Mirror degradation in orbit due to space radiation exposure

Mirror coatings designed for use on satellite remote sensing instruments were exposed to a simulated geostationary orbit radiation flux of combined ultraviolet, electron, and proton radiation. Reflectance measured in vacuum before, during, and after exposure demonstrated that some mirror coatings are much more resistant to damage than others. The laboratory test results agree with in-orbit mirror temperature increases observed on GOES satellite instruments. The laboratory tests also confirm the necessity of measuring reflectance change in vacuum, due to the rapid recovery of reflectance loss upon exposure to room atmosphere.