Predicting spacecraft surface degradation under atomic oxygen in Low Earth Orbit

Abstract Poor knowledge on the degradation behaviour of surfaces exposed to atomic oxygen ( O 1 ) in Low Earth Orbit has long impeded the development of accurate satellite aerodynamic models for thermospheric research. Although in situ studies such as the Materials International Space Station Experiments (MISSE) 2–8 have measured the erosion yields of various protective coatings and examined atomic oxygen-induced surface roughening at the microscopic scale, a first-principles theoretical framework to explain these processes has yet to be established. Herein, we establish a physical link between the O 1 reactivity of materials and the micro-scale morphologies that emerge over prolonged exposure. We present a first-principles multiscale framework that predicts both the erosion yield and the evolving surface microstructure of a material directly from its chemical composition. We resolve the atomic-scale dynamics with an extensive suite of thermostatted, long-timescale reactive molecular dynamics (MD) simulations (mean bombardment duration ~800 ps) and treat the macro-scale evolution statistically using a poly-Gaussian surface model. The framework reproduces measured erosion yields from MISSE 2 for Kapton H, Teflon ETFE, Teflon PTFE and Teflon FEP with a maximum relative error of 19%, and qualitatively captures the conical morphologies observed via field emission scanning electron microscopy at an O 1 fluence of 8.43 × 10 21 atoms cm −2 across multiple incidence angles. Finally, we identify a strong correlation between erosion yield and surface roughness, quantified by the standard deviation of the surface slopes, and leverage this relationship to infer roughness parameters for all 41 MISSE 2 materials.