The Technology of Discovery : Radioisotope Thermoelectric Generators and Thermoelectric Technologies for Space Exploration

The Technology of Discovery Incisive discussions of a critical mission-enabling technology for deep space missions In The Technology of Discovery: Radioisotope Thermoelectric Generators and Thermoelectric Technologies for Space Exploration , distinguished JPL engineer and manager David Woerner delivers an insightful discussion of how radioisotope thermoelectric generators (RTGs) are used in the exploration of space. It also explores their history, function, their market potential, and the governmental forces that drive their production and design. Finally, it presents key technologies incorporated in RTGs and their potential for future missions and design innovation. The author provides a clear and understandable treatment of the subject, ranging from straightforward overviews of the technology to complex discussions of the field of thermoelectrics. Included is also background on NASA's decision to resurrect the GPHS-RTG and discussion of the future of commercialization of nuclear space missions. Readers will also find: A thorough introduction to RTGs, as well as their invention, history, and evolution Comprehensive explorations of the contributions made by RTGs to US space exploration Practical discussions of the evolution, selection, and production of RPS fuels In-depth examinations of technologies and generators currently in development, including skutterudite thermoelectrics for an enhanced MMRTG Perfect for space explorers, aerospace engineers, managers, and scientists, The Technology of Discovery will also earn a place in the libraries of NASA archivists and other historians. Cover 1 Title Page 5 Copyright Page 6 Contents 7 Foreward 13 Note From the Series Editor 15 Preface 17 Authors 21 Reviewers 23 Acknowledgments 25 Glossary 27 List of Acronyms and Abbreviations 35 Chapter 1 The History of the Invention of Radioisotope Thermoelectric Generators (RTGs) for Space Exploration 41 References 45 Chapter 2 The History of the United States’s Flight and Terrestrial RTGs 47 2.1 Flight RTGs 47 2.1.1 SNAP Flight Program 47 2.1.1.1 SNAP-3 48 2.1.1.2 SNAP-9 48 2.1.1.3 SNAP-19 49 2.1.1.4 SNAP-27 51 2.1.2 Transit-RTG 53 2.1.3 Multi-Hundred-Watt RTG 53 2.1.4 General Purpose Heat Source RTG 55 2.1.4.1 General Purpose Heat Source 55 2.1.4.2 GPHS-RTG System 56 2.1.5 Multi-Mission Radioisotope Thermoelectric Generator 57 2.1.6 US Flight RTGs 58 2.2 Unflown Flight RTGs 58 2.2.1.1 SNAP-1 58 2.2.1.2 SNAP-11 58 2.2.1.3 SNAP-13 58 2.2.1.4 SNAP-17 62 2.2.1.5 SNAP-29 62 2.2.1.6 Selenide Isotope Generator 63 2.2.1.7 Modular Isotopic Thermoelectric Generator 64 2.2.1.8 Modular RTG 64 2.3 Terrestrial RTGs 65 2.3.1 SNAP Terrestrial RTGs 65 2.3.1.1 SNAP-7 65 2.3.1.2 SNAP-15 66 2.3.1.3 SNAP-21 66 2.3.1.4 SNAP-23 66 2.3.2 Sentinel 25 and 100 Systems 67 2.3.3 Sentry 68 2.3.4 URIPS-P1 68 2.3.5 RG-1 69 2.3.6 BUP-500 70 2.3.7 Millibatt-1000 71 2.4 Conclusion 71 References 71 Chapter 3 US Space Flights Enabled by RTGs 75 3.1 SNAP-3B Missions (1961) 75 3.1.1 Transit 4A and Transit 4B 75 3.2 