RF signal impact study of an SPT
Stationary plasma thrusters (SPTs) are currently being tested and considered for use aboard next generation spacecraft for North-South station keeping, repositioning, and orbit transfer due to their high thrust efficiency and nearly optimal specific impulse (ISp). However, because the thruster's plume generates plasma densities with corresponding plasma frequencies approaching 3 GHz, consideration must be given to possible interactions with satellite electromagetic systems such as for communication, navigation, and remote-sensing. The plume potentially can degrade the electromagnetic link through attenuation as well as added amplitude or phase noise. Previous experimental and theoretical studies have investigated the phase modulation at a range of frequencies and have experimentally verified signal attenuation. This paper provides the physical mechanism and ray tracing modeling method to understand the possible amplitude modulation produced by the SPT thruster. The study also experimentally quantifies the rather significant plume impact to phase and amplitude for a signal at 1.575 GHz (GPS frequency) which is outside the theoretical limit of the modeling technique. A summary is provided of ray tracing simulations characterizing both phase and amplitude effects at frequencies from 3 to 17 GHz and axial positions from 0.25 m to 1.5 m. The results correlate well with known data. The low frequency measurements also provide good correlation to the trends exhibited in the simulations.
