Description
Book SynopsisFundamentals of Electric Propulsion Understand the fundamental basis of spaceflight with this cutting-edge guide
As spacecraft engineering continues to advance, so too do the propulsion methods by which human beings can seek out the stars. Ion thrusters and Hall thrusters have been the subject of considerable innovation in recent years, and spacecraft propulsion has never been more efficient. For professionals within and adjacent to spacecraft engineering, this is critical knowledge that can alter the future of space flight.
Fundamentals of Electric Propulsion offers a thorough grounding in electric propulsion for spacecraft, particularly the features and mechanisms underlying Ion and Hall thrusters. Updated in the light of rapidly expanding knowledge, the second edition of this essential guide detailed coverage of thruster principles, plasma physics, and more. It reflects the historic output of the legendary Jet Propulsion Laboratory and promises to conti
Table of Contents
Note from the Series Editor xi
Foreword xiii
Preface xv
Acknowledgments xvii
1 Introduction 1
1.1 Electric Propulsion Background 2
1.2 Electric Thruster Types 3
1.2.1 Resistojet 3
1.2.2 Arcjet 4
1.2.3 Electrospray/FEEP Thruster 4
1.2.4 Ion Thruster 4
1.2.5 Hall Thruster 4
1.2.6 Magnetoplasmadynamic (MPD) Thruster 4
1.2.7 Pulsed Plasma Thruster (PPT) 5
1.2.8 Pulsed Inductive Thruster (PIT) 5
1.3 Electrostatic Thrusters 6
1.3.1 Ion Thrusters 6
1.3.2 Hall Thrusters 7
1.4 Electromagnetic Thrusters 7
1.4.1 Magnetoplasmadynamic Thrusters 8
1.4.2 Pulsed Plasma Thrusters 9
1.4.3 Pulsed Inductive Thrusters 9
1.5 Beam/Plume Characteristics 11
References 12
2 Thruster Principles 15
2.1 The Rocket Equation 15
2.2 Force Transfer in Electric Thrusters 17
2.2.1 Ion Thrusters 17
2.2.2 Hall Thrusters 18
2.2.3 Electromagnetic Thrusters 19
2.3 Thrust 20
2.4 Specific Impulse 23
2.5 Thruster Efficiency 25
2.6 Power Dissipation 27
2.7 Neutral Densities and Ingestion 29
Problems 30
References 31
3 Basic Plasma Physics 33
3.1 Introduction 33
3.2 Maxwell’s Equations 33
3.3 Single Particle Motions 34
3.4 Particle Energies and Velocities 37
3.5 Plasma as a Fluid 39
3.5.1 Momentum Conservation 39
3.5.2 Particle Conservation 41
3.5.3 Energy Conservation 43
3.6 Diffusion in Partially Ionized Plasma 45
3.6.1 Collisions 46
3.6.2 Diffusion and Mobility Without a Magnetic Field 49
3.6.2.1 Fick’s Law and the Diffusion Equation 50
3.6.2.2 Ambipolar Diffusion Without a Magnetic Field 53
3.6.3 Diffusion Across Magnetic Fields 54
3.6.3.1 Classical Diffusion of Particles across B Fields 54
3.6.3.2 Ambipolar Diffusion Across B Fields 56
3.7 Sheaths at the Boundaries of Plasmas 57
3.7.1 Debye Sheaths 58
3.7.2 Pre-sheaths 60
3.7.3 Child-Langmuir Sheath 62
3.7.4 Generalized Sheath Solution 63
3.7.5 Double Sheaths 65
3.7.6 Summary of Sheath Effects 67
Problems 69
References 70
4 Hollow Cathodes 71
4.1 Introduction 71
4.2 Cathode Configurations 76
4.3 Thermionic Electron Emitters 80
4.4 Insert Region 85
4.5 Orifice Region 100
4.6 Cathode Plume Region 110
4.7 Heating and Thermal Models 117
4.7.1 Hollow Cathode Heaters 117
4.7.2 Heaterless Hollow Cathodes 118
4.7.3 Hollow Cathode Thermal Models 120
4.8 Hollow Cathode Life 122
4.8.1 Dispenser Cathode Insert-Region Plasmas 122
4.8.2 BaO Cathode Insert Temperature 124
4.8.3 Barium Depletion Model 127
4.8.4 Bulk-Material Insert Life 130
