Global modelling and performance analysis of a water-fueled radio-frequency gridded ion thruster

This study presents a global model analysis of a water-fueled Gridded Ion Thruster (GIT) powered by a Radio-Frequency (RF) inductive coil. A comprehensive reaction set is developed to capture the complex plasma chemistry of water, including the formation and ionization of secondary neutrals generated through dissociation and neutral-wall recombination reactions. The global model solves coupled particle and energy balance equations to predict plasma properties and thruster performance as a function of operating parameters such as the input RF power and propellant mass flow rate. The results demonstrate that while water exhibits a greater discharge complexity than xenon, the dissociative pathways contribute only marginally to the formation of light ions such as H+ and H2+. The discharge is instead dominated by heavier ions like H2O+, O+, and OH+, which contribute to meaningful thrust production. Compared with xenon (for a 12-cm diameter thruster studied here), water exhibits higher electron temperatures and an enhanced coil-plasma power transfer efficiency, although the propellant mass utilization efficiency and thrust-to-power ratio are lower. A thrust performance analysis reveals that water can achieve a competitive thrust and specific impulse at higher input powers, establishing its viability as an alternative propellant. Overall, the model provides a robust foundation for the development of future water-fuelled electric propulsion systems and addresses a critical gap in general low-temperature water plasma research.