In-situ Measurement of Erosion of Boron Nitride for Hall Thruster Lifetime Research

Hall Thrusters (HT) are a compelling choice for spacecraft propulsion due to their relatively high thrust-to-power ratio and high specific impulse [1]. Erosion of HT acceleration channel walls, made of ceramic material, by ionized propellant has a significant impact on HT lifetime [1-2]. To predict HT lifetime, experiments running the HT for thousands of hours under vacuum conditions are necessary. Measuring erosion as a function of the time during these tests necessitates either breaking vacuum repeatedly and using ex-situ methods or implementing an in-situ erosion measurement system. This work describes the preliminary testing of a long-distance microscope (LDM) and Shape-From-Focus approach [3] to measure erosion of a Boron Nitride (BN) surface under conditions similar to those in the HT acceleration channel. Tests were conducted with a Maksutov-Cassegrain type LDM mounted on a motorized stage. The BN surface was modified to accelerate the erosion process to speed up testing. Optimal sample geometry was determined based on a semi-empirical sputtering model [4].