article III of the Outer Space Treaty, and this can also help define a practical way forward. Principles such as the right to national defense and intergenerational equity come particularly into play. Thus Article III of the UN Charter (UN Charter) can assist both in understanding a coordinated international effort related to space hazards and methods to proceed with regard to planetary defense (Outer Space Treaty). For the purpose of this analysis, notions like the right to act in self-defense, the responsibility to protect, and the intergenerational equity remain of particular significance in mounting a response to a cosmic hazard. While self-defense is a right attributed to States under Art. 51 of the United Nations Charter, the responsibility to protect and the concept of intergenerational equity are not strictly legal rights and/or obligations but norms of international law which are currently strongly emerging in connection with gross human rights violations and environmental protection. It is important, however, to point out that the application of these

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_79-1 # Springer International Publishing Switzerland 2014

principles to a natural cosmic threat is not an automatic process, as normally they are utilized in different contexts and to pursue different goals, most notably on a nation to nation basis. Recently, the international community has started acknowledging the danger that natural space objects, particularly near-Earth objects (NEO), pose and taking concrete step to address it. The COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities has recognized not only the threat of space debris and near-Earth objects but has also recognized space weather and other cosmic hazards. This has been reflected in the formation of expert groups to consider these dangers from space. The initiatives undertaken within the United Nations have focused on the technical aspects of cosmic hazard prevention and mitigation, rather than addressing legal problems. Most recently the Legal Subcommittee of COPUOS has also begun to consider the legal and regulatory matters as well. Nongovernmental organizations such as the Security World Foundation have also contributed to the discussion and preliminary considerations of legal issues that are involved. Even though international space law does not include measures dedicated to the organization and implementation of planetary defense initiatives, this does not amount to saying that it is irrelevant for that purpose. Actually quite the reverse is true. Instead, existing international space treaties and conventions may very well contribute to setting up similar initiatives, which, in any case, must be consistent with the basic international space law principles (Outer Space Treaty; Registration Convention; Rescue Convention, Liability Convention, Charter of the United Nations).

Positive Contribution of Current International Law for a Planetary Defense From the discussions currently taking place within the Technical and Scientific Subcommittee of the UN Committee on the Peaceful Uses of Outer Space (UN COPUOS), it appears that States view international cooperation as the foundation for any action aimed at responding to the threat posed by a natural cosmic hazard. This means that in the most likely scenario any such action will not be carried out by a State unilaterally but rather by a group of willing countries as shown in the diagram below. This approach is consistent with the fundamental principles of international space law, which can be seen as actually favoring similar multilateral initiatives. Indeed, the importance of promoting and enabling international cooperation is emphasized in the UN space treaties on multiple occasions. Additionally, the legality of an international action for a planetary defense is, at least indirectly, supported by the words of Article I, paragraph 1, of the Outer Space Treaty, which stipulates that “the exploration and use of outer space. . . shall be carried out for the benefit and in the interests of all countries. . . and shall be the province of all mankind” (Outer Space Treaty). This provision is broadly understood to signify that the exploration and use of outer space shall not be the “private business” of a single State but that all countries should directly or indirectly benefit from any such activity in outer space (Hobe (2009)). In the event of a collective action for planetary defense, it is clear that such an action would not be intended to benefit and protect only the States taking part in it but all countries or, better, humankind as a whole (International Cooperation). The Outer Space Treaty also contains provisions that are relevant for the preparation and the implementation of an international initiative for planetary defense. For example, on one side it requires State Parties to undertake appropriate international consultations before proceeding with a space activity or experiment that may cause harmful interference with the activities of other States, and, on the other side, it demands them to guarantee, to the greatest extent feasible, transparency about their operations in space (Outer Space Treaty, art. IX and XI). Thus, the States involved in a planetary defense initiative must timely inform other States about the dangers that it may pose and

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_79-1 # Springer International Publishing Switzerland 2014

guarantee an adequate level of transparency over their activities. Such duties would be even more pressing if the initiative would be undertaken on a unilateral basis. Importantly, no State can be forced to undertake or cooperate in an international action for planetary defense. States are free to determine when to participate in international cooperation and under which conditions. This idea is clearly affirmed in the 1996 Space Benefits Declaration. In particular Principle two states: “States are free to determine all aspects of their participation in International cooperation in the exploration and use of outer space on an equitable and mutually acceptable basis. Contractual terms in such cooperative ventures should be fair and reasonable and they should be in full compliance with the legitimate rights and interests of the parties concerned as, for example, with intellectual property rights” (Declaration on International Cooperation).

Key Gaps in International Law Relating to Planetary Defense Initiatives Despite providing a basic contribution toward organizing a planetary defense, international space law leaves numerous and fundamental questions related to the preparation, implementation, and consequences of such an action open. Some of these questions are briefly discussed below:

Duty to Intervene A preliminary but important issue is whether or not States have a duty to intervene in the event of a natural cosmic hazard threatening the Earth (Legal Aspects of NEO Threat Response). Essentially, the question is if in the presence of reliable data confirming the danger posed by a natural cosmic body and of effective means to avoid its collision with the Earth, are States to be considered under the obligation to take action? The answer currently is that no explicit obligation exists. Under present general international law and international space treaties and conventions, no legal requirement exists. This, however, does not amount to say that States do not have a right to intervene or even have a “moral” responsibility to do so. Eventually, an effective duty to take action might be agreed upon at a later stage. International space law contains provisions that, in principle, can be used to support a right to intervene in case of a natural cosmic threat. For example, the Outer Space Treaty calls for mutual assistance, for “conduct by States of their activities (. . .) with due regard to the corresponding interests of other States,” and for space activities “to avoid (. . .) adverse changes in the environment of the Earth” (Outer Space Treaty, art. XI). These provisions encourage States to take actions, to the greatest extent possible, for the collective good rather than in the interest of a single State. Nevertheless, due to their abstract nature and lack of concrete standards of behavior, they cannot be seen as imposing on technologically advanced States a collective duty to protect the Earth in the event of a natural cosmic threat. Significantly, in the context of disaster prevention and mitigation, a practice has emerged according to which States possessing advanced (remote sensing) satellite capabilities voluntarily make their resources available to less advanced States to warn them about upcoming natural dangers and to help coordinating post-disaster rescue operations. Such a practice, which has its origin in the UN Remote Sensing Principles (Principles Relating to Remote Sensing), has found concrete implementation within the International Charter on Space and Major Disasters. The Charter is an instrument that has been put in place to encourage cooperation in the use of space facilities to support the management of crisis arising out of natural and man-made disasters (International Charter on Space). Parties to the Charter are not States, but space agencies and space system operators. From a legal standpoint, the Charter is not a legally binding per se, but it is an instrument to which Parties participate on a voluntary basis without exchange of funds among them. Although the Charter is not Page 4 of 14

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directly legally binding on States, one should always keep in mind that space agencies are governmental agencies and, as a consequence, their activities are coordinated with and are financed by the respective governments. Thus, the success of the Charter that has now been activated hundreds of times shows that States, operating through their space agencies, may fruitfully cooperate in using their space-related resources to achieve common goals, rather than pursuing mere individual ones. From this perspective the Charter represents a significant precedent for States willing to take collective action to protect the Earth from a natural cosmic disaster (International Charter on Space; Legal Aspects of NEO Threat Response). General international law, while containing principles that may provide a legal foundation for an international action for planetary defense, does not establish a clear-cut obligation to do so. In this respect, one could think of the so-called responsibility to protect, a concept which has emerged in connection with human right protection. Accordingly, in view of gross violation of human rights in a State’s territory and of the incapacity of the government of that State to halt it, the international community may have the responsibility to intervene. This responsibility, it has been submitted, may include a “responsibility to react,” a “responsibility to prevent,” and a “responsibility to rebuild” as well as an evaluation of the costs and benefits of intervention versus nonintervention (Legal Aspects of NEO Threat Response). There are, nevertheless, issues related to the possible application of a “responsibility to protect” in relation to a planetary defense initiative. Firstly, it is doubtable whether such a “responsibility” constitutes a rule of international law. Secondly, it is unclear whether it establishes an “obligation” to take action. Thirdly, it raises questions of violation of territorial sovereignty of the State in which the intervention takes place. Fourthly, a “responsibility to protect” should be seen as a collective responsibility and should be implemented through collective security arrangements established under the UN Charter, i.e., within the General Assembly or the Security Council. Thus, no single State could likely validly unilaterally claim the responsibility to protect (The Responsibility to Protect). For the above reasons, it seems problematic to rely too much on the “responsibility to protect” principle to justify a planetary defense. However, if one wants to proceed in this direction despite these reservations, the following two preconditions should be, arguably, present: (a) the threat should be detected and detectable, and it should be presumably agreed upon to be of sufficient severity; (b) acceptance of the idea that while a State is primarily responsible to protect fundamental human rights of their respective populations, including the right to life, in case such a State would be unable to provide protection against a major natural cosmic threat, the international community should be attributed a secondary obligation to do so. Every State has the right to defend its citizens against, essentially, any threat provided that its actions are consistent with relevant international obligations and do not cause disproportionate harms to other States. The UN Charter recognizes the right of States to act in self-defense and the possibility to exercise this right both individually or collectively (Charter of the United Nations). The UN Charter limits its applicability to the need to respond to an armed attack by another State. As in the case of a natural cosmic threat, the element of an “armed attack” would be missing, the right to act in self-defense to counteract a natural cosmic threat could be debatable. However, if one accepts a broader understanding of the concept of self-defense, which includes the right of a State to take actions to protect its citizens without threatening the territorial sovereignty of another State, there would be room to argue that the right of self-defense could be used to sustain the legality of a planetary defense initiative. Nevertheless, recognizing the right to act in (global) self-defense to protect the Earth from a cosmic hazard does not equate to say that there is a duty for States to do

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so. Theoretically, a duty to act would exist if it were enshrined in a rule of customary nature; nevertheless, a similar rule is far from being present at the present stage. It could also be possible to support the argument that States have a responsibility to take action for a planetary defense initiative based on the concept of intergenerational equity. Such a concept has become an integral component of international law dealing with environmental protection, resource utilization, and socioeconomic development. In short, it calls States to take into account the rights of present and future generation in relation to the use of resources and the preservation of the environment. The concept of intergenerational equity, which has found expression, for example, in the 1972 Stockholm Declaration and in a number of other subsequent documents (The Stockholm Declaration) and in the UN Agenda 21 (Agenda 21 of 1992 UN Conference), does not have mandatory nature and its implementation is left to the will of and coordination among States. Considering the devastating effects that the impact of a NEO would have on Earth and its longlasting negative impact on mankind, the concept of intergeneration equity, thus, provides an additional element to support a collective response to such a cosmic threat.

Need for Authorization Another relevant question is whether an international action for planetary defense would require authorization, and, if so, who would be the entity entitled to grant it. Before addressing this question, one should keep in mind that such an international action would be undertaken on behalf of mankind and, most likely, would also include the use of weapons. Mankind does not exist as an independent legal subject under international law; therefore, States could not be directly authorized to carry out a planetary defense initiative by mankind or by a body representing it. One could argue that the United Nations represents mankind, because nearly all States are members in it. However, this does not automatically makes it a “representative” of mankind as a whole and is not a sufficient reason per se to claim that States should obtain a permission before carrying out a planetary defense response. The need for obtaining a UN mandate could be derived from the envisaged recourse to armed force in the context of this response. One of the main goals of the United Nations and, in particular, of the UN Security Council is to maintain international peace and security. In the presence of a threat to them, the Security Council may decide measures not involving the use of armed force as well as armed measures. These measures are officially authorized by means of a dedicated Security Council Resolution. Authorization by the Security Council is a condition sine qua non for the use of force under the UN Charter system (Charter of the United Nations, Chapters VI and VII). A natural cosmic hazard could be viewed to constitute, at least indirectly, a threat to international peace and security, due to the potential devastating consequences that it could have upon impact on the Earth’s surface. If such interpretation of the expression “threat to international peace and security” is accepted, there would be room to argue that an international initiative to respond to a natural cosmic threat should be authorized by the Security Council, especially if it would include the use of armed force. Such an approach would have the advantage of utilizing practices and procedures already existing within the United Nations. One, however, should always be aware that an authorization by the Security Council is automatic, as some of its permanent members (i.e., China, France, the Russian Federation, the UK, and the USA) could veto it. Presumably since all countries could be a direct or indirect risk, this would not be the case.

Unilateral Planetary Defense Initiative In principle, the existing law does not prevent a State to organize and undertake a planetary defense initiative on a unilateral basis. However, it seems unlikely that a State might follow this path, due to Page 6 of 14

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the high costs and risks involved. It is realistic to imagine that a State might decide to act on its own if: (a) it is technically capable to do so and (b) no other State is willing to join it. This might be particularly the case if the area expected to be directly affected by the impact of the natural cosmic hazard would be exclusively in its national territory. The logic of countries choosing to or not to participate on such a basis would remain questionable since most major cosmic hazards, despite the area of impact, would eventually have worldwide consequences. The question is whether such a unilateral action would require an authorization from the UN Security Council. Under the UN Charter, a State is entitled to act in self-defense until the Security Council intervenes (Charter of the United Nations, art 51). Thus, if one accepts the idea that a planetary defense initiative constitutes an act of self-defense, it could be argued that a State need not wait for the approval of the Security Council before proceeding with its individual initiative. However, this argument could be counteracted by pointing out that, as a consequence of the danger that this initiative would pose to operational space objects (i.e., satellites) and to the space environment, a State should obtain authorization from the Security Council prior to the commencement of operations. Such an authorization would provide a legal basis for the use of military force in space and would constitute a valid instrument to ensure that the authorized State complies with international obligations and does not intentionally endanger or disrupt other States’ space assets. Additionally, such a State would have to address liability issues for damage caused in the context of its unilateral planetary defense initiative. Indeed, there would be room to claim that, irrespective of the humanitarian character of the initiative, the State that undertakes it on a unilateral basis would assume full responsibility and liability for any damage it may cause.

Participation by Private Entities Another relevant point is whether or not private entities should be allowed to participate in a planetary defense initiative (Legal Aspects of NEO Threat Response). States could indeed consider drawing the private sector into this context of this initiative due to its high costs; at the same time, private entities could view their involvement as a potentially profitable and beneficial opportunity. Any involvement of the private sector should be limited by the understanding that a planetary defense mission is a public (government) affair, the primary goal of which is humanitarian. Obviously, much will depend on the role that private entities will effectively play that could range from merely being involved in the manufacturing process to be a partner in a public-private partnership or even to act as a stand-alone profit-generating venture. The more the entity will act independently and for profit-related purposes, the more there will be a need for an authorization and control by a State. These considerations would also apply in the event that a private entity or nongovernmental agency was asked to participate in a recovery operation in an instance where the government in the jurisdiction was not able to request aid due to damages. Under international space law, private entities may carry out space activities as long as they do so under the umbrella of an “appropriate State,” which authorizes and continuously supervises these activities (Outer Space Treaty, art. VI). The appropriate State is internationally responsible for the authorized private space activities and is obliged to ensure, inter alia, their compliance with international obligations. Such a State might also face liability claims for damage occurring in the course of the authorized and supervised activities of the private companies or nongovernmental organization.

Use of Weapons, Including Nuclear Weapons, in a Planetary Defense Mission A planetary defense initiative most likely will encompass recourse to physical force in space (a kinetic vector impacting the NEO), perhaps also nuclear force. It is worth exploring the legality Page 7 of 14

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of similar plans in the light of general international law and the specific international space law regime. Currently, a specific and comprehensive legal regime governing the use of force in outer space does not exist, and relevant rules had to be drawn from different instruments. The Outer Space Treaty only prohibits the placing and orbiting of nuclear weapons and weapons of mass destruction in outer space (Tronchetti (2011)). This provision is generally understood to mean that, in principle, the placing of conventional weapons in outer space is not forbidden (Schrogl and Neumann (2009)). As far as the use of conventional weapons is concerned, international law and, in particular, the Charter of the United Nations established a general prohibition on the threat or use of force against the territorial integrity and political independence of any State, or in any other manner inconsistent with the purposes of the United Nations (Charter of the UN, art. 2(4)). The UN Charter lays down two exceptions to this prohibition: a) the right to use force in self-defense and b) the use of force authorized by the UN Security Council. Thus, States are forbidden from using force, specifically conventional weapons, in outer space to threaten or harm the territorial sovereignty or properties (i.e., space objects) of other States, unless this constitutes the exercise of the right of self-defense or it is expressly permitted by the Security Council. This is, of course, relevant in the context of a planetary defense mission. Indeed, provided that the use of force falls within one of the two exceptions described above, there does not seem to be any specific legal obstacle to using conventional weapons during such a mission (Legal Aspects of NEO Threat Response). The only prohibition that would seem to exist would be to place weapons on the surface of the Moon with the purpose of firing them at an incoming cosmic threat, as the Outer Space Treaty and, in particular, the Moon Agreement fully demilitarize the Earth’s natural satellite (Outer Space Treaty and Moon Treaty). The situation is more complicated if one considers recourse to nuclear weapons to avert a natural cosmic threat (Legal Aspects of NEO Threat Response). On one side, it is quite possible that a nuclear device would not only encounter a NEO threat and at the same time affect the surrounding environment, possibly including the Earth’s environment, and orbiting space debris objects. On the other side, international space law does not deal with the possibility to use nuclear weapons in space. In this respect, while Article IV of the Outer Space Treaty prohibits the placing in outer space of nuclear weapons, it is silent about the option to recur to these weapons as an ultima ratio in extreme circumstances. If one looks outside of the limited circle of the specific space law instruments, some useful elements can be obtained. For example, the Nuclear Test Ban Treaties forbid any nuclear explosion in outer space. However, this should not be interpreted as banning any use of nuclear weapons if unequivocally necessary to protect mankind from an “extraordinary” danger, such as a NEO (Legal Aspects of NEO Threats). In any case States would always have the option to withdraw from these treaties if national security reasons would dictate so. Overall, it is unquestionable that the legality of the threat or use of nuclear weapons, even in an extreme circumstance of self-defense, is still currently debatable under present international law (Legality of the Threat). Therefore, even if one constructs the use of nuclear weapons as a last-resort option, it is advisable that States define clear parameters related to the use of these weapons prior to the start of the planetary defense mission.

Liability Issues Related to a Planetary Defense Mission Liability considerations are crucial with respect to the preparation and implementation of a planetary defense mission. It is foreseeable that in the course of such a mission, damage to third-party space objects and, possibly, to the Earth’s environment may occur. Arguably, damage may happen in three

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cases: (a) the lack of an action, (b) action undertaken successfully, and (c) action not completely successful (Legal Aspects of NEO Threat Response). As far as case “a” is concerned, as previously described, under current international law there is no obligation for States to take action to respond to a NEO threat. As a consequence, States cannot be held responsible as well as liable for the damage that may result from their lack of intervention, for example, for the damage resulting from the impact of a NEO on the Earth’s surface. An established principle of international law provides that a State committing an internationally wrongful act is under the obligation to make reparation for such an act. As there is no duty to act in case of a NEO menace, States would not commit an internationally wrongful act by deciding not to intervene. Thus, the States that theoretically possess the technological ability to act could not be forced to compensate the damage that a NEO collision with the Earth may cause. With regard to cases “b” and “c,” one should first ascertain the relevance of the 1972 Liability Convention, which is the primary legal instrument regulating liability for damage arising in the context of outer space activities. The Convention deals with the damage caused by space objects either on Earth, i.e., on the ground, or to an aircraft in flight, or in outer space. The first category of damage is governed by a regime of absolute liability, the latter by a fault-based liability scheme. Inter alia, the Convention declares that “a space object includes components parts of a space object as well as its launch vehicle and parts thereof” (Liability Convention). Undoubtedly, damage might occur during the launching phase of a mission aimed at responding to a cosmic threat. As this situation would not be different from any other case of damage happening during the launching of a space object, the Liability Convention would be fully relevant in such an event (provided, of course, that those damages are of international nature). A different scenario could be envisioned in relation to damage occurring in outer space. Assuming that a planetary defense initiative would be undertaken using a kinetic impactor, it is conceivable that, as a consequence of the collision between the impactor and the NEO, pieces of the latter would be released in the void outer space and would hit space objects belonging to States not involved in the initiative. In such a circumstance, the Liability Convention would most likely not be applicable to compensate the damage caused to those objects. First of all, the Convention deals with (physical) damage caused by a space object; as NEOs as such, clearly, are not space object, any damage that they may cause falls outside of the scope of the Convention. Secondly, the Convention covers indirect damage only when the primary damage derives from a collision between two space objects. However, in our case, as the collision would involve a space object (the kinetic impactor) and a NEO (which is not a space object), indirect damage to active orbiting space objects would not be compensable under the Convention. Thirdly, as described above, a fault liability regime applies to damage in outer space. Thus, even if one would argue that indirect damage resulting from the planetary defense mission should be coverable, the claimant States (or private entities) would still have to prove that the operators of the mission have committed fault and that a causal link between the fault and damage exists (Liability Convention). Conversely, one could argue that damage to a third State’s space objects would have not occurred if a planetary defense action had not been undertaken (Legal Aspects of NEO Threat Response): thus, the operators of the action should be held accountable for them. Furthermore, it could be claimed that such damage should still be viewed as “damage caused by that space object,” leading, therefore, to the liability of the launching State(s) of the planetary defense response mission, mostly because the object causing the collision, i.e., the kinetic impactor, is a space object. Additionally, Article IV of the Liability Convention provides that, in the event of an impact between two space objects resulting in a damage to a third party, if the collision was the consequence of the fault, the launching State (s) would be liable for the damage caused to such third party (Legal Aspects of NEO Threats). Page 9 of 14

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Similarly, if the collision between the kinetic impact and the NEO was characterized by the fault of the launching State(s), such State(s) could be deemed liable for the secondary damage caused to the space objects of a third State. Nevertheless, there is room to claim that, because a planetary defense mission would presumably be undertaken jointly by a group of States with the ultimate goal of saving mankind (or parts thereof) from a devastating impact (and not with the intention of harming third States and/or their properties), these States should be exempted from liability for damage that they may cause. Indeed, taking into account their bona fide effort, States not involved in the planetary defense mission should consider the waiving of any liability claim against the operators carrying out such a mission. A similar approach is already in place within the context of the International Charter on Space and Major Disaster where “no legal action will be taken against the parties in the event of bodily injury, damage or financial loss arising from the execution or non-execution of activities, services or supplies arising out of the Charter” (International Charter on Space and Major Disasters, art. 5 (4)). Furthermore, numerous States incorporate at national level the so-called “Good Samaritan” principle, according to which person who injures another in imminent danger while attempting to aid him (as long as not under an obligation to do so) is not to be charged with contributory negligence and/or liabilities unless the rescue attempt is an unreasonable one or the rescuer acts unreasonably in performing the attempted rescue (Legal Aspects of NEO Threat Response). Notably, the practice of waiver of liability is not uncommon in the context of space activities, particularly in connection with those presenting a high level of risk. For example, States taking part in the management and operation of the International Space Station have accepted to reciprocally waive liability claims with the exclusion of those resulting from criminal acts and willful misconduct (1998 Intergovernmental Agreement on the Civil International Space Station). In any event, there is little doubt that a global acceptance to waive liability claims against the States taking part in a planetary defense mission would represent as a further incentive for those States to actually undertake such a mission. However, liability should not be waived when damage would be the consequence of: (a) fault and (b) a disproportionate use of force. The former is a classic reason to exclude liability waivers. In the context of a response to a NEO threat, fault could be conceivable in case of an unjustifiable wrong maneuver (i.e., a man-made mistake not caused by a technical failure) or an unannounced change of the mission plan which would result in a failure and damage to third states. The latter refers to the unnecessary use of powerful devices, such as nuclear weapons, during a planetary defense mission. A similar scenario could occur when, despite being in the presence of data demonstrating that recourse to nuclear weapons is not needed, States would anyhow decide to make recourse to such weapons and such a choice would lead to several collateral damages in outer space and, possibly, also on Earth. To end on a note of realism, a nation under direct threat of extinction would likely act and then sort out any legal issues or claim after the planetary threat had been averted. Clearly resolving these liability issues in advance would be the preferred solution.

Organizational Framework for a Planetary Defense Mission Another relevant question is how a planetary defense mission could be structured from an organizational point of view, in particular in terms of decision-making procedures and relation among the States involved in it. In principle, such a mission should be, at least in some manner, open to all, not only to those States capable of making a significant and effective contribution. Such an element should be considered essential in order to give a State the right to participate in the decision-making process. Importantly, this process should be structured in a way to attribute to the States most directly involved in the preparation and implementation of the planetary defense mission a stronger possibility to influence Page 10 of 14

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_79-1 # Springer International Publishing Switzerland 2014

Fig. 1 Diagram of initial concepts being considered by the IAWN and SMPAG (Conceptual Representation Developed by Dr. Sergio Camacho-Lara of Action Group 14)

it. A similar approach is already in use within the context of the International Seabed Authority and largely resembles the way the Security Council of the UN is structured. The process outlined in Fig. 1 would have the UN Committee on the Peaceful Uses of Outer Space with about 80 members from around the world acting as a key enabler of action. Other chapters in this handbook suggest that the Secretary-General should be authorized to dispatch UN peace-keeping forces to respond to global cosmic disasters. Clearly the General Assembly and COPUOS in coordination with the newly created IAWN and the SMPAG will all play a role. As noted above the UN Security Council will undoubtedly have some role to play as well. Clearly a future international treaty or convention on this subject should clarify the best and most efficient organizational framework that could be deployed under various types of planetary threats. States taking part in a planetary defense action should be willing to accept the risks that such an action encompass and, consequently, waive liability claims (i.e., cross-waiver of liability) among each other for damage arising in the context of this action (Legal Aspects of NEO Threat Response). Furthermore, these States should, to the greatest possible extent, share costs, be guided by the principles of transparency and mutual cooperation and agree on the procedure to be followed for the settlement of disputes. With respect to the latter point, States could set up a dedicated dispute settlement procedure or make reference to already available possibilities, such as recourse to the International Court of Justice or arbitration under the Permanent Court of Arbitration (PCA) (Optional Rules for Arbitration of Disputes Relating to Outer Space).

Conclusion If a planetary defense system is planned, it should be international in nature and scope. The setting up of these arrangements will likely be led by technological and economically advanced States that will play a major role. Naturally and logically, this system should be governed by international law. The above analysis has demonstrated that current international law, including space law, does not provide a comprehensive legal framework dealing with the prevention and mitigation of natural cosmic threats as well as recovery activities. Clearly numerous issues remain open for discussion. More importantly, it poses numerous legal and organizational challenges related to a planetary defense. These issues include the possibility of liability and illegality in the use of (nuclear) force. In the absence of a uniform and legally binding regime, there will be uncertainty, diverging interpretations, and, potentially, conflicts among the States involved in such a response. It would, thus, be Page 11 of 14

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advisable that States, particularly those that intend to take part in a planetary defense, should develop a dedicated legal framework to govern the preparation, implementation, and aftermath of a response to a natural cosmic threat. More specific details, such as setting up a comprehensive structure, decision-making processes, emergency response plans, technical and human resources for monitoring, and research about risks posed by near-Earth objects, space debris, adverse space weather, dispute settlement, the transparency of operations, etc., could be left to a later date. Ultimately these should be covered in an international treaty on some type of convention. Ultimately it might be realized that the issue of climate change is, in fact, a type of cosmic hazard and closely linked to severe space weather conditions, and in this respect, the issues of planetary defense and environmental controls, as related to climate change, may be considered in this broader context. More importantly, these proposed arrangements must have clauses incorporating cross-waiver of the liability and permission to use (nuclear) force, if it becomes necessary, as well as other provisions amending those treaties that might be seen as legal barriers in the creation of a planetary defense system. Other elements to be considered for inclusion are the arrangements for disaster response in the event governments experiencing a cosmic disaster in the case of a major catastrophe are not in a position to request relief and whether UN peace-keeping forces should be deplored in such instances. The international regulatory framework must strike a fair balance between the interest of mankind in its survival, the acceptance of the main positions of States taking an active part in planetary defense initiatives, and the meaningful participation of private companies and nongovernmental organizations. It is also recommended that the Working Group on Near-Earth Objects established by the Technical and Scientific Subcommittee of the COPUOS as well as the Long-Term Sustainability of Outer Space Activities (LTSSA) established by the full COPUOS body should become more active and seek extensive and interdisciplinary input from nongovernmental organizations, governmental bodies, international institutions (like IADC, IAWN, SMPAG, IAU), academics, and the private sector.

Acknowledgment The author of this chapter wishes to thank Dr. Joseph Pelton and Mr. Kuan-Wei (David) Chen for reviewing its earlier draft. Their comments significantly enhanced the quality of this section. Undoubtedly, the author remains exclusively responsible for the text of the section and any errors or omissions it may contain. – Fabio Tronchetti

Cross-References ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Major Gaps in International Planetary Defense Systems: Operation and Execution ▶ Planetary Defense, Global Cooperation, and World Peace ▶ Risk Management and Insurance Industry Perspective

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References Declaration on International Cooperation in the Exploration and Use of Outer Space for the Benefit and in the Interest of all States, Taking into Particular Account the Needs of Developing Countries, UNGA Res 51/122, UN Doc A/RES/51/122 (13 Dec 1996) Draft Articles on Responsibility of States for Internationally Wrongful Acts (2001) of the International Law Commission, art. 31. http://legal.un.org/ilc/texts/instruments/english/draft%20articles/9_6_2001.pdf. May 2014 Hobe S (2009) Article I. In: Hobe S, Schmidt-Tedd B, Schrogl KU (eds) Cologne commentary on space law, vol 1. Carl Heymanns Verlag, Cologne, pp 25–44 Intergovernmental Agreement (1998) the Agreement among the Government of Canada, Governments of Member States of the European Space Agency, the Government of Japan, the Government of the Russian Federation, and the Government of the United States of America concerning Cooperation on the Civil International Space Station (also known as the Intergovernmental Agreement), Washington, done 29 January 1998, entered into force 27 March 2001; TIAS No. 12927; Cm. 4552; Space Law – Basic Legal Documents, D.II.4, art. 17 International cooperation in the peaceful uses of outer space, UNGA Res 68/75, UN Doc A/RES/68/ 75 (2013), para 8. UNCOPUOS, Report of the Scientific and Technical Subcommittee on its fiftieth session, held in Vienna from 11 to 22 February 2013, UN Doc A/AC.105/1038, particularly Annex II “Legality of the Threat or Use of Nuclear Weapons”, Advisory Opinion (1996) International Court of Justice. Rep 226 Liability Convention – Convention on international liability for damage caused by space objects (hereafter Liability Convention), London/Moscow/Washington, done 29 March 1972, entered into force 1 September 1972; 961 UNTS 187; TIAS 7762; 24 UST 2389; UKTS 1974 No. 16; Cmnd. 5068; ATS 1975 No. 5; 10 ILM 965 (1971) International Charter on Space and Major Disasters, Signed on 20 Oct 2000, online at: International charter on space and major disasters http://www.disasterscharter.org/web/charter/charter. Last accessed May 2014 Permanent Court of Arbitration (PCA) Optional rules for arbitration of disputes relating to outer space (effective 6 Dec 2011), http://pca-cpa.org/shownews.asp? ac¼view&pag_id¼1261&nws_id¼323. Last accessed May 2014 Principles Relating to Remote Sensing of the Earth from Outer Space, UN Resolution 41/65, 3 December 1986, Principle X Registration Convention – Convention on Registration of Objects Launched into Outer Space (hereafter Registration Convention), New York, done 14 January 1975, entered into force 15 September 1976; 1023 UNTS 15; TIAS 8480; 28 UST 695; UKTS 1978 No. 70; Cmnd. 6256; ATS 1986 No. 5; 14 ILM 43 (1975) Rescue Agreement – Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space,London/Moscow/Washington, done 22 April 1968, entered into force 3 December 1968; 672 UNTS 119; TIAS 6599; 19 UST 7570; UKTS 1969 No. 56; Cmnd. 3786; ATS 1986 No. 8; 7 ILM 151 (1968) Schrogl KU, Neumann J (2009) Article IV. In: Hobe S, Schmidt-Tedd B, Schrogl KU (eds) Cologne commentary on space law, vol 1. Carl Heymanns Verlag, Cologne, pp 75–76 The Declaration of the United Nations Conference on the Human Environment, adopted on 16 June 1972, by the United Nations Conference on the Human Environment, Principles 2, 4

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The Outer Space Treaty – Treaty on principles governing the activities of States in the exploration and use of outer space, including the moon and other Celestial bodies London/Moscow/Washington, done 27 January 1967, entered into force 10 October 1967; 610 UNTS 205; TIAS 6347; 18 UST 2410; UKTS 1968 No. 10; Cmnd. 3198; ATS 1967 No. 24; 6 ILM 386 (1967) “The Responsibility to Protect”, Report of the International Commission on Intervention and State Sovereignty (ICISS), December 2001, } 2.29. http://www.iciss.ca/pdf/Commission-Report.pdf. Last accessed May 2014 The Stockholm Declaration. The Declaration of the United Nations Conference on the Human Environment, adopted on 16 June, 1972, by the United Nations Conference on the Human Environment, Principles 2, 4 Tronchetti F (2011) Preventing the weaponization of outer space: is a Chinese-European-Russian common approach possible? Space Policy 27:81–82 United Nations Conference on Environment and Development (UNCED) (1992) Agenda 21 voluntary action plan on sustainable development. http://www.unep.org/Documents.Multilingual/ Default.asp?documentid¼52. Last accessed May 2014 United Nations Conference on Environment and Development (UNCED). Agenda 21 http://www. unep.org/Documents.Multilingual/Default.asp?documentid¼52. Last accessed May 2014 von der Dunk F, rapporteur for the study (2010) Legal aspects of NEO threat response and related institutional issues http://www.swfound.org/media/40426/legal_aspects_neo_response_institutional_issues_final_report.pdf. Last accessed May 2014

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_80-1 # Springer International Publishing Switzerland 2014

Economic Challenges of Financing Planetary Defense Henry R. Hertzfelda* and Pierre-Alain Schiebb,c a Space Policy Institute, Elliott School of International Affairs, The George Washington University, Washington, DC, USA b NEOMA Business School, Reims, France c Consultant to the OECD, Paris, France

Abstract This chapter examines analyses that have been used to assess various types of large-scale economic risks that could apply to the global economy and attempts by such groups as the World Economic Forum to examine what the impact of various types of “Black Swan” catastrophes might be. In particular it indicates why economic systems are generally not well equipped to address major global disasters with worldwide impact that also have a very low probability of occurrence. In light of economic scarcity, conflicting political priorities, and a number of other factors, there is currently little likelihood that a systematic economic response mechanism or a global disaster response fund will be created within the United Nations system or any other global institution. The general conclusion reached is that the evolution of new types of space technologies that might be developed for other purposes such as space debris removal, on-orbit servicing, etc. – may represent the most logical way forward.

