In 2022 I helped found a student group developing liquid bi-propellant rocket technology at Cal Poly.
Our first goals:
- 35 LBF Thrust,
- Pressure-Fed (Argon), GOX and Ethanol,
- sub $3000 Budget,
- Built to expand for future projects,
The Design:
A 3 piece modular thrust chamber assembly. Vertical firing configuration.
My Part:
- Arc Igniter design manufacturing testing.
- Manufacture injector manifold with CNC mill.
- Teach members how to use a Mill, Lathe, welding equipment, brazing.
- General manufacturing advice
Arc Igniter
For this project i did a lot of material selection and experimentation to determine the best way to manufacture this arc igniter. My initial design was about half as small with a .065 inch ceramic rod, however with the lathe tooling available and the necessary material (316 stainless), the part was impossible to manufacture because the force exerted by my cutting tool sheared the part in half at the thread relief section of the insert.
I did a lot of design work for this project with extensive spreadsheets, but ultimately the thing that moved this project forward was building and testing. I learned valuable lessons about the importance of saving time by just making something. For my stainless prototype part I calculated that the .007 inch wall thickness at the thread relief section would be strong enough to support the chamber pressure loading, but when it came time to manufacture the stresses of turning on the lathe sheared the thin walls.
I was able to take this lesson and make better decisions later in the design process like when I was trying to determine if my selected adhesive would contain the pressure of the chamber. Instead of spending another 5 hours doing calculations I spent 20$ and experimentally verified that the adhesive could work with a hydraulic pressure testing chamber.
Critical Design Review Slides
Presented to engineers from SpaceX, Stratolaunch, and Hermeus.
Unfortunately due to a last minute electrical short on the control box, my igniter design was not able to be used and permanent changes were made to the igniter chamber mount that prevented future installation. A magnesium chemical igniter triggered by Nichrome wire was used as a last minute back up ignition source.
Additionally I milled and welded other components like parts of the test stand and injector manifold.