4.8.5 Cathode Poisoning 131
4.9 Keeper Wear and Life 134
4.10 Discharge Behavior and Instabilities 136
4.10.1 Discharge Modes 136
4.10.2 Suppression of Instabilities and Energetic Ion Production 141
4.10.3 Hollow Cathode Discharge Characteristics 143
Problems 146
References 147
5 Ion Thruster Plasma Generators 155
5.1 Introduction 155
5.2 Idealized Ion Thruster Plasma Generator 157
5.3 DC Discharge Ion Thrusters 162
5.3.1 Generalized 0-D Ring-Cusp Ion Thruster Model 164
5.3.2 Magnetic Multipole Boundaries 166
5.3.3 Electron Confinement 167
5.3.4 Ion Confinement at the Anode Wall 170
5.3.5 Neutral and Primary Densities in the Discharge Chamber 174
5.3.6 Ion and Excited Neutral Production 175
5.3.7 Electron Temperature 177
5.3.8 Primary Electron Density 178
5.3.9 Power and Energy Balance in the Discharge Chamber 180
5.3.10 Discharge Loss 182
5.3.11 Discharge Stability 187
5.3.12 Recycling Behavior 189
5.3.13 Limitations of a 0-D Model 192
5.4 Kaufman Ion Thrusters 193
5.5 rf Ion Thrusters 197
5.6 Microwave Ion Thrusters 206
5.7 2-D Models of the Ion Thruster Discharge Chamber 216
5.7.1 Neutral Atom Model 217
5.7.2 Primary Electron Motion and Ionization Model 219
5.7.3 Discharge Chamber Model Results 221
Problems 223
References 225
6 Ion Thruster Accelerators 229
6.1 Grid Configurations 229
6.2 Ion Accelerator Basics 234
6.3 Ion Optics 237
6.3.1 Ion Trajectories 237
6.3.2 Perveance Limits 240
6.3.3 Grid Expansion and Alignment 241
6.4 Electron Backstreaming 243
6.5 High Voltage Considerations 249
6.5.1 Electrode Breakdown 250
6.5.2 Molybdenum Electrodes 251
6.5.3 Carbon-Carbon Composite Materials 253
6.5.4 Pyrolytic Graphite 254
6.5.5 Voltage Hold-off and Conditioning in Ion Accelerators 255
6.6 Ion Accelerator Grid Life 256
6.6.1 Grid Models 257
6.6.2 Barrel Erosion 260
6.6.3 Pits and Groves Erosion 261
Problems 264
References 265
7 Conventional Hall Thrusters 269
7.1 Introduction 269
7.1.1 Discharge Channel with Dielectric Walls (SPT) 270
7.1.2 Discharge Channel with Metallic Walls (TAL) 271
7.2 Operating Principles and Scaling 273
7.2.1 Crossed-field Structure and the Hall Current 273
7.2.2 Ionization Length and Scaling 276
7.2.3 Plasma Potential and Current Distributions 278
7.3 Performance Models 281
7.3.1 Thruster Efficiency Definitions 281
7.3.2 Multiply Charged Ion Correction 284
7.3.3 Dominant Power Loss Mechanisms 285
7.3.4 Electron Temperature 292
7.3.5 Efficiency of Hall Thrusters with Dielectric Walls 294
7.3.6 Efficiency of TAL Thrusters with Metallic Walls 296
7.3.7 Comparison of Conventional Hall Thrusters with Dielectric and Metallic Walls 297
7.4 Discharge Dynamics and Oscillations 298
7.5 Channel Physics and Numerical Modeling 301
7.5.1 Basic Model Equations 301
7.5.1.1 Electron Motion Perpendicular to the Magnetic Field 302
7.5.1.2 Electron Motion Parallel to the Magnetic Field 304
7.5.1.3 Electron Continuity and Energy Conversation 305
7.5.1.4 Heavy Species: Ion and Neutrals 306
7.5.2 Numerical Modeling and Simulations 308
7.5.2.1 Modeling in One Dimension 308
7.5.2.2 Modeling in Multiple Dimensions 311
7.6 Operational Life of Conventional Hall Thrusters 321
Problems 326
References 328
8 Magnetically Shielded Hall Thrusters 337
8.1 Introduction 337
8.2 First Principles of Magnetic Shielding 338
8.3 The Protective Capabilities of Magnetic Shielding 340
8.3.1 Numerical Simulations 340
8.3.2 Laboratory Experiments and Model Validation 341
8.4 Magnetically Shielded Hall Thrusters with Electrically Conducting Walls 349
8.5 Magnetic Shielding in Low Power Hall Thrusters 351
8.6 Final Remarks on Magnetic Shielding in Hall Thrusters 353
References 355
9 Electromagnetic Thrusters 361
9.1 Introduction 361
9.2 Magnetoplasmadynamic Thrusters 361
9.2.1 Self-Field MPD Thrusters 362
9.2.1.1 Idealized Model of the Self-Field MPD Thruster 363
9.2.1.2 Semi-empirical Model of the Self-Field MPD Thrust 368
9.2.2 Applied-Field MPD Thrusters 369
9.2.2.1 Empirical and Semi-empirical Thrust Models 371
9.2.2.2 First-principles Thrust Model 372
9.2.2.3 Lithium Applied-Field MPD Thrusters 374
9.2.3 Onset Phenomenon 376
9.2.3.1 Anode Starvation 379
9.2.3.2 Plasma Instabilities 380
9.2.3.3 Other Onset Effects 380
9.2.4 MPD Thruster Performance Parameters 380
9.3 Ablative Pulsed Plasma Thrusters 382
9.3.1 Thruster Configurations and Performance 383
9.3.1.1 Rectangular Configurations 386
9.3.1.2 Coaxial Configurations 387
9.3.2 Physics and Modeling 389
9.3.2.1 Numerical Simulations 389
9.3.2.2 First-principles Idealized Models 392
9.4 Pulsed Inductive Thrusters (PIT) 395
9.4.1 Thruster Performance 397
9.4.2 Physics and Modeling 398
9.4.2.1 Numerical Simulations 398
9.4.2.2 First-principles Idealized Modeling 402
References 408
10 Future Directions in Electric Propulsion 417
10.1 Hall Thruster Developments 417
10.1.1 Alternative Propellants 417
10.1.2 Nested Channel Hall Thrusters for Higher Power 418
10.1.3 Double Stage Ionization and Acceleration Regions 419
10.1.4 Multipole Magnetic Fields in Hall Thrusters 420
10.2 Ion Thruster Developments 421
10.2.1 Alternative Propellants 421
10.2.2 Grid Systems for High Isp 422
10.3 Helicon Thruster Development 422
10.4 Magnetic Field Dependent Thrusters 424
10.4.1 Rotating Magnetic Field (RMF) Thrusters 424
10.4.2 Magnetic Induction Plasma Thrusters 425
10.4.3 Magnetic Reconnection Thrusters 426
10.5 Laser-Based Propulsion 427
10.6 Solar Sails 427
10.7 Hollow Cathode Discharge Thrusters 428
References 430
11 Electric Thruster Plumes and Spacecraft Interactions 437
11.1 Introduction 437
11.2 Plume Physics in Ion and Hall Thrusters 438
11.2.1 Plume Measurements 439
11.2.2 Flight Data 440
11.2.3 Laboratory Plume Measurements 442
11.3 Plume Models for Ion and Hall Thrusters 443
11.3.1 Primary Beam Expansion 443
11.3.2 Neutral Gas Plumes 447
11.3.3 Secondary Ion Generation 448
11.3.4 Combined Models and Numerical Simulations 450
11.4 Spacecraft Interactions 453
11.4.1 Momentum of the Plume Particles 453
11.4.2 Sputtering and Contamination 454
11.4.3 Plasma Interactions with Solar Arrays 456
11.5 Interactions with Payloads 458
11.5.1 Microwave Phase Shift 458
11.5.2 Plume Plasma Optical Emission 458
Problems 461
References 464
12 Flight Electric Thrusters 467
12.1 Introduction 467
12.2 Ion Thrusters 467
12.3 Hall Thrusters 476
12.4 Electromagnetic Thrusters 480
References 481
Appendix A Nomenclature 487
Appendix B Gas Flow Units Conversions and Cathode Pressure Estimates 497
Appendix C Energy Loss by Electrons 501
Appendix D Ionization and Excitation Cross Sections for Xenon and Krypton 503
Appendix E Ionization and Excitation Reaction Rates in Maxwellian plasmas 509
Appendix F Electron Relaxation and Thermalization Times 511
Appendix G Clausing Factor Monte Carlo Calculation 515
Index 519
