Contamination assessment of a freely expanding green propellant thruster plume

A number of propellant/thruster combinations are under development in recent years that aim to replace the prevailing hydrazine-driven reaction control thrusters with less hazardous substances ("green propellants"). With some of these systems already in orbit, characterizing their contamination potential in a space environment becomes relevant. In this paper we discuss experiments on plume induced contamination from a novel propene/nitrous oxide bipropellant thruster, including high-speed imaging, SEM-EDS analysis, QCM measurements and in-situ mass spectrometry. Additional measurements of combustion chamber pressure complement the overall characterization of the thruster performance in a high vacuum environment. The main findings of this exploratory study are strong indications of solid and liquid phase particles being ejected from the nozzle, which will be investigated in a subsequent phase of the activity.