ML12 Spacecraft Contamination and Coatings Degradation Flight Experiment

摘要

The ML12 experiment was launched 30 Jan 79, on the USAF Space Test Program P78-2 spacecraft, sometimes called SCATHA. It was designed to determine if spacecraft charging contributes significantly to the rate that contaminants arrive at exterior spacecraft surfaces, and to establish some of the characteristics and effects of these contaminants. Two sensor types are used in the experiment: (1) A combination retarding potential analyzer (RPA) and temperature controlled quartz crystal microbalance (TOCM). With it, distinction can be made between charged and uncharged arriving molecules, and information can be obtained concerning the temperature dependence of contaminant adsorption and desorption rates. (2) A tray of calorimetrically mounted thermal control coating (TCC) samples. Samples of different spacecraft surface materials are exposed to arriving contaminants, and the solar absorptances sa of these materials are continuously measured. The two RPA/TQCMs are both accumulating mass but the accumulation rates and characteristics of the mass differ. Ultraviolet from the sun is the likely reason. Non-line-of-sight contamination transport has been found to be important at geosynchronous altitudes. With one exception, the early orbital values of sa are in good agreement with prelaunch values indicating little contamination during prelaunch activities. The very small change in sa for an optical solar reflector and other space-stable samples indicates that the SCATHA spacecraft was exceptionally clean. As a result, large sa changes for other TCCs are attributed to the effects of radiation damage.