The limitations of finite fuel and the rigors of space travel demand a propulsion system that maximizes the thrust-to-power ratio. For electrically powered propulsion systems, xenon’s low ionization threshold and its high atomic mass have made it the industry’s preferred choice. But its rarity, its expense, and competing Earth-based applications have prompted researchers to look for more sustainable alternatives.
One such promising candidate is iodine, which has an atomic mass similar to xenon and a lower ionization threshold. Researchers have begun to investigate iodine’s potential. Most recently, Dmytro Rafalskyi from the French aerospace company ThrustMe and his colleagues have showcased the new propellant’s feasibility in space.
Unlike xenon, which is often stored as a supercritical fluid at pressures of 10–20 MPa, iodine can be kept as an unpressurized solid. Freed from the need to pressurize the fuel, the researchers designed a propulsion system that consists of an iodine storage tank piped directly to an inductively coupled plasma source. Nearby heaters sublimate the iodine, and a RF antenna ionizes the iodine gas to form a plasma. In that state, a set of charged grids then extracts and accelerates the iodine ions to produce thrust.
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