Propellant Utilization in Hall Thrusters

TLDR

Fuel‑optimal trajectories for electrically propelled spacecraft require varying thrust acceleration, yet Hall thruster operation at variable thrust suffers performance degradation when mass flow rate changes. The study aims to operate the electric thruster with a variable thrust‑to‑power ratio at maximum input power to meet fuel‑optimal trajectory needs. Implementation requires adjusting both mass flow rate and discharge voltage throughout flight. Experiments show that reduced propellant utilization at low mass flow rates causes performance degradation, but altering channel length and profile improves utilization and overall thruster performance, as demonstrated by tests across multiple operating points.

Abstract

Fuel optimal trajectories for electrically propelled spacecraft require a varying thrust acceleration. To achieve this requirement the electric thruster has to be operated with a variable thrust to power ratio at the maximum available input power. In order to implement this operating mode with a Hall thruster it is necessary to modify both the mass flow rate and the discharge voltage during the flight time. A crucial problem, associated with Hall thruster operation in a variable thrust mode, is the degradation of thruster performance under mass flow rate variations. Experiments with a laboratory Hall thruster have indicated that this degradation is mainly caused by a reduction of the propellant utilization at lower values of the mass flow rate. Modifying the channel geometry, namely, the channel length and channel profile, improvements in the behavior of the propellant utilization at small mass flow rate and consequently an improved thruster performance have been achieved. Results of experimental tests of a Hall thruster at various operating points and geometry are presented.