Design and testing of flat-panel pixel electrospray thrusters

Abstract

Electrospray thrusters are a promising form of electric propulsion due to their compactness and high mass efficiency, making them advantageous in most mission scenarios, especially for small spacecraft. These thrusters operate through the emission of charged particles from an electrically-conductive liquid flowing inside an array of capillaries or sharp permeable structures from applying a potential difference between the liquid and a downstream extractor electrode. Emission is most efficient when operated in the pure ionic regime (PIR), with recent designs utilizing sharp porous structures to transport the liquid and provide electric field enhancement to induce ion evaporation. However, these structures are often difficult to manufacture uniformly at the scales required to ensure stable PIR emission. Existing electrospray thrusters also suffer in reliability due to the monolithic nature of their extractor design, which is prone to induce full array failure upon the shortage of a single emitter structure. These issues can be mitigated by a design that utilizes (1) a flat-panel array configuration, where the geometry and arrangement of each emitter element meets the physical requirements that ensure consistent manufacturing and PIR operation, and (2) a series of fuses interconnecting individual extractor rings for each emitter structure, which would break upon shortage, protecting the rest of the extractors in an array in case of a single emitter shortage. These fuses would allow each emitter to function as a pixel on an LED screen, where the outage of a single pixel does not prevent the rest of the pixels from producing the rest of the image. Through this research, an emitter design is properly fabricated with properties that favor PIR emission, as a capillary fabricated on top of a porous glass substrate. The required starting voltage based on this approach is simulated and a preliminary characterization is performed using a non-integrated extractor. Though degradation of the emitter is experienced over time due to the preliminary extractor set-up, it is found that the emitter capillary can properly wick propellant and operate at moderate voltages for tens of minutes.