Simulated space environmental exposure of optical coatings for spacecraft solar rejection

Dielectric multilayers composed of niobium pentoxide and silicon dioxide, designed for broadband solar rejection, were exposed to a simulated space environment of ultraviolet light and low-energy (10-20-keV) electron radiation. Samples exhibited various degrees of exposure-induced absorption extending from the ultraviolet to the infrared. Processing variations were correlated to damage susceptibility, and methods were identified that produced parts that exhibited no degradation even though the same materials and coating design were used. Coatings prepared under energetic deposition conditions that provided the densest and most moisture-stable coatings exhibited the best stability to the exposure conditions used.