An automated mass flow control system for condensable propellant thrusters was demonstrated. The control system has the ability to arrest thermal runaway in a direct-evaporation feed system and stabilize the discharge current during voltage-limited operation of a magnesium-fueled Hall-effect thruster. The system supplemented plasma discharge heating at the evaporative anode with a resistive heater located behind the anode. Steady-state operation at constant voltage with discharge current variations less than 0.35 A was demonstrated for 60 minutes. A thrust of 44 mN was measured at a discharge voltage of 300 volts at 6 Amps, yielding a thrust-to-power of 24.4 mN/kW. A thrust of 50 mN was measured at a discharge voltage of 300 volts at 7 Amps, also yielding a thrust-to-power of 23.8 mN/kW. For a thruster operating at 2.1 kW, the steady-state supplemental heater power was 136 watts representing only 6% of the total system power.
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