Saturday, May 2, 2009

Historic Amateur Rocket Launch

Although our team did a nice job, this launch of a 1/10 scale Saturn V really takes the cake. At 1648 pounds and 36 feet tall, it is one serious rocket. I've seen a K motor launch a 7+ foot hybrid rocket to about 3500 feet. That went up with an impressive roar. This one must have been something to see in person.



See also this guy's photographs, such as this one (notice the person in the foreground for scale!), and some of the "related" videos. For example, this video follows the flight from launch to deployment.

By the way, notice the scaling laws at work here. It is 1/10 as tall as a 363 foot tall Saturn V, but a tiny fraction of the 6,699,000 pound original. This is not just due to the difference between length and volume scaling. Scaling up the mass by a factor of 103, which keeps the density constant, only gives 1,648,000 pounds. The missing factor of four or so is due to the fuel (and extra thrust) needed to put a 260,000 pound payload (a lot even if scaled down to 260 pounds) into low earth orbit rather than "just" send the rocket up to 4440 feet.

The thrust of the model rocket was 7700 pounds force, almost exactly 1/1000 of the 7,648,000 lb-force thrust of the Saturn V's first stage. The much greater thrust-to-mass ratio of the model makes it take off "like a rocket" rather than lumber off of the pad as the real one did, but the latter could burn for 150 seconds. If you never saw the Apollo rocket go up, here is one video of the usual TV launch view we saw (where you get a sense of the fact it took more than 10 seconds to clear the tower), and another (higher resolution) view looking down at the first stage engine section from the point where the final fueling connection is broken, about a dozen seconds before ignition. (A similar sequence is used on the Shuttle, which also has a connection to the main fuel tank that remains until it is time to pressurize the tank.)