Keywords Economics; Finance; Risk; Risk analysis; Disasters; Funding; Catastrophe; Resilience

Introduction Economic activity tends to work best within a well-established regulatory regime where values, markets, and financial incentives and risks are well known. Accurate and current information about economic conditions also supports economic efficiency. A major cosmic event such as a massive hit by an asteroid or a coronal mass ejection from the sun of epic proportion that could destroy a massive amount of global infrastructure is almost the worst possible case for developing a systematic and efficient economic response to such a catastrophe. These types of events have an extremely low probability of occurring, but they do have potentially huge socioeconomic consequences. Creating an economic fund in advance for the purpose of responding to such a low-probability event via a conventional-type insurance or risk-management scheme is unlikely for a number of reasons that will be explored in this chapter. First of all, fund raising – for whatever purpose – is always difficult. Whether it is for charitable purposes, business ventures, or government programs, there are numerous challenges to obtaining the necessary funds. The economics of funding is basically quite simple: investors want a low-risk,

*Email: [email protected] Page 1 of 11

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_80-1 # Springer International Publishing Switzerland 2014

short-term payback. Money has time value – the longer it takes to obtain a return, the larger that return must be to overcome the lost opportunities that inevitably will be present. And, the larger the up-front investment is, the more difficult the hurdles are to funding. For purposes of this chapter, the focus will be on the worst possible scenario – a very large asteroid crashing into the Earth and having an impact that affects all life on Earth. Other scenarios concerning space objects doing terrestrial damage are more analogous to the “typical” types of natural disasters that occur very frequently on Earth – volcanic eruptions, earthquakes, hurricanes, etc. The effects of these incidents are localized, and there is an extensive literature available on managing and recovering from these types of risks. In virtually all cases, the regions and nations involved are resilient and recover, sometimes quite quickly, from these damages. And, sometimes the results from an economic perspective may even (but not always) be quite positive over time where the rebuilding effort creates new jobs and infrastructure and consequently revitalizes a region that was in decline. Space technologies can help in predicting, identifying, and characterizing damages as well as in the planning and organizing of a recovery. International organizations and international cooperative efforts also are helpful, particularly in responding to regional disasters. But, the more challenging question, for which there is no definitive answer, is how collectively human beings and space technology can be mobilized to identify and possibly even prevent a catastrophic disaster that could affect the entire Earth. Most studies of this problem focus on the first step – identifying and monitoring space for potentially hazardous Near-Earth Objects (NEOs). That process is relatively inexpensive and is closely coupled with other space-monitoring programs. These programs are funded for other purposes – safety of operations in space, identification of potential resources and other uses of various celestial bodies or orbits, and security/national defense. The challenge for funding is to address the eventual issue of defending our planet from a catastrophic impact originating from space, which is a global effort with unknown risks and costs.

Measuring the Probability of Risks and Losses The list below of Asteroid Fast Facts prepared by the NASA Jet Propulsion Laboratory describes the types and sizes of asteroids that could cause potential harm to Earth (NASA Fast Facts). Note that the risks are very low for a catastrophic occurrence (NASA Jet Propulsion Laboratory). Asteroid Fast Facts (Source: NASA, Jet Propulsion Laboratory)

Size and Frequency

• Every day, Earth is bombarded with more than 100 tons of dust and sandsized particles • About once a year, an automobile-sized asteroid hits Earth’s atmosphere, creates an impressive fireball, and burns up before reaching the surface. • Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the area. • Finally, only once every few million years, an object large enough to threaten Earth’s civilization comes along. • Impact craters on Earth, the moon, and other planetary bodies are evidence of these occurrences. • Space ricks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth’s atmosphere and cause little or no damage. • If a rocky meteoroid larger than 25 meters but smaller than one kilometer (a little more than ½ mile) were to hit Earth, it would likely cause local damage to the impact area.

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Small NEO with no impact

Large NEO, impact small (occurs in remote area or “near miss”)

Resilience: none needed Total Cost: zero to very low Funding for R&D: No new funds— included with other monitoring programs

Resilience: fast--minor disruptions Total Cost: affordable by nation(s) Funding for R&D: Very large, same as for one with major impact

Probability: high

Probability: low

Small NEO, impact major but localized

Large NEO, major impact on all humanity

Resilience: major issue locally, but manageable nationally Total Cost: large but “affordable” to nation(s) Funding for R&D: Moderate to large depending on global interest

Resilience: Not resilient Total Cost: Very high; global, not recoverable Funding for R&D: Very large with significant risk—attempts at protection may fail

Probability: moderate

Probability: very low

Fig. 1 Probability of a catastrophic loss

• We believe anything larger than one to two kilometers (one kilometer is a little more than one-half mile) could have worldwide effects. At 5.4 kilometers in diameter, the largest known potentially hazardous asteroid is Toutatis. • By comparison, asteroids that populate the main asteroid belt between Mars and Jupiter, and pose no threat to Earth, can be as big as 940 kilometers (about 583 miles) across.

Figure 1 compares four cases. Only the one shaded dark red is of a major concern for humanity as a whole. All the others are, as mentioned above, manageable and society and property are relatively resilient over time. Current space-monitoring systems can be improved and will help provide regions and localities with advance warning disaster relief efforts. However, focusing only on major space weather events or asteroid risks is misleading. The real question is where does this activity fit in relation to the multitude of other risks facing the Earth and humanity. The World Economic Forum each year publishes a chart comparing the likelihood of major threats occurring with the impact of these risks, and the most recent is reproduced below (World Economic Forum 2014) (Fig. 2). There are several possible explanations of the recent flurry of interest in the risks of damage from asteroids. The first is the Feb. 15, 2013, event where an asteroid measuring about 14 m in width detonated in the skies over the Russian city of Chelyabinsk, causing millions of dollars of damage and injuring 1,500 people. As dramatic and disruptive to the region that this was, it was no threat to humanity in general or to the planet. However, with today’s speed of communications, instant and ubiquitous distribution of photographs and video, and other media coverage, people everywhere were aware of what previously would have been a footnote in most newspapers appearing days after the event. Second, relatively recent documentation of previous asteroid impacts on Earth has led to the realization that this is not an uncommon phenomenon and that serious damage has been done in the past. Coupled with an increasing world population, increasing concentrations of people in urban areas, and increasing property values in some areas vulnerable to natural disasters (coastal property, hillsides prone to mudslides, etc.), the economic damage from all natural disasters has also increased

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_80-1 # Springer International Publishing Switzerland 2014

over time. (This has been balanced by better forecasting of natural events, which has led to better mitigation techniques and resilience but nonetheless increased perception of risk.) Third, space technology and capabilities are expanding rapidly. Our ability to monitor space and observe activity in space has increased dramatically, partly from better technology and partly as a result of the recent concerns about human-created space debris and its possible detrimental effects on active satellites. Furthermore, with the advent of possible multiple types of in-space activities such as satellite servicing, resource extraction, and debris removal (all with possible commercial as well as public value), the monitoring of asteroids from both the perspective of danger and a source of valuable materials has increased. Fourth, some of those in-orbit future capabilities may also be applicable to allow the development of techniques to move asteroids that are threatening the Earth to orbits that will safely avoid the planet. (However, it must be noted that with any human-created technology, especially untested ones, there also could be an increased probability of errors and mistakes that could actually increase risks of damage instead of decreasing them.) Fifth, the increasing dependence of terrestrial economies on space assets and satellite applications such as communications and navigation has added attention to the protection of those assets for the continuity and effective operation of many Earth-based economic activities. And, finally, with these motivational drivers, the space-monitoring efforts of the past decade have detected previously unknown asteroids that have the potential of an impact on Earth. Although the actual probability of an impact with Earth has not changed over thousands of years, our knowledge

The global risks landscape

Fiscal crises Climate change Water crises Unemployment and underemployment

5.0 Biodiversity loss and ecosystem collapse

Critical information infrastructure breakdown

Failure of financial mechanism or institution

Political and social instability Weapons of mass destruction

Extreme weather events

Cyber attacks

Income disparity

Global governance failure Pandemic

average 4.56

Natural catastrophes

Food crises

Antibiotic-resistant bacteria

Liquidity crises

4.5 State collapse

Terrorist attack Oil price shock

Data fraud/theft Man-made environmental catastrophes Interstate conflict

Economic and resource nationalization Corruption Failure of critical infrastructure 4.0

Impact

Chronic diseases

Decline of importance of US dollar

Mismanaged urbanization

Organized crime and illicit trade 3.5

Likelihood

4.5

4.0 4.31 average

5.0

5.5 plotted area

Fig. 2 World Economic Forum Global Risks Page 4 of 11

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has. And with that knowledge, the perceived risks are now considered to be higher, even if the probability of a major strike is still quite low. Figure 2 shows one compilation of risk likelihood and potential impact produced by the World Economic Global Forum. It is significant that space-based risks are not separately identified in this chart. However, space catastrophes may affect global infrastructure and space systems may be able to help mitigate the impacts of natural disasters.

Costs A US National Academy of Sciences review of hazards and mitigation strategies for NEOs included an analysis of estimated costs for eight different programs ranging from telescopes for monitoring space to several types of proposals for mitigating the danger from NEOs (US National Academy of Sciences). The range of estimates was, on the lower end for telescopes, $90 million to almost $2 billion. On the upper end, for deflection or destruction of NEOs, the costs ranged from $1.7 billion to over $3.5 billion. These figures are the ones calculated in the study that the estimators reported at the 95 % confidence level (there were lower total costs at lower statistical confidence thresholds). It should be also noted that these costs were calculated in 2010$ US, and when and if the government programs associated with those cost estimates were to be funded, they would have to be adjusted upward to account for inflation. It is also noted that in the past cost estimating models typically understate the actual costs by 30–50 %. And if these efforts to monitor and mitigate large NEO impacts are a global effort involving many nations, international cooperative programs may result in lower expenditures for each nation participating, but in a total cost that is greater than what would be needed if a single nation funded and managed the projects. Finally, the costs do not include any risks of accidents, mistakes, or unforeseen damages in space or on Earth from these activities. Although these additional factors may be minimal for equipment in space used in monitoring efforts since those technologies are well proven and similar to many types of existing satellites, they could be very significant for moving NEOs to different orbits or destroying a NEO, neither of which has ever been done or tested to date. NASA’s Planetary Science Research Program currently does have a $40 million budget for the identification and characterization of objects in the solar system that pose threats to Earth or offer resources for human exploration. It is noteworthy that this line item has been doubled in FY 2014 from the prior year’s budget but is projected to remain flat at $40 million in the future (NASA 2014). In the United States, the Space Situational Awareness efforts are led by the Department of Defense. The total annual costs of the satellites, launches, ground equipment, and other supporting and associated equipment and personnel are unknown, partly due to security classification and partly due to the reality that these systems serve more than one purpose and the costs are difficult to allocate to specific goals. However, manufacturing and launching sophisticated tracking satellites can easily cost upward of $500 million each, and the future S-Band Space Fence facility will cost billions of dollars (US). Therefore, it is not unreasonable to estimate that well over $1 billion per year of the DOD budget is dedicated, directly or indirectly, to the types of monitoring of space that detects and analyzes the trajectories and risks associated with space debris, missile launches, and NEOs. NASA missions such as NEOWISE, the proposed NEOCAM, and other activities involve additional major expenditures. Expenditures of lesser amounts for monitoring space also are made by other nations, and there are also multimillion initiatives by other organizations such as the B612 Foundation that are planning to implement the Sentinel infrared space telescope project. Clearly, even accounting for these large expenditures, all nations are still in the infancy of having a full knowledge of celestial bodies and NEOs that could threaten the Earth. And, even if that information were available, technologies for predicting the trajectories and true risk to Earth of any of these objects are still under development and not perfected. Page 5 of 11

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The conclusion is fairly obvious that even though very significant annual funding is being devoted to direct and indirect surveillance of space, it is currently insufficient for purposes of accurately detecting and predicting the dangers to Earth of a catastrophic incident. It is also unknown if human beings will ever be able to predict such an event with enough advance notice to mitigate the impact, although more research and development, monitoring, and other actions should improve on current knowledge. NASA and other nations have also spent billions of dollars to learn more about the sun, solar flares, and coronal mass ejections, but in this area preventive actions are at an even more rudimentary level of development.

Funding Mechanisms for a NEO Program A program designed to identify and move NEOs so they will not have an impact on Earth would have to: • • • •

Be a long-term commitment, possibly spanning decades Be coordinated with other ongoing space R&D efforts Involve many nations, either directly or indirectly Overcome associated issues of national security and classified technology and information

Any nation undertaking a program of this sort would experience difficulties in developing justifications for a long-term budget commitment. In the United States, for example, budgets are determined annually. Any commitment to any given year’s funding is subject to many economic and political factors, all of which may change from year to year. As witnessed over the years by many programs (Shuttle, International Space Station, expendable launch vehicle development, human exploration), there have been multiple changes, program cancellations, and budget reductions, even for the most beneficial and important programs. Similar fluctuations occur in other nations, although the specific triggers and methods of approving budgets vary considerably among different governments. Planetary defense presents a particularly difficult challenge; one so large that it is likely that there will never be funds raised at a sufficient level for a dedicated government program, international program, or business venture for this purpose unless there is a clear and imminent threat to a nation or to Earth. The latter is unlikely, as the probability of life as we know it on Earth being destroyed by a Near-Earth Object (NEO) is extremely low. In fact, the probability has remained the same over thousands of years. Just because there was recently massive press coverage of a “near miss” over Russia in 2013 of a NEO that was not large enough to do anything more than severe local damage does not warrant a panic response, nor does it signify an increased probability of a catastrophic event. Recent data collected from nuclear detection monitoring systems has confirmed that impacts from asteroids are up to ten times more frequent than previously thought to be the case. Disasters that affect a region or a nation may not be insignificant or minor. Lives are lost, property is damaged, and a nation’s economic growth may be harmed. Recovering from a major earthquake, tsunami, volcanic eruption, or even an industrial accident can be lengthy and painful. However, these incidents are localized and the resiliency of human beings has been quite remarkable over time. Space activity and space technology is, however, changing and advancing. In the very near future, there will be both government and private ventures that will make use of space with new capabilities that include building platforms, servicing space assets, and extracting resources from other celestial bodies. Associated with those activities is an increasing need to monitor assets and orbits, assess the dangers to assets from space debris, and protect any human lives that are on space platforms such as the International Space Station (ISS). The technologies developed for monitoring and for Page 6 of 11

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performing these activities may also greatly contribute to our knowledge of NEOs and to our ability to protect the Earth. In short, the financing for planetary protection will continue to be largely indirect – it will progress from the technology and uses of space that will have direct near-term government and commercial paybacks. This chapter will address those developments. One of the most important considerations in any program designed to operate in the high-risk/ long-payback space environment is funding. Access to space is risky and expensive, particularly for new and untried or unproven technologies and applications. Working in space is even more difficult – if it weren’t, there would today be many more types of in-orbit activities happening. Addressing risks to Earth from Near-Earth Objects is something that is clearly still in a research and development stage. We still do not know how to “save” the Earth from a major NEO catastrophe or extreme solar events. There is no guarantee that any national or any multinational program to accomplish this task is: 1. 2. 3. 4.

Needed in the near-term horizon Technologically sound Affordable Could not be accomplished without increased risks and possibly liability

The newly established United Nations International Asteroid Warning Network and the Space Mission Planning Advisory Group will undoubtedly have to address such issues. The ability to carry out a NEO program is currently limited to only a very few nations that have the technology, experience, and launch capabilities. Yet the location of a possible NEO incident could be anywhere on Earth. The immediate destruction would be local but the damage over time could be spread over the entire globe. Who benefits, who loses, and who pays are all critical questions that cannot be definitively and directly answered today. Although the purpose of this chapter is to review the issues related to funding a program directed toward NEOs and extreme cosmic hazards, funding is really a derivative issue. The key question of whether we should or should not seriously begin a planetary defense effort is addressed elsewhere in this book. Funding issues will be addressed in two ways – evaluating riskmanagement issues and summarizing analogies to the handling of other global catastrophic-type events. These issues are compounded when other considerations are added to the mix. In particular, planetary defense is a global threat – if a meteor or asteroid is determined to threaten the Earth, as mentioned above, the exact location may be unknown and indeterminate until the threat is upon us and it is too late to act. From a financing perspective, this exacerbates the risks since no one government in any one nation is likely to find the money to save another nation. Thus, unknown risks, unknown timing of an occurrence, unknown locations, unknown costs, unknown technologies needed, and unknown probabilities of success make for a very difficult case for any government (or anyone else) to defend current budget proposal or actual expenditures. Clearly, the usual economic investment criteria of risk, return on investment, and opportunity costs cannot be applied to this problem. Similarly, standard economic methodologies such as benefit cost analysis, internal rates of return, and decision analysis cannot be quantified in this case. One may ask, what is, then, the point of even analyzing the funding issues for this problem? The answers vary. First, there will not be any planetary defense if our society can’t find a way to fund it. Second, a look at other analogous high-risk/low-probability threats may provide insights into finding ways to begin allocating funds to this issue. Third, a clear awareness of this huge problem Page 7 of 11

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and the international aspects of it may provide a new way of viewing and organizing resources designed to address both this and other global issues that are well documented but difficult to amass international support and mechanisms to alleviate or at least lower future risks. Solutions are unlikely, but awareness and planning for the future are possible and deserve attention.

Evaluating Possible Methods of Governance and Financing There is no international organization that governs space, nor is there likely to be one. For specific purposes, nations have joined collectively to share information, monitor world situations, and develop the means to cooperate on both political and economic matters. The United Nations Committee on the Peaceful Uses of Outer Space (COPUOS), the UNISPACE Conferences, and the Inter-Agency Space Debris Coordination Committee (IADC) and the newly formed International Asteroid Warning Network (IAWN) and the United Nations Space Missions Planning Advisory Group (SMPAG) are today the closest approximation of worldwide space coordination. Hypothetically, if scientists today made a prediction that a very large NEO was headed toward a devastating collision with Earth in 5 years, there is no doubt that those nations with the resources to help prevent that from happening would find a way to go to work on the problem. But, if those same scientists predicted that the NEO would land harmlessly in the ocean, the result might be different. Or, if the prediction was that it would hit the Earth in midtown Manhattan, there likely would be a major effort on the part of the United States to prevent that, but it is unknown how much other nations would contribute to that before the incident occurred. (After the fact, it is well demonstrated that nations most often offer to help in the recovery.) Spacefaring nations have joined forces on some issues. The UN Disaster Charter is an example where nations have formed an agreement to share and exchange remote sensing information without charges after a major natural or other disaster. This information is invaluable in helping to organize and mobilize a recovery mission. Even in the commercial world, companies that operate satellites in the geostationary orbit have recognized the need to share information about their satellite location and possible debris threats. They have recently formed a private company (the Satellite Data Association chartered in the Isle of Man) that collects the corporate data, assesses the vulnerability of satellites, and issues warnings and recommendations to help prevent collisions in space. Governments have also joined in this recent effort, illustrating that a threat of significant economic loss coupled with collective interest in preventing future losses can be funded and managed. It is conceivable that a joint effort requiring little new funding or technology to share information on what is known about NEOs and to monitor their movements could build on these models of international cooperation. Scientists and space agencies routinely share these types of data, and an existing organization, either under the United Nations or another international entity, could fill this need. But the possibility of similar international cooperative efforts for managing NEO threats requires a very different approach. There is no specific economic asset at risk, the technology to move or deflect NEOs is both undeveloped and has embedded in the R&D that will need to be performed significant issues with the sharing of sensitive information, and the funding would require very large contributions.

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Is It All Worth Worrying About? Fear, risk, and governmental action are the subjects of many interesting academic analyses. For example, an article from the Harvard University Law Review (Sunstein and Zeckhauser 2008) highlights the points this chapter is emphasizing. To quote from their conclusions: . . .when risks are vivid, people are likely to be insensitive to the probability of harm, particularly when their emotions are activated. If terrible outcomes are easy to visualize, large scale changes in thought and behavior are to be expected, even if the statistical risks are dramatically lower than those associated with many activities where the stakes are equivalent but do not raise public concern. This claim about action bias helps explain public overreaction to certain highly publicized, low-probability risks, including those posed by sniper attacks, abandoned hazardous waste dumps, anthrax, and perhaps terrorism more generally. With financial crises, as late 2008 made tragically clear, fears and anxieties, and the action bias they induce, may dramatically magnify both the likelihood and size of a severe adverse outcome. It follows that government regulation, affected as it is by the public demand for law, is likely to stumble on the challenge of low probability harms as well. The government should not swiftly capitulate if the public is demonstrating action bias and showing an excessive response to a risk whose expected value is quite modest. A critical component of government response should be information and education. But if public fear remains high, the government should determine which measures can reduce most cost effectively, almost in the spirit of looking for the best “fear placebo.” Valued attributes for such measures will be high visibility, low cost, and perceived effectiveness. Reducing fear offers two major benefits: (1) Fear itself imposes significant costs. (2) Both private and public responses in the face of fearsome risks are likely to be far from rational. These observations lead to the difficult questions of how to monetize and reduce public fear. The answers lie well beyond the current topic.

In a similar vein, the extract below from the Global Economic Forum Report discusses similar types of reactions from major catastrophes and specifically mentions the asteroid threats to humanity. An Emerging Spectrum of Catastrophic Risks: Existential Threats ({originally} Contributed by the Global Agenda Council on Catastrophic Risks) Throughout history, humanity has been all too familiar with catastrophes affecting life and livelihoods on a major scale: earthquakes, floods, drought, tsunamis, cyclones and so on. Increasingly, however, the new risks coming into focus are more complex, more uncertain and potentially exponentially more consequential. These are existential risks – those that could either annihilate intelligent life or permanently and drastically curtail it potential. Natural disasters could conceivably trigger existential risks in combination with new technologies – a possibility suggested by the March 2011 tsunami that caused a meltdown at the Fukushima nuclear power plant in Japan. There is also the theoretical potential for “error or terror” in emerging sciences, such as nanotechnology or synthetic biology: within a few decades, for example, it may become as feasible to create real viruses in a home laboratory as it now is to create computer viruses on a home computer. Among other existential risks is the possibility that breakthroughs in artificial intelligence could move rapidly in unexpected directions; the spread of antibiotic-resistant bacteria could dramatically set back modern medicine; solar super-storms could devastate vital information and communications technology networks; climate change could tip into a self-reinforcing, runaway phase of rising temperatures; a meteorite could hit a densely-populated area or an asteroid could strike the earth. Although these threats sound forbidding, there areways to prevent most of them, or at least to mitigate their impacts. While research and innovation can provide new approaches, established institutions can also play an important role. For example, in October 2013 the UN General Assembly approved the creation of an International Asteroid Warning Group. It is important for the public and private sectors to work together to address existential risks. The private sector has experience and expertise to offer in the realms of strategic planning, organizational design, institutional adaptation, research, scientific investigation and technological innovation. However, effective public-private collaboration will require vision, strategy and commitment to more extensive, consistent and systematic approaches at the country, regional and international levels. This, in turn, requires an appreciation that existential risks exist not only in the realism of science fiction but also in reality. Note: Existential risks as defined by Nick Bostrom of Oxford University.

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It is not, therefore, surprising that a number of analyses of similar low-probability/highconsequence disasters result in recommendations that call for monitoring and increased research and development. That R&D would be oriented toward both better monitoring and mitigation aimed at reducing the threat itself, but it would also extend to methods for a recovery from such a disaster. Examples are found in the Organization for Economic Cooperation and Development’s report on systemic risks (OECD), the National Academy of Sciences report on NEOs (US National Academy of Sciences), and the UN Office for Disaster Risk Reduction (UN Office for Disaster Risk Reduction, UNISDR). The United Nations report lists five categories that it tracks where nations have increased their programs to deal with potential disasters of all sorts. The categories are governance and institutional arrangements, risk identification and early warning, knowledge and education, underlying risk, and preparedness and response (UNSIDR). A disaster of the magnitude discussed in this report is assumed to be inevitable and avoiding it is not an option. The monitoring and mitigation efforts, ones that have the greatest potential to alleviate public fear, are emphasized. The literature on NEOs is slightly different. The engineering- and science-dominated space agencies are more focused on programs to avoid a NEO hitting the Earth than they are on disaster mitigation and recovery. Balancing that, the few studies that have been done by international organizations such as the UN and the OECD focus more on the near-term responses – monitoring and prediction technologies. The US National Academy of Sciences report on NEOs mentioned above covers both aspects – monitoring and preventing a NEO impact – but its clear recommendations are near term and realistic, improving the detection and prediction. Finally, one of the fears underlying the large asteroid hitting the earth is the evidence that such an event led to the extinction of the dinosaurs. The analogy is that the same type of event could have similar effects on human beings. A very new study has developed a theory from scientific evidence that the asteroid’s effect on the climate of the Earth during the reign of the dinosaurs was only one event in a series of other preceding natural events that created a “perfect storm,” and the combination of climate changes and the NEO impact in Mexico acting together led to the demise of the dinosaurs (Ghosh 2014). If future research confirms this theory, there is a reasonable probability that even the “global catastrophe” of a NEO event may not have as severe an impact upon human beings as feared and that the Earth and its inhabitants are resilient and could survive.

Conclusion In summary, for the foreseeable future, humanity will likely have to bear the risk and uncertainty associated with a highly improbable NEO catastrophe or an extreme solar weather event that might threaten widespread or even global mass extinction. Such an event would, of course, threaten not only humanity but many other species as well. Funding and programs that are specifically directed toward avoiding such an occurrence are unlikely to be forthcoming in the near term. Major international funding initiatives will likely depend on numerous factors that include technological breakthroughs in detection, new space servicing and robotics, and a political and macroeconomic environment that is amenable to global agreements for an international defense fund. However, as with other types of natural disaster potentials, there are many ongoing indirect R&D programs, technologies, and mechanisms that are currently funded which will increase our understanding of NEOs, help alleviate excessive fear of the unknown, and contribute to the ability to monitor and predict possible impacts on Earth. These along with the continued technological developments for in-space activities extending lifetime of satellites, removing human-created debris Page 10 of 11

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in space, on-orbit space servicing, and new space technologies that might be deployed to use valuable space-based natural resources may also be directly applicable to protecting the Earth from experiencing the worst-case scenario of a devastating threat to human beings.

Cross-References ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Regulatory Aspects Associated with Response to Cosmic Hazards ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards

References B612 Foundation, Sentinal, Data Sheet, http://sentinelmission.org/sentinel-mission/sentinel-datasheet/ (accessed 12/16/14). Ghosh P (2014) ‘Bad luck’ ensured that asteroid impact wiped out dinosaurs. BBC News, 28 July 2014. Accessed at: http://www.bbc.com/news/science-environment-28488044 Kliesen KL (1994) The economics of natural disasters, The Regional Economist, St. Louis Federal Reserve Bank, April 1994. https://www.stlouisfed.org/publications/re/articles/?id=1880. Accessed 30 July 2014 NASA Jet Propulsion Lab. http://www.jpl.nasa.gov/asteroidwatch/fastfacts.cfm. Accessed 31 July 2014 NASA, Asteroid fast facts. Jet Propulsion Laboratory, Pasadena. http://www.jpl.nasa.gov/ asteroidwatch/fastfacts.cfm. Accessed 31 July 2014 NASA (2014) FY2015 President’s Budget Summary Request. National Aeronautics and Space Administration, Washington, DC, p PS-2 Natural disasters: counting the cost of calamities|The economist. http://www.economist.com/node/ 21542755/print (accessed 12/16/2014) Sunstein CR, Zeckhauser R, (2008) Overreaction to fearsome risks, Harvard University Law School Program on risk regulation, research paper no. 08–17, Dec 2008 UNISDR (2013) From shared risk to shared value – the business case for disaster risk reduction. Global assessment report on disaster risk reduction. United Nations Office for Disaster Risk Reduction (UNISDR), Geneva US National Academies of Science (2010) Defending planet earth: near-earth object surveys and hazard mitigation strategies. National Academy Press, Washington, DC World Economic Forum (2014) Global risks 2014, 9th edn. World Economic Forum, Geneva

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Major Gaps in International Planetary Defense Systems: Operation and Execution Michael Potter* International Institute of Space Commerce, Douglas, Isle of Man

Abstract The current focus related to planetary defense concentrates on detecting cosmic hazards. However, the largest gap in planetary defense is the organization of an appropriate response revolving around operations, command, and control and execution of a planetary defense mission against all threats to the world today. This need for a global response capability applies whether this involves an asteroid, a comet, or a coronal mass ejection of some other threat. There is a need for clear management and control structures that are built on a framework that is based on multilateral enforcement and peacekeeping conventions. Some action has recently been initiated within the United Nations framework via the Committee on the Peaceful Uses of Outer Space at the behest of the General Assembly. But this is really an initial step that must be considered as inadequate in terms of implementing a truly full-scale global response to a major and potentially devastating event with a potentially global impact. Without such framework it is not possible to begin to properly plan for operationalizing planetary defense.

Keywords Asteroid; Global cooperation; Space hazard; International cooperation; Multilateral; Near-Earth object; Peacekeeping; Practical models; Structures; International relations

Introduction Most experts spend a significant amount of time trying to identify the various cosmic hazards that exist. Thus they bring attention first to the larger existential issue of space threats and secondly to the challenge of building systems of detection and early warning of space hazards. Certainly there is a sequential logic to emphasizing public awareness and support, and there is absolutely a requirement for the development and deployment of detection and alert infrastructure or even a plan for one. It is also logical to argue that beyond detection and beyond alert, the greatest gap in planetary defense, at this moment, is that there is no effective planetary defense infrastructure. It is important to note that the asteroid 2012 DA14, with the potential impact power of 1,000 atomic bombs, that missed the Earth (on the same day that the completely unrelated and undetected Chelyabinsk meteor hit Russia) was detected by an amateur astronomer ▶ http://www. nasa.gov/content/goddard/around-the-world-in-4-days-nasa-tracks-chelyabinsk-meteor-plume/#.UwIWPldVUc. This potential major city-killing asteroid was found not by a ministry of defense or *Email: [email protected] Page 1 of 7

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a national space agency. It was, in fact, discovered by an amateur astronomer, a Spanish oral surgeon. Apparently this surgeon represents a significant part of our planetary defense detection infrastructure. And further, perhaps it could be argued that the citizens of Chelyabinsk and the inhabitants of Tunguska, where an asteroid with the power of 1,000 Hiroshima’s hit 106 years ago, are also essentially human cogs in our planetary defense system (Around the World) ▶ http://earthsky.org/ space/what-is-the-tunguska-explosion. Assuming that humanity can indeed make substantial progress on the space hazard detection and warning front in the coming years, the next critical question is what is the next step from an operational and execution point of view? In the near-to-medium term, there are two realistic response scenarios – a response that is effectively dominated by a single country or region, or a response that is truly multinational in substance. In order to be truly effective in the longer term, the multinational capability, backed by an agreed international framework, is essential.

Detecting Cosmic Risks Is Just the Start of What Needs to Be Done If one views the common dilemma that many national leaders confront, it is not unusual to be presented with two options, with both being bad options but hopefully with one option being slightly less worse than the other. In the case of actively confronting a planetary hazard, the first challenge would likely be assessing relative probabilities of risks. How likely would the hazard affect the planet? What sort of danger does it present? How many lives are at stake? What sort of economic impact and dislocation might it cause? How much will it cost to mount a defense, and what are some of the consequences from mounting a defensive mission? Will the action from the defensive measure adversely affect one nation or population more than another? Is there a possibility that a defensive action can create more future hazards? Could mounting a mission to target a smaller more immediate threat make it difficult to respond to a larger less immediate threat? Assuming that a leadership team can satisfy themselves on the above issues, it is still clear that a response mission dominated by a national or regional player will still involve a great deal of international communications and cooperation. Nevertheless, ignoring the scientific and technical challenges for a moment, simply from a mission command and control point of view, the operation would very much resemble a space agency mission or require something akin to a military tactical operation.

Creating a Planetary Defense Capability A planetary defense mission is extremely complex due to its international leadership and integration implications, including design, development and testing, and the scale of its operational execution requirements, not to mention funding. These represent huge challenges in today’s political environment. Additionally there is the issue of the dual-use technologies that are interconnected to planetary defense. The same technologies that can protect the planet can also provide offensive military capabilities. This “dual use” aspect of military systems for humanitarian and civilian purposes can be observed in a variety of ways today. In the area of orbit debris response, high-powered laser systems that might divert a space-based collision could also be a potential space weapon. The systems to track orbital debris and maintain space situational awareness are also designed to track missile Page 2 of 7

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strikes. The systems that are used to track asteroids, observe extreme solar weather events, monitor terrestrial storm systems, and so on may be operated by defense agencies to support military operations. Under the limits of current national political realities and budgetary allocations, one must try to imagine and assess what the scale of space hazards might be and what resources are needed to face these hazards. This risk assessment process would include an attempt to bind the magnitude of the cost and the scope of complexity of a planetary defense effort and the potential size of a recovery response. The larger the scale and complexity, the greater the need to stimulate a more robust and unified international response to a true “black swan” event. In the area of multilateral peacekeeping, it is not necessarily the scale of the actual task that drives internationalism but often the political complexities and political sensitivities of a particular region or mission. While international peacekeeping, for example, may broaden international participation, such multinational effort may be less efficient in terms of command and control than if carried out by a single nation which might be entrusted with carrying out the same sort of activities. Internationalism, almost by definition, carries more administrative and leadership overheads and costs than a do-it-alone approach would have entailed. Often with mega-science and technology projects, when the lofty project mission and vision statements are stripped away, we often see them strongly influenced by the development of a national industrial base. A large and complex industrial base, while arguably required to support national missions and future state goals, can often be translated into the need for awkward industry subsidies and institutional inefficiencies (One hundred year starship study). One must always trade off efficiencies in order to obtain multinational support and participation. One of the key questions that will impact the scope of a global response to a space hazard, or a possible massive response effort, will revolve around the size of the hazard and the amount of time that we on Earth have to respond to the hazard – either before, in the case of an asteroid or comet threat, or perhaps after, in the case of a recovery from a massive and damaging extreme solar event. The larger the hazard and the greater the period of time for preparation and prevention or for a massive recovery effort, the greater will be the need for orchestrated and institutionalized global participation to respond to the particular space hazard. Alternatively stated, the smaller a specific hazard, involving a shorter time horizon, that might be effectively dealt with by one or two players, the more likely there will be an efficient unilateral or limited multilateral response. In such instances there is likely no global participation and response accomplished outside an international institutional structure. Often multinational mega-science projects seem to revolve more around job creation and the building of indigenous industrial capabilities, rather than executing the original intended goal of the project itself. National political and economic concerns often trump almost everything else including longer-term goals such as coping with climate change or planetary defense. Currently no nation has a powerful, focused national space strategic plane development that is being undertaken for the purpose of making humanity a multi-planetary species. Likewise developing commercial space plane systems is not being undertaken as part of a robust planetary defense.

A New Set of Priorities of Space Agencies Space agencies need to update their strategic plans in several regards. The first change would be to explicitly identify the identification of cosmic hazards and to undertake planetary defense against Page 3 of 7

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such hazards as a primary goal. The second change would be to seek to integrate planetary defense efforts and technology development within the context of its other longer-term programmatic goals and objectives. In fact, the longer-term goal of developing the technologies and systems needed to become a multi-planetary species is a logical plan B in case we fail at plan A in defending our planet. Depending on the particular planetary threat to be faced, money may not be the most significant issue. Planetary defense is not so much a technical issue, as it is a matter of national and international political prioritization and the allocation of funding among alternative programs. Recently, NASA launched two initiatives. One program is the so-called 100-Year Starship and the other is the “Fragile Oasis” program. Fragile Oasis is inspired by the increasing awareness of the fragility of our planet, when viewing the Earth from outer space – the so-called overview effect (100-Year Starship). The 100-Year Starship project is an initiative which challenges thinkers and policymakers to strategize the key issues that would be involved with running a multigenerational project to launch a starship that could reach beyond the Milky Way galaxy. If the two initiatives were, for instance, viewed in the longer-term context of planetary defense and preservation of the human race, these two initiatives would seem to dovetail nicely together. Both program initiatives address the logical conclusion of an ultimate planetary defense strategy. As many astrophysicists such as Stephen Hawking have said, we must leave the cradle of the Earth sometime if only for the purpose of not putting all of the eggs of humanity into one basket. The goal of becoming a multi-planetary species is thus ultimately not about industrial expansion or space technology development but the preservation of humanity and the ultimate planetary defense.

