Plastic Rockets: Stability and optimal design of resilient ion electrospray thrusters*

Electrospray thrusters operating in the pure ionic regime are an attractive technology for a variety of space missions given their potential of high efficiency and scalability from very low to medium power levels. These thrusters are composed of a large number of individual microscopic “emitters” that transport an ionic liquid (a room-temperature molten salt), which is the thruster propellant. Each one of these emitters produce and accelerate an ion beam when a strong electric field is applied at the liquid-surface interface. The right selection of materials and manufacturing techniques of these devices is essential to make significant improvements in their lifetime, resilience, performance and scalability beyond what is possible today. To achieve this goal, it is most important that contemporary designs take advantage of the recent progress made in the scientific understanding of the electrospray ion emission process, while at the same time move away from monolithic designs, in which if a single emitter fails, the whole thruster array might fail. The first step is to define the properties of single emitter elements that could be independently clustered in a thruster array. Multi-physics models are used to establish optimal geometries and operational conditions that maximize the stable behavior of ion-emitting menisci on these single elements. A key finding of this approach is that electrified menisci working in the pure ionic regime, are exceptionally small and have only a limited range of voltages in which emission is stable. The understanding of such behavior and characteristics is essential to move towards the fabrication and testing of near-optimal emitter elements. These novel configurations will be made with a variety of materials not commonly used in the aggressive environment of conventional space thrusters and will have better performance and be significantly more robust to failure.