Performance measurements and modeling for a 25W porous electrospray array thruster*

Porous ionic liquid ion sources are electrohydrodynamic devices that evaporate ion beams from an ionic liquid infusing a porous substrate.  While these systems are attractive for in-space propulsion because of their high inherent thrust density, to date they have been limited to less than 5 W power.  The key barrier is that higher power requires aggregating many hundreds of emitters together.  The chance that at least one emitter in an array fails and produces a life-ending electrical short increases with the size of the system, a consequence of variability in emitter behavior.

To overcome this difficulty, we have proposed two key innovations. The first is a resilient extractor architecture whereby faults are automatically removed from the system in a process analogous to the burn-in of film capacitors.  The second is adopting a probabilistic modeling framework that accounts for uncertainty in emitter behavior, such that we can identify system designs that are robust to emitter variability.

As an illustration of these techniques, we have designed, built, and tested a 25 W electrospray system incorporating our resilient extractor design. We present the results of operating that thruster and show that it can achieve comparable performance to state of the art at smaller power. Finally, we compare the experimental data to those predicted by our model as an illustration that by accounting for manufacturing tolerances we can provide a useful tool for performing model-based design.