The Risk of Cosmic Hazards Is Larger than Popularly Known A recent report from the World Economic Forum in Davos (2014), Switzerland, from one of its committees – in this case one related to space activities – stated the risks to the world economy posed by cosmic hazards in this fashion: “Catastrophic risks from space are low-likelihood but high impact events. Extreme space weather, for example, could harm satellites, disrupt pipelines and telecommunications networks, and collapse electric grids. Large objects impacting Earth could cause even greater regional or global damage” (“Bringing Space”). This report notes the possibility of great damage but minimizes the danger by characterizing the risks as being of “low likelihood.” Such reassuring assessments, however, conveniently ignore a lot of evidence. A reanalysis of historical astronomical observations from Mexico suggests that the Earth narrowly avoided a “near-extinction event” just over a hundred years ago. There is considerable evidence that a billion-ton comet may have missed Earth by only a few hundred kilometers as recently as 1883. Each fragment was bigger than the asteroid or round comet thought to have hit Tunguska, Russia, in 1908 that created great damage to the region. (This day. . .) Analysis of the 1883 photographic evidence suggests that had the 1883 comet hit Earth, it would have been the equivalent of 3,275 Tunguska events occurring in the span of 2 days. This could indeed have been an event so devastating that many species, including humans, may not have survived (Hubert Foy 2013) (Fig. 1). In 2012, there was a coronal mass ejection from the sun that largely headed away from the Earth, but if this event had occurred just a week later, it would have been comparable to the Carrington event, and it may have wiped out much of our space infrastructure and perhaps much of our global Page 4 of 7

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_81-1 # Springer International Publishing Switzerland 2014

Fig. 1 A fragmenting comet that nearly missed Earth in 1883 would have looked similar to this Hubble image of the Schwassmann-Wachmann 3 Comet

electrical and telecommunication grids. In addition the world population, urban concentration, and dependence on electric power system, modern transportation, and space systems have grown exponentially in the last century, and this means our vulnerability level has actually soared without it being that obvious.

The Need for Urgent Action Must Be Recognized Planetary defense should be viewed both as morally right and technically feasible by the entire world community. For those who are not interested in defending the planet, they should recognize the extent of the risk and the dangers of the lack of foresight and inaction. The words of former US president George H. Bush (1991) at the opening of the US Holocaust Museum are in this regard remarkably apt: Here we will learn that each of us bears responsibility for our actions and for our failure to act. Here we will learn that we must intervene when we see evil arise. Here we will learn more about the moral compass by which we navigate our lives and by which countries will navigate the future. (George H. Bush)

The context of President George H. Bush’s words was quite different, but the lesson is vividly clear. There is a price for inaction. There is a need for an active program to create a global framework for planetary defense against all types of cosmic perils. Unless there is an effort to create an active defense initiative, there could well come a time where there is a need to build memorial parks, to honor the millions that were condemned to death through a lack of comprehension and inaction.

A Planetary Defense Model Based on Multilateral Peacekeeping Operational action plans should be developed for response when a space hazard is discovered. Demonstration test missions should be designed and flown to demonstrate and validate the most promising defense options for planetary hazards.

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The current UN Committee on the Peaceful Uses of Outer Space (COPUOS) efforts to develop a framework for international decisions and coordinated actions are a worthwhile first step. Even so there remains serious doubt as to whether such a framework would be sufficient or truly adequate to a true global crisis. Ultimately there is a need for a much more commanding model. This is for a framework that creates a mechanism for multilateral enforcement and global peacekeeping mechanisms. The strength of multilateral peacekeeping is that the objective is usually humanitarian, with a tremendous focus on political and legal legitimacy and immediate positive impact. The weakness of multilateral peacekeeping generally revolves around: – – – –

Mission creep Exit strategy Discipline and professional conduct of one’s own troops The frailties, complexities, and dangers of dealing with competing local religious, tribal, warlord, and other constituencies – A serious study of how to apply the model of multilateral peacekeeping to a global response to either an imminent cosmic hazard and planetary defense or recovery from a cosmic hazard needs to consider these factors. This means both an assessment of the weaknesses and what the appropriate corrective actions might be could be applied.

Conclusion Chapter VII of the Charter of the United Nations provides the framework within which the Security Council may take enforcement action. It allows the Council to “determine the existence of any threat to the peace, breach of the peace, or act of aggression” and to make recommendations or to resort to nonmilitary and military action to “maintain or restore international peace and security.” For over half of a century, the United States has utilized the Chapter VII military sanctions under UN authorization. Desert Shield/Desert Storm in the early 1990s represented only the second American initiative, one which was provided a UN license for the use of force without restricting the manner in which the US-led coalition was to “secure Iraq’s immediate and unconditional withdrawal of its forces from Kuwait.” While required to provide periodic updates to the UN Headquarters, the coalition was allowed full planning and operational freedom to use “all necessary means” to execute the mission. This may indeed be the most efficient and effective model and framework for organizing a mission to defend against cosmic hazards. In addition the UN should declare that all people should be able to lead their lives free from fear of preventable space hazards. This should become a fundamental human right. Those who undertake efforts to protect humanity from space hazards ought to be able to do so free of the threat of legal liabilities and concerns relating to compensation under the auspices of a sort of cosmic “Good Samaritan” legal standard. These concepts need to be further developed and incorporated into the existing legislation and conventions – perhaps those related to space liability. An obvious data point in terms of both international space activities and cost is the International Space Station (ISS). By the time the ISS is decommissioned in the coming years, between $150 billion and $200 billion dollars will have been spent in a fully cost-loaded analysis. Compared to the International Space Station, planetary defense needs to be viewed as a low-cost global insurance policy. The B612 Foundation has pioneered the use of the nonprofit model for the detection of near-Earth objects. The Sentinel Project is a remarkable example of what can be accomplished by international Page 6 of 7

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cooperation within the constructs of a nongovernmental organization. In fact, developing a plan for a global grassroots planetary defense initiative can accomplish a great deal in a very efficient and cost-effective manner. Initiatives such as “open source” hardware and software development can be an important factor in helping to save our “fragile oasis.” In the global computer technology ecosystem, hundreds of billions of dollars have been saved through open-source initiatives. With clear management and control structures built on the framework that we have previously seen with existing multilateral enforcement and peacekeeping conventions, we can close the largest piece of the planetary defense gap. Such integrated systems and international frameworks can ensure that humanity has a fighting chance of defending all life forms here on planet Earth. Note: Portions of this chapter are protected under the Creative Commons, Attribution, Non Commercial (CC BY-NC) license, 2014. Published with permission of Michael Potter.

Cross-References ▶ Active Orbital Debris Removal and the Sustainability of Space ▶ Directed Energy for Planetary Defense ▶ Economic Challenges of Financing Planetary Defense ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Planetary Defense, Global Cooperation and World Peace ▶ Regulatory Aspects Associated with Response to Cosmic Hazards ▶ Risk Management and Insurance Industry Perspective on Cosmic Hazards ▶ Strategic Issues Involved with Planetary Defensive Systems and Active Debris Removal Systems

References Around the world in four days: NASA tracks Chelyabinsk meteor plume. http://www.nasa. gov/content/goddard/around-the-world-in-4-days-nasa-tracks-chelyabinsk-meteor-plume/#.UwIWPldVUc Bringing space down to Earth. World economic forum annual meeting, Jan 2014, Davos Bush GH (1991) Remarks on the occasion of the dedication of the Holocaust Museum. Washington, DC Foy H (2013) Re-Analysis of 1883 observations suggest that a billion-ton comet buzzed Earth. Space Saf Mag. http://www.spacesafetymagazine.com/2013/01/02/reanalysis-observationsrecorded-1883-zacatecas-mexico-suggest-fragments-billion-ton-comet-close-earth/ One hundred year starship study. NASA. http://100yearstarshipstudy.com/ This date in science: the explosion. http://earthsky.org/space/what-is-the-tunguska-explosion

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Planetary Defense, Global Cooperation, and World Peace Michael K. Simpson* Secure World Foundation, Broomfield, CO, USA

Abstract Out of a growing sense of shared vulnerability on a planet whose cosmic environment is recently better known and seemingly less benign than it once appeared, an international response to the cosmic hazards posed by some near-Earth objects and other significant space phenomena has begun to take shape. Although asteroid strikes are far from the only or even most likely threats posed by Earth’s cosmic neighborhood, they have a tangible character that makes them easy to visualize by many people, and they could, in a worst-case scenario, lead to apocalyptic consequences. Thus, among the many very real hazards covered in this handbook, the threat of asteroid impacts is one that has inspired sufficient study and political action to have brought two new institutions into being with the mission of protecting not just a few select countries but the entire planet. Seeking to draw some insights for the problems remaining to be addressed from the progress made in the area of defense against NEOs and to a certain extent other major space hazards, this chapter looks at the political environment and pathways for cooperation that have led to this progress. Lastly, it looks at some of the work remaining to be done to ensure that institutions that have been designed on paper could actually someday meet the challenge of delivering protective measures including something as dramatic as deflecting a massive space rock bound for an unwelcome rendezvous with Earth.

Keywords Asteroid; Global cooperation; Outer Space Treaty (OST); Transparency; Liability; Association of Space Explorers Panel on Asteroid Threat Mitigation (PATM); Inter-Agency Space Debris Coordination Committee (IADC); Space Data Association (SDA); Disaster Charter; Group on Earth Observation (GEO); UN Committee on the Peaceful Uses of Outer Space (UN COPUOS); International Code of Conduct for Outer Space Activity (ICoC); Group of Governmental Experts on Outer Space Transparency and Confidence Building Measures (GGE); International Asteroid Warning Network (IAWN); Space Mission Planning Advisory Group (SMPAG); Action Team-14 (AT-14); UNISPACE III

Introduction As many chapters in this volume have pointed out, humankind has made some considerable progress in its ability to identify many cosmic hazards including asteroids and comets that present a possible risk of collision with Earth. We have even advanced some creative ideas about how asteroids in particular, detected early enough, might be deflected sufficiently for them to pass us by harmlessly.

*Email: [email protected] *Email: [email protected] Page 1 of 11

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Until very recently, however, progress has been much less substantial on the critical questions of how we would decide to act at all and who would take that decision. In some ways this is hardly surprising. Much of human history has focused most attention on decisions about how to defend oneself from other groups of humans perceived to be hostile or potentially so. Throughout this long social evolution, humankind has developed a distinct preference for maximizing the autonomy of its decision making and preserving independence and freedom of action in the face of outside threats whether real or imagined. This period of history has also been characterized until very recently by a tacit acceptance of the fact that human beings could not act effectively to prevent a threat posed by cosmic hazards. Such action was in the hands of either God or random fortune. In the last 50 years, things have changed rapidly. First humankind proved its ability to reach space with rocket propulsion and to orbit objects it had created. Then it demonstrated the ability to go to the Moon, to the inner planets, to more distant planets, and even to much smaller targets like asteroids and comets. Along the way humanity perfected space navigation, developed great skill in rendezvous, and honed its capacity for space surveillance. By the early twenty-first century, it was no longer possible to argue credibly that humankind had no possibility of conceiving and executing a mission capable of affecting the course of an asteroid. Although a similar statement about most comets, especially those with orbits highly inclined relative to that of Earth, may yet be impossible to make, asteroids represent the vast majority of space objects with a significant chance of striking the Earth. Thus, we entered the new century in a technical environment in which deflection of an Earthbound asteroid, however difficult or costly, was understood to be possible. Ironically, this good news left us with a political problem and several ethical dilemmas. The problem was rooted in the reality that although an inbound asteroid threatened the entire planet due to “nuclear winter” effects and uncertainty about the actual point of impact, there were very few countries that actually possessed the technical and financial means to mount a deflection mission. Since none of these countries had agreements that could be construed to cover shared decision making with each other let alone other countries that might be affected, the default option would have been an independent action, probably conducted under the usual cloak of military secrecy and viewed with intense suspicion by other space-capable and non-space-capable countries around the world. As one expands the implications of this scenario, we could quickly reach a point where the greatest threat posed by an incoming asteroid of “city-killer” size was how nervous countries reacted to each other’s independent and politically opaque preparations to intervene. Ethically, the challenges related to the inevitable reality that to deflect an asteroid bearing down on the Earth, one would often have to temporarily make some parts of the Earth’s surface more at risk as the asteroid was nudged to a trajectory that eventually would cause it to miss the planet altogether. Since many non-space-capable countries were likely to occupy those parts of the surface, independent, opaque action would be likely to leave them very anxious, if not enraged. A second moral issue is equally disturbing. What if the technically advanced nations were each individually to determine that an asteroid of significant size was on a collision course with Earth but presented zero likelihood of significantly impacting them and then chose to do nothing but “take the hit”? The effect of these independent decisions would then be to open the possibility that the eventual collision devastated some part of the world with no capability of protecting itself. Preventable deaths and material devastation would not have been avoided. To a large extent, this chapter is about how these political and ethical issues have been confronted, the progress that has been made, and the work remaining to be done. It presents an interesting story of international and cooperative initiative. Unlike some of the world news we confront these days, it also provides some reasonable grounds for optimism. Page 2 of 11

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The Political Environment Understanding the relationship of any space activity to global cooperation and world peace requires understanding the unique political characteristics of the cosmos. Space is universal high ground. Navigating through it necessarily puts an object above every sovereign state on Earth and as such arouses the concern of every military leader charged with protecting national territory. No military planners have ever wanted to see anyone, especially a potential adversary, occupy a position higher than their own, even briefly. Yet objects orbiting Earth can routinely pass over head at regular intervals. The situation looked even scarier in the mid-1960s as the Soviet Union and the United States raced each other to the Moon. Then, the stakes were not limited to occasional overflights by satellites; they included the possibility that the victor in the Moon race might also gain permanent control of the high ground of Earth’s natural satellite on which military bases and powerful weapons could be placed. With neither the United States nor the Soviet Union absolutely confident that it would get to the Moon first, and with many states that were not in the race fearful that the victor might try to lay territorial claim to it much as Balboa had once claimed all lands bordering the Pacific Ocean in the name of the Spanish Crown, the conditions were right for the first of the five space treaties to be negotiated. The result of that first negotiation was the Outer Space Treaty (OST) of 1967 (UN Treaties 2008, pp. 3–8). In a somewhat revolutionary act, it secured the agreement of its parties to forsake for all time any claim of sovereignty over a celestial body beyond Earth. In so doing it created a legal and political environment that was unprecedented and simultaneously gave birth to the inevitable need for cooperation in resolving any conflicting objectives in space activity. There is no attempt here to make this a definitive synopsis of all the legal tenets and principles that might impact a mission to intercept and deflect an asteroid or otherwise undertake an active mission to protect Earth from a threat from space, but some ideas are so central to understanding the context in which peaceful cooperation in such an endeavor could be carried out that they are worth mentioning. The Outer Space Treaty conferred full responsibility for any activities carried out in space on nationstates (Article VI). It established the “principle of cooperation and mutual assistance” as a guiding principle and incorporated “due regard to the corresponding interests of all other States Parties to the Treaty” as an obligation (Article IX). The treaty also came down squarely on the side of transparency in a way that would establish a useful foundation under the efforts 40 years later to broaden the international base of information available to track near-Earth objects passing near to Earth: In order to promote international cooperation in the peaceful exploration and use of outer space, States Parties to the Treaty conducting activities in outer space, including the Moon and other celestial bodies, agree to inform the Secretary-General of the United Nations as well as the public and the international scientific community, to the greatest extent feasible and practicable, of the nature, conduct, locations and results of such activities. On receiving the said information, the Secretary-General of the United Nations should be prepared to disseminate it immediately and effectively. Article XI

Consistent with its Cold War origins, the Outer Space Treaty also revealed one of the great phobias that, having survived the end of the Cold War, would inevitably impact discussions about how to respond to an asteroid threat: States Parties to the Treaty undertake not to place in orbit around the Earth any objects carrying nuclear weapons or any other kinds of weapons of mass destruction, install such weapons on celestial bodies, or station such weapons in outer space in any other manner. Article IV

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Political discussions of asteroid response always seem to include arguments for and against the use of nuclear devices. Opinions can range from those who resist any use of them whatsoever to those who argue that to use anything else is to place the planet needlessly at risk. As more and more creative solutions for altering an asteroids trajectory have been advanced, the debate gets increasingly interesting. It certainly will not be resolved here. Nonetheless it is impossible to understand the intensity of some countries’ reactions to any asteroid response option that defaults to independent action by nuclear capable countries without being aware of how deeply rooted in some quarters is opposition to the use of nuclear devices even in apparent defense of the planet. It is also worth noting that although the OST also bans “any other kinds of weapons of mass destruction” from space, no objections to the proposed use of kinetic impactors massive enough to deflect asteroids (and therefore large enough to cause considerable terrestrial damage) have surfaced. Other options such as focused beam systems that are now proposed were not developed at the time that the OST was negotiated. Ultimately concern about restricting the nuclear option would play a role in creation of the first international, cooperative institutions charged with responding to an eventual asteroid threat. Before leaving the discussion of the effect of space treaties on the political environment in which countries would confront decisions to respond to an Earth-bound asteroid, it is useful to know that two of these treaties specifically address the issue of liability and that that liability is essentially unlimited. Especially under the Liability Convention of 1972, a country launching a mission to intercept and deflect an asteroid could find itself completely liable for any resulting damage no matter how catastrophic: A launching State shall be absolutely liable to pay compensation for damage caused by its space object on the surface of the Earth or to aircraft in flight. Article II

No doubt a lot of ink would flow to create the legal briefs necessary to determine whether a bungled deflection mission that leads to a catastrophic impact on Earth would constitute damage caused by a space object, but even if a country acting independently did avoid legal liability for such a catastrophe, the political liability would be enormous. This alone would provide an incentive to find a structure for cooperative, multilateral response. Beyond the legal agreements, the political environment of asteroid response includes strong concerns about the weaponization of space. Every technology powerful enough to change the course of an asteroid has some military potential. Any sensor network good enough to look for objects large enough to inflict significant damage on Earth has the potential to gather military intelligence. Some of the earliest discussions of the need for coordinated, cooperative response to potentially hazardous objects addressed this concern and came quickly to recognize that only processes that were largely open and transparent would avoid facing crippling opposition from countries who suspected that asteroid response was merely an excuse for developing high-tech tools for powerful military systems. Inevitably skepticism and suspicion also arose out of the large differences in size and substantial asymmetry of national space capabilities. Although several countries could claim the ability to launch large missions to intercept an asteroid, the relative experience of those countries in rendezvousing with fast moving objects far from Earth differed widely. Furthermore, distribution of detection capability was very uneven, with only the United States having funded a significant program dedicated to finding potentially hazardous asteroids of 140 m diameter or bigger. The inclusion of near-Earth objects as one of the three focus areas of ESA’s Space Situational Awareness initiative and the possibility of adding the International Scientific Optical Network (ISON) headed by Russia to the pantheon of NEO detection capabilities hold the promise of expanded capacity

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going forward. The Sentinel infrared telescope proposed by the B612 Foundation, a nongovernmental organization based in the United States, would dramatically enhance detection capabilities if it can be successfully funded. Although most countries might have been very glad to leave the expense of asteroid detection to others, they were not immune to worries that countries with detection capabilities might sound a false alarm for political purposes or to provide cover for a weapons development program. To some people such fears may seem irrational, but they can be expected where great differences in power are present. More importantly for our purposes, they are present in the current political environment confronted by those trying to deliver on the promise of a cooperative global response to a threatening NEO. As noted in the introduction, some countries also worried that space-capable states might simply choose to do nothing if their tracking of an incoming asteroid indicated that their own territory faced little or no risk. When the Association of Space Explorers Panel on Asteroid Threat Mitigation (PATM) was meeting regularly between 2005 and 2008, one of the countries eager to host it was Costa Rica, which lay directly under the path of danger then predicted for a possible impact from the recently discovered asteroid, Apophis. One of the questions posed more than once during the session held there concerned how small states could be certain that larger ones would act to protect their interests in cases where the larger ones appeared to be at less risk. With this political environment of skepticism, suspicion, and anxiety, any broadly accepted solution would need to make use of every pathway for cooperation available. Fortunately there were many to choose from.

Pathways for Cooperation Despite the competitive and military roots of much space activity, it has proven to be a fertile ground for acts of cooperation and collaboration. Early work on the four broadly adopted space treaties, especially the Astronaut Treaty, reflected an understanding that space was a special place where the need for synergy could easily overwhelm the desire for independence. The International Space Station Intergovernmental Agreement (IGA) particularly reflects this cooperative bias, bonding 15 countries into a team that has built and managed one of the most complex human-made structures ever created. Given that key players include the United States, Russia, Japan, France, Germany, Italy, and Canada, various combinations of which have been at war with each other in recent history, the cooperative governance of the ISS is particularly noteworthy. There are other interesting examples of cooperative activity emerging from space activity. The Inter-Agency Space Debris Coordination Committee (IADC) joins 12 space agencies in an effort to identify cooperative opportunities for mitigating space debris (IADC TOR, pp. 7–8). The Space Data Association (SDA) links 18 members and participants in a cooperative effort to avoid satellite collisions through improved conjunction analysis, the Disaster Charter (Charter On Cooperation To Achieve The Coordinated Use Of Space Facilities In The Event Of Natural Or Technological Disasters). This latter agreement has institutionalized cooperation in the use of space facilities and data to respond rapidly and effectively to the management of disaster situations and the delivery of relief to victims (Disaster Charter, Article 2). Lastly, drawn from a population of examples that really is quite large, there is the Group on Earth Observations (GEO) founded in 2002 with the task of coordinating the integration of independent national systems of Earth observations into a “system of systems.” Under this concept the many sources of Earth observation data including that supplied by

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satellites could be made more useful to the goals of economic development, Earth research, disaster recovery, and terrestrial applications. The tradition of cooperation in dealing with the use and benefits of space activity is thus pretty firmly rooted in contemporary practice. This too is part of the political environment confronted by those seeking to address cosmic hazards cooperatively and is part of the political culture of several key political institutions that played important roles during the effort to create a structure for cooperation to meet the global threat posed by potentially hazardous asteroids. As Sergio Camacho’s chapter on the UN System has shown, cooperative, international engagement on the peaceful uses of outer space has roots almost as deep as the space age itself. Although the ultimate authority of UN action in this domain comes from its Charter and the action of the UN General Assembly (UNGA), the heavy lifting has mostly fallen to the UN Committee on the Peaceful Uses of Outer Space (UN COPUOS) and its two subcommittees, Legal (LSC) and Scientific and Technical (STSC). These bodies would play a critical role in the effort to build institutions equal to the task of confronting an asteroid threat internationally. During the 5 years from 2008 to 2013 that the UN System worked to build those institutions, there were two other major political processes under way that also strengthened the spirit of openness and cooperative intent that they would require to succeed. One was the broadening debate over the possible creation of an International Code of Conduct for Outer Space Activity (ICoC), and the other was the Group of Governmental Experts on Outer Space Transparency and Confidence Building Measures (GGE). Notwithstanding a focus on the anthropogenic threats of space activity that left no room to consider cosmic hazards, these organizations would provide a backdrop of cooperative possibility that would allow discussions of protection from cosmic hazards of all types and very specifically asteroid defense to proceed with optimism. Although hobbled by an awkward start that left some countries worried about the intent of the initiative, the effort to negotiate an ICoC for outer space activities steadily gained political ground as it broadened the base of input and listened carefully to the concerns of the early skeptics. Although not directly connected to the process of developing institutions to meet cosmic threats, the lessons of the ICoC discussion seemed to be well learned by those trying to mitigate threats to Earth from space hazards. Every effort was made to include all countries with an interest in the process, and countries that might otherwise have seen the issue as unimportant made the effort to stay in touch with the discussions, decision points, and arguments. This breadth of attention would have a very important impact on the institutional solutions that ultimately emerged. The role of the GGE was important but more subtle. For one thing this was the second GGE to tackle the challenge of improving transparency and building confidence in outer space activities. The first had delivered its report to the United Nations in 1993, and the mere fact that a second was needed 20 years later leads some to conclude that the first had not had the impact desired. In fact a close reading of the recommendations emerging from the 1993 GGE report shows that it was on track toward several innovations and developments that were to improve information flow and cooperation in the years that followed (GGE 1993, pp. 84–89). Particularly with respect to improvements in data sharing concerning potential collision between satellites and improved sharing of Earth observation data in connection with disaster mitigation and economic development, much progress was made on the 1993 recommendations in the two decades following the report. Thus, by the time the second GGE on space TCBMs convened in 2011, its focus on the importance of transparency and confidence building to the sustainability of any long-term political cooperation in space activity resonated perfectly with the need for cooperation in the face of a PHA. Perhaps even more importantly, as it reached consensus on a report to the UNGA in 2013, it demonstrated not only that cooperation was possible between great space powers that had not Page 6 of 11

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always agreed on key matters of policy in recent times but also that that agreement could extend more broadly to include other countries whose abilities, capacities, and experiences with space activity extended over a very wide range. All of this cooperative karma in the background would prove useful, because no matter how well drafted the working document developed by the PATM might have been, once submitted to UN COPUOS, it needed to achieve political consensus to move from an object of discussion to a basis for action.

Progress Through Consensus Ultimately, what emerged from the discussions and debates at UN COPUOS was a recommendation that two institutions be endorsed for the purpose of advancing an international response to future asteroid threats. The first is the International Asteroid Warning Network (IAWN) that would gather and share asteroid data from around the world and provide assessments from an international team of experts. This maximizes data acquisition while also assuring users of the data that it is credible and not subject to political spin. The second institution is the Space Mission Planning Advisory Group (SMPAG) that would combine many of the world’s space agencies into an expert team able to advise UN COPUOS on actions that should be endorsed and taken in concert to avert or mitigate impact. Much has already been said about the critical role of the UN system in building the political foundations for international response to an asteroid threat. There was a dynamic interaction in that process that bears review, however, if we want to understand the full role of cooperation in peacefully advancing planetary defense. One important challenge confronted by a consensus-based system like that practiced by UN COPUOS is overcoming the political inertia present at the beginning of nearly every policy-making discussion. UN COPUOS has overcome this inertia with an elaborate network of working groups and action teams that can do enough initial work on an issue area to permit developing momentum slowly enough for others to get on board comfortably along the way. With an issue as complex and multifaceted as planetary defense, however, the inertia is increased by political anxieties over military implications, information sharing, power asymmetries, and technical complexities. In the case of asteroid defense, it proved useful to have a working document produced outside the system by civil society and then presented as a point of departure to those whose task would be to create a politically viable proposal from it. It also proved useful that the coordinator of the input from civil society was an international group whose expertise and credibility were unassailable, the Association of Space Explorers (ASE). Representing the international community of people who have been among the early pioneers in human space flight and admitting only those who have flown in space, ASE came to the discussion of asteroid defense with a combination of technical expertise and the experience of having gazed at the fragility of Earth from above its atmosphere. ASE shared with the Secure World Foundation (SWF), one of their principal funders and like ASE an official observer at UN COPUOS, the belief that humanity knew more about how to detect and deflect asteroids than it knew about how to make a decision to do either. Acting on this belief, ASE created a Panel on Asteroid Threat Mitigation (PATM) and invited experts from many countries and disciplines to join in the search for a politically acceptable, technically well-grounded, and operationally effective means of coordinating a global response to what would inevitably be a global threat were a large asteroid to be found tracking on a collision course with Earth.

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Working on the project from 2005 to 2008, the PATM produced a thoughtful document with enough solid, practical suggestions for Action Team-14 (AT-14) of UN COPUOS to use it as the foundation of the hard political thinking and institution building necessary to bring the IAWN and SMPAG into existence (Asteroid Threats). AT-14 was itself a part of the UN COPUOS response to the Third United Nations Conference on the Exploration and Peaceful Uses of Outer Space. Created in 2001, this action team reflects the desire of UN COPUOS to pursue concrete opportunities for implementing the Conference’s many declarations, one of which dealt very directly with near-Earth objects and the potential risk they posed to the planet (UNISPACE III, p. 3): To improve the international coordination of activities related to near-Earth objects, harmonizing the worldwide efforts directed at identification, follow-up observation and orbit prediction, while at the same time giving consideration to developing a common strategy that would include future activities related to near-Earth objects

While the other international, cooperative initiatives cited here have been important for the background of cooperative practice, they provided during the discussion of building a structure for cooperation in the face of asteroid threats here the UNISPACE III declarations indicated a clear sense that NEOs and their potential threat to Earth were a matter that deserved international attention. The work would prove difficult, but at least now UN COPUOS had assigned the task to a body that would take it very seriously indeed and the principle that collective UN action against a cosmic threat was possible would have a tangible example. AT-14 had therefore been at its work for nearly 8 years when it received the PATM report in 2009, and over the next 3 years, the action team carefully shaped it into a document that could not only muster political consensus but could also meet the criteria of technical grounding and effective operation. Along the way the three institutions recommended by PATM were re-crafted into two, and the role of the Security Council that PATM had assumed would be at the center of response was reassigned to UN COPUOS itself. In some ways this reassignment reflected the triumph of the cooperative ideal in this endeavor since it demonstrated a desire to make use of an agency that understood the technical issues, that did not have a tradition of great power veto, and that broadly included the large number of countries whose interest in space was sufficient for them to join willingly in the pursuit of planetary defense against a threat from space. As the world moves now from conceiving and launching institutions designed to protect it against asteroid threats toward the detailed work of establishing terms of reference, operational procedures, and patterns of work that can fulfill its mission, there is some reason to believe that we have proven a model for cooperative global response that may address other cosmic threats as well. Coronal mass ejections, solar flares, and increased cosmic radiation in the wake of a reduced terrestrial magnetic field and improved methods of addressing orbital debris are now next in line. Since these hazards can threaten the world’s electronic grids and cause and threaten significant damage on Earth’s surface, this is a very good thing. Hopefully these may all lend themselves to solutions developed out of a similar blend of cooperative tradition and the proven efficacy of collaborative solutions.

The Work Ahead It is not always the devil who lurks in the details. Sometimes long-sought angels and helpful sprites can be concealed there as well. For IAWN and SMPAG, the quest for those angels and sprites will pass through the development of terms of reference, operating procedures, and habits of communication. The experience of the ISS and its IGA will help as will lessons learned from the IADC and

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even the nongovernmental SDC. There will be more countries involved in this process, however, and so we can expect there will be more lessons learned and more input to assess along the way. We can also expect the volume of data to increase as well as the IAWN extends its sources to more and more countries, and those countries become ever better at gathering information. If the B612 foundation proves successful in funding, launching, and operating its Sentinel mission, the data growth could prove exponential. That data is certain to reveal many more potentially hazardous objects than anyone would have predicted just a few decades ago as it gives us the ability to detect smaller objects and those spending a large portion of their orbital period inside Earth’s orbit where the Sun’s glare currently shields them from view. It may also generate the ability to intervene against objects as small as the one that exploded over Chelyabinsk in February 2013, an object far too small to be detected by current means, but one large enough to have caused significant damage and injury in a city that it effectively missed by over 100 km. On the one hand, this will be good news, but it will also greatly increase the theater of operations confronted by the recently created institutions and likely increase the number of countries who find themselves eager to be involved in the process of assessment and planning. It will also greatly increase the challenge of communication faced by the new institutions. A working group convened in Boulder, Colorado, in 2011 concluded that although manageable, there were many challenges to communicating about near-Earth objects and the dangers they represented (NEO Communications, pp. 18–21 and 28–29). Here, too, the challenge will be to cooperate sufficiently to ensure that messages are received accurately irrespective of the culture or language of the recipient. This is a good example of the wisdom that a cooperative and global response to a cosmic threat does not mean that all aspects of the response will be uniform or homogeneous. Synergy thrives on difference and we can expect a great deal of difference in the way people react to cosmic hazards. Of course, not everyone welcomes this level of international diversity. There will almost certainly be advocates for a return to national independence and supposed freedom of action. Although no one doubts that major space powers could eventually act alone in the face of a serious asteroid threat to their territory and any demonstrated reluctance to act on the part of the new institutions, complete independence of action is now clearly understood as a myth and probably always should have been. No independent action taken apart from broad international consensus could ever have been launched against an asteroid without creating enough anxiety in other states to bring about a political situation perhaps more dangerous than the asteroid threat, itself. At least now, pre-consultation, transparency of information, and an international exchange of concerns are largely guaranteed. Knowing whether that will be sufficient to coalesce into an international response may just have to wait for the detection of a space rock that has Earth undeniably in its cross hairs.

Conclusion Although Earth-threatening situations have often been the subject of mythology, until recently science confined its planetwide, apocalyptic scenarios to the distant future or to those situations where humans spoiled their environment through war or environmental pollution. As we learn more about our cosmic environment, science has revealed other threats where the danger can confront us in real time and the origins clearly lie beyond the realm of human causation. Faced with a real and external threat to which they did not respond, however, people could still bear the responsibility for any eventual catastrophe, because they would bear the burden of inaction.

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Given the state of technology available to humankind, we no longer have the luxury of shrugging in helplessness after some future piece of space rock, perhaps no bigger than the Tunguska object of 1908, lays waste to a large part of the human community. With a significant number of the world’s countries engaged through the IAWN in the search for hazardous space objects and SMPAG representing a cooperative structure in place to facilitate synergy of action rather than response at cross purposes, excuses for inaction are rapidly evaporating. The same will likely also become true for threats that appear less tangible like those resulting from solar flares or radiation storms. As communication becomes more democratized and the flow of information across political lines less easy to control, threats that genuinely put the whole planet at risk will increasingly be recognized as such and widely known. People and their sovereigns will clamor to be informed of the risk’s magnitude and involved in developing patterns of response. The result is likely to be more global cooperation and more examples of the power of a world at peace to act effectively in its own defense.

