Stratospheric Balloons: Science and Commerce at the Edge of Space [1 ed.] 3030681297, 9783030681296

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Stratospheric Balloons: Science and Commerce at the Edge of Space [1 ed.]
 3030681297, 9783030681296

Table of contents :
Dedication
Foreword
Acknowledgments
Preface
Contents
1 Introduction
2 Stratospheric Balloon Descriptions
3 Balloon Elements
4 Mission Drivers and Operations
5 Commercial Corporations and Applications
6 Launch Sites
7 Scientific Flight Types
8 Accomplishments
9 The Balloon World
10 Educating the Next Generation
11 Conclusions
Appendix 1 A Brief History of the NSBF/CSBF
Appendix 2 Scientists and Engineers in Ballooning
Appendix 3 Interesting Stories
Appendix 4 Quotes
Appendix 5 Planetary Balloons
References
Glossary and Terminology
About the Author
Index

Citation preview

Manfred “Dutch” von Ehrenfried

Stratospheric Balloons Science and Commerce at the Edge of Space

Stratospheric Balloons Science and Commerce at the Edge of Space

Manfred “Dutch” von Ehrenfried

Stratospheric Balloons Science and Commerce at the Edge of Space

Manfred “Dutch” von Ehrenfried Cedar Park, TX, USA

SPRINGER-PRAXIS BOOKS IN SPACE EXPLORATION Springer Praxis Books Space Exploration ISBN 978-3-030-68129-6    ISBN 978-3-030-68130-2 (eBook) https://doi.org/10.1007/978-3-030-68130-2 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Project Editor: David M. Harland Cover design: Jim Wilkie This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Other Springer-Praxis Books by Manfred “Dutch” von Ehrenfried

Stratonauts: Pioneers Venturing into the Stratosphere, 2014 ISBN: 978-3-319-02900-9 The Birth of NASA: The Work of the Space Task Group, America’s First True Space Pioneers, 2016 ISBN: 978-3-319-28426-2 Exploring the Martian Moons: A Human Mission to Deimos and Phobos, 2017 ISBN: 978-3-319-52699-7 Apollo Mission Control: The Making of a National Historic Landmark, 2018 ISBN: 978-3-319-76683-6 From Cave Man to Cave Martian, Living in Caves on the Earth, Moon and Mars, 2019 ISBN: 978-3-030-05407-6 The Artemis Lunar Program: Returning People to the Moon, 2020 ISBN: 978-3-030-38512-5

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Dedication

This book is dedicated to all of the scientists, graduate students, engineers, technicians, managers and administrators that supported the scientific balloon flights of past generations; to the corporations and organizations that have pioneered the use of stratospheric balloons for commercial applications; and to the international scientific organizations and commercial enterprises that also strive, in their own unique way, to advance the state of the art of ballooning. A special dedication goes to those students, of all ages, who are participating in ballooning as part of their studies of science, technology, engineering, and mathematics. While they may not yet know their future career paths, it is to be hoped that some of them will join the next generation of balloonists and that their participation will lead to a better understanding of our place in the universe. At least we know from others who blazed the trail before them, that their lives and society will be enriched by their efforts. This book is also dedicated to those in a position to guide NASA in its use of balloon programs for the advancement of science, including the Science Mission Directorate at NASA Headquarters which funds the Balloon Program. Within that organization are the various science divisions that manage, support, and fund scientific balloon missions. And this book is dedicated to the organizations that conduct balloon missions, notably the Wallops Flight Facility of the Goddard Space Flight Center, which includes the Balloon Program Office and their operational site; the Columbia Scientific Balloon Facility. And last, but not least, this book is dedicated to the students who have actually taken part in launching balloons as part of their studies. Not only have they been working towards graduating, they have been learning the fundamentals of balloon operations including pre-flight preparations, flight operations, recovery, and postflight analysis. This book is therefore dedicated to the next generation of balloon scientists, engineers and technicians, for they are the future. vii

Foreword

The following are comments by three eminent scientists who spent their early formative careers launching instruments and payloads on balloons into the stratosphere. Dr. John C. Mather and Dr. George F. Smoot shared the 2006 Nobel Prize in Physics for their work on the Cosmic Background Explorer that led to the “discovery of the black body form and anisotropy of the cosmic microwave background radiation”. As an astronaut, Dr. John M. Grunsfeld helped to service and repair the Hubble Space Telescope. He went on to become NASA’s Chief Scientist. Their balloon experiences surely made lasting impressions on them and helped to define their scientific interests and future paths. They are truly an inspiration for young students and future scientists, as well as to those who are already involved in ballooning.

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Foreword   ix

Dr. John C. Mather Senior Astrophysicist in the Observational Cosmology Laboratory NASA’s Goddard Space Flight Center I got my start in scientific ballooning at the University of California, Berkeley. I was looking for a Ph.D. thesis project in 1970, after two years of graduate school classes on particle physics and relativity and quantum mechanics and studying in the library, and I was giving up on my dream of being a theoretical physicist like Richard Feynman. I really wanted to build something. I felt my hands itching to hold a screwdriver. I found Paul Richards and Charles Townes and Mike Werner, who were all thinking about how to measure the newly discovered Cosmic Microwave Background Radiation. I said yes, I want to play! So the first project was to build an instrument and take it up to White Mountain in eastern California, on the east side of the Owens Valley. We built it and it worked, and we learned a new technology, but it wasn’t surprising, it just agreed with expectations that the cosmic background seemed to have a temperature of about 3 degrees Kelvin. Then Paul went off to England for a sabbatical and came back with an idea for a balloon payload that could get an instrument above most of the interference of the Earth’s atmosphere. It would be a satellite on a string, as I called it. The plan was to make a new kind of interferometer, which Paul had learned about in England, called a Polarizing Martin-Puplett, and use it as a spectrometer. It would

x  Foreword measure the temperature of the cosmic background radiation at wavelengths from about 0.5 mm to 5 mm if we were lucky. It would have to be immersed in a bath of liquid helium, it would have to fly to an altitude of 40 km, and it would have a window that would open up after the payload had reached the target altitude. It had all the ingredients of a satellite, except it wasn’t going to really be in outer space. It had a big battery (although no solar cells, it wouldn’t operate in the daytime), a radio transmitter and receiver, some command processors, a magnetometer so that we would know which way we were pointing, electronics boxes to operate the motors and detectors, and a big rotating momentum wheel to control the orientation. It fit inside a 2 m cubical frame made of aluminum. We built it up and tested it in the lab at Berkeley until it seemed to work the way we hoped and expected. David Woody and I were now the lab partners working on it, so we loaded it into a big yellow university truck and drove it to the National Scientific Balloon Facility at Palestine, TX. This place was chosen because it was very flat and not very populated, and at the right latitude so that once in a while the high altitude winds would die down and we could get a very long flight. It’s a beautiful place in its own way. Many of the neighbors and staff at the base were watermelon farmers in real life, and those melons sure are juicy and sweet! At any rate we got there, set up our equipment, and got ready for the flight. We’d never seen anything like it before. The balloon is a gigantic bag of very thin polyethylene, and there is a method to unroll it and fill it partially with helium while our part, the payload, is suspended from a huge modified earthmoving machine called Tiny Tim with jaws 7 m in the air to hold the payload, until the balloon was ready to pull it up. The launch is done at dusk so the equipment will reach altitude just after dark. After a lot of fiddling and fussing, and discovering that the antenna had fallen off the payload because I’d made a bad solder joint, finally we were all ready, and up it went. It’s an extraordinary sight, rising slowly and then faster, going not quite straight up, and almost out of sight. But alas, the helium gods were not appeased. We used to keep a little Buddha in the lab and rub his tummy for good luck, but that wasn’t enough. By the time our equipment reached the planned altitude, the motor turning the screw in the interferometer wouldn’t go, and the preamp for the detector was sending out a big signal even though it shouldn’t. We got zero scientific data and I wondered what I would do next. We got the payload back – it comes down on a parachute if we’re lucky. We drove back to Berkeley with it and set to work. David thought of a way to build a test chamber to find out what was the matter, using Styrofoam boards and dry ice, which would get our big cubical frame down to the right temperature, about minus 70°C. He found out that we had three different reasons for failure. Two would have been found with the dry ice test, but the third we would have

Foreword   xi missed. The motor had rusted up because water got inside because of the 100% humidity in the evening in Texas and the cooling from the boiling liquid helium. That never would have been discovered in Berkeley. I set to work writing my thesis. A little before that I had gotten a job offer from NASA in New  York City, so I had to hurry and get finished before the golden coach turned into a pumpkin. The thesis was about the working experiment at White Mountain, and the design of the failed balloon payload. It was enough to let me finish school and take a job. My plan was to become a radio astronomer, and to give up on this cosmic background radiation work  – it’s much too hard for a young person. Meanwhile David and Paul and the rest of the team rebuilt the apparatus and fixed the problems and got it ready to fly again. That time it worked. Little did I know that NASA was preparing to ask for new satellite mission proposals. A few months after I took my new job, the announcement came out, and my new boss, Patrick Thaddeus, asked for ideas. I said, my thesis project failed but we should try it in outer space. He recognized that this maybe could work, so we called our colleagues and agreed to write a proposal. I did a lot of typing and copying and editing and we sent it in. I didn’t think we had a chance. But we did. After exploring some other possibilities with us, NASA decided in 1976 to form a new scientific team and to assign an engineering team to develop the idea at NASA Goddard Space Flight Center in Greenbelt, MD. I was now 30 years old and suddenly the head scientist for an outrageously creative and difficult concept. Fortunately, I was now embedded in a team of senior people who knew what to do and how to think, and we made it work. I’ll skip over a few details to say the Cosmic Background Explorer (COBE) was launched successfully on November 18, 1989 and it worked immediately. Within weeks we announced our first measurements (made with the upgraded version of the balloon payload) to the American Astronomical Society and received a standing ovation. Two years later we made our second announcement and got first page news coverage around the world. After that, more people went into the subject, an industry grew about measuring the cosmic background, and in 2006 I got a call from Stockholm. What did I learn from ballooning? First, it’s a great start for a career. Balloon payloads are small enough that a student can learn everything about one, and know something of many engineering disciplines: optics, electronics, mechanical, thermal, cryogenics, telemetry, computers; the works: teamwork, working full blast for a deadline. Second, it’s humbling. Knowing that all your work can fail because of a lack of testing really changes people. And third, it’s empowering. If we can build a little thing and open up a new domain of science, then let’s keep on going! Who knows how far we can go?

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Dr. George F. Smoot University of California, Berkeley and the Lawrence Berkeley National Laboratory. I have had extensive experience with scientific ballooning, having spent more months in Palestine, TX, than I would otherwise have expected. As a young scientist it was very exciting and challenging and often dangerous to our equipment etc. From it, I learned the key disciplines of structure, check lists, and sufficient design and testing. Once the balloon lifts off with your equipment slung beneath it, you can no longer fix it except in very limited ways – if you prepared properly ahead of time. With space research, when your satellite launches on the rocket, you’ll never physically touch it again. You can only fix things you have put in redundancy. You need to have made it well in order to survive the rigors of the launch and the environment of space or near space. In that way, satellites and balloons are very alike. Their primary difference is cost and time line. Also with a satellite you usually get a much longer flight. Before the three satellite experiments, we always had successful balloon-borne prototypes of the experiments. These all produced significant scientific results before the satellite experiments and were pioneer stages and the satellite results the next generation. That means I made three sets of campaigns to the scientific ballooning facility(ies). We were fortunate to recover fairly often with minimal damage to our equipment. We had seven flights on the first program and on one the pressure shell was destroyed, but we were able to replace it.

Foreword   xiii The second program – a CMB version – had three successful flights: two in the north hemisphere covering the northern sky and only one in the south where the payload was lost in the jungles of Brazil for nearly a year and suffered severe damage. A next generation CMB program had multiple flights with first generation, and then a second generation with more resolution and pixels. So we not only got to develop the instrumentation, techniques and software, but we also were getting cutting edge scientific results.

Dr. John M. Grunsfeld Astronaut and former NASA Chief Scientist As an undergraduate physics major at the Massachusetts Institute of Technology, I was captivated by the study of cosmology, black holes, and neutron stars – the physics of the universe. After working on a theory project with Professors Ken Brecher and Philip Morrison it was time to decide on a thesis project. Professor Morrison advised that if I wanted to be a theorist, I should do an experiment in order to understand the issues with making a real measurement and how crucial experimental physics is to unravelling the mysteries of the universe. I joined a group at MIT that was building a small experiment for a high-altitude balloon to observe a highly magnetic neutron star orbiting an ordinary star, called an X-ray pulsar. This sounded exciting, but at the time I had no idea how it would change my life. My job was to prepare the sensitive detectors at the heart of the little

xiv  Foreword telescope, and work with John Vallegra, whose Ph.D. thesis depended on the success of the mission, and others assembling the rest of the balloon payload. I already knew I loved building things from summers working construction jobs, and building and launching model rockets. Growing, preparing, and testing the mercuric iodide crystals at the heart of the X-ray detectors and getting them to work in the laboratory gave me great pleasure. I am at heart an optimizer, and I wanted those detectors to have the best energy resolution and efficiency possible. At the time, I did not realise I was also learning the essential elements of a field called systems engineering, and also project management. As a physicist working alongside other students who were studying mechanical engineering and electrical engineering, we had to perform all the duties that are required to engineer and manage any high-tech project. After about a year of work we packed up and delivered the little X-ray telescope to the National Scientific Balloon Facility in Palestine, Texas in early summer of 1980. I had just graduated but wanted to see the project through, at least my part of making sure the detectors would perform. Our whole team relocated to Texas, including our advisor Dr. George Ricker. George went on to build instruments for the Chanda X-ray Observatory, and was Principal Investigator for the High Energy Transient Observatory-2 and also the Transiting Exoplanet Sky Survey Explorer. I learned an incredible amount from George about how to manage a group of talented individuals all working towards a high-performance challenge like building and fielding a scientific balloon payload. The biggest impact of the whole expedition was seeing my first balloon launch there on the plains of East Texas. In the early morning twilight, I marveled at the teamwork of the NSBF staff as they laid out the delicate balloon. With the coming of the dawn the team began to fill the balloon with a bubble of helium until the balloon slowly came to life and lifted off the launch pad. A huge industrial vehicle, named “Tiny Tim”, held the payload and drove along to position itself underneath the balloon until the whole chain of balloon, parachute, and payload were in a straight line up to the sky. At that moment, Tiny Tim released the payload and slowly the balloon ascended. I heard the thin polyethylene material rustling as the balloon climbed, heading towards its destination 130,000 feet above us. For me it was a magical experience – I had discovered the romance of scientific ballooning. I went on to the University of Chicago in 1981 for my Ph.D., and specifically selected a group led by Professors Peter Meyer and Dietrich Muller who were working on projects using scientific balloons to study the composition of highenergy cosmic rays. I flew several balloon payloads while a graduate student at Chicago and loved every expedition. I was also given a lot of responsibility for the execution of the missions and this furthered my education in managing groups of scientists, engineers and technicians, and especially the logistics necessary to perform a scientific expedition. Following my Ph.D.  I took a job at the California

Foreword   xv Institute of Technology working with Professor Thomas Prince, again because of the group’s involvement in scientific ballooning. While there I also applied to the astronaut program and in 1992 was accepted into the 14th group, reporting to the NASA Johnson Space Center. Over the course of my career as an astronaut, flying five Space Shuttle missions, including three to upgrade and service the Hubble Space Telescope, I frequently looked back at my time doing scientific ballooning. The NASA scientific ballooning program provided me with the complete and quintessential scientific experience, going from concept to hardware, observations and scientific analysis of the results – all in the time frame of a few years. I’m convinced that knowing how to build instruments, repair them in the field, the logistics of undertaking a balloon expedition, and the technology involved in commanding and controlling the payloads, all prepared me to fly in space and perform spacewalks to fix the Hubble and my other missions.

Acknowledgments

A special thanks to the reviewers of my initial proposal to Springer-Praxis and to people who contributed to the book: Dr. James L. Rand, former President of Winzen Engineering and Professor of Aerospace Engineering at Texas A&M; Henry M.  Cathey, New Mexico State University’s Physical Science Laboratory; and I.  Steve Smith, Southwest Research Institute. Together they have almost a century of science and engineering ballooning experience. They in turn led me to engineer Dwight Bawcom, former site manager of the National Scientific Balloon Facility, who reviewed much of the text. These men spent their careers supporting both the Air Force and the NASA Balloon Programs and have traveled the world supporting scientists and launching balloons into the stratosphere. Also, many thanks to the following scientists and engineers (listed in alphabetical order) who answered my questions and provided input for the book: Prof. W. Robert Binns SuperTIGER balloon mission Washington University in St. Louis Jessie L. Crain NSF Office of Polar Programs Alexandria, VA Prof. Peter Gorham ANITA balloon mission University of Hawaii Manoa Dr. John M. Grunsfeld NASA astronaut and Chief Scientist

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Acknowledgments   xvii Dr. John C. Mather NASA Goddard Space Flight Center Greenbelt, MD Steven Peterzen ISTAR Sisters, OR Dr. Brian Flint Rauch Principal Investigator for SuperTIGER-II. Washington University in St. Louis Prof. Eun-Suk Seo Principal Investigator, CREAM balloon mission University of Maryland Dr. Jose V. Siles Project Manager, ASTHROS balloon mission NASA JPL in Pasadena, CA Prof. George F. Smoot University of California, Berkeley and the Lawrence Berkeley National Laboratory Dr. Alan L. Strauss Director, Mount Lemmon SkyCenter University of Arizona Dr. John Tomsick Research Scientist, COSI balloon mission University of California at Berkeley Dr. Christopher Walker Professor of Astronomy, Steward Observatory University of Arizona Many thanks also to the following corporate individuals for their contributions to the book: Grant Anderson Paragon Space Development Corporation Houston, TX Kerry T. Nock, President, Global Aerospace Corporation Irwindale, CA

xviii  Acknowledgments Michael Odenheimer Marketing Contractor, Loon Saratoga, CA Jane Poynter Co-CEO, Space Perspectives Tucson, AZ Many thanks also to the following education organizations for their contributions: Katharine Allen Accounts Manager, Spaceweather Advertising Bishop, CA Meaghin Woolie, Program Manager Louisiana Space Grant Consortium (LaSPACE) Louisiana State University Baton Rouge, LA A special thanks to StratoCat, a non-profit, educational and informative website created, developed, and programmed by Luis E. Pacheco in Argentina. This site was a constant reference for me and any balloon enthusiast. And at NASA: Jeremy L. Eggers Associate Chief, Office of Communications NASA, Goddard Space Flight Center/WFF Michael W. Lentz Art Director, Conceptual Image Lab NASA, Goddard Space Flight Center There are many other scientists mentioned in the References, along with their reports. In addition to contributions from many individuals, I acknowledge the assistance of Wikipedia and Google. These websites enabled me to fill in the pieces of the puzzle on just about any subject. Their inputs are woven into many sections. Also, many thanks go to the people who have given me the opportunity to write about this unique program, particularly Hannah Kaufman, Associate Editor with Springer in New York, Clive Horwood of Praxis in Chichester, England, Praxis cover designer Jim Wilkie in Guildford, England. A special thanks to David M. Harland, who edited this, my seventh Springer-Praxis book and eighth in total. After over seven years of communications solely by email, hopefully I shall be able to meet and thank him in person someday. Thanks everyone, I hope you like the book and find it a handy quick reference.

Preface

There is a very silent realm where few people have been but many have studied from afar. Some even dare to play there, if just for a few hours. Some have spent their entire careers studying the place, as vast as it is. I am speaking of that thin envelope that blankets the Earth, in relative terms no thicker than the skin on an apple. It provides us with the air and moisture we need, and shields us from the harmful radiation and particles that would surely annihilate life. In particular, I’m addressing that portion of our atmosphere we call the stratosphere. This is a huge and potentially dangerous place that even astronauts scurry through on their way to space. While this portion of the atmosphere varies with latitude and with the season, we can approximate the definition (for the purposes of this book) as altitudes between roughly 18 km (60,000 ft) and 50 km (164,000 ft). This swath of very thin air is a region that we are seeking to address for both scientific and commercial reasons. It is above the weather, but below orbit. To reach it costs a fraction of the cost of using launch vehicles and spacecraft to conduct experiments from orbit. There are literally thousands of people who study this area today, and there were thousands before them. Most of them used very special kinds of balloons to give them the information they wanted. Some of these vehicles are quite sophisticated, as they need to be in order to investigate the broad range of sciences they support. To be a bit more specific, this book will describe what is happening today in the world of science as well as the world of commercial uses of the stratosphere with balloons. This book will cover the new world of 21st century balloon flights. It is hard to believe there have already been 2,300 stratospheric flights since 1962. The pace seems to be increasing. In 2018 there were 181flights and in 2019 there were 218 flights. The 2020 numbers are lower because of the Covid-19 pandemic. Most xix

xx  Preface of the recent flights have been commercial rather than scientific. As of this writing (in late 2020), there are about a hundred commercial balloons flying today all over the world. Balloon-borne instruments have studied the atmosphere in many wavelengths, studied the Earth and the heavens, and have used or invented a wide variety of instruments to obtain the desired data. Observations have ranged from bacteria and viruses in the upper atmosphere to dust clouds in distant galaxies. This new era of balloon flights makes use of the digital world, the “internet of things” and interconnectivity. While the internet seems to rule the world, roughly half of the world’s population is not connected to it and hence are excluded from the socio-­ economic benefits of digital connectivity. Most of us can’t image a world without the internet, yet billions of people long for the day they achieve access to it. Many nations can’t afford the necessary infrastructure. But there is another way! There have been thousands of commercial stratospheric balloon flights, most having to do with providing internet connectivity to unserved or underserved populations. What was once the realm of the scientists, now there are down-to-Earth balloon applications related to the survival of people who have just suffered a disaster such as a hurricane, tornado, or flood. It is now possible to provide broadband phone service for natives in the remotest villages. It is now an era of providing seamless communications and navigation to maritime shipping, surveillance of drug traffickers, illegal border crossings, and of course military applications. These new applications have required the expansion of real-time operations, coordination with both national and international users of airspace, and rapid recovery of payloads in remote areas. Balloon flights can often go from one country to another, and even from one continent to another. There are some countries which do not permit balloons in their air space, regardless of their purpose. This impacts mission planning, site selection, navigation, flight and recovery operations. The invention and perfection of the “super-pressure” balloon, together with the state of the art of meteorology, offers the seemingly uncanny ability to not only control a stratospheric balloon but also to control – to some degree – its relative position and time over a particular site. Although not as precise as for example a geostationary satellite, it is possible to control a balloon to a sufficient degree to acquire the desired target of interest at a considerably reduced cost. There are now many applications for balloons that would have previously been considered folly, and not that long ago either. While we expected that someday tourists would want to go to space, we didn’t envision them going to 100,000 feet in a novel gondola with WiFi, a bar, music and rest rooms. This is actually being planned today. It brings new meaning to the expression “up, up and away”! For only $X, you too can be a “Stratonaut” and be awarded a Certificate to prove it! While that sounds bizarre, there is now another company that will improve your company’s brand by lofting your product or logo into the stratosphere and taking

Preface   xxi photos and video for streaming to your customers and prospects. KFC has already sent their new Zinger sandwich up to 30 km (100,000 ft). While many students are learning about science and launching their simple experiments to the stratosphere, others have seen the financial potential and have started businesses to launch your favorite photos or possessions and take a picture of them with the curvature of the Earth in the background as a prized possession for only $X. It will be interesting to watch the explosion of commercial applications for stratospheric balloons. This book will discuss these scientific and commercial balloon flights from sites all across the world. It includes explanations of the many types of balloons, their applications, launch locations, and the companies that produce them. Included is NASA’s Balloon Program and their launch capabilities and facilities. There is also a list of the international organizations and their balloon programs. Also included is a partial list of balloon flights that have made contributions to unique scientific discoveries, as well as what numerous scientific organizations, including NASA, have contributed to the history of ballooning. One of the major focuses of the book is the role student’s play in ballooning and the importance of keeping them interested in studying the sciences, technology, engineering and mathematics. There are literally thousands of students  – of all ages  – actively involved today in launching balloons and learning from those experiences. Many schools and universities have balloon education programs with hands-on experience. Similarly, corporations actively involved in ballooning have education programs at their home offices. These activities feature in the chapter entitled “Educating the Next Generation”. It is to be hoped this book will inspire students to stay involved in ballooning, for they truly are the next generation of scientists and engineers that will explore the world and the universe beyond. The book gives interesting topics to study and includes over 100 images, many hours of videos, and references to the literature. Three Nobel Prize winners and other internationally renowned scientists spent their early careers using balloons to carry their instruments into the stratosphere. Along the way, young graduate and postgraduate students assisted their principal investigators and fellow scientists in conducting experiments. They now carry the torch that lights the path to new discoveries of the 21st century. It is hoped that this book will contribute to young people’s interest in ballooning and inspire them to study the sciences, technology, engineering and mathematics subjects that are essential for many careers. Manfred “ Dutch” von Ehrenfried Cedar Park, TX, USA Winter of 2020-2021

Contents

Frontispiece�����������������������������������������������������������������������������������������������������������������   vi Dedication ������������������������������������������������������������������������������������������������������������������   vii Foreword���������������������������������������������������������������������������������������������������������������������  viii Acknowledgements�����������������������������������������������������������������������������������������������������  xvi Preface�������������������������������������������������������������������������������������������������������������������������  xix 1 Introduction��������������������������������������������������������������������������������������������������������    1 2 Stratospheric Balloon Descriptions������������������������������������������������������������������    8 2.1 Types ����������������������������������������������������������������������������������������������������������    8 2.2 Zero-Pressure Balloons (ZPB)��������������������������������������������������������������������   10 2.3 Super-Pressure Balloons (SPB)������������������������������������������������������������������   16 2.4 Long and Ultra long Duration Balloons������������������������������������������������������   22 2.5 Commercial Stratospheric Balloons������������������������������������������������������������   25 3 Balloon Elements������������������������������������������������������������������������������������������������   28 3.1 Balloon Envelopes��������������������������������������������������������������������������������������   28 3.2 Parachutes ��������������������������������������������������������������������������������������������������   38 3.3 Instrument Carriers/Gondolas ��������������������������������������������������������������������   41 3.4 Support Equipment�������������������������������������������������������������������������������������   49 3.5 Technology Examples ��������������������������������������������������������������������������������   59 4 Mission Drivers and Operations����������������������������������������������������������������������   64 4.1 Mission Drivers ������������������������������������������������������������������������������������������   64 4.2 Mission Operations ������������������������������������������������������������������������������������   70

xxii

Contents   xxiii 5 Commercial Corporations and Applications ��������������������������������������������������   82 5.1 Loon������������������������������������������������������������������������������������������������������������   82 5.2 World View Enterprises������������������������������������������������������������������������������   89 5.3 Space Perspective����������������������������������������������������������������������������������������   96 5.4 Raven Indutstries/Aerostar��������������������������������������������������������������������������   99 5.5 Near Space Corporation������������������������������������������������������������������������������  105 5.6 Stratobus������������������������������������������������������������������������������������������������������  107 5.7 Zero 2 Infinity ��������������������������������������������������������������������������������������������  108 5.8 ISTAR����������������������������������������������������������������������������������������������������������  110 5.9 HAPS����������������������������������������������������������������������������������������������������������  113 5.10 Global Aerospace����������������������������������������������������������������������������������������  114 6 Launch Sites ������������������������������������������������������������������������������������������������������  122 6.1 NASA����������������������������������������������������������������������������������������������������������  123 6.2 Commercial ������������������������������������������������������������������������������������������������  139 6.3 International������������������������������������������������������������������������������������������������  141 7 Scientific Flight Types����������������������������������������������������������������������������������������  145 7.1 Atmospheric Studies ����������������������������������������������������������������������������������  145 7.2 Earth Studies ����������������������������������������������������������������������������������������������  150 7.3 Solar, Astronomy and Cosmology��������������������������������������������������������������  152 7.4 Instrument and Technology Development��������������������������������������������������  157 7.5 Recent and Future Flights ��������������������������������������������������������������������������  164 8 Accomplishments ����������������������������������������������������������������������������������������������  175 8.1 Scientific Discovery Examples�������������������������������������������������������������������  175 8.2 Commercial Successes��������������������������������������������������������������������������������  190 8.3 NASA/WFF/CSBF��������������������������������������������������������������������������������������  192 8.4 U.S. Accomplishments��������������������������������������������������������������������������������  194 9 The Balloon World ��������������������������������������������������������������������������������������������  196 9.1 Scientific Organizations������������������������������������������������������������������������������  196 9.2 University Scientists and Students��������������������������������������������������������������  209 9.3 International Organizations ������������������������������������������������������������������������  216 9.4 Military and Security����������������������������������������������������������������������������������  225 10 Educating the Next Generation������������������������������������������������������������������������  230 10.1 Funding Sources������������������������������������������������������������������������������������������  230 10.2 Examples of Balloon Education Programs ������������������������������������������������  235 10.3 Examples of Corporate Education Programs����������������������������������������������  244 10.4 Youthful Entrepreneurs ������������������������������������������������������������������������������  247 11 Conclusions��������������������������������������������������������������������������������������������������������  249

xxiv  Contents Appendices 1  A Brief History of the NSBF/CSBF ����������������������������������������������������������������  256 2  Scientists and Engineers in Ballooning ����������������������������������������������������������  270 3  Interesting Stories ��������������������������������������������������������������������������������������������  300 4  Quotes����������������������������������������������������������������������������������������������������������������  310 5  Planetary Balloons��������������������������������������������������������������������������������������������  314 References ������������������������������������������������������������������������������������������������������������������  322 Glossary and Terminology����������������������������������������������������������������������������������������  329 About the Author�������������������������������������������������������������������������������������������������������  344 Index����������������������������������������������������������������������������������������������������������������������������  347

1 Introduction

A Brief History

Balloons have been around for over two hundred years. Some accounts go back three hundred years. Louis XVI and Marie Antoinette loved to watch them. So did Benjamin Franklin and his son, who witnessed some of the first flights. Certainly one of the first scientists ever to go aloft was Jacques Charles, French inventor, scientist, mathematician, and balloonist. Today, we know him best by Charles’ Law that describes how a gas expands as the temperature increases; conversely, a decrease in temperature will lead to a decrease in volume. This fundamental law of physics is known to every balloon scientist. But two thousand years earlier, Archimedes of Syracuse discovered an even more basic law when thinking about “floating bodies” and buoyancy. Balloons are, indeed, floating bodies buoyed up by the weight of the air they displace. Balloons have been used for just about anything you can think of, be it for good or for ill. It only took eleven years after the first untethered balloon flight for the French to realize the military applications of the technology. The first use was on June 2, 1794 for reconnaissance during an enemy bombardment. Fast forward less than a hundred years and Thaddeus Lowe was telegraphing a message to President Lincoln to demonstrate the balloon’s application during the Civil War. He soon became Chief Aeronaut of the newly formed Union Army Balloon Corps. Of course, there was a little bit of unrecognized technology transfer going on even then. Count Ferdinand von Zeppelin, then aged 24, was visiting the U.S. and observing Lowe’s flights. He took his new found knowledge back to Prussia and certainly capitalized on what he learned about balloons.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 M. von Ehrenfried, Stratospheric Balloons, Springer Praxis Books, https://doi.org/10.1007/978-3-030-68130-2_1

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2  Introduction Fast forward only to the end of the 19th century, and there were two French meteorologist sending up sounding balloons with instruments. Two Prussians, Professor Reinhard Süring and Dr. Arthur J. S. Berson ascended in balloons to take temperature and pressure readings. At 10.8  km (35,432 ft) they dozed off from lack of oxygen, but luckily they awoke in time to land safely. Professor Richard Assmann and Leon De Bort published a paper in 1902 that vertically separated the atmosphere into the troposphere and stratosphere. A quarter of a century later, the Manual of Meteorology said this was “the most surprising discovery in the whole history of meteorology”. While this book is not a history of human balloon flight, there was certainly some balloon science going on at altitude during the 1920’s and 30’s but the frailties of man clearly showed it was not the place to be for very long. Many people died in balloon accidents caused by everything from fire, hypoxia, and altitude sickness to crashes. It was clear that more science could be obtained with uncrewed flights. If ever there was a “first family of the stratosphere” then it would be the Piccards. This includes Auguste Piccard, his twin brother Jean, Jean’s wife Jeannette, and their son Don who, with Ed Yost, was the first to cross over the English Channel in a hot air balloon, plus Bertrand, grandson of Auguste, who, with Brian Jones, was the first to fly around the world in a balloon. Advance just another generation or so to WWII and the Cold War and we saw the Japanese bombing the U.S. using balloons, and the U.S. using balloons to spy on Russia and to explode nuclear weapons in the atmosphere. Now we are using balloons for science as well as commerce, even for providing internet services to remote areas and to those impacted by natural disasters such as hurricanes. Today

This book is all about balloons rising through the troposphere and deep into the stratosphere, even into the mesosphere. For the general observer the troposphere reaches beyond the tops of the thunder clouds, which can go as high as about 20 km (65,600 ft). Most of the clouds you see are in the troposphere. But there can also be clouds in the stratosphere, which extends from the top of the troposphere up to what is generally defined as the top of the second layer at 50 km (164,000 ft), although this boundary varies with latitude. One can rarely see the clouds in the mesosphere; for example, noctilucent clouds or night shining clouds, which are tenuous cloud-like phenomena that occur in the upper atmosphere. They are the highest clouds and are located in the mesosphere at altitudes of around 50 to 85 km (164,000 to 279,000 ft). This is an area above the maximum altitude for aircraft and balloons, but below the minimum altitude of orbital vehicles. The mesosphere is the least understood portion of the atmosphere. It is of scientific interest but is beyond the current capabilities of balloons, although a couple of balloons have reached the lower levels for short periods. Sounding rockets have only brief access to the mesosphere and provide much less data.

Introduction 3

Fig. 1.1  The atmosphere. A look at our atmosphere from the U.S. Space Shuttle with cumulonimbus clouds, the troposphere (orange), stratosphere (white-blue), and mesosphere (dark blue) areas indicated. Photo courtesy of NASA.

Balloon flights in the lower troposphere have to contend with various winds and the decrease of temperature and pressure with altitude. In the upper troposphere there have been major problems due to the extremely low temperatures and their effects on the envelope of the balloon. The temperature averages −51°C (−60°F) near the tropopause, the boundary with the stratosphere. The film of the envelope can become very brittle. Balloons have failed and their missions lost. NASA and their balloon manufacturers made major efforts to investigate this problem and to develop and test alternate films to solve it; successfully. Then in the stratosphere the temperature begins to increase, attaining an average of −15°C (5.0°F) near the mesosphere. The stratosphere is stratified (layered) in temperature, with warmer layers higher and cooler layers nearer the Earth. This increase of temperature with altitude is a result of the absorption of the Sun’s ultraviolet radiation by the ozone layer. This is in contrast to the troposphere below, in which the temperature decreases with altitude. Temperatures also vary within the stratosphere as the seasons change,

4  Introduction reaching particularly low temperatures in the polar winter night. The winds in the stratosphere can reach nearly 209 km/h (130 mph) in the southern polar vortex. Balloon scientists seem to love to fly astrophysics balloons there, watching them circumnavigate Antarctica and then recovering their payloads nearby. Over just the past generation the sophistication and complexity of payloads has steadily increased, in some instances potentially yielding scientific returns that can rival or exceed what can be accomplished in a much more expensive orbital mission. In fact many instruments and components flown, tested and developed on balloons are later adapted for spacecraft. Scientific balloons have been perfected with the unique capability for ultra-­ long duration flight above 99.5% of the atmosphere, widely referred to as the edge of space. They are unique in being able to maintain sustained flight altitudes in the upper stratosphere, enjoy a relatively short development time from the inception of a scientific research project and flight, and expand the frontiers of Earth and space sciences at low cost. Scientific balloons carry considerable payloads and can enter the stratosphere and remain there for extended periods of time, all the while obtaining data to provide a better understanding of the world, or in some cases the universe. The demand for balloon flights outstrips NASA’s ability to launch them. At any given time there is often a backlog of missions waiting for flight which both delays the delivery of science to the community and increases its associated cost. Launch Sites

Scientists are very particular about where they want to launch their precious balloon payloads. They have spent years designing them for a specific purpose and have spent a lot of time, energy and money on them. Some want to go as high as possible, some want to carry as much weight (payload) as possible, some want to stay aloft as long as possible, and some want to go to a specific geographical area or look in a particular direction. All of these different requirements dictate a launch site, or a select number of sites. Hence, considering the number of nations involved in ballooning there are many sites around the world. NASA operates several sites for those missions designed for test and technology evaluation that offer safety and satisfactory air traffic control. Some of those also satisfy scientific requirements. NASA has agreements with the National Science Foundation (NSF) to use their site at Williams Field in McMurdo, Antarctica as well as agreements with Australia, Sweden, New Zealand, Brazil, and others. International scientists also use these as well as their own launch sites. This book discusses all the different organizations, both foreign and domestic, involved with stratospheric balloons. There are tens of thousands of people all over the world involved in scientific ballooning, not counting those involved in sport ballooning and world competition.

Introduction 5 Some commercial companies have developed their own launch site capabilities and have made arrangements with their sponsor countries. For example, Loon launches many flights from Puerto Rico, Kenya and other countries where they support the government by providing internet services. World View Enterprises launches balloons from their Tucson, AZ facility. Those wanting more northern latitudes use sites in Norway, Sweden and Canada. There are also launches from sites in France, Spain, India, Hawaii, China and Japan. Small balloons such as weather balloons are launched from hundreds of locations all over the world. It is interesting that high school and college students often use small balloons for experiments that are launched locally, in coordination with air traffic control. The Future

There are balloons planned for the near future whose wide-field-sky imaging capability meets or exceeds that of the Hubble Space Telescope, expanding on that heritage of discovery at a fraction of the operational cost. The operational cost of Hubble is $98 million per  annum and it is over subscribed. So scientists are employing the latest in balloon design and instrumentation to achieve their objectives. Because many flights were canceled in 2020 owing to the Covid-19 pandemic there is a backlog for the 2021 manifest. Antarctic flights must fly in the austral summer, hence there is a relatively short window in December and January for observation and recovery of their experiments. Commerce

While science teams are developing the latest designs and preparing for the next season of ballooning, there is another group who are new users of balloons: the “commercial” balloonists. Balloons have progressed into many aspects of the world of commerce. Once balloon meteorologists and engineers had conquered the winds they were no longer at their mercy. The hot air balloonist would drift anywhere and everywhere, even into power lines, houses and lakes, but modern balloonists have learned to exploit the winds to their advantage. Even Columbus knew he had to use the wind for both speed and navigation on the ocean. These new balloonists have used the latest state of the art in meteorology to pick and choose the best altitudes to navigate to their desired targets and even to “persist” in the vicinity of their targets. In effect balloons are now providing a needed and marketable set of services, rather than just drifting with the wind and acquiring scientific data along the way. Nevertheless, the flight controllers cannot always tame the winds and many a payload has been lost at sea. Delivering internet services to unserved and underserved regions of the world, the Loon Project is somewhat representative of balloon commerce up thru 2020.

6  Introduction This service also includes providing emergency services on a demand basis when a disaster strikes. They have learned to launch constellations of balloons, using an autolauncher that puts one balloon up after another. Up until 2021, they have been launching more balloons than NASA or anybody else. Other international companies are also competing for this type of service. One, the High Altitude Platform Station (HAPS) Alliance, has the target of ensuring member companies can collectively advocate for HAPS business development with the relevant authorities in various countries to create a cooperative HAPS ecosystem, develop common product specifications and promote standardization of HAPS network interoperability. All of these activities are key to the Alliance’s aim of creating new value by providing telecommunications network connectivity worldwide through the utilization of high altitude vehicles including balloons and aerostats. Other balloon commerce is structured to provide basic services across the spectrum to the point of designing, manufacturing, launching and recovering customer payloads, be these scientific, commercial, safety or military. There are such companies all around the world. One company, World View Enterprises built a huge balloon complex in Tucson, AZ and started off by providing internet services and supporting some scientific missions, then expanded to providing a broad range of services for both science and commercial flights. In 2019-2020, they continue to develop their Stratollite balloon and Stratocraft gondola, making several test flights called GRYPHON. Two of the original owners of World View Enterprises started another company, Space Perspectives to provide flights for tourists to the edge of space. They have plans to launch tourists from the Kennedy Space Center’s Space Shuttle landing area and recover them in the Atlantic Ocean for return to Florida on a ship. They are also considering other locations including landing in the Gulf of Mexico and off Hawaii in the Pacific Ocean. The vision of the commercialization of stratospheric balloons has reached the point where a company can advertise their products by photographing them from 30 km (100,000 ft) with the curvature of the Earth in the background and stream the images to the internet, and then to their customers and prospects. But this is nothing new. Even the Montgolfier brothers teamed with wallpaper manufacturer Jean-Baptise Reveillon to construct their balloon with beautiful, embellished art to advertise their wall paper designs. But the well-funded companies have some competition. There are high school children who, for a modest price, will launch just about any small, lightweight object into the stratosphere, including a picture of a wedding couple or a bobble head doll of Captain Kirk, and provide an image of it with the curvature of the Earth in the background. In addition to basic laws of physics they have learned the rules of supply and demand – the tools of finance and entrepreneurship. The balloon world has evolved from Noble Prize winning science to the essence of human nature.

Introduction 7 Educating the Next Generations

One of the primary objectives of this book is to provide reading and reference material that interests the next generation of balloon users, scientists, engineers and technologists. Balloons have historically played a major role in education. Over the years, experiments flown on scientific balloons have helped to develop future scientists. It is possible for undergraduate and graduate students to design and conduct a balloon based scientific study within 2 to 5 years required to get a degree. Professors are developing many of the latest scientific balloon payloads with team members from the graduate and undergraduate student body. Hopefully this book will prompt students to pursue studies for careers in balloon related science and technology, giving them a foundation of knowledge germane to the current and future worlds of ballooning, because the future of this world is highly promising. Many balloon corporations and government agencies (such as NASA) have programs to teach students, of all ages, about science, technology, engineering and mathematics (STEM) and their applications to ballooning. This applies to international organizations as well. There are literally thousands of students involved in ballooning, launching their experiments and learning about the roles of balloons in acquiring scientific data. After graduation, students that are going after advanced degrees often work with established science teams and gain practical field experience. Many go on to obtain their masters and doctoral degrees. Scientific ballooning is an excellent environment in which to train graduate students and young postdoctoral scientists. Many leading astrophysicists gained early experience in the balloon program including Nobel laureates Victor Hess, John Mather and George Smoot. So too did former astronaut and NASA Chief Scientist John Grunsfeld. Precursors for the detectors developed for the Cosmic Background Explorer (COBE) satellite were tested first on balloon flights, and probably half of the COBE science team were former balloon scientists. This is probably true for many other satellite experiments as well. Many other balloon scientists have received national and international acclaim. This book describes many balloon missions, giving the names and affiliations of the participants as well as pictures of some of the teams, the payloads, instruments, balloon types and missions. There are also appendices, references, and internet video links to interesting historical and educational resources. Someday, the experiences gained using stratospheric balloons will provide us with the technology to fly in the atmospheres of Venus and Mars. I hope that a student who reads this book will be inspired to become one of the engineers or scientists on such a mission. Image Link Fig. 1.1  https://www.esrl.noaa.gov/gmd/news/CumulonimbusInTwilight%20w-­labels.jpeg

2 Stratospheric Balloon Descriptions

2.1  TYPES NASA’s Balloon Program Office uses multiple types of balloons to lift science payloads into the atmosphere. The same is true for both U.S. and international commercial organizations. In general, a balloon used to launch a payload to an altitude of 18 km (60,000 ft) or more is designed for stratospheric flight. A few are even capable of briefly reaching into the lower part of the mesosphere, which is generally considered to be 50-80 km (164,000-262,000 ft), although such an altitude is not currently sustainable. NASA officials have said the zero-pressure balloon called the “Big 60” set a new sustainable record by reaching 48.5 km (159,000 ft) during an 8 hour flight on August 17, 2018, traveling well into the stratosphere and ascending 8 km (5 mi) higher than the next-largest balloon prototype. Stratospheric science balloons are not weather balloons, although some weather balloons can climb out of the troposphere (where the weather is) to penetrate the stratosphere. A weather balloon, also known as a sounding balloon, is a type of high altitude balloon that carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by using a small, expendable measuring device called a radiosonde. To obtain wind data, they can be tracked by radar, radio direction finding, or navigation systems such as the satellite-based Global Positioning System (GPS). Balloons that must remain at a constant altitude for long periods of time are known as transosondes. Weather balloons that do not carry an instrument package are used to determine upper-level winds and the heights of cloud layers. For such balloons, a theodolite or tracking station is used to track the balloon’s azimuth and elevation, which are then converted to estimated wind speed and direction and/or cloud height, as applicable. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 M. von Ehrenfried, Stratospheric Balloons, Springer Praxis Books, https://doi.org/10.1007/978-3-030-68130-2_2

8

2.1 Types 9 Weather balloons, as compared to scientific stratospheric balloons, are usually made of a highly flexible latex material, though chloroprene (a synthetic rubber) may also be used. They are generally filled with hydrogen, but occasionally the more expensive helium. When released, the balloon is about 1.5 m (~5 feet) in diameter and gradually expands as it rises owing to the decrease in air pressure. When the balloon achieves a diameter of 6 to 8 m (20 to 25 feet) in diameter it bursts. A small, orange colored parachute slows the descent of the radiosonde, minimizing the danger to lives and property. Weather balloons typically fly to ~35 km (~115,000 feet) but they can achieve ~40 km (~131,000 ft) or more. The altitude is limited by diminishing pressures causing the balloon to expand to such a degree that it disintegrates. Above that altitude, sounding rockets are used. For even higher altitudes, it is necessary to launch satellites. In 2002 one weather balloon set an altitude record of 52.7 km (173,000 ft). See Chapter 9 for details of the National Weather Service. While weather balloons are about the size of a man, a scientific stratospheric balloon can be the size of a football stadium. They are of a fantastic size, but provide fantastic science and real-world applications. In the U.S., they are the responsibility of the NASA Balloon Program Office (BPO) at the Wallops Flight Facility (WFF) of Goddard Space Flight Center, which supports numerous space and Earth science research missions. There are different balloons to meet various scientific requirements. The two types of balloons currently used by NASA, as well as other organizations, are zero-pressure and super-pressure. Either type of balloon can be used for any flight, but zero-pressure balloons typically are used for short flights and super-pressure for Long Duration Balloons (LDB) or Ultra Long Duration Balloons (ULDB).

Fig. 2.1  Balloon types. Graphic courtesy of NASA/WFF/BPO

10  Stratospheric Balloon Descriptions 2.2  ZERO-PRESSURE BALLOONS (ZPB) Zero-pressure balloons are so called because the atmospheric pressure inside the balloon is the same as the atmospheric pressure outside the balloon, giving zero-­ pressure at the point where the duct opens to the atmosphere. With a zero-pressure balloon, additional layers of material are added outside the shell layer to handle the higher gas pressure toward the top of the balloon. These “caps” are added in a graduated manner to handle the increased loads; that is, the caps are of different lengths down the gore with the maximum number of caps at the apex of the balloon. The zero-pressure balloon carries the scientific instrument to a density altitude which is determined by the total mass of the system (suspended mass plus the balloon mass) divided by the fully inflated balloon volume. The balloon is only partially filled at the time of launch and expands to reach its full volume as the balloon approaches its float altitude. NASA currently uses helium as the lifting gas. The zero-pressure balloon has openings to the atmosphere, called vent ducts, to release the excess gas known as free-lift, which provides the lifting force during ascent. The balloon will continue to float at its equilibrium-density altitude until there is a change in the radiation environment, such as occurs at sunrise or sunset and upwelling Earth thermal flux. At sunset, the gas cools, the volume decreases, and the balloon falls about ~9-15 km (~30,000-50,000 ft) to a lower equilibrium altitude determined by the atmospheric temperature lapse rates and the radiation environment. Altitude can be maintained by the reduction in total system mass through release of ballast, which nominally amounts to about 8% per day. Thus flights are limited by the total mass available as ballast. The duration of a flight is typically 5-6 days in the mid-latitudes but much longer flights are possible at the poles in the summer time when the Sun doesn’t set and cause the balloon to cool. ZPB characteristics are: • • • •

The balloon is inflated though sides. When the balloon reaches float altitude, excess helium vents out from ducts. The balloon uses “load tapes” to carry suspended load. The balloon shell/envelope is made of 0.8 mil (0.0008 in) single layer co-­ extruded Linear Low-Density PolyEthylene (LLDPE) film. • Requires diurnal ballast (6-8% of system mass) to stay floating overnight. The flight missions are conducted from various U.S. and foreign sites throughout the world. Over the past several years, the NASA Balloon Program has delivered successful performance across the spectrum of balloon sizes, an accomplishment that is unprecedented in ballooning given the large, heavy balloons that comprise most of the program today. The program presently has five standard conventional zero-pressure balloon designs ranging in volume from 30,000 m3 (1.06 million ft3) to 1.13 million m3 (40 million ft3). The largest of these standard balloons will lift in excess of 3,600 kg (8,000 lb) to an altitude of higher than 37 km (121,000 ft).

2.2  Zero-Pressure Balloons (ZPB) 11 New balloon designs using “spin-off” ULDB technologies are under development to fly higher and heavier payloads. (See the LDB and ULDB sections below.) For the Antarctic Impulsive Transient Antenna (ANITA) the balloon is a typical zero-pressure balloon but the “untypical” payload has shaken the theoretical and experimental physics worlds with its observations of “peculiar” particles coming from the ice below. See Section 8.1.2 for details. The following are the ANITA I’s specifications (balloon sizes can vary):

Fig. 2.2  The ANITA prior to launch. Photo courtesy of NASA

12  Stratospheric Balloon Descriptions

Fig. 2.3  The ANITA II ascent with insert. Photo courtesy of NASA

• • • • • • •

Volume: 830,000 m3 (29.47 million ft3). Gore Length: 180.6 m (592.4 feet). 159 gores. Film Thickness: 0.8 mil (0.0008 in) (20 μm). Inflated height: 102 m (335 ft). Diameter: 129 m (424 ft). Vent Duct Diameter 3.8 m (12.6 ft).

2.2  Zero-Pressure Balloons (ZPB) 13 Note that balloon envelope thickness is generally expressed in units of 1 millionth of a meter, or micron, using the ‘μ’ symbol of the Greek alphabet. Sometimes the American standard is used; mil, which is one thousandth of an inch. 2.2.1  Ultra High Altitude Balloon (UHAB) Since the start of scientific ballooning, researchers have sought to lift increasingly heavier, more sophisticated, payloads to higher altitudes. In the 1960’s and 1970’s advances in film extrusion and balloon fabrication techniques enabled the creation of increasingly larger balloons, culminating with a 1.5 million m3 (53 million ft3) behemoth successfully launched in 1975. The ability to create significantly larger balloons was constrained primarily by limitations in materials, including films. BU60-1

The Japanese Institute of Space and Astronautical Science (ISAS) launched a balloon in 2002 designated BU60-1 to test the flight performance of an envelope manufactured with a newly developed ultra-thin film only 3.4 μm thick made of polyethylene. It had a volume of 30,000 m3 (1.06 million ft3). The empty weight of this balloon was only 60% of conventional high altitude balloons of the same volume. It reached an altitude of 53  km (173,900 ft) which broke the previous record set in 1972. As 1 μm equals roughly 0.00004 in, the film was 3.4 times that, or 0.000133858 in thick. See Section 3.1.5 for a discussion on Ultra-Thin Films. Big 60

The UHAB development started in March 2002, when NASA requested Raven Industries to undertake a study on a series of ultra-high altitude zero-pressure balloon platforms. After analyzing several load-altitude targets, NASA chose a 1.7 million m3 (60 million ft3) design with an ultimate payload capacity of 750  kg (1,653 lb). The balloon was designed using traditional zero-pressure techniques, but the shell and cap material was chosen to be Stratofilm-430, which was based upon the Stratofilm-420 developed for the ULDB program. It comprised a three-­ layer co-extruded film using the same resins as Stratofilm-420. The overall film thickness was 10.2 μm (0.40157 mil) for the shell and 13.2 μm (0.51965 mil) for each of the two cap layers. Relative to traditional zero-pressure balloon film, the Stratofilm-430 had higher strength and ductility at normal surface temperatures, enabling the shell to better withstand dynamic launch loads. Production of the balloon, unofficially christened the “Big 60”, required some minor rearrangement of production space at the Raven factory to accommodate the almost 230 m (756 ft) gore length. That’s twice the length of a football field including the end zones. They did it using two tables half the length. Due to its similarity to standard zero-pressure designs, the fabrication of the balloon was

14  Stratospheric Balloon Descriptions relatively straightforward and uneventful. Because of the delicate film, special considerations were made for the process of expelling excess air and loading the balloon. The film limits are always based on current material strength capability. Balloon films with increased strength-to-weight ratios greatly increase payload capabilities for missions requiring flight above 50 km (164,000 ft).

Fig. 2.4  The “Big 60” with its reflection in Lynn Lake. Photo courtesy of NASA/ WFF/CSBF

The payload was the Low Energy Electron (LLE) experiment. The observations from LEE provided one of the few highly precise measurements of the electron spectrum over an extended period of time. The first test flight number 508N was conducted on August 25, 2002 at Lynn Lake Airport, Manitoba, Canada. After a successful launch, the balloon climbed to a peak altitude of 49.4 km (162,000 ft) and was terminated normally after approximately 23 hours of flight time. As the largest balloon ever successfully flown, it beat the world record set in 1975.

2.2  Zero-Pressure Balloons (ZPB) 15 The next launch using the Big 60 was flight 685NT from Fort Sumner, NM on August 17, 2018. This flew for a total of 8 hours and reached an altitude of 48.5 km (159,000 ft). One of the additional experiments was an advanced spherical steerable antenna system developed by FreeFall Aerospace of Tucson, AZ, in partnership with the University of Arizona. It was located in the left side of the gondola in a specially added frame, while in a similar structure in the right side was a parabolic antenna also built by FreeFall Aerospace. The other experiment was the CHERP (CHErenkov Radiator Payload) supplied by Gannon University in Erie, PA.  This was a cosmic ray instrument to detect high-energy particles of astrophysical origin in the energy range from 1.5 to 20 giga-electron-volt using two Cherenkov radiation detectors. A second test, flight number 687NT was also launched using the same dynamic method on August 25, 2018. After a slow ascent lasting over 4 hours, the Big 60 reached a float altitude above 47 km (155,000 ft). During the ascent the balloon moved initially to the northeast, but later on acquired a more or less stable flight path to the west with a slight deviation north that would be unaltered during the remainder of the flight. During the flight the balloon experienced some drops of altitude that could be have been related to the presence of a very cold storm front in the area. It flew for 9 hours 40 minutes. The Big 60 is NASA’s largest zero-pressure balloon to date. If the polyethylene material were to be spread out on the ground it would cover about 20 acres. The larger size enables the balloon to float about 8 km (26,250 ft) higher than other zero-pressure balloons; equivalent to about 20 Empire State Buildings closer to the edge of space than NASA’s next largest balloon. In addition to its larger size, the Big 60 is also half as thick as the other balloons that NASA flies. At 10.2 μm (0.40157 mil) the plastic film covering the balloon is a little less than the thickness of kitchen plastic wrap. These films go through three stages of testing before they are flight ready, including quality control tests at the Balloon Research and Development Lab of the Wallops Flight Facility. In the stratosphere where the balloon floats, the temperature is typically –76°F, but the films are rated to withstand –130°F in the lab. The Big 60 uses the CSBF designed gondola, which has support instrumentation such as tracking, video and telemetry, together with tertiary experiments flying to round out the 748 kg (1,650 lb) suspended payload. The test flights evaluated the Big 60’s overall design and ability to conduct science missions. Future tests will go a step further and allow researchers to test new instruments. In addition to providing unprecedented altitudes for scientific observations, the UHAB also opened new avenues for long duration ballooning at mid-latitudes. With altitude excursions of only 10-12  km (6-7 mi), these balloons are able to execute long duration flights without the need for large quantities of ballast. If augmented by a small super-pressure anchor balloon, altitude excursions can be minimized. While not as capable as the ULDB for carrying heavy payloads, the

16  Stratospheric Balloon Descriptions UHAB would add another capability for scientists with relatively light payloads who desire to maximize mission time and altitude. The UHAB platform further offers the opportunity to extend the duration of mid-latitude flights through the implementation of Radiation-Controlled Ballooning. This concept was designed to take stratospheric measurement of cyclical radiation levels at different altitudes between 20-40 km (65,600-131,000 ft) in response to the daily cycles of solar radiation. These are referred to as RACOON balloons. 2.3  SUPER-PRESSURE BALLOONS (SPB) The very first prototype of a super-pressure balloon was the one constructed in August 1783 by the Roberts brothers for Professor Jacques Charles (of Charles’ Law fame). It was a sealed hydrogen filled balloon constructed using a rubber coated fabric. It was unmanned and burst during the ascent. Then in December, Jacques and Nicolas-Louis Robert lifted off in a hydrogen balloon from the area that is now the location of the Eiffel Tower, and flew for over two hours. About 400,000 spectators were estimated to have watched, including Benjamin Franklin and his son. Fast forward now about two hundred years to the modern era. There are opposing requirements among the users of both scientific and commercial balloons. Some want altitude, some want larger payloads, others want duration, some want to look at the Earth and its atmosphere, and others desire to look out toward the heavens. NASA not only faces the challenge of meeting the scientists’ requirements and providing the system capabilities but also has the responsibility to control costs while developing the necessary technologies and capabilities. At the same time, there were studies on various polyethylene films, advances in balloon systems technologies, and ground support systems and facilities in various locations. In 1991, the Balloon Working Group was established to counsel NASA on the performance and plans of the NASA Balloon Program with particular emphasis on the operation and support of what was then known as the National Scientific Balloon Facility (NSBF).1 The group is a forum for the exchange of information on balloon systems, operational support, and those scientific developments that affect the Balloon Program. There are 12 members, one of whom is the NASA Balloon Project Scientist who serves as Chairman. The others were appointed from the principal scientific disciplines that were served by ballooning and from the technical and management support areas of importance to the NASA Balloon Program. Members are appointed by the Director, Goddard Space Flight Center. The NASA Headquarters Balloon Program Scientist is an ex-officio member. 1  In 2006, NASA renamed it the Columbia Scientific Balloon Facility (CSBF) in honor of the Space Shuttle astronauts.

2.3  Super-Pressure Balloons (SPB) 17 2.3.1  Program Goals The goals for the development of the NASA Super-Pressure Balloon (SPB) are related to supporting a specific science mass lifted to a set stable altitude for an extended duration. The program level requirements for the SPB are as follows: • It shall be capable of lifting 1,000 kg (2,200 lb) of science instruments. • It shall be capable of sustained flight altitude of 33.53+ km (110,000+ ft). • It shall be capable of sustained flight with an allowable altitude variation of plus infinity (no limit on height) and minus 1,524 m (5,000 ft) during normal operations. (Rare, extreme low temperature events shall allow an occasional dip to lower altitudes.) • It shall be capable of sustained flight duration of up to 100 days. • Its function and performance shall be independent of science mission type. 2.3.2  The Balloon In view of the program goals, it was determined that the SPB would be designed to be flown at any latitude on the globe regardless of day/night cycles, including mid-latitude flights. It will fly at a constant density altitude with a known mass of payload hanging from the balloon. It always maintains a positive internal pressure in relation to the environment in which it is floating. The SPB is a sealed structure filled with a measured and specific amount of helium lifting gas. The balloon rises after launch and the helium expands as the ambient pressure falls with increasing altitude. When the balloon reaches the desired float altitude the extra helium isn’t vented but fills out the shape and pressurizes the balloon. The initial helium load is the amount needed to lift the entire flight system plus some extra to provide an upward force. This extra helium is sufficient to pressurize the balloon at the float altitude but not so much as to cause it to rupture. The SPB is designed to fly with a positive internal pressure at all times. When the Sun heats the balloon during the day, it has a higher internal pressure. This is also called the differential pressure since it represents the difference in pressure above that of the atmosphere where it is flying. As the balloon cools down at night, the differential pressure is much lower, but remains above ambient. The differential pressure range of the SPB is up to 180 Pa (0.0261 psi). Although this is a rather small internal pressure, it is enough to keep the balloon flying through the night. As a result of maintaining near constant volume, the SPB has greater stability at float altitude, with minimal altitude excursion during the day/night cycles. This improved stability and extended duration allows mid-latitudes science missions that are not feasible using ZPB.

18  Stratospheric Balloon Descriptions 2.3.3  Size and Shape The overall shape of the SPB is an oblate spheroid (like a sphere, only squashed on the top and bottom) with the height about 60% of the diameter. It consists of many panels called gores that run from the top to the bottom. At the edge of each gore is a very strong and lightweight tendon that also runs from top to bottom to maintain the structure of polyethylene super-pressure balloon. These tendons are often made of braided Zylon strands. This is the material of choice due to its low weight, high tensile strength, and thermal properties. A gore has a slightly curved lobed shape when under pressure, which is why this type of envelope is known as a “pumpkin” balloon.

Fig. 2.5  Artistic rendering of a “pumpkin” balloon. Courtesy of NASA

Even with very small internal pressures, the forces are quite large because of the size of the balloon. The strength required for the film materials is a function of the internal pressure times the radius divided by the film thickness. If the balloon were spherical in shape, this very large radius would lead to a very high strength requirement for the film. But higher strength requirements often require stronger materials and those are often heavier. The films used for the NASA balloons are very thin and lightweight. See Chapter 3 for details.

2.3  Super-Pressure Balloons (SPB) 19 NASA chose two methods to reduce these very high strength requirements. The first was to make each of the gore sections slightly lobed and reducing the local radius of the film to around 1 m (3.28 ft). Reduced radius translates to reduced strength requirements in the horizontal or hoop direction for the film. Secondly, the tendons that run from top to bottom resolve the forces in that direction. Each tendon can take about 7,000 newtons (~1,600 lb). That means the fittings on the top and bottom of the balloon must resolve a total force of ~1,960,000 newtons (~448,000 lb) for the 280 tendons used in the envelope. See also the Raven special purpose SPB balloons described in Section 5.4. 2.3.4  Test Flights There have been test flights of the Super-Pressure Balloon to explore the design, deployment, and flight duration. These flights improved the balloon fabrication techniques through new and innovative production processes. Advancements in the launch operations techniques have also been achieved. The project’s approach has focused on incremental gains in balloon volume and payload capability. There are always challenges with both production and launch operations as the size of a balloon increases. The incremental stepwise approach to building bigger balloons was employed in an effort to effectively manage these challenges and provide continuity for the process. Balloon volumes have steadily increased over time. Coupled with the increased balloon volume are increases in the number of gores in the balloon and the payload carrying capability. Below is a list of the balloon designs flown using the current design approach as part of this incremental development process. Volume ~56,800 m (~2,006,000 ft ) ~200,000 m3 (~7,000,000 ft3) ~422,400 m3 (~14,900,000 ft3) ~532,000 m3 (~18,800,000 ft3) 3

3

Gores

Suspended payload

200 200 230 280

~295 kg (~650 lb) ~680 kg (~1,500 lb) ~1,800 kg (~4,000 lb) ~2,270 kg (~5,000 lb)

The step up in volume, number of gores, and payload carrying capability can be clearly seen below: Year

Test Flight #

Launch site

Balloon Volume

2005 2006 2008 2008 2011 2012 2014 2015 2017

540NT 555NT 586NT 591NT 616NT 631NT 657NT 662NT 679NT

Fort Sumner, NM Kiruna, Sweden Fort Sumner, NM McMurdo, Antarctica McMurdo, Antarctica Kiruna, Sweden McMurdo, Antarctica Wanaka, NZ Wanaka, NZ

6,200,000 ft3 6,200,000 ft3 6,200,000 ft3 7,000,000 ft3 14,000,000 ft3 18,000,000 ft3 18,000,000 ft3 18,800,000 ft3 18,800,000 ft3

Note that the sizes of the SPBs tripled from 2005 to 2012.

20  Stratospheric Balloon Descriptions Details of the largest SPB flown during the test flights are as follows: • • • • • • • • • • •

Inflated volume ~18.8 million cubic feet. Number of gores = 280. Length of each gore ~492 feet. Inflated diameter ~376 feet. Inflated height ~233 feet. Shell film thickness ~1.5 mil (0.00015 in); much thinner than a ZPB. Final overall weight exceeded 2,268 kg (5,000 lb). Fitting diameter was 1.22 m (4 ft); previously was 1.46 m (4.8 ft). Number of gore width measurements was 6,440. Amount of load tape tendon in balloon ~41.8 km (26 mi). Amount of film visually inspected, re-rolled and dispensed for this balloon exceeded 1.3 million square feet; over 30 acres of film! • Minimum amount of walking just to seal balloon was 55 miles! After a few more years of testing in New Zealand, the key lessons regarding the balloon design were again demonstrated with the launch of the football-stadium-­ sized, heavy-lift SPB from the facility at Wanaka, NZ on April 25, 2017. It was flight 679NT (the ‘N’ meaning a flight outside the main CSBF balloon base of Palestine, Texas, and the ‘T’ indicating a test of a new technology). The mission was the International Extreme Universe Space Observatory (EUSO-SPB) using a 532,000 m3 (18.8 million ft3) balloon with an overall weight of 2,495 kg (5,500 lb). It reached an altitude of 33.2 km (109,000 ft), sprung a leak and after a little more than 12 days it landed in the South Pacific – but not before it provided the scientists with 60 GB of data.

Fig. 2.6  EUSO-SPB launch in 2017 from New Zealand. NASA’s Super-Pressure Balloon stands fully inflated and ready for lift-off from Wanaka Airport, New Zealand. The balloon took flight at 10:50 a.m. local time April 25, 2017 and splashed down in the South Pacific on May 7th. Photo courtesy of NASA/Bill Rodman

2.3  Super-Pressure Balloons (SPB) 21 For a 1:29 minute video of the EUSO-SPB launch, go to: https://www.nasa.gov/feature/wallops/2017/nasas-super-pressure-balloon-takesflight-from-new-zealand At launch the balloon sounds like far away thunder. Toward the end of the video the “pumpkin” shape of the balloon is apparent. 2.3.5  The Future As will be shown in Chapter 5, commercial applications of the SPB are coming along nicely, but the future for scientific applications, especially in the fields of cosmology and fundamental physics, although predictable, is yet to be realized. Considerable progress has been made on the development of the SPB platform, but more focused investment in its development will be required to advance the state of SPB operations to that of the Antarctic LDB platform to enable not only the realization of the scientific potential of this imaging capability but also other applications to planetary and astrophysical particle sciences. A 2019 white paper by a large team of scientists led by Dr. William C. Jones of Princeton University proposed increased support and prioritization of: • A regular cadence of long duration SPB flights from a mid-latitude site (Wanaka, NZ). • Infrastructure to support SPB payloads (integration facilities, launch vehicles) of size and complexity comparable to the LDB program. • Training and support of the launch crews necessary to support multiple annual campaigns. • Development of technologies/procedures for supporting increased science mass on the SPB platform. • Development of improved telemetry rates and commanding. • Development of payloads, including facility class observatories, in order to realize the scientific potential of the SPB platform. The team proposed a stratospheric balloon-borne observatory whose wide-field imaging capability will far exceed that of Hubble, expanding on that heritage of discovery at a fraction of the operational cost. This was based on the 2015-2018 successes of the Balloon-borne Imaging Telescope (SuperBIT) data that gave a clear path forward for a diffraction-limited 2 m class observatory. They identified the principal challenges in scaling up from SuperBIT’s 0.5 m aperture and gave a cost estimate which the team hoped would be funded by the NASA Astrophysics Research and Analysis (APRA) Program for a flight in the 2025-2026 time frame. The Balloon Program Analysis Group simply recommended that NASA continue to advance the lift capability and float altitude of SPBs until commensurate with current ZPB capabilities.

22  Stratospheric Balloon Descriptions 2.4  LONG AND ULTRA LONG DURATION BALLOONS 2.4.1  Long Duration Balloons (LDB) A Long Duration Balloon (LDB) mission will normally either traverse between continents or circumnavigate the world. It may last up to three weeks and make use of satellite-based electronic systems for command and data. All throughout the 1990’s and into the 21st century, LDB support systems and scientific payloads were refined with increased reliability, pre-mission testing, and scientific data real-time downlink bandwidth plus on-board data capacity. In the mid-1990’s, NSBF staff worked with Motorola to develop a transponder for the LDB system to utilize the NASA Tracking and Data Relay Satellite System (TDRSS) capabilities. This transponder improved uplink and downlink capability and reliability. In the years since 1989, approximately 35 LDB flights have been launched from McMurdo, Antarctica. The longest was over 40 days, and it made three circuits around the southern continent. The NASA LDB has proven to be a reliable and affordable vehicle for researchers doing state of the art science and developing new sensor systems. Starting in 1996-1998, the huge “Work Horse” 1.13 million m3 (40 million ft3) zero-pressure balloon performed many LDB flights.

Fig. 2.7  The “Work Horse” zero-pressure balloon. Photo courtesy of NASA/WFF

An example of an LDB that is actually a smaller SPB is the following. Test flight 662NT launched from Wanaka, NZ (44.4°S) in 2015, was the first LDB intended to undertake a long duration mission at middle latitudes, and as such it

2.4  Long and Ultra Long Duration Balloons 23 carried no scientific experiments. The payload slung below the balloon was a specially built square gondola fitted with instruments aimed to control and monitor the behavior of the balloon in flight. Although these instruments were similar to those used in conventional flights, the longer flights needed systems that had higher reliability. It included: • Flight control and data storage including redundant flight computers for telemetry, ballast, and terminate. • Communication systems for line of sight as well as long range satellite communications. • Other flight systems to support unique needs for the SPB flights including differential pressure measurements, environmental measurements, tendon loads and many more parameters. • Small and lightweight camera systems with fixed focal length, a capability for pan/tilt/zoom, and systems to obtain images from over the horizon. • Reliable solar power and charging systems. The balloon was launched from Wanaka Airport on March 27, 2015, reached an altitude of 33 km (110,000 ft) and landed on April 27th near the border between New South Wales and Queensland in Australia after a flight of 32 days, 5 hours and 51 minutes during which it remained in the desired mid-latitudes.

Fig. 2.8  Flight 662NT ground track super imposed on the Earth. Photo courtesy of Google Earth and UNSW Sydney

24  Stratospheric Balloon Descriptions For a 1:15 minute video of the launch of 662NT, go to: https://stratocat.com.ar/fichas/2015/WNK-­20150326.htm There have been two other LDB flights using SPBs: one in 2016 and 2018, and development of the SPB continues to this date. 2.4.2  Ultra Long Duration Balloons (ULDB) In order to achieve the science requirements for even longer flights, the Balloon Program’s capabilities were expanded in 1996 with the development of an Ultra Long Duration Balloon (ULDB). The objectives were to: • Determine what the ULDB could do for science. • Identify the kind of science most benefited by the capability to lift a 2,700 kg (6,000 lb) payload to the edge of space and float for an extended period of ~100 days or more at constant altitudes. • Prove the technology require to sustain an ULDB capability. The ULDB is made of advanced materials and also uses the pumpkin-shaped balloon design to achieve flights of up to 100 days. It is completely sealed and pressurized to maintain a constant altitude, night/day. The payload consists of a solar power system, radio receivers and transmitters, computers, batteries, and other systems needed for science experiments. This type of balloon significantly increases the amount of data that can be collected during a single mission. The technological advances included the marriage of a ZPB anchored by a smaller SPB which would be less susceptible to the diurnal day/night temperature cycles. This concept and technology was demonstrated in the early 1990’s by a series of seven flights sponsored by NASA and the NSF known as Extended Life Balloon-Borne Observatories (ELBBO). Two lasted over 100 days, and another two over 90 days. In addition to enhancing the technology, these missions provided useful science about the effects of X-rays on the Earth’s ozone layer and atmosphere. Increasingly scaled up tests continued during the first decade of the 21st century, with new lessons being learned from each flight. This culminated in 2009 with an average of 18 scientific balloon flights each year. A new milestone was achieved in 2007 by launching three ULDB flights within a single Antarctic summer. This included the so called ABC missions: • Advanced Thin Ionization Calorimeter (ATIC). • Balloon-borne superconducting Spectrometer (BESS). • Cosmic Ray Energetics and Mass (CREAM) experiment. What is also amazing is that all three experiments were aloft simultaneously!

2.5  Commercial Stratospheric Balloons 25

Fig. 2.9  The ATIC team and their experiment. Courtesy of NASA

2.4.3  The Sky Anchor The Sky Anchor System was a two balloon system developed and tested by the National Scientific Balloon Facility during the 1970’s and 1980’s and is still in use today. The concept involves a zero-pressure primary balloon carrying a super-pressure balloon to its operational altitude during the day. On the way the super-pressure balloon fills and pressurizes. As the super-pressure balloon continues to ascend it loses more and more lift. When sunset occurs the entire system descends to a new equilibrium altitude at which the increase in lift on the super-pressure balloon just equals the sunset effect on the main balloon. Although its volume is decreased no gas is lost from the primary balloon. At sunrise the main balloon will expand and the system will once again rise. In so doing, the super-pressure balloon will lose the lift that it gained at sunset and the system should stabilize at the same altitude as the preceding day. Since there is no change in suspended weight on the main balloon, it should not overshoot and again there will be no loss of gas. As in the usual super-pressure system, assuming there are no leaks the flight duration will be limited only by creep, gas diffusion, and ultraviolet degradation. See Chapter 5 and the World View Stratollite of Fig. 5.6 for the latest application of a Sky Anchor. 2.5  COMMERCIAL STRATOSPHERIC BALLOONS The commercial world of ballooning is quite diverse. Some corporations provide contract services for flights that may or may not be for scientific purposes. Some are actually involved in providing internet connectivity to under-served areas and

26  Stratospheric Balloon Descriptions others are more interested in giving tourists access to the stratosphere. Still others are providing services to the military or law enforcement. This section only provides an introduction to those companies that manufacture and/or provide balloons for their own endeavors, or to government agencies and universities. Chapter 5 describes the corporations and their stratospheric balloon businesses and applications. 2.5.1  Loon One commercial company, Loon LLC or just Loon, has launched hundreds of balloons to the stratosphere. The record of 223 days aloft set by one such flight could easily be broken in the near future. Loon’s purpose is to fly a balloon to provide internet services to specific areas. As such they carry a well-designed flight system with a Raven Aerostar Super-Pressure Balloon. There have been hundreds of flights up thru 2020. For details see Section 2.5.4. and Section 5.1. 2.5.2  World View Enterprises Another company, World View Enterprises located in Tucson, AZ, has several potential business applications involving different flight systems designs. Their primary design is the Stratollite system. This includes a primary super-pressure balloon and two small externally mounted balloons that provide ballast control. There is a standardized version for other customers and applications. Currently, they are planning to fly high resolution optical, infrared and radar missions. The typical balloon is 40 m (131 ft) tall and 23 m (75 ft) across; three times the size of the Loon balloon. They carry about 500 kg (1,100 lb) of equipment that includes batteries, solar panels, flight control electronics, tanks, heaters, a GPS transponder (to alert other aircraft as it ascends and descends through commercial airspace), 50-100 kg (110-220 lb) of cameras or other cargo, and a parachute to return everything to Earth at the end of the mission. See Section 5.2 for further details. 2.5.3  Space Perspective World View has launched a new venture called the Space Perspective which will use those same massive balloons discussed above to fly customers up to 100,000 feet, or close to 19 miles high. This business is still in the formative stages. Eight passengers and a pilot will ride in a special Neptune capsule launched from Cape Canaveral to experience “near space” in relative comfort and then use a parafoil type chute to splash down in the Atlantic Ocean or the Gulf of Mexico. They are considering recovery methods similar to SpaceX’s recovery of rockets. This will require modifications to the World View Stratollite balloon. See Section 3.3 and Section 5.3 for more details.

