Gas-Surface Interaction Model for Very Low Earth Orbit (VLEO) Systems

Accurate estimation of the drag force is essential for spacecraft in very low Earth orbit (VLEO), as it significantly impacts orbit prediction, control, and collision avoidance. Accurate gas-surface interaction (GSI) models are crucial for predicting drag, particularly in collisions involving hyperthermal atomic oxygen with spacecraft surfaces operating in VLEO environments. This work examines the scattering of atomic oxygen on amorphous silica, a common satellite material, using reactive molecular dynamics. A comparison of angular scattering distributions and energy transfer between molecular dynamics calculations and experiments reveals excellent agreement. Based on the physical insights from molecular dynamics calculations, a new hybrid GSI model has been developed. The new model, termed the diffuse-Cercignani-Lampis-Lord (DCLL) model, combines velocity contributions from non-drifting diffuse Maxwellian and impulsively scattering drifting distributions. The new model reproduces angular flux distributions observed in molecular dynamics and beam experiments, while preserving a structure suitable for implementation into particle solvers. The DCLL model is both simple and accurate, effectively bridging molecular-level fidelity with practical usability and providing a reliable tool for drag prediction and orbital analysis of VLEO spacecraft.