A laboratory-model Hall-effect spacecraft thruster was developed that utilizes bismuth as the propellant. Xenon was used in most prior Hall-effect thrusters. Bismuth is an attractive alternative because it has a larger atomic mass, a larger electron- impact- ionization cross-section, and is cheaper and more plentiful.
The design of this thruster includes multiple temperature-control zones and other features that reduce parasitic power losses. Liquid bismuth (which melts at a temperature of 271°C) is supplied by a temperature-controlled reservoir to a vaporizer. The vaporizer exhausts to an anode/gas distributor inside a discharge channel that consists of a metal chamber upstream of ceramic exit rings. In the channel, bismuth ions are produced through an electron impact ionization process and accelerated as in other Hall-effect thrusters. The discharge region is heated by the discharge and an auxiliary anode heater, which is required to prevent bismuth condensation at low power levels and at thruster start-up. A xenon discharge is also used for preheating the discharge channel, but an anode heater could provide enough power to start the bismuth discharge directly.
This work was done by James Szabo, Charles Gasdaska, Vlad Hruby, and Mike Robin of Busek Co., Inc. for Marshall Space Flight Center. For further information, contact Sammy Nabors, MSFC Commercialization Assistance Lead, at sammy.a.nabors@ nasa.gov. Refer to MFS-32440-1.