May 3, 2004
Armadillo Aerospace Close to Hovering
John Cormak and the team over at Armadillo Aerospace have been experimenting with control systems to get their x-prize rocket to hover. I think that this is a very interesting development, and I love the fact that they publish everything they do, good and bad. This movie is pretty neat.
The second hop lifted off and hung at an angle, picking up horizontal velocity, so I cut it off quickly. I probably could have steered it back, but it was easier to just kill it. On reviewing the video and telemetry, we found that for the time that it was in the air, it was flying perfectly steady.
This is the behavior we would expect from either an offset center of gravity or vanes that weren’t calibrated straight up. We knew the mounting of the electronics had biased the weight forward, so we clamped ten pounds of weight on the back side for the next test flight. This time it flew basically straight up, still with the extreme smoothness, but we lost GPS lock almost immediately after liftoff.
We went through several tests trying to figure out what was going on. I could fly it on manual throttle just fine, but the Ashtech G12-HDMA was losing lock within a quarter second or so of liftoff. Communication with the GPS continued without a hitch, but the values would come in all the same for a ten second or so stretch. We tried mounting the amplified GPS antenna on some soft foam and even completely enclosing it in foam for acoustic protection, with no change. Russ had an idea that sounded really logical – that it wasn’t liftoff that caused the problem, but instead it was the condition of high chamber pressure on throttle up that caused the spark plug to misfire, generating RF noise. I changed the code so I only had the spark going during warmup and not during liftoff, but it didn’t change anything. I have a new GPS antenna arriving soon that we will test with on Tuesday.
We decided to go ahead and do a long run with me manually controlling the throttle and steering. I had it throttled up for 19 seconds, but I wasn’t perfectly centered under the lift when I started descending, so the last couple seconds pulled taut on the tether. Still, it was at least a 16 second perfectly controlled flight. If it hadn’t been on a tether, this test would have required a federal launch license complete with environmental assessment, which rather clearly shows how silly the burn time limit is. It looks like AST is going to grant us a burn time waiver, but only for tests at SWRS (southwest regional spaceport), which is a two-day trip away.
Posted by elkaim at May 3, 2004 2:50 PM