Radiometric Analysis from the 26-Kilowatt Electric Propulsion Space Experiment Flight

Abstract

The U.S. Air Force Research Laboratory's 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 this flight, an array of onboard contamination sensors was used to assess the effect of the arcjet and other environments on the spacecraft. The sensors consisted of microbalances to measure material deposition, radiometers to assess material degradation due to thermal radiation or contamination, and solar cell segments to investigate solar array degradation. Over eight firings of the ESEX arcjet, and 33 min, 26 s operating time, the radiometer near the thruster, viewing the arcjet plume and body, experiences a change in the thermal properties of its coating from the firings. Radiometers with no view of the arcjet, or a view of only the plume, show no change. In general, degradation effects are observed only on sensors near the thruster exhaust nozzle, a location unlikely to be used in an operational high-power electric propulsion system. No degradation effects are observed in the backplane of the thruster. For future programs, although engineering measures may be needed for spacecraft equipment in the immediate vicinity of the thruster body, the arcjet environment is generally benign.