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The space grade silicone elastomers Elastosil S-690 was subjected to the environmental loads experienced by a coverglass adhesive in a geostationary orbit environment. UV radiation, particle radiation as well as elevated temperatures all might impact the transmission of the silicone in orbit. In parallel with the established coverglass adhesives DC93-500 and Elastosil S-695, Elastosil S-690 was subjected to 10000 equivalent sun hours of UV radiation, a total dose of 2.2 MGy of 1 MeV electrons and a temperature of 200 °C for 30 days. It is impossible to cover the 15 years of UV exposure in orbit experimentally. The evolution of the transmission was therefore measured as a function of UV dose during 4 intermediate inspections and extrapolated subsequently. The sun spectrum, filtered by a CMX coverglass, was found to cause a stronger loss in transmission in the wavelength region below 400 nm in Elastosil S-690 compared to DC93-500. Taking into account the spectral sensitivities of the entire solar cell assembly stack, this degradation has a very limited effect on its end of life performance. A power impact of − 1.8 % for Elastosil S-690 was determined from the experimental data, extrapolated to end of life, compared to − 0.7 % for DC93-500. Both the electron irradiation as well as long term high temperature testing resulted in a negligible impact on silicone transmission. These results demonstrate that Elastosil S-690 is an excellent choice for a coverglass adhesive in conjunction with CMX coverglasses.