Microwave Electrothermal Thruster Performance

• Published in: Journal of propulsion and power 2007-01, Vol.23 (1), p.27-34
• Main Authors: Diamant, Kevin D, Zeigler, Byron L, Cohen, Ronald B
• Format: Article
• Language: English
• ISSN: 0748-4658; 1533-3876
• DOI: 10.2514/1.19571

Thrust, specific impulse, thrust efficiency, and coupling efficiency were measured for a nominally 1 kW microwave electrothermal thruster operating on He, N2, and N20, and for a 5 kW model operating on water. For He, N2, and N20, thrust varied from approximately 100 to 700 mN at discharge pressures from 6.7 x.104 to 2.7 x 105 Pa and magnetron input powers from 900 to 1500 W. Thrust measurements agree well with calculations assuming one-dimensional, isentropic flow of a perfect gas with constant specific heats. Peak specific impulses for He, N2, and N20 were 418, 243, and 209 s, respectively. Water was run at magnetron input powers from 2.1 to 4.1 kW and discharge pressures from 4.0 x 104 to 1.5 x 105 Pa. Thrust varied from approximately 100 to 250 niN with a peak specific impulse of 428 s. Incorporating an impedance matching capability improved coupling efficiency with water to over 96%, but did not increase specific impulse. Measurements with a residual gas analyzer indicate that the water plume may be 50 to 70% dissociated, and that the lack of dependence of specific impulse on specific energy results from a tradeoff between dissociation losses at low specific energy and heating of the thruster body at high specific energy.