Wednesday, October 31, 2007

Surprising Simplicity in the Biggest Engine Ever Made


Last Christmas, my wife's present to me was a trip to Space Camp as part of their three day adult program. In all honesty, it was a lot of fun. Space Camp is directly adjacent to and has free access to the U.S. Space & Rocket Center, which has a museum and a rocket garden filled with various rockets and their assorted hardware bits. Saturn V F-1 engines are about as ubiquitous there as doorstops. Which got me to investigating the various components that make up an F-1 engine, the biggest single combustion chamber engine ever made. I was surprised to discover that the F-1 is comparatively simple. A single turbine, fed with a fuel rich mixture from the LOX and RP-1 lines, spins a single shaft which drives two large pumps (one for LOX and one for RP-1) which look not very different than the centrifugal pumps used in swimming pool plumbing. The exhaust from the turbine is sent out the at bottom of the regeneratively cooled engine bell. This is done, I assume, to film cool the last 8 feet or so of the engine bell, which isn't cooled regeneratively.

The SSME by comparison, is a nightmare out of necessity. This is mostly because pumping liquid hydrogen up to pressure is particularly non-trivial, and requires a multitude of turbines and pumps to operate. As a result, the thrust to weight ratio of the SSME is substantially lower (73.12) than the F-1's (94.07) even with the obvious differences in maximum available Isp of their different fuel mixtures. NOTE: figures provided by Astronautix.com. It makes one wonder if the improvements in Isp
have really been worth it.


AFTERWORD:

Space Camp was a worthwhile vacation. I recommend it to other space geeks everywhere. Yeah, it's camp, with its obligatory camp food, but at least they have a salad bar and you get to hang out with a lot of similarly minded people.

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