Drag Measurements in a Simulated Low-Earth Orbit Environment

Abstract

An overview of the development of a magnetically filtered atomic oxygen plasma source and the application of the source to study low-Earth orbit drag on different geometries is presented. Plasma diagnostics show that the magnetic filter plasma source produces atomic oxygen ions (O + ) with streaming energies equivalent to the relative orbital environment of approximately 5eV and can supply the appropriate density for LEO simulation. Previous research has demonstrated that momentum transfer between ions and metal surfaces is equivalent to the momentum transfer expected for neutral molecules with similar energy, due to charge exchange occurring prior to momentum transfer. Total drag measurements of aluminum cuboid geometries of varying length to diameter ratios immersed in the extracted plasma plume are presented as a function of streaming ion energy. The plasma source can be operated at a variety of discharge currents and gas flow rates, of which the plasma parameters downstream of the source are dependent. The characteristics of the generated plasma were examined as a function of these operating parameters to optimize the production of O + ions with energy relevant to LEO applications, where the ram energy of the ions due to the motion of the satellite relative to the LEO plasma is high (e.g. 7800 m/s, which corresponds to approximately 5 eV of kinetic energy for O+ ions). The plasma downstream of the source consists of streaming ions with energy of approximately 5 eV and ion species fraction that is approximately 90% O + . NomenclatureA ref = cross-sectional area a drag = acceleration due to drag AO = atomic oxygen B = magnetic field strength C D = coefficient of drag ChAOSS = Chamber for Atmospheric and Orbital Space Simulation d = separation distance E = energy e = elementary charge eV = electron volt F D = total drag force LEO = low Earth orbit MFOPS = magnetically filtered oxygen plasma source m = mass nNTS = nano-Newton thrust stand n p = particle number density ρ = density z = charge state RPA = retarding potential analyzer RGA = residual gas analyzer