Space Environment Effects on the Electron Yields of Thermal Control Coatings

Abstract

Space-environment-induced degradation of white thermal control coatings from the Long Duration Exposure Facility (LDEF) was investigated. Much of the exterior of the LDEF was painted with a white thermal control coating, Aeroglaze A276; and most of the interior was coated with a black thermal control coating, Aeroglaze Z306. Outgassing from these coatings and other LDEF materials interacted with the white surface when exposed to sunlight after volatile materials condensed on the LDEF surfaces. Surface morphology was characterized by optical and scanning electron microscopies. Fourier-transform infrared spectroscopy and energy-dispersive x-ray spectroscopy were used to identify the chemical compounds and elements present in the contamination film. Many material properties were modified due to the prolonged approximately six year low-Earth-orbit exposure, but electron yield (EY) was the focus of this study due to its dominance in spacecraft charging. Measurements showed an increase in maximum EY with increased contamination, with the maximum EY more than doubling in some cases. The NASA Charging Analyzer Program simulations for simplified models of the LDEF showed the impact of the degradation on spacecraft charging under different environmental conditions; equilibrium surface potentials varied by more than 100% in some cases.