The week leading up to STF 4 did not go quite as smoothly as weeks prior to our cold flow tests. Due to an oversight, a late-night hydrostatic test had to be performed on the rocket plumbing. Then, the night before STF, while connecting the instrumentation and testing the valves and pressure transducers something was connected incorrectly and fried one of our transistor chips. There were no replacements in stock and we were forced to convert our whole ignition sequence to hard switches. There were a few people that had to stay up all night to get this done, but they had successfully saved our STF plans for the next day in one night. STF 4 did not go as expected, however. The test procedures were effective during setup, as all members completed their tasks in parallel and ahead of schedule despite unavoidable delays. Filling the tank went nominally, as did the ignition sequence. Upon opening the main valve, the fuel ignited and burned, producing visible Mach diamonds at the nozzle. Approximately 1.5 seconds after the main valve was actuated, the injector housing, oxidizer plumbing, and tank separated from the combustion chamber and longerons. The combination of chamber pressure and cold gas thrust lifted the tank off the test stand before it fell (vertically oriented) into the flame trench. See video below.
After evacuation procedures, we returned to survey the damage and collect the components. We were somewhat in shock since no one had expected anything like this to happen. After getting back to campus, some failure analysis was done on the system, the flaws in the system that led to the failure were found, and plans were made for them to be corrected during the following semester.