Laboratory investigations of low earth orbit environmental effects on spacecraft

Operations in low earth orbit (100-500 km) must take into consideration the highly oxidative character of the environment. Partial pressures in the range of 10/sup -6/10/sup -7/ torr of atomic oxygen are present which produces extensive oxidation of materials facing the direction of travel (ram direction). The ram oxidation is most severe not only because of the high flux (10/sup 15/ O-atoms/s-cm/sup 2/) caused by the orbital velocity of the spacecraft but also because of the high collision energy of oxygen atoms with the ram surfaces (translational energy equivalent to approx.60,000K). Ground based simulation of these conditions has been accomplished using a CW laser sustained discharge source for the production of 1-5 eV beam of O-atoms with a flux of up to 10/sup 17/ O-atoms/s-cm/sup 2/. The reactions of atomic oxygen with kapton, Teflon, silver, and various coatings have been studied. The oxidation of kapton has an activation energy of 2.3 Kcal/mole over the temperature range of 25 C to 100 C at a beam energy of 1.5 eV and produces low molecular weight gas phase reaction products (H/sub 2/O, NO, CO/sub 2/). Teflon reacts with approx.0.1-0.2 efficiency to that of kapton at 25 C and both surfaces show amore » rug like texture after exposure to the O-atom beam. Angular scattering distribution measurements of O-atoms show a near cosine distribution from reactive surfaces indicating complete accommodation of the translational energy with the surface while a nonreactive surface (nickel oxide) shows specular like scattering with little accommodation (50%) of the translational energy with the surface. A technique for simple on orbit chemical experiments using resistance measurements coated silver strips is described. 9 refs., 11 figs.« less