Cross-References ▶ Basics of Solar and Cosmic Radiation and Hazards ▶ Comet Shoemaker-Levy 9 ▶ Deflecting or Disrupting a Threatening Object ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ International Ground Observatories for Potentially Hazardous Asteroid Detection ▶ Keyholes ▶ Legal and Regulatory Considerations ▶ Minor Planet Center ▶ NEO Shield Program of the EU ▶ Potentially Hazardous Asteroids and Comets ▶ Private Initiatives: The Sentinel Project ▶ Spaceguard Survey by NASA – Behind Schedule and Seeking to Increase Mapping Capabilities ▶ The B612 Foundation’s Sentinel Space Telescope to Create a Hundred Year Warning Program ▶ The Palermo and Torino Scales (Risk Assessment of NEO Collisions and Magnitude of Impact) ▶ United Nation Activities (AT-14) ▶ Working Group on Near Earth Objects (WGNEO) of the International Astronomical Union

References Asteroid Threats Association of space explorers, asteroid threats: a call for global response, (Houston, Texas USA: 2008). Text available at. http://www.space-explorers.org/committees/ NEO/docs/ATACGR.pdf. Accessed on 4 Mar 2014 Disaster Charter Charter on cooperation to achieve the coordinated use of space facilities in the event of natural or technological disasters Rev.3 (25/4/2000).2. Text at. http://www.disasterscharter.org/ web/charter/charter. Accessed on 4 Mar 2014 GGE (1993) United Nations General Assembly, prevention of an arms race in outer space, study on the application of confidence-building measures in outer space, A/48/305, 15 October 1993, 144 pp

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IADC TOR Inter-Agency Space Debris Coordination Committee, terms of reference for the InterAgency Space Debris Coordination Committee (IADC)” IADC-93-01 (rev.11.2, public version), Status: July 11, 2011. Index to text at. http://www.iadc-online.org/index.cgi?item¼docs_pub. Accessed on 4 Mar 2014 NEO Communications Secure World Foundation, near earth object media/risk communications working group report, (Broomfield, CO: June 2012) in cooperation with the Association of Space Explorers UN Treaties (2008) Office for Outer Space Affairs, United Nations treaties and principles on outer space, United Nations, New York, Reference: ST/SPACE/11/REV.2 UNISPACE III United Nations general assembly, report of Third United Nations Conference on the exploration and peaceful uses of outer space (Vienna, 19–30 July 1999), A/conf.184/6, 157 pp

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Introduction to the Handbook of Cosmic Hazards and Planetary Defense Joseph N. Peltona* and Firooz Allahdadib a Executive Board, International Association for the Advancement of Space Safety (IAASS) and Director Emeritus, Space & Advanced Communications Research Institute (SACRI), George Washington University, Arlington, VA, USA b Space Science & Environmental Research, ARA Corporation, Albuquerque, NM, USA

Abstract Each year humans travel through space on their own very special spacecraft called planet Earth, but that trip around the Sun is actually a very hazardous journey. Without the benefit of a space program, the human species has spent millions of years unaware of the wide range of cosmic dangers that lurk out in space. In some ways humans are playing Russian Roulette with a random set of rock and metal bullets that were first fired at this small six sextillion ton planet millions if not billions of years ago. These bullets are potentially hazardous asteroids, bolides, and meteorites. In addition there are comets that streak down toward the Sun from the Oort Cloud every few years. Perhaps an even greater danger to humans come from the nearby nuclear furnace called the Sun. Solar flares, coronal mass ejections, and continuous radiation from the Sun are warded off by the Van Allen Belts, the Earth’s geomagnetosphere, and the ozone layer that sits atop the stratosphere. During the height of the Sun’s activity that follows an 11-year cycle, the radiation and solar eruptions from the Sun hit very dangerous levels. Current research that examines the Van Allen Belts and the Earth’s magnetic shielding suggests that the protective magnetosphere shielding that protects life could be changing. And then there are other hazards from space. These risks include increasing levels of orbital debris and returning spacecraft that may contain nuclear, radiological, or chemical dangers, or even biological dangers. The Handbook of Cosmic Hazards and Planetary Defense seeks to examine in depth the various dangers that the delicate Earth Habitat could be exposed to from outer space risks and what research needs to be done to understand in greater depth the nature of these dangers. And the editors and the authors of this book are defining “cosmic hazards” in the broadest possible terms. Thus, these hazards from outer space include comets, asteroids, and bolides that might collide with Earth. The risks to humans and modern global infrastructure include solar flares, coronal mass ejections, solar proton events, and other space weather events, as well as changes to the Earth’s protective shielding from cosmic hazards such as a lessened magnetosphere, altered Van Allen Belts, and a depleted ozone layer. This chapter also addresses orbital debris (in terms of its impact on Earth and aircraft as well as such debris possibly endangering vital infrastructure and satellite networks). This chapter even considers such hazards as cosmic radiation, antimatter events, and lethal biological agents that could come to Earth in various forms, including via returning spacecraft or astronauts. The last part of the chapter builds on what is known about the dangers of outer space and presents the various types of activities that humans are beginning to undertake to protect life on Earth. This latter part of the handbook sets forth what types of activities can serve to protect humans and indeed all types of life-forms from mass extinctions. Such massive loss of species that include a third or more of all types of life-forms has been documented to have occurred at least five times during the *Email: [email protected] Page 1 of 25

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Earth’s existence. These past mass extinction events have come about, on average, every 300 million years or so, over the last two billion years. These massive losses of life serve as powerful reminder that not only are there powerful hazards that can wipe out life on a massive scale, but that unless protective measures are undertaken, they could happen again with devastating effect. The rise of mass urbanization that may exceed 70 % of all people living in towns of cities by 2,100 coupled with the enormous dependence on modern infrastructure such as electric power grids, telecommunications and information systems, and vast utility plants make twenty-first-century vulnerabilities to cosmic risks far greater than any previous time in human history. The objective of this chapter is thus to present in detail what is known about the hazards of outer space and the scientific and technical nature of these threats. Further this handbook seeks to identify but what steps can be undertaken to initiate a creditable planetary defense effort. It is such an effort that can unite all the people of planet Earth in a great and common undertaking.

Keywords Advanced Composition Explorer (ACE); Antimatter; Bolides; Biological and radiological contamination from space; Carrington event; COPUOS; Coronal mass ejections; Earth guard; ESA; Gamma rays; Geomagnetosphere; Mass extinctions; Millennium ecosystem assessment; NearEarth objects; NASA; NEOWISE; Orbital debris; Palermo scale; Potentially hazardous asteroids; Sentinel infrared space telescope; Solar and Heliospheric Observatory (SOHO); Solar flares; Solar max/solar minimum; Sustainability of space; Space weather; Torino impact hazard scale; UNISPACE; United Nations; Van Allen Belts; Van Allen storm probe; Wide-Field Infrared Survey Explorer (WISE); X-Rays

Introduction The threats that come from outer space are both frightening and numerous in types and nature. The Earth and its various life-forms – both animal and plants – are only protected by a thin atmosphere and a magnetosphere subject to change and weakening over time. There are powerful eruptions from the Sun and a large number of potentially deadly asteroids that only in the last 50 years have become systematically detectable by scientific satellites. Likewise it is only recently that scientific investigation has revealed the true nature and magnitude of mass extinction events where a significant number of species living on planet Earth were wiped out. Today the extent of dangers to human survival and the scope of risks to modern ways of life that come from outer space are much more clearly understood than ever before. And these dangers come from many different sources that include near-Earth objects, potentially hazardous asteroids and comets, solar flares, coronal mass ejections, solar proton events, cosmic radiation as well as solar weather events and even more exotic concerns such as matter-antimatter collisions. And human activities involving space exploration and applications can also lead to threats and dangers. These include orbital debris that can threaten vital space infrastructure like communications satellites, meteorological spacecraft, and positioning navigation and timing satellites. There is even risk from reentering spacecraft that can bring back chemical, radiological, nuclear, or even biological threats. As orbital debris mounts and more and more satellites deorbit, this could bring physical danger to aircraft or people and facilities on the ground. Today exponential population growth and human industrial activity that generates greenhouse gases when interacting with the Sun’s energy

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Fig. 1 The 180 km across meteor crater on the Yucatan plateau (Graphic Courtesy of NASA)

can lead to climate change and global warming that could lead to life-annihilating results such as the runaway heating that occurred years ago on the planet Venus. Even this is a form of risk from the cosmos, but because so much is being written on this subject and is a matter of such broad concern, it is not explicitly addressed in this handbook. This handbook thus defines “cosmic hazards” broadly. The purpose of this book is to explore all of these dangers that come from outer space and shares as much technical and scientific knowledge as is now known about these “space threats.” It continues on to explore what actions might be undertaken to prevent or mitigate these space threats in terms of a concerted effort to undertake a planetary defense against these dangers. This introductory chapter seeks to provide an overview of the various elements addressed in the totality of the handbook to provide a synoptic context as to the nature of the threats and how space research and ground-based observations are constantly seeking to learn about these various potential threats and to begin charting a course forward toward a systematic and hopefully effective planetary defense of life on Earth.

The Threat from Near-Earth Objects In the last few decades, scientists have discovered more and more evidence of the various types of cosmic hazards that lurk out in space. In 1980s a huge circular crater was discovered that is 180 km across and 900 m deep. This huge and perfectly shaped circular crater ranges along the coast of Mexico’s Yucatan plateau and extends well out into the Gulf. By the 1990s space imaging was able to confirm that this was indeed the remnant of the giant asteroid that smashed into Earth. This event, which was the equivalent to the explosion of tens of thousands of nuclear bombs blocked out the Sun with the cloud of dust that ensued. This was an event termed “Nuclear Winter” during the Cold War era. This mass extinction event (known as the K-T event) not only killed off the dinosaurs some 65 million years ago but it also extinguished about two thirds of all plant and animal species that were alive on the day of this devastating impact. This was Earth’ Big Bang. The ultimate verification that this was the remnant of a huge meteor collision proved that not only could potentially hazardous

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asteroids could hit Earth but do so in a way that can wipe out human civilization as it is known today (Dinosaur Killer 2003) (Fig. 1). The more recent wake-up call about space hazards that can crash into planets at supersonic speeds came in 1994. This was when astronomers were able to train their telescopes on Jupiter and watch the impact of a multi-part comet as it crashed at tremendous velocity into the Solar System’s largest planet. This all occurred some 20 years ago when the Comet P/Shoemaker-Levy 9 (note that its formal designation is D/1993 F2) collided with Jupiter. This comet that was first witnessed on March 24, 1993, by Carolyn and Eugene Shoemaker and David Levy at the Palomar Observatory in California had, of course, been predicted well before this catastrophic event actually occurred. There were actually twenty-one discernible parts to the comet “complex” – with some parts being as large as 2 km in diameter (Comet Shoemaker-Levy Collision with Jupiter 1994). During a 6-day period from 16 to 22 July 1994, pieces of the comet bombarded Jupiter with explosive force that could easily be seen through telescopes. This was the first such collision of two Solar System bodies ever to be observed and recorded, and the impact on Jupiter and its atmosphere were truly spectacular. A previous encounter with Jupiter’s gravitational field in 1992 had actually pulled the comet apart to form the 21 pieces. The observed speed of collision was at 216,000 km/h or at134,000 miles/h. The huge scars from the impact left on the surface of Jupiter were larger than the Great Red Spot and remained apparent for many months. Since the size of the Great Red Spot is more than ten times the entire cross section of the Earth, one can only imagine the destructive power of this six day galactic bombardment (Comet Shoemaker-Levy Collision with Jupiter 1994). It is completely plausible that if this 21 piece avalanche of space rocks had hit Earth, human life as it is known with all its modern life and societal infrastructure would have been completely wiped out along with vast numbers of plants and animals. The fact that Comet P/Shoemaker-Levy 9 impacted Jupiter rather than Earth is not at all unusual because comets and asteroids hitting Jupiter are calculated to be at least 2000 times more likely because of Jupiter’s huge cross section and its tremendously strong gravitational field. In short Jupiter’s enormous gravity well along with the Sun actually serves as a sort of “cosmic vacuum sweeper” to attract dangerous space rocks to crash into this giant planet or the solar furnace rather than Earth. Saturn and Uranus to an extent help as well, but Jupiter serves a particularly vital function in protecting Earth from comets and potentially hazardous asteroids. For those who say that such threats can be forgotten since they are millions of years away, they need to focus on the destructive force of the Shoemaker-Levy comet that would have destroyed human civilization and that this event occurred only two decades ago. Scientists have tried to come to terms with the types of threats that near-Earth objects of various kinds that exist out there and to try to put these dangers into some form of perspective. The result was the so-called Torino Scale that was formally adopted by the scientists that attended the Unispace II Conference in Vienna, Austria. The concept of the Torino Impact Hazard Scale was to create a system analogous to the Richter Scale for Earthquakes. The problem is that the general public has difficulty dealing with very small probabilities combined with hugely disastrous consequences. Tell them they have a 1 % chance of surviving an operation and this makes some sense. Tell them that within a range of 50 years to over a 1000 years, there is a very serious chance of a big space rock doing very serious damage to global society, and they are perplexed but have no clue what to do about it. If it is not immanent, the public tends to say let’s move on to today’s crisis. When the Shoemaker-Levy comet was smashing into Jupiter, the Jet Propulsion Labs web site on this topic had millions of hits in 1994, but today the event is all but forgotten (Fig. 2). The Torino Scale helps us assess the enormity of a threatening collision by a near-Earth object. There is also something called the Palermo Scale that provides a useful assessment of the likelihood Page 4 of 25

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Fig. 2 Torino impact scale for potentially hazardous asteroid (Graphic Courtesy of the UN Unispace Conference) http://neo.jpl.nasa.gov/torino_scale.html

that a rogue space object will actually collide with Earth. NASA maintains a so-called Sentry Risk Table that monitors all known near-Earth objects and assigns to those that could come into conjunction with Earth a Palermo Scale number. Near-Earth object 2007 VK384, for instance, will swing by Earth in 2048 and has a Palermo scale number of
1.57 which means a very low probability (NASA Sentry Risk Assessment). The problem is that the needed inventory of the skies is far from complete. But fortunately scientists and engineers are developing improved infrared space telescopes that when combined Page 5 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Fig. 3 Charting the orbits of potentially hazardous asteroids (Graphic Courtesy of NASA)

with Earth observatories, can help us better map the heavens to discover possible threats to Earth with the hope that a major threat could be averted before it could destroy human civilization. The Wide-Field Infrared Survey Explorer (WISE) has helped identify an estimated 80 % of all potentially hazardous asteroids that are greater than 1 km in size that might possibly collide with Earth (WISE: The Wide-field Infrared Survey Explorer). Unfortunately a near-Earth object that is just 30–40 m in size can be a “city killer,” and only a small fraction of these smaller potentially hazardous asteroids have been identified. Despite the fact Jupiter “vacuums” up many potentially hazardous asteroids, there are a surprising number of space rocks out there that could still do us a great deal of harm. The following graphic shows in blue the orbital characteristic of a “typical” near-Earth asteroid and in red is a “typical orbit for a potentially hazardous asteroid (See Fig. 3 below). It is far from reassuring to know that there are tens of thousands of these potentially hazardous space rocks out there circling the Sun in orbits that could intersect with Earth twice each time they go around the Sun. This “typical” PHA orbit, which relates to asteroids known as the “Apollo” type of near-Earth objects, actually represents about 62 % of the population according to JPL scientists. As can be seen in Fig. 4, there are also asteroids that have larger orbits than that of the Earth and thus are greater than one astronomical unit in size. These types of asteroids could become a problem if their orbits decay over time. These “Amor” asteroids are about 32 % of the population. Then there are the Aten asteroids that have an elliptical orbit that goes near the Sun in their perihelion and then reach an apogee well above the Earth’s orbit and can also cut across Earth’s orbit twice a year. These represent about 6 % of the population (Jet Propulsion Laboratory background on PHAs).

Different Types of Near-Earth Objects and Their Various Kinds of Orbits Former Congressman George Brown, who headed the Congressional Science and Technology Committee for many years was memorialized by a US legislation passed in 2005 to assign the

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Apollo

Aten

Amor

Semimajor Axis ≥ 1.0 AU Perihelion ≤ 1.02 AU Earth Crossing

Semimajor Axis < 1.0 AU Aphelion ≤ 1.0167 AU Earth Crossing

1.02 AU < Perihelion ≤ 1.3 AU

Inner Earth Objects (IEOs) Aphelion < 0.983 AU Always inside Earth’s orbit (aka Apohele)

Type Apollo

Near-Earth Population 62% of known asteroids

Aten Amor

6% of known asteroids 32% of known asteroids

IEO

6 known asteroids

Fig. 4 Different types of orbits for near-Earth objects (Graphic Courtesy of the Jet Propulsion Laboratory)

task to NASA and Earth observatories to chart 90 % of all near-Earth objects (larger than 140 m) by 2020 (Section 321 of the NASA Authorization Act of 2005). This initiative is sometimes informally known as Spaceguard. And NASA together with other space agencies and ground observatories has been working on this quite hard for well over a decade. The good news is that the paths of about 80 % of the biggest of these rocks that are a kilometer or more in size are now known. The WISE space telescope and especially the NEOWISE program and Earth observation have given us a good deal of good information. This is reassuring. Yet, those nearEarth objects that are under 1 km in diameter are still 90 % unknown despite the efforts that NASA and others have made. One might be tempted to say: “Probably that is okay because it is the really big space rocks that would really do catastrophic harm.” But they would be wrong. Let us consider something like the space rock known as Apophis, which is only about 300 m in diameter. This particular space rock will whiz by Earth in 2029 and again in 2036. This “small space rock” could do enormous harm. At a speed of 60,000–70,000 km/h, damage from an Apophis-sized rock could be equivalent to thousands of atomic bombs, and at the right location, it could trigger a tsunami that could destroy the Eastern Coast of the USA or Tokyo and Osaka in Japan. When it realizes that over 80 % of the space rocks of this size are still unknown, then any sense of reassurance evaporates away again. NASA has admitted that it cannot achieve the objective of 90 % mapping of all near-Earth objects 140 m in size or larger by 2020 in its formal report to the Congress in 2007. The 2005 Act also required a report to the Congress that analyzed possible options that might be employed to divert a hazardous space rock from colliding with Earth if actual threats were detected. While the NASA report did analyze options, it also indicated that better technology needed to be developed and no single method (with the possible exception of nuclear devices being used) provided a high level of confidence as to a fully effective response. This lack of progress as reported in 2007 and in the years that have followed is why the B612 Foundation has started its own initiative to launch the Sentinel infrared space telescope to increase a planetary early warning system for life-threatening space rocks. This new initiative that was formally announced on June 28, 2012, will be dedicated to surveying and identifying all near-Earth objects down to 140 m in size and has the potential to identify threats down to 30–40 m in diameter. As currently designed and engineered, this space telescope could even seek to create over time an inventory of virtually all space rocks that could create major damage. This is a $450 million project

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Fig. 5 Representation of sentinel infrared space telescope deployed in space (Courtesy of B612 Foundation – Not to Scale)

that is seeking to build, deploy and operate an infrared space telescope that could provide us consistent and long-range warning of any possible future strikes by a potentially hazardous asteroid that might be lurking out there in space (The B612 Foundation) (Fig. 5). And unfortunately there is much more to be known than just the presence and the precise orbits of these space rocks – even though this is clearly the place to begin. One needs to know about the composition of these asteroids (i.e., rock, dirt, chemicals, or various metals from light to very heavy) and their shape and their relative velocity with respect to Earth. It is also important to know how the Sun’s radiation and gravity can impact these asteroids as well. A smaller asteroid consisting of heavy metals and traveling at a relative velocity of 100,000 km/h might actually do more damage than a larger and “softer” space rock traveling at a slower pace. Here is a calculation based on a 30 m asteroid with a radius of 15 m traveling at 100,000 km/h or 27,500 m/s and based on the assumption that, like Earth, the mass density is six times that of water or about 6,000 kg/m3. The amount of power released by the impact would be 7.250 terawatts. If one were to calculate what an asteroid that is at the low end of what the US Congress specified that NASA would use in surveying the heavens for space rocks, i.e., 140 m across, then the calculated power release would be 740 terawatts. And to assess the impact of an asteroid that is 1 km in diameter, the calculated power release would be 260 quadrillion watts. This is 260,000,000,000,000,000 W. This represents enough energy to keep the Earth running for many, many years if converted to electrical energy. The “typical hurricane” power release, which is much greater than a nuclear bomb, is around 50 trillion watts. Knowledge of the composition is important to know not only in terms of the damage that might be done, but also this is key know in terms of devising a scheme to ward off the impact as well. There is actually a good deal being done to map the orbits of these space rocks. There are research programs to learn about how the Sun’s gravity might create a so-called keyhole effect to change the orbit of a deadly asteroid. These investigations that are seeking information about the Yarkovsky effect are also seeking to learn how the Sun’s radiation can alter over time and thus change the orbit of potentially hazardous asteroids as well. Page 8 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Fig. 6 The so-called String of Pearls Shoemaker-Levy comet streaking in the sky (Graphic Courtesy of NASA from the Hubble Space Telescope)

Activities such as NEOShield (2012) and the Spaceguard Foundation (The Working Group 1995) are now underway to study the best methods to ward off a catastrophic collision with Earth. This is the good news. The more sobering news is that humans are not equipped to deal effectively with a killer asteroid or other potentially hazardous near-Earth object. This is particularly true if it was learned that an asteroid would impact Earth in just a matter of weeks. Fortunately no such fate is immanent.

Comets The number one concern with regard to near-Earth objects is actually asteroids and bolides. This is simply because of their sheer numbers. There are many thousands of these objects that are large enough to cause catastrophic damage to Earth if they should actually collide. Their high relative velocity and mass make them a very lethal encounter of the most unwelcome kind. Yet there are other types of space objects that also could come close to Earth that are also worthy of careful study as well. These are the comets that come streaking down from the Oort Cloud region beyond Pluto on a periodic basis and then go zooming back outside of the Solar System. The most famous of these is the Halley’s comet, but in terms of understanding the threat that a comet might pose to planet Earth, the so-called Shoemaker-Levy 9 comet has no peer (See Fig. 6). The Shoemaker-Levy comet (or indeed its multiple elements) that smashed into Jupiter in 1994 with such devastating force demonstrates with an exclamation point that it is important to track and monitor comets as well. This 1994 event was actually helpful to researchers of cosmic hazards in several ways. It allowed us for the first time to observe and record the effects of comet elements as they smashed into a planet. It also helped us to understand even more clearly the extent to which Jupiter does act as a protector of Earth by virtue of its huge gravity well. The gravitational effect of this huge planet helps to capture

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

both near-Earth asteroids, bolides, and comets that might otherwise someday crash into Earth. Although the same could also be said about other elements of the Solar System with gravitational mass, the truth is that the Sun and Jupiter are by far the main line of defense. Thirdly Jupiter and the Sun could also become logical “ultimate destination targets” if it became possible to develop the technology to divert the orbits of near-Earth objects that are directly threatening Earth – assuming the threat is detected early enough in time. This means that it is the current objective to deploy systems out into space that are capable of changing the path of potentially hazardous asteroids and to redirect them so that they would then be captured by the gravity of the Sun or Jupiter. This would be so as to avoid the danger that they could eventually come back and threaten Earth again at a later date. It has been thought for some time that threat from comets is less than that of potentially hazardous asteroids, but recent reexamination of data from observations made in 1883 from Mexico of what is now thought to possibly be a large comet that very narrowly hit Earth. The following image suggests that humans and indeed all animal life on Earth may have escaped a very large “cosmic comet-based bullet” just a century and half ago. The only reason that comets are considered less of a concern is really a matter of numbers and statistical probabilities. There are only scores of comets to track and be concerned about, while there are many thousands of asteroids and bolides (which are big space rocks that are smaller than asteroids but larger than mere meteorites or micrometeorites), although programs such as the NASA WISE infrared telescope (especially during its NEOWISE stage) have helped to identify a large number of the potentially hazardous asteroids. Nevertheless there is still a long way to go to get an accurate assessment of the space rocks out there that are in the range of 140 m to 1 k in diameter. The Sentinel infrared telescope might even eventually allow us to do an inventory down to the 30 m range. Statistical evidence indicates that there are tens of thousands of near-Earth objects in this range. As noted in the previous section, even a 30 m space rock can release the power of 7 terawatts which is a pretty powerful wallop.

Overview of Threats from Space Rocks The truth is that despite serious efforts to come to grips with the danger from various types of space rocks in near-Earth orbit, there is still a long way yet to go. Scientists are, in effect, in the infancy of mapping cosmic dangers. There are many hidden dangers within the Solar System still to discover. In order to sum up the various types of danger, it is necessary to be concerned about the information provided in Table 1 below (Types of Near-Earth Objects (JPL)). As can be seen in this chart, the Apollo group of asteroids represents 62 % of the known population, Amors represent 32 %, Atens represent 6 %, and there are only a very few Atiras and IEOs. Yet one must survey the sky for all of these different groups of asteroids because any one could be extremely dangerous.

The Sun The Sun is the largest and most powerful object in the Solar System. The amount of energy that reaches Earth each day some 93 million miles (or 149 million kilometers) away from the Sun’s surface is 10,000 times the total amount that all of humanity actually consumes. To say that the Sun is both the life force for planet Earth as well as a potentially destructive force that could also destroy Page 10 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Table 1 Overview of types of “Space Rocks” constituting cosmic hazards to Earth Brief name NECs

Description of hazard Near-Earth comets

NEAs

Near-Earth asteroid or potentially hazardous asteroid

PHAs

Potentially hazardous asteroids. These are considered the most dangerous. These asteroids that come with 0.05 A.U.s. to Earth are thus within 4.65 million miles or 7.5 million kilometers of Earth Atiras NEAs which fly around the same orbit as the Earth (named after NEA Atira Atens Atens cut across Earth Orbit. Since this is at the apogee (or aphelion) Atens are moving at their slowest velocity. This maximizes the likelihood of collision but would likely decrease the speed of impact Apollos Apollos have an orbit very similar to Earth. They travel inside Earth orbit at perihelion but above Earth Orbit at aphelion Amors Earth-approaching NEAs with orbits exterior to Earth’s but interior to Mars’s (named after asteroid 1,221 Amor) IEO Inter Earth objects

Definition Typical period is less than 200 years and trajectory within 0.3 AU of Earth Asteroids whose trajectory come within 0.3 AU of Earth Potentially hazardous asteroids: NEAs whose Minimum Orbit Intersection Distance (MOID) with the Earth is 0.05 AU or less and whose absolute magnitude (H) is 22.0 or brighter Asteroids whose orbit around the Sun are within 0.0167 AU of Earth (very few Atiras exist) NEAs which cut across the Earth’s orbit twice. Its semi-major axis is less that 1.0 AU, while apogee is 1.0167 AU or less (see Fig. 4). Atens represent about 6 % of known NEAs These near circular orbit NEAs have a semi-major axis of less than 1.0 AU but an apogee of 1.02 AU or less. Apollos represent 62 % of all known NEAs Those that are considered potentially hazardous are orbits between 1.017 and 1.3 A.U.s. Amors constitute about 32 % of NEAs or PHAs IEOs have a maximum aphelion of 0.983 AU. Only six such asteroids have been identified

Key terms An astronomical unit: Is 93 million miles or 149 million kilometers and is the mean distance between the Earth and the Sun Perihelion and aphelion: Perihelion is the closest approach point to the Sun, while aphelion is when that object is furthest away. (It is like perigee and apogee for a satellite orbiting Earth) Major axis and semi-major axis: The major axis is the long distance across an ellipse, while the semi-major axis is the short distance across an ellipse (This chart is composed from information supplied by the Jet Propulsion Laboratory)

all life is to state the obvious. Solar activity follows a well-known but not well-understood 11-year cycle that moves from solar minimum to solar maximum. The latest peak in the cycle has reached the during Fall season of 2013 (see Fig. 7). What is known is that there are several types of destructive eruptions that come from the Sun and create hostile space weather for our planet. These are known as solar flares that are associated with sunspot activity and solar proton events (SPEs) and coronal mass ejections (CMEs) that are typically but not always associated with such flares. These eruptions (in terms of violence and frequency), follow this 11-year cycle. A solar flare perceived from Earth is a sudden brightening on the Sun’s surface and a manifestation of a very large energy eruption, like KABOOM. The amount of this energy release is equivalent to millions of atomic bombs going off all at once. The energy release if one actually uses the precise terms of physics can be up to a staggering 60,000,000,000,000,000,000,000,000 J of energy. This is equivalent to one sixth of all the energy the Sun produces each second or the same as 160 million atomic bombs each with a rated explosive power of 1 gigatons of TNT. If one were to try to compare this energy release with the power released in 1 s, it would be 25,000 times greater than the impact power of all of the parts of the comet Shoemaker-Levy when they hit Jupiter. Page 11 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Fig. 7 Images from an observatory in Mexico taken in 1883

This huge energy release, or solar flare (see Fig. 8), is often also accompanied by a blast of plasma mass (or CME) being expelled from the Sun. It is Earth’s good fortune that any CME must travel 93 million miles (or 149 million kilometers) before it encounters Earth’s protective shield in the form of the Van Allen Belts and the world’s geomagnetic field. Usually these coronal mass ejections go off harmlessly into space. This is because Earth actually constitutes a very small target at its location one astronomical unit away (Fig. 9). Flares occur in active regions around sunspots that develop over a period of only minutes in times. Flares create radiation at all frequencies from highly energetic gamma rays and X-rays down through radio waves. Flares that are directed toward the Earth can and indeed do create radio outages. The blast of radiation can disable satellites and can be quite deadly for astronauts in space as well. The power for these eruptions are thought to come from the magnetic energy within the Sun – perhaps just below the corona. These incredibly powerful energy releases are, as noted above, closely associated with coronal mass ejections (CMEs). The exact link between CMEs and flares is still not well established and a flare that is associated with sunspots does not always result in large scale coronal mass ejections. In 1997 the Solar and Heliospheric Observatory (SOHO), a joint undertaking of NASA and the European Space Agency (ESA), was launched in order to study the Sun. The SOHO mission spacecraft was very successful and had a 15-year lifetime that extended through 2012. Although this spacecraft cost $1.5 billion (US), the sharing of costs between the two space agencies made this project more affordable for both of these space agencies. The SOHO research satellite was particularly designed to achieve a better understanding of the concept of harmful space weather from the Sun. Its prime mission was to understand in greater detail and cause of the powerful coronal mass ejections and their relation to the powerful solar radiation flares that occur at varying levels of intensity and frequency during the course of the Sun’s 11-year cycle (NASA-SOHO 1997). During solar max, the Sun can each day have as many as three coronal mass ejections that typically accompany violent solar flares. During the solar minimum, however, CMEs can be as few as once every 4 or 5 days. The reason for this periodic cycle of solar turmoil (in terms of both solar flares and related coronal mass ejections) is still a matter of intensive research and study. The most

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

ISES Solar Cycle Sunspot Number Progression Observed data through Oct 2013 175

150

Sunspot Number

125

100

75

50

25 0

0 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 n− Ja

0 n− Ja

Smoothed Monthly Values Updated 2013 Nov 4

Monthly Values

Predicted Values (Smoothed) NOAA/SWPC Boulder,CO USA

Fig. 8 Solar cycle for the period 2000–2018 (Graphic Courtesy of the U.S. National Oceanic and Atmospheric Administration)

Fig. 9 A solar flare emission from a sunspot (shown in false color to reflect radiation patterns) (Image Courtesy of NASA)

puzzling enigma is why intense solar weather eruptions from the Sun can be 15 times more frequent during solar max in comparison to the more dormant conditions solar minimum (in this case “dormant” only makes sense by comparing conditions to the much more turbulent conditions during solar max). There must be a reason why the nuclear fusion engine that generates so much solar heat and generates great loops of magnetic flux follows with such great regularity this well-documented Page 13 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

11-year cycle. Despite targeted research the reason for this rather precise cycle has eluded solar scientists to date. The SOHO mission nevertheless added new levels of understanding. It is now understood that while the mass ejections do indeed spew forth from the corona, solar flares, in contrast, are now thought to be emitted from the layer of the Sun underneath the corona where sunspots form. Highintensity radiation flares and coronal mass ejections can occur in parallel or separately. Both become more intense and frequent during solar max. SOHO has allowed NASA and ESA scientists to capture 3-D images of sunspots that form below the Sun’s super-hot corona (i.e., 1,000,00 C). It also allowed a better understanding of so-called slow and fast solar wind. The greater understanding of flares and CMEs has allowed up to 3 days warning of intense solar weather conditions. NASA also launched the Advanced Composition Explorer (ACE) satellite in 1997 to study solar activities, and then in 2006, it launched two additional solar research satellites appropriately known as “Stereo.” The Stereo name comes from the fact that the two satellites will fly in formation so that eruptions from the Sun can be imaged in 3-D by being able to record these events from two perspectives. The ACE and Stereo satellites are both focused on solar flares and coronal mass ejections, but the main emphasis is on recording slow and fast solar wind as it travels between the Sun and Earth and to study the highly destructive coronal mass ejections (CMEs) as they blast away from the Sun’s corona. These satellites are thus discussed further in the next section and of course later in the handbook. These spacecraft, despite their prime focus on CMEs, have also produced useful information with regard to sunspot activity and high-energy radiation events as well. Of prime interest in terms of studying the extreme radiation solar flares is the NASA satellite known as the Solar Dynamics Observatory. This satellite monitors flares, especially those in the M-Class up through the X-Class levels, since flares of this magnitude can create radio outages and damage to spacecraft and threaten the safety of astronauts in orbit. An X-Class event is at the highest levels, while an M-Class is ten times less energetic. Solar flares that emanate from disconnected magnetic loops below the corona dramatically affect all layers of the solar atmosphere. These layers of the outer Sun are known as the photosphere, the chromosphere, and the corona. When the flare occurs it produces a plasma medium that is heated to tens of millions of degrees. This intense plasma accelerates electrons, protons and heavier ions of helium that exist within the Sun to velocities that can reach to near the speed of light. These flares produce radiation at all energy ranges from radio waves up to light and ultraviolet radiation. Most of the energy, however, is released as X-rays and gamma rays. The same magnetic surges that create the flares often result in coronal mass ejections as well. Solar flares, as a result of their tremendous power, are dangerous and the ultraviolet radiation, X-rays, and gamma rays can and do blast artificial satellites in Earth orbit and zap the Earth’s ionosphere. Without the Van Allen Belts, without the magnetosphere, and without the ozone layer (which mitigates these blasts and diverts the radiation toward the polar regions), humankind would be in big-time trouble. These flares disrupt long-range radio communications such as shortwave transmissions (i.e., high frequency, very high frequency, and ultra high frequency). This can adversely affect ham radio operators; radar systems; shortwave long-distance, microwave transmission; and over-the-air television transmissions. A solar flare of the highest X-Class range with the exact directionality to hit Earth square on could do even more damage. The so-called Carrington event of 1859 was perhaps the first time that people realized the destructive power of solar events. Carrington, a solar astronomer, was observing the Sun on a “typical Thursday morning” in London when he suddenly saw the development of huge sunspots linked together on the surface of the Sun. These “spots” were many times the diameter of the Earth. Carrington was so excited that he ran downstairs to gather his staff to witness this unique event that Page 14 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

he hastily sketched. The massive “fast” solar wind that originated from this flare hit Earth the next day. This flare and then accompanying CME represented an unprecedented blast of solar fury in all of modern times. The Aurora Borealis was witnessed as far south as Hawaii and Cuba. There was at the time very little electrical devices in use at the time, but at several telegraph offices, paper caught on fire as the coronal mass ejection associated with the flare burned through the ionosphere to the Earth’s surface (Pelton 2013). Today in the age of widespread computers and electrical power use that permeates society, no one knows what the consequences would be if such an event were to happen again. The asteroid strike that destroyed the dinosaurs may be a once in every 600 million years event, but a “Carrington event” that involved a solar flare and a coronal mass ejection may be a once in every 100 and 50 years occurrence if not perhaps of greater frequency. On August 31, 2012, a major coronal mass ejection occurred as registered by the Solar Dynamics Observatory (SDO) satellite. The event was actually on a similar scale to the Carrington Event and the ejection speed was at 5.5 km an hour (or about 900 miles a second). If this CME had directly hit Earth, the scale of this hit might well have taken out most of the world’s satellites and destroyed much of the energy grids as well. A solar flare is also potentially dangerous in many ways as well. Its high-energy radiation might take out most communications and navigation satellites and disable much of the radar tracking systems. Fortunately the Earth’s atmosphere and magnetosphere provide us reasonable levels of protection, except for such issues as skin cancer and genetic mutation. Coronal mass ejections (CMEs) will create much more severe consequences. Fortunately we receive more warning against the impact of this massive onslaught of ionic plasma. The radiation from a flare can reach Earth in a matter of about 8 min, but the “slower” mass ejections that still travel at millions of kilometers/hour typically reach Earth a day to 2 days later. Billions of tons of the solar ionic mass traveling at these incredible velocities, if they were to travel on a trajectory to hit Earth, would create the most extensive damage possible.

