Sputtered coatings for protection of spacecraft polymers

Abstract

Kapton® polyimide oxidizes at significant rates (4.3 × 10 −24 g per incident oxygen atom) when exposed in low earth orbit to the ram atomic oxygen flux. Ion-beam-sputter-deposited thin films of Al 2O 3 and SiO 2 as well as a codeposited mixture of predominantly SiO 2 with a small amount of polytetrafluoroethylene were evaluated and found to be effective in protecting Kapton from oxidation both in laboratory plasma ashing tests as well as in space on board shuttle flight STS-8. A protective film of 96% SiO 2 or more and 4% polytetrafluoroethylene or less was found to be very flexible compared with the pure metal oxide coatings and resulted in mass loss rates that were 0.2% of that of the unprotected Kapton. The optical properties of Kapton for wavelengths investigated between 0.33 and 2.2 μm were not significantly altered by the presence of the coatings or changed by exposure of the coated Kapton to the low earth orbital ram environment.