Simulation of Gas-Surface Interactions in a Very-Low Earth Orbit Wind Tunnel Using PICLas

Very low Earth orbit (~150–350 km) missions rely on accurate prediction of plasma–surface interactions to quantify drag, material degradation, and plume–spacecraft coupling in air-breathing electric propulsion (ABEP) concepts. In this work, we use the PICLas PIC–DSMC framework to simulate a mixed-species plasma plume expanding inside a finite vacuum chamber and interacting with an inclined plate representative of a VLEO-relevant flow. The source is modeled as a flux boundary at one end of the chamber, and the resulting plasma potential, electric fields, and ion densities are resolved self-consistently for two configurations: a baseline case without internal hardware and a case with a 3"x3" inch plate mounted at 45° to the plume. In the baseline configuration, the plume forms a collimated ion core that broadens downstream, with smoothly curved potential and density contours rather than the idealized straight-edged cones often assumed in analytical models. The plasma potential exhibits a localized hill near the source with values of order 10–20 V and decays toward the grounded chamber walls, while the associated axial and transverse electric fields are O(10-10²) V/m, driving axial acceleration and weak radial spreading. When the inclined plate is introduced, the global plume shape and near-source acceleration region remain largely unchanged, but a sheath forms around the conducting surface, focusing ions onto the upstream face and producing a depleted, low-potential wake downstream. PICLas predicts a net ion-induced drag of 66.87 µN on the plate under the studied operating condition, in excellent agreement with available literature on VLEO drag predictions. These results demonstrate that chamber-scale plume expansion and localized plasma–surface interaction can be captured within a single, self-consistent kinetic model, providing a quantitative basis for interpreting laboratory measurements and extrapolating plasma-induced drag to VLEO-relevant configurations.