Ionic Liquid Electrospray Beam Target Performance Characterization

Electrospray thruster technology ground testing is of critical importance to their eventual adoption for long duration flight missions. While there has been substantial work to understand the beam physics and plume dynamics of electrospray thrusters and the implications thereof on performance and lifetime, there is a gap in an understanding of facility effects. Interactions with an electrospray plume and the vacuum chamber test facility have implications on both performance and lifetime. Therefore, any effort to characterize an electrospray thruster must be done so with an understanding of how the facility plays a role. In some ways, this is no different than the significant investment that has been made to understand the facility effects for the testing of plasma thrusters. However, there are different challenges involved with the management of positively charged, negatively charged, and neutral particles across a distribution of particle charge and mass as is observed when testing electrospray thrusters in a vacuum chamber. The focus of this paper is a characterization of the secondary particles from the impact with an electrospray beam target for ionic liquid thrusters. Results on secondary current and mass flux are presented with some initial results on secondary time-of-flight measurements. Additionally, modeling results are presented to inform the experimental observations. The results show that mitigating facility effects, while a challenge, can be done with an appropriately designed and biased beam target. If no consideration of facility effects is accounted for when testing electrospray thrusters, performance, reliability, and lifetime can be adversely affected and premature thruster failure may result. The work presented here improves our test capabilities to qualify and acceptance test electrospray thrusters for flight for long duration missions.