Reactions of spacecraft materials with fast atomic oxygen

Silver films with thicknesses in the range 600-3200 Angstrom were exposed to high velocity atomic oxygen in a laboratory facility at flux levels simulating those experienced by surfaces in the low Earth orbit. Reaction rates were calculated from the resistance changes as the conducting silver was converted to its non-conducting oxides. A two-stage reaction process was observed, consisting of a rapid linear rate to a depth of approximately 340 Angstrom followed by a slower, diffusion limited parabolic rate. The reaction rates of polyethylene, PTFE, carbon and silica were established by exposing sensors comprising thin film overlays of the test material on a 300 Angstrom silver substrate to atomic oxygen. The reaction rate of PTFE was found to be higher than found in orbit, whereas the rates for polyethylene, silica and carbon were similar to reported values.