Date of Award:

12-2026

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Mechanical and Aerospace Engineering

Committee Chair(s)

Stephen A. Whitmore

Committee

Stephen A. Whitmore

Committee

Larry Gardner

Committee

Douglas Hunsaker

Abstract

Hybrid rockets store solid fuel and fluid oxidizer separately, mixing only upon entry to the combustion chamber. This arrangement is generally safer to handle than a mixed solid propellant and simpler than a fully liquid engine, presenting an alternative for tactical rocket motors currently dominated by solid-propellant systems. Two commonly studied solid-phase hybrid fuels are three-dimensionally printed acrylonitrile butadiene styrene and paraffin wax. Paraffin is known for its high regression rate, which has been suggested to enable shorter grains and more compact overall systems, while the printed polymer is stronger, prints directly to shape, and retains structural integrity under military storage temperature requirements. The hypothesis tested here is that the printed polymer is the superior overall propellant for volume-limited tactical nitrous oxide hybrid thrusters despite the higher regression rate of paraffin. Thirty-nine hot-fire tests were completed on low-thrust nitrous oxide motors, using a purpose-built pyrotechnic igniter so both fuels could be fired on the same hardware. The campaign proceeded in three phases: an initial series with a flight-like printed-plastic motor, a paraffin-focused pathfinder, and a final refinement study of the printed polymer. Paraffin demonstrated rapid regression, but that faster burn did not translate into a smaller system per unit impulse. Liquid wax was observed leaving the chamber and burning in air, releasing uncaptured energy. The printed plastic delivered more impulse per unit mass of propellant and packed more impulse into a fixed volume. Casting the wax frequently cracked the grain, a problem avoided with the printed polymer. These results support the hypothesis that acrylonitrile butadiene styrene is the better fuel for a compact hybrid rocket because it demonstrated superior volumetric impulse.

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