Experimental evaluation of hydrogen peroxide catalysts for monopropellant attitude control thrusters

Abstract

Currently the space community relies on propellants such as hydrazine and its derivatives in propulsion systems aboard satellites and spacecraft. However their highly toxic and carcinogenic nature results in significant costs in handling, storage and transport compared to less toxic propellants. It is due to this benefit that there is a renewed interest in ‘green’ or less toxic propellants. One such green propellant is hydrogen peroxide. This liquid propellant must be catalytically decomposed into steam and oxygen within the thruster. The current PhD is charged with advancing the state of hydrogen peroxide heterogeneous catalysts and associated thruster hardware. To this end a range of assessment techniques have been employed to develop solid catalysts based on metallic gauze, metallic foam and ceramic pellets. In all cases these catalysts must be suitable for the decomposition of up to 99% hydrogen peroxide concentration by mass. This work assesses these catalysts under both laboratory and fully representative conditions using 87.5% hydrogen peroxide concentration by mass.

This thesis contains a detailed literature review into heterogeneous catalysts and catalyst supports. This has resulted in the procurement and manufacture of thirty-eight candidate catalysts from all three support types. A selection of these catalysts have undergone physical assessment using a range of surface characterisation techniques in an attempt to understand their performance. The results of a review into experimental hardware have led to the development of two laboratory-based apparatus designed to measure initial performance and catalyst longevity. The results have been described and used to down-select from thirty-eight candidate catalysts to a final selection of four.

Additional testing of these four catalysts has been conducted within a highly instrumented catalyst bed to provide performance data under fully representative conditions. With their performance verified an engineering bread-board (EBB) thruster has been developed to investigate the effect of various changes to thruster hardware such as injector and catalyst bed geometry, pre-heating methodology and effect of anti-channelling baffles.

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