Effect of Spacecraft Charging on Performance of Ion Electrospray Propulsion Systems

Abstract

Ion electrospray propulsion systems are known to induce moderate levels of spacecraft charging when operated in a passive dual-polarity neutralization scheme. Here, the relationship between this charging and the performance of the electrospray thrusters is experimentally assessed. We characterize a passively-fed ion electrospray thruster in a simulated spacecraft charging environment with the ionic liquid propellant EMI-BF4. Performance metrics, including thrust, specific impulse, and component efficiencies are estimated with the thruster operated at emission currents of ±150 µA for prescribed spacecraft biases between 0 and ±800 V. When the spacecraft and plume are the same polarity, thrusters exhibit a narrower plume and produce more thrust with increasing spacecraft bias. Conversely, when the spacecraft and plume are opposite polarities, thrusters show increasingly divergent plumes that are attracted back to the spacecraft, resulting in less thrust being produced at higher spacecraft biases. The combined thrust output for a dualpolarity pair of thrusters was estimated to decrease by about 36% at a spacecraft bias of 800 V and 25% at a spacecraft bias of −800 V. These results show that spacecraft charging is a critical consideration for determining the true in-space performance of ion electrospray propulsion systems.