LOW-EARTH-ORBIT EFFECTS ON INDIUM TIN OXIDE AND POLYESTER AND COMPARISON WITH LABORATORY SIMULATIONS

Laboratory simulation of the low Earth orbit (LEO) environment using o xygen plasma ashers are discussed. Their effectiveness as space simula tors are compared with LEO through analysis of indium tin oxide (ITO) thin films and bulk polyester exposed to both environments. Spectropho tometry and atomic force microscopy have been used to characterize opt ical and microstructural changes as a result of exposure to the simula ted (oxygen plasma asher) and the actual space environment aboard shut tle flight STS-46. Results show that the low Earth orbit space environ ment is much harsher than the plasma asher on the optical properties o f ITO as well as the surface roughness of polyester. On space-exposed samples, a significant shift in the ITO absorption edge is seen for fl uences of 2 x 10(20) atoms cm-2 but not on films exposed in the asher. The surface roughness of polyester exposed in the asher increases by a factor of 5.5, while that of polyester exposed in space increases by a factor of 20 for the same atomic oxygen fluence. The directional na ture and higher kinetic energy of atomic oxygen in LEO serves to erode polyester more than in the asher. The different results obtained in t he asher for both ITO and polyester bring into question the suitabilit y of using plasma ashers as space simulators for these materials.