Effects of Modeling Measured Surface Roughness on Orbital Drag in Low Earth Orbits

We are interested in predicting the drag acting on a spacecraft in low Earth orbit (LEO). The presence of atomic oxygen (AO) in the residual atmosphere at these altitudes causes erosion of the spacecraft surface. We perform Direct Simulation Monte Carlo (DSMC) modeling to investigate how the roughness caused by AO exposure affects the surface scattering dynamics and therefore the drag acting on the spacecraft. The associated experimental investigations measure the microscopic roughness profile of materials which have been exposed to an AO molecular beam, simulating LEO conditions. The experimentally obtained surface profile is used directly in the DSMC computations with the microscopic roughness features resolved by the mesh. Roughness resolving simulations of germanium coated Kapton showed that the effects of changes of roughness of less than 10 $\mu$m can result in 25% variations of drag. For germanium coated silicon samples, drag changes were negligible due to minimal changes in surface roughness. The reduction of drag with a germanium coated silicon material compared to a purely diffuse one (such as AO exposed bare Kapton) was close to 40%.