SNAP-9A Missions (1963–1964) 76 3.2.1 Transit 5BN-1, 5BN-2, and 5BN-3 76 3.3 SNAP-19 Missions (1968–1975) 78 3.3.1 Nimbus-B and Nimbus III 78 3.3.2 Pioneer 10 and 11 81 3.3.3 Viking 1 and 2 Landers 83 3.4 SNAP-27 Missions (1969–1972) 85 3.4.1 Apollo 12–17 85 3.5 Transit-RTG Mission (1972) 87 3.5.1 TRIAD 87 3.6 MHW-RTG Missions (1976–1977) 88 3.6.1 Lincoln Experimental Satellites 8 and 9 88 3.6.2 Voyager 1 and 2 90 3.7 GPHS-RTG Missions (1989–2006) 92 3.7.1 Galileo 92 3.7.2 Ulysses 93 3.7.3 Cassini 95 3.7.4 New Horizons 97 3.8 MMRTG Missions: (2011-Present (2021)) 99 3.8.1 Curiosity 99 3.8.2 Perseverance 101 3.8.3 Dragonfly–Scheduled Future Mission 102 3.9 Discussion of Flight Frequency 104 3.10 Summary of US Missions Enabled by RTGs 113 References 114 Chapter 4 Nuclear Systems Used for Space Exploration by Other Countries 117 4.1 Soviet Union 117 4.2 China 121 References 122 Chapter 5 Nuclear Physics, Radioisotope Fuels, and Protective Components 125 5.1 Introduction 125 5.2 Introduction to Nuclear Physics 126 5.2.1 The Atom 126 5.2.2 Radioactivity and Decay 128 5.2.3 Emission of Radiation 130 5.2.3.1 Alpha Decay 131 5.2.3.2 Beta Decay 132 5.2.3.3 Photon Emission 132 5.2.3.4 Neutron Emission 133 5.2.3.5 Decay Chains 134 5.2.4 Interactions of Radiation with Matter 134 5.2.4.1 Charged Particle Interactions with Matter 136 5.2.4.2 Neutral Particle Interactions with Matter 137 5.2.4.3 Biological Interactions of Radiation with Matter 140 5.3 Historic Radioisotope Fuels 142 5.3.1 Polonium-210 144 5.3.2 Cerium-144 144 5.3.3 Strontium-90 145 5.3.4 Curium-242 146 5.3.5 Curium-244 146 5.3.6 Cesium-137 147 5.3.7 Promethium-147 147 5.3.8 Thallium-204 148 5.4 Producing Modern PuO2 148 5.4.1 Cermet Target Design, Fabrication, and Irradiation 150 5.4.2 Improved Target Design 151 5.4.3 Post-Irradiation Chemical Processing 152 5.4.4 Waste Management 153 5.4.5 Conversion to Production Mode of Operation 154 5.5 Fuel, Cladding, and Encapsulations for Modern Spaceflight RTGs 155 5.5.1 Evolution of Radioisotope Heat Source Protection 155 5.5.2 General Purpose Heat Source 159 5.5.3 Fine Weave Pierced Fabric (FWPF) 160 5.5.4 Carbon-Bonded Carbon Fiber (CBCF) 161 5.5.5 Heat Transfer Considerations 162 5.5.6 Cladding 162 5.6 Summary 165 References 165 Chapter 6 A Primer on the Underlying Physics in Thermoelectrics 173 6.1 Underlying Physics in Thermoelectric Materials 173 6.1.1 Reciprocal Lattice and Brillouin Zone 175 6.1.2 Electronic Band Structure 175 6.1.3 Lattice Vibration and Phonons 178 6.2 Thermoelectric Theories and Limitations 181 6.2.1 Best Thermoelectric Materials 181 6.2.2 Imbalanced Thermoelectric Legs 183 6.3 Thermal Conductivity and Phonon Scattering 184 6.3.1 Highlights of SiGe 185 References 185 Chapter 7 End-to-End Assembly and Pre-flight Operations for RTGs 191 7.1 GPHS Assembly 191 7.2 RTG Fueling and Testing 199 7.3 RTG Delivery, Spacecraft Checkout, and RTG Integration for Flight 212 References 221 Chapter 8 Lifetime Performance of Spaceborne RTGs 223 8.1 Introduction 223 8.2 History of RTG Performance at a Glance 225 8.3 RTG Performance by Generator Type 229 8.3.1 SNAP-3B 229 8.3.2 