Spacecraft-Charging Characteristics Induced by the Operation of Electrospray Thrusters

Theoretical and experimental methods were developed to investigate the charging characteristics anticipated to be observed on spacecraft during the operation of electrospray thrusters. These devices produce positively and negatively charged particles of similar mass and velocities. An electrical model of this configuration was created to predict the charging properties of electrically isolated systems. This model simulates a bipolar electrospray-thruster system. Experiments were conducted on a test bed, in which a mock-up satellite is magnetically levitated inside a vacuum chamber. The mock-up is equipped with batteries, power conditioning, radio transmitter, and electrospray thrusters. The results from the experimental tests demonstrate that neutralization with heavy ionic species is indeed possible. The thrusters are able to fire in a bipolar configuration for long periods of time inducing bounded spacecraft charging in the range from −400 to +600 V when emitting currents of about 20 μA. It was found that the presence of low-energy ions produced by the fragmentation of large clusters plays a significant role in the neutralization characteristics. This electrical model was verified by reproducing the experimental results, thus validating its use to estimate bulk spacecraft-charging properties.