Single-Polarity Ion Electrospray Propulsion

Abstract

Electrospray thrusters are highly efficient spacecraft propulsion devices that accelerate ions sourced from ionic liquid propellants to produce thrust. Typically, electrosprays are fired in a dual-polarity configuration in which the polarity of the ion beam is periodically reversed. This strategy is difficult to implement and imposes limitations on system size and performance. We instead propose a single-polarity design where negative ions are emitted continuously from the thruster, enabling extreme miniaturization, faster startup, better emission stability, and simpler power processing. This thesis investigates two challenges associated with the single-polarity design. First, system lifetime is of principal importance for electrospray propulsion systems in general and must be verified for a single-polarity implementation. Long-duration electrospray tests are performed, demonstrating that single polarity thrusters achieve comparable lifetimes and performance to state of the art systems with high mass utilization and minimal hardware degradation. An additional challenge is propellant electrochemistry, triggered when positive counterions accumulate in the ionic liquid. A suite of experiments is conducted to identify and characterize electrochemical processes, including electrical double-layer potential evolution and gas-phase product formation, in electrospray thrusters over long firing durations.