Half Cat Static Launch 1 - April 3, 2021
Partial Success
Mid-air explosion
The first launch of Half Cat took place on April 3rd, 2021 after an extremely intense week of constructing an airframe day and night while preparing everything needed for the trip. On the rocket’s first attempt at filling oxidizer Saturday morning, the fuel line burst due to higher pressure than had been experienced in prior static tests.
Nitrous oxide saturation pressure is dependent on temperature. In this case, the Mojave desert in the daytime was appreciably hotter than the Florida nighttime conditions we had been testing in. The nylon plumbing lines were being used above their rating - this is the case for many fittings and parts on the rocket, but we accept that as a risk. Unfortunately for this first flight attempt, the elevated temperatures bumped the oxidizer pressure just enough above the material’s failure point, so that the fuel line (which is also pressurized by the nitrous oxide) burst approximately 10 seconds into the oxidizer fill cycle.
After the nitrous tank emptied itself (through the always-open static vent), the rocket was disassembled, re-fueled, and reassembled for a second attempt in an impressively short time frame. Knowing the result was likely to be the same, we chose to proceed with a launch regardless of how what was going to happen.
When the fuel line again burst shortly into oxidizer fill, the igniter and valves were initiated. For a second, the rocket took off and accelerated, running as an almost pure nitrous oxide decomposition thruster since most of the fuel had leaked out. Residual fuel inside the plumbing section, along with nitrous vapor from the disconnected oxidizer fill line, was ignited by combustion gases leaking out of the burst line. The resulting explosion separated the combustion chamber (which landed near the launchpad), while the rest of the vehicle partially deployed its parachutes before hitting the ground.
Despite the explosion, the engine was mostly fine. One valve was freed from the rocket and lost, and the brass fuel injection fittings needed to be replaced, but after replacing these Half Cat was reassembled for static test 6.