Development of meso and micro scale liquid propellant thrusters

This paper reports on the design, fabrication and testing of liquid-propellant chemical microthrusters for propulsion of small and micro-spacecraft. The propellant formulations include energetic oxidizers (hydrazinium nitroformate, ammonium dinitramide, and hydroxylammonium nitrate), alcohol fuels, and water as the liquid carrier and electrical conductor. Asymmetric whirl combustion has been studied in combustion chamber volumes ranging from approximately 10 to 170 mm³ with gaseous fuel (H₂, CH₄, and C₃H₈) - air mixtures as a means to stabilize the reaction and minimize heat losses in the microthruster. Based on these vortex flow combustor studies, microthrusters have been designed and fabricated from aluminum oxide using ceramic stereolithography. The microthrusters have throat diameters ranging from approximately 300 - 700 μm, an exidthroat area ratio of approximately 2, and a combustion chamber volume of approximately 60 mm³. Initial hot frre tests have been conducted with H₂-air mixtures to enable preliminary thermal structure analysis, diagnostics testing and model development. In separate tests, electrolytic ignition techniques have been investigated for initiation of the liquid propellants.