Magnesium Hall Thruster with Active Thermal Mass Flow Control

An active thermal mass flow control system for condensable propellant Hall-effect 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 2 kW magnesium-fueled Hall-effect thruster. The system supplemented plasma discharge heating at the evaporative anode with a resistive heater located behind the anode. A proportional-integral-derivative control algorithm was implemented to enable automated operation of the mass flow control system using the discharge current as the measured variable and the anode heater current as the controlled parameter. Steady-state operation at constant voltage with discharge current excursions less than 0.35 A was demonstrated for 70 min. A thrust of 44 mN was measured at a discharge voltage of 300 V at 6 A, yielding a thrust-to-power ratio of 24.4±0.8 mN/kW. A thrust of 50 mN was measured at a discharge voltage of 300 V at 7 A, yielding a thrust-to-power ratio of 23.8±0.6 mN/kW. For a thruster operating at 2.1 kW, the steady-state supplemental heater power was 136 W, representing only 6% of the total system power.