PACECRAFT in low Earth orbit (LEO) are immersed in a potentially hostile charged-particle environment. In order to determine the performance of such systems in this environment, and to ensure their reliability, it is desirable to have ground-based facilities that simulate the LEO plasma environment to the highest fidelity possible. Orbital dynamics dictate that the orbital speed v0 of a LEO spacecraft is approximately 8 km/s. This speed is characteristically greater than the thermal speed vth, i of the ions in the LEO plasma, but less than the thermal speed vth, e of the electrons, so that it is often designated as a “mesothermal” speed. 1 Furthermore, the ions and electrons in the plasma are tied together by electric field interactions, so that a more descriptive measure of the relative speed of the spacecraft’s orbital motion is the mach number M, given as the ratio of the orbital speed to the ion acoustic speed cs in the plasma, where