MASTER'S THESIS Strategies and Geant4 Simulations for Radiation Protection on an EML-2 Mission Marc-Andre Chavy-Macdonald 2015 Master of Science (120 credits) Space Engineering - Space Master Luleå University of Technology Department of Computer Science, Electrical and Space Engineering Marc-André Chavy-Macdonald Strategies and Geant4 Simulations for Radiation Protection on an EML-2 Mission Department of Computer Science, Electrical and Space Engineering Division of Space Technology Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Technology Paris, December 31, 2013 Instructor: Alessandra Menicucci European Space Agency Electromagnetics and Space Environment Division Supervisors: Scott Hovland Professor Johnny Ejemalm European Space Agency Luleå University of Technology Development and Future Projects Division Division of Space Technology Human Spaceflight and Operations Directorate Preface This overly long thesis began with a six-and-a-half month internship at ESA’s ESTEC facility, under the dual tutelage of the Space Environment Section and Development and Future Projects Division of the Human Spaceflight and Op- erations Directorate. The purpose was to evaluate the radiation risk for inter- planetary missions, and apply the findings to an EML-2 mission design. The internship finished in mid-September 2012, having finished the simulations but virtually none of the analysis. A short internship report was handed in at this time; its results have all been updated here. The author feels he should apologise for both the length and tardiness of this thesis. Obviously these factors are linked, however approximately 6 months were completely wasted as the author soul-searched, worked for money and had fun in Paris instead of writing the thesis. The remaining time was stretched out due to the necessity of working in parallel. This thesis is too long to be enjoyably read. The astute reader will pick and choose relevant or seemingly interesting chapters. For the novice to the space radiation field, chapters 2-4 may be interesting. Chapter 5 may be interesting for the space exploration enthusiast or designer. Chapters 6 and 7 will especially appeal to specialists of the space radiation community keen on examining re- sults. The practical aspects of these results are presented in Chapter 8; together with Chapter 10 this may appeal to Human Spaceflight specialists interested in radiation protection with an application by a novice designer. Chapter 9 will interest those looking in to active shielding. ii 0.1 Acknowledgements The author wishes to very gratefully thank almost everyone at ESA’s ESTEC facility, particularly the people he met. He would further like to single out all radiation specialists of TEC-EES, who were all utterly necessary for the results presented here. Their incredible patience and helpfulness stood like a shining beacon of hope in the dark, cold abyss of malfunctioning simulations. On the Human Spaceflight, system design, and CDF end, the author would like to deeply thank all those with whom he interacted. Without their invaluable engineering experience and insights, relating dose results to concrete recommen- dations and a design attempt would have been impossible. Externally, the author also thanks Thomas Berger, Daniel Matthiä and Chris- tine Hill from the Radiation Biology Department of the Deutschen Zentrums für Luft- and Raumfahrt (DLR) for their kind cooperation, Tatsuhiko Sato from the Japanese Atomic Energy Agency (JAEA) for many fruitful conversations, and three unnamed reviewers for their very constructive criticism to the related IEEE TNS paper. Paris, December 31, 2013 Marc-André Chavy-Macdonald iii Luleå University of Technology Department of Computer Science, Electrical and Space Engineering Abstract of the Master’s Thesis Author: Marc-André Chavy-Macdonald Strategies and Geant4 Simulations for Radiation Protection on Title of the thesis: an EML-2 Mission Date: December 31, 2013 Number of pages: 217 Division: Space Technology Programme: Master’s Degree Programme in Space Science and Technology Supervisors: Scott Hovland (ESA) Professor Johnny Ejemalm (LTU) Instructor: Alessandra Menicucci (ESA) Radiation shielding is of primary importance in the planning of new interplanetary manned missions, and the ISS represents the largest laboratory for radiation shielding in space ever built. The ISS radiation environment has been thoroughly characterised by the Monte Carlo-based high-energy physics toolkit Geant4, finding that the ISS structure is quite effective at shielding from most forms of radiation, largely due to its internal arrangement. The internal environment found is consistent with literature values and astronaut dosimetry, and results indicate that the internal configuration