O-ATOM ETCHING OF GRAPHITE IN LOW-EARTH-ORBIT

Samples of highly ordered pyrolytic graphite were placed aboard the sp ace shuttle Atlantis (mission STS46) and exposed to the atmosphere pre sent in low earth orbit to observe the effects of chemical etching by atomic oxygen on carbon-based materials. During the 43 h exposure, app roximately 2.25 mum of graphite were removed from the sample, which co rresponds to an etch yield of one C atom for every eight incident O at oms. The topography of the etched samples was analyzed quantitatively within the framework of scaling theory, and the experimental data agre e with the static scaling behavior predicted for a model in which surf ace diffusion and reaction at step edges dominates the etching mechani sm.