High-Power Plasma Propulsion at NASA-MSFC

Transcription

1 High-Power Plasma Propulsion at NASA-MSFC January 2012 Dr. Kurt Polzin Propulsion Research and Development Laboratory NASA - Marshall Space Flight Center

2 Basics of Rocketry Rocket Equation m 0 = total initial rocket mass m f = final rocket mass after thrusting u e = exhaust velocity of propellant relative to rocket v = velocity change after exhausting m propellant Requires u e v for a reasonable mass fraction Want a significant fraction of m 0 to be brought to final velocity Substantial amount of propellant is required when u e << v 2

3 What is Electric Propulsion? Chemical Rocket Chemical Energy Thermal Energy Directed Kinetic Energy Electric c Rocket Electrical l Energy Radiators Power source and converter Thermal Energy Electromagnetic Field Energy Directed Kinetic Energy Directed Kinetic Energy Thrusters 3

4 Electric Propulsion Mass Implications Power source is decoupled from propellant No longer constrained by the energy available in chemical bonds Electrically accelerate propellants to high velocities (u e v) Tempered by mass of power supply, conversion efficiency, etc. 4

5 Types of Electric Propulsion Electrothermal Electrical energy into thermal energy Large number on-orbit orbit Electrostatic Applied electric field directly accelerates ions Increasing use on-orbit / in deep space Electromagnetic (Plasma) Interacting currents and magnetic fields directly accelerate plasma 5

6 Usage Through the Years

7 Usage Through the Years

8 Usage Through the Years

9 Usage Through the Years

10 Recent High-Profile EP Missions ESA s Smart (Moon) JAXA s Hayabusa (Itokawa) NASA s Dawn USAF AEHF (Vesta and Ceres) 2010 (Geo Orbit) 10

11 EP at MSFC Pulsed Inductive Thrusters High power, high thrust density Electrodeless (requires high power switches) Many propellant options Impulse ~ 0.1 N-s, I sp ~ 2000-s to s High impulse maneuvers, primary planetary propulsion Research level (single shot, η t ~ 50% on ammonia) Higher thrust density enables this: Instead of this! *From NASA CR , by C.L. Dailey and R.H. Lovberg, 1993 See also K.A. Polzin, J. Propuls. Power, Vol. 27, No. 3,

12 Pulsed Inductive Thruster Characteristics High voltage (15 kv) and energy (4 kj/pulse) Complexity (18 capacitors, 18 switches) Stringent switching requirements Simultaneous closing of 18 switches High voltage holdoff, high current switching Presently spark gap switched Difficult to scale to small size Separate ionization and acceleration mechanisms Preionization lowers energy/voltage required to operate ~100 J/pulse vs. 4 kj/pulse All other advantages of inductive acceleration Easier to scale to small size 12

13 Thruster Development Flat-plate geometry Conical geometry 13

14 Critical Issues - Preionization Helicon discharge (~1000 W) MHz Microwave-driven ECR discharge (~1 kw) 2.45 GHz Inductively-coupled discharge (35-50 W) ~ MHz 14

15 Critical Issues - Continued Switching High voltage holdoff (multiple kv) High current conduction (10s of ka) Fast (> 100 ka/µs rise time) Repetition rate (> 100 Hz for high power) Fast turn off / reset for next pulse Pulsed Gas Injection Power systems Fast open and close (1-3 ms total) Transform spacecraft bus power to current / Low latency in propellant lines voltage needed by thruster Low leak rate (0.001 sccs GHe) DC / AC input power Lifetime ( pulses) Repetitive capacitor charging to multiple kv Charging rate commensurate with capacitor switching capabilities Operate in environment (vacuum) Remove / dissipate heat in system 15

16 Measurement at MSFC High-fidelity thrust stand Thrust levels ~1 mn 1 N (50 µn resolution) Impulsive resolution below 1 mn-s * Steady-state or pulsed in-situit calibration *Rev. Sci. Instrum., by Wong, Toftul, Polzin, Pearson, Feb

17 For Information on Co-op / Internship Cooperative Education Internships Opportunities listed under the links "Higher Education" and "Other Educational Opportunities." Mona Miller (mona.miller@nasa.gov) Tina Haymaker (tina.c.haymaker@nasa.gov) To apply for internships nasa Student Opportunity PODCASTS available at 17

18 Contact Dr. Kurt Polzin Propulsion Research and Development Laboratory NASA-Marshall Space Flight Center 18