Long Duration Wear Test of the NASA HERMeS Hall Thruster

The NASA Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5-kW Hall thruster is the subject of extensive technology maturation by NASA GRC and JPL in preparation for development into a flight propulsion system. As part of this on-going effort, a series of three wear tests have been conducted to identify erosion phenomena and the accompanying failure modes as well as to validate service-life models for magneticallyshielded thrusters. This paper presents an overview and summary of the results obtained over the first 1715 h of the third wear test, which has the overall goal of serving as a pathfinder to identify and correct design or facility issues prior to the flight qualification campaign. Overall, negligible changes in performance and stability are observed as a function of operating time as well as relative to previous wear tests. Erosion of the inner and outer front pole covers is shown to vary by 76-300% as a function of discharge voltage and by up to 40% as a function of magnetic field strength. Shifting the cathode position upstream relative to the pole covers is shown to reduce keeper erosion rates by 84%, which supports this approach for mitigating the elevated keeper wear observed during previous wear tests.