Development of a Novel Feed System for Porous Electrospray Thrusters

Abstract

Electrospray systems offer an attractive solution for small spacecraft propulsion due to their high specific impulse, precise thrust control, and scalability. Among the various electrospray architectures, porous electrospray thrusters enable high emitter densities and increased thrust compared to other emitter morphologies, while also providing the ability to operate in a pure ionic regime through control of the emitter substrate pore size. These devices rely on passive capillary-driven transport to deliver ionic liquid propellant from an intermediate porous reservoir to the emitter tips, significantly simplifying propellant management. However, current porous electrospray architectures present two major limitations. First, state-of-the-art systems either lack a physical barrier between the propellant and the surrounding environment, creating contamination risks during handling and rideshare launch operations, or require complex electrowetting valves. Second, the total propellant capacity is contained by the volume of the individual reservoirs, limiting both thruster lifetime and achievable total impulse. While several efforts have investigated the integration of feed systems within multimodal propulsion architectures, limited work has been reported on dedicated feed systems capable of repeatedly replenishing porous electrospray thrusters. This thesis therefore investigates the feasibility of a hybrid propellant supply architecture, where propellant is actively fed into the thruster head and passively distributed to the emitter tips, through the design, manufacture, and experimental validation of a diaphragm-tank-based blowdown feed system for clustered porous electrospray thrusters. The work was conducted in support of the upcoming in-orbit demonstration mission of the PET flight demonstrator developed by URA Thrusters. To evaluate the proposed architecture, the individual subsystems were manufactured, integrated, and tested through an experimental campaign involving tank characterisation, assessment of fluid delivery precision, accuracy, and uniformity, and validation of the reservoir refill procedure. The results demonstrated that the proposed diaphragm tank can achieve propellant capacities of up to 39.48 ml and expulsion efficiencies of up to 88.2%. The distribution manifold successfully delivered fluid to four porous reservoirs, although a measurable flow imbalance of up to 105% was observed due to channel layout effects. The valve-controlled refill strategy achieved high repeatability and precision (CV < 2%), with maximum delivery errors of 4.6%, while staged refill sequences were shown to reduce the risk of reservoir overfilling by allowing propellant redistribution within the porous substrate. Although testing with the intended ionic liquid propellant and under vacuum conditions could not be completed within the project schedule, the experimental results validated the core functionality of the proposed feed system. The work establishes a foundation for future development towards a flight-representative feed system capable of supporting long-duration electrospray propulsion missions.