Solar‐radiation‐resistance improvement of second‐surface mirrors and optical solar reflectors by deposition of interference filters

Abstract

Second‐surface mirrors (SSM) and optical solar reflectors (OSR) are employed for satellite thermal control. In space the solar‐absorption coefficient αs of Teflon FEP foil and also Suprasil glass deteriorates with time of solar exposure. For retardation of the αs deterioration, interference filters may be deposited on such thermal control surfaces. A few filters and filter components were exposed to simulated solar radiation of seven solar constants. The solar‐absorption coefficients were measured in situ under vacuum before, during, and after exposure to uv, proton, and electron radiation. Only ZnS, ThF4, and Al2O3 films were stable enough for incorporation in filters. To study the solar‐radiation stability of their αs, standard filters and those with the selected components were exposed to simulated solar radiation. The investigations confirmed that it is possible to reduce the αs degradation of Teflon FEP and of Suprasil glass by application of such coatings.