Hall Thrusters using Water as a Propellant*

Hall thrusters have emerged as a leading technology for Electric Propulsion applications and offer considerable propellant mass savings over chemical propulsion counterparts. Modern Hall thrusters typically use heavy noble gas propellants – Xenon and Krypton. However, the availability and cost of these propellants have prompted many studies into viable alternatives. Our research has focussed on the use of water as a propellant, which is either electrolyzed into oxygen and hydrogen (to the anode and cathode respectively) or fed directly as water vapour. Water offers system level advantages in terms of low propellant cost, low environmental impact, and high specific impulse. Nevertheless, there are challenges due to the highly corrosive nature of oxygen plasmas, and the energy loss mechanisms associated with lightweight molecular plasmas.

The sizing and performance optimization of water-based Hall thrusters has been approached through a combination of numerical modelling and experimental investigation. An in-house particle-in-cell code was used to optimize the geometric parameters of a Hall thruster to work with oxygen and water vapour. Compared to a xenon-fuelled thruster, it was found that a much smaller channel volume, and therefore higher power density, was needed to achieve comparable ionization fractions. This presentation will focus on the performance characteristics observed through direct thrust measurements, and the insights into the physics of operation from numerical simulations.