of a spacecraft may be key to the radiation environment within it. Simulation results are then presented characterizing the interplanetary case, including detailed comparisons with other codes, with good agreement. Recommendations, guidelines and require- ments for interplanetary manned mission design are presented using these findings. These include prioritizing an SPE shelter, managing configuration and scheduling missions to avoid solar minimum to diminish GCRs. Alternative mitigation strategies such as active shielding are looked at, a magnetic shielding study is found to offer inferior protection to cheaper and lighter passive shielding. Maximum durations in interplanetary space for solar maximum and minimum under different shielding is es- timated and compared to NASA results. It is found that uncertainty in the biological effects of radiation conditions time in space and is a priority for future research. Keywords: Biological effects of radiation, computer simulation, radiation safety, ion radiation effects, system-level design. iv Contents 0.1 Acknowledgements ......................... iii 1Introduction 1 1.1 Radiation Environment Simulation . 2 1.2 FutureDeep-SpaceMannedMissions . 3 1.3 The Author’s Contribution . 4 1.4 Outline................................ 4 1.5 Thebasicsofradiationprotection . 5 2TheSpaceRadiationEnvironment 6 2.1 The Sun, heliosphere and magnetosphere . 7 2.2 SEPsandSPEs........................... 11 2.3 GCRs ................................ 16 2.4 Trapped particles . 19 2.5 Secondary and albedo particles . 20 3RadiationEffectsandQuantities 23 3.1 Biological EffectsandHumanDoses. 24 3.1.1 Human phantom models . 28 3.2 Dose Quantities and Limits . 28 3.2.1 Long-term dose quantities and limits . 29 3.2.2 Short-term dose quantities and limits . 31 4MethodsinRadiationEngineering 34 4.1 An Overview of Current Methods in Radiation Modelling . 34 4.2 Radiation Transport . 37 4.3 The Geant4 Toolkit and suite of applications . 38 4.3.1 MULASSIS ......................... 39 4.3.2 SSAT . 39 4.3.3 GRAS . 40 4.4 EnvironmentModels ........................ 40 v 4.5 OtherConsiderations . 41 5ArchitectureofHuman-tendedMissions 43 5.1 PreviousMissions.......................... 43 5.1.1 Salyut . 46 5.1.2 Mir.............................. 52 5.1.3 Shorter-duration LEO missions . 58 5.1.4 Apollo . 61 5.1.5 Skylab . 62 5.1.6 ISS . 64 5.2 Architectural Considerations and Design Drivers . 70 5.3 Overview of Proposed Missions : the Exploration Roadmap and Building Blocks . 72 6DoseDeterminationAboardISS 75 6.1 Overview of Dosimetry and Simulations of the ISS Radiation Environment............................. 75 6.2 Validation Study Using Dosimetry and Columbus Geometry . 76 6.2.1 Experimentalsetup. 76 6.2.2 Results . 78 6.3 Comparison with dosimetry and other literature . 86 6.4 Summary .............................. 94 7DeterminationoftheInterplanetaryRadiationEnvironment97 7.1 MethodsandApproach....................... 97 7.1.1 Important ions . 98 7.1.2 Use of conversion coefficients . 99 7.2 InterplanetaryGCRdoses . 99 7.3 SPEsininterplanetaryspace. 103 7.3.1 The 95 and 99% C.I. and August 1972 SPEs : comparison to NASA . 105 7.3.2 The Piers event and comparison to Carrington event worst- case literature . 108 7.3.3 SPEdoseresults ...................... 110 7.4 The interplanetary radiation environment . 114 7.4.1 Long-term limits . 114 7.4.2 Short-term limits . 116 vi 7.4.3 Shielding materials . 119 8RadiationMitigationStrategiesforDeepSpaceSystems 120 8.1 GeneralConsiderations:SystemDesign . 120 8.1.1 Problemsimplification . 121 8.1.2 Comparisontocurrentoperations . 125 8.2 SPEShielding............................ 127 8.2.1 Storm shelter design : an optimisation process . 130 8.3 GCRShielding ........................... 136 8.3.1 SolarcycleandGCRmitigation . 138 8.4 Uncertainties in risk assessment . 143 8.5 Safe days in interplanetary space . 144 8.6 Recommendations for Interplanetary Manned Mission Design . 148 9AlternativeMethodsinSpaceRadiationMitigation 152 9.1 Active Shielding . 152 9.1.1 Redesign of Geom13sc . 156 9.1.2 Redesign of complete active system . 159 9.1.3 Overview of active shielding results ; desirability of 4 Tm system . 162 9.2 BiologicalMeasures. 169 10 System Engineering for Deep Space Missions : an EML-2 case study 171 10.1 Requirements . 172 10.2 Missionandsystemdescription . 174 10.2.1 Missionscenario. 174 10.2.2 System description . 176 10.3 Drivers and trade-offs........................ 178 10.3.1 Habitable volume and system architecture . 178 10.3.2 ECLSclosureandlogistics . 181 10.3.3 Radiation . 182 10.4 SubsystemsandConfiguration . 186 10.4.1 Configuration . 187 10.4.2 AOCSandpropulsion . 188 10.4.3 ECLSsystemandlogistics . 188 10.4.4 Power and electrical systems