Selection and Characterization of Green Propellants for Micro-Resistojets

The number of launches of nano- and pico-satellites has significantly increased over the past decade. Miniaturized subsystems, such as micropropulsion, for these classes of spacecraft are rapidly evolving and, in particular, micro-resistojets have shown great potential of applicability. One of the key points to address in the development of such devices is the propellants selection, since it directly influences the performance. This paper presents a methodology for the selection and characterization of fluids that are suitable for use as propellants in two micro-resistojet concepts: vaporizing liquid micro-resistojet (VLM) and the low-pressure micro-resistojet (LPM). In these concepts, the propellant is heated by a nonchemical energy source, in this case an electrical resistance. In total 95 fluids have been investigated including conventional and unconventional propellants. A feasibility assessment step is carried out following a trade-off using a combination of the analytical hierarchy process (AHP) and the Pugh matrix. A final list of nine best-scoring candidates has been analyzed in depth with respect to the thermal characteristics involved in the process, performance parameters, and safety issues. For both concepts, water has been recognized as a very promising candidate along with other substances such as ammonia and methanol.