Optical and Scanning Electron Microscopy of the Materials International Space Station Experiment (MISSE) Spacecraft Silicone Experiment

Abstract

Under a microscope, atomic oxygen (AO) exposed silicone surfaces are crazed and seen as “islands” separated by numerous crack lines, much analogous to mud-tile cracks. This research compared the degree of AO degradation of silicones by analyzing microscopic images of samples exposed to low Earth orbit (LEO) AO as part of the Spacecraft Silicone Experiment. The experiment consisted of eight silicone samples exposed to different AO fluence levels (ranged from 1.46 to 8.43 × 10²¹ atoms/cm²) during two Materials International Space Station Experiment (MISSE) missions. Image analysis software was used to analyze optical microscopic images. The fraction of sample surface area occupied by crack lines was obtained and used to characterize silicone degradation and the resulted loss of specular transmittance. SEM images from the eight samples exposed to different AO fluences suggest a sequence of surface shrinkage, stress, and crack, followed by re-distribution of stress and shrinking rate on the sample surface. Energy dispersive spectra (EDS) indicated that after long AO exposure, silicone samples will eventually have a SiO₂ surface layer with some trapped CO and CO₂.