Space Weather and Coronal Mass Ejections (CMEs) As noted earlier solar flares and coronal mass ejections are closely related phenomena. The amount of energy associated with the flare is like millions of nuclear bombs going off at once, and if Earth were not 93 million miles or 149 million kilometers away from the Sun, virtually all life on Earth would be in big-time trouble. If a Carrington event were to happen today, it might actually disable many of telecommunication, remote sensing, meteorological, scientific, and military satellites. And the damage would not stop there. A massive CME could wipe out a large percentage of the world’s computers and processors not only in homes and offices but on airplanes, automobiles, and within vital infrastructure that routes transportation and utilities. Thus, this massive surge of space weather could wipe out the electronic controls for water and sewage plants as well as those that control the delivery of electrical power supplies. But the controls for power plants might quickly become a moot point. This is because there would no power to supply. The CME surge of ions that comes with a massive solar storm would also likely knock out most of the world’s power transformers as well. Underground pipelines carrying fuel would not be exempt. These pipes might suddenly carry a huge electrical surge as the CME ions penetrated the ground and travel hundreds of miles (kilometers) to zap distribution lines or blow up inflammable fuels. A big-time hit by a CME is a disaster for which modern technological society is clearly not prepared. Indeed if the CME of August 31, 2012, had occurred just a week later, the Earth and humanity might have encounter the biggest natural disaster of the modern era. Assessments of Page 15 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

this event by NASA scientists have concluded that there is about a 12% chance that a similar extreme solar event could impact Earth within the coming decade. In short the extent of the danger is not known. If a massive CME, like that associated with the Carrington event, did occur, would it indeed send most of human civilization back to the Stone Age? In the most extreme case, such a catastrophe (just like a massive electromagnetic pulse (EMP)) might wipe out most airplanes, trucks, buses, and automobiles by destroying their electronics and making them inoperable. It is possible that a strong enough CME would torch electrical power transformers and eliminate much of today’s electrical power supply. Likewise there is no clear information as to whether such an event might serve to shut down most if not all modern telecommunications and computer networks. Within a brief period of time a truly massive wave of space weather could possibly zap through the Earth’s atmosphere in a way that wipes out most of modern infrastructure. In the worst case condition, much of the world could be without power, telecommunications, reliable water and sewage systems, or modern transport. In large cities, at the very least, food supplies would very quickly become a critical problem as transportation and distribution systems rapidly begin to break down. The exact cause of a CME and its specific relationship to a solar flare remains to be definitively explained. Nevertheless recent scientific research has tended toward the conclusion that the phenomenon known as “magnetic reconnection” is responsible for both coronal mass ejections (CMEs) and solar flares. This term refers to the violent shift of magnetic field lines that occurs when two oppositely directed magnetic fields are suddenly brought together. It is now generally believed that “magnetic reconnection” may happen on what are characterized as solar arcades. It is currently thought that there are many loops of magnetic lines of force that occur just below the corona and that these multiple levels or arcades are defined by the extremes of these magnetic loops. These magnetic lines of force can and do quickly reconnect into a lower arcade of loops, leaving a helix of magnetic field unconnected to the rest of the arcade. The resulting unconnected helix of magnetic field is thought to be the cause of a sudden surge of energy. And this is a truly big – like in gargantuan – solar flare. The energy released can be up to 60 septillion joules. The unconnected magnetic helical field and the material that it contains may (or may not) violently expand outward to form the deadly ionic plasma that result in a coronal mass ejection – the CME. This explanation of magnetic loops disconnecting and violently reconnecting helps to provide a rationale as to why CMEs and solar flares typically erupt from sunspot regions where magnetic fields tend to be stronger. What is not at all clear is why there is an ongoing 11-year cycle where solar flares and CMEs are much less common and energetic, and then build up to solar maximum, and then die down again (Holman 2006). There is a constant flow of space weather from the Sun that is characterized by what is called solar wind. The normal flow of particles from the Sun is sometimes called “slow” solar wind. The most recent research data from the Stereo satellites that are able to capture three-dimensional images of coronal mass ejections show that when the explosive mass ejections occur that the faster CME ions overtake the slower solar wind and in “eating up,” the slower particles create an even more powerful solar weather event by the time it reaches Earth. The power of the impact on the Earth’s protective shield is incredibly strong. The artist representation of solar wind blasting into the protective Van Allen Belts and the shockwaves that this creates give some feel for the enormity of space weather. It is really not easy to convey what the force of perhaps billions of tons of ions hitting the Earth’s protective shield at millions of miles (or kilometers) an hour is (Fig. 10). The question that naturally comes to mind is this: “How likely is a CME event likely to cause global devastation to Earth and to human civilization?” The answer at this stage of scientific space Page 16 of 25

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_85-1 # Springer International Publishing Switzerland 2014

Fig. 10 Artist representation of solar weather hitting the Van Allen Belts (Graphic courtesy of NASA – note Earth is the small blue sphere)

exploration is that the answer is not known. Currently modern society is simply not prepared for something like the Carrington CME event to occur. In 1989 a much less powerful CME event, known as the Quebec event, fried transformers in Chicago, Illinois, and in Ontario and Quebec, Canada. This knocked out electronic power systems for millions of people. It is known that a very powerful CME event would be in a number of ways akin to an electromagnetic pulse (EMP) that a nuclear explosion in space would create. A single EMP event for instance could disable hundreds of millions of computers and processors that permeate the modern world. What is known is that there are a number of key questions to pursue that fall into these two categories: How can research scientists better understand the workings of the Sun, its 11-year cycle, and especially solar flares and coronal mass ejections (CMEs)? The second set of questions relates to how to develop new or better technology to protect modern human society from a massive solar event that could potentially bring much of human civilization back to the Stone Age in virtually a blink of the eye. The dinosaurs had 1 s of warning against the giant asteroid hitting Earth. Earth might have only short warning against a massive CME, and today there is very little that can be done even if there were a day or two warning.

Cosmic Radiation The Sun is the nearest star and it is the main source of radiation. It showers the Solar System and Earth with a tremendous amount of energy – particularly in the ultraviolet frequencies and a constant stream of X-rays and gamma rays. There are billions and billions of stars that are doing the same throughout the universe. Current understanding of the Sun, solar flares, and coronal mass ejections is derived, in part, by studying other stars in the galaxy and beyond. Stars everywhere seem to perform the same types of nuclear fusion processes and emit flares and mass ejections. Here on Earth there is a constant bombardment not only by solar radiation but by cosmic radiation that come from the nuclear reaction in stars, novae and supernovae, and even the mysterious pulsars. Some may think that all needed to be done to protect against cosmic radiation is to put on some sunscreen. Recent experience and scientific study suggest that there are dangers from cosmic radiation that truly need to be taken seriously. It is only through Earth observation satellites that ozone holes in the upper atmosphere layers above the polar regions have been discovered. The Van Allen Belts are formed through the Earth’s

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magnetic field, and space weather ions are diverted from the higher latitudes toward the polar regions and accelerated as they approach the poles. It is for this reason that the Aurora Borealis and Aurora Australis (i.e., the northern and southern lights) light up the polar regions as well as create eerie noises. This aurora zones are typically 10–20 latitude from the magnetic North and South Poles. Radiation is also shielded by the Van Allen Belt and the ozone layer at the top of the stratosphere also serves to screen the most intense ultraviolet radiation. Since this most intense and powerful radiation in the UV frequencies is above the optical range, it is not directly “seen,” but it can certainly be “felt.” In January during the summer months in the South of Australia (Melbourne and Adelaide), Chile, New Zealand, South Africa, or Antarctica or in July the Northern parts of Canada Europe and Russia, one can certainly “feel” the intense radiation coming through. If over time, in response to climate change and upper altitude jet and rocket combustion, the ozone holes widen even further, the danger can increase beyond concerns about sunburn. Already elevated levels of skin cancer have been recorded among those living in the high latitude areas of the world (Mirsky 2012). Even more alarming has been the detection of increased levels of genetic mutation among frogs and amphibians. There is reason to believe that if the ozone holes widen further and no protective measures taken, humans and other plant and animal lives will be subject to genetic mutation that over time could be deadly to the human species (Norby 2012). Today there has been a connection made between climate change and its impact on many parts of the world’s protective biosphere. Thus, there are concerns that go beyond simply global warming to a range of concerns. Thus, scientists are beginning to explore in much greater depth such aspects as the increase in the ozone holes in the polar regions and how this could have adverse impacts that range from skin cancer to genetic mutation to plants and animals.

Geomagnetic Distortions and “Cracks” It is a human fallacy to assume that today’s reality is somehow a norm and that continuity of experience is the norm. In fact the Earth and the species of life that live on it are quite dynamic. Less than 1 % of all species that have ever lived on Earth over time exist today. The so-called K-T mass extinction event that wiped out the dinosaurs actually wiped out some two thirds of all species. There have been at least four other mass extinction events that have come not from cosmic collisions but from climate change and to be more precise due to heat increases. What is important to learn is the extent to which major changes to the Earth and the biosphere linked to what might be characterized as “cosmic events.” It is thought that about every 66000 years, there is a shift in the Earth’s magnetic poles. It is also suspected that when this reversal of polarity occurs, some rather dramatic shifts also occur, but there are precious little details as to exactly what to expect in terms of the impact on modern infrastructure. Since there was no farming and fixed towns and cities nor scientific investigators before 8000 BCE, there is a great deal that is not known. A study published in 2012 by a group from the German Research Center for Geosciences suggests that a brief complete reversal occurred only 41,000 years ago during the last ice age. The reversal lasted about 440 years with the actual change of polarity lasting around 250 years. During this change, according to this study, the strength of the magnetic field dropped to 5 % of its present strength. This part of the reversal process could be a very bad problem indeed for modern electronic infrastructure. What is currently known is that after some 400 years of relative stability, the Earth’s North Magnetic Pole has moved nearly 1,100 km out into the Arctic Ocean during the twentieth century and at its present rate could move from northern Canada to Siberia within the next half century. Page 18 of 25

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Fig. 11 Earth’s magnetic field today and during a reversal (Graphic Courtesy of NASA)

The impact that this reversal of the Earth’s magnetic field might have, in terms of the protective levels of the Van Allen Belts that ward off coronal mass ejections, is far from clear. The likelihood is that it could be catastrophic if not for human life – at least for all of a large percentage of today’s computers, processors, and electrical power systems and much of the infrastructure that modern society completely depends on (Fig. 11). If it is true humans do not have to worry about another polar shift and a diminished greatly geomagnetic field for several more thousand years, this would be a great relief. By the year 27,000, for instance, scientists probably will be a whole lot smarter. But what if there is not some 25000 years left? If there is a major magnetic polar shift coming much sooner, there may be big trouble ahead (Vincent et al. 2006). And there are reasons to have some concerns as to whether “cracks” could be occurring in the Earth’s magnetosphere. As early as 1961 James Dungey of the United Kingdom predicted that “cracks” might form in the Earth’s magnetic shield when the solar wind contained a magnetic field that was oriented in the opposite direction to a portion of the Earth’s field. In these regions with the competing two magnetic fields, it is possible that this can create a “crack” in the Earth’s normal geomagnetic patterns. As noted earlier the process of “magnetic reconnection” can trigger solar flares of greater power and intensity. Here on a much more modest scale, a “magnetic reconnection” could lead to the forming of a modest crack in the Earth’s shield. In this case electrically charged particles of the solar wind as well as ions from the Van Belt could flow below the geomagnetic field. This can bring not only deadly radiation but poisonous gases such as hydrogen cyanide. These small “cracks” were first detected using the International Sun-Earth Explorer (ISEE) satellite as early as 1979. This potentially very serious threat has thus been under study since that time (The Earth’s Magnetosphere Shield 2003). A joint space mission funded by NASA and the European Space Agency, named the IMAGE satellite, has been launched to monitor these “cracks” and to determine the degree to which the Earth’s geomagnetic field might be weakening and to explore whether these dangerous conditions might be increased over time. In early January 2011 there what seemed to be a freak phenomenon where perhaps many millions of birds as well as fish were suddenly killed all at once in various locations around the world. The theory put forth by Russian scientists was that hydrogen cyanide had managed to leak through from the lower Van Allen Belt to an altitude where it could kill birds. The further theory is that this hydrogen cyanide was captured in a way that it fell with rain water and thus was able to also kill a large number of fish (Adams 2011; Stewart and Lynch 2007). Page 19 of 25

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If it is true that solar wind interacting with the Earth’s magnetosphere can create serious cracks to let through poisonous gases or if the polarity shift is occurring earlier than expected and could cause the geomagnetosphere to reduce in strength by a factor of 20, this development could become the most severe cosmic challenge that humanity will face in the next few decades.

Antimatter and Matter Collisions Another threat that is considered today to be obscure but may well be a hazard that should be considered with some scientific care is that of a collision between matter and antimatter. Today within the CERN nuclear accelerator, scientists are able to create minute bits of antimatter that when exposed to matter explode with tremendous force. Some researchers believe that collisions that are ascribed to an asteroid hitting Earth or exploding in the atmosphere might actually be an antimatter and matter collision. In 2007, a supergiant star 200 times bigger than the Sun was utterly obliterated by runaway thermonuclear reactions triggered by gamma ray-driven antimatter production. The resulting blast was visible for months because it unleashed a cloud of radioactive material over 50 times the size of the Sun. SN 2007bi was discovered by the Lawrence Berkeley National Laboratory. The explosion ejected more than 22 solar masses of silicon and other heavy elements into space, including more than six solar masses of radioactive nickel which caused the expanding gases to glow brightly for many months. Giant stars are supported against gravitational collapse by gamma ray pressure. The hotter the core, the higher the energy of these gamma rays – but if they get too energetic, these gamma rays can begin pair production: creating an electron-positron matter-antimatter pair out of pure energy as they pass an atom. The antimatter fueled by gamma rays is generated and then this antimatter is annihilated with its opposite which is regular matter. But this is still a critical delay that allows the gamma-ray pressure to still up the star. As this process occurs the outer layers sag inward and thus compress the core more, raising the temperature, making more energetic gamma rays even more likely to make antimatter, and suddenly the whole star is a runaway nuclear reactor of almost imaginable explosive force. The entire star explodes at once. With this type of super supernova, there is no neutron star or black hole left. The result is an expanding cloud of newly radioactive material and empty space (The Antimatter Super Nova, 2012). The question is whether a fluke event could allow a sizable amount of antimatter to collide with matter in proximity to Earth. Currently it is thought that the bulk of antimatter in the Milky Way is at the very center of the galaxy where it is extremely hot. Currently the Sun does form gamma rays but not in sufficient quantity to generate large amounts of antimatter. Some believe that the collision of antimatter and matter is not known about antimatter. The antimatter detector that is now installed on the ISS is telling us a great deal about antimatter and how it is formed. Currently the collision of matter and antimatter in a sufficient amount that it could endanger Earth and humanity seems remote, yet this phenomenon seems worthy of much more detailed study because of the enormous potential energy release – greater than any other single source in the universe known to date (Fig. 12). Up to this point the cosmic threats that have been considered are those that come from “out there” and humanity cannot be thought to be responsible for the creation of these threats and indeed humanity’s role has been to study these threats so as to eliminate or mitigate these threats through technology. But there are two types of “cosmic threat” in which humanity may well have some Page 20 of 25

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Fig. 12 The colossal supernova driven by runaway gamma ray production and antimatter explosions (Graphic Courtesy of Lawrence-Berkley Laboratories)

complicity. These relate to orbital debris and the possibility that elements might return to Earth and bring with them radiological or biological agencies that could threaten life – at least to some degree – back here on Earth.

Radiological and Biological Contamination from Space For over a half century, humans have been launching mass into orbit with little thought to the “sustainability of space.” The result is that there are now about 6,500 t of mass in Earth orbit with about 2,800 t (or over 40 %) of this being low earth orbit. Some of the space objects are active satellites and spacecraft, but a good deal of it is space debris. Some of the defunct space objects contain noxious gases like hydrazine, and others contain nuclear power sources that threaten radiological contamination when they deorbit. Rockets have lifted humans into space to explore the Moon and to carry out missions on “manned platforms.” Scientists are still in early days in studying space biology and the biochemistry of life in outer space. There is far from complete knowledge about how the space environment with zero (or near zero) gravity, radiological phenomena up to gamma rays, and intense thermal gradients might affect not only the human physiology but viruses and bacteriological organisms. A major miscalculation could give rise to pandemics if mutated bacteria returned from space to the Earth environment. Certainly there are sophisticated isolation and decontamination processes for all missions returning from outer space, but only one lapse in these procedures could give rise to a deadly outbreak that could conceivably turn into a pandemic. Even beyond human space exploration exobiology is still a young area of scientific pursuit. Some believe that organic chemistries trapped in falling meteors or bolides could bring new life-forms to Earth. In light of the huge thermal gradients that are involved this certainly seems unlikely. Yet some scientists have expressed ideas about “life-forms” that are non-carbon based such as perhaps sulfurbased life-forms that could withstand much greater heat than life-forms known to us here on Earth. As systematic ways are undertaken to prepare for planetary defense, care must be taken in all of these Page 21 of 25

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areas. Research activities must not prematurely rule out radiological or biological dangers that are not thought possible.

Orbital Debris Today, concerns about orbital debris are not focused so much on the dangers of radiological or biological contamination or even space junk falling down in such a manner as to damage buildings or to kill or maim people, but rather the prime concern is focused on what is known as the Kessler Syndrome. This is the danger that was first formally anticipated by Donald Kessler in the 1980s. Kessler suggested that a “tipping point” could be reached where the buildup of space debris would continue to increase in the form of a cascade effect and that this deadly rise in space junk could endanger vital space infrastructure and thus in time make it impossible to achieve safe access to outer space. Today radar systems are actively tracking some 22,000 objects that the size of baseball or larger. It is also known that there are some 500,000 objects that are about the size of a marble and over 100 million that are the size of a grain of salt. These space objects that are traveling at speeds of many thousands of kilometers per hour can actually be deadly to an astronaut suit. Even with new voluntary guidelines approved by the United Nation’s Committee on the Peaceful Uses of Outer Space (COPUOS), the problem space debris continues to mount. Efforts are now underway to work toward active debris removal programs with a focus on the largest space debris elements because collisions of large space objects can give rise to thousands of new debris elements. With an increasing number of satellites being launched and a wide range of new small satellite initiatives, there is a need to include active debris removal in an overall program to create a planetary defense effort for Earth.

Sustainability It is in recent times that the whole importance of “sustainability” has become apparent to people who care about the long-term survival of the human species – not for another century but for another eon. Sustainability has been defined by the Merriam-Webster dictionary as “a method of harvesting or using a resource so that the resource is not depleted or permanently damaged” (Merriam-Webster 2012). But at its most basic level, “sustainability” means that Earth can allow human civilization to survive for the long term, and “space sustainability” means that humans will be able to access and to utilize space and space systems to survive. At the global scale, scientific data now indicates that humans are living beyond the “carrying capacity” of the spaceship known as planet Earth. There are good rules of physics and mathematics why this cannot continue indefinitely. This scientific evidence comes from many sources but is presented in detail in such sources as the “Millennium Ecosystem Assessment (Turner 2008). A 2012 review in Nature by 22 international researchers expressed concerns that the Earth may be “approaching a state shift” in its biosphere (Barnosky et al. 2012). One very useful measure human consumption is what is called an ecological footprint. This index addresses such aspects as the biologically productive land needed to provide the resources and absorb the wastes of the average global citizen. According to various studies humans are already exceeding that limit by borrowing from either the past or the future. But even if one disputes these calculations, one need only note that the total human population was 800 million in 1800, was 1.8 billion by 1900, over 6 billion by 2000, and will be somewhere in the range of 10–12 billion in 2100. Page 22 of 25

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Somewhere along this exponential rise in human population, spaceship Earth has taken on too many passengers to sustain itself and to sustain itself in terms of food, power, climate, jobs, or other measures of sustainability and sanity. If there is to be a credible plan for planetary defense, there will likely need to be some finite limits set for “one planet” consumption. In short it is not possible to divorce entirely space sustainability from sustainability here on Earth.

Structure of the Handbook So what is the purpose of this chapter? It is to cover in a comprehensive fashion all aspects of cosmic hazards and possible strategies for contending with these threats through a comprehensive planetary defense strategy. The earlier portions of the handbook address various forms and types of threats that are poised by our cosmic environment. The middle portion of the chapter addresses the various types of scientific and observational spacecraft that helps us to better understand the physics and behavior of various types of cosmic threats. Likewise there is information presented about various ground observation activities that complement data collected from spacecraft. The editors of this chapter have sought to bring together in a single reference work a rich blend of information about the various types of cosmic threats that are posed to human civilization by asteroids, comets, bolides, meteors, solar flares and coronal mass ejections, cosmic radiation, and other types of threats that are only recently beginning to be understood and studied. These other areas include investigation of the “cracks” in the protective shield provided by the Van Allen Belts and the geomagnetosphere and of matter-antimatter collisions, orbital debris, and radiological or biological contamination. Some areas that are addressed involve areas about which there is a good deal of information that has been collected for many decades by multiple space missions by many space agencies, observatories, and scientific researchers. Other areas involve areas of research and study that have only recently begun.

Conclusion A concerted attempt has been made to assemble some of the world’s foremost experts in each of these areas. The purpose of this effort has been to provide up-to-date and scientifically verifiable information about both the nature of these cosmic threats and possible strategies to alleviate, mitigate, or eliminate these threats. Although much of the work in these various areas have been conducted by space agencies, an expanding range of work is also being carried out by observatories, by universities and other research centers, and even by private foundations and professional organizations such as the B612 Foundation and the Planetary Society. The purpose of this work is thus severalfold. The first objective was to provide the latest information and most systematic research from around the world in a single reference work. Secondly the goal has been to provide not only the most recent information, but where relevant the authors have sought to note where there are significant gaps in our knowledge or where new research, spacecraft, observatories, or other initiatives are needed to fill in critical missing information. Finally the third goal has been to provide the best possible information about preventative actions that might be taken against cosmic threats and to identify various alternative strategies that are now underway or planned to cope with these various threats.

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Some might argue that this chapter might well have included information about the search for extraterrestrial intelligence since such cosmic life-forms could potentially pose a future threat to humanity. In light of well-documented information about the various SETI programs now underway and the current belief that livable planets are safely hundreds if not thousands of light years away, the editors have chosen not to include this topic in the chapter. Likewise, for reasons noted earlier, the issue of climate change has not been explicitly addressed since there has been so much materials addressed to this topic elsewhere.

Additional Information The Working Group on Near-Earth Objects (WGNEO) of the International Astronomical Union held a workshop in 1995 entitled Beginning the Spaceguard Survey which led to an international organization called the Spaceguard Foundation (1995).

Cross-References ▶ Biological Hazards from Space ▶ Coronal Mass Ejections and their Cause and Nature ▶ Cosmic Radiation Management ▶ Deflecting or Disrupting a Threatening Object ▶ Earth’s Atmosphere, and the Ozone Layers ▶ Global Leadership and Strategies for Planetary Defense ▶ Institutional and Financial Arrangements for Orbital Debris Mitigation ▶ International Cooperation and Collaboration in Planetary Defense Efforts ▶ Mounting Hazards of Man-Made Orbital Debris ▶ Nature of Coronal Mass Ejections and Historical Patterns of Their Occurrence ▶ Nature of Solar Flares and Historical Patterns of Their Occurrence ▶ Planetary Defense, Global Cooperation and World Peace ▶ Potentially Hazardous Asteroids and Comets ▶ Private Initiatives: The Sentinel Project ▶ Protection Against Coronal Mass Ejections ▶ Solar and Cosmic Radiation and Hazards: The Basics ▶ United Nation Activities ▶ Van Allen Belts and What We Know and Don’t Know About Them

References Adams M Natural news, Earth’s magnetic pole shift unleashing poisonous space clouds lined to mysterious bird deaths. http://www.naturalnews.com/030996_bird_deaths_pole_shift.html. Accessed 13 Jan 2011 Barnosky AD, Hadly EA et al (2012) Approaching a state shift in Earth’s biosphere. Nat Rev 486:52–58. doi:10.1038/nature11018 Comet Shoemaker-Levy Collision with Jupiter (1994) http://www2.jpl.nasa.gov/sl9/

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“Dinosaur-killer” asteroid crater imaged for first time. National Geographic News. http://news. nationalgeographic.com/news/2003/03/0307_030307_impactcrater.html. Accessed Mar 2003 Holman G The mysterious origins of solar flares. Scientific Magazine. http://www.scientificamerican.com/article.cfm?id¼the-mysterious-origins-of-solar-flares/. Accessed 26 Mar 2006 Ice age polarity was global event: extremely brief reversal of Geomagnetic field, climate variability, and super volcano. Science News. http://www.sciencedaily.com/releases/2012/10/ 121016084936.htm. Accessed 16 Oct 2012 Jet propulsion laboratory background on different types of orbits for potentially harmful asteroids. http://neo.jpl.nasa.gov/neo/groups.html. Accessed 9 Apr 2014 Merriam-Webster dictionary (2012) www.merriam-webster.com/dictionary/sustainable/ Mirsky S Northern lights make noise, too. Scientific American. July 11, 2012 NASA sentry risk assessment site. http://geology.about.com/gi/o.htm?zi¼1/ XJ&zTi¼1&sdn¼geology&cdn¼education&tm¼104&f¼20&su¼p284.13.342.ip_&tt¼2&bt ¼2&bts¼24&zu¼http%3A//neo.jpl.nasa.gov/risk/. Accessed 9 April 2014 NASA-SOHO www.nasa.gov/mission_pages/soho/. Accessed August 2014 NEOShield (2012) The near earth object shield: preparing to protect the planet an European Union Project. http://www.neoshield.net/en/index.htm Norby K The sunburned country: skin cancer in Australia. http://www.biology.iastate.edu/ InternationalTrips/1Australia/04papers/NorbySunburn.htm. Accessed August 2014 Pelton JN (2013) Orbital debris and other threats from outer space. Springer Press, New York Section 321 of the NASA Authorization Act of 2005 (Public Law No. 109–155), also known as the George E. Brown, Jr. Near-Earth Object Survey Act. http://www.nasa.gov/pdf/ 171331main_NEO_report_march07.pdf Stewart I, Lynch J (2007) Earth: the biography. National Geographic Society, Washington, DC, pp 57–63 The antimatter supernova: one of the largest cosmic explosions ever recorded. The daily galaxy. http://www.dailygalaxy.com/my_weblog/2012/12/the-antimatter-supernova-largest-cosmicexplosion-ever-recorded.html. Accessed 28 Dec 2012 The B612 foundation and the sentinel space telescope. http://b612foundation.org/sentinelmission/ The Earth’s Magnetosphere Shield. http://science.nasa.gov/science-news/science-at-nasa/2003/ 03dec_magneticcracks/. (Last accessed in August 2014) The solar magnetosphere and when does it shift Poles? Global event: extremely brief reversal of GeoMagnetic field, climate variability, and super volcano. Science News. http://www. sciencedaily.com/releases/2012/10/121016084936.htm. Accessed 16 Oct 2012 The Space Guard Foundation spaceguard.iasf-roma.inaf.it/ (Last accessed in August 2014) The Working Group on Near-Earth Objects (WGNEO) of the International Astronomical Union (September 18–22 1995) “Beginning the Spaceguard Survey”. Vulcano, Italy Turner G (2008) A comparison of the limits to growth with thirty years of reality. Commonwealth Scientific and Industrial Research Organisation (CSIRO) sustainable ecosystems Types of near earth objects by types and grouping, JPL. http://neo.jpl.nasa.gov/neo/groups.html. Accessed 9 Apr 2014 Vincent WF, Rautio M, Pienitz P (2006) Climate control of biological UV exposure in polar and alpine aquatic ecosystems”. In: Orbaek JB, Kallenborn R, Tombre IM (eds) Environmental challenges in arctic-alpine regions. Springer, New York, pp 117–157 WISE: the wide-field infrared survey explorer: the NASA infrared space telescope. http://www.nasa. gov/mission_pages/WISE/main/index.html. Accessed 9 Apr 2014

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Impact Risk Estimation and Assessment Scales Steve Chesley* and Paul Chodas Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Abstract This chapter addresses the current state of the art in assessing the impact risk from any of the known near-Earth objects over the next century or so. The assessment is made by determining the orbits of potentially hazardous asteroids and comets using the latest sets of tracking measurements and then projecting into the future the possible positions for these objects during close approaches to the Earth. The chapter discusses various computerized risk assessment systems that perform these assessments, along with the scales that are used to assess these risks. The second part of the chapter addresses two important issues in accurately predicting the risk of impact on Earth that have been identified and addressed in recent years. The first of these is the “Yarkovsky effect,” which is the small recoil acceleration acting on an asteroid due to thermal emissions from its surface and which can now be detected, modeled, and accounted for. The second topic to be discussed is the phenomenon of “keyholes,” which are gravitational gateways that can take an asteroid from a close approach on one passage by the Earth to a later impact with our planet. Mapping the keyholes for a potential impactor is an important step in assessing the asteroid’s impact hazard and in planning a possible deflection mission.

Keywords Asteroids; Astrodynamics; CLOMON impact monitoring system; Comets; Keyholes; Near-Earth asteroids; Near-Earth objects; Palermo Scale; Potential impactor; Potentially hazardous asteroids; Sentry impact monitoring system; Torino Scale; Virtual impact concept; Yarkovsky effect

Introduction While the detection and discovery of a near-Earth object is an essential step for understanding the hazards it might pose, that first step must be followed by a thorough assessment of the impact risk, and that assessment must be revised every time new observations are made of the asteroid. Here we turn to the NEO trajectory prediction and hazard assessment problems, which have sparked significant theoretical advances in astrodynamics in the last 15 years.

Impact Monitoring One of the first serious analyses of the impact possibility of a real asteroid occurred in early 1998, for asteroid 1997 XF11 (Marsden 1999). A possible impact in 2028 was proposed but then determined

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to never have been possible (Chodas and Yeomans 1999). During the subsequent discussions, however, researchers probed for potential impacts beyond 2028, a difficult problem because of the nonlinearities introduced from the 2028 close approach of this asteroid. Potential post-2028 impacts from the original orbit were successfully identified, although the orbit had already been refined so that the possibility of those impacts was eliminated (Chodas and Yeomans 2000). Nonetheless, the 1997 XF11 scare had the very beneficial effect of motivating significant research into impact hazard assessment and led to the identification of the concept of keyholes and the creation of automated nonlinear impact monitoring systems. The first verified potential impact of an NEO was reported shortly thereafter for asteroid 1999 AN10 (Milani et al. 1999), although its impact probability was only of order 10
9 (or one in a billion). Later that same year, a second asteroid, 1998 OX4, was found to have a small potential for collision with Earth (Milani et al. 2000). The 1998 OX4 case presented an interesting problem because the asteroid had become lost due to difficult observing circumstances, and it was no longer possible to predict where to observe the asteroid again to resolve the threat. However, the virtual impactor concept (Milani et al. 2000) was introduced that provided a technical approach to predicting the sky-plane ephemeris under the assumption that the potential impactor is actually a true impactor. The future impact constraint allowed precise orbital predictions, and one could simply search the associated region on the sky with a suitable telescope. If the object was not present, then it is safe to conclude that it is not on an impact trajectory and does not pose a threat. If the object was seen, the measurements could be used to update the orbit and hazard assessment, which would presumably be high, and in any case the asteroid would no longer be lost. But applying the virtual impactor approach to eliminate impact risks was clearly unsatisfying, both because the asteroid generally remained lost and there was not a good mechanism to validate the associated negative observations. A superior approach to managing the potential risk from known asteroids would be to identify any threatening object shortly after its discovery, while its position could still be accurately predicted, thereby allowing appropriate follow-up tracking to be used to refine the orbit. This required an automated system that could continually monitor the near-Earth asteroid catalog as new discoveries are added and as new observations are added to prior discoveries. The first version of such a system began operation at the University of Pisa by late 1999. CLOMON, as the system was called, was complemented in 2002 by the JPL Sentry system. These two computer-based impact monitoring systems were independently developed and continue to operate today, providing the operational redundancy and cross-verification that is so desirable in such a high-profile arena (Milani et al. 2005). Both Sentry and CLOMON continually monitor the asteroid catalog for asteroids with potential impact solutions, and both systems automatically post these risk results to their respective websites. This information is routinely used by asteroid follow-up observers to select targets for further tracking. The posted information includes such essential information as the object designation, the estimated object size and impact energy, and the list of potential impact dates and their associated probabilities. In addition, the risk pages allow a quick evaluation of each particular case by tabulating the Torino and Palermo hazard scales, which are described in the next subsection.

Impact Hazard Metrics: The Torino and Palermo Scales As the asteroid surveys began to hit their stride in 1998–1999, particularly the LINEAR (Lincoln Near-Earth Asteroid Research) program, potentially hazardous asteroids were being discovered at Page 2 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_87-1 # Springer International Publishing Switzerland 2014

Fig. 1 A graphical representation of the algorithm used for the Torino Impact Hazard Scale

an unprecedented pace. By 1999, in the wake of the 1997 XF11 scare, the need for some sort of hazard scale to communicate with the public about potential impacts was widely accepted in the scientific community. The advent of the automated impact monitoring systems mentioned above made such a tool absolutely vital. The first hazard scale to see widespread use was the Torino Scale (Binzel 2000), which was explicitly designed to facilitate communication with the public at large. The Torino Scale is a 1–10 integer system with green-yellow-red color coding to indicate severity, much like the Richter scale for earthquakes. The scale values are determined by the combination of impact energy and impact probability, with higher energy and higher probability generally leading to higher scale values. How exactly these scale values are derived from the input parameters is not particularly intuitive (see Fig. 1), but each value has an associated narrative (see Fig. XX, chapter 1) that can be used to put a potential impact situation in better context. The simplicity of the Torino Scale makes it useful for communication with the public, but also means that it is less valuable for technical use when dealing with large numbers of potential impacts. The Torino Scale does not make any account of the time available before the impact, which can be of crucial importance in assessing the level of attention that is appropriate. A potential impact gets the same rating whether the collision is a month away or decades in the future. Furthermore, as it is currently defined, the Torino Scale is inapplicable to potential impacts more than 100 years into the future. The Palermo Scale (Chesley et al. 2002), on the other hand, was designed to help technical analysts categorize and organize the large numbers of potential impact solutions that were being identified by the computer-based impact monitoring systems, CLOMON in Italy and Sentry at JPL. Without the need to be intuitive to the general public, a continuous logarithmic scale could be used, and color codes were unnecessary. Of particular importance, the time-to-go aspect is included in the equation for the Palermo Scale value, given by PS ¼ log

PImpact f B DT

Here PImpact is the probability of the given impact event, DT is the time remaining before impact, and fB is the background impact frequency for events greater than the given impact energy. The denominator gives the probability of a larger impact from a different object occurring before the potential impact being considered. The Palermo Scale thus gives the ratio of the probability of the

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_87-1 # Springer International Publishing Switzerland 2014

event in question to the probability of a random “background” event in the same time interval. For example, a PS = 0.0 event has the same probability as a random event with the same or greater energy. A PS value of +1.0 means the event is ten times more likely than a background event, and a PS =
1.0 value means that a background event is ten times more likely. To provide a point of reference, events with TS = 0 or PS <
2.0 are considered routine, meaning additional observations are warranted, but no special analyses or public actions are necessary. As long as DT >1 year, the automated impact monitoring services Sentry and CLOMON automatically post such results to their respective websites. Cases with TS = 1 or
2.0 < PS < 0.0 are more interesting and may warrant additional analyses or the application of more extraordinary tracking resources. These cases are always cross-checked by the Sentry and CLOMON analysts for validation before they are posted to the Web. Potential impact events with TS  2 or PS  0.0 are extraordinary in some sense and will often merit significantly increased attention for follow-up observations, hazard assessment, public communication, and possibly even impact mitigation planning. Of course, each individual case is unique and must be treated so. It is impossible to capture all of the relevant information for a high-risk situation into a single hazard-scale value. The future observability of an object or its accessibility for spacecraft missions may prove crucial in understanding the situation. The same Palermo Scale value may be found, for example, for a high-energy event decades in the future or a much smaller event only a month away. The hazard scales can tell us that an event is unusual and that it merits special attention, but they cannot tell us what to do about the event.

