Effects of non-uniform operation of emission sites on characteristics of a porous electrospray thruster.

The electrospray thruster relies on a large number of emission sites that simultaneously emit ions or charged droplets to generate thrust. The operation uniformity of the emission sites is of great significance to ensure the stable work of the thruster and improve its thrust level. However, there was little in-depth study of it before, especially of its influence on the thruster's characteristics. To this end, four porous electrospray thrusters with different degrees of non-uniform operation of emission sites were adopted, and their emission site distribution characteristics, volt-ampere characteristics, and current fluctuation characteristics were investigated. Emission site distribution of all thrusters showed a certain degree of unevenness. On their emission surfaces, there were some dark zones where few emission sites located on, highlight zones where emission sites were too concentrated, and intermediate zones where emission sites repeatedly appeared and disappeared. The appearance of a dark zone could cause a decrease in the growth rate of emitted current with voltage, and electric sparks that happened in the highlight zones could directly interrupt the operation of thrusters and suppress the increase of thrusters' thrust level. A periodic fluctuation, which should be caused by the flow rate difference between emission sites, emerged on the plume current of almost all thrusters. Various experimental results indicated that part of the liquid in high-flow-rate areas spread to low-flow-rate areas while the current fluctuated periodically. It could effectively reduce negative effects caused by the non-uniform operation of emission sites. The flow resistance of one of the four thrusters was greatly reduced. As a result, the operation uniformity of emission sites was greatly improved, but the overflow problem in high-flow-rate areas was exacerbated. • The evolution of the emission site array with voltage was obtained by collecting the emitted faint light. • A low-frequency periodic fluctuation of the plume current was discovered. • Properly reducing the flow resistance of the thruster can improve the operation uniformity of emission sites. • A mathematical model for volt-ampere characteristics of porous ES thrusters was derived. [ABSTRACT FROM AUTHOR]