Dan M. Goebel, PhD, is a Fellow and Senior Research Scientist at the Jet Propulsion Laboratory, and Adjunct Professor of Aerospace Engineering and Electrical Engineering at UCLA. He is a Member of the National Academy of Engineering, and also a Fellow of the National Academy of Inventors, the IEEE, the AIAA, and the American Physical Society. He is presently the Chief Engineer of the NASA Psyche Mission. Ira Katz, PhD, is an Aerospace Consultant specializing in electric propulsion and spacecraft charging. He retired from the Jet Propulsion Laboratory after leading the Electric Propulsion group and researching electric propulsion physics. Previously, he worked in industry investigating spacecraft charging and headed the team that developed the NASA Charging Analyzer Program, NASCAP. Ioannis G. Mikellides, PhD, is a Senior Research Scientist at the Jet Propulsion Laboratory and a Fellow of the AIAA. In the last three decades his research on the theory and numerical simulation of plasmas has spanned a wide range of applications, both in and beyond electric propulsion. He is also the main author of the scientific plasma codes OrCa2D and Hall2De, which have been supporting NASA’s space flight qualification of hollow cathodes and Hall thrusters.

• Note from the Series Editor xiForeword xiiiPreface xvAcknowledgments xvii1 Introduction 11.1 Electric Propulsion Background 21.2 Electric Thruster Types 31.2.1 Resistojet 31.2.2 Arcjet 41.2.3 Electrospray/FEEP Thruster 41.2.4 Ion Thruster 41.2.5 Hall Thruster 41.2.6 Magnetoplasmadynamic (MPD) Thruster 41.2.7 Pulsed Plasma Thruster (PPT) 51.2.8 Pulsed Inductive Thruster (PIT) 51.3 Electrostatic Thrusters 61.3.1 Ion Thrusters 61.3.2 Hall Thrusters 71.4 Electromagnetic Thrusters 71.4.1 Magnetoplasmadynamic Thrusters 81.4.2 Pulsed Plasma Thrusters 91.4.3 Pulsed Inductive Thrusters 91.5 Beam/Plume Characteristics 11References 122 Thruster Principles 152.1 The Rocket Equation 152.2 Force Transfer in Electric Thrusters 172.2.1 Ion Thrusters 172.2.2 Hall Thrusters 182.2.3 Electromagnetic Thrusters 192.3 Thrust 202.4 Specific Impulse 232.5 Thruster Efficiency 252.6 Power Dissipation 272.7 Neutral Densities and Ingestion 29Problems 30References 313 Basic Plasma Physics 333.1 Introduction 333.2 Maxwell’s Equations 333.3 Single Particle Motions 343.4 Particle Energies and Velocities 373.5 Plasma as a Fluid 393.5.1 Momentum Conservation 393.5.2 Particle Conservation 413.5.3 Energy Conservation 433.6 Diffusion in Partially Ionized Plasma 453.6.1 Collisions 463.6.2 Diffusion and Mobility Without a Magnetic Field 493.6.2.1 Fick’s Law and the Diffusion Equation 503.6.2.2 Ambipolar Diffusion Without a Magnetic Field 533.6.3 Diffusion Across Magnetic Fields 543.6.3.1 Classical Diffusion of Particles across B Fields 543.6.3.2 Ambipolar Diffusion Across B Fields 563.7 Sheaths at the Boundaries of Plasmas 573.7.1 Debye Sheaths 583.7.2 Pre-sheaths 603.7.3 Child-Langmuir Sheath 623.7.4 Generalized Sheath Solution 633.7.5 Double Sheaths 653.7.6 Summary of Sheath Effects 67Problems 69References 704 Hollow Cathodes 714.1 Introduction 714.2 Cathode Configurations 764.3 Thermionic Electron Emitters 804.4 Insert Region 854.5 Orifice Region 1004.6 Cathode Plume Region 1104.7 Heating and Thermal Models 1174.7.1 Hollow Cathode Heaters 1174.7.2 Heaterless Hollow Cathodes 1184.7.3 Hollow Cathode Thermal Models 