Subscale Liquid Rocket

Our first vehicle, Subscale, is our proof of concept vehicle to learn and test all systems before the team is ready to complete Full Scale. Subscale will launch in the Fall of 2021 after the team performs two full duration static fires with our new regen cooled engine. The vehicle uses liquid oxygen and Jet 1-A as propellants, is capable of producing about 800-900 pounds of thrust, and has a thrust to weight ratio around 3:1.

My part was to design the primary load path structure for this vehicle. In summer 2021, I helped to redesign our stringer-coupler interface after the team had problems accessing leaks and replacing fluids components in our flight feed system. The updated design is easier to assemble.

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I also designed the tank mounts for the rocket. Thermal expansion was an issue, so my design utilizes spring steel bands to hold the LOX tank in place. At first we decided to go with welded aluminum tanks for liquid oxygen and Jet 1-A. I conducted a testing campaign in which we sent aluminum 7075 coupon pieces to be welded by a professional welder. We then tensile tested the coupons with a custom machine to find out if the weld on our tanks would hold. After testing tens of coupon welds, we found out that the tanks would hold the tank pressure, but unfortunately we did not have a reasonable factor of safety. Furthermore, we found out that aluminum's ignition temperature in liquid oxygen environment is low, which is why it's not recommended to use aluminum tanks to hold LOX. Due to these reasons, we decided to make our tanks from welded steel. Unfortunately, this increased the vehicle mass a bit, but this provided a reasonable factor of safety with which the team was more comfortable.