Ionic liquid monopropellants for electric propulsion: species, decomposition, and implementation.

Interest in ionic liquid monopropellants has been steadily increasing due to the fact that they are significantly less toxic than Hydrazine and tend to have better performance parameters. This, in addition to increasing interest in a common propellant for spacecraft refueling purposes has resulted in significant attention to the possibility of using ionic liquid monopropellants in electric propulsion devices. These monopropellants lend themselves nicely to use in electrospray propulsion systems that already utilize ionic liquids, and it is important to understand how the propellant behaves and potentially degrades when separated into its anions and cations during emission. Furthermore, research into operation regimes (droplet, pure ionic, etc.) and onset voltage is necessary to understand thruster performance and efficiency. In addition to electrospray thrusters that can use an ionic liquid monopropellant without modification of the liquid, there is interest in using ionic liquid monopropellants in gas phase electric propulsion devices, such as Hall Effect Thrusters and electrodeless thrusters. The ionic liquid cannot be directly injected into the thruster as a liquid, and therefore, it must be vaporized or decomposed first. In this talk, I discuss work to use ionic liquid monopropellants in electrospray thrusters. I will discuss methods and results for measuring the thermal decomposition products of Hydroxylammonium Nitrate (HAN), and ASCENT, and I will suggest future work to determine a method for decomposition of ionic liquid monopropellants for injection into gas phase electric propulsion devices.