A FAR liquid rocket launches within a minute of a UCLA liquid rocket

March 18, 2023
Back in March, when I was still filming to a 1080p60 standard, we launched FAR's very own LR1 rocket for the first time. The launch was to test a simplified pressure fed rocket for a kit rocket program, and the hardware is designed to do away with the finicky bends and bulky GSE hardware common with student rockets. There is only one tube bend in the whole rocket, and it's an optional configuration. To facilitate this, the fuel line runs through a tunnel in the LOX tank with insulation in between.
This insulation proved perfectly adequate during static testing, which saw nominal burns, but it ended up being problematic as various delays left the lines to chill down. In the first attempt, the igniter failed to light, which meant that ice started to form in the dwelling propellants as the igniter was switched out for a quick second attempt. This ice formation blocked the fuel line, so that the fuel dumped only after all of the LOX had gone.
In the third attempt, the rocket was prevented from launching as soon as it was ready, as UCLA personnel for the record breaking ARES launch that same day were late in evacuating the range in the midst of imminent launch window closure. With preloaded regulated pressure tanks, the UCLA rocket was launched first once the range was finally cleared. The fuel was left to dwell for a slightly shorter time than before, but still long enough that ice formed to delay fuel drainage. This resulted in a loss of performance as LOX dumped alone for some time before the fuel finally kicked in, and less than a minute after the UCLA rocket launched, the LR-1 coughed and then roared into the sky.
While the delays from clearing the range were not ideal, it would not have proved as much of an issue as it was if it weren't for a design flaw with the fuel downcomer insulation. Such things should be considered as natural developments in rocket launch operations. Welding errors with the inner tunnel left a considerable overhang that reduced the clearance for insulation, and the spiral spacer which filled in the gaps was inadequate for moderate durations. A wider tunnel and transition to better and thicker insulation increases the margin for good propellant conditions. A proposed switch from 70% to 90% ethanol would also reduce the freezing point significantly.
While the combustion was less than perfect, the flight up was otherwise nominal. A mysterious avionics glitch caused the flight computers to momentarily shut off after the drogue was deployed, so the main parachute failed to deploy. The resulting hard landing chipped the single use nozzle extension and left a nasty looking but repairable bend to the midsection. The damage included some shorn bolt holes, so while new tanks are being prepared with the larger tunnels, the meat on the the coupler has also been optimized. The rocket was not really designed to descend only on drogue, but pushing the rocket to its limit with a fast descent is a good way to identify the weaker points in the design.
These changes take time for us busy volunteer FAR staff, so it may be a while before the next flight, but once the itch to fly returns, so will the LR1.

[@suntrakker1]

Derek, thanks for the update. What is the LR1 sim'd to assuming the valve delay gets fixed?

[@DerekHonkawa]

It was originally simmed to 9000 feet, but that was using a whole bunch of bad data and assumptions that were thrown around in the months prior. I gathered what data I had to properly characterize the rocket after the launch. I'll ask Mike to do another sim since I don't have MATLAB anymore, but it sounds like it should be able to go much higher.

[@DerekHonkawa]

I have a question for you, and might as well ask it here. What is the highest liquid rocket that SDSU have flown in the past? and was it mostly student designed and built or was it public-private partnership like at Long Beach?

[@suntrakker1]

@@DerekHonkawa SDSU's highest liquid flew to 13,205 feet in the FAR DPF contest. It was all student designed and built.

[@DerekHonkawa]

@@suntrakker1 Thanks. Luckily I found a paper written by SDSU students which happened to outline their past launches. Documentation sure is important.