™
Go UP young man!
We've had three test firings since our last news update with varying degrees of success. I'm just now getting aroud to putting them on the web. All three firings are in one video below. For some reason, the sound didn't come through on the second and third clip.
The first firing was from Feb 27th. In retrospect, this has been our most successful firing so far. After the normal startup sequence the rocket fired for 8 seconds to peroxide depletion. Then in the video you will see it switch to more of a blowtorch. This is because we pressurized the peroxide with GOX and let the motor keep burning with the GOX.
It turns out it takes a long time for all the GOX to go through the orifice that's sized for peroxide, and the mass flow is so low that the rocket unchokes. But if it were fired in vacuum that wouldn't happen. Since we've got to have pressurant gas anyway why not use oxygen instead of nitrogen and get a little extra oxidizer for free. GOX at 10 bar pressure has 1/50th the free oxygen by volume of liquid peroxide, so it's not a lot, but it's not negligible either.
While this test burned completely successfully, we didn't get a thrust measurement due to operator error. We also didn't get an O/F ratio measurement because there was no way to know how much of the fuel burned with the peroxide and how much with the GOX. So we were hoping to have a similar good test soon, but get good numbers from it.
The second firing was from Apr 3. The camera angle is bad because the wind blew the camera over between the time we set it up and when we fired. The rocket is just out of frame in the upper left corner, and you can see the plume when we fire.
The firing started normally with a white cloud of peroxide followed by ignition. And it burned normally for a few seconds. But then it went back to a white cloud. This was a little puzzling. One thing we did differently in this test was to leave the ground bottle of pressurant attached and do a regulated run rather than blowdown. The fuel has a star shaped profile that gives a regressive fuel flow rate. Normally, with blowdown pressurization the oxidizer flow would be regressive to, but with regulated pressure it wasn't. My best guess is that we had an unstart due to reaching the lower flammable limit of fuel flow.
We did get a thrust measurement for this test of 34 lbf. This is the basis of the estimate I gave at Space Access of 300 lbf for the big engine with 3x the throat diameter. But no O/F ratio measurement because we really can't say how much of the peroxide flowed during the time it was burning.
The third firing was from May 2, and we had a hard start. To avoid the unstart problem and improve Isp, we decided to try a different fuel grain shape with more surface area. Also, to reduce ignition delay time I slathered on the catalyst paint. The catalyst paint has catalyst mixed into a paint, and I'm sure the paint portion burns as fuel. Maybe it has a higher regression rate than polyethylene. I think we just got a traditional hard start with too much oxidizer and fuel in the chamber on ignition. We can go back to less surface area on the grain, and just paint three stripes of catalyst like I had been instead of coating the whole thing. In any case, we've got some things to fix before we test again.