Quote:
Originally Posted by the-red-scare
In Spaceships where mass flow rate can vary by a factor of 300,000, seems like it might come up…
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Increasing the area by a factor of 300,000 means increasing the linear dimensions by a factor of 550.
The Saturn V had five F-1 engines on the first stage, which was 33 feet wide. The entry point into the nozzles for those engines was about 1.7 feet across. (The wide end of the nozzle was a bit over 12 feet wide, but all the propellant mass had to make it through the little hole, too.)
Expand that by a factor of 550, and you wind up with a nozzle entry 930 feet across. This is a bit less than 4x the beam of a Ford-class carrier (365,000 tons, 1100 ft long) or oil supertanker (ULCC, 564,000 DWT, 1400 ft long). So, those ships are SM+13 to SM+14. Bump them to SM+15, 3x the dimensions, and they'd be just about big enough to hold our oversized SM+15 F1 rocket engine. (Not that there's any reason you'd have to have a spaceship shaped like they are -- you could easily make them wider and shorter without the drawbacks that has for an ocean vