DOCTORAL T H E SIS Department of Computer Science, Electrical and Space Engineering Division of Space Technology Kanika Garg Autonomous Navigation System for High Altitude Balloons System for High Autonomous Navigation Kanika Garg ISSN 1402-1544 ISBN 978-91-7790-486-1 (print) ISBN 978-91-7790-487-8 (pdf) Luleå University of Technology 2019 Autonomous Navigation System for High Altitude Balloons Kanika Garg Onboard Space Systems AUTONOMOUS N AVIGATIO N SYSTEM FOR HIGH ALTITUDE BALLOO NS kanika garg Supervisors:thomas kuhn & olle norberg IndustrialSupervisor:kent andersson Kanika Garg : Autonomous Navigation System for High Altitude Balloons, c November 2019 Printed by Luleå Technical University, Graphic Production 2019 ISSN 1402 − 1544 ISBN 978 − 91 − 7790 − 486 − 1 (print) ISBN 978 − 91 − 7790 − 487 − 8 (pdf) Luleå 2019 www.ltu.se ABSTRACT High-altitude scientific balloons are platforms for space and environmental research as well as for testing future spacecraft and instruments. However, operating such balloons is a challenging task. Balloons work on the principle of buoyancy, and once deployed in the atmosphere, they are subjected to various dynamical and thermal forces. These forces make the balloon flight complex, as they are dependent upon various atmospheric parameters, which are not easy to estimate. Furthermore, a few hours after deployment, a high-altitude balloon reaches equilibrium in terms of buoyancy and floats in the direction of the winds, making the balloon flight uncertain as winds are not known to a great extent at such altitudes. To alter the trajectory, the balloon has to be taken to different wind layers with different wind directions or speeds. Presently, to explore the wind layers the balloon itself is used as a probe. The two manoeuvres that are used by the balloon pilot for exploring these wind layers are ballasting and venting. However, the number of ballasting and venting operations per flight is limited due to a limited amount of lift gas and ballast material, and continuous search for wind layers is thus not possible. As a result, balloon trajectory forecasting poses several challenging problems since the subject is both complex and multidisciplinary. Consequently, balloon mission preparation requires an accurate and re- liable prediction methodology for both weather and trajectory, in order to accomplish the mission successfully. This research work focusses on two aspects of ballooning: (a) determination of balloon ascent and (b) finding an optimal sequence of manoeuvres in order to navigate balloons autonomously. To solve problem (a), a standard analytical model, a fuzzy model, and a statistical regression model are developed and compared to predict the zero-pressure balloon ascent. To solve problem (b), different sensors and data models are studied in order to understand the environment in which these scientific balloons fly and challenges associated with that. Next, rein- forcement learning algorithms are applied to optimize the manoeuvres and to allow for autonomous flights. iv SAMMANFATTNING Höghöjdsballonger är plattformar för rymd- och miljöforskning, såväl som för tester av framtida rymdfarkoster och instrument. Att flyga sådana bal- longer är en utmanande uppgift. Ballongerna verkar enligt Arkimedes princip, och när de släppts i atmosfären utsätts de för olika dynamiska- och termiska krafter. Dessa krafter gör ballongflygningen komplex, då de beror på olika atmosfärsparametrar vilka är svåra att uppskatta. Några timmar efter att en höghöjdsballong släppts når den ett jämviktsläge vid en viss höjd och driver då i vindriktningen, vilket ytterligare ökar ovissheten kring flygningen då det endast finns begränsad kunskap kring vindarna på dessa höjder. För att ändra flygbanan måste ballongen föras till olika vindlager, med olika vindriktningar eller vindstyrkor. I nuläget används ballongen själv som sond för att utforska de olika vindlagren, och de två manövrar som ballongpiloten använder är att släppa ballast och att släppa ut gas. Antalet manövrar per flygning är dock begränsat på grund av den begränsade mängden ballast och gas ombord, kontinuerligt sökande efter vindlager är därför inte möjligt. Banberäkningar för höghöjdsballonger består som ett resultat av detta av ett flertal utmanande problem, då området är både komplext och multidisciplinärt. Framgångsrika ballongflygningar kräver precisa och tillförlitliga metoder för väderprognoser och banberäkningar. Detta forskningsarbete fokuserar på två aspekter av ballongflygning: (a) bestämning av ballongens uppstigning och (b) att hitta en optimal sekvens av manövrar för att autonomt kunna navigera ballongen. För att lösa problem (a) utvecklas och jämförs en analytisk-, en oskarp logik-, och en statistisk modell i syfte att kunna förutse ballongens uppstigning. För att lösa problem (b) studeras olika sensorer och datamodeller för att förstå omgivningen i vilken höghöjdsballongerna flyger och de utmaningar som detta medför, varefter förstärkningslärande algoritmer används för att optimera manövrar och åstadkomma autonoma flygningar. v PUBLICATIONS Kanika Garg and Reza Emami. “Aerobot Design for Planetary Explorations.” In: 2016 AIAA SPACE, p. 5448 Kanika Garg and Reza Emami. “Fuzzy Modelling of Zeropressure Balloon Ascent.” In: 2018 Modeling and Simulation Technologies, p. 3753 Kanika Garg and M Reza Emami. “Balloon ascent prediction: Comparative study of analytical, fuzzy and regression models.” In: Advances in Space Research 64.1 (2019), pp. 252–270 Kanika Garg and Thomas Kuhn. “Balloon Balloon design for Mars, Venus, and Titan atmospheres.” Submitted to: Applied Sciences in October 2019 Kanika Garg, Tobias Roos, Thomas Kuhn & Olle Norberg, “Wind based nav- igation of ZP balloons using reinforcement learning.” Submitted to: Advances in Space Research in November 2019 vii ACKNOWLEDGMENTS This work is influenced by the contributions of a lot of people who along the way supported me, encouraged me or simply inspired or fascinated me, and here are a few acknowledgements. Thomas, I am grateful to you for your guidance, help, and support. Olle, I would like to express my gratitude to you for all the help during this past one year and for career advice. Mikael Danielsson, I am thankful to you for providing me the balloon flight data and for all the discussions regarding stratospheric winds and balloon ascent. Kent, thank you for your support with the collaboration with Swedish Space Corporation. Mark, thanks a lot for all the discussions regarding my research tasks, and for providing valuable guidance and feedback. Rita, thank you for your help during these past few months with the wind data and your feedback and help with it. I would also like to thank my previous supervisor Reza Emami. Chris, Sumeet, Niklas, and Moses! You guys are great office colleagues, and now friends. Thank you for your support and understanding. Victoria, Maria, and Anette, thank you for your warmness, and patience. To the entire present and past LTU staff, I am grateful to you for these four years and for all the help. Thanks to the Graduate School of Space Technology, Space for Innovation and Growth (RIT), Swedish National Space Agency, and SSC, for funding this work and for organizing different activities. I really appreciated it. Marta-Lena and Magnus, thank you for your patience, advice, and commitment to the graduate school. Christina, I would like to extend my deep gratitude to you for all the productive sessions. Advice given by you has been of a great help. Prof Ramesha C and Dr B.N. Suresh, it has been many years (almost 9) since I saw you last, but I think of both of you often. You have inspired me in a way no one has. Thank you, for everything. Robert, Jule, Piritta, Maria, Angéle, and Philipp! Thanks for providing happy distraction to rest my mind outside of my research! Looking forward to your many visits to Stockholm! Chandru and Vishal! Thank you for being there, anytime and everytime, I needed you! Mum and Papa, kismat wale bacho ko aapke jaise parents milte hai, aapka dhnyawad duniya ke koi shabd nai kar sakte! To my siblings (Radhika, Abhi, Parth) - thank you for listening to me at odd hours, and for bringing in good and happy spirit all the time. ix Tobias, there can not be a better partner than you - personally & profes- sionally. I will forever be grateful to you! Thank you for all the discussions, enthusiasm, and proof reading. Thanks for keeping up with me! To different open source communities (LATEX Stack Overflow, Medium Work, etc), thank you for providing answers to so many odd questions and for writing articles that are easy to understand! To my favorite authors, Robert Jordan, and Arthur C Clarke, your books have been my safe escape for the entire duration of my PhD, thank you! To Carl Sagan - You are - and will always be the inspiration! x CONTENTS 1 introduction 1 1.1 History of ballooning 1 1.2 High-altitude balloon flight 5 1.3 Research aim and methodology 6 1.4 Contribution of this work 7 1.5 Thesis outline 8 2 ascent prediction - analytical simulation 9 2.1 Analytical Simulation 10 2.1.1 Input data 11 2.1.2 Illustrative results 13 2.2 Validation of simulation 15 2.2.1 Case 1 - HADT-1B flight May 2019 15 2.2.2 Case 2 - HADT-1A flight August 2018 16 2.3 Monte Carlo simulations 18 2.3.1 Operational uncertainty 20 2.3.2 Environment uncertainty 21 2.4 Conclusion and future work 25 3 ascent prediction - data models 27 3.1 Linear regression models 27 3.2 Regression trees 28 3.3 Support vector machines 29 3.4 Ensembles of trees 31 3.5 Summary and conclusion 32 4 wind