David Friedrich Woerner is the Systems Formulation manager for NASA's Radioisotope Power Systems Program (RPSP) where he oversees several RPS developments. Before joining the RPSP, he oversaw the MMRTG's development and integration for the Mars Science Laboratory Project, and he was the MMRTG and Launch Services office manager for the MSL Project that successfully landed the MMRTG-powered Curiosity rover on Mars on August 6, 2012. He has won numerous NASA awards including earning NASA's Exceptional Service and Exceptional Achievement Medals.

• Foreward xiNote from the Series Editor xiiiPreface xvAuthors xixReviewers xxiAcknowledgments xxiiiGlossary xxvList of Acronyms and Abbreviations xxxiii1 The History of the Invention of Radioisotope Thermoelectric Generators (RTGs) for Space Exploration 1Chadwick D. BarklayReferences 52 The History of the United States’s Flight and Terrestrial RTGs 7Andrew J. Zillmer2.1 Flight RTGs 72.1.1 SNAP Flight Program 72.1.1.1 Snap-3 82.1.1.2 Snap-9 82.1.1.3 Snap-19 92.1.1.4 Snap-27 112.1.2 Transit-RTG 132.1.3 Multi-Hundred-Watt RTG 132.1.4 General Purpose Heat Source RTG 152.1.4.1 General Purpose Heat Source 152.1.4.2 GPHS-RTG System 162.1.5 Multi-Mission Radioisotope Thermoelectric Generator 172.1.6 US Flight RTGs 182.2 Unflown Flight RTGs 182.2.1.1 Snap-1 182.2.1.2 Snap-11 182.2.1.3 Snap-13 182.2.1.4 Snap-17 222.2.1.5 Snap-29 222.2.1.6 Selenide Isotope Generator 232.2.1.7 Modular Isotopic Thermoelectric Generator 242.2.1.8 Modular RTG 242.3 Terrestrial RTGs 252.3.1 SNAP Terrestrial RTGs 252.3.1.1 Snap-7 252.3.1.2 Snap-15 262.3.1.3 Snap-21 262.3.1.4 Snap-23 262.3.2 Sentinel 25 and 100 Systems 272.3.3 Sentry 282.3.4 URIPS-P 1 282.3.5 RG-1 292.3.6 BUP-500 302.3.7 Millibatt-1000 312.4 Conclusion 31References 313 US Space Flights Enabled by RTGs 35Young H. Lee and Brian K. Bairstow3.1 SNAP-3B Missions (1961) 353.1.1 Transit 4A and Transit 4B 353.2 SNAP-9A Missions (1963–1964) 363.2.1 Transit 5BN-1, 5BN-2, and 5BN-3 363.3 SNAP-19 Missions (1968–1975) 383.3.1 Nimbus-B and Nimbus III 383.3.2 Pioneer 10 and 11 413.3.3 Viking 1 and 2 Landers 433.4 SNAP-27 Missions (1969–1972) 453.4.1 Apollo 12–17 453.5 Transit-RTG Mission (1972) 473.5.1 TRIAD 473.6 MHW-RTG Missions (1976–1977) 483.6.1 Lincoln Experimental Satellites 8 and 9 483.6.2 Voyager 1 and 2 503.7 GPHS-RTG Missions (1989–2006) 523.7.1 Galileo 523.7.2 Ulysses 533.7.3 Cassini 553.7.4 New Horizons 573.8 MMRTG Missions: (2011-Present (2021)) 593.8.1 Curiosity 593.8.2 Perseverance 613.8.3 Dragonfly–Scheduled Future Mission 623.9 Discussion of Flight Frequency 643.10 Summary of US Missions Enabled by RTGs 73References 744 Nuclear Systems Used for Space Exploration by Other Countries 77Christofer E. Whiting4.1 Soviet Union 774.2 China 81References 825 Nuclear Physics, Radioisotope Fuels, and Protective Components 85Michael B.R. Smith, Emory D. Collins, David W. DePaoli, Nidia C. Gallego, Lawrence H. Heilbronn, Chris L. Jensen, Kaara K. Patton, Glenn R. Romanoski, George B. Ulrich, Robert M. Wham, and Christofer E. Whiting5.1 Introduction 855.2 Introduction to Nuclear Physics 865.2.1 The Atom 865.2.2 Radioactivity and Decay 885.2.3 Emission of Radiation 905.2.3.1 Alpha Decay 915.2.3.2 Beta Decay 925.2.3.3 Photon Emission 925.2.3.4 Neutron Emission 935.2.3.5 Decay Chains 945.2.4 Interactions of Radiation with Matter 945.2.4.1 Charged Particle Interactions with Matter 965.2.4.2 Neutral Particle Interactions with Matter 975.2.4.3 Biological Interactions of Radiation with Matter 1005.3 Historic Radioisotope Fuels 1025.3.1 Polonium-210 1045.3.2 Cerium-144 1045.3.3 Strontium-90 1055.3.4 Curium-242 1065.3.5 Curium-244 1065.3.6 Cesium-137 1075.3.7 Promethium-147 1075.3.8 Thallium-204 1085.4 Producing Modern PuO2 1085.4.1 Cermet Target Design, Fabrication, and Irradiation 1105.4.2 Improved Target Design 1115.4.3 Post-Irradiation Chemical Processing 