Multimodal electrospray thruster for small spacecraft: design and experimental characterization

Electrospray thrusters are a promising electric micropropulsion technology which could be used to meet the propulsion needs of nanosatellites, or for fine attitude control of larger spacecraft. Multimodal propulsion is the integration of two or more propulsion modes into a system which utilizes a common propellant. Indeed, spacecraft mission simulations and models have shown that this type of multimode propulsion capacity is exciting because of the flexibility and adaptability it provides mission designers and planners. A single spacecraft would have potential to execute drastically different mission profiles, and the exact mission could even be determined post-launch. The current paper investigates a micro-propulsion system which combines a droplet and ion mode electrospray emitter into a unified multimodal system (using an ionic liquid as the common propellant for both systems). The high relative thrust droplet mode emitter was fabricated from P3 borosilicate glass while the high efficiency ion mode emitter, Carbon Xerogel dense porous substrate, was fabricated in-house. To characterize the multimodal thruster, a full beam and time-of-flight (ToF) experimental setup were developed at the RMC Advanced Propulsion and Plasma Exploration Laboratory (RAPPEL) and experiments were conducted using a custom vacuum chamber. The ion mode emitter, with a beam comprised purely of ions had an onset voltage around 1400 V with an estimated thrust performance of 0.14 \(\mu N\) $\mu N$ and specific impulse of 4040 s. For droplet mode, with a mixed beam comprised of around 17 \(\%\) $\%$ droplets and 83 \(\%\) $\%$ ions, an onset voltage of 1375 V with an estimated performance of thrust at 14 \(\mu N\) $\mu N$ and specific impulse of 140 s were measured. The prototype thruster demonstrates how various electrospray emitters could be combined into a multimodal system to provide flexibility and adaptability in providing effective thrust for small satellites.