Novel Propellants for Variable Thrust/Isp Colloid Thrusters

ABSTRACT: Advanced spacecraft will demand thrusters that provide both extremely efficient operation for attitude control and high thrust for orbital transfer maneuvers, albeit with lower specific impulse. The colloid thruster, the most efficient of the electric thruster concepts, forms a Taylor cone to emit charged particles and produce thrust. Colloid thrusters typically emit charged droplets and accelerate them to high velocity. Pure ion emission mode only occurs with highly conducting fluids, such as the ionic liquids (ILs). In this mode the thruster emits only ions and therefore, thrust is lower, but the specific impulse and propulsive efficiency are much higher. Unfortunately, only a few propellants can emit pure ions and the reasons for this are not fully understood. Therefore, in Phase I TDA Research and the University of Colorado developed a model to correlate fundamental physical properties of ILs with their ability to emit in these regimes. We then used the model to identify new propellants that will improve colloid thruster performance, and ran tests in our Electric Propulsion Vacuum Facility that demonstrated that our model could successfully identify new propellants that function as ion emitters. In Phase II we will specifically design and demonstrate propellants that can vary the thrust by allowing a single thruster with a single fuel to operate, on demand, in either the droplet or ion mode. BENEFIT: Colloid thruster propulsion system(s) that can efficiently produce either high or low thrust levels on-demand will enable the deployment of spacecraft able to provide low-cost communications, space research and surveillance. Further, of the electric propulsion systems, only the colloid thruster can be miniaturized for use in nanosats. Because many small, low-cost nanosats can be put into orbit at once,"constellations"offer flexibility and redundancy in mission programming. The loss of one satellite will have little effect on the performance of the entire system. The development of affordable colloid thruster systems that utilize the propellants to be developed in this project will provide the performance needed to perform these missions.