D-1 Solid Rocket Motor

Objective

Design a motor for the club's rocket. The D-1 had to deliver about 113 N·s of total impulse (G-class) to reach a target apogee of about 200 m. It also had to be built from materials we could source in Sofia.

My role

I lead SCAE's 4-person propulsion team, which designs and manufactures the club's rocket motors. For the D-1, I did the calculations, the design and CAD, the material and seal selection and the grain inhibition, and wrote its documentation and drawings. The igniter was a team effort, and the parts were machined by others. I also mentor team members and review their simulation work.

What I did

• Did the motor calculations and designed it around a KNDX BATES grain, sized for about 113 N·s (G-class).
• Modelled the full motor in SolidWorks and produced the D001 assembly drawing (A2, 1:1).
• Selected the materials (6082 aluminium casing, S45C steel nozzle and top cap, M5 bolts) and the seals (Viton O-rings in standard AS568 sizes).
• Designed the nozzle joint: threaded retention and O-ring sealing, with a check against galling in the aluminium threads.
• Designed the grain inhibition: an epoxy and fibreglass wrap on the outer surface of each grain.
• Designed the igniter together with the team.
• Wrote the motor's 41-page design document.
• Reviewed teammates' simulation work, including OpenMotor grain simulations and a Simulink 6-DOF flight simulation.
• Started the D-2 revision: a hanging nozzle that moves the bolts and O-rings aft, so both nozzle and casing need less material.

Results

• Design complete, with a 41-page design document and the full assembly drawing.
• All parts machined; the team is preparing for the static test.
• Grain inhibition and igniter designs finished.

Challenge

For the next revision, the goal is a lighter motor without weakening the joints. In D-2, the nozzle's divergent cone hangs outside the casing, so the bolts and O-rings move aft and both the nozzle and the casing need less material. The nozzle stays steel; the forward bulkhead switches to aluminium. Lesson: where you place a joint decides how much material the parts around it need.

Next

• Instrumented static test to measure thrust and chamber pressure and check the design
• First flight about two weeks after the static test
• Finish the D-2 revision
• Write up the static-test campaign as a paper