Light Metal Propellant Hall Thrusters

The feasibility of using magnesium (Mg) and zinc (Zn) vapor as Hall Effect Thruster propellant was proven. Mg and Zn are plentiful, non-toxic, low cost alternatives to xenon and krypton. Because Zn and Mg are lightweight, specific impulse of 2500-4200 s is possible at discharge voltages of 300 V, enabling the use of existing power processors for a high specific impulse system. In the program that is described, Busek demonstrated both Zn and Mg Hall thruster systems. The Zn configuration was very stable, enabling measurements of thrust, discharge oscillations, and the variation of current with magnetic field strength. The measured thrust to power with a discharge potential of 250 V was as high as 49 mN/kW. The specific impulse at 250 V, 1-kW peaked at >2100 s, +/- 16%. The breathing mode oscillation was 21-23 kHz. The Mg configuration was less fully characterized. Busek also developed and characterized under vacuum a novel wire-based feed system that can provide precise control of Zn and Mg feed rates in future thruster systems. This system also enables long term, low pressure, ambient temperature propellant storage. Zn vaporization rates up to 3 mg/s were demonstrated. Mg sublimation rates up to 0.84 mg/s were also demonstrated.

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