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.
Table of Contents
Foreward xi
Note from the Series Editor xiii
Preface xv
Authors xix
Reviewers xxi
Acknowledgments xxiii
Glossary xxv
List of Acronyms and Abbreviations xxxiii
1 The History of the Invention of Radioisotope Thermoelectric Generators (RTGs) for Space Exploration 1
Chadwick D. Barklay
References 5
2 The History of the United States’s Flight and Terrestrial RTGs 7
Andrew J. Zillmer
2.1 Flight RTGs 7
2.1.1 SNAP Flight Program 7
2.1.1.1 Snap-3 8
2.1.1.2 Snap-9 8
2.1.1.3 Snap-19 9
2.1.1.4 Snap-27 11
2.1.2 Transit-RTG 13
2.1.3 Multi-Hundred-Watt RTG 13
2.1.4 General Purpose Heat Source RTG 15
2.1.4.1 General Purpose Heat Source 15
2.1.4.2 GPHS-RTG System 16
2.1.5 Multi-Mission Radioisotope Thermoelectric Generator 17
2.1.6 US Flight RTGs 18
2.2 Unflown Flight RTGs 18
2.2.1.1 Snap-1 18
2.2.1.2 Snap-11 18
2.2.1.3 Snap-13 18
2.2.1.4 Snap-17 22
2.2.1.5 Snap-29 22
2.2.1.6 Selenide Isotope Generator 23
2.2.1.7 Modular Isotopic Thermoelectric Generator 24
2.2.1.8 Modular RTG 24
2.3 Terrestrial RTGs 25
2.3.1 SNAP Terrestrial RTGs 25
2.3.1.1 Snap-7 25
2.3.1.2 Snap-15 26
2.3.1.3 Snap-21 26
2.3.1.4 Snap-23 26
2.3.2 Sentinel 25 and 100 Systems 27
2.3.3 Sentry 28
2.3.4 URIPS-P 1 28
2.3.5 RG-1 29
2.3.6 BUP-500 30
2.3.7 Millibatt-1000 31
2.4 Conclusion 31
References 31
3 US Space Flights Enabled by RTGs 35
Young H. Lee and Brian K. Bairstow
3.1 SNAP-3B Missions (1961) 35
3.1.1 Transit 4A and Transit 4B 35
3.2 SNAP-9A Missions (1963-1964) 36
3.2.1 Transit 5BN-1, 5BN-2, and 5BN-3 36
3.3 SNAP-19 Missions (1968-1975) 38
3.3.1 Nimbus-B and Nimbus III 38
3.3.2 Pioneer 10 and 11 41
3.3.3 Viking 1 and 2 Landers 43
3.4 SNAP-27 Missions (1969-1972) 45
3.4.1 Apollo 12-17 45
3.5 Transit-RTG Mission (1972) 47
3.5.1 TRIAD 47
3.6 MHW-RTG Missions (1976-1977) 48
3.6.1 Lincoln Experimental Satellites 8 and 9 48
3.6.2 Voyager 1 and 2 50
3.7 GPHS-RTG Missions (1989-2006) 52
3.7.1 Galileo 52
3.7.2 Ulysses 53
3.7.3 Cassini 55
3.7.4 New Horizons 57
3.8 MMRTG Missions: (2011-Present (2021)) 59
3.8.1 Curiosity 59
3.8.2 Perseverance 61
3.8.3 Dragonfly-Scheduled Future Mission 62
3.9 Discussion of Flight Frequency 64
3.10 Summary of US Missions Enabled by RTGs 73
References 74
4 Nuclear Systems Used for Space Exploration by Other Countries 77
Christofer E. Whiting
4.1 Soviet Union 77
4.2 China 81
References 82
5 Nuclear Physics, Radioisotope Fuels, and Protective Components 85
Michael 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. Whiting
5.1 Introduction 85
5.2 Introduction to Nuclear Physics 86
5.2.1 The Atom 86
5.2.2 Radioactivity and Decay 88
5.2.3 Emission of Radiation 90
5.2.3.1 Alpha Decay 91
5.2.3.2 Beta Decay 92
5.2.3.3 Photon Emission 92
5.2.3.4 Neutron Emission 93
5.2.3.5 Decay Chains 94
5.2.4 Interactions of Radiation with Matter 94
5.2.4.1 Charged Particle Interactions with Matter 96
5.2.4.2 Neutral Particle Interactions with Matter 97
5.2.4.3 Biological Interactions of Radiation with Matter 100
5.3 Historic Radioisotope Fuels 102
5.3.1 Polonium-210 104
5.3.2 Cerium-144 104
5.3.3 Strontium-90 105
5.3.4 Curium-242 106
5.3.5 Curium-244 106
5.3.6 Cesium-137 107
5.3.7 Promethium-147 107
5.3.8 Thallium-204 108
5.4 Producing Modern PuO2 108
5.4.1 Cermet Target Design, Fabrication, and Irradiation 110
5.4.2 Improved Target Design 111
5.4.3 Post-Irradiation Chemical Processing 112
5.4.4 Waste Management 113
5.4.5 Conversion to Production Mode of Operation 114
5.5 Fuel, Cladding, and Encapsulations for Modern Spaceflight RTGs 115
5.5.1 Evolution of Radioisotope Heat Source Protection 115
5.5.2 General Purpose Heat Source 119
