On the selection of propellants for cold/warm gas propulsion systems

Abstract

Cold/warm gas spacecraft propulsion systems generate thrust by accelerating a cold or moderately heated gas through a nozzle. Despite their simplicity compared with typical chemical or electric propulsion systems, the choice of propellant nonetheless represents an important consideration that affects the design, operation, and performance of such thrusters. Here we review different propellants that have been used or proposed for cold/warm gas propulsion systems, and we perform a study investigating almost 5000 other possible alternatives. Propellants include organic and inorganic substances that can be stored in solid, liquid, gaseous, and multi-phase states at ambient conditions, and which undergo a phase change to a pure gaseous state (where needed) by heating before being ejected from the thruster. The different propellants are assessed by considering important evaluation factors, such as propulsive performance, storage requirements and storage density, mission suitability, safety, and cost. While conventional thruster performance metrics like the specific impulse are low for some propellants, the design and operational advantages they offer, together with a higher total impulse mass density (i.e. the impulse per propulsion system wet mass), make them superior choices for many missions.