Design and testing of an additively manufactured advanced hybrid rocket motor propulsion unit for cubesats (PUC)

CubeSats continue to become popular for universities and businesses to affordably conduct research in low Earth orbit. Falling within the nanosatellite category, the CubeSat standard form factor typically consists of a 1U, 1.5U, 2U, or 3U configuration. More recently, 6U CubeSats have been developed. To date, CubeSats have been limited by the orbit into which they are deployed, either as an auxiliary payload on a rocket carrying a primary payload to its required orbit or from the International Space Station. With the development of a safe and reliable propulsion system, CubeSats will be capable of performing orbital control maneuvers, such as orbit raising to extend the lifespan of the satellite and provide onboard instruments with additional data collection time. The propulsion unit in the current work was developed in collaboration with The Aerospace Corporation to provide a 6U CubeSat with this ability. The baseline design of the approximately 1U propulsion unit consists of an additively manufactured carbon-filled polyamide structure and integrated nitrous oxide tank with a cartridge-loaded, 3D-printed solid fuel grain of ABS or paraffin/acrylic composition and performance-enhancing geometry. Strength testing of the structure material characterized its properties as-received and after exposure to nitrous oxide. A significant plasticizing effect was observed for the material exposed to nitrous oxide. Ultimate tensile strength decreased by over 20% and modulus of elasticity decreased by over 40%, while elongation to break was increased. For this reason, future work will investigate an additively manufactured metal propulsion unit. Hot-fire testing of various solid fuel grain compositions and geometries revealed interesting behavior. Increased regression rate was observed for ABS fuel grains with star-swirl port geometry, as was expected, and for paraffin/acrylic diaphragm grains. An iteration on the diaphragm design included an acrylic mixing section that was shown to increase combustion efficiency over pure paraffin and the original paraffin/acrylic design.