Document Type
Restricted Campus Only
Publication Date
5-7-2025
Abstract
This report outlines the design, fabrication, testing, and evaluation of a custom composite-propellant rocket motor developed by the Custom Rocket Motor Team. The primary goal of this design project was to overcome the limitations of off-the-shelf rocket motors by creating a system capable of delivering tailored impulse and burn profiles within a highly constrained geometry. Specifically, the team targeted a motor with a 3.125-inch diameter and a total impulse between 3,000 and 5,120 N-s, aligning with Tripoli High-Power Rocketry Level 2 requirements while allowing for improved control over rocket altitude.
The final design successfully met or exceeded all core objectives. A custom pressure vessel and nozzle assembly were developed and validated using analytical calculations and finite element analysis (FEA), ensuring a minimum structural safety factor of 2.0 across all components. The nozzle featured a bell-shaped contour optimized for isentropic flow, designed using MATLAB tools and OpenMotor simulations. The team also formulated and cast their own composite propellant, based on the “Reliant Robin” Ammonium Perchlorate Composite Propellant (APCP) formulation. This process included multi-stage mixing, vacuum degassing, and a controlled curing process to ensure consistency and safety.
To manage extreme thermal conditions, the team implemented a phenolic liner, which was selected due to challenges in achieving uniform results across the full motor length while spin-casting. Additionally, a simple relay ignition system was developed to ensure safe and reliable motor ignition.
The full-scale static fire test, conducted at the Law family ranch in Pipe Creek, TX, served as the project’s primary test. The motor was mounted on a modified test stand equipped with a 500 kg load cell and a 2500 psi-rated pressure transducer. A remote ignition system with a 300-foot safety zone and 100-foot DAQ clearance distance was implemented to ensure safety for the team and equipment. During the test, the motor delivered an estimated 5,250 N-s of total impulse, exceeding the targeted performance range and technically qualifying the motor at Level 3 (L-3). Comparing this impulse to the mass of propellant suggested a delivered specific impulse of 251.2 seconds, substantially higher than the initially predicted 236.6 seconds. This performance increase is attributed to high chamber pressures and beneficial erosion-chamber pressure relationships during the burn in the nozzle.
While the pressure transducer failed to record data during the test, likely due to thermal or wiring issues, chamber pressures were estimated indirectly through the load cell data, visual indicators, and CEA. These methods suggested average internal pressures between 1600 and 2000 psi, significantly above the design target of 1250 psi. The nozzle showed measurable erosion, with a 17% increase in exit diameter and 8% increase in throat diameter, validating the material choices made during the design. Thermal protection systems functioned effectively, as evidenced by external case and nozzle temperatures remaining below the 200°C limit for 6061-T6 aluminum.
All essential objectives of the project were met in addition to one optional objective. This project clearly demonstrated the team’s ability to design, build, and validate a high-performance solid rocket motor. Possible improvements include, but are not limited to, increasing the design pressure, refinements to the manufacturability of motor components, and higher aluminum content propellant. Future iterations of this project could improve upon it by mixing and spin-casting a custom thermal liner and by acquiring pressure transducer data during a static fire test. Farther into the future, teams may be able to improve manufacturability of both hardware and propellant, as well as redesign the nozzle to be optimized at the higher chamber pressures.
Repository Citation
Gantt, Simeon; Parcell, Austin; Saleh, Saif; and Tubbs, Kailey, "Final Project Report: Custom Rocket Motor" (2025). Engineering Senior Design Reports. 98.
https://digitalcommons.trinity.edu/engine_designreports/98
Comments
Dr. Eliseo Iglesias, Team Advisor