The Yarkovsky Effect The trajectory for most asteroids can be computed with sufficient accuracy by modeling only the Newtonian gravitational perturbations of the planets, several of the larger asteroids, and the relativistic terms of the solar gravity. In some cases, however, the combination of long optical tracking data sets and/or radar measurements can lead to extremely well-constrained orbits, which require modeling of additional and far more subtle accelerations. Chief among these small perturbations is the slight recoil acceleration associated with the emission of thermal photons from the asteroid. The phenomenon is known as the Yarkovsky effect, after the Polish civil engineer Ivan Yarkovsky (1844–1902) who originated the idea (Beekman 2006). The Yarkovsky effect produces a monotonic increase or decrease in orbital energy, leading to a steady drift in the orbital semimajor axis, the asteroid’s mean distance from the Sun. The cause of this is the fact that the afternoon terminator is warmer than the morning terminator on an asteroid, and thus there is an excess of thermal photons from the afternoon terminator. This leads to a photon recoil acceleration that always has some component oriented toward the morning terminator. An asteroid in direct rotation (orbital and rotational angular momenta roughly aligned) will gain energy and drift away from the Sun, while a retrograde rotator will lose energy and cause a decreasing semimajor axis. If the rotation pole is near the plane of the orbit, the Yarkovsky effect is substantially nulled. The Yarkovsky effect is small, only a fraction of a Newton for a typical half-kilometer NEA, and yet this minute force accumulates quadratically in time to produce tens or hundreds of kilometers of orbital deviation after a few decades. Such an orbital deviation was first unambiguously detected on an asteroid in 2003 (Chesley et al. 2003) and is now seen in the orbits of a few dozen asteroids (Nugent et al. 2012; Farnocchia et al. 2013a). Slow as it is, over tens of millions of years this Page 4 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_87-1 # Springer International Publishing Switzerland 2014

Yarkovsky-driven orbital drift is responsible for pushing main belt asteroids into orbital gravitational resonances that send them into the inner solar system where they can become near-Earth asteroids. In a small number of potential impact events, the Yarkovsky effect is a critical aspect of the trajectory and risk analysis, even though in some cases the rate of drift, and often even its direction, is unknown. More specifically, a proper accounting of the Yarkovsky effect is often required in cases where the interval to impact is long (>100 years, say) or when the potential impact is preceded by an intervening close approach to Earth. In the long integration case, the additional acceleration can accumulate enough that the trajectory shifts by an amount sufficient to move the prediction uncertainty footprint significantly closer to or farther away from the Earth. An example is the case of asteroid (29075) 1950 DA, which for a time held a small chance of collision in 2,880 and for which the Yarkovsky effect was the primary obstacle in calculating the impact probability (Giorgini et al. 2002). With current data and a careful assessment of the Yarkovsky effect, the impact odds for 1950 DA in 2,880 are 1 in 4,000. Another case where the Yarkovsky effect can be crucial to the risk assessment involves close approaches (through “keyholes,” see below) that amplify the otherwise minor Yarkovsky deviations so that the impact prediction region depends heavily on the correct Yarkovsky modeling and the associated uncertainties. The classic example here is Apophis, which will pass at 38,000 km from the geocenter on April 13, 2029. This approach has a scattering effect on nearby trajectories so that small differences in orbital period are amplified by a factor 40,000. Now, neglecting the Yarkovsky effect, the trajectory uncertainty in 2029 is well under 100 km; however, careful assessment of the Yarkovsky uncertainties increases the prediction uncertainty to several 100 km, in large part due to the fact that Apophis’ spin axis orientation is unknown. While the Earth remains clear in 2029 in either case, the wider Yarkovsky-based uncertainty allows for a large number of potential future impacts that would not be possible otherwise. With this approach, the current maximum impact probability for Apophis is 1 in 435,000 for an impact in April 2068 (Farnocchia et al. 2013b). While the Yarkovsky effect can raise a challenge for impact risk assessment, in some cases it also can provide critical physical information. For instance, (101955) Bennu, the asteroid target of NASA’s OSIRIS-REx asteroid sample return mission, has been well studied by optical, infrared, and radar (Hergenrother et al. 2013; Emery et al. 2014; Nolan et al. 2013, respectively) and it has a precisely determined Yarkovsky drift (Chesley et al. 2014). And Bennu’s possible future trajectories include a number of potential impacts between 2,175 and 2,196. Because the Yarkovsky effect depends on the asteroid bulk density, this wealth of data leads to a constraint on the mass with only 12 % uncertainty (Chesley et al. 2014), pointing to a completely new approach to asteroid mass estimation. While the mass is of great interest to OSIRIS-REx mission designers, it is also key to understanding the hazard that Bennu may pose to Earth late in the twenty-second century and is of crucial importance in understanding mitigation options should they become necessary.

Keyholes Hazardous asteroids and comets follow orbits about the Sun that approach very close to the Earth’s orbit. The very definition of a potentially hazardous asteroid (PHA) requires that the asteroid’s orbit approach to within 0.05 AU of the Earth’s orbit. An object on a potential impacting trajectory may very well also experience close approaches to the Earth during the decades before impact. The major role these pre-impact close approaches can play in the assessment of orbital uncertainties and impact probabilities is best explained through the concepts of the target plane and keyhole.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_87-1 # Springer International Publishing Switzerland 2014

Fig. 2 The uncertainty region of Apophis in the 2029 b-plane, using observations through 2008, with the 2036 keyhole highlighted in red. The roughly 2,000-km-long uncertainty region is depicted using 50,000 Monte Carlo tracer trajectories, while the trajectories tracing the keyhole are extracted from a much denser set. The keyhole width is only about 600 m

Close approach and impacting trajectories are most conveniently analyzed in the so-called target plane, which is the plane centered on the Earth and perpendicular to the asymptote of the incoming geocentric hyperbolic path of the asteroid. The target plane is often referred to as the b-plane, because it contains the b vector of the hyperbolic encounter trajectory (Kizner 1961). A trajectory is represented in this plane as a single point located where the asymptote intersects the plane; motion along the trajectory is removed. Since the focusing effects due to the Earth’s gravity are also removed, variations in the geocentric trajectories are more linearly related to the variations in the heliocentric orbits than they would be if the plane was simply perpendicular to the velocity vector at close approach. The position uncertainty of an object can also be projected into this plane, producing an uncertainty region often represented as an ellipse. In the b-plane for the final, impacting plunge of an object, the impact probability is calculated by looking at the area of intersection of the uncertainty ellipse with the disc of the Earth (which must be enlarged to account for gravitational focusing). A keyhole is a narrow region of the target plane containing trajectories that are perturbed by the close approach in such a way that they impact at a later encounter with the Earth (Chodas and Yeomans 2000). Trajectories that impact the Earth disc directly are thus not the only hazardous ones: keyholes provide gravitational gateways that also lead to impact, although in later years. Each keyhole is associated with an orbital resonance: the keyhole for a 7:6 resonance, for example, would place an object on orbit that makes exactly six complete revolutions about the Sun, while the Earth makes exactly seven. Valsecchi et al. 2003 outline the mathematical theory behind keyholes and describe how their locations can be predicted as a function of the heliocentric orbit and the particular keyhole resonances. Keyholes are typically quite narrow, ranging in width from less than a kilometer to hundreds of kilometers. The Apophis 2036 keyhole in the 2029 b-plane, shown in Fig. 2, for example, is very narrow, at about 600 m wide. The narrowness is due to the fact that close approaches tend to scatter initially neighboring trajectories, due to differential perturbations. Even slight differences in the close approach distance, for example, will produce slightly different post-encounter semimajor axes, leading to a secular spreading apart along the orbit path. Any sequence of neighboring trajectories along the orbit path will be scattered apart by the close approach and can become widely separated by the time of the potential impact, sometimes wrapping many times around the complete orbit. Simply stated, close approaches stretch neighboring trajectories apart, and the closer the approach,

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_87-1 # Springer International Publishing Switzerland 2014

the greater the rate of spreading. Keyholes can be thought of as pre-images of the Earth mapped back to the pre-impact b-plane: when the stretching is reversed, the Earth disc at impact compresses down to the width of the keyhole in the pre-impact plane. A close approach can spawn many keyholes and even multiple keyholes leading to impact in the same future year. Some resonant orbits will not have associated keyholes, because of gravitational perturbations from other planets. Also note that particular keyholes can be eliminated as a concern simply through continuing to observe the object. As the orbit becomes more certain, the b-plane uncertainty ellipse will shrink, and since keyholes are located at fixed positions in the b-plane, the ellipse may no longer include one or more keyholes. The Apophis 2036 keyhole shown in Fig. 2, for example, has now been eliminated, because the asteroid has been observed more extensively, its orbit is known better, and the uncertainty region in the b-plane no longer extends to the location of that keyhole. Although keyholes are indicative of a hazard, they also offer an advantage for mitigating the hazard as well: they provide deflection leverage in the sense that they magnify the effect of a prior deflection. This is particularly evident for the 2036 keyhole in the Apophis 2029 b-plane (Fig. 2). If the asteroid trajectory was known to lie within the 600-m keyhole, a deflection effort would have to shift it no more than 300 m to make it miss the keyhole in 2029 and therefore miss the Earth in 2036. Deflection after the keyhole passage would require a much larger trajectory shift, up to a full Earth radius. The ratio of the shifts in the respective b-planes is the deflection leverage, in this case a factor in the tens of thousands. Of course, most keyholes are wider than 600 m and will therefore provide less leverage, but the advantage of a pre-keyhole deflection can still be significant. Statistical studies suggest that about 20 % of impactors will have keyholes providing leverage of at least a factor of 3 within 25 years of impact (Chodas 2012). These studies also address the question of how close an object needs to approach the Earth to form a keyhole: for a time horizon of 50 years between close approach and impact, the close approach must be closer than about 0.15 AU in order to form a keyhole. Interestingly, distant pre-impact close approaches can have an effect opposite to that of keyhole encounters: instead of spreading uncertainties apart, these shallow encounters can focus pre-impact uncertainties. Deflection efforts applied prior to these shallow approaches can be partially reduced or even wholly undone by this focusing effect (Chodas 2012). Keyholes should be an important consideration in the design of a deflection campaign. Although the object may be deflected away from the Earth disc in the b-plane for the potential impact, care should be taken to avoid deflecting the trajectory into one of the many nearby keyholes. A useful tool for understanding the geography of hazards in a b-plane is the keyhole map. The map is formed by taking finely spaced steps along the major axis of an object’s uncertainty region at a current epoch, propagating the trajectories forward in time to get their coordinates in a pre-impact b-plane and continuing forward for many decades looking for the minimum geocentric distance for each trajectory (and artificially allowing trajectories to pass through the volume of the Earth). Figure 3 shows a keyhole map for asteroid 2011 AG5, from an assessment of its hazard (Yeomans et al. 2012). Along the horizontal axis is the z-component in the 2023 b-plane, which is basically aligned with the major axis of the uncertainty (Valsecchi et al. 2003). Points below the dotted horizontal line indicate trajectories that impact: the year of the impact noted. The zero point on the x-axis is at the center of a large keyhole that leads to an impact 2040 impact solution; the 360-km width of the keyhole can be clearly seen as the horizontal width of the portion of the blue curve below the dotted line. The downward spikes are secondary returns to Earth that could be spawned by the 2040 encounter, and those that pass below the dotted line represent secondary keyholes. Just as primary keyholes surround the Earth disc in a b-plane, secondary keyholes surround primary keyholes. Since secondary keyholes are produced by two close approaches, and therefore two levels Page 7 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_87-1 # Springer International Publishing Switzerland 2014

Fig. 3 A keyhole map for asteroid 2011 AG5 in the 2023 b-plane. The vertical axis shows the post-2023 minimum geocentric distance for each trajectory, through the year 2100. Points below the dotted horizontal line represent keyholes leading to impacts; the year of the impact is noted, up to the year 2060

of trajectory stretching, they are generally even narrower than primary keyholes, sometimes only meters or tens of meters wide. The positions of the secondary keyholes should be taken into account in the design of an asteroid deflection. If 2011 AG5 were headed for the 2040 keyhole, for example, a good strategy would be to design the deflection to slow the asteroid enough that its trajectory shifts at least 1,500 km leftward on this map, moving into a region clear of keyholes.

Conclusion Careful monitoring of potentially hazardous asteroids and comets is important to the long-term planetary defense of the Earth. In recent years the ability to detect, track, and determine the orbital and physical characteristics of asteroids and comets has steadily improved. Upgraded capabilities at ground observatories, as well as new space-based surveys like NEOWISE and the proposed NEOCam and Sentinel missions, have contributed or will contribute to an increasingly complete catalog of potentially hazardous asteroids and comets. These data are shared globally, and new organizations such as the International Asteroid Warning Network (IAWN) will further strengthen worldwide involvement. Over the last decade and a half, new techniques have been developed to more accurately analyze the possible future trajectories of NEOs, accounting for uncertainties in their orbital and physical parameters. Methods have been developed that more accurately project into the future the complete ranges of possible orbits for these objects, and these have been implemented in software systems that flag potential future impacts representing the highest level of risk. An improved understanding of a small force known as the Yarkovsky effect has led to better predictions of future impact probabilities, and the notion of a keyhole has emerged as a useful concept for understanding how these probabilities change and how deflection missions might be designed. This chapter also outlined the difference between the risk alert scales developed to measure the degree of concern that theoretically possible future impacts represent. The Torino Scale is designed for broad distribution to the public and includes color coding of the hazard but does not take into Page 8 of 10

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account how far in the future the impact is predicted to occur. The Palermo Scale is designed for use by scientists and provides a more finely tuned measure that includes the length of time until the potential impact.

Acknowledgments The research described in this chapter was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Cross-References ▶ Defending Against Asteroids and Comets ▶ International Astronomical Union and the NEO Hazard ▶ Key Reports on Cosmic Hazards and Planetary Defense Issues and Initiatives

References Beekman G (2006) I. O. Yarkovsky and the discovery of ‘his’ effect. J Hist Astron 37, Part 1(126):71–86 Binzel RP (2000) The Torino impact hazard scale. Planet Space Sci 48(4):297–303 Chesley SR, Chodas PW, Milani A, Valsecchi GB, Yeomans DK (2002) Quantifying the risk posed by potential earth impacts. Icarus 159(2):423–432 Chesley SR et al (2003) Direct detection of the Yarkovsky effect by radar ranging to Asteroid 6489 Golevka. Science 302:1739–1742 Chesley SR et al (2014) Orbit and bulk density of the OSIRIS-REx target Asteroid (101955) Bennu. Icarus 235:5–22 Chodas P (2012) Keyholes and Jabbas: the role of pre-impact close approaches in asteroid deflection, asteroids, comets and meteors meeting, Niigata, 2012 Chodas PW, Yeomans DK (1999) Orbit determination and estimation of impact probability for nearearth objects. Paper 99-002, 21st annual AAS guidance and control conference, Breckenridge Chodas PW, Yeomans DK (2000) Predicting close approaches and estimating impact probabilities for near-earth objects. In: Howell KC et al (eds) Astrodynamics 1999, vol 103 (pt. III), Advances in the astronautical sciences. Univelt, San Diego Emery JP et al (2014) Thermal infrared observations and thermophysical characterization of OSIRIS-REx target (101955) Bennu. Icarus 234:17–35 Farnocchia D et al (2013a) Near Earth Asteroids with measurable Yarkovsky effect. Icarus 224(1):1–13, ISSN 0019-1035 Farnocchia D et al (2013b) Yarkovsky-driven impact risk analysis for asteroid (99942) Apophis. Icarus 224(1):192–200 Giorgini JD et al (2002) Asteroid 1950 DA’s encounter with Earth in 2880: physical limits of collision probability prediction. Science 296:132–136 Hergenrother CW et al (2013) Lightcurve, color and phase function photometry of the OSIRIS-REx target Asteroid (101955) Bennu. Icarus 226(1):663–670

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Kizner W (1961) A method for describing miss distances for lunar and interplanetary trajectories. Planet Space Sci 7:125–131 Marsden BG (1999) A discourse on 1997 XF11. J Br Interplanet Soc 52(5–6):195–202 Milani A, Chesley SR, Valsecchi GB (1999) Close approaches of asteroid 1999 AN10: resonant and non-resonant returns. Astron Astrophys 346:L65–L68 Milani A, Chesley SR, Boattini A, Valsecchi GB (2000) Virtual impactors: search and destroy. Icarus 145(1):12–24 Milani A, Chesley SR, Sansaturio ME, Tommei G, Valsecchi GB (2005) Nonlinear impact monitoring: line of variation searches for impactors. Icarus 173(2):362–384 Nolan MC et al (2013) Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations. Icarus 226(1):629–640 Nugent CR, Margot JL, Chesley SR, Vokrouhlický D (2012) Detection of semimajor axis drifts in 54 Near-Earth Asteroids: new measurements of the Yarkovsky effect. Astron J 144:60–72 Valsecchi GB et al (2003) Resonant returns to close approaches: analytical theory. Astron Astrophys 408:1179–1196 Yeomans D et al (2012) Report on Asteroid 2011 AG5 hazard assessment and contingency planning, NASA Near-Earth Object Program Office report, 27 Apr 2012

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Water Impact Modeling Souheil M. Ezzedine* and Paul L. Miller Lawrence Livermore National Laboratory, Livermore, CA, USA

Abstract Earth impact by an asteroid or comet represents a rare but potentially catastrophic hazard. Since the majority of Earth’s surface is covered by water, such events are statistically likely to involve oceans or seas. Issues associated with modeling water impacts, from the impact event that generates waves to wave propagation and interaction of the waves with shorelines, are discussed. Simulation results for several scenarios are presented to illustrate the problem and demonstrate the current state-of-theart methods used for modeling water impacts.

Keywords Asteroid; Comet; Water; Impact; Impactor; Tsunami; Tidal wave; Wave

Introduction Two thirds of Earth’s surface is covered by seas and oceans; therefore, an asteroid impact is statistically more likely to occur over water than land areas. Impact of asteroids on the ocean surface can lead to the generation of high-amplitude, long-wavelength waves. Such waves can propagate to shorelines, with potentially catastrophic consequences such as flooding the coast, destroying infrastructures, debilitating industries, and affecting emergency evacuations and responses. This chapter describes techniques developed to model generation of long-wavelength (tsunami) waves, their propagation, and their interaction with land infrastructures. Tsunami generation resulting from asteroid impact in oceans is still considered in early stages of development (Ward 2010). On the other hand, tsunami generation due to earthquakes or landslides is a fairly mature field of research and engineering (Liu and Yeh 2008). This chapter discusses the physical phenomena and numerical challenges central to modeling tsunamis due to asteroid impacts. Several scenarios of impact of a hypothetical asteroid in different locations nearby US shorelines (Ezzedine et al. 2015) are presented for illustration purposes using state-of-the-art coupling between hydrocodes and water-wave codes.

*Email: [email protected] Page 1 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Discussion Source Generation Source Generation Background Tsunami waves can be generated by earthquakes, underwater landslides, or asteroid impacts. Comparative analytical analysis of the first two tsunami sources is given by Okal and Synolakis (2003); sources of tsunamis generated by asteroid impact are reported in Ward (2010). The numerical modeling of tsunami caused by asteroid impacts requires an understanding of the physical mechanisms of the event in order to design a realistic tsunami source for wave propagation codes. To define the source, time-dependent motion of the water surface must be specified, along with the ocean bathymetry. If the asteroid is of considerable size and/or the ocean is shallow, the ocean bathymetry may also need to be specified as a function of time and should be consistent with the evolution of the ocean/atmosphere interface, which is a challenging task. It is often assumed that the ocean is an elastic medium and that the area where the asteroid impact takes place encompasses all nonlinear phenomena. The determination of the initial tsunami waveform from asteroid impact depends on a number of factors. The most important parameters are the characteristics of the asteroid itself, the impact velocity, and the depth of the ocean (that affects the transfer of energy from the surface of the ocean to the seafloor). A standard approach is to assume a short impact time for the asteroid and conservatively convert the displaced volume of water into a waveform based on correlations of asteroid-equivalent energy yield with size of impact footprint (crater). This step typically involves a recalibration of the tsunami source to minimize modeling errors by matching historical run-ups and buoy records. While such an approach has been employed to explain observations, it is inadequate for accurate prediction. Physics-based approaches (e.g., McGlaun et al. 1990; Shuvalov 2000; Gisler et al. 2013–2014; Ezzedine et al. 2015) represent the nextgeneration methods for predicting tsunamis generated from asteroid impacts. Based on field studies and computer modeling, it is recognized that asteroid impact in the ocean presents unique mechanisms and formation stages due to the presence of the ocean water column (Higgins and Butkovitch 1967; Kieffer and Simonds 1980; McKinnon and Goetz 1981; Melosh 1981; Gault and Sonett 1982; McKinnon 1982; Roddy et al. 1987; Ormo and Miyamoto 2002; Shuvalov 2002). The majority of both conceptual and quantitative studies of ocean impacts deal with large asteroids and with the cratering processes in deep ocean (Ahrens and O’Keefe 1987; Roddy et al. 1987; Nemchinov et al. 1993; Hills et al. 1994; Hills and Goda 1999; Artemieva and Shuvalov 2002; Wiinnemann and Lange 2002). Other studies stressed the need of fully coupled atmospheric entry and water impact simulations (Gault and Sonett 1982; McKinnon 1982; Roddy et al. 1987; Ormo and Miyamoto 2002; Shuvalov 2002). Only a few studies were dedicated to shallow oceans such as the Mjolnir event (Tsikalas et al. 1998a, b, c, 1999; Shuvalov et al. 2008). Only few studies dedicated to smallsized asteroids such as Ward and Asphaug (2000). Ward and Asphaug (2000) used semi-analytical solutions to drive the generated source to shorelines using ray tracing methods, with several corrections. Such a method is limited mainly to vertical impacts and can overestimate run-ups. Oberbeck et al. (1993) (see Fig. 1) published a conceptual model for an impact into shallow water. Paog et al. (2004) described the Oberbeck model as follows. The model involves several steps and focuses on the excavation and modification stages of crater development, delineating several stages in the tsunami initiation and propagation. In the first stage, during excavation, a mixture of water and fragmented rocks forms a slurry rim, which extends upward from the sea surface and forms a raised lip around the transient crater. McKinnon (1982) suggested that, because the shock-wave velocity in the crust exceeds that in water, material from the ocean floor will be mixed with ocean water during crater formation. A cone-shaped curtain of ballistically ejected target fragments spreads from the Page 2 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 1 Hypothetical sequence of events produced by impact of a mantle-penetrating bolide striking a shallow sea. Sequence one to seven would occur over a period of several hours (Oberbeck et al. 1993). Vertical scale is exaggerated (Adapted from Paog et al. (2004))

crater center. Debris trailing from the ejecta curtain’s base settles onto the shallow seafloor (Paog et al. 2004). At that point, the slurry rim then moves landward and seaward and initiates a giant tsunami wave that re-suspends and erodes the ocean floor. Subsequently, the wall of the seawater cavity collapses back into the excavation and rushes toward the center of the crater, where it produces a central slurry spout, whose collapse initiates a second tsunami wave which could be more damaging than the first one, followed by additional slurry spouts and tsunami waves, until wave oscillations over the crater are sufficiently damped. The return flows of the tsunamis produce further close-shore erosion and deposition. Most effects of the tsunami wash-back in the Oberbeck model are concentrated in the near-shore region (Paog et al. 2004). Water spouts formed in the collapse of the transient crater have been confirmed by experiment (Gault and Sonett 1982). As described, the physical processes involved in ocean impact, cratering, and tsunami generation are very complex, and a physics-based approach is essential to differentiate between the different physical and mechanical processes and to address the parameters that drive the tsunami generation. Page 3 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Access to high-performance computing and availability of hydrocodes within research institutions is furthering this field of research and setting new standards of end-to-end asteroid-to-shore simulations. Studies employing hydrocodes such as CTH (Kring and Boslough 2014) at Sandia National Laboratories, SAGE (Gisler 2008) at Los Alamos National Laboratory, and GEODYN (Lomov et al. 2013) at Lawrence Livermore National Laboratory (LLNL) illustrate capabilities of source generation for the tsunami from a physically based approach. As a demonstration, the subsequent sections discuss scenarios modeled with the GEODYN hydrocode to generate the source for the tsunami initiation. Similar practices are being employed elsewhere within the comet and asteroid hazard communities. Source Generation Using the Hydrodynamic Code GEODYN Description of GEODYN Following Vorobiev et al. (2007), Lomov et al. (2013), and Ezzedine et al. (2015), the simulations presented here are conducted using GEODYN – a parallel Eulerian compressible solid and fluid dynamics code with adaptive mesh refinement (AMR) capabilities (Antoun et al. 2001; Lomov and Rubin 2003). Among its many features are high-order material interface reconstruction algorithms (Hertel and Bell 1992) and advanced constitutive models that incorporate salient features of the dynamic response of geologic media (Rubin and Lomov 2003). GEODYN is able to simulate materials under extremely large deformations and resolve details of wave propagation at small scales with high accuracy and uses a continuum damage mechanics approach to represent fracture. The Eulerian framework of adaptive mesh refinement (Berger and Colella 1989) is a relatively mature technique for dynamically applying high numerical resolution to those parts of a problem domain that require it, while solving less sensitive regions on less expensive, coarser computational grids. Adaptive mesh refinement can help to simulate the entire process region while allowing focus on greater details in interesting locations. In combination, Eulerian Godunov methods with AMR have been proven to produce highly accurate and efficient solutions to shock-capturing problems. The method used here is based on several modifications of the single-phase high-order Godunov method, which is not as straightforward as Lagrangian FEM. For completeness the method is briefly summarized below. For solid mechanics, the governing equations consist of the laws of conservation of mass, momentum, and energy, an equation for distortional elastic deformation, and a number of equations that represent specific rheological time-history-dependent parameters (i.e., porosity, plastic strain). The viscoplasticity is modeled with a measure of elastic deformation as a symmetric, invertible, positive definite tensor which is determined by integrating the correspondent evolution equation (Rubin et al. 2000). The numerical scheme for a single fluid cell is based on the approach of Miller and Puckett (1996), with some modifications to account for the full stress tensor associated with solids. The multidimensional equations are solved by using an operator-splitting technique, in which the one-dimensional Riemann problems for each direction are solved using Strang-splitting order to keep second-order accuracy, while the source term is always applied at the end of the time step. Each directional operator is the update of the cell from two-consecutive present-future step times with fluxes computed at the edges of the cell. Edge fluxes are then calculated based on upwind characteristic tracing following Miller and Puckett (1996) and to Riemann solver in an acoustic approximation, while the estimate for the velocity gradient is also calculated in the Riemann solver step. Source Generation Using GEODYN Ezzedine et al. (2015) use GEODYN to simulate the source wave at several impact sites in the Gulf of Mexico. The size of the assumed spherical asteroid is 50 m in diameter. The density of the asteroid is assumed to be 2.2 g/cm3 and the impact velocity is 15.4 km/s. Page 4 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 2 Three views of the simulation of the source of the water waves at 3.211 ms obtained using GEODYN simulation. Air (blue) and water (red) are shown. A basaltic ocean floor is not shown here

The entry angle is set to 130onorth/39oazimuth. This 3-D simulation required initially four million nodes, four levels of adaptive mesh refinement, and a total of 10,000 CPU-h. Figure 2 shows three side views at 3.211 ms time in the numerical simulation. The domain is composed of three materials: atmosphere (air), ocean (water), and ocean base (not shown here) that is assumed to be basalt. Both vertical side views show the entry trajectory (yellow arrow), formation of cavity impact, splash/rim of the water ejecta, and phase changes. Note the ring of compressed water around the impact site. The aerial view is a slice view at the sea/air interface level.

Water-Wave Propagation It is often assumed that any source of disturbance (and in particular, tsunamis) propagates in the open ocean as linear, non-dispersive surface waves, and therefore the shallow-water equations (SW) are often used. The assumption of linearity of the waves stems from the fact that the ratio of water surface displacement to the depth is small. For non-dispersive waves, the propagation speed does not depend on their frequency. Dispersion alters wave speeds causing the waves with shorter wavelength to travel more slowly. In the long wave limit (or hydrostatic approach), all waves travel with the same speed (e.g., Stoker 1992). This wave-speed relationship makes it relatively easy to estimate travel time for a tsunami event. Tsunami modeling based on linear shallow-water (LSW) equations can predict an initial arrival time quite accurately, because the leading wave in a real wave train is the longest and propagates with the greatest wave speed. However, for more accurate prediction of wave amplitude, wave forms, and lengths, both nonlinearity and dispersion effects need to be incorporated (Stoker 1992). The assumption of linearity and often dispersion as well breaks down as tsunami wave fronts shoal into shallow water and build in height as they approach shore. The waves steepen and either break before arriving at the still water shoreline or surge over the near-shore bathymetry. Time history of the water wave from the source is recorded past the Hugoniot elastic limit region (which splits the linear from the nonlinear regimes – dark red region around the impact region in Fig. 2) for several azimuthal directions. The time histories are then used as a source to water-wave propagation codes for tsunami generation. Page 5 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Models that include nonlinearity but still neglect effects of frequency dispersion are governed by the nonlinear shallow-water (NLSW) equations. NLSW-based models quite often can provide good prediction of run-up heights of the leading wave (Liu and Yeh 2008). The principal limitation of their accuracy in predicting shoreline inundation for tsunami applications stems from factors that are not covered by the basic theory: frequency dispersion that can lead to different wave heights and wave forms, an inability to simulate wave breaking due to singularity in the free-surface description, interaction with fixed structures, and the interaction with the mass of transported debris resulting from destruction of structures. While effects of dispersion still can be included as an extension to the SW equation, other effects mentioned above require a more complicated approach (Stoker 1992; Liu and Yeh 2008). One of the most advanced examples of NLSW modeling is MOST (Method of Splitting Tsunami (Titov and Synolakis 1998) used at NOAA (National Oceanic and Atmospheric Administration). A number of applications of this model to different tsunami scenarios are described in the literature (Tang et al. 2009; Gonzalez et al. 2009). Another model, GeoClaw, employing NLSW, the Godunov method, and adaptive mesh refinement (AMR) technique, was proposed by LeVeque et al. (2011). Ezzedine et al. (2015) used the same approach but implemented it using the SAMRAI framework for adaptive mesh refinement developed at LLNL (Gunney et al. 2006). SAMRAI is also used by GEODYN, facilitating coupling between the hydrocode and the water-wave code. Another class of wave propagation code based on deriving a weakly dispersive model using the Boussinesq equations was proposed by Peregrine (1967). More recent research has extended these equations further to include nonlinear and weakly dispersive waves (Lynett and Liu 2002; Lai et al. 2010). FUNWAVE, a widely used numerical model based on the Boussinesq theory, was developed by Kennedy et al. (2000). It employs a set of equations that resemble the shallow-water equations but contain high-order correction terms. However there is a significant computational overhead for doing this, approximately an order of magnitude longer run times. Grilli et al. (2007) used their Boussinesq model FUNWAVE to model the Bay of Bengal and compared the results to a version solving the NLSW. They found differences of up to 20 % in surface elevations between the Boussinesq and NSWE simulations for the westward propagated wave. Kulikov (2005) used satellite altimetry data – based on observed data from the Indian Ocean tsunami of Dec 26, 2004 – that was subject to wavelet analysis and found that the generated tsunami waves were highly dispersive. An alternative method is to retain the vertical momentum equation with the non-hydrostatic pressure. This leads to depth-averaged set of equations that are similar to the shallow-water equations but maintain the non-hydrostatic pressure terms. Such models are able to correctly model dispersive waves but they require additional vertical resolution in contrast to 2-D methods. Recently, most of the ocean models were extended to incorporate non-hydrostatic high-frequency effects for both internal and surface waves: MITgsm model (Marshall et al. 1996), POM model (Kanarska and Maderich 2003), ROMS model (Kanarska et al. 2010), and FVCOM (Lai et al. 2010). An example from the FVCOM work is shown in Fig. 3 (adapted from Chen et al. 2014). Effects of friction on tsunami propagation were studied in Myers and Baptista (2001) for the Hokkaido NanseiOki event. They used a Manning coefficient with three different values and different friction parameterization. The greatest differences were observed at 0–10 m depths as well as in the amount of the land inundation. The range of maximum run-up difference is from 6 to +6 m, indicating that selection of the friction coefficient definitely influences the calculation of wave run-ups. Finally, the effects of Coriolis force on transoceanic tsunami have been studied by several authors. Results show differences in wave height but not much difference in arrival time. The general conclusion is that the Coriolis force has little influence on small-period waves, but distinctive difference in the amplitude observed on the large-period waves. Page 6 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 3 Tsunami run-up near Japan coast (Adapted from Chen et al. (2014))

Example of End-to-End Simulations Using GEODYN-SWWP Coupling

In this section the application of GEODYN-SWWP coupling to three sites is presented. The first site is located in the Atlantic off the Delmarva Peninsula and is referred to as Scenario #1. Scenario #1 was designed for a NASA-FEMA tabletop exercise (TTX1) conducted in 2013. The site is characterized by open seas and the trajectory of the impactor is away from the shoreline (divergent waves). The second site, referred to as Scenario #2, is located off San Francisco Bay (SFB), and the impactor and its trajectory are the same as in Scenario #1 except the impact location is oriented toward the shoreline of the San Francisco Bay (convergent waves). Waves propagate and funnel through the Golden Gate channel and get trapped in the SFB. The third site, Scenario #3, is located in the Gulf of Mexico where the impactor characteristics and its trajectory are different from the first two scenarios. Scenario #3 was designed for the second NASA-FEMA tabletop exercise (TTX2) conducted in 2014 and features four different impact locations, and the waves are mostly contained within the Gulf (entrapped waves). Scenario #1: Impact Off Maryland Shore The following scenarios are based on a hypothetical NEO. The impact is set on 3 May 2013, 8:00 am EDT. The ocean impact location is at latitude-longitude coordinates (37.0–74.0). The impactor (asteroid) is made of iron with a density of 7.9 g/cm3. The final impact velocity is estimated to be 12.7 km/s with impact energy of 10MT, or 4.17  1016 J. The entry angle is set to 20 from the horizon (see Fig. 4). Simulation of the impact and wave propagation was conducted using SWWP and overlaid on Google Earth. An example of the waves 30 min after the impact is shown in Fig. 5. Much of the East Coast is affected. Warning stations and live-ship feed are highlighted in Fig. 6. Assessment of the impact of the waves reaching and flooding the shorelines was conducted for several sectors – maritime (coast guard posts, navigation), military infrastructures (bases, national guard), transportation (road and bridges), utilities (electric, gas, and nuclear power plants), government agencies (law enforcements, post offices, and prisons), emergency (shelter, hospitals) – but is not shown here (see Ezzedine et al. 2015 for an exhaustive analysis). It is worth noting that the floods take 1–3 days to recede.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 4 Impact location in May 2013 off Delmarva Peninsula

Fig. 5 Wave propagation off of Delmarva Peninsula 30 min after impact. The shoreline-flooding surface waves reach +12 m, followed by 12 m troughs

Scenario #2: Impact Near San Francisco Bay For the next scenario, the trajectory and characteristics of the impactor are the same as Scenario #1 except the impact location is moved to the west of San Francisco Bay. The location of the impactor is shown in Fig. 7, in the upper left-corner frame. A time history of the wave propagation is also displayed in the same figure. Time sequence flows from left to right and then top to bottom. Note the sharp distinct wave moving toward the SFB coast after the first half hour from impact, followed by several wave refractions from the shorelines. Within 1.5 h the waves penetrate the Golden Gate channel reaching the East Bay (i.e., Berkeley, Oakland). Waves are trapped in SFB and reach as far as the north and south ends of the bay (see Figs. 7 and 8). All shores within SFB are affected within 4 h from impact. Water waves reach as high as 3 m above sea level. Note that the California Energy Commission (CEC) has conducted a 2012 study on the impact of sea-level rise on the flooding of the SFB shoreline. It was found that, due to global warming, the sea level could rise 1.4 m in 100 years. Subsequently, utility companies with plants on the shorelines are

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 6 Surface waves reach +12 m followed by 12 m troughs. Much of the East Coast is affected. Warning stations and live-ship feed are highlighted here. Floods take 1–3 days to recede

Fig. 7 Time snapshots every 0.5 h. Note wave intrusions into the SF Bay. Significant flooding is possible at the Port of Oakland. The San Francisco and Oakland airports are also vulnerable to flooding

subject to floods. The CEC (2012) has identified those stations and they are included in Fig. 8. For the impact Scenario #2, the consequence of a 3 m tsunami wave would be the same as in CEC (2012), if not more severe. Scenario #3: Impact in the Gulf of Mexico Scenario #3 is based on a hypothetical NEO orbit very similar to that of the Chelyabinsk impactor (50 m diameter, density of 2.2 g/cm3, impact velocity of 15.4 km/s, and entry angle of 130onorth/

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 8 Impacts of sea-level rise (1.4 m) on the San Francisco Bay (CEC 2012)

39oazimuth). For the scenario, initial uncertainties in the orbit result in a “risk corridor,” and the impact probability takes almost 2 years to reach 100 % (Chodas 2014; Fig. 9). The following is a compilation of material developed for the second FEMA-NASA asteroidimpact tabletop exercise (TTX2) held at FEMA HQ on 20 May 2014. In preparation for the exercise, simulations were carried out of possible water impacts in the Gulf of Mexico. As the scenario plays out during the exercise, the impact occurs on land in the vicinity of Pasadena, Texas, rather than in the Gulf. Figure 10 depicts the locations of five locations within the risk corridor before a more precise impact point is determined. Location TTX2-0 will not be discussed since it is a ground impact. The characteristics of the other impact locations are TTX2-1, shallow-water impact (near Louisiana); TTX2-2, deep-water impact (central Gulf); TTX2-3, shallow-water impact (near Florida Page 10 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 9 (For hypothetical Scenario #3) Left and middle frames: impact footprint (“risk corridor”) in early 2015, a year after discovery. Right frame: impact footprint (“risk corridor”) in March 2018 (Chodas 2014)

Fig. 10 Possible impact locations within the TTX2 tabletop scenario, before the impact location was further refined (Adapted and modified from Chodas 2014)

Keys); and TTX2-4, Straits of Florida (near Cuba). Results of the numerical simulations are described below.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 11 Water waves in the Gulf of Mexico for impact at TTX2-1

• Scenario TTX2-1: a wave of 1.5–2.0 m hits the Louisiana coast within the first 4 h. Interestingly, Yucatán peninsula receives waves of up to 1–1.5 m; however, Florida, Alabama, and Mississippi coasts receive waves of up to 1–0.75 m (see Fig. 11). • Scenario TTX2-2: Louisiana, Mississippi, Alabama, Florida, and the Yucatán peninsula all receive waves of up to 1.2 m in height. It is worth noting that most of the energy dissipates toward the south-east direction (see Fig. 12). • Scenario TTX2-3: Cuban coast is hit by a large wave of 2.5 m within the first hour after impact. The south/southwest tip of Florida and the Florida Keys experience 2 m water waves for almost 2 h after impact. The coasts of Alabama, Mississippi, and Louisiana are subject to waves and ripples of 0.5 m height (see Fig. 13). • Scenario TTX2-4: the impact location is close to Anguilla-Cays. Florida and Cuba are the two most affected locations with waves as high as 1.25 m registered in West Palm Beach. The Bahamas receives waves and ripples of 0.5 m and waves reach as far as Freeport, Grand Bahamas (see Fig. 14). It is worth noting that the worst of the floods takes place in the first 4 h after impact, in most scenarios, and that the waves and floods subside within 6–8 h after impact. For comparison purposes all four scenarios are plotted in the same figure (Fig. 15), 1 h after impact.

