High-resolution direct thrust characterization of electrospray thrusters with EMI-BF4 at different temperatures and polarities

Abstract

Electrospray thrusters have garnered significant attention throughout the years as an exceptional propulsion technology for nano- and picosatellites due to their efficiency and precise thrust control. They operate on the principle of electrostatically accelerating charged particles (liquid droplets, pure ions or their mixtures) from ionic liquids and other low-volatility propellants, which are extracted from a Taylor-cone formation on top of porous emitter arrays. In this work we characterized the thrust performance of electrospray thrusters with the ionic liquid 1-ethyl-3-methylimidazoliumtetrafluoroborate (EMI-BF4) as well as an attempt with an acetate-based ionic liquid. The arrays were operated at different polarities and at elevated temperatures of up to 43 °C which led to a decrease in viscosity and enhanced current emission for EMI-BF4 with a factor of 1.43 at equal voltage levels. Temperature related effects resulted in a thrust difference of 3% between the maximum and minimum temperature throughout the tested current range. Thrust measurements for emission currents between 10 µA and 200 µA revealed a detectable and temperature independent difference between the positive and negative mode in favor of the negative polarity, indicating different ion-regimes compared to most data found in literature. The paper presents a novel thrust measurement setup for micro-propulsion systems based on a counterbalanced double pendulum thrust balance that achieves nanonewton resolution with the option to heat several thrusters. A comprehensive overview of the test setup and calculations of obtained electrospray parameters from experimental data is presented.