Development of a Power Efficient, Restartable, "Green" Propellant Thruster for Small Spacecraft and Satellites

This paper details the development of an innovative "green" hybrid rocket propulsion system, applicable to small spacecraft. When fully developed this propulsion technology has the potential to act as a "drop in" replacement for propulsion system utilizing hazardous propellants such as hydrazine. Fuel grains are manufactured using a form of additive manufacturing known as Fused Deposition Modeling (FDM). Using FDM overcomes multiple technical issues frequently associated with hybrid propulsion systems. Issues include lowoutput-rate manufacturing, a lack of system restartability, and poor volumetric efficiency. FDM reduces development and production costs by supporting high production rates across a wide range of form factors. Using FDM, thermoplastic fuel grains can be fabricated with port shapes that enhance burn properties and increase volumetric efficiencies. Most significantly, because FDM-processing builds the specimen one layer at a time, most thermo-plastic materials fabricated via FDM possess unique electrical breakdown properties that greatly enhance system ignitability and restartabilty. When FDM-processed fuel materials are subjected to a high-voltage inductive charge, an electrical-arc develops along the layered material surface and Joule heating produces a small amount of pyrolized vapor. When the arc occurs simultaneously with the introduction of an oxidizing flow, the pryolized hydrocarbon vapor "seeds" combustion and produces immediate ignition along the entire length of the fuel material. Fuel regression rates are compared with analytical predictions to conclude this paper. Keywords—hybrid-propulsion; small-spacecraft; additivemanufacturing; environmental-sustainability; low-hazard, arc-