20-kW Bismuth Hall Thruster with Evaporative Anode

High-power Hall thrusters operating at high thrust-to-power ratios will consume and emit unprecedented amounts of xenon propellant. The inherent costs associated with xenon use have significantly hindered development of such devices. Metallic propellants, specifically bismuth, have recently emerged as potentially higher-performing, lower-cost alternatives to xenon. When used in a Hall thruster, bismuth will likely enable improved thruster efficiency, which will translate to lower spacecraft inert mass. Furthermore, the use of bismuth will reduce mission propellant costs by a factor of 200 and may reduce the cost of developing high-power thrusters by a factor of 10. As bismuth is a solid at STP, an energy-efficient means of producing and controlling bismuth vapors is a prerequisite to Hall thruster use. In this document, a unique method of propellant vapor control is proposed and a plan-of-work is described to develop a 20-kW bismuth Hall thruster. The metal propellant will be maintained in a liquid state within the primary anode using waste heat dissipation within the thruster. The propellant supply rate will be controlled through a power-sharing shim electrode, which intercepts a fraction of the plasma discharge current, thereby regulating the liquid metal temperature within the primary anode and hence the evaporation rate.