Open Access
Kerr, Evan M
Graduate Program:
Aerospace Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 24, 2018
Committee Members:
  • Richard A Yetter, Thesis Advisor
  • Michael Matthew Micci, Thesis Advisor
  • Amy Ruth Pritchett, Committee Member
  • CubeSat
  • Propulsion unit
  • hybrid rocket
  • additive manufacturing
  • powder bed fusion
  • direct metal laser sintering
  • DMLS
  • PBF
CubeSats are a standardized class of small satellites based on combinations of 10x10x10cm units called ‘U’s. These small satellites are revolutionizing the space industry, but their general lack of propulsion options limit their operational capabilities. Previous research at Penn State into the use of additive manufacturing to create an integrated hybrid propulsion unit for CubeSats showed promise, but material limitations eliminated the possibility of using the polymer materials investigated. In this work, development of an additively manufactured propulsion unit for CubeSats was continued with the goal of creating a metal design. Estimations of performance parameters for the proposed propulsion unit were made using previous work, basic orbital mechanics, and computer models. Initial estimates indicated the propulsion unit could provide 160 m/s of velocity change to a 3U CubeSat weighing approximately 5 kg. Feasibility studies conducted using these performance parameters showed that an integrated hybrid propulsion unit for CubeSats can enable significant orbital maneuverability without the cost and hazards associated with the sparse market alternatives. Specifically, models suggest that the propulsive capability enabled by the propulsion unit can extend the lifetime of a 3U CubeSat deployed from the International Space Station from a number of months to a number of years. Based on the positive results of the feasibility study, a titanium hybrid propulsion unit for CubeSats was subsequently designed, additively manufactured, and tested through a series of pressure, leak, and hot-fire tests. The propulsion unit was designed to utilize paraffin-based grains and nitrous oxide as the fuel and oxidizer, respectively. The printed propulsion unit, with a mass of 550g, showed some minor deformations from the manufacturing process that were corrected using post processing or accounted for in the design of subsequent tests. Pressure and leak testing verified that the oxidizer tank could withstand high pressures and that the additively manufactured pressure vessel did not leak at expected operating pressures. A specialized nozzle assembly was designed and manufactured to withstand the extreme conditions of a hot-fire test. The propulsion unit was designed to take standardized 1.5” diameter, 2.5” long fuel grain cartridges. Hot-fire testing demonstrated the propulsion unit in a laboratory environment, satisfying the conditions necessary to bring the propulsion unit to Technology Readiness Level 4. A unique fuel grain geometry featuring a length of straight port paraffin with a downstream ABS diaphragm and mixing section was used and characterized during the hot-fire tests. Initial calculations suggest these fuel grains achieved a c* combustion efficiency of around 0.60-0.80, reflecting relatively high performance for such short fuel grains. Recommendations for future work necessary to advance the propulsion unit to Technology Readiness Level 6 (component demonstration in a relevant environment) were made based on the knowledge gained in this research.