2.5  Commercial Stratospheric Balloons 27 2.5.4  Raven Aerostar Raven Aerostar located in Sioux Falls, SD has been manufacturing many types of stratospheric balloons for NASA for decades. They provide total support to many commercial entities involving many balloon types. These include the very largest of ZPB and SPB, as well as those provided to Loon and others. The typical Loon balloon is made of polyethylene plastic that is about 3 mils (0.0030 in) thick. The balloon really consists of a balloon within a balloon; the inner filled with helium and the outer filled with varying amounts of air in order to adjust for altitude. The overall dimensions when fully inflated are typically 15 m (49 ft) across and 12 m (39 ft) tall, giving it the “pumpkin” shape. The overall weight of the balloon and payload is only about 150 kg (330 lb). This is relatively small compared to SPBs used for much heavier science payloads. See Section 5.4 for further details. See also Chapter 7 for descriptions of some of the very large scientific balloons, some of which could swallow a large football stadium. 2.5.5  Near Space Corporation This relatively new corporation is based at the Tillamook Airport in Oregon. It is a full service company offering balloon design, manufacturing, launch, and flight operations at their test range. It has the necessary tooling and equipment to build custom balloons and inflatable articles optimized for the specific mission. It can also prototype a balloon for a customer utilizing a wide variety of materials and methods. With an extensive range of custom in-house sealers, sewing machines, and testing equipment, NSC can rapidly construct and test specialized inflatables and balloons. See Section 5.5. 2.5.6  International and Other Corporations Others supporting stratospheric balloon programs use balloons supplied by the commercial companies or their country’s agency; for example ISTAR, Zero to Infinity, Stratobus and others. See Chapter 5 for details. IMAGE LINKS Fig. 2.1 https://sites.wff.nasa.gov/code820/images/charts/Balloon_types.jpg Fig. 2.2 https://www.nasa.gov/sites/default/files/thumbnails/image/img_3578_sto-­2_balloon_on_ice_0.jpg Fig 2.3 https://www.researchgate.net/profile/W_Binns/publication/45906348/figure/fig4/AS:[email protected]/The-­ANITA-­II-­ payload-­on-­ascent-­with-­the-­lower-­eight-­horn-­antennas-­deployed-­The-­payload.png Fig. 2.4 https://lh3.googleusercontent.com/-­IsazamfZfikzhoTKZGvMMfIncU6eQsnDypQqn_7DJWiqe67NIca9evJHWSebCdMkAU9xw=s85 Fig. 2.5 https://sites.wff.nasa.gov/code820/images/supporting_images/spb_in_space.jpg Fig. 2.6 https://lh3.googleusercontent.com/m07IjF3VIUvo1X579G3bzKjrRYS3ce6b5jWYJGAUMWX5f8US3IVs1eh-­u03uocvfV7mmuA=s85 Fig. 2.7 Fig. 2.8 https://62e528761d0685343e1c-­f3d1b99a743ffa4142d9d7f1978d9686.ssl.cf2.rackcdn.com/files/83486/width668/image-­20150601-­17832-­169yrey.jpg Fig. 2.9 Graphic showing the ATIC team and their experiments. https://es.wikipedia.org/wiki/Archivo:ATIC_closeup.jpg

3 Balloon Elements

3.1  BALLOON ENVELOPES 3.1.1  Schjeldahl/Winzen Although these two men are long gone, they are recognized as the pioneers in the development of the plastic materials which enabled the development of envelopes for stratospheric balloons. In the 1940’s Gilmore Tilmen Schjeldahl started his career at Armour and Co., where he began working with polyethylene. Later, with his own company, he secured a contract in April 1955 to create atmospheric research balloons made with Mylar polyester film that was held together with an adhesive system that Schjeldahl and his wife developed. The G. T. Schjeldahl Co., received national fame for designing and building the first communications satellite, Echo I. The company worked on Echo I, Echo II, and the Stargazer and Stratoscope II science projects. It also made the laminate and adhesive materials for the Polaris missile program. In 1949 Otto and his wife Vera founded Winzen Research, Inc., to better develop their own plastic balloons. Shortly thereafter, Otto pioneered a polyethylene resin in the manufacture of his balloons. This was produced from ethylene, a petroleum derivative, and was used to adhere the individual pieces of plastic together to form the balloon. The polyethylene was light, fairly inexpensive, and was not affected by ultraviolet radiation, making it ideal for altitudes at which ultraviolet from the Sun is stronger. To make the balloons even thinner and therefore lighter, Winzen convinced his suppliers to make their plastics slimmer. In fact, he was able to get the material so thin that the plastic measured only 0.002 inches thick, thinner than human hair. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 M. von Ehrenfried, Stratospheric Balloons, Springer Praxis Books, https://doi.org/10.1007/978-3-030-68130-2_3

28

3.1  Balloon Envelopes 29 During the manufacturing process, the balloons were laid out on long, thin tables. One section of the balloon would be sealed by running a heat sealer the length of one edge. That was then attached to the next section, sealed, and so on… until the balloon was done. The polyethylene was so fragile that the “balloon girls” worked in stocking feet and checked their fingernails every morning to make sure nothing on them could tear the balloons.

Fig. 3.1  “Balloon girls” at Winzen. Photo courtesy of the General Mills archives

Winzen created a number of polyethylene balloons that he sold to the U.S. Army and Navy, including the Skyhook balloon and the Air Force’s Project Man High. In 1972 he developed the Winzen Research Balloon. This achieved the record for the highest unmanned balloon flight, reaching 51.8 km (170,000 ft) above Chico, CA. The introduction of StratoFilm in 1965 solved a number of problems related to materials that had plagued the balloon community until that time. As payloads and float altitudes increased over the years, the balloons became much larger. In the late 1970’s and early 1980’s catastrophic failures with stratospheric balloons began to erode the confidence of their scientific users. At the same time, balloon manufacturers intensified their efforts to produce the high quality film essential for a reliable, low-cost platform that would operate in the stratosphere. Winzen took the approach of blending newly developed resins such as linear low density polyethylene with other polymers to achieve the desired properties. The resulting film, called StratoFilm 372 (a.k.a. Winzen SF-372) enjoyed a 100% successful flight record for over three years.

30  Balloon Elements

Fig. 3.2  Otto and Vera Winzen, circa 1949. Photo courtesy of Raven Aerostar

Vera Winzen acted as vice-president and chief of production at Winzen Research, managed the facility, the personnel, and the production process, and was forever improving the construction and design of the balloons. She also came up with new systems to ensure consistent quality in Winzen products. During her time at WRI she obtained four patents and was a central figure in the planning and execution of Air Force and Naval manned research flights. In addition, she played a major role in the development of high altitude gas balloons and was recognized as the finest plastic gas balloon builder in the world. In 1957 she represented the United States at the 30th Annual International Gas Balloon Races in Holland, receiving a gold medal for her contributions to gas balloon research. Note: I met Vera (then Simons) in the early 1970’s in Washington DC and gave her a rough design for a “two level” gondola. This later evolved into her DaVinci gondola. During that period, I also met Dr. Walter Lewin at his office at MIT and met Otis Imboden, Vera’s National Geographic photographer.

3.1  Balloon Envelopes 31 3.1.2  Raven Aerostar Raven Aerostar has the capability to make any balloon type. It provides envelopes and other systems as required for NASA, DOD, corporations and institutions. The balloons can be different in film and thickness. In recent years, there has been a big demand for balloons used for accessing the internet in remote locations. For example, the balloons manufactured for Loon are quite different from those used by NASA for large scientific payloads. The balloon envelopes used by the Loon project are based on the Raven Aerostar Super-Pressure Balloon. These balloons employ polyethylene plastic that is about 75 μm (0.0030 in) thick. They are filled with helium and are 12 m (39 ft) tall and 15 m (49 ft) across, fully inflated. They carry a custom air pump system known as the “Croce” that pumps in or expels air in order to ballast the balloon and control its altitude. A small box weighing 10 kg (22 lb) that hangs underneath the inflated envelope contains each balloon’s electronic equipment. This box contains circuit boards that control the system, radio antennas and a Ubiquiti Networks “Rocket M2” radio to communicate with other balloons and with internet antennas on the ground, plus batteries to store solar power so the systems can function during the night. Each balloon’s electronics are powered by an array of solar panels that sit between the envelope and the hardware. In full Sun, the panels produce 100 watts of power. This is sufficient to keep the unit running while also charging a battery for use at night. A Raven Aerostar Payload Recovery Parachute is attached to the payload for a controlled descent, landing, and payload recovery. In the case of an unexpected failure, the chute deploys automatically. When taken out of service, a balloon is guided to a hopefully easily reached location and the helium is vented. The balloons typically have a maximum life of approximately 100 days, although Loon claims that its tweaked design can enable them to stay aloft for closer to 200 days. Their record is 223 days. The envelopes made for NASA’s scientific missions are considerably larger than those for Loon. They have gone through modifications and testing over decades. The improvements could only be made following analysis and testing of existing film, in order to fully understand the materials stress levels under different loads and pressures, and degradation caused by temperature changes and exposure to ultraviolet radiation, X-rays and cosmic rays. Furthermore, the improved films can perform differently for different balloon design parameters. NASA puts the manufacturer’s films through three stages of testing before they are flight ready, including quality control tests at the Balloon Research and Development Lab of the Wallops Flight Facility. While the balloons will experience temperatures of around –76°F in flight, the films will be subjected to –130°F in the laboratory. For example, after Stratofilm-430 was tested in the lab it was used to produce a NASA zero-pressure balloon. This was a three-layer co-extruded film that used the same resins as Stratofilm-420. Compared to traditional zero-pressure balloon

32  Balloon Elements film, the new film (often listed as SF-430) gave higher strength and ductility at normal surface temperatures, making the shell better able to withstand dynamic launch loads. The Raven-made balloon was launched from the Scientific Flight Balloon Facility at Fort Sumner, NM on September 30, 2006 as flight 561NT. It had a payload of 1,971 kg (4,033 lb) and total weight of 2,721 kg (6,000 lb). The test exceeded all pre-flight basic requirements for the SF-430 film, as well as the new Universal Terminal Package (UTP)-3. For a general 2:34 minute video of Raven Engineered Films, go to: https://www.youtube.com/watch?v=1Kd5wNb8Ayo 3.1.3  World View World View Enterprises, Inc., is a private American near-space exploration and technology company headquartered in Tucson, AZ. They were founded with the goal of increasing access to, and the utilization of the stratosphere for scientific, commercial, and economic purposes. The company designs, manufactures, and operates stratospheric balloon flight technology for a wide variety of customers and applications. In 2017, they dedicated a new building that spans more than 135,000 ft2; long enough to build balloon envelopes and parachutes. They claim it is the world’s first building designed solely for developing stratospheric flight. World View manufactures and tests out balloons made to travel up to approximately 30 km (100,000 ft). In addition to a stratospheric balloon manufacturing table 165 m (540 ft) long there is a 100-foot-tall tower to test parafoils intended for use on stratospheric flights. World View has designed, built and flown their Stratollite balloon. This is meant primarily for internet and other applications. It inflates to 40 m (130 ft) tall and 23 m (75 ft) across, completely dwarfing conventional weather balloons. It can lift a payload of 500  kg (1,100 lb) of equipment, including batteries, solar panels, flight control electronics, tanks, heaters, a GPS transponder, 50-100 kg (110-220 lb) of cameras or other cargo, and a parachute to return everything to Earth at the end of the flight. World View has a proprietary system that uses exterior balloons (below the primary balloon) for altitude control. See Section 5.2 for a detailed discussion of the company, its goals and its capabilities. An affiliate company, Space Perspective, will also use the World View facilities to manufacture balloon envelopes, parachutes, and support equipment for their tourist business. See Chapter 5 for details. 3.1.4  Near Space Near Space Corporation is a flight test provider supporting NASA’s JSC’s Flight Opportunities Program. The Johnson Near Space Center, which is located at the uncontrolled Tillamook Airport on the Oregon coast, first began operation in the

3.1  Balloon Envelopes 33 spring of 2013. NSC has the necessary tooling and equipment to produce custom balloons and inflatable articles optimized for the specific mission. They have the ability to prototype a balloon for a customer by using a wide variety of materials and techniques. They have an extensive range of custom in-house sealers, sewing machines, and testing equipment. NSC can rapidly construct and test specialized inflatables and balloons. See Section 5.5 for details. 3.1.5  Other Balloon Envelopes International Companies

There are many other balloon types in use today, especially in other countries. For example, since 1971 CNIM Air Space (formerly Airstar Aerospace) has gained a lot of experience in textile design and manufacturing of stratospheric balloons as well as tethered balloons and even airships. It has a manufacturing, engineering, research and testing unit near Toulouse which is the heart of the aeronautics and space industry in France and a base of operations and flight tests in Chambley in the far north east of the country. The facilities host R&D, prototyping, production and quality control equipment in order to respond to the most complex demands from aeronautics and space customers. It also has a clean room, characterization equipment, numerical simulation, test benches and an aerodrome for flight tests. CNIM Air Space’s stratospheric balloons are mostly employed by the scientific community to study the atmosphere, its chemistry and dynamics. They are also valuable tools for astronomers and biologists or for demonstrating technologies. Their balloons lift anything from a few kilograms to several tons and are able to operate at an altitude as low as several hundred meters all the way up to 40 km (131,000 ft). It is the supplier for many space agencies, including the European Union and CNES in France. For other international companies, some of which can manufacture their own balloons, see Section 9.3. Weather Balloons

Other types of balloon are capable of stratospheric flight, for example a weather or meteorological balloon, but most are for much lower altitudes. This book will not cover those but it is interesting to note that the classic weather balloon is used extensively in training students about STEM subjects related to the atmosphere. See Chapter 10 for details. Starting in 1896, the French meteorologist Léon Teisserenc de Bort launched hundreds of weather balloons from his observatory in Trappes, France. These experiments enabled him to discover the tropopause and stratosphere.

34  Balloon Elements The modern weather balloon, of which there are several types, are usually made of a highly flexible latex material but chloroprene can also be used. The weather balloons used by the National Weather Service (NWS) for the past 80 years are made of latex or synthetic rubber (neoprene) about 51 μm (0.002 in) thick, filled with hydrogen or helium. Note that this thickness is about 5 times thicker than a typical zero-pressure balloon, and more than 10 times thicker than the thinnest balloon. These balloons are released twice a day at 92 upper-air sites across the U.S. Also twice a day, every day of the year, a 6-foot-or-so-diameter balloon is released from 900 locations worldwide. They can pass through the troposphere into the stratosphere. See Section 9.1.5 for NOAA/NWS. Kaymont Consolidated Industries (KCI) of Melbourne, FL is the world’s largest distributor of weather balloons made by Totex of Kanto, Japan, and has supplied the scientific community for over 30 years. Kaymont balloons have been used by the U.S. space program for more than 15 years, and are launched by the National Weather Service on a daily basis. Kaymont high altitude balloons are used for civilian near-space photography, aeronautic studies, and atmospheric testing. The largest weather balloon is a sounding balloon for weather forecasting. Typically, sounding balloons carry a small electronic package (radiosonde) which transmits the data necessary for weather prediction, pressure, temperature and humidity. Some radiosondes also contain a GPS. Positional data is transmitted to a ground station to enable wind speed and wind direction to be calculated. When their mission is over, sounding balloons burst. Depending on observation requirements the “burst diameter” varies from 2 m (7 ft) at an altitude of 21 km (70,000 ft) to a diameter of 13 m (43 ft) at an altitude of 38 km (125,000 ft). The burst altitude will depend on payload mass, weather conditions at the tropopause, and other environmental factors. Larger balloons formulated for cold-weather launch and ultra-cold conditions at altitude are used to carry ozonesondes to 30 km (98,000 ft) or in some cases even higher. 3.1.6  Ultra-Thin Films The balloon designer needs a film that can stand the loads and stresses of flight and can satisfy the mission objectives. The balloon must be resistant to ultraviolet light and extreme cold. It must also be able to stand the rigors of manufacturing, packaging, shipping and launch as well to survive transit through the tropopause to the desired height in the stratosphere; possibly even to the mesosphere. Given the desire by scientists to reach even greater heights, the designer must strive to keep the weight down in order to carry a reasonable payload. Consequently, the films used for balloon envelopes have gone through extensive development over decades by both U.S. and international manufacturers. The average person can relate to thin films by comparison to something they are familiar with, such as kitchen food wraps and garbage bags. It’s another thing to

3.1  Balloon Envelopes 35 expect to understand the chemistry, physics, engineering, and manufacturing of stratospheric balloon films. Although plastics such as polyethylene are used in thousands of roles, the one application that resembles a balloon envelope is the plastic wrap in your kitchen. That is the kind of wrap typically sold on rolls in boxes with a cutting edge. It clings to many smooth surfaces and can stay tight over the opening of a food container without adhesive. Common plastic wrap is roughly 12.5 μm (0.0005 in) thick. A human hair is thicker at 75 μm (0.003 in). Thus it is difficult to conceive of a balloon made of such thin material that is as tall as a 25-40 story building. But wait; there’s more! Or should I say less? The Balloon Facility of the Tata Institute of Fundamental Research (TIFR) in Hyderabad, India has created thin films that have a thickness of 5-6 μm (0.0002-0.00024 in) for the fabrication of sounding balloons for probing the stratosphere up to 42  km (137,800 ft). They have also carried out R&D on films of various thickness not only for that type of balloon but also for other scientific applications. In 2011, they started work on balloon grade ultra-thin polyethylene film that had a thicknesses of 2.8-3.8 μm (0.0001-0.00015 in) for fabrication of balloons which would penetrate into the mesosphere to meet the needs of scientists working in the area of atmospheric dynamics. Tests continued through 2014. While these were very small balloons with only 10-30 kg (22-66 lb) payloads, the tests yielded useful data. One of the 2014 flights reached the mesosphere with an altitude of 51.666 km (169,464 ft). The altitude record is held by the Japanese Institute of Space and Astronautical Science (ISAS) which, in 2002, built and launched a 60,000 m3 (2.12 million ft3) balloon using an ultra-thin film with a thickness of only 3.4 μm (0.000136 in). It ascended to 53.0 km (173,840 ft), the highest altitude yet achieved by a balloon. This opened a new era for scientific observations in the mesosphere. The Blown Film Process

But first a clarification. A polymer is a substance that has a very large molecular structure consisting chiefly (or entirely) of a great many repeating similar units bonded together; for example, many synthetic organic materials used as plastics and resins. These ought not to be confused with natural polymers such as cotton, wool, and wood. The definition relates to the repeating nature of large molecules. Blown film extrusion is one of many polymer manufacturing techniques and it is used to make commodity and specialized polymer films that are typically used in packaging such as shrink, stretch, barrier films (used to protect deli meat), frozen food packaging, and shopping bags. The process for balloon films is similar but further processing is necessary to achieve an envelope the size of a stadium. There are many types of polymers that can be used in blown film extrusion (the most common being polypropylene and polyethylene) to make low density, high density, and linear low density polyethylene (LDPE, HDPE and LLDPE). This method can manufacture monolayer films as well as more complex multi-layer films that involve co-extrusion in order to combine more than one plastic into a

36  Balloon Elements single film. The first step is to melt the polymer in an extruder. Polymer resin, often in the form of beads, is loaded into a hopper, then fed into a heated barrel which employs a screw to transport the polymer down its length. The beads are gradually heated to melt the polymer. The heat profile is an important aspect of extrusion, because the polymer may thermally degrade if overheated. When the molten material reaches the end of the barrel it is extruded through a die. It is at this point that blown film extrusion differs from other extrusion processes. Several different types of dies are used in blown film extrusion, with the most common being annular (a simple circle die). The molten polymer enters the die head and air is injected via a hole in the die center to radially inflate the polymer into a thin tube many times its original, extruded diameter. It is this step that can be adjusted to achieve the desired film thickness and width. The hot tube film is then cooled, typically with high speed air, and pulled up by an apparatus known as nip rollers. On most medium to large size film lines, this vertical tube might easily extend several stories into the air. As the film cools it crystallizes at what is called the frost line. As the tube reaches the top of the line, the film is cool enough to flatten, and is now referred to as lay-flat or collapsed tubing. The film is then transported downstream by rollers for further processing (e.g. slit, printed, vented, converted into bags) and is eventually wound into rolls. There are several advantages to manufacturing film by the blown film extrusion process, including the ability to manipulate the mechanical properties of the final plastic based on the process conditions and base polymer(s) used. For example, it inflates the polymer radially while at the same time drawing the polymer upward using rollers. As these forces stretch the polymer in both the transverse and draw directions, they give strength to the film. The extent of inflating and drawing can be adjusted to attain the desired strength in the transverse and draw directions of the final product. Blown film extrusion is also versatile and able to manufacture a variety of single or multi-layer films with a range of film thicknesses and widths. For a 34 minute video of the Lab Tech Blown Film complete process, go to: https://youtu.be/FHfaVNk2Gyg You will appreciate that it took a bit of genius just to design the factory to support the process. 3.1.7  Film Technology and Tests The introduction of StratoFilm in 1965 overcame a number of materials problems that had plagued the balloon community prior to that time. As payloads and float altitudes increased over the years, the balloons became much larger. It was found that as a balloon penetrated high into the tropopause and the temperature dropped as low as –57°C (–70°F) the balloon film became brittle and lost its strength. The confidence of the scientific community was eroded by catastrophic failures in the late 1970’s and early 1980’s.