Wave Breaking and Inundation Modeling Estimating inundation has been one of the most difficult aspects of tsunami prediction for several reasons. The behavior of future tsunami waves will be highly variable depending on source, propagation, and shoaling effects. The run-up and breaking of the waves at the shoreline depends

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 12 Water waves in the Gulf of Mexico for impact at TTX2-2

Fig. 13 Water waves in the Gulf of Mexico for impact at TTX2-3

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

Fig. 14 Water waves in the Gulf of Mexico for impact at TTX2-4

Fig. 15 Water waves in the Gulf of Mexico for impacts at TTX2-1, TTX2-2, TTX2-3, and TTX2-4 1 h after impact. The waves are influenced by the depth and shape of the Gulf seafloor. Waves travel faster in deeper waters

on the shoaling history and topography and the nature of any coastal structures. A coastline with high cliffs would likely experience less damage from a tsunami, while a low-elevation shoreline is more easily overrun. Variations in wave characteristics can occur over very short distances along the coast due to differences in local refraction, diffraction, and shoaling. In Thailand, plunging waves with heights of 4–6 m were experienced on Phuket Island, while 65 km to the north, in Khao Lak, a

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

moving wall of water came ashore with a height over 11 m (Kawata et al. 2005). Inundation maps for communities, based on hypothetical and historical tsunamis, provide planners with information about areas that might require evacuation. The full problem is very difficult to model. For coastal communities within the wave run-up region, the tsunami flows around, through, and over buildings. This turbulent, fast-moving flow results in building damage, collapse, and washing away of structures. In the future, numerical models incorporating some of these complexities may provide accurate estimates of inundation, but for now, the available approaches have limitations. Most of the existing run-up and inundation models make use of a variation of the shallow-water equations, with a few exceptions that use Boussinesq models for the wave propagation. While models based on the shallow-water equations are only valid for simulating non-breaking waves, they have some capability to produce reliable inundation maps in cases where the inundation occurs in a slow and smooth way. However, recent studies developed in the frame of MAREMOTI and SCHEMA projects (Gardi et al. 2011) with the help of NLSW models show that modeled inundation is highly dependent on digital terrain model (DTM) resolution and that even differences of only 3 m in the resolution can affect the results. The Boussinesq models are able to include breaking effects only in a limited way, since in the case of a breaking wave, the free surface becomes singular. But an even more challenging problem is the interaction of waves with buildings. The problem is essentially three dimensional and requires very accurate treatment of fluid and solid interfaces. Presently, modern numerical techniques, such as volume-of-fluid (VOF) and level-set (LS) methods that allow water surface tracking in Eulerian models, Lagrangian particle methods such as SPH (smoothed particle hydrodynamics), and LBM (Lattice Boltzmann methods), are promising useful tools for onshore flows, but they are still difficult to apply to real cases since they are quite expensive (Dalrymple et al. 2006). VOF simulations are described in Wu and Liu (2008). There are few techniques available in the CFD community to describe fluid-structure interactions that include also moving objects in a fluid flow such as immersed-boundary (IB) technique (Peskin 1977) and fictitious-domain method (FDM) (Glowinski et al. 1999; Patankar 2001; Kanarska et al. 2011). Those methods, combined with the previously mentioned methods such as VOF or LS, could provide significant contribution for predicting tsunami interaction with coastal structures using modern parallel computers.

Conclusion Methods used to model tsunami generation, propagation, and inundation have been reviewed. Waves generated by asteroid impacts have the potential to cause significant damage to a range of infrastructure. Accurate source generation of a tsunami requires the use of a hydrocode. The physical processes that take place during an impact are very nonlinear and depend on the size of the asteroid as well as whether the ocean is shallow or deep. The situation becomes more complicated when including the interactions of the seafloor and the asteroid that affect the result and the source generation of the tsunami. For wave propagation modeling, modern tsunami research employs two opposite approaches: one is to include more physical phenomena, and the other is to simplify and speed up the code for use in operational tsunami forecasting. The choice on what phenomena to include depends on objectives and available computational resources. For operational forecasting one may choose a fast code (e.g., based on Nonlinear wave equation approach, e.g., MOST code) that covers the whole range of tsunami processes from generation to run-up. At the other extreme, a research code based on complete 3-D equations can incorporate full tsunami physics, including wavePage 15 of 19

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_88-1 # Springer International Publishing Switzerland 2014

structure interactions, but at significant developmental and computational cost. Nevertheless, more complete physics is needed to improve modeling and provide more realistic scenarios of tsunami inundation, and advanced research codes are an active area of research. Finally, numerous studies have been conducted about tsunami-structure interactions. While some work has addressed simple geometries, e.g., uniform slope, vertical wall, or cylinder, recent work with more complex geometries has been reported (Thusyantan and Gapal 2008; Lindt et al. 2009). However, the accurate prediction of run-up onto real coastlines with structures still remains a challenge. A potential improvement to current tsunami-modeling capabilities would be an efficient 3-D model that captures detailed fluid-solid interaction, coupled to a macroscale tsunami propagation model.

Acknowledgments This work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Authors would like to thank Paul Chodas for providing the TTX exercises and Mark Boslough for several discussions on both exercises. Partial support for the work was provided by the Near-Earth-Object Program Office at NASA HQ. LLNL-BOOK-664555-DRAFT.

Cross-References ▶ Defending Against Asteroids and Comets ▶ NEO Discovery and Follow-Up Surveys ▶ Potentially Hazardous Asteroids and Comets

References Ahrens TJ, O’Keefe JD (1987) Impact on the Earth, ocean, and atmosphere. Int J Impact Eng 5:13–32 Antoun TA, Lomov IN, Glenn LA (2001) Development and application of a strength and damage model for rock under dynamic loading. In: Elsworth D, Tinucci J, Heasley K (eds) Proceedings of the 38th U.S. Rock Mechanics Symposium, Rock Mechanics in the National Interest. A. A. Balkema Publishers, pp 369–374 Artemieva N, Shuvalov V (2002) Numerical simulations of the Mjølnir marine impact crater. J Geophys Res Planets 107(E7):1–13 (1991–2012) Berger MJ, Colella P (1989) Local adaptive mesh refinement for shock hydrodynamics. J Comput Phys 82(1):64–84 CEC California Energy Commission (2012) The impacts of sea level rise on the San Francisco Bay, prepared by the Pacific Institute for the CEC, 32 pages, CEC-500-2012-014 Chen C et al (2014) Available online at http://fvcom.smast.umassd.edu/2014/01/10/3-outreachmarch-11-2001-japan-tsunami/. Accessed 20 Oct 2014 Chodas P (2014) NEO threat tabletop exercise #2 (TTX2), 20–21 May 2014, proposed scenario; personal communication and email 3 Apr 2014

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Ezzedine S, Lomov IN, Miller PL, Dearborn D, Dennison D, Antoun TH (2015) Tsunami generation and wave propagation from asteroid impacts, Procedia Eng 60, The 14th Hypervelocity Impact Symposium 2015, Boulder, Colorado Gardi A, Valencia N, Guillande R, Andre C (2011) Inventory of uncertainties associated with the process of tsunami damage assessment on buildings. Nat Hazards Earth Syst Sci 11:883–893 Gault DE, Sonett CP (1982) Laboratory simulation of pelagic asteroidal impact: atmospheric injection, benthic topography, and the surface wave radiation field. Spec Pap Geol Soc Am 190:69–92 Glowinski R, Pan TW, Hesla TI, Joseph DD (1999) A distributed Lagrange multiplier fictitious domain method for particulate flow. Int J Multiphase Flow 25:755–794 Gonzalez FI, Geist EL, Jaffe B, Kanoglu U, Mofjeld H, Synolakis CE, Titov VV, Arcas D, Bellomo D, Carlton D, Horing T, Johnson J, Newman J, Parsons T, Peters R, Peterson C, Priest G, Veturanto A, Weber J, Wong F, Yalciner A (2009) Probabilistic tsunami hazard assessment at Seaside, Oregon, for near- and far-field seismic sources. J Geophys Res 114:1–19 Grilli ST, Ioualalen M, Asavanant J, Shi F, Kirby T, Watts P (2007) Source constraints and model simulation of the December 26, 2004, Indian Ocean tsunami. J Waterw Port Coast Ocean Eng 133:414–428 Gunney BTN, Wissink AM, Hysom DA (2006) Parallel clustering algorithms for structured AMR. J Parallel Distrib Comput 66(11):1419–1430 Hertel ESJ, Bell RL (1992) An improved material interface reconstruction algorithm for Eulerian codes, Sandia Nat Lab SAND-92-1716C, 17 p Higgins GH, Butkovich TR (1967) Effects of water content, yield, medium, and depth of burst on crater radii. Lawrence Radiation Laboratory Report UCRL5023 Hills JG, Goda MP (1999) Damage from comet-asteroid impacts with earth. Physica D 133:189–198 Hills JG, Nemchinov IV, Popov SP, Teterev AV (1994) Tsunami generated by small asteroid impacts. In: Gehrels T (ed) Hazards due to comets and asteroids. University of Arizona Press, Tucson, pp 779–789 Kanarska Y, Maderich V (2003) A non-hydrostatic numerical model for calculating free-surface stratified flows. Ocean Dyn 53:176–185 Kanarska Y, Lomov IN, Antoun TH (2011) Mesoscale simulations of particulate flows with parallel distributed Lagrange multiplier technique. Comput Fluids 48:16–29 Kawata Y, Tsuji Y, Sugimoto Y, Matsutomi H, Okamura Y, Hayashi I, Kayane H, Tanioka Y, Fujima K, Imamura F, Matsuyama M, Takahashi T, Maki N, Koshimura S (2005) Comprehensive analysis of the damage and its impact on coastal zones by the 2004 Indian Ocean tsunami disaster. http://www.tsunami.civil.tohoku.ac.jp/sumatra2004/report.html Kennedy AB, Chen Q, Kirby JT, Dalrymple RA (2000) Boussinesq modeling of wave transformation, breaking and runup. J Waterw Port Coast Ocean Eng 126(1):39–47 Kieffer SW, Simonds CH (1980) The role of volatiles and lithology in the impact cratering process. Rev Geophys Space Phys 18:143–181 Kring D, Boslough M (2014) Chelyabinsk: portrait of an asteroid airburst. Phys Today 67(9):32 Kulikov E (2005) Dispersion of the Sumatra tsunami waves in the Indian Ocean detected by satellite altimetry. Report from P. P. Shirshov Institute of Oceanography. Russian Academy of Sciences, Moscow, 27 p Lai Z, Chen C, Cowles G, Beardsley RC (2010) A non-hydrostatic version of FVCOM, part I: validation experiments. J Geophys Res Oceans 115:C11010. doi:10.1029/2009JC005525 LeVeque R, George DL, Berger M (2011) Tsunami modeling with adaptively refined finite volume methods. Acta Numerica 20:211–289 Page 17 of 19

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Lindt JW, Gupta R, Garcia R, Wilson J (2009) Tsunami bore forces on a compliant residential building model. Eng Struct 31:2534–2539 Liu PLF, Yeh H (2008) Advanced numerical models for simulating tsunami waves and runup, advances in coastal & ocean engineering. World Scientific Publishing Company, Singapore, 334 p Lomov IN, Rubin MB (2003) Numerical simulation of damage using an elastic-viscoplastic model with directional tensile failure. J Physique IV 110:281–286 Lomov IN, Herbold EB, Antoun TH, Miller PL (2013) Influence of mechanical properties relevant to standoff deflection of hazardous asteroids. Procedia Eng 58:251–259, The 12th Hypervelocity Impact Symposium 2013 Lynett P, Liu P (2002) A numerical study of submarine-landslide-generated waves and run-up. Proc R Soc Lond A 458:2885–2910 McGlaun JM, Thompson SL, Elrick MG (1990) CTH: a three-dimensional shock wave physics code. Int J Impact Eng 10:351–360 McKinnon WB (1982) Impact into the Earth’s ocean floor: preliminary experiments, a planetary model, and possibilities for detection. Spec Pap Geol Soc Am 190:129–142 McKinnon WB, Goetz P (1981) Impact into the Earth’s ocean floor during the last billion years: preliminary experiments, theoretical models, and possibilities for geological detection. In: Conference on large body impacts and terrestrial evolution: geological, climatological, and biological implications. Lunar and Planetary Institute, Houston, pp 1–34 Miller GH, Puckett EG (1996) A high-order Godunov method for multiple condensed phases. J Comput Phys 128(1):134–164 Myers EP III, Baptista AM (2001) Analysis of factors influencing simulations of the 1993 Hokkaido Nansei-Oki and 1964 Alaska tsunamis. Nat Hazards 23:1–28 Oberbeck VR, Marshall JR, Aggarwal H (1993) Impacts, tillites, and the breakup of Gondwanaland. NASA, Publications, paper 74 Okal EA, Synolakis CE (2003) A theoretical comparison of tsunamis from dislocations and landslides. Pure Appl Geophys 160(10–11):2177–2188 Ormo J, Miyamoto H (2002) Computer modeling of the water resurge at a marine impact: the Lockne crater, Sweden. Deep Sea R Part Il 49:983–994 Paog CW, Koeberl C, Reimold WU (2004) The Chesapeake Bay crater geology and geophysics of a late eocene submarine impact structure. Springer, USA, 539 p Patankar NA (2001) A formulation for fast computations of rigid particulate flows. Cent Turbul Res Ann Res Briefs 2001:185–196 Peregrine DH (1967) Long waves on a beach. J Fluid Mech 27:815–827 Peskin CS (1977) Numerical analysis of blood flow in the heart. J Comput Phys 25:220–252 Roddy DJ, Schuster SH, Rosenblatt M, Grant LB, Hassig PJ, Kreyenhagen KN (1987) Computer simulations of large asteroid impacts into oceanic and continental sites – preliminary results on atmospheric, cratering and ejecta dynamics. Int J Impact Eng 5:525–541 Rubin MB, Lomov IN (2003) A thermodynamically consistent large deformation elasticviscoplastic model with directional tensile failure. Int J Solids Struct 40(17):4299–4318 Rubin MB, Vorobiev OY, Glenn LA (2000) Mechanical and numerical modeling of a porous elasticviscoplastic material with tensile failure. Int J Solids Struct 37(13):1841–1871 Shuvalov VV (2000) Multi-dimensional hydrodynamic code SOVA for interfacial flows: application to thermal layer effect. Shock Waves 9:381–390 Shuvalov VV (2002) Numerical modeling of impacts into shallow sea, in impact studies. In: Plado J, Pesonen LJ (eds) Impacts in Precambrian shields. Springer, New York, pp 323–336

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Shuvalov VV, Trubetskaya I, Artemiev N (2008) Marine target impact. In: Adushkin V, Nemchinov I (eds) Catastrophic events caused by cosmic objects. Springer, USA, 273 p, Chapter 9 Stoker JJ (1992) Water waves: the mathematical theory with applications. Wiley-Interscience, New York, 600 p Tang L, Titov VV, Chamberlin CD (2009) Development, testing, and application of site-specific tsunami inundation models for real-time forecasting. J Geophys Res 114(C12):1–22 Titov VV, Synolakis CS (1998) Numerical modeling of tidal wave runup. J Waterw Port Coast Eng 124(4):157–171 Tsikalas F, Gudlaugsson ST, Eldholm O, Faleide JI (1998a) Integrated geophysical analysis supporting the impact origin of the Mjølnir structure, Barents Sea. Tectonophysics 289:257–280 Tsikalas F, Gudlaugsson ST, Faleide JI (1998b) Collapse, infilling, and postimpact deformation at the Mjølnir impact crater, Barents Sea. Geol Soc Am Bull 110:537–552 Tsikalas F, Gudlaugsson ST, Faleide JI (1998c) The anatomy of a buried complex impact structure: the Mjølnir structure, Barents Sea. J Geophys Res 103:30,469–30,483 Tsikalas F, Gudlaugsson ST, Faleide JI, Eldholm O (1999) Mjølnir structure, Barents Sea: a marine impact crater laboratory. Spec Pap Geol Soc Am 339:193–204 Vorobiev YO, Liu BT, Lomov IN, Antoun TH (2007) Simulation of penetration into porous geologic media. Int J Impact Eng 34(4):721–731 Ward SN (2010) Tsunamis, encyclopedia of physical science and technology. Springer, USA, 18 p Ward SN, Asphaug E (2000) Asteroid impact tsunami of 2880 March 16. Geophys J Int 153(3): F6–F10 Wiinnemann K, Lange MA (2002) Numerical modeling of impact-induced modifications of the deep-sea floor. Deep Sea Research Part II 49:969–982 Wu TR, Liu PLF (2008) A large eddy simulation model for tsunami and runup generated by landslides. In: Advanced numerical models for simulating tsunami waves and runup. Advances in coastal and ocean engineering, World Scientific Pub, Singapore, vol 10. pp 101–162

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

Minor Planet Center Gareth V. Williams* and Timothy B. Spahr Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA, USA

Abstract A brief overview is presented of the current and historical processing of observations and orbits by the Minor Planet Center (MPC). The MPC is delegated by the International Astronomical Union with organizing the cataloging of minor bodies in the solar system.

Keywords Minor planet center; Minor planet circulars; Observations; Orbits; Near-Earth Objects

Introduction During a typical day at the MPC, automated routines receive, ingest, and process over 50,000 observations of several thousand different minor planets. Observers from around the world use MPC web tools to determine if they may have discovered new Near-Earth Objects (NEOs), to observe candidate NEOs on the NEO Confirmation Page, and to provide routine observations for orbit update and maintenance of all types of minor planets and comets. The MPC Ephemeris Service is used by observers worldwide to aid in observing all types of solar-system objects. The MPC even facilitates communication among worldwide NEO observers through a blog interface, allowing critical observing time to be shared and distributed efficiently. As is evidenced below, much of the effort of the MPC goes into processing, distributing, and publishing observations of objects that are not NEOs. The MPC’s historical job has been handling all minor planets; the emphasis on NEOs in the MPC processing hierarchy is a relatively recent development.

Historical Background In the nineteenth century, numbers (and/or names) were applied to new minor planets immediately upon discovery. Given the poor state of orbits and ephemerides at the time, this meant that previously known objects were sometimes given new numbers. By the early 1890s, there were over 320 numbered minor planets. Observations were published in numerous journals and observatory publications, meaning that orbit computers had to search to find the observations they needed to compute orbits. Detailed indexes in the journals meant that this task was manageable, if somewhat time consuming. Orbit computations were done by hand, so approximations had to be made in order to keep the calculations manageable. When objects were observed to be far from the predicted position, rather than computing new orbits, simple empirical corrections were made to the mean

*Email: [email protected] Page 1 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

anomaly and/or mean motion to make the new observations fit the orbit. In many cases, the new observations did not belong to the object in question and the empirical corrections were therefore erroneous. A perturbed orbit calculation, which might include perturbations by only a few of the major planets, for a comet or minor planet could earn the orbit computer a doctorate! The precursor to the MPC was the Astronomisches Rechen-Institut (ARI) located in Dahlem, a district of Berlin, which undertook the organization of minor planets in the early 1890s. The introduction of photography to the observing process by Max Wolf (1892) increased the rate of discovery such that by 1900 there were over 450 numbered minor planets. Provisional designations for new discoveries were introduced in 1892 (Krueger 1892), with the intention that numbering would occur only when good orbits were obtained. In practice, this meant being observed over only 1 or 2 months. Urgent material was transferred from the Astronomische Nachrichten to a series of Beobachtungs-Zirkulars in 1919, and the ARI began publication of its RI Circulars in 1926. Even after the IAU was founded in 1919 and its Commission 20 set about arranging international cooperation in minor planet astronomy, the Germans remained the ultimate authority. The dire situation in Germany in 1945 meant that the work of the ARI could not continue. The last RI Circulars were issued in April 1945. Of the 1,564 numbered minor planets in 1945, about 200 had been observed only at their discovery opposition or were otherwise very poorly observed. The end of World War II was the catalyst for the birth of the Minor Planet Center. Its foundation was instigated by IAU President Harold Spencer Jones, who understood that the organization of the tracking of minor planets had collapsed and that an international clearing house for collating and publishing the observations of minor planets was necessary. Spencer Jones approached Paul Herget of the Cincinnati Observatory about setting up such an entity. The MPC was founded in 1947 at the Cincinnati Observatory under the direction of Herget. Observations were published in the Minor Planet Circulars (MPCs), issued in batches on an irregular schedule, along with ephemerides, new orbits, and new identifications. The MPCs also announced new numberings and new names. In addition to collecting new observations of minor planets, comets, and Pluto, an early task of the MPC was to coordinate the recovery of the lost numbered minor planets (e.g., Edmondson 1952). The orbits of some 400 of the 1,564 numbered objects had problems (less than four observed oppositions or no observations in the previous 10 years), and some 200 of them were effectively lost. The MPC was an early pioneer in the use of electronic computers, and Herget borrowed time on machines owned by various US companies in order to compute perturbations of minor planet orbits. Herget’s mandatory retirement from the Cincinnati Observatory in 1978 and the curtailment of funding of the Observatory by the city of Cincinnati necessitated the relocation of the MPC. Following the successful transfer of the IAU’s Central Bureau for Astronomical Telegrams a few years earlier, the MPC was transferred to the Smithsonian Astrophysical Observatory (Cambridge, MA) in 1978, under the direction of Brian Marsden. The transfer was eased by the movement of Conrad Bardwell, who had worked at the MPC since 1958, to Cambridge. At that time, there were 2,060 numbered minor planets and about 200,000 observations in the MPC’s files. Only 23 numbered minor planets remained lost. Some 40 other numbered objects had ephemeris errors of more than five arcmin. The aim for ephemeris prediction was 2.5 arcmin. The publication schedule of the MPCs became monthly, this change coinciding with a noticeable increase in observational activity. An early task in Cambridge was to correct the numerous errors and misidentifications that were present in the observational data inherited from Cincinnati. This was a slow and painful job, done in fits and starts over the next 13 years. The checking of the final set of data, that for minor planets (1) through (700), took a full year, finally being completed in 1991 January.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

Programs of greater automation and extensive series of updates to procedures were initiated in the early 1990s and continue to this day. The web presence of the MPC began in 1995, with a rather simple site that was typical of web sites at the time. The web site has grown in content and capabilities since then. Vastly increased observational activity in the late 1990s necessitated the removal of the observations from the MPCs to a new journal, the Minor Planet Circulars Supplement (MPS), beginning in 1997. The orbits were moved to another new journal, the Minor Planet Circulars Orbit Supplement (MPO) in 2000. With the removal of subscriptions in 2008, as a consequence of being fully funded by NASA, the physical printing of these journals ceased. All MPC journals are now published in electronic form only. A series of quick-alert electronic-only circulars, the Minor Planet Electronic Circulars (MPECs), was begun in 1993. The last two lost numbered minor planets to be recovered were (878) Mildred (Williams et al. 1991) and (719) Albert (Larsen et al. 2000). The current ephemeris uncertainty for most numbered minor planets is under one arcsecond, which is a factor of 100 better than the situation in 1980. Histories of and descriptions of the work undertaken by the MPC have been given by Herget (1971), Marsden (1980, 1996), and Spahr and Williams (2009).

MPC Datasets The primary datasets collected by the MPC are: – – – –

Observations of minor solar-system bodies Orbits of minor solar-system bodies Lists of identifications involving minor planets Observatory codes, listing the parallax constants for the sites (both professional and amateur) that perform astrometry of minor planets

The types of minor solar-system bodies that are of interest to the MPC are minor (and dwarf) planets, comets, and outer irregular satellites of the giant planets. This last category includes those satellites that can be (and have been) mistaken for minor planets.

Current Data Collection Observations are reported to the MPC by observers across the planet. Most of the observations arrive via e-mail to the e-mail address [email protected]. The ability to submit observations via cURL has recently been introduced, which allows an instant acknowledgement that the batch has been received. Submission of very large observational datasets via (s)ftp will be possible when institutional network blocks on the MPC’s anon-ftp site are lifted. As time permits, observations of minor planets and comets from the pre-1939 literature are also entered into observational datasets. Where possible, these old observations, particularly those visual observations made with micrometers, are rereduced with modern comparison star positions.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

Prior Data Collection The earliest observation submissions to the MPC arrived by postal letter. This mode of submission continued to be the primary submission into the early 1990s. Urgent submission of new NEO candidates (many of which turned out to be routine Hungaria- or Phocaea-type minor planets) was via telex or telegram. Brian Marsden even had a telex machine installed in his basement. E-mail submissions of observations began in the 1980s, but the date and the details of the first submission have been lost. It was not until the 1990s that e-mail submission became the standard submission method. Certain very large sets of observations were transferred to the MPC via ftp, but that method has not been available for a number of years due to the aforementioned institutional blocks.

Current Observation Processing It should be noted that the description below will summarize the general operating procedures of the MPC. Nearly 99% of the CPU time used by MPC computers is for non-NEO observation processing. Our charter dictates that the MPC publish and distribute orbits and observations for many different solar-system object classes. NEOs are but one part of the work of the MPC. It is also important to note that not all NEOs are identifiable simply based on motion, and therefore, expedient processing of all batches is essential and required for efficient NEO handling. Observations that are sent via e-mail are received by AUTOACK. This is an automated process that scans incoming e-mail, identifies the messages that contain observations, extracts those messages from the mail system, and sends an acknowledgment e-mail to the sender. Any messages that do not contain observations are ignored by AUTOACK. AUTOACK also processes the batches that are submitted via curl. Once an observation batch is extracted, the format of the observations is checked and minor formatting issues are corrected. Various checks are then performed on the observations. These include checking for single observations of an object on any night, that the observed arc of each object on each night is not too short, that the departure from great-circle motion is not too great, and that there are no repeated or nearly identical observations. If a batch fails any of these checks, it is rejected and returned to the sender, with a short note explaining why the batch was rejected, for amendment and possible resubmission. If a batch is accepted for further processing, an acknowledgement e-mail is sent back to the sender, and the observational header information is extracted and stored so that the observational details associated with the observations can be located when they are published. The observations are then examined. If the observer has attempted to identify the observations, AUTOACK splits a single file into multiple new files, each new file containing the observations of one type of object: unnumbered comets; numbered comets, natural satellites, numbered minor planets, unnumbered minor planets with perturbed orbit solutions, unnumbered minor planets with unperturbed orbit solutions, new or unidentified minor planets, new Near-Earth Object candidates (which will be posted on the NEOCP), and existing NEOCP objects. The final task of AUTOACK is to hand off each file to an appropriate storage queue for subsequent processing by another automated or semiautomated processes. Each type of object has its own storage queue. More than a dozen other automated processes scan the storage queues, waiting for new entries to appear in the queue for which they are responsible. When a batch is found, it is extracted from the storage queue and processed:

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

– For numbered minor planets, this processing involves generating the residuals – any observation with a residual less than 200 is accepted. The orbit of the numbered object is not redone at this point. Numbered minor planet orbit improvements are done in large batches just before each batch of MPCs is prepared. – For unnumbered minor planets, an orbit improvement (perturbed or unperturbed, as appropriate) is attempted. Acceptance requires the new observations to be included in the new orbit solution. – Observations of NEOCP objects are included in new orbits and the predictions on the NEOCP are updated. – Observations of new NEO candidates are run through automated check procedures that try to identify the object(s) with known minor planets, comets, natural satellites, and high-altitude artificial satellites. If any matches are found, the observations of the matched objects are extracted and resubmitted to AUTOACK for processing. Any remaining objects are run through DIGEST2 to assess the probability that they are NEOs. Any objects so flagged are then posted to the NEOCP. – Observations of new or unidentified objects are run through automated check procedures that try to identify the object(s) with known minor planets, comets, and natural satellites. Nearly 99 % of observations submitted to the MPC are left unidentified by the survey teams. Rapid, efficient, and precise identification of unknowns is a specialty of the MPC. Once the MPC has identified the observations of matched objects, these are extracted and resubmitted to AUTOACK for processing. Any remaining objects are moved to another storage queue for single-night detections. – Every two hours, another automated process runs that checks the single-night detections queue and grabs any batches it finds. Each batch is then compared to other recent single-night detections and attempts are made to make linkages. If any linkages are found, both sets of observations are extracted, under the earlier-submitted designation, to a storage queue for two-night detections. – The two-night detections are handled semiautomatically by an MPC staff member using a process that reperforms the check routines done earlier. Removal of identifiable objects is controlled by the staff member. When all identifiable objects are removed, the new objects are designated and the observations are filed for publication. Automatic checks for additional observations and identifications are then made. – Observations of comets and natural satellites are handled manually. If the automated processes detect problems (perhaps an orbit converges poorly or the new observations degrade the solution or a numbered minor planet is running off the prediction), then the problem cases are returned to the storage queues for manual examination by an MPC staff member.

Changes to Submitted Observations The only change that is made by the MPC to a submitted observation that is correctly identified by the observer is the addition of the publication reference. This change is made to all published observations. If an observation was submitted as an unknown, the temporary observer-assigned designation is replaced by either a permanent or provisional designation. If an observation was submitted with an incorrect designation, the incorrect designation is replaced with the correct designation.

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Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

In the past, if an observer submitted high-precision observations, those observations may have been rounded to standard precision if prior experience showed that the observer was not capable of producing meaningful high-precision observations. In the current processing pipeline, it is not possible to submit high-precision observations unless the submitter is on an approved list. Observers not on the approved list have the observations returned to them, with an appropriate note.

Priority of Processing Observations There is a hierarchy applied to the processing of incoming observations. In decreasing priority order, the hierarchy is new potential NEOs, current NEOCP objects, unnumbered non-NEO objects, and numbered non-NEO objects. In addition, there is an automated process that constantly monitors the new orbits that are added to the NEOCP. If it detects the possibility that an object on the NEOCP might approach to within six Earth radii of the geocenter within the next 6 days, an alert is sent out to a mailing list consisting of MPC staff members, the NASA NEO Program Executive and the JPL NEO Program Office. The announcement of objects (via MPECs) that are subject to such an alert is delayed until the possibility of an actual Earth impact is removed or suitably quantified.

Current Orbit Processing Most orbit computations at the MPC are done by completely automated routines. These routines extract the necessary observations and a starting orbit, then perform an orbit improvement. Depending on the type of orbit and the observed arc, the orbit improvement may be perturbed or unperturbed. All multiple-opposition orbits are perturbed. One-opposition orbits of NEOs are usually perturbed from the first published orbit. Perturbations in one-opposition orbits are usually added when the observed arc exceeds 60 days. “Tricky” orbits (such as very close approachers with a very short observed arc or attempts to link two very short arcs at different apparitions) may be done manually via interactive versions of the same routines. All perturbed orbit solutions are done considering perturbations by (at least) the eight planets, Mercury through Neptune (treating Earth and Moon separately for certain NEOs), and the three minor planets, (1) Ceres, (2) Pallas, and (4) Vesta. Additional minor planets can be added as perturbers as necessary. In addition, nongravitational forces in the style of Marsden et al. (1973) or Yabushita (1996) can be considered, along with relativistic effects and effects due to the oblateness of the earth. Perturbing planet coordinates are currently taken from DE403, while the coordinates of the perturbing minor planets were generated in-house. The perturbing scheme and perturbers included is recorded on each orbit. New identifications (i.e., the linkage of observations of one designated object at one apparition to the observations of another designated object at another apparition) are done by semiautomated processes. Typically, an automated process attempts a large number of possible linkages that have been suggested by the checking processes. Many, sometimes most, of these attempts fail. Those that do not fail are checked for validity by a staff member before being inserted into the secondary files for publication. In addition, new identifications may be submitted by outside contributors. The MPC generally reworks the submitted orbits, to look for additional observations, and it is the MPC orbit that usually appears in the MPC publications. The outside contributor is, of course, credited with the identification. Page 6 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

Residual blocks for new orbit solutions show how well the observations are represented by the new orbit. The residual blocks for new identifications or new recoveries are published in the MPCs. Orbits for perturbed orbit improvements or unperturbed orbits do not have published residual blocks, but those blocks are available in the on-line web services.

