Additive manufacturing as an enabling technology for "green" hybrid spacecraft propulsion

This paper details the developmental of an innovative "green" hybrid propulsion system, applicable to small spacecraft, using a form of additive manufacturing known as Fused Deposition Modeling (FDM). When fully developed this cross cutting propulsion technology has the potential to act as a "drop in" replacement for most hydrazine-based propulsion systems. Using FDM overcomes multiple technical issues frequently associated with hybrid propulsion systems. Issues include low-output-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, 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 results 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 "seeds" combustion and produces immediate ignition along the entire length of the fuel material.