3.1  Balloon Envelopes 37 The NASA Balloon Program initiated a series of tests that included the extrusion process. They enlisted the support of balloon manufacturers who intensified their efforts to produce the high quality film essential for a reliable, low-cost platform operating in the stratosphere. One manufacturer managed to make a consistently high quality film for this application. Its approach was to blend newly developed resins such as linear low density polyethylene (LLDPE) with other polymers to achieve the desired properties. The resulting StratoFilm-372 film enjoyed a 100% successful flight record for over three years. Another manufacture, Raven Aerostar, introduced the results of their research as Astrofilm-E2. The effects of stress and temperature on the mechanical properties of their film were studied using two techniques. The first was based on uniaxial tensile measurements of pre-strained strips of the film measured as a function of temperature. Data was analyzed in terms of two temperature coefficients (one a stiffness coefficient and the other a strength coefficient) and then comparing the areas under the stress-strain curves. The second technique investigated the effect of stress and temperature on inflated cylinders of the same material. The changes in the mechanical properties due to preconditioning in the biaxial stress state were evaluated using the ball burst test. Preliminary findings indicated the material to be stress and temperature path dependent. Changes in stiffness coefficient, draw strength, and toughness were measured and analyzed. As a result of both NASA’s and the manufacturers’ efforts, the switch was made from LDPE to LLDPE with two resulting film candidates: Winzen Stratofilm SF-372 and the Raven Astrofilm-E. NASA made several test balloons with each and flew them. Based on the results of those flights, the mechanical properties of all of the films were modeled and a statistical specification was developed which all future film needed to satisfy. These changes virtually eliminated all catastrophic balloon failures in the troposphere. As part of the fallout from this investigation, NASA enjoyed multiple years of 100% success as well as increasing the balloon suspended payload from 2,132 kg (4,700 lb) to 3,629 kg (8,000 lb). Flight 561NT was launched at Fort Sumner, NM on September 30, 2006 using a 0.8 million m3 (39.57 million ft3) zero-pressure balloon made by Raven Aerostar. This was a qualification test of the new Stratofilm-430 polyethylene film for the NASA/CSBF zero-pressure balloons with a three-layer co-extruded film and the same resins as for Stratofilm-420. The total film thickness was 10.2 μm (0.0004 in) for the shell and 13.2 μm (0.0005 in) for each of the two cap layers. Relative to traditional zero-pressure balloon film, the Stratofilm-430 had higher strength and ductility at normal surface temperatures and this improved the ability of the shell to withstand dynamic launch loads. The main objective of the flight was to demonstrate the ability of the balloon to fly under normal flight conditions near the maximum permissible launch stress index of 1,800 psi. The payload weight was 1,814  kg (4,033 lb) and the overall weight was 2,722  kg (6,000 lb). It was a success.

38  Balloon Elements 3.2  PARACHUTES 3.2.1  The Basic Design Parachutes are employed on most scientific balloon flights to lower the scientific payload upon termination of the ballooning phase of the flight. A parachute is also used as a safety device on virtually every flight, even though the balloon system is to be brought down intact by releasing gas from the envelope. The basic design for this type of application consists of a woven textile or plastic canopy which is attached to the payload by means of suspension lines, also called shroud lines. There are various forms of parachute canopy, but they are usually axially symmetric about the vertical axis and can be made with or without holes. For some special purposes the canopy is made of ribbons. A parachute with its payload and ancillary equipment is termed a parachute system. The suspension lines connect to the canopy at its outer periphery, or skirt. They are usually fastened at the seams between gores. They may or may not continue up over the canopy to the vent on the top (not all parachutes possess vents). The payload may be fastened directly to the lower end of the risers, but if there is a reason to suspend it lower then extension lines may be used. A suspension point consisting of two or more cables is commonly utilized. If it is desirable that the payload be free to turn independently of the parachute, a swivel may be placed in the suspension system somewhere below the risers. Parachutes are commonly described by their nominal diameter. For example, the nominal diameter of a flat circular canopy is the diameter of the material when in its flat form. The effective diameter is the projected diameter in its inflated state. The latter is a function of the parachute’s design and the load that it is carrying. Packed parachutes are rarely used in scientific ballooning. Instead, the parachute is fully deployed (extended) at all times and inflation can start immediately upon being separated from the balloon. The parachute is often a link in the suspension system between the balloon and the payload. The most important factors in selecting a parachute for use in scientific ballooning are those which are directly concerned with safety. At the very least, a parachute must open reliably and be sufficiently strong to withstand any opening shocks and carry the weight of the payload in every conceivable operating condition. It must also be capable of slowing the entire system to an acceptable vertical velocity for landing. Other features may also be desirable, for example that the parachute not swing or spin during descent. Two proven types of parachute have been used for scientific ballooning. One has a flat circular canopy with a vent in the center, and the other has a canopy in the form of a cross with no vent. The flat circular canopy is known to open reliably and rapidly, even at the high altitudes. It is commercially available in sizes up to 30 m (~100 ft) in diameter. If necessary, two or more chutes can be used jointly. The terminal velocity can be predicted accurately when it is used within proper load limits. Its chief drawback is its tendency to oscillate more than is desirable during

3.2 Parachutes 39 descent. Parachutes with cross-shaped canopies have been employed in scientific ballooning almost exclusively by Raven Aerostar (the company that manufactures them). Apart from a time in the 1960’s, they were rarely used for scientific balloons. Although they performed well in all respects and were less subject to oscillation than flat canopies, they were never preferred over the flat canopies. 3.2.2  Raven Aerostar Raven Aerostar’s recovery parachutes have performed reliably on thousands of balloon flights conducted by NASA, Loon, government entities, and other space agencies around the world. These parachutes are especially designed to recover payloads from altitudes up to 48.7 km (160,000 ft). In fact, at 3,629 kg (8,000 lb) Raven Aerostar’s payload recovery parachute holds the record for the heaviest payload recovered from a stratospheric balloon flight. The parachute allows for a controlled descent, landing and payload recovery when a balloon is ready to be taken out of service. In the event of an unexpected failure, the parachute deploys automatically.

Fig. 3.3  Raven circular payload recovery parachute. Photo courtesy of Raven Aerostar

40  Balloon Elements

Fig. 3.4  Raven cross-shaped payload recovery parachute. Photo courtesy of Raven Aerostar

3.2.3  World View Enterprises Since World View Enterprises has the total capability to manufacture a complete balloon and payload, it is assumed they have the capability to either manufacture a parachute or order one from Raven Aerostar. No other information is currently available. 3.2.4  Other Manufactures Pioneer Aerospace Corporation began production in 1938. In 1988, it became a part of Zodiac’s Aerosafety Systems Group. It is one of the largest aerodynamic deceleration manufacturers in the world. Its main factory and distribution centers are located in Columbia, MI and South Windsor, CT.

3.3  Instrument Carriers/Gondolas 41 Zodiac Parachute & Protection America, which was bought by Safran in 2018, has been operating in Columbia for more than 50 years and plans to remain for generations to come. The business primarily operates on government contracts, despite its origin as a company making uniforms. While the company produces everything to do with airplanes ranging from engines to refreshment carts, seats and safety slides, the Columbia office specializes is building parachutes and the harnesses which support parachutes. The Columbia office of 163 team members physically sew 90% of everything that goes into making a parachute; 90-95% of what Zodiac does is sewing, which is almost a lost art! The Columbia office is proud of manufacturing the parachute for the NASA InSight Mars lander which set down on the Red Planet on November 26, 2018. Rocketman Enterprise, Inc., of Bloomington, MN designs and manufactures the parachutes used for the recovery of small scientific payloads and weather-type balloons from high altitude flights. The parachutes come with a loop sewn on the apex of the chute that is used to attach it to the base of the balloon. The payload hangs from the risers of the open parachute. Rocketman parachutes have proven themselves many hundreds of times. They are made of low-porosity 1.1 rip-stop Nylon, and come in sizes up to 5.5 m (18 ft) in diameter. During the descent of a high altitude balloon, the parachute normally opens at about 18.4 km (60,000 ft) when there is sufficient air in the atmosphere to open the canopy. In many cases it will drift for 160  km (100 mi), and take an hour to descend. Rocketman provides a parachute release control unit which enables the operator to choose the altitude at which the parachute will open. It is compatible with any type of parachute. 3.3  INSTRUMENT CARRIERS/GONDOLAS 3.3.1  CSBF Gondolas

The gondolas used for scientific balloons are not like the ones used by Auguste Piccard, nor do they resemble the boats of the Venetian canals. In effect they are just carriers of the instruments hung from a balloon. They can be very specialized or generalized for multiple instruments. They are often supplied by NASA/CSBF but may be built by the principal investigator’s university. They typically consists of a square metal structure to carry the instrument and all the balloon’s associated systems, such as the command data module (CDM), instrument support structure (ISS), solar array panel support system, antenna support systems, ballast hopper, and crush pads. Gondolas are fabricated to NASA’s balloon flight requirements, taking into consideration the nominal shock of parachute opening at termination and the ground impact at landing. The design also considers the need to recover the instruments and support systems using minimal tools at a remote site.

42  Balloon Elements It would not be practicable to describe all of the various gondolas, but here is a representative example described (in extract) by the University of Alabama at Huntsville with support by the NASA Marshall Space Flight Center (MSFC).1 A gondola that can carry a number of different scientific instruments on a single balloon flight has been designed, manufactured and flown on a test flight in support of NASA’s Exploration Program. The Deep Space Test Bed (DSTB) facility was designed to utilize suborbital exposures on high altitude balloons in Earth’s polar regions as a window to the ionizing radiation in interplanetary space. The facility was designed to accommodate several science experiments and prototype instruments on a single integrated carrier that provides the mechanical structure, power, telemetry and instrument operation and control. The DSTB can support science investigations in all NASA disciplines: astrophysics, atmospheric, Earth, heliospheric and planetary sciences. The National Space Science and Technology Center (NSSTC) has laboratory facilities and experienced personnel at MSFC and the University of Alabama in Huntsville to support instrument integration and flight operations. The DSTB is suitable for any launch site that NASA’s Balloon Program utilizes. The DSTB was designed with simple and robust interfaces for mechanical, power and communications systems that are widely used by investigators. The simple interfaces give science teams without previous balloon flight experience the ability to quickly conduct their investigation, and it provides them with an introduction to scientific balloon operations. The facility comprises the structural gondola, solar arrays or batteries for power, and a power distribution system that manages power for the different instruments. It has a flight data system with standard interfaces that transfers the instrument data to the CSBF balloon instrument package for telemetry and it controls and monitors the subsystems onboard. There is a ground support computer system that is used for testing during payload integration and serves as the ground station during flight operations. The DSTB is designed to accommodate a total payload mass of up to 1,800 kg (4,000 lb). It is designed to support circumpolar flights in the Arctic and Antarctic lasting up to a few weeks. It successfully completed an 8 hour test flight in New Mexico with several science instruments, demonstrating its capabilities and readiness for Antarctic operations. There are several instrument attachment points that provide different fields of view: skyward, nadir or horizon. It also has the capability to carry instruments on booms extended away from the gondola as well as to sling instruments down below the gondola.

 https://www.uah.edu/rsesc/projects/past/deep-space-test-bed

1

3.3  Instrument Carriers/Gondolas 43 The power system is designed to provide 600 watts (550 watts for the experiments) using solar arrays and batteries for long duration flights. Batteries can be used for short flights. Power is provided to each instrument through a switched, resettable circuit breaker to isolate it from the rest of the instruments. The on-board flight communication and data system (FCDS) provides individual communication links for each instrument and manages the system level functions. The power, communication rate and data storage resources are allocated among the instruments as needed for each flight. The command and data streams for each instrument are recorded on board. The FCDS can also deliver command lists to each experiment for autonomous operations. When the payload is within line of sight telemetry (less than 400 miles), the FCDS feeds the high rate transmitter with bandwidth up to 1 Mbs. Over the horizon communication is available through a TDRSS allocation that has provided 6 kbps data rates in the past with nearly continuous coverage. The DSTB ground station serves as a repository for the data steam and permits the investigators access to flight data through the web so that they may monitor their instrument remotely from their home institution. The facility and its operations have been designed to minimize the interface burden on the scientific teams. The instrument interfaces to the facility have been well documented. The high-bay facility at NSSTC is designed to support balloon flight payloads and is available for instrument integration prior to deployment. Members of the DSTB team have developed balloon instruments and conducted scientific flights for more than 3 decades and have participated in campaigns all over the world. The team members include scientists and engineers (electrical, mechanical, software). Two gondolas have been developed to insure availability of the facility for annual flights. While one gondola takes part in a campaign, the second is available for investigators to commence integrating their payload for a launch opportunity the following year. The gondola facility described has been constructed and its functionality demonstrated in a test flight. It is available for investigators to utilize on balloon flights provided through the NASA scientific balloon program. The DSTB and its support staff permit investigators with no previous balloon experience to easily take advantage of balloon flight for their research. The facility provides a clear and user-friendly interface and direct access to an experienced team. In this scenario the science instrument development remains with the experienced science team. This team can train young scientists and engineers in a mission environment that is more conducive to developing hands on experience while obtaining valuable scientific data.

44  Balloon Elements

Fig. 3.5  The Deep Space Test Bed (DSTB) ready for launch. The photo was taken at the Scientific Flight Balloon Facility, Fort Sumner, NM. The Big Bill vehicle is holding the DSTB ready to start Flight 546N with an 800,000 m3 (28 million ft3) zero-pressure balloon built by Raven Aerostar. The payload weighs 1,222 kg (2,695 lb) and the overall weight is 1,823 kg (4,018 lb). Photo courtesy of NASA/WFF/CSBF

3.3.2  Space Perspective’s Neptune Section 5.3 discusses the business proposal of Space Perspective. Here we shall only discuss their concept for a gondola or, as they call it, a capsule. The capsule was designed in collaboration with the UK studio PriestmanGoode, which is also working on a passenger module concept for Elon Musk’s transport system known as Hyperloop. The 5 m (16 ft) diameter capsule is supported by a polyethylene balloon 100 m (328 ft) in diameter when fully inflated. It uses the same technology NASA has used for scientific stratospheric balloons for many decades. It will be inflated using hydrogen, because helium is much rarer, more costly and has other uses; including medical. Nigel Goode, designer and co-founder of PriestmanGoode, describes a long-­ time working partnership with the Space Perspective team. Their “Neptune” capsule is the culmination of a long-term collaboration that has resulted in the only

3.3  Instrument Carriers/Gondolas 45 capsule specifically designed with the human experience at its core. It was designed from the inside out, placing an emphasis on the passenger (or “explorer”) experience. The designers looked at all the different elements that would make the experience not just memorable, but truly comfortable as well. It includes all the essentials for a journey of 6 hours including a bar and a lavatory. The passengers will be able to get 360° unobstructed views and be free to move about during the journey.

Fig. 3.6  The Space Perspective Neptune gondola. Artistic rendering by Richard Hollingham/Images by Chris Hinkle. Photo courtesy of Space Perspective

The capsule has the following characteristics: • There is a specific area for instruments in addition to the ability to place instruments in areas on the top and bottom of the capsule. • The windows will give a 360° panorama of the Earth below and heavens above. The gold on the windows is similar to the gold on an astronaut’s helmet. It provides shading and keeps the Sun’s ultraviolet from entering the capsule. • There are nine seats for the eight passengers and a pilot arranged around the capsule with the bar and lockers in the middle. The seats will recline for landing. • The lavatory is below the main deck in the splash down cone that gives a smooth landing in the water. • An array of sensors and communications equipment give the passengers and pilot information such as altitude, wind and temperature. Passengers will also be able to communicate in-flight and post on social media. See Section 5.3 for more details on the flight.

46  Balloon Elements

Fig. 3.7  Space Perspective’s capsule/gondola at float. Artistic rendering by Richard Hollingham/Images by Chris Hinkle. Photo courtesy of Space Perspective

3.3.3  Sage Cheshire Aerospace Sage Cheshire, Inc., located in Lancaster, CA is best known for manufacturing the Red Bull Stratos gondola for Felix Baumgartner. They also supplied gondolas for stratospheric science missions. They have over 40 years of experience in design, engineering, research and development, and prototype or finished production of aircraft parts or full flight articles. Their pressurized capsules can accommodate research payloads of varying sizes and weights. The interior is a 6-foot-diameter pressure sphere that can maintain pressurization for the duration of a flight. Their open gondolas are ideal STEM projects for educational research missions. Sage Cheshire Aerospace works with key balloon-launch partners to provide an end-to-end solution for those needing to do high altitude research. Key features include: • • • • • • • •

2,400 watts on-board continuous power for about 10 hours. Soft take-off and landing. Protected and pressurized payloads. Station-keeping maneuverability. Communication downlinks. Professional flight crew. Custom branding and marketing opportunities. Ideal for university research programs and STEM initiatives.

3.3  Instrument Carriers/Gondolas 47

Fig. 3.8  Sage Cheshire Aerospace’s open gondola. Photo courtesy of Sage Cheshire

3.3.4  CNES Many countries and their support contractors have gondola designs for a variety of scientific purposes. This is just one example: a representative list of gondolas used by the Centre National d’Etudes Spatiales (CNES). They are also used by Canada and Australia. These four generally apply to science categories. • • • •

BANA: 2 × 0.8 × 1 m (6.56 × 2.6 × 3.28 ft). HELIOS: 2.06 × 1.43 × 1.44 m (6.8 × 4.7 × 4.7 ft). CARMENCITA: 2.45 × 1.85 × 2.20 m (8 × 6 × 7.2 ft). CARMEN: 2.45 × 1.85 × 3 m (8 × 6 × 9.8 ft).

Depending on the payload, the gondolas provide the usual support equipment such as power, instrumentation, pointing, temperature control, data links, and communications. The largest of the abovementioned (CARMEN) is a multi-payload stabilized gondola that was developed with several concepts in mind: • Modularity to allow the inclusion of several instruments devoted to the same or different research areas during a single mission. • Reusability to overcome the difficulty of adapting a platform specifically designed around an instrument to another, thereby reducing the cost and development time. • The cargo volume can be maximized to allow the installation of many instruments onboard. It was introduced by the CNES team in late 2012.

48  Balloon Elements

Fig. 3.9  The CNES CARMEN gondola. Photo courtesy of CNES

3.4  Support Equipment 49 3.4  SUPPORT EQUIPMENT 3.4.1  Ground The CSBF provides maintenance, operations and logistics support for NASA’s scientific balloon program and facilities. In addition, they provide sophisticated ground and flight systems for launch, control, data retrieval, commanding, and recovery. Other facilities and equipment available to support a launch include: • • • • • • •

Operations Control Center. Payload Integration Hanger. Vacuum Chamber. Tracking radar. Tracking Aircraft. Specialized launch equipment such as collar restraints, test equipment. Support vehicles such as helium trucks, balloon trucks, etc.

