Armadillo 65-second hover
John Carmack wrote to aRocket, the Alternative Rocketry mail discussion group, about Armadillo Aerospace‘s Lunar Lander Challenge progress:
It didn’t rain on us in Oklahoma this weekend, so we got to do a long hover test. We intended to run it straight through, but we stopped at 17 seconds when the engine got ratty sounding. We inspected the engine, and it still seemed ok, so we vented the lox back down to atmospheric to cool it off and repressurized.
We lifted off again and hovered for 65 more seconds before we hit lox depletion. The engine went in and out of the ratty performance, but it kept going. I believe that the ugly sounding engine is when lox starts boiling in the injector manifold.
That would always be goodbye injector with aluminum, but the stainless injector seems to get through it, and the poor performance eventually lets it cool back down enough for it to go back to smooth flow and combustion. The big conical pockets on the lox cooling holes are definitely acting as flameholders, I’m pretty sure after we weld them all closed and remachine them as just straight holes that the engine will stay smooth continuously.
We expected to hit lox depletion originally, but venting the tanks and going through our leveling procedure before the restart tossed out a good chunk more lox. We still had a quarter of our fuel load left in the tanks after the flight, and we could load 50% more total propellant if necessary (at the cost of a higher initial ullage pressure). This combination does the 90 second challenge easy.
I am slowly chewing my way through our high performance twisted injector in stainless steel, hopefully for testing on Tuesday.
We had a couple X-Prize Cup folks at the test today, but there is a decent chance we will do our official qualification flights for level 1 next week, and level 2 the week after that. We have been considering the possibility of using the high performance engine for both the level 1 and 2 challenges, possibly doing level 1 as a touch-and-go with no refueling, but I am currently leaning towards using the low performance engine for level 1 because it is a lot easier on the chamber, leaving the glowing chamber for level 2.