Prior Orbit Processing Many of the early orbits published in the MPCs were computed by hand or with the aid of simple calculating devices. Consideration of planetary perturbations was a major undertaking, often worthy of a doctoral thesis. Perturbed solutions computed years before would often still be used, their decreasing utility as time passed (since the orbits were not updated to current epochs) being mitigated by the application of empirical correction to the mean anomaly or to the mean motion to make new observations fit. Even after Herget introduced computers into the process, a perturbed orbit improvement would be a split process: a computer would compute the planetary perturbations; a human computer would compute the differential correction; and the process would repeat until the solution converged. By the late 1960s, the MPC was using programs that could do both the computation of the planetary perturbations and the differential corrections. From 1978, the standard procedure was to include full planetary perturbations only for the numbered minor planets or new NEOs. Orbits for unnumbered objects seen at more than one opposition would be computed considering perturbations by just the four giant planets. The acquisition of faster computers in the early 1990s negated the need to use this time-saving computational shortcut and any remaining Jupiter-Neptune orbits were recomputed with full perturbations. In addition, the arc-length at which perturbations are included in non-NEO one-opposition orbits has decreased from 90 days, to 75, to the current 60 days.

Current Archiving The MPC maintains master and secondary copies of all data files. The master data files are for internal use only. All public data distribution is from secondary copies of the master files. Archiving of data is performed on four timescales: – “Monthly” – observations of minor bodies, orbits for minor bodies, and identifications of minor planets are incorporated into the master files. This coincides with the publication of the monthly Minor Planet Circulars, Minor Planet Observation Supplement, and Minor Planet Orbit Supplement. – “Weekly” – observations of minor planets published in the mid-monthly Minor Planet Observation Supplement are incorporated into the secondary files. – “Daily” – observations of NEOs and orbits of minor planets and natural satellites, published on the nightly Daily Orbit Update Minor Planet Electronic Circulars, are incorporated into the secondary files. – “Instant” – observations and orbits of newly discovered (or recovered) objects announced on Minor Planet Electronic Circulars are incorporated into the secondary files. It is important to emphasize that the only time that the master copies of the primary data files are modified is during the monthly archiving of data. Page 7 of 10

Handbook of Cosmic Hazards and Planetary Defense DOI 10.1007/978-3-319-02847-7_89-1 # Springer International Publishing Switzerland 2014

Prior to insertion of new data into the weekly secondary or monthly master files, numerous checks are performed on the new data to ensure that is valid. For both the weekly and monthly updates, these checks include: – That there are no duplicate or near-duplicate observations – That the same observations do not appear under two different designations – That the observed object was above the observer’s horizon and that the sun was below the horizon at the time of observation – That an identical or nearly identical observation has not been published already – That there are no observations under non-assigned designations – That there are no observations of newly designated objects without a discovery observation – That there are no discovery observations that lack other observations – That there are orbits for all objects that have new observations and have perturbed orbits – That there are orbits for all objects that have new observations and are newly observed at a second opposition For the monthly checks, the following additional checks are made: – That the format of the perturbed and unperturbed orbits is correct. These checks include: – Nonstandard epoch – Incorrect H or G values – Incorrect formatting of designations – That there is not more than one new orbit for the same object – That the unperturbed orbits include all published observations – That the number of observations included in the orbit matches the number of published observations (once observations rejected from the orbit are considered) – That the observed arc included in the orbit matches the arc of published observations (once observations rejected from the orbit are considered) – That the same identification or double designation is not present more than once with the order of the designations changed – That there are no identifications or double designations that include as-yet-unassigned designations – That the residual blocks for perturbed orbits represent all published observations – That an orbit for a numbered object is not present under a provisional designation If problems related to the insertion of observations or orbits into either the master or secondary data files are detected subsequently, the correction of those problems is handled in the following batch of Minor Planet Circulars, via the sections listing Corrected Observations, Deleted Observations, Identification Changes, and Erroneous Identifications.

Prior Archiving The first archiving of observations by the MPC was on punched cards (Herget 1949). Each observation was stored on an individual punched card. The initial set of observations that were stored on punched cards consisted of all the observations that had appeared in the Rechen-Institut Circulars and the MPCs and was intended to be complete for all observations made since the start of Page 8 of 10

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1939. That was the first year that a detailed index of minor planet observations was not given in the Jahresbericht. The pages of the MPCs were typed by hand as newly submitted observations were received by the MPC. Sometime later, the observations would be stored on punched cards. The checks that were made on incoming observations were minimal: many of the early observations are only approximate and there were numerous misidentifications of objects. In 1960 the punched card storage system was extended (Herget 1960) so that observations were entered onto punched cards as they were received. The pages of the MPCs were then prepared from the punched cards. By 1971 the observations were stored on magnetic tape (Herget 1971), with the punched cards being stored as a backup.

Distribution of Datasets Current distribution of datasets is via the MPC’s website. Complete datasets are downloadable from the ECS links, while extraction of information for individual objects is via the MPC DB link. A magnetic tape containing observations was transferred to SAO in 1978. At intervals beginning in 1981, copies of the magnetic tape of observations were available from the MPC.

Web Services The MPC maintains many web pages and services that aid observers in selecting objects for observation, and finding key areas of sky not scanned for NEOs. In an attempt to facilitate cooperation among observers, the MPC maintains a sky coverage web page, showing which areas of sky have recently been observed (and which allows the download of the raw coverage files supplied by the observers), and also the NEO Blog, to allow users to communicate among themselves about NEOs they are targeting for orbit improvement.

MPC Personnel Observations and orbits are processed by the current MPC staff members: Timothy B. Spahr, Gareth V. Williams, Sonia Keys, and Michael Rudenko. Other current MPC staff members are Jose Luis Galache and James Davies. In addition, various automated processes are responsible for vetting observations and orbits. Others who have contributed (either as MPC staff members, consultants, visitors, or volunteers) to observation and/or orbit processing in the past include Paul Herget (former MPC director, Cincinnati Observatory), Eugene Rabe (Cincinnati), Conrad M. Bardwell (Cincinnati and SAO), Brian G. Marsden (former MPC director, SAO), Daniel W. E. Green (SAO), Eric Fogelin (SAO volunteer), Syuichi Nakano (MPC consultant), Andreas Doppler (SAO visitor), and Carl Hergenrother (MPC consultant).

Conclusion The basic operation of the MPC has been described. It is not practical to go into any more depth as that would involve command-line-specific details that are subject to frequent modification. Page 9 of 10

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Cross-References ▶ Defending Against Asteroids and Comets ▶ European Operational Initiative on NEO Hazard Monitoring ▶ European Space Agency’s Program on Potentially Harmful Asteroid ▶ International Astronomical Union and the NEO Hazard ▶ NEOSHIELD – A Global Approach to Near-Earth Object Impact Threat Mitigation ▶ Potentially Hazardous Asteroids and Comets ▶ The NASA Sentry Risk Table ▶ The Palermo and Torino Scales (Risk Assessment of NEO Collisions and Magnitude of Impact) ▶ The Yarkovsky Effect ▶ U.S. Ground Observatories

References Edmondson F (1952) Report of the observing program at the Goethe link observatory, Indiana University. Minor Planet Circ 816 Herget P (1949) Index of minor planet observations. Minor Planet Circ 191 Herget P (1960) Editorial notice. Minor Planet Circ 2033 Herget P (1971) The work at the minor planet center. In: Physical studies of minor planets. Scientific and Technical Information Office, Washington, pp 9–12 Krueger A (1892) Notiz betr. dir Nummerirung der kleinen Planeten [Notice on the designation of minor planets]. Astron Nachr 130:159 Larsen JA, McMillan RS, Scotti JV, Hicks M, Fevig R, Williams GV (2000) (719) Albert =2000 JW8. IAU Circ 7420 Marsden BG (1980) The minor planet center. Cel Mech 22:63–71 Marsden BG (1996) From telescope to MPC: organizing the minor planets. IAU Symp 172:153–164 Marsden BG, Sekanina Z, Yeomans DK (1973) Comets and non-gravitational forces. V. Astron J 78:211–225 Spahr TB, Williams GV (2009) Minor planet center activities in the next generation of search programs, submitted to 2009 IAA Planetary Defense Conference Proceedings Williams GV, Elst EW, Zhuravleva LV, McNaught RH, Hawkins MRS, Gibson J, Nicholson SB, Shapley H (1991) (878) Mildred. IAU Circ 5274 Wolf M (1892) Photographische aufnahmen von kleinen planeten [Photographic images of minor planets]. Astron Nachr 129:337–342 Yabushita S (1996) On the effect of non-gravitational processes on the dynamics of nearly parabolic comets. Mon Not R Astron Soc 283:347–352

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United Nations Activities Joseph N. Peltona* and Sergio Camacho-Larab a International Association for the Advancement of Space Safety, Arlington, VA, USA b Science and Technology Education for Latin America and the Caribbean (CRECTEALC), Mexico City, Mexico

Abstract This chapter addresses the several actions that the United Nations has undertaken to address various types of natural and anthropogenic origin cosmic hazards. The primary organizational units that address these issues within the United Nations are the General Assembly; the Committee on the Peaceful Uses of Outer Space (COPUOS) and its Scientific and Technical Subcommittee, Action Team on Near-Earth Objects (Action Team 14); and, in parallel, the Group of Governmental Experts on Transparency and Confidence-Building Measures in Outer Space Activities established by the Secretary-General of the United Nations. In the past decade significant progress has been made by the United Nations in addressing these issues. In 2007 COPUOS agreed on the Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space. In December of that year, the guidelines were endorsed by the General Assembly in its resolution 62/217 (General Assembly, Official Records Sixty-second session, 2007, Supplement No. 20 (A/62/20) Annex “Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space”. http://www.unoosa.org/pdf/gadocs/A_62_20E. pdf. Last accessed Oct 2014). This COPUOS action (i.e., to adopt these voluntary guidelines) is significantly based on the coordinated action that came out of the Inter-Agency Space Debris Coordination Committee (IADC). The IADC is an international forum of governmental bodies for the coordination of activities related to the issues of man-made and natural debris in space. The primary purpose of the IADC is to exchange information on space debris research activities between member space agencies, to facilitate opportunities for cooperation in space debris research, to review the progress of ongoing cooperative activities, and to identify debris mitigation options. The IADC adopted its first set of Space Debris Mitigation Guidelines in 2002 and revised them in 2007 (IADC (2007) IADC space debris mitigation guidelines. http://www.iadc-online.org/index.cgi?item=docs_ pub. Last accessed Oct 2014). The IADC mitigation guidelines is a living document and may be updated as new information becomes available regarding space activities and their influence on the space environment. In February of 2010, COPUOS, through its Scientific and Technical Subcommittee, established a working group on the Long-term Sustainability of Outer Space Activities (LTSSA) that is working on another set of draft guidelines to preserve the use of space in the long term. The draft guidelines address four thematic areas: (a) sustainable space utilization supporting sustainable development on Earth; (b) space debris, space operations, and tools to support collaborative space situational awareness; (c) space weather; (d) and regulatory regimes and guidance for actors in the space arena. These activities by COPUOS are addressed in this chapter along with its many significant actions related to near-Earth objects. Recommendations concerning the international response to an asteroid impact threat, now approved by the UN General Assembly as of December 2013, have largely derived from the Third United Nations Conference on the Exploration and Peaceful Uses of

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Outer Space (UNISPACE III Follow Up Action Teams. http://www.unoosa.org/oosa/unisp-3/ followup/teams_contact_list.html#recomm14. Last accessed Oct 2014) held in July 1999 in Vienna, Austria. The Action Team 14 that was formed in 2001 and charged with the follow-up to recommendation 14 from this major conference recommended the new international processes to provide global warning and responsive actions now being implemented. The International Telecommunication Union (ITU) also has concerns related to extreme solar weather and orbital debris, but these are not prime functions and ITU representatives to COPUOS provide a coordinative point of contact. This chapter not only addresses the history of United Nations actions in the three major cosmic hazards areas but also reports on continuing actions and likely trends for the future.

Keywords Action Team 14; Association of Space Explorers (ASE); United Nations Committee on the Peaceful Uses of Outer Space (COPUOS); Group of Governmental Experts on Transparency and ConfidenceBuilding Measures in Outer Space Activities; Inter-Agency Space Debris Coordination Committee (IADC); International Asteroid Warning Network (IAWN); International Telecommunication Union (ITU); Outer Space Treaty; Secure World Foundation (SWF); Space Liability Convention; Space Mission Planning Advisory Group (SMPAG); Space Registration Convention; Transparency and confidence-building measures (TCBMs); UNISPACE III; United Nations General Assembly; United Nations Office for Disarmament Affairs (UNODA); COPUOS Working Group on the Long-Term Sustainability of Outer Space Activities

Introduction The Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies (better known as the Outer Space Treaty), was adopted in 1967 (Outer Space Treaty). This treaty is the primary basis of all international laws related to outer space, although there have been several other space-related agreements that were agreed within the United Nations framework in the 12 years that followed. These other conventions and agreements include: “the Agreement on the Rescue of Astronauts, the Return of Astronauts, and the Return of Objects Launched into Outer Space” (1968) (Rescue Agreement); “the Convention on International Liability for Damage Caused by Space Objects”; or the “Space Liability Convention” (1972), the “Convention on Registration of Objects Launched into Outer Space” (1976) (Space Registration Convention), and the “Agreement Governing the Activities of States on the Moon and Other Celestial Bodies” (1979) (the Moon Agreement). In the context of human-caused cosmic hazards, it is the Space Liability Convention and the Space Registration Conventions that are most relevant. Article XI of the Outer Space Treaty creates a framework and indeed an obligation for information related to space activities and key data related to outer space to be broadly shared on a timely basis. Article IX of the Outer Space Treaty explicitly states the following: In order to promote international cooperation in the peaceful exploration and use of outer space, States Parties to the Treaty conducting activities in outer space, including the Moon and other celestial bodies, agree to inform the Secretary-General of the United Nations as well as the public and the international scientific community, to the greatest extent feasible and practicable, of the nature, conduct, locations and results of such activities. On

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receiving the said information, the Secretary-General of the United Nations should be prepared to disseminate it immediately and effectively.

Article IX states that “In the exploration and use of outer space, including the Moon and other celestial bodies, States parties to the Treaty shall be guided by the principle of cooperation and mutual assistance . . ..” This cooperation and mutual assistance have consistently been applied to efforts to address cosmic hazards, and thus nations are expected to be transparent in all their activities to combat such hazards by sharing relevant information (Article IX, Outer Space Treaty). For the last 35 years, i.e., since 1979, there have been no treaties or conventions adopted by the General Assembly. The Moon Treaty, adopted in 1979 and that came into force in 1984, has only 15 ratifications. Thus, cooperation in space over the past 35 years has largely come through less formal means such as through declarations and guidelines and by strengthening transparency, confidence-building measures, and information sharing. Also, since the 1970s, we have seen another key change in space. This transition has been an evergrowing amount of space activities conducted by private business. Even entities that were once public international organizations such as Intelsat, Inmarsat, and Eutelsat have been privatized and are thus no longer publicly owned. A number of challenges have come along with this increased private activity and commercialization of space. These concerns include such issues as the buildup of orbital debris, especially in low Earth orbit, increased demand for and use of radio frequency spectrum shared by an ever-increasing range of users, demand for orbital assignments in the geosynchronous orbital arc, and concern about the placing and use of the so-called space weapons. Article VI of the Outer Space Treaty indicates that it is the states that are responsible for all national space activities. The Space Liability Convention again places all responsibilities on the launching state. Yet in this newly commercialized world of space activities, it is clear that the language adopted in the 1970s is no longer a reasonable characterization of current reality regarding possible losses related to commercial exploitation of resources on the Moon and other celestial bodies. In addition to these challenges related to the expanded use of space, the last half century has been a time of tremendous change for planet Earth. The global population has more than doubled to over seven billion people, and for the first time more than half the people live in towns and cities and are more and more dependent on modern infrastructure that is vulnerable to some form of catastrophic loss. By 2050 perhaps 70 % of the world’s population will live in cities and be more vulnerable than ever. Although floods, hurricanes, typhoons, earthquakes, volcanoes, and other natural disasters are of prime concern, it is now increasingly recognized that cosmic hazards such as solar flares, coronal mass ejections, and near-Earth objects pose a risk to world society. Thus, today cosmic hazards are of increased concern since they could destroy vital infrastructure and put very large populations – perhaps numbered in the billions – at risk. The United Nations, through various bodies and cooperative programs, are assisting in the establishment of independent entities to coordinate capabilities and international processes to address these various cosmic hazards. The greatest attention is today being given to orbital space debris, extreme space weather, and near-Earth objects. The prime body that is addressing these cosmic hazards, under the guidance of the UN General Assembly, is the Committee on the Peaceful Uses of Outer Space (COPUOS) together with its various working groups and consultative bodies. Required collaborative efforts to address threats to the sustainability and security of outer space activities are addressed by the UN Committee on Disarmament and by the Group of Governmental Experts (GGEs) on Transparency and Confidence-Building Measures in Outer Space Activities, which was established by the Secretary-General of the United Nations.

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United Nations Committee on the Peaceful Uses of Outer Space (COPUOS) The Committee on the Peaceful Uses of Outer Space (COPUOS) has addressed a number of issues and problems related to cosmic hazards for decades. These include efforts to characterize and reduce orbital debris, efforts to address the threat of near-Earth objects hitting Earth, and most recently the issue of extreme space weather events.

Orbital Debris Mitigation Through its Scientific and Technical Subcommittee, COPUOS took up the issue of orbital debris in 1994, considering that international cooperation was needed to expand appropriate and affordable strategies to minimize the potential impact of space debris on future space missions. In order to have a firm scientific and technical basis for future actions, the subcommittee agreed on a multiyear work plan, beginning in 1995 and finishing in 1999, to focus on debris-measuring techniques; mathematical modeling of the space debris environment, characterizing the space debris environment; and measures to mitigate the risk of space debris, including spacecraft design measures. Throughout this period, the Inter-Agency Space Debris Coordination Committee (IADC) provided annual technical reports to the subcommittee on the work that it was conducting to identify debris mitigation options. The IADC was formally established in 1993, initially by ESA, Japan, NASA, and the Russian Space Agency (RSA). The IADC membership would subsequently increase to at present 12 members, representing major space agencies. The added value of introducing space debris as an agenda item of the subcommittee and in due course the guidelines developed by the IADC for consideration by the subcommittee was the endorsement, and thus buy-in, by all member states of the United Nations, not only of the governments represented in the IADC by their space agencies. The work between the subcommittee and the IADC was well coordinated. While the IADC worked throughout the year through various technical working groups, its annual report to the subcommittee kept the government representatives of countries not represented in the IADC informed of the importance and complexities of the issue of space debris. It in this setting that the subcommittee became familiar with an initial set of Space Debris Mitigation Guidelines agreed by the IADC in 2002 and then revised and improved in 2007. That procedure set the stage for the subcommittee and then the committee to act. After a few amendments, there was consensus agreement within the COPUOS to adopt the Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space, a set of voluntary guidelines to mitigate space debris. Although these procedures are “voluntary,” they are now rather universally observed by space-faring nations. The implementation of the guidelines is essentially left to the launching state. The UN COPUOS guidelines are today quite useful, but perhaps even more useful are national laws based on those guidelines that are binding and in several cases even stricter. The French Space Operations Act (FSOA), for instance, has set specific goals for limiting debris and to ensure the reentry of satellites within the 25-year rule. Many believe that the provisions of this French law will become a model law that many other space-faring nations will follow. Such national laws to prevent the creation of orbital debris are subject to legislative enforcement, while the UN guidelines are simply voluntary. Problems with small satellites and CubeSats that are not formally registered under the Registration Convention and are launched into orbits above a few 100 km are currently addressed by national laws but not explicitly covered by the UN COPUOS guidelines. Many organizations continue to work on the issue of orbital debris, both in terms of preventing the creation of additional debris as well as the even more difficult issue of active debris removal or Page 4 of 11

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orbital changes to prevent in-orbit collisions. These organizations include: (i) COPUOS and the Working Group on the Long-Term Sustainability of Space Activities (LTSSA) of its Scientific and Technical Subcommittee; (ii) the Space Data Association, which is a group of satellite operators that exchange data on their spacecraft to seek to avoid collisions; (iii) the IADC with its four working groups that work on measurements (WG1), environment and database (WG2), protection (WG3), and mitigation (WG4) and consider active debris removal issues; and, of course, the national civil and military space programs of space-faring nations – especially those such as the United States with active satellite tracking organizations. In general there is excellent communication between and among these organizations as well as organizations with a special interest in these issues such as the Secure World Foundation, the Council on Space Research (COSPAR), the International Astronomical Union (IAU), etc.

Working Group on the Long-Term Sustainability of Space Activities and Extreme Solar Weather The topic of the long-term sustainability of space activities had its genesis within COPUOS in 2005 when Karl Deutsch, Chairman of the Scientific and Technical Subcommittee for the period 2001–2003, made a special presentation on the scientific and technical aspects of the work of the committee and the way ahead to the 48th session of the committee. At that same session, the then Chairman of COPUOS Adigun Ade Abiodun (Nigeria) prepared an informal paper entitled “Planning for Future Roles and Activities of the Committee,” for consideration by the committee. The committee agreed that this was an important subject and requested the Office for Outer Space Affairs to prepare a working paper which summarized the presentation, the informal paper, and the discussion in the committee on this matter for further consideration by the committee in 2006. The General Assembly, in its resolution 61/111 (2006), noted with satisfaction that COPUOS had agreed to consider, at its fiftieth session, the issue of the future role and activities of the committee. On the basis of open-ended informal consultations, the Chairman of COPUOS for the period 2006–2007, Gerard Brachet (France), presented a working paper entitled “Future Role and Activities of the Committee on the Peaceful Uses of Outer Space.” The committee agreed that the working paper provided a good basis for further consideration of the future work of the committee. As a result, by 2010 the Working Group on the Long-term Sustainability of Outer Space Activities was established as a working group of the Scientific and Technical Subcommittee of COPUOS. This working group that is currently chaired by Peter Martinez (South Africa) has developed a draft report that covers many issues and aspects of the longer-term sustainability of space. The two prime topics in terms of cosmic hazards that are being discussed are orbital debris and extreme space weather. In particular there is Group B, “space debris, space operations, and tools to support collaborative space situational awareness,” and Group C, space weather (Working Group). Currently, the Group B work program is to “Develop a consolidated set of voluntary best practices and guidelines focused on practical and prudent measures that could be implemented in a timely manner in the areas of: • Space debris • Space operations • Tools to support collaborative space situational awareness”

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The focus with regard to space debris issues was noted to be twofold, namely, “to reduce the creation and proliferation of new debris” as well as to examine “technical developments and possibilities regarding debris removal” (Expert Group B). The Group C on space weather has a much greater range of issues to address since there had previously been limited attention paid to these areas within the UN COPUOS. The Group C report thus developed some preliminary guidelines and identified a number of best practices that might be followed under each of these four guidelines. The most challenging and newest part of such guidelines is, of course, that of mitigation practices. These guidelines included: Guideline 1: Space actors and member states and their national and international agencies should support and promote the collection, sharing, inter-calibration, and dissemination of critical space weather data. Guideline 2: Member states and their national and international agencies should support and promote further coordinated development of advanced space weather models and forecast tools in support of identified user needs. Guideline 3: Member states and their national and international agencies should support and promote the sharing and dissemination of space weather model outputs and forecasts. Guideline 4: Member states and their national and international agencies should support and promote the collection, sharing, dissemination, and access to information relating to best practices for mitigating the effects of space weather on ground- and space-based systems and related risk assessments (Proposed candidate guidelines). The UN processes via COPUOS and the Working Group on the Long-Term Sustainability of Outer Space Activities will continue to address space debris and space weather issues. At this time there is considerable focus on addressing space debris, space operations, and space situational awareness not only within COPUOS but also within the UN Office for Disarmament Affairs (UNODA) and the Group of Governmental Experts on Outer Space. The goal is to seek new answers related to changing orbits to avoid collisions and to develop processes to cover active debris removal and still at the same time avoid the use of the so-called space weapons. In addition to these formal international coordination processes, there are other consultations outside of the UN mechanisms. US Assistant Secretary of State Frank A. Rose at a recent Asian Space Conference held in Tokyo, Japan, noted how coordination with Vietnam had served to change the orbit of a Vietnamese satellite to avoid a collision. He also noted that transparency, confidence-building measures, and codes of conduct can also help to address space debris and related concerns pending formal UN agreed procedures (Rose 2014).

Near-Earth Objects, UNISPACE III, Action Team 14, and the UN General Assembly The issue of near-Earth objects that include potentially hazardous comets, asteroids, and bolides has received much more public and media attention – especially after a spectacular event in which a large meteor exploded over Chelyabinsk, Russia, on February 15, 2013, and caused considerable damage. The UN COPUOS organized the UNISPACE III Conference in 1999. This global space conference focused a good deal of attention on the issue of potential asteroid strikes. At this forum space scientists agreed to the Torino Impact Hazard Scale. This scale shows the various sizes of asteroids, their likelihood of impact, and the expected level of hazard they would likely bring. Page 6 of 11

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The final report of the UNISPACE III Conference in 1999 ended up making 33 major recommendations, but only the 14th recommendation explicitly urged actions related to cosmic hazards. The 14th recommendation for action stated that there was a need to: “Improve the international coordination of activities related to near-Earth objects.” This led in 2001 to the formation of “Action Team 14” to address the UNISPACE III recommendation on near-Earth objects (NEOs). This Action Team 14 was set up under the cochairmanship of delegates from the United Kingdom and Mexico and included the following members: Australia, Brazil, China, the Czech Republic, Finland, Germany, Iran, Japan, Kazakhstan, Lebanon, Malaysia, Nigeria, Pakistan, Poland, the Russian Federation, Saudi Arabia, the Syrian Arab Republic, and the United States. Organizational members included: the Association of Space Explorers, European Space Agency (ESA), Committee on Space Research (COSPAR), International Astronomical Union (IAU), National Space Society, Space Generation Advisory Council, European Science Committee, European Science Foundation, and the SafeGuard Foundation. The Action Team 14 working group held an extended set of meetings and discussions in the following decade (Recommendations of UNISPACE III). The Action Team 14 working group in 2013 recommended two specific actions to the Scientific and Technical Subcommittee. These recommendations were approved in February 2013 by the subcommittee, by the full COPUOS in June 2013, and finally by the UN General Assembly in October 2013. The recommended and now approved actions endorsed by the General Assembly are as follows: 1. “The establishment of an international asteroid warning network (IAWN) by linking together the institutions that are already performing many of the proposed functions, including: discovering, monitoring and physically characterizing the potentially hazardous NEO population; maintaining an internationally recognized clearing house for the receipt, acknowledgment and processing of all NEO observations; recommending policies regarding criteria and thresholds for notification of an emerging impact threat; and developing a strategy using well-defined communication plans and protocols to assist Governments in the analysis of impact consequences and in the planning of mitigation responses.” 2. “The establishment of a space mission planning advisory group (SMPAG) by Member States with space agencies, facilitated by the United Nations on behalf of the international community, with no financial implications for the budget of the United Nations. Its responsibilities should include laying out the framework, timeline and options for initiating and executing response activities, informing the civil-defence community about the nature of impact disasters and incorporating that community into the overall mitigation planning process through an impact disaster planning advisory group” (Near-Earth Objects). The general intended thrust of these recommended actions was not to create new bodies or organizational entities but rather to work with existing bodies such as the Minor Planet Center (at Harvard University), the SafeGuard Foundation in Italy, and relevant units within space agencies and ground observatories to create the International Asteroid Warning Network. The Russian delegation to COPUOS has recently, however, suggested in a COPUOS document that a new clearing house for near-Earth objects might be created under the United Nations auspices. Experts for the Space Mission Planning Advisory Group have also been recruited with the first round of policy discussions being held in early February 2014. This group is expected to develop its first set of recommendations by the end of 2015 or early 2016.

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The recent rapid UN action to move ahead on this issue through the subcommittee of COPUOS, to the full COPUOS body, and then onto the General Assembly from the start in February 2013 with final action in October 2013 was a remarkably swift course of action that is quite promising.

The SPIDER Program and the United Nations Ability to Respond to a Cosmic Hazard COPUOS as constituted with some 70 participating countries that represent a wide range of economic, social, political, scientific, and technical capabilities is more of a deliberative body than an action arm of the United Nations. The Office of Outer Space Affairs that supports COPUOS has a small staff and limited means to implement global programs. In recent years, however, the OOSA has managed a program called SPIDER that allows the rapid deployment of Earth stations to areas where disasters had occurred and emergency communications are needed. It is clear that this would largely be the extent to which COPUOS could respond to major disaster such as an asteroid strike or a major coronal mass ejection from the sun. It is noted elsewhere in this handbook that the United Nations needs to address its capability to respond to a major disaster such as an asteroid actually hitting Earth or a major coronal mass ejection to provide large-scale emergency relief to affected areas. One suggestion is that UN peacekeeping forces could be detailed to such a major response. Currently, there are provisions to use remote sensing data to cope with major disasters, and organizations such as the Red Cross and Red Crescent would surely respond, but a much more structured capability from the United Nations should be a part of future discussion regarding the issue of cosmic hazards that could have a devastating impact on the Earth.

The United Nations Office for Disarmament Affairs One of the many jurisdictional issues that the United Nations organization faces in the area of outer space is that there is in most countries around the world a strict division between civil space on one hand and military space programs on the other. Essentially, COPUOS addresses civil space activities, and the UN Office for Disarmament Affairs (UNODA) and the UN Institute for Disarmament Research address the military- and defense-related programs. Civil space issues are considered in Vienna, Austria, at COPUOS, and military space issues are addressed in Geneva, Switzerland, within the UNODA processes. Fortunately, there is a reasonable level of communications and coordination between these UN entities. Certainly, some of the issues being addressed in Group B of the Working Group on Long-Term Sustainability of Outer Space Activities such as active space debris removal, space operations, and space situational awareness as well as responses to asteroid threats are as much a military space issue as a civil space issue. In both the cases of active debris removal and asteroid diversion, there are not only concerns as to whether this might entail the deployment of technology which might be considered “space weapons” but also issues related to liability claims by injured parties if such efforts are not successful. Thus, entities involved in orbital debris removal or diversion of asteroids would undoubtedly wish to seek some degree of liability immunity that is not currently available under the Space Liability Convention (Diederiks and Kopal).

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The Group of Governmental Experts on Outer Space Activities Currently, such issues are being considered in the several UN entities involved with space activities but especially so in the Group of Governmental Experts on Transparency and Confidence-Building Measures (TCBMs) for Space Activities as convened by the United Nations. In July 2013 under the chairmanship of Victor Vasiliev, this GGE reached consensus on a set of recommendations. This GGE report that reflected the unanimous views of 15 different countries was sent to the SecretaryGeneral of the UN with a set of specific recommendations for collaborative efforts to address threats to the sustainability and security of the outer space (Secure World Foundation’s statement). The GGE in this report identified six explicit areas where the development of transparency and confidence-building measures would be desirable and should be pursued. The fifth recommended area is of special relevance: “(e) Measures related to establishing norms of behaviour for promoting spaceflight safety such as launch notifications and consultations that aim at avoiding potentially harmful interference, limiting orbital debris and minimizing the risk of collisions with other space objects” (UN 2013, Report of the Group of Governmental Experts). The fact that actions are now envisioned in the form of transparency and confidence-building measures and by implication codes of conduct in outer space in many ways reflects today’s reality. A major new treaty on outer space or even amendments to the Outer Space Treaty or the Space Liability Convention seem unlikely. Instead, space-faring nations discuss and agree to forms of behavior that seem to be mutually acceptable. The new International Asteroid Warning Network (IAWN), the Space Mission Planning Advisory Group (SMPAG), and the Working Group on LongTerm Sustainability of Space Activities (LTSSA) are creating new international mechanisms for coordination and agreement in the most sensitive areas of active orbital debris removal, space operations, space situational awareness, and asteroid diversion. It is in these areas where collaboration between the various entities within the COPUOS and UNODA structure is most important, and recent advances in the international discussions within both bodies seem more promising.

Conclusions The United Nations structural units that address space activities over the last 20 years have taken on the various issues of orbital space debris, space situational awareness, space operations and debris removal, asteroid detection and diversion, as well as extreme solar weather. As the world has become more populous, more urban, and more dependent on advanced modern infrastructure, including various types of applications and scientific satellites, these various space-related issues have become more vital to global prosperity – and perhaps even survival. A number of organizations outside of the UN structure have consistently provided support, research efforts, and advice with regard to these critical matters. These organizations include the Association of Space Explorers, the B612 Foundation, the Council on Space Research (COSPAR), the International Academy of Astronautics, International Astronomical Union, the Minor Planet Center, the SafeGuard Foundation, the Secure World Foundation, and, of course the various space agencies around the world and their cooperative units such as the Inter-Agency Space Debris Coordination (IADC) Committee. The United Nations has made significant progress in agreeing on voluntary guidelines regarding space debris mitigation, the creation of the International Asteroid Warning Network (IAWN) and the Space Mission Planning Advisory Group (SMPAG), and the ongoing work of the Long-Term Sustainability of Space Activities (LTSSA). Yet much more needs to be done. If there is a UNISPACE IV, then much more emphasis should be placed on orbital debris, potentially hazardous Page 9 of 11

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asteroids and comets, and extreme solar weather. The Association of Space Explorers has called for much more effort to create space telescopes capable of identifying the up to one million potentially hazardous asteroids (30 m or larger in size). New liability provisions to hold harmless those that could engage in active orbital debris removal or diversion of hazardous asteroids should also be sought. Finally, it would seem desirable for the UN to consider how it could assist on a large-scale way to a major asteroid impact or extreme solar event that could potentially adversely impact a billion or more people such as by making the full range of UN peacekeeping forces and equipment available for this purpose.

Cross-References ▶ Directed Energy for Planetary Defense ▶ Hazard of Orbital Debris ▶ International Legal Consideration of Cosmic Hazards and Planetary Defense ▶ Major Gaps in International Planetary Defense Systems: Operation and Execution ▶ Planetary Defense, Global Cooperation and World Peace ▶ Potentially Hazardous Asteroids and Comets

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Recommendations of Unispace III. http://parviztarikhi.files.wordpress.com/2010/07/ats-list.pdf. Last accessed Oct 2014 Rose FA (2014) Assistant Secretary of State, Bureau of Arms Control, Verification and Compliance Second ASEAN Regional Forum (ARF) Workshop on Space Security, Tokyo, 9 Oct 2014. http:// www.state.gov/t/avc/rls/2014/232773.htm. Last accessed Oct 2014 Secure World Foundation Statement of 11 Feb 2014. http://secureworldfoundation.org/media/ 165792/SWF%20Statement%20on%20LTS%20for%20STSC%20-%20Feb%202014.pdf. Last accessed Oct 2014 The Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (1979) http://www.oosa.unvienna.org/oosa/SpaceLaw/moon.html. Last Accessed Oct 2014 The Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space (1968) http://www.oosa.unvienna.org/oosa/SpaceLaw/rescue.html. Last Accessed Oct 2014 Torino Impact Hazard Scale. http://neo.jpl.nasa.gov/torino_scale.html. Last accessed Oct 2014 UN (2013) Report of the Group of Governmental Experts on Transparency and ConfidenceBuilding Measures in Outer Space Activities, UN General Assembly, 29 July 2013, A/68/189 Working Group on the Long Term Sustainability of Outer Space Activities. http://www.unidir.ch/ files/conferences/pdfs/un-copuos-scientific-technical-subcommittee-s-working-group-on-the-longterm-sustainability-of-outer-space-activities-en-1-939.pdf

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