Nozzle Plume Impingement on Spacecraft Surfaces: Effects of Surface Roughness

An experimental and numerical effort was undertaken to assess the effects of a cold gas (To=300K) nozzle plume impinging on a simulated spacecraft surface. The nozzle flow impingement is investigated experimentally using a nano-Newton resolution force balance and numerically using the Direct Simulation Monte Carlo (DSMC) numerical technique. The Reynolds number range investigated in this study is from 0.5 to approximately 900 using helium and nitrogen propellants. The thrust produced by the nozzle was first assessed on a force balance to provide a baseline case. Subsequently, an aluminum plate was attached to the same force balance at various angles from 0 (parallel to the plume flow) to 10. For low Reynolds number helium flow, a 16.5% decrease in thrust was measured for the plate at 0 relative to the free plume expansion case. For low Reynolds number nitrogen flow, the difference was found to be 12%. The thrust degradation was found to decrease at higher Reynolds numbers and larger plate angles. The roughness of the simulated spacecraft surface will be a variable in the testing to be performed for this manuscript.