1125.4.4 Waste Management 1135.4.5 Conversion to Production Mode of Operation 1145.5 Fuel, Cladding, and Encapsulations for Modern Spaceflight RTGs 1155.5.1 Evolution of Radioisotope Heat Source Protection 1155.5.2 General Purpose Heat Source 1195.5.3 Fine Weave Pierced Fabric (FWPF) 1205.5.4 Carbon-Bonded Carbon Fiber (CBCF) 1215.5.5 Heat Transfer Considerations 1225.5.6 Cladding 1225.6 Summary 125References 1256 A Primer on the Underlying Physics in Thermoelectrics 133Hsin Wang6.1 Underlying Physics in Thermoelectric Materials 1336.1.1 Reciprocal Lattice and Brillouin Zone 1356.1.2 Electronic Band Structure 1356.1.3 Lattice Vibration and Phonons 1386.2 Thermoelectric Theories and Limitations 1416.2.1 Best Thermoelectric Materials 1416.2.2 Imbalanced Thermoelectric Legs 1436.3 Thermal Conductivity and Phonon Scattering 1446.3.1 Highlights of SiGe 145References 1457 End-to-End Assembly and Pre-flight Operations for RTGs 151Shad E. Davis7.1 GPHS Assembly 1517.2 RTG Fueling and Testing 1597.3 RTG Delivery, Spacecraft Checkout, and RTG Integration for Flight 172References 1818 Lifetime Performance of Spaceborne RTGs 183Christofer E. Whiting and David Friedrich Woerner8.1 Introduction 1838.2 History of RTG Performance at a Glance 1858.3 RTG Performance by Generator Type 1898.3.1 Snap-3B 1898.3.2 Snap-9A 1898.3.3 Snap-19B 1918.3.4 Snap-27 1948.3.5 Transit-RTG 1968.3.6 Snap-19 1978.3.7 Multi-Hundred Watt RTG 2018.3.8 General Purpose Heat Source RTG 2048.3.9 Multi-Mission RTG 207References 2109 Modern Analysis Tools and Techniques for RTGs 213Christofer E. Whiting, Michael B.R. Smith, and Thierry Caillat9.1 Analytical Tools for Evaluating Performance Degradation and Extrapolating Future Power 2139.1.1 Integrated Rate Law Equation 2149.1.2 Multiple Degradation Mechanisms 2159.1.3 Solving for k′ and x 2179.1.4 Integrated Rate Equation 2209.1.5 Analysis of Residuals 2209.1.6 Rate Law Equations: RTGs versus Chemistry versus Math 2219.1.6.1 Application to RTG Performance 2229.2 Effects of Thermal Inventory on Lifetime Performance 2229.2.1 Analysis of GPHS-RTG 2239.2.2 Analysis of MMRTG 2269.3 (Design) Life Performance Prediction 2289.3.1 RTG’s Degradation Mechanisms 2299.3.2 Physics-based RTG Life Performance Prediction 2339.4 Radioisotope Power System Dose Estimation Tool (RPS-DET) 2359.4.1 Motivation 2359.4.2 RPS-DET Software Components 2369.4.3 RPS-DET Geometries 2379.4.4 RPS-DET Source Terms and Radiation Transport 2389.4.5 Simulation Results 2399.4.6 Validation and Verification 2409.4.7 Conclusion 240References 24110 Advanced US RTG Technologies in Development 245Chadwick D. Barklay10.1 Introduction 24510.1.1 Background 24610.2 Skutterudite-based Thermoelectric Converter Technology for a Potential MMRTG Retrofit 247Thierry Caillat, Stan Pinkowski, Ike C. Chi, Kevin L. Smith, Jong-Ah Paik, Brian Phan, Ying Song, Joe VanderVeer, Russell Bennett, Steve Keyser, Patrick E. Frye, Karl A. Wefers, Andrew M. Lane, and Tim Holgate10.2.1 Introduction 24710.2.2 Thermoelectric Couple and 48-Couple Module Design and Fabrication 24810.2.3 Performance Testing of Couples and 48-Couple Module 25210.2.4 Generator Life Performance Prediction 25510.3 Next Generation RTG Technology Evolution 257Chadwick D. Barklay10.3.1 Introduction 25710.3.2 Challenges to Reestablishing a Production Capability 26010.3.2.1 Design Trades 26010.3.2.2 Silicon Germanium Unicouple Production 26110.3.2.3 Converter Assembly 26210.3.3 Opportunities for Enhancements 26410.4 Considerations for Emerging Commercial RTG Concepts 265Chadwick D. Barklay10.4.1 Introduction 26510.4.2 Challenges for Commercial Space RTGs 26610.4.2.1 Radioisotopes 26710.4.2.2 Specific Power 26710.4.2.3 Launch Approval 26810.4.3 Launch Safety Analyses and Testing 27010.4.3.1 Modeling Approaches 27010.4.3.2 Safety Testing 27110.4.3.3 Leveraging Legacy Design Concepts 271References 273Index 277