Some of the more visible categories of ground support equipment are the vehicles that are present when preparing the balloon for launch. No matter the launch site, they are always required for what is called the “dynamic method” of launch. This established methodology is the safest way to launch such large balloons carrying very expensive payloads (often costing millions of dollars). In addition to the launch vehicle that brings out the gondola and instruments and launches it are all the others that prepare the launch site, carry helium, materials, personnel, and various equipment. The following are descriptions and photos of the launch vehicles. Tiny Tim

The first launches from Palestine, TX were performed using a rented crane with outriggers to keep the launch vehicle from tipping over onto its side. The NSBF owned a 35 ton crane that was used for a long time, but during a balloon launch under heavy wind the front end of the crane lifted off the ground and turned the crane about 90°. NASA realized that renting a local crane to assist with inflation and bringing the balloon and its payload to the site was inappropriate for the job. NSBF engineers designed a more suitable, more sophisticated, and considerably larger launch vehicle with the flexibility to provide an adequate launch platform for any launch configuration and for heavy payloads. They let a contract to R. G. LeTourneau Co., to develop the specialized new launch vehicle. This became the famous “Tiny Tim”. This vehicle helped to improve the launch success rate. The initial vehicle was a three wheeler, was difficult to maneuver and didn’t distribute the load on the pad sufficiently. Later it was modified to a four wheel vehicle that had hydraulic steering and reduced the loads on the launch pad.

50  Balloon Elements

Fig. 3.10  The original Tiny Tim launcher. Photo courtesy of NASA/WFF/CSBF

Fig. 3.11  The updated 1981 Tiny Tim launcher. The vehicle went through many modifications during the years. In this case it was carrying the Japanese American Collaborative Emulsion Experiment (JACEE) experiment. Photo courtesy of NASA/WFF/CSBF

Big Bill

The requirement for a transportable payload launch vehicle capable of handling increasingly heavier payloads resulted in the design and purchase of the Mobile Launch Vehicle (MLV). The large NSBF Palestine based payload launch vehicle called Tiny Tim was not able to be moved from NSBF due to its extremely wide wheelbase and inability to be easily disassembled. The uniqueness of the vehicle specifications made a commercial procurement attempt untenable, so NSBF was tasked to design and fabricate the MLV. PSL-NMSU had a shop in Las Cruces,

3.4  Support Equipment 51 NM that had been building trailers and vans for instrumentation/telemetry jobs, and the engineers there were confident they could build it. The MLV utilizes the motor and drive wheel system of a Michigan brand large articulated front loader. The part in front of the articulation point uses the articulation hardware from the original. PSL added a structure and a boom and gave the vehicle a 7.3 m (24 ft) wheelbase that used solid foam-filled wheels that could be removed for ease of transportation. While the vehicle is transportable, it is primarily used at the Fort Sumner facility where it delivers heavy lift payload capabilities. It has two configurations, one is for transporting on a highway and the other is for launch. Transitioning from the road configuration to the launch configuration can be accomplished by a team of four people in four hours; the reverse takes six hours. In its launch configuration the MLV weighs over 50 tons, measures approximately 13 m (42.65 ft) long by 7 m (23 ft) wide (across its widest point), and has a launch boom that can be raised about 12 m (39 ft) above the ground. This one-of-a-kind vehicle was delivered to Fort Sumner in 1991, then declared operational during the fall campaign the next year. It is used along with a spool mounted in a large bulldozer-type vehicle that holds the semi-inflated balloon at launch time. The MLV dynamic launch capabilities are for balloons with a gross inflation of 6,727 kg (14,800 lb) while the suspended load of 3,636 kg (8,000 lb) is some 680 kg (1,500 lb) greater than Tiny Tim could handle. The MLV was called “Big Bill” after the nickname for Bill Harrison, one of the NSBF mechanical technicians who grew up in Palestine and started working at the balloon base when he was young. Being the primary driver of Tiny Tim, he went on to inherit the new vehicle. Over the years, other launchers were built for the other launch sites, including in Antarctica. The extreme width of the tread in the back relative to the front of the current vehicle at the Fort Sumner provides the necessary lateral stability for the great weight of the payload, especially if there is even the slightest wind. Some launchers at other sites had additional outriggers to provide this function. There was another MLV version that held the balloon in place prior to launch. For a 6:31 minute video of a launch in Kiruna, Sweden that shows a lot of ground support equipment and the launch, go to: https://www.youtube.com/watch?v=0oxd9-­Wl-­Qg The Boss

From the start of the balloon operations at Williams Field the launch method was the dynamic technique. The launch vehicle used during the first 15 years was the “Delta III”, a special Antarctic truck which had a large crane to hold the payloads. But it had low maneuverability and a load capacity of only 2,038 kg (4,500 lb).

Fig. 3.12  The Big Bill vehicle holding a qualification test load. This was a flight qualification test of the new 9.74 million m3 (34.4 million ft3) balloon design with a fully loaded payload of 3,630 kg (8,000 lb). Photo courtesy of NASA/WFF/CSBF

Fig. 3.13  The spooler launch vehicle. Photo courtesy of NASA/WFF/CSBF

3.4  Support Equipment 53 By 2002, the NSBF had completed the design and fabrication of a new launcher for Antarctica. It was named “The Boss” after the popular name of the Antarctic explorer Ernest “The Boss” Shackleton. The 40 ton truck is 58 feet long and its tires measure over 4 ft wide. The vehicle needed to be able to travel through ice, snow and four feet of water and be capable of climbing a 50° slope forward and backward and traversing a 30° side slope. It had also to operate in temperatures well below –45°C (–50°F) and allow launch of payloads up to 3,623 kg (8,000 lb). Although the new vehicle is much more versatile than the Delta III, there had to be some terrain preparation prior to a launch. Currently it takes a contractor 3-4 weeks per year to pack the launch area in order to eliminate any voids that may have developed over the winter and to compact the surface.

Fig. 3.14  The launch vehicle at Williams Field, Antarctica named “The Boss”. Photo courtesy of NASA/WFF

3.4.2  Flight The CSBF provides a science team with a standard set of electronic flight support equipment for telemetry, command and tracking. This also includes equipment to interface with the Tracking and Data Relay Satellite System (TDRSS) and Iridium satellites for command and data acquisition. CSBF personnel are also available to assist with equipment interfaces and to provide information on CSBF electronics capabilities. What follows describes some of the flight support equipment that is provided to a scientific balloon team.

54  Balloon Elements Operations Control Center (OCC) and Remote OCC (ROCC)

The OCC at the CSBF in Palestine, TX is the solitary point of interface for the scientist/experimenter for command and telemetry support to/from the payload when out of sight. It has terminal access to TDRSS and Iridium satellites. The TDRSS return telemetry and forward commanding are available only from the OCC. The OCC is manned continuously throughout a flight to monitor balloon performance and to assure proper operation of the balloon systems. It is able to monitor up to three payloads simultaneously. It can also provide FAA airspace coordination as appropriate. The ROCC is the primary control center for both Antarctica and the mid-­latitude launch sites during the launch and line of sight phase of a flight. It is the primary CSBF operational control during launch, after the balloon reaches float altitude, and prior to it leaving the range of launch site telemetry. Operational control is then handed over to the OCC at Palestine. The ROCC has line of sight data return and command forwarding systems, and maintains communications with the OCC via commercial telephone, Iridium telephone, and the internet. The Legacy Rotator Pointing System

This is a system provided upon request of the user. It is a functional and operating coarse-pointing system for any balloon-borne platform with a suspended payload of less than 2,500 kg (5,500 lb). The legacy rotator currently utilized for a balloon mission is a standardized balloon flight subsystem that is mounted right above the payload, and it separates the rotation of the gondola from the balloon. The legacy rotator is about 56 kg (124 lb) and was designed to support a maximum payload of 3,630 kg (8,000 lb) and to withstand an axial termination load factor of 10 g. A majority of balloon payloads are no greater than 2,500 kg (5,500 lb), therefore the legacy rotator is over designed for most flights. Reduction of mass of the rotator is important. A reduction of mass permits either a longer flight duration or more instrumentation to be added to the payload. Either would allow for more science data to be collected per balloon flight. There was a perceived requirement for a coarse azimuth pointing system that was at least 25% lighter than the legacy rotator for a maximum suspended payload of 2,500 kg (5,500 lb) and a 10 g axial termination load factor. Standardized Coarse Azimuth Pointing System

The Standardized Coarse Azimuth Pointing System (SCAPS) is 34% lighter than the legacy rotator for a suspended payload of less than 2,500 kg (5,500 lb), and it separates the rotation of the gondola and the payload from the balloon. It utilizes GPS and solar sensors for commanding orientation of the payload. Solar sensors at the top of the rotator provide a 360° view. A guidance, navigation and control system commands sensors to look at a specific point. For example, sensors can detect the position of the Sun. The sensor command is sent through the avionics

3.4  Support Equipment 55 packages on board to start the motor and turn the shaft until the sensors provide feedback that they are at the commanded position. The rotator holds the payload at that position until commanded otherwise. The rotator is designed to provide a 5 arc-minute pointing capability, and it has demonstrated a 1.4 arc-minute accuracy. The motor has a 28 volt battery source. The system is designed to operate in a thermal range of –80°C to +50°C (–112°F to +122°F). The system can also accommodate a slip ring which has 20 channels for power, Digital Subscriber Line (DSL) link, and Addressable Asynchronous Receive Transmit (AART) communications. SCAPS features a hollow titanium shaft, 3D printed solar sensor mounts, 3D printed avionics package mounts, and a custom motor frame mount. The system also uses 3D printed templates to standardize the assembly of both rotators, so that non-uniform match drilling is not a problem. Consolidated Instrument Package

CSBF has developed a command and data acquisition system for routine use in the balloon program. User interface and balloon control is accomplished using several mature electronic systems which retrieve science data as well as provide the essential control functions for safe and successful ballooning. The Consolidated Instrument Package (CIP) is the command and data acquisition system utilized on conventional balloon flights. It is a self-contained electronics package that is readily configured to fit the individual needs of science groups. It fulfills the functional requirements of transmitting CSBF housekeeping as well as user-generated analog or digital data, and it receives science and balloon control commands sent from the control tower or tracking aircraft but not from satellites. CIP is made up of a card rack containing printed circuit boards that provide the means for receiving and decoding commands, subcarrier oscillators, pulse code modulation (PCM) encoder, dual GPS receivers, pressure transducers, ATC Air Traffic Control (ATC) transponder and RF transmitters. It employs a 16-bit data word and can accommodate 77 discrete commands. Support Instrument Package

As part of the equipment provided to science teams this enables their payload to communicate with both the Tracking and Data Relay Satellite System (TDRSS) and Iridium system of low Earth orbit satellites to provide a command path and return telemetry if the payload is out of line of sight. Commands to the payload can be sent during testing from the ROCC at the launch site or from the OCC in Palestine, TX. Data from the payload is received at the OCC and can be verified from the ROCC. There are different modes of communications. In addition to the Iridium satellites in low Earth orbit, the balloon payload can communicate with the network of geosynchronous TDRSS satellites. Nominal TDRSS support for LDB offers 6-kbps return telemetry continuously (high-rate and low-rate science interfaces) using an omni antenna. The Support Instrument Package

56  Balloon Elements can optionally record science data onto its flight computer hard drives when using the omni antenna. These hard drives are only recovered at the end of the flight. The OCC in Palestine is the only location from which TDRSS science data and commanding is accessed during flight. Support is available in the field to verify TDRSS return and forward telemetry using a special test set. After launch, and while the balloon is still visible, an L-Band or S-Band telemetry transmitter can be made available for the science team to monitor data. See the OCC/ROCC discussion above. Wallops Arc Second Pointer

The Wallops Arc Second Pointer (WASP) System is a NASA provided support system that can point telescopes on balloon gondolas at inertial targets with arc-­ second accuracy. WASP is intended to be a flexible system that can be used to support a variety of science-provided instruments and sensors to meet specific mission performance requirements. Its major components are reusable and this reduces the overall costs to the Balloon Program Office and to users. During tests in 2011-2012, WASP successfully demonstrated positional stability at sub-arc-second levels in flight. In September 2013 it supported its first pointed science instrument, the HyperSpectral Imager for Climate Science (HySICS) that was created by the Laboratory for Atmospheric and Space Physics (LASP) of the University of Colorado at Boulder. The mission was launched from Fort Sumner, NM.

Fig. 3.15  The WASP gondola for Test Flight 2. Photo courtesy of NASA/CSBF

The WASP system points an instrument mounted on a steel beam using a gondola mounted pitch/yaw articulated gimbal. The range of motion of the yaw-­ gimbal is purposely minimized in order to reduce kinematic coupling during fine

3.4  Support Equipment 57 pointing. The gondola itself is suspended beneath a standard NASA rotator to enable large angle azimuth targeting and coarse azimuth stabilization. Sub-arc-second pointing derives from the mechanical design of the WASP gimbal hubs. A pair of hubs on opposing sides of the gimbal are utilized to establish each articulated axis of rotation. Each hub uses high-precision angular contact bearings to float the rotor side and stator side of the hub on a central shaft, and the central shaft in each hub is itself rotated by a small diameter torque motor through a gear box to eliminate static friction. The shafts in each hub pair are counter-­rotated to minimize the residual kinetic friction that the control system must correct. A large-diameter brushless direct current torque motor is utilized to provide the torque for each control axis. The current in the three electrical phases in each of the control motors is commutated in software and set by using power in a motor interface circuit. The rotor-to-stator angle for each torque motor is determined by the use of resolvers and positional encoders, with one pair for each control axis. After the initial test flight, a number of system modifications and improvements were made to the WASP and a new gondola was designed. The system changes included incorporating the star tracker into the control system loop, changing the mock telescope from a 24 foot steel tube to a 16 foot tube with significantly less inertia, moving the avionics deck from the outer frame onto the mock telescope, and adding angular positional encoders to the resolver hubs. For a briefing on the WASP, go to: https://core.ac.uk/download/pdf/83529822.pdf Star Tracker

High altitude balloons are capable of supporting astronomical observations with virtually no image degradation from atmospheric turbulence. To take advantage of this space-like “seeing”, a telescope must be pointed and stabilized with sub-arc-­ second precision. This involves providing an error signal, then using that to correct the pointing. The University of Colorado Aerospace Capstone Program created a star tracker called DayStar with support from Southwest Research Institute, an independent non-profit applied R&D organization headquartered in Antonio, TX. It is meant to improve upon the pointing accuracy and daytime performance of the ST5000, the star tracker commonly used by NASA’s sounding rockets. The ST5000 was shown to work on a balloon at night but it failed to acquire stars during the day. DayStar overcomes this by filtering light below a wavelength of 620 nm and by using a sensor with high red-performance and resolution that attenuates most of the sky background. In combination with custom star identification algorithms, this enables stars be seen during the day. To validate modeling and demonstrate daytime acquisition, a DayStar prototype flew on a high altitude balloon in September 2012. The filtered camera typically saw three stars during daytime, proving its ability to operate diurnally. Additional

58  Balloon Elements analysis evaluates DayStar’s ability to centroid stars, match stars between frames, and use a series of images to track the orientation. This links the precision of star centroiding algorithms with the pointing acuity for both day and night conditions. The results will be used to validate the performance model and examine DayStar as a potential star tracker for high altitude balloon observatories. Under WFF’s Balloon Program, engineer Scott Heatwole and his team developed a precision attitude sensor (or star tracker) developed specifically for the WASP. This would use the star tracker’s data to point a balloon-borne scientific payload with extreme accuracy and stability at an altitude of 36 km (120,000 ft). Though relatively dark at those altitudes, the scattering of sunlight off the atmosphere can overwhelm the starlight in most star cameras.

Fig. 3.16  Scott Heatwole with his Star Tracker. Photo courtesy of NASA/WFF

3.5  Technology Examples 59 3.5  TECHNOLOGY EXAMPLES Over time, the sophistication and complexity of balloon payloads has increased, in some instances potentially yielding scientific returns that can rival or exceed what can be achieved by a far more expensive orbital mission. What ultimately limits the type and quality of the science that can be performed from a balloon platform is the altitude of the carrier balloon. In particular, experiments in high energy astrophysics often require both high altitude and high suspended weight, as well as long flight durations to increase the likelihood of detections. Similar statements can also be made for overcoming the absorptive and scattering/seeing effects of the atmosphere for payloads operating in the ultraviolet and optical. In the infrared and far-infrared, it is atmospheric water vapor that limits sensitivity. In all cases the deleterious effects of the atmosphere decrease exponentially with height, so even modest increases in the altitude limits of carrier balloons are able to yield significant increases in science return. Thus great efforts have been made over the decades to address all the individual technologies that facilitate these types of flights, including the technologies that relate to both ground and flight support equipment. Some advances were simple but enhanced a specific phase of a mission, such as improving a collar or launch spool. Some were more complex, such as requiring a better way to separate the balloon from the parachute or to terminate the flight. Furthermore, technologies were enhanced to provide greater data acquisition and to record vast volumes of data on board as well as to telemeter it to the ground. As the digital age became more advanced and available, the balloon world had to adapt and even innovate. The era of the internet and more advanced technologies opened the way for the commercial balloon applications. Now corporations are advancing technologies associated with flying constellations of balloons to service remote locations that have no or little internet service. These commercial applications have advanced the technology of controlling the altitude and location of balloons which used to be at the mercy of the prevailing winds. During the mid-1980’s a number of engineering advances were made in balloon systems. These included: • Design of a new balloon helium valve. • Design of an automatic burst detector. • A computer augmented platform for telecommunication and navigation of LDB flights. • Construction of an Omega data sampling receiver for LDB flights. • Work on linear low-density polyethylene (LLDPE) balloon grade film. • Testing of a new technique for launching heavy payloads. • Work on a new super-pressure design concept.

60  Balloon Elements Activities remain high with respect to balloon related technology. These include both terrestrial and extra-terrestrial balloon developments as well as development of support systems such as power systems, trajectory control, telecommunication systems, and flight control systems. Technology development has progressed in advanced materials, balloon design, modeling methods, testing methods, and mission concepts. This work is funded through several mechanisms either directly from the NASA Balloon Program or through Small Business Innovative Research (SBIR) contracts, GSFC Director’s Discretionary Funds (DDF), GSFC Internal Research and Development (IRAD) and other sources. The following are a few examples of improvements in technology. 3.5.1  Loon Trajectory Control Progress is continuing in the area of controlling the trajectory of a balloon. Some innovations are operational, such as the use of super-pressure balloons to control the altitude of zero-pressure balloons. Some technologies are more advanced but haven’t yet been accepted over those used by the commercial balloon world such as Loon. See Section 5.1 for details. Free balloons carrying science instruments typically drift freely in the prevailing wind at the operating altitude. In many cases, their launch must be delayed until forecast winds are projected to carry the balloon system either into an area that is of interest, or away from a forbidden zone. Frequently, such balloon flights must be terminated prematurely to preclude flying over countries that have not given overflight permission, or to ensure that the payload descends into an appropriate landing site, or to avoid endangering populated regions. Even a small amount of trajectory control capability could eliminate these reasons to terminate the flight early. A Trajectory Control System (TCS) that is suspended well below a balloon to take advantage of natural wind differences and provide a lateral aerodynamic force can be used to control the trajectory of the balloon. Such an approach: • • • • • • • • • • • •

Offers increased balloon operations flexibility and cost reduction. Permits the balloon to remain at a fixed (or nearly fixed) altitude. Avoids overflight of uncooperative countries. Increases number of potential landing sites. Enables the balloon to travel over desired locations. Passively exploits the natural wind conditions. Does not require consumables (such as ballast). Avoids payload disturbances caused by propulsive trajectory control methods. Requires very little electrical power. Operates day and night. Offers a wide range of control directions regardless of wind conditions. Can be made of lightweight materials.

