Crafting feed systems for solid/liquid propellants in Hall and ion thrusters: Present state, obstacles, and future outlook

As space missions demand greater affordability, higher efficiency, longer durability, and broader exploration capabilities, conventional rare gas fuels like xenon face challenges. Owing to their limited storage capacity, steep costs, and intricate storage and supply mechanisms, they are progressively inadequate for the evolving needs. The evolution of electric propulsion has been significantly influenced by solid and liquid propellants, known for their dense storage capacity, affordability, safety, and suitability for on-site resource use. The article systematically reviews the physical properties and research progress of five solid working media - bismuth, zinc, magnesium, iodine, adamantane - and two liquid working media - mercury and water. It focuses on the analysis of the design of feed systems corresponding to each type of working medium. Depending on the trajectory of phase change, systems for storing and supplying solid working mediums are categorized into solid-liquid-gas phase change and solid-gas phase change types, whereas those for liquid working medium storage and supply are segmented into liquid-gas phase change and substance change types. The coupling between the feed systems and the thruster, focusing on flow stability, vapor purity, and coordinated integration, was influenced by the advanced refinement of crucial technologies in the feed system's design. This included strategies for thermal control and heating, precise flow measurement, material compatibility, system integration, fluid filling, and replenishment in orbit, along with multi-physical field coupling simulations. Finally, future directions such as the screening of new working fluids, intelligent perception and adaptive control are discussed, providing theoretical support and technical references for the engineering application of solid/liquid working fluid electric propulsion feed systems.