Detailed modeling and analysis of spacecraft plume/ionosphere interactions in low Earth orbit

Detailed direct simulation Monte Carlo/particle-in-cell simulations involving the interaction of spacecraft thruster plumes with the rarefied ambient ionosphere are presented for steady thruster firings in low Earth orbit (LEO). A nominal mass flow rate is used to prescribe the rocket exit conditions of a neutral propellant species for use in the simulations. The charge exchange interactions of the steady plume with the rarefied ionosphere are modeled using a direct simulation Monte Carlo/particle-in-cell methodology, allowing for a detailed assessment of nonequilibrium collisional and plasma-related phenomena relevant for these conditions. Results are presented for both ramand wake-flow configurations, in which the thrusters are firing into (ram) or in the direction of (wake) the free stream ionosphere flow in LEO. The influence of the Earth’s magnetic field on the development of the ion plume is also examined for three different field strengths: two limiting cases in which B → 0 and B → ∞, and the LEO case in which B = 0.5 Gs. The magnetic field is found to have a substantial impact on the resulting neutral and ion plumes, and the gyroscopic motion of the magnetized ions results in a broadening of the ion energy distribution functions. The magnetic field model also incorporates a cross-field diffusion mechanism which is shown to increase the current density sampled far from the thruster.