1204.8 Hollow Cathode Life 1224.8.1 Dispenser Cathode Insert-Region Plasmas 1224.8.2 BaO Cathode Insert Temperature 1244.8.3 Barium Depletion Model 1274.8.4 Bulk-Material Insert Life 1304.8.5 Cathode Poisoning 1314.9 Keeper Wear and Life 1344.10 Discharge Behavior and Instabilities 1364.10.1 Discharge Modes 1364.10.2 Suppression of Instabilities and Energetic Ion Production 1414.10.3 Hollow Cathode Discharge Characteristics 143Problems 146References 1475 Ion Thruster Plasma Generators 1555.1 Introduction 1555.2 Idealized Ion Thruster Plasma Generator 1575.3 DC Discharge Ion Thrusters 1625.3.1 Generalized 0-D Ring-Cusp Ion Thruster Model 1645.3.2 Magnetic Multipole Boundaries 1665.3.3 Electron Confinement 1675.3.4 Ion Confinement at the Anode Wall 1705.3.5 Neutral and Primary Densities in the Discharge Chamber 1745.3.6 Ion and Excited Neutral Production 1755.3.7 Electron Temperature 1775.3.8 Primary Electron Density 1785.3.9 Power and Energy Balance in the Discharge Chamber 1805.3.10 Discharge Loss 1825.3.11 Discharge Stability 1875.3.12 Recycling Behavior 1895.3.13 Limitations of a 0-D Model 1925.4 Kaufman Ion Thrusters 1935.5 rf Ion Thrusters 1975.6 Microwave Ion Thrusters 2065.7 2-D Models of the Ion Thruster Discharge Chamber 2165.7.1 Neutral Atom Model 2175.7.2 Primary Electron Motion and Ionization Model 2195.7.3 Discharge Chamber Model Results 221Problems 223References 2256 Ion Thruster Accelerators 2296.1 Grid Configurations 2296.2 Ion Accelerator Basics 2346.3 Ion Optics 2376.3.1 Ion Trajectories 2376.3.2 Perveance Limits 2406.3.3 Grid Expansion and Alignment 2416.4 Electron Backstreaming 2436.5 High Voltage Considerations 2496.5.1 Electrode Breakdown 2506.5.2 Molybdenum Electrodes 2516.5.3 Carbon-Carbon Composite Materials 2536.5.4 Pyrolytic Graphite 2546.5.5 Voltage Hold-off and Conditioning in Ion Accelerators 2556.6 Ion Accelerator Grid Life 2566.6.1 Grid Models 2576.6.2 Barrel Erosion 2606.6.3 Pits and Groves Erosion 261Problems 264References 2657 Conventional Hall Thrusters 2697.1 Introduction 2697.1.1 Discharge Channel with Dielectric Walls (SPT) 2707.1.2 Discharge Channel with Metallic Walls (TAL) 2717.2 Operating Principles and Scaling 2737.2.1 Crossed-field Structure and the Hall Current 2737.2.2 Ionization Length and Scaling 2767.2.3 Plasma Potential and Current Distributions 2787.3 Performance Models 2817.3.1 Thruster Efficiency Definitions 2817.3.2 Multiply Charged Ion Correction 2847.3.3 Dominant Power Loss Mechanisms 2857.3.4 Electron Temperature 2927.3.5 Efficiency of Hall Thrusters with Dielectric Walls 2947.3.6 Efficiency of TAL Thrusters with Metallic Walls 2967.3.7 Comparison of Conventional Hall Thrusters with Dielectric and Metallic Walls 2977.4 Discharge Dynamics and Oscillations 2987.5 Channel Physics and Numerical Modeling 3017.5.1 Basic Model Equations 3017.5.1.1 Electron Motion Perpendicular to the Magnetic Field 3027.5.1.2 Electron Motion Parallel to the Magnetic Field 3047.5.1.3 Electron Continuity and Energy Conversation 3057.5.1.4 Heavy Species: Ion and Neutrals 3067.5.2 Numerical Modeling and Simulations 3087.5.2.1 Modeling in One Dimension 3087.5.2.2 Modeling in Multiple Dimensions 3117.6 Operational Life of Conventional Hall Thrusters 321Problems 326References 3288 Magnetically Shielded Hall Thrusters 3378.1 Introduction 3378.2 First Principles of Magnetic Shielding 3388.3 