High-Power Plasma Propulsion at NASA-MSFCJanuary 2012

Dr. Kurt Polzin (kurt.a.polzin@nasa.gov) Propulsion Research and Development LaboratoryNASA - Marshall Space Flight Center

Basics of Rocketry

Rocket Equation

• m0 = total initial rocket mass

• m = final rocket mass after thrusting• mf = final rocket mass after thrusting

• ue = exhaust velocity of propellant relative to rocket

• ∆v = velocity change after exhausting ∆m propellant

Requires ue ≈ ∆v for a reasonable mass fraction• Want a significant fraction of m0 to be brought to final velocity• Substantial amount of propellant is required when ue << ∆v

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What is Electric Propulsion?

• Chemical Rocket Chemical Energy

Thermal Energy

Directed Kinetic Energy

• “Electric” Rocket

Directed Kinetic Energy

El t i l E Power source ec c oc e Electrical Energy

Thermal Energy Electromagnetic Field Energy

and converter

Radiators

Directed Kinetic Energy Directed Kinetic EnergyThrusters

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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 ≈ ∆v)Electrically accelerate propellants to high velocities (ue ≈ ∆v)• Tempered by mass of power supply, conversion efficiency, etc.

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Types of Electric Propulsion

• Electrothermal– Electrical energy into thermal energy

Large number on orbit– Large number on-orbit

• Electrostatic– Applied electric field directly accelerates ions– Increasing use on-orbit / in deep space

• Electromagnetic (Plasma)g ( )– Interacting currents and magnetic fields

directly accelerate plasma

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Usage Through the Years19851985

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Usage Through the Years19941994

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Usage Through the Years20012001

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Usage Through the Years20102010

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Recent High-Profile EP Missions

ESA’s Smart 12003-2006 (Moon)

JAXA’s Hayabusa2003-2010 (Itokawa)

NASA’s Dawn USAF AEHF

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2007-2015 (Vesta and Ceres) 2010 (Geo Orbit)

EP at MSFC – Pulsed Inductive Thrusters• High power, high thrust density• Electrodeless (requires high power switches)• Many propellant options

Imp lse 0 1 N s I 2000 s to 10000 s• Impulse ~ 0.1 N-s, Isp ~ 2000-s to 10000-s• High impulse maneuvers, primary planetary propulsion• Research level (single shot, ηt ~ 50% on ammonia)

Higher thrustHigher thrust density enables

this:

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Instead of this!

*From NASA CR-191155, by C.L. Dailey and R.H. Lovberg, 1993

See also K.A. Polzin, J. Propuls. Power, Vol. 27, No. 3, 2011.

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

• Separate ionization and acceleration mechanisms

• Preionization lowers energy/voltage required• Simultaneous closing of 18 switches• High voltage holdoff, high current switching• Presently spark gap switched

Preionization lowers energy/voltage required to operate

• ~100 J/pulse vs. 4 kJ/pulse• All other advantages of inductive acceleration

• Difficult to scale to small size• Easier to scale to small size

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Thruster Development

Flat-plate geometry Conical geometry

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Critical Issues - Preionization

Helicon discharge ( 1000 W)(~1000 W)

13.56 MHz

Microwave-driven ECR discharge (~1 kW)2.45 GHz

Inductively-coupled discharge (35-50 W)~600-900 MHz

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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)• Low latency in propellant lines• Low leak rate (0.001 sccs GHe)• Lifetime (108 109 pulses)

• Transform spacecraft bus power to current / voltage needed by thruster

• DC / AC input power• Repetitive capacitor charging to multiple kV• Lifetime (108-109 pulses) Repetitive capacitor charging to multiple kV• Charging rate commensurate with capacitor

switching capabilities• Operate in environment (vacuum)

• Remove / dissipate heat in system

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• Remove / dissipate heat in system

Measurement at MSFC

High-fidelity thrust stand• Thrust levels ~1 mN – 1 N (50 µN resolution)• Impulsive resolution below 1 mN-s *

St d t t l d i it lib ti• Steady-state or pulsed in-situ calibration

16*Rev. Sci. Instrum., by Wong, Toftul, Polzin, Pearson, Feb. 2012

For Information on Co-op / Internship

• Cooperative Education – http://coop.msfc.nasa.gov

• Internships – http://www.nasa.gov/centers/marshall/educationp p g– Opportunities listed under the links "Higher Education" and "Other Educational

Opportunities." – Mona Miller (mona.miller@nasa.gov)

Ti H k (ti h k @ )– Tina Haymaker (tina.c.haymaker@nasa.gov)

• To apply for internships – http://intern nasa gov/To apply for internships http://intern.nasa.gov/

• Student Opportunity PODCASTS available at www.nasa.gov/nsopp y g

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Contact

Dr. Kurt Polzinkurt.a.polzin@nasa.gov

Propulsion Research and Development Laboratory18

Propulsion Research and Development LaboratoryNASA-Marshall Space Flight Center