5.5.3 Fine Weave Pierced Fabric (FWPF) 120
5.5.4 Carbon-Bonded Carbon Fiber (CBCF) 121
5.5.5 Heat Transfer Considerations 122
5.5.6 Cladding 122
5.6 Summary 125
References 125
6 A Primer on the Underlying Physics in Thermoelectrics 133
Hsin Wang
6.1 Underlying Physics in Thermoelectric Materials 133
6.1.1 Reciprocal Lattice and Brillouin Zone 135
6.1.2 Electronic Band Structure 135
6.1.3 Lattice Vibration and Phonons 138
6.2 Thermoelectric Theories and Limitations 141
6.2.1 Best Thermoelectric Materials 141
6.2.2 Imbalanced Thermoelectric Legs 143
6.3 Thermal Conductivity and Phonon Scattering 144
6.3.1 Highlights of SiGe 145
References 145
7 End-to-End Assembly and Pre-flight Operations for RTGs 151
Shad E. Davis
7.1 GPHS Assembly 151
7.2 RTG Fueling and Testing 159
7.3 RTG Delivery, Spacecraft Checkout, and RTG Integration for Flight 172
References 181
8 Lifetime Performance of Spaceborne RTGs 183
Christofer E. Whiting and David Friedrich Woerner
8.1 Introduction 183
8.2 History of RTG Performance at a Glance 185
8.3 RTG Performance by Generator Type 189
8.3.1 Snap-3B 189
8.3.2 Snap-9A 189
8.3.3 Snap-19B 191
8.3.4 Snap-27 194
8.3.5 Transit-RTG 196
8.3.6 Snap-19 197
8.3.7 Multi-Hundred Watt RTG 201
8.3.8 General Purpose Heat Source RTG 204
8.3.9 Multi-Mission RTG 207
References 210
9 Modern Analysis Tools and Techniques for RTGs 213
Christofer E. Whiting, Michael B.R. Smith, and Thierry Caillat
9.1 Analytical Tools for Evaluating Performance Degradation and Extrapolating Future Power 213
9.1.1 Integrated Rate Law Equation 214
9.1.2 Multiple Degradation Mechanisms 215
9.1.3 Solving for k′ and x 217
9.1.4 Integrated Rate Equation 220
9.1.5 Analysis of Residuals 220
9.1.6 Rate Law Equations: RTGs versus Chemistry versus Math 221
9.1.6.1 Application to RTG Performance 222
9.2 Effects of Thermal Inventory on Lifetime Performance 222
9.2.1 Analysis of GPHS-RTG 223
9.2.2 Analysis of MMRTG 226
9.3 (Design) Life Performance Prediction 228
9.3.1 RTG’s Degradation Mechanisms 229
9.3.2 Physics-based RTG Life Performance Prediction 233
9.4 Radioisotope Power System Dose Estimation Tool (RPS-DET) 235
9.4.1 Motivation 235
9.4.2 RPS-DET Software Components 236
9.4.3 RPS-DET Geometries 237
9.4.4 RPS-DET Source Terms and Radiation Transport 238
9.4.5 Simulation Results 239
9.4.6 Validation and Verification 240
9.4.7 Conclusion 240
References 241
10 Advanced US RTG Technologies in Development 245
Chadwick D. Barklay
10.1 Introduction 245
10.1.1 Background 246
10.2 Skutterudite-based Thermoelectric Converter Technology for a Potential MMRTG Retrofit 247
Thierry 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 Holgate
10.2.1 Introduction 247
10.2.2 Thermoelectric Couple and 48-Couple Module Design and Fabrication 248
10.2.3 Performance Testing of Couples and 48-Couple Module 252
10.2.4 Generator Life Performance Prediction 255
10.3 Next Generation RTG Technology Evolution 257
Chadwick D. Barklay
10.3.1 Introduction 257
10.3.2 Challenges to Reestablishing a Production Capability 260
10.3.2.1 Design Trades 260
10.3.2.2 Silicon Germanium Unicouple Production 261
10.3.2.3 Converter Assembly 262
10.3.3 Opportunities for Enhancements 264
10.4 Considerations for Emerging Commercial RTG Concepts 265
Chadwick D. Barklay
10.4.1 Introduction 265
10.4.2 Challenges for Commercial Space RTGs 266
10.4.2.1 Radioisotopes 267
10.4.2.2 Specific Power 267
10.4.2.3 Launch Approval 268
10.4.3 Launch Safety Analyses and Testing 270
10.4.3.1 Modeling Approaches 270
10.4.3.2 Safety Testing 271
10.4.3.3 Leveraging Legacy Design Concepts 271
References 273
Index 277
