Spacecraft contamination under simulated orbital environment

Abstract

Volatile condensable material (VCM) measurements on a number of spacecraft materials have indicated that contamination rates onto surfaces at subambient temperatures cannot be predicted from standard outgassing tests, particularly where long-term exposures are involved. Contamination rates may depend markedly on temperature differentials between source and collector, the collection temperature, the source geometry, and the exposure time. Contamination rates also may be influenced by solar irradiation. The results of this study were obtained on a new VCM facility that overcomes many deficiencies experienced in earlier designs and permits accurate simulation of space environmental conditions. Advantages of the present system include an oil-free high-vacuum chamber (10~8—10~9 Torr), source temperatures from ambient to 125°C, collection temperatures from -140° to + 125°C, total mass-loss measurements, in situ VCM mass measurements with use of an internal-temp erature-compensated quartz-crystal microbalance, in situ vacuum ultraviolet irradiation of either the specimen or of the collected VCM, and infrared identification of the VCM by multiple internal reflection spectroscopy. The system also features automated data acquisition and data processing.