Wednesday, April 15, 2009
Despite being among the most impressive amateur launches ever, I have yet to post about this project. The reason for posting at this time (many years later) is because I was recently given the flight data for this launch.
The best article about this boosted dart flight is not online, but rather in the November 1997 edition of "High Power Rocketry." HPR was by far the best rocketry magazine ever made. It is really more of a journal. In any event, the same magazine that got me started with the OuR rocket, had great coverage and analysis of this flight as well. That great coverage is exactly what is now missing from so many other projects. Perhaps it is tempting to just move on after a project, particularly if the flight fails, but that is doing a great disservice to the community. So in other words, please put as much effort into the debrief as you can for the sake of others.
This was an R motor with a stainless steel boosted dart on top. The dart carried a camera and transmitted images from near space, including a shot of the Blackrock lake bed looking about as big as a thumbnail. Both the booster and dart were recovered, the apogee was around 55 miles, give or take. Here are some of the interesting data that were sent to me by RRS member Bill Claybaugh:
To help catch everyone up on this flight profile; essentially the booster burn was about 4 seconds long, at which point the dart was released. Boosted darts are thin, dense, and designed to coast really well. It makes sense for a short burn booster in this case, so the dart spends most of its time alone coasting with limited drag. After the dart flew on, the booster was actually unstable because without the dart, and above mach 3, the CP and CG were overlapping. This caused the booster to corkscrew (yet somehow survive the stresses involved) and lose velocity really quickly. The booster, an R motor, only hit about 3 miles! The dart flew on, took footage, and nearly hit space. Incredible performance. This chart shows clearly how the dart maintained velocity well. At the end of the radar documentation, the dart is at about 25,000 feet and still cooking above mach 3.
Here are some fun numbers (keeping in mind I do not know the errors involved, but the listed stats are interesting to me and judged at least initially to be realistic.)
- The booster accelerated at around 35 gs, cutting out at around 4 seconds into the flight.
- On burnout, the booster saw very wild g swings including what looks like decelerations of 60, 70, and even at a few moments 100 or more gs. This is how it drops down from supersonic to zero in just a few seconds. Granted these were abnormal conditions, but even under normal flight this boxy R motor would probably have seen 20 or 30 gs deceleration anyway.
- The rocket was supersonic only about 1 second into the flight, just about 500 feet off the ground!
- By contrast, the dart was slowed down by only about 8 gs in the lower atmosphere (tending towards 1 g as drag was reduced).
- The dart staged near burnout, around 2 miles altitude. This is interesting because that means it coasted for around (or nearly) 50 miles after this!
Thanks again to Bill Claybaugh for these interesting data. I am (as are my 100 loyal daily readers) ready for similar data from the CSXT, if they would like to send them. We accept images, videos, and raw data.
*Update 2/6/2010 - Two new videos showing on-board footage from the dart (to near space) and the ground view of the launch. The latter is of particularly low quality. In any event, one can see the booster spiral out of control as soon as the dart flies away. As said above, the change in center of gravity caused this problem, but only at high mach numbers. This remains one of the most important flights of its kind, and if there were just a K or L motor in that dart, this probably would have beaten the CSXT to space.