Mass Deposition Measurements from 26-Kilowatt Electric Propulsion Space Experiment Flight

Abstract

The Electric Propulsion Space Experiment (ESEX) was launched and operated in early 1999 to demonstrate the compatibility and readiness of a 30-kW class ammonia arcjet for satellite propulsion applications. As part of the onboard sensor array, thermoelectric quartz crystal microbalances were used to measure material deposition at selected locations on the spacecraft surface. The sensors were held at a temperature that would allow them to condense metallic materials eroded from the electrodes, but that are insensitive to possible deposition of the propellant gas. The ESEX arcjet was fired eight times, constituting 33 min and 26 s of operating time. No material deposition was observed that could be attributed to nominal the arcjet firings, although during the first firing, significant deposition was observed near the arcjet nozzle. This deposition is attributed to contaminants within the arcjet body, collected during handling and storage, which were ejected during the first firing. For future programs, although engineering measures may be needed to protect spacecraft equipment in the immediate vicinity of the thruster body, the arcjet environment causes negligible deposition of electrode material.