SNAP-9A 229 8.3.3 SNAP-19B 231 8.3.4 SNAP-27 234 8.3.5 Transit-RTG 236 8.3.6 SNAP-19 237 8.3.7 Multi-Hundred Watt RTG 241 8.3.8 General Purpose Heat Source RTG 244 8.3.9 Multi-Mission RTG 247 References 250 Chapter 9 Modern Analysis Tools and Techniques for RTGs 253 9.1 Analytical Tools for Evaluating Performance Degradation and Extrapolating Future Power 253 9.1.1 Integrated Rate Law Equation 254 9.1.2 Multiple Degradation Mechanisms 255 9.1.3 Solving for k′ and x 257 9.1.4 Integrated Rate Equation 260 9.1.5 Analysis of Residuals 260 9.1.6 Rate Law Equations: RTGs versus Chemistry versus Math 261 9.1.6.1 Application to RTG Performance 262 9.2 Effects of Thermal Inventory on Lifetime Performance 262 9.2.1 Analysis of GPHS-RTG 263 9.2.2 Analysis of MMRTG 266 9.3 (Design) Life Performance Prediction 268 9.3.1 RTG’s degradation mechanisms 269 9.3.2 Physics-based RTG Life Performance Prediction 273 9.4 Radioisotope Power System Dose Estimation Tool (RPS-DET) 275 9.4.1 Motivation 275 9.4.2 RPS-DET Software Components 276 9.4.3 RPS-DET Geometries 277 9.4.4 RPS-DET Source Terms and Radiation Transport 278 9.4.5 Simulation Results 279 9.4.6 Validation and Verification 280 9.4.7 Conclusion 280 References 281 Chapter 10 Advanced US RTG Technologies in Development 285 10.1 Introduction 285 10.1.1 Background 286 10.2 Skutterudite-based Thermoelectric Converter Technology for a Potential MMRTG Retrofit 287 10.2.1 Introduction 287 10.2.2 Thermoelectric Couple and 48-Couple Module Design and Fabrication 288 10.2.3 Performance Testing of Couples and 48-Couple Module 292 10.2.4 Generator Life Performance Prediction 295 10.3 Next Generation RTG Technology Evolution 297 10.3.1 Introduction 297 10.3.2 Challenges to Reestablishing a Production Capability 300 10.3.2.1 Design Trades 300 10.3.2.2 Silicon Germanium Unicouple Production 301 10.3.2.3 Converter Assembly 302 10.3.3 Opportunities for Enhancements 304 10.4 Considerations for Emerging Commercial RTG Concepts 305 10.4.1 Introduction 305 10.4.2 Challenges for Commercial Space RTGs 306 10.4.2.1 Radioisotopes 307 10.4.2.2 Specific Power 307 10.4.2.3 Launch Approval 308 10.4.3 Launch Safety Analyses and Testing 310 10.4.3.1 Modeling Approaches 310 10.4.3.2 Safety Testing 311 10.4.3.3 Leveraging Legacy Design Concepts 311 References 313 Index 317 EULA 333 "Radioisotope Thermoelectric Generators (RTGs) produce continuous, quiet electrical power for spacecraft exploring our solar system and the space beyond. These generators use thermoelectric technologies to convert heat produced by the natural decay of radioisotopes into electrical power. Two leading thermoelectric material systems have emerged as contenders to supplant currently available thermoelectric materials. Each is at a differing level of readiness for flight. Both are poised to emerge from the laboratory and be brought to production for newer, potentially more powerful RTGs. This should enable spacecraft and mission designers to save on mass and radioisotope fuel consumption. In addition, one of the technologies is so efficient and powerful as to enable new mission types."-- Provided by publisher