3.5  Technology Examples 61 In summary, TCS technology is important to world balloon programs because it simplifies missions by mitigating overflight and safety concerns, expands flight termination options, and minimizes payload recovery logistics. 3.5.2  GAC TCS Technology Over twenty years ago, Global Aerospace Corporation in Irwindale, CA created a unique system to control the trajectory of a stratospheric balloon. They developed a flight prototype of a wing assembly called the StratoSail TCS which exploits the natural difference in wind speed at different altitudes to produce a horizontal force on a balloon to: • • • • •

Avoid regions of high population density. Minimize flights over geopolitically sensitive areas. Enter regions of high scientific value. Maintain the geometry of multiple balloon constellations. Other options for trajectory control were also investigated, for example station-keeping.

The flight segment uses a wing assembly, a tether, a gondola interface package, and software. The gondola interface package remains physically attached to the gondola of the balloon. A winch system reels out a very long tether that carries the wing assembly. The wing assembly is stowed compactly with the gondola at launch, and the tether is rolled on a very large spool. The package also includes interface hardware and software to accept commands from and relay data to the balloon payload. The wing assembly is lowered by the tether. The main element of this assembly is the wing that generates the aerodynamic forces that alter the flight path. The wing assembly includes a rudder to control the direction of the wing’s pull. An electronics module in the wing assembly uses solar power and batteries to control the rudder, to process data from various sensors, and also to communicate with the package by radio link. Tests verified the expected behavior, but further development was not pursued owing to the acceptance of the current capabilities to control altitude, especially by the techniques used by Loon and others. Nevertheless, it remains a potential technology that could be developed in the future. See Section 5.10 for details. 3.5.3  Parachute Technology Balloon parachutes have been tested many times over the decades. Some of the problems in opening a parachute have resulted in excessive shock to the payload and its sensitive and valuable instruments. Some of these problems were solved by the development of the rip-stich technology. At flight termination there is the risk of contacting the collapsing balloon. Another is the need to rapidly separate from the payload and collapse the chute at landing to preclude dragging it across the ground and damaging it. Separate technologies were developed to solve these potential problems.

62  Balloon Elements One example of a technology to address the latter issue was flight 667NT, out of Fort Sumner in 2015. The main goal of was to test technology developments and also carry out missions of opportunity. Among the technical tests performed was the second test of a new Semi-Automatic Parachute Release (SAPR) deflation system to ensure the payload would not be dragged by the parachute acting as a sail if caught by the wind after landing. The flight also tested an azimuth rotator, the Wallops Low-Cost TDRSS Transceiver, and the CSBF solar panel. Also on the flight were five scientific payloads. The termination used normal procedures, with the test rip-stitch system operating in-line. The on-board video showed that the rip-stitch system significantly reduced the opening shock. The parachute was successfully separated by the SAPR system. In addition, the Gondola Automatic Parachute Release (GAPR) system, operating in an off-line capacity, functioned as intended.

Fig. 3.17  Technology Test Flight 667NT payload. Photo courtesy of NASA/WFF/ CSBF

3.5.4  Future Technology Needs In their “Roadmap for Scientific Ballooning” for 2020-2030, the NASA Balloon Program Analysis Group called for the development of telescopes with apertures of up to 3 m (~10 ft) diameter that would be flown on balloons.

3.5  Technology Examples 63 To achieve this goal, they recommended: • Thermal stabilization of optical assemblies. • Wavefront sensors to generate real-time in-flight wavefront errors. • A wavefront correction scheme (e.g. deformable mirrors) to compensate for optical assembly aberrations. They also recommended improvements to the following: • Provide even better stabilization of the WASP for potential observatory-­ class balloon-borne telescopes. • Increase payload downlink bandwidth to keep up with science needs with a goal of 10 MB/s average through a flight to enable an increased science return. • Prepare to support the April 8, 2024 solar eclipse. • Increase the capacity of launch facilities and particularly those located at high magnetic latitudes. The rapid advance of technologies in many areas are enabling NASA’s Balloon Program to update its ground and flight systems in order to improve the science results delivered by the program. IMAGE LINKS Fig. 3.1 https://www-­tc.pbs.org/wgbh/americanexperience/media/filer_public_thumbnails/filer_public/d3/f5/d3f526ed-­a1fe-­4cb6-­b24f-­edcc35577a 2d/high_alt_girls_es_6159m_generalmills_19550101.jpg__400x305_q85_crop_subsampling-­2_upscale.jpg Fig. 3.2 https://www-­tc.pbs.org/wgbh/americanexperience/media/filer_public_thumbnails/filer_public/25/f1/25f18251-­12df-­4f31-­af20-­7002e0c8dace/ high_alt_winzen_es_5526m_ravenaerostar_19570101.jpg__400x488_q85_crop_subsampling-­2_upscale.jpg Fig. 3.3 http://s3.amazonaws.com/com-­ravenaerostar-­cdn/general-­uploads/_910x540_fit_center-­center/FIRST_Spr_05_landing_site_mp.jpg?mtime= 20171019161224 Fig. 3.4 http://s3.amazonaws.com/com-­ravenaerostar-­cdn/general-­uploads/_910x540_fit_center-­center/parachutes-­3.jpg?mtime=20170830105626 Fig. 3.5 https://stratocat.com.ar/globos/fotos/dstb05b.jpg Fig. 3.6 https://thespaceperspective.com/wp-­content/uploads/2020/02/Space-­Perspective_Journey.png Fig. 3.7 https://encrypted-­tbn0.gstatic.com/images?q=tbn%3AANd9GcTG7WMJuZJAxCw9qrdSaRIbbQqCP7hC9-­ws7A&usqp=CAU Fig. 3.8 http://www.sagecheshire.com/images/OpenGondola2.jpg Fig. 3.9 https://stratocat.com.ar/globos/fotos/carmen_gondola_hangtest.jpg Fig. 3.10 http://stratocat.com.ar/artics/imgs/tn_tiny-­tim-­3w.jpg Fig. 3.11 http://stratocat.com.ar/globos/fotos/jacee_03b.jpg Fig. 3.12 http://stratocat.com.ar/fichas-­e/2008/FSU-­20080531.htm Fig. 3.13 https://stratocat.com.ar/bases/imgs/tn_fsu_spool.jpg Fig. 3.14 http://stratocat.com.ar/bases/imgs/tn_the_boss.jpg Fig. 3.15 https://stratocat.com.ar/globos/fotos/wasp12a.jpg Fig. 3.16 https://www.nasa.gov/sites/default/files/styles/side_image/public/thumbnails/image/scott_heatwole01.jpg?itok=01h5wXtp Fig. 3.17 https://stratocat.com.ar/globos/esq/tn_esq_test_2015_2.jpg

4 Mission Drivers and Operations

4.1  MISSION DRIVERS 4.1.1  Pre-Mission Planning The planning of a mission depends on a lot of factors. For example, is it to be a single flight or a campaign of many flights? Where is the launch site? Are there adequate launching facilities? Is it in a foreign country? Are there any overflight restrictions? Are there international participants? The answers to these questions drive the implementation of a mission and its flight operations. Antarctic Example

Probably the most difficult missions to plan are those that will be launched from one of the polar regions. Antarctica is unique in many ways. While those flights receive outstanding support from the National Science Foundation and its Polar Program, it is still very far away and an extreme environment. As a result there are demanding pre-mission planning constraints. Even before a mission is ready to fly, there are critical logistics questions that must be addressed. The CSBF typically ships balloons and helium one year in advance of a scheduled flight. Thus by May of the preceding year (two years in advance of the scheduled date) the science instrumentation, payloads, balloon, communications interface and any special or unique requirement must be clearly identified and approved by the Balloon Program Office, by the science team and by the CSBF Operations Department.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 M. von Ehrenfried, Stratospheric Balloons, Springer Praxis Books, https://doi.org/10.1007/978-3-030-68130-2_4

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4.1  Mission Drivers 65 While that is underway, the flight instruments might still be under construction. When completed, the CSBF will hold the Mission Readiness Review (MRR) at Palestine, TX. Once the instrument and flight equipment passes that review, all equipment, including the science payloads and any ground support equipment, is shipped to the launch site. The trip to Antarctica starts at Port Hueneme, CA, where the apparatus is loaded onto a ship. Upon arrival at Christchurch in New Zealand it is transferred to aircraft for delivery to Williams Field at McMurdo Station. For a flight that is scheduled from December 1st to January 10th, CSBF launch personnel usually start to arrive by November 1st, so there is a short window of opportunity. Flights are not scheduled after that time to allow sufficient time to recover the payload and the balloon and begin preparations to depart McMurdo for New Zealand and, in due course, home to the U.S.A. Once in Antarctica, all logistics, housing, meals, and other on-site support is provided by the National Science Foundation. One of the “horror stories” experienced by Henry Cathey relating to his travel is in described in Appendix 3. As an example, pre-mission planning typically includes the following: • Submit CSBF Flight Application Form two years in advance of the planned mission. • NASA/WFF led Project Initiation Conference one year in advance. • Pre-Deployment Integration & Test with CSBF support systems in Palestine, TX six months prior to mission. • Arrive at the launch site and start pre-flight readiness preparations 2-4 weeks prior to planned launch date. • There is a 6 month lead time for processing of personnel who intend to travel to Antarctica. 4.1.2  Requirements and Constraints All balloon flights are subject to various requirements and constraints, both pre-­ mission and during flight operations. In the formal parlance of NASA, requirements are defined by “shall” statements which indicate the responsible organization. In most cases, the range user (where ever the launch is to take place) or vehicle program is responsible for meeting the requirements. The term “range user” is typically associated with the flight vehicle provider that is conducting an operation at a launch range/site at which the WFF Safety Office holds operational responsibility. The term “program” here refers to NASA programs and other projects conducted under the cognizance of the WFF and the Balloon Program Office. These formal requirements are spelled out in what is known as a “text box”. The information provided in a text box identifies alternatives that satisfy the intent

66  Mission Drivers and Operations of the requirement, and may be used by the range user to deal with a requirement to their specific case and to provide additional clarifying information, requirement rationale, or recommended practices. The range user coordinates with the WFF Safety Office to determine its applicability and enforcement. 4.1.3  Range Safety Requirements The overall objective of the ground safety technical requirements is to guarantee personnel and property involved in conducting range operations are protected by the mitigation of hazards and the management of associated residual risks. It is a working rule that all systems be designed such that it will take a minimum of two “independent unlikely failures” to occur for personnel to be exposed to a hazard. The WFF Range Safety Manual addresses those hazards representing heightened concern that are often not routine throughout industry but are common at a launch range. Unique hazards that are not addressed by this document are addressed on a case-by-case basis, and related mitigations and controls are documented by WFF in several plans. Types of Hazards • • • • • • • •

Chemical Systems. Radiation Systems. Pressure Vessels and Pressurized Systems. Cryogenic Systems. Battery Systems and High Voltage. Lithium Ion Battery Systems. Operations Controls and Procedures. Radio Frequency (RF) Controls.

Restrictions for Tour Groups and Official Visitors include: • • • • •

Electrostatic Discharge Protocols. Electrical Storm Protocols. Hazardous Operations Training and Certification Requirements. Nominal Recovery or Planned Land Impacts Procedures. Emergency Procedures.

Satisfying these requirements can give rise to a great many documents. 4.1.4  Overflight Planning and Coordination Wherever in the world a balloon is launched, it might travel in airspace that is controlled by a regulatory agency. At issue are potentially disastrous conflicts involving aircraft. In the case of the FAA in the U.S., the governing chapter is Title 14 of the Code of Regulations, Part 101, Subpart D for “Unmanned Free Balloons”.

4.1  Mission Drivers 67 Most of those regulations pertain to sport hot air balloons and student balloons, but there are situations where the scientific or commercial high altitude balloon still has the responsibility to adhere to the rules and coordinate its activities with the FAA. In some situations the balloon must climb above controlled airspace or descend to pass through it. This is why most NASA sites are far from controlled airspace and they make every effort to terminate flights in uncontrolled airspace. In the past, when airports were used for launch sites, the airport was shut down for a period and this was coordinated with the FAA. Because most commercial aircraft fly well below 12 km (40,000 ft) and military aircraft typically have their own controlled airspace and scientific & commercial balloons fly above those altitudes, there is rarely a problem. Most balloon flights are above controlled airspace, which typically cuts off at 18 km (60,000 ft). Even so, NASA and commercial companies such as Loon and World View Enterprises maintain close communications with the FAA. There can also be dangerous situations above controlled airspace. I remember a time when I was in the RB-57F at 20 km (65,000 ft) and the FAA warned us of an aircraft coming at us at our 12 o’clock. It was an SR-71. At that altitude, it’s difficult to see the other aircraft, and very difficult to maneuver without losing altitude or getting off your desired ground track and targets. The launch sites used by NASA have been selected to avoid heavily populated areas and are in uncontrolled airspace. Nevertheless, depending upon the winds aloft, balloons can temporarily impinge on controlled airspace as they climb to higher altitudes. 4.1.5  Meteorological Forecasts In meteorology, a forecaster can never have too much data. Due to the inherent remote locations of ballooning campaigns, obtaining a sufficient amount of data can often be a challenge. Lack of data can give rise to uncertain forecasts, so it is important to collect and distribute as much data as possible. The forecaster uses many sources of data, including: • Surface observations including temperature, dew point, wind, pressure and other parameters. • Frequent and timely satellite imagery. • Radar. • Upper air observations. • Atmospheric model data. One of the major sources of data available to the forecaster is NOAAPort. The National Oceanic and Atmospheric Administration (NOAA) broadcasts weather observations, forecasts, images, models, watches/warnings, and hazard-related

68  Mission Drivers and Operations information to internal and external users via a C-band satellite system named NOAAPort. Since the system went live in 1998 the array of data that it supplies has continued to expand. It is disseminated freely. Planetary Data, Inc., (PDI) provides NASA balloon launches with NOAAPort Receive Systems (NRS) for weather data direct from a C-band ground station or via an internet feed from a PDI ground station. Availability is 24/7 depending on local computers, workstations and servers. The WFF and the CSBF at Palestine, TX and Fort Sumner, NM make use of this data. When balloon scientists need weather information they work through NOAA’s NWS. This also has data from international meteorological contacts such as the World Meteorological Organization (WMO). The NWS carries out its principal task via a collection of national and regional centers and 122 local Weather Forecast Offices (WFO). It supports the aviation community, including the balloon community, by creating a number of forecasts. Each WFO has responsibility for the issuance of Terminal Aerodrome Forecasts (TAF) for airports in its jurisdiction. TAFs are concise, coded 24 hour forecasts for a specific airport (or 30 hour forecasts for certain airports). They are issued every 6 hours with amendments as appropriate. As opposed to a public weather forecast a TAF only addresses the weather elements critical to aviation, such as wind, visibility, cloud cover, and wind shear. The crews at the various balloon launch sites monitor the NWS and its TAFs. Foreign operators draw upon their own equivalent services, as well as those of the WMO. Because balloons are only launched when the conditions on the ground and aloft are acceptable the launch teams constantly monitor the local weather, that along the projected flight path, and that at the potential termination and recover areas. There are 21 NWS Center Weather Service Units (CWSU) collocated with the Air Route Traffic Control Centers (ARTCC) of the Federal Aviation Administration (FAA). Their main responsibility is to provide up-to-the-minute weather data and briefings to the Traffic Management Units and control room supervisors. Special attention is given to conditions that could be hazardous to aviation or impede the flow of air traffic in the National Airspace System. In addition to its scheduled and unscheduled briefings for decision-makers in the ARTCC and other FAA facilities, CWSU also issues two unscheduled products. The Center Weather Advisory (CWA) is an aviation weather warning relating to thunderstorms, icing, turbulence, low ceilings and visibilities. A Meteorological Impact Statement (MIS) is a 2-to-12 hour forecast outlining weather conditions which are expected to impact ARTCC operations. The OCC or ROCC may also contact their nearest ARTCC for the latest weather information. This monitoring is carried out both prior to and after a balloon launch. See Section 4.2.3 for Real-­ Time Weather and Winds.

4.1  Mission Drivers 69 4.1.6  Pre-flight Reviews & Tests Long before a balloon project achieves the point where the scientific payload is being checked out at the CSBF, it has already gone through a formal process of reviews that can begin years ahead of time. These reviews would have included Program Approval, a variety of Program Assessment Reviews, Internal Reviews, as well as others. They would have involved people from the sponsoring NASA Headquarters level down through the Directorate, Division and Center levels of management. Once the balloon project got to the WFF Balloon Program Office, this would trigger another set of reviews. Once the payload got to CSBF, there would be other more specific tests and reviews, and the same would be true on arrival at the launch site. Once a payload has been through all the programmatic reviews in Washington, Goddard Space Flight Center and the Wallops Flight Facility/Balloon Program Office, the payload is shipped to the CSBF were it is finally assembled with all the payload components, all the balloon components, the SSBF equipment, the solar panels and so on. Then the functional tests during the Compatibility Test involve a “hang test” on the launch vehicle. At this stage the team verifies that everything is working as planned. Usually a Mission Readiness Review (MRR) occurs shortly thereafter. If the CSBF is the launch site, it remains there for final tests and launch, otherwise it is disassembled, packed and shipped to the launch site. Once the payload arrives at the launch site, the assembly process is repeated as well as a Compatibility Test and, finally, a Flight Readiness Review (FRR) just prior to launch. With the balloon and its payload fully integrated at the pad, the CSBF team invites the Principal Investigator to give a “thumbs up” to proceed with the launch. While the above might be the general rule, each payload is different, as are the particular scheduled events. For a specific example, the following is an actual case for the recent launch of SuperTIGER at Williams Field, McMurdo Station as provided by the Principal Investigator, Dr. Brian Rauch of the Washington University in St. Louis. It has been edited and summarized. August 15, 2019

October 4, 2019 November, 2019 December 11, 2019 December 12, 2019 December 16, 2019 January 16, 2019

The Compatibility Test at the CSBF: The payload is taken outside and suspended on a crane or launch vehicle where it must show it can operate on its own power over all of the communications channels, including receiving commands and sending telemetry. Mission Readiness Review (MRR): Required prior to shipment of the payload to Antarctica. The team deploys. Completed the Compatibility Test and Flight Readiness Review (FRR): Final payload weight and ballast. Final plan details and CSBF/BPO responsibilities discussed. Received the Authority to Proceed (ATP) from BPO. Launched. Landed.

70  Mission Drivers and Operations 4.1.7  Success Criteria Prior to a flight, programmatic, scientific, technological and operational success criteria are established. Often the flights carry other experiments of opportunity, and they have their own criteria. For the payload engineer success may mean the instrument worked as designed. For the scientist success may mean it observed a gamma-ray burst or received the neutrinos as intended. Sometimes a science team can determine fairly early whether their payload and instruments were successful. If there is telemetry then they begin their analysis immediately, although they might not have sufficient data to provide a complete assessment. In addition to monitoring the health of the instrument, scientists can see if they are getting the data they expected and hoped for. The following is a more specific example of how the SuperTIGER Principal Investigator, Dr. Brian Rauch, described the process (edited and summarized): We sign off on official pre-flight minimum success criteria that are based on what can be achieved based upon CSBF flight expectations. I agreed to 8 days or one rotation around the continent, whichever came first, but I wanted to fly as long as possible (we got 32 days). I wanted to fly as high as possible, but ended up signing off on a minimum of 110,000 ft. I provided a science data requirement of (~0.4 million iron events and equivalent numbers of cosmic ray nuclei 10