alternative Rocketry inside scoop
From: John Carmack
Subject: Re: [AR] X-Prize Cup Preparations?
Date: October 13, 2006 12:15:40 PM PDT
The 180 second flight started off great, with a good liftoff and smooth burning on the full propellant load, but at 52 seconds into the burn, the carbon wrapped graphite chamber let go. The injector was still in perfect shape (details on the technical changes that finally resolved this next update), and based on the fuel remaining we were going to exceed 180 seconds, but it looks like the chamber can’t handle the higher pressure / higher Isp for an extended period of time. Everything was glowing orange hot, and it probably oxidized away most of the external carbon reinforcement.
We solved all the things we thought were problems, but we had been considering these chambers essentially indestructible, and it turns out they aren’t.
We have done four 90+ second flights in the last couple weeks, so we feel pretty good about that, but now that we know that the chambers can just completely lose it at the higher performance levels, we aren’t going to risk wrecking anything trying for another 180 second qualifier.
After we do the level 1 flights at the cup we will probably try for a 180 second hover under the crane, since we have added more film cooling and an oxidation protection barrier on the outside. If the chamber lets go again, the crowd will love it. 🙂
If it works, they might let us try for official flights, but I’m not happy after seeing this failure mode. It wasn’t what I expected from a fiber wrapped chamber.
We are probably going to work on providing a little bit of cooling for graphite chambers after the cup.
No word at all from AST today. We will write a post-mortem on the process after the cup.