Hotfire zero was the first full test of Titan 2. We planned to use a flight-configuration injector plate that would hopefully yield us sufficient oxidizer flow to generate 1200 lbf of thrust, but to only supply half the flight-configuration mass of oxidizer so that the burn time would be 3.5 seconds. Unfortunately, we encountered two problems: 1) we had half the desired flow rate, doubling the test's burn time, and 2) we had an extremely slow startup transient. On top of that, there was an issue with the load cell, so there is no force data for this test.

The feedline pressure started a little low - 650 psi - so the pressures measured will naturally be a little lower. The first smoke shows at 1.41 seconds into the data, and 2 seconds after we see the first signs of a full burn, although we are only reaching half of the peak thrust at this point. The engine doesn't fully get up to speed until a second and a half later. We suspect that this was due to the injection system that we used for this hotfire, which was replaced in the next two hotfires. The two and a half seconds it takes the engine to fully start is a little worse than hotfire 2, in which we saw two seconds, and significantly worse than hotfire three, which fully started in less than one and a half seconds.

The nozzle actually remained intact for the full duration of this hotfire, unlike hotfires 2 and 3. We suspect that this is due to the relatively low pressures the nozzle experienced owing to the lower oxidizer flow rate.

At first it may appear that the data is de-synced, given that the injector pressure starts to drop much after the combustion chamber starts to drop. However, it's probably correct - the discrepancy is due to a drop in the sampling rate. Because of the lower fidelity it's difficult to discern, but it looks like the gas-only phase begins about 11.5 seconds after the burn started.