Molecular dynamics study of erosion and scattering of atomic oxygen on aluminum surface under very low earth orbit conditions

Atomic Oxygen (AO) in the Very Low Earth Orbit (VLEO) environment readily adsorbs onto and erodes spacecraft surfaces, modifying microscopic scattering properties and complicating macroscopic drag prediction. Investigating these complex AO-involved Gas-Surface Interactions (GSIs) presents substantial challenges for both experimental and numerical research. Using the Molecular Dynamics (MD) method, this study systematically explores the AO erosion of aluminum and the subsequent atoms scattering behavior on the erosion-induced rough surfaces. First, a simulation scheme balancing physical fidelity and computational efficiency is proposed, based on the analysis of timescales for microscopic heat transfer and MD thermostat settings. Using this scheme, the formation of oxide layer and surface roughness on aluminum surface under high-speed AO impact are simulated across different incident velocities, angles, and wall temperatures. The distinct erosion mechanisms for normal incidence versus grazing incidence, along with the roughness morphology at different wall temperatures, are discussed. Subsequently, AO scattering characteristics are investigated, yielding accommodation coefficients that align with data derived from orbital observations. Finally, this study also assesses the protective role of pre-oxidized layers formed in ground environment against high-speed AO erosion, as well as their influence on scattering characteristics. This research is anticipated to deepen the insight into the complex GSIs involving high-speed AOs, and to serve as a valuable reference for accurate drag modeling and intake optimization for new VLEO spacecrafts, especially for those with elongated configurations.