Experimental demonstration of the effects of an electric thruster plasma plume on microwave propagation

Electric thrusters are being considered for a wide variety of space missions because of the significant propellant savings that result from the use of high performance, electric propulsion technologies. The impact of electric thruster plasma plumes on microwave propagation is a key integration concern for planners of the next generation of spacecraft. Arcjets were the first electric thrusters to be considered for operational missions. The effect of arcjet plumes on propagation was studied by Ling, et al. (see IEEE Transactions on Antennas and Propagation, vol.39, no.9, p.1412-1420, 1991). Arcjets produce a lightly ionized plume and Ling's analysis predicted that the plume would have a negligible effect on communication. Arcjets are now operational on the AT&T Telstar 401 satellite, and the analysis has been validated by in-space operations. However, plumes from the higher performance thrusters being developed exhibit higher ionization levels, plasma temperatures and particle velocities than arcjets. Therefore a need has risen to determine the effects of these plumes. To address this need, the authors have designed and performed an experiment to assess the attenuation and phase shift caused by these types of plasmas. The challenge with this experiment was that it was a microwave propagation experiment that had to be performed inside a metal vacuum chamber. Thus the experiment had to be designed to minimize multiple reflections within the chamber. This paper describes the experiment and presents some of the results that were obtained.