The Protective Capabilities of Magnetic Shielding 3408.3.1 Numerical Simulations 3408.3.2 Laboratory Experiments and Model Validation 3418.4 Magnetically Shielded Hall Thrusters with Electrically Conducting Walls 3498.5 Magnetic Shielding in Low Power Hall Thrusters 3518.6 Final Remarks on Magnetic Shielding in Hall Thrusters 353References 3559 Electromagnetic Thrusters 3619.1 Introduction 3619.2 Magnetoplasmadynamic Thrusters 3619.2.1 Self-Field MPD Thrusters 3629.2.1.1 Idealized Model of the Self-Field MPD Thruster 3639.2.1.2 Semi-empirical Model of the Self-Field MPD Thrust 3689.2.2 Applied-Field MPD Thrusters 3699.2.2.1 Empirical and Semi-empirical Thrust Models 3719.2.2.2 First-principles Thrust Model 3729.2.2.3 Lithium Applied-Field MPD Thrusters 3749.2.3 Onset Phenomenon 3769.2.3.1 Anode Starvation 3799.2.3.2 Plasma Instabilities 3809.2.3.3 Other Onset Effects 3809.2.4 MPD Thruster Performance Parameters 3809.3 Ablative Pulsed Plasma Thrusters 3829.3.1 Thruster Configurations and Performance 3839.3.1.1 Rectangular Configurations 3869.3.1.2 Coaxial Configurations 3879.3.2 Physics and Modeling 3899.3.2.1 Numerical Simulations 3899.3.2.2 First-principles Idealized Models 3929.4 Pulsed Inductive Thrusters (PIT) 3959.4.1 Thruster Performance 3979.4.2 Physics and Modeling 3989.4.2.1 Numerical Simulations 3989.4.2.2 First-principles Idealized Modeling 402References 40810 Future Directions in Electric Propulsion 41710.1 Hall Thruster Developments 41710.1.1 Alternative Propellants 41710.1.2 Nested Channel Hall Thrusters for Higher Power 41810.1.3 Double Stage Ionization and Acceleration Regions 41910.1.4 Multipole Magnetic Fields in Hall Thrusters 42010.2 Ion Thruster Developments 42110.2.1 Alternative Propellants 42110.2.2 Grid Systems for High Isp 42210.3 Helicon Thruster Development 42210.4 Magnetic Field Dependent Thrusters 42410.4.1 Rotating Magnetic Field (RMF) Thrusters 42410.4.2 Magnetic Induction Plasma Thrusters 42510.4.3 Magnetic Reconnection Thrusters 42610.5 Laser-Based Propulsion 42710.6 Solar Sails 42710.7 Hollow Cathode Discharge Thrusters 428References 43011 Electric Thruster Plumes and Spacecraft Interactions 43711.1 Introduction 43711.2 Plume Physics in Ion and Hall Thrusters 43811.2.1 Plume Measurements 43911.2.2 Flight Data 44011.2.3 Laboratory Plume Measurements 44211.3 Plume Models for Ion and Hall Thrusters 44311.3.1 Primary Beam Expansion 44311.3.2 Neutral Gas Plumes 44711.3.3 Secondary Ion Generation 44811.3.4 Combined Models and Numerical Simulations 45011.4 Spacecraft Interactions 45311.4.1 Momentum of the Plume Particles 45311.4.2 Sputtering and Contamination 45411.4.3 Plasma Interactions with Solar Arrays 45611.5 Interactions with Payloads 45811.5.1 Microwave Phase Shift 45811.5.2 Plume Plasma Optical Emission 458Problems 461References 46412 Flight Electric Thrusters 46712.1 Introduction 46712.2 Ion Thrusters 46712.3 Hall Thrusters 47612.4 Electromagnetic Thrusters 480References 481Appendix A Nomenclature 487Appendix B Gas Flow Units Conversions and Cathode Pressure Estimates 497Appendix C Energy Loss by Electrons 501Appendix D Ionization and Excitation Cross Sections for Xenon and Krypton 503Appendix E Ionization and Excitation Reaction Rates in Maxwellian plasmas 509Appendix F Electron Relaxation and Thermalization Times 511Appendix G Clausing Factor Monte Carlo Calculation 515Index 519