Vehicle Overview
This was the first liquid rocket the team developed. It used Nitrous Oxide (self pressurizing) and Ethanol as propellants in a blowdown configuration. It flew short of its altitude target due to a valve failure mode not caught in testing (a valuable lesson on the “swiss-cheese” model of failures.) It was manufactured entirely in-house.
Engine Design
The engine uses Nitrous Oxide and Ethanol in a pressure fed blow down configuration. The chamber is composed of an aluminum cylinder with a phenolic ablative liner. The nozzle is machined from graphite, with a stainless steel extension. Overall analysis for this engine was heavily focused on the injector design, as it was the first bi-prop injector for us. Most ablative and nozzle design was adapted from what we learned in past years testing hybrid rocket engines. We conducted four static fires of this engine prior to flight.
Motorized Valve
For main propellant valves, the main constraint was space. The plumbing bay diameter was 6”, so most off-the-shelf solutions didn’t fit. I modified a window lift motor (the thing that raises your car window) to couple with the valve stem of a ball valve. This had the advantage of having a built-in right angle gear box which packaged well in the space available. Hysteresis in the valve coupler/feedback control caused the valve to only open partially during flight, which reduced engine performance and impacted altitude. We noticed this issue during a static fire, but incorrectly concluded it was related to a sub-optimal fill level in the oxidizer tank.