Arcjet Plasma Neutralization of Hall Thrusters, Part 1: Hybrid Thruster Mission Analysis

Abstract

Clustering multiple thrusters has emerged as a favored option for extending Hall effect thruster propulsion to very high powers (100‐150 kW). However, there are inherent difficulties in the simultaneous neutralization of several Hall effect thrusters. Chief among these is the issue of unequal current sharing among multiple cathodes. For this reason, it might prove advantageous to use a single, high current neutralizer. Conventional Hall effect thruster neutralizers, hollow cathodes, typically consume 10% of the propellant flow and produce little or no thrust. An arcjet is an electrothermal electric thruster with moderate efficiency and specific impulse ranges. It is also a high plasma density device that is capable of supporting and amplifying electron current through volume ionization and is capable of neutralizing single or clusters of Hall effect thrusters. By using an arcjet as a neutralizer, Hall effect thrusters will also produce useful thrust from their neutralizers. Because of the arcjet’s lower specific impulse, the hybrid arcjet-Hall system will have a lower specific impulse than that of a pure Hall effect system. However by choosing suitable propellants, the hybrid Hall cluster will retain the high thrust efficiencies typical of pure Hall effect systems with the added benefit of lower total wet mass for select missions caused by a higher system thrust density. This work examines the application of an arcjet-neutralized cluster of Hall effect thrusters for a low Earth orbit to geosynchronous orbit transfer. The analysis shows that hybrid Hall effect clusters neutralized by a single medium power arcjet are advantageous for some orbit raising missions. Helium arcjet neutralizers coupled with conventional xenon Hall effect anodes appear to be the superior configuration because of their relatively high efficiencies and low tankage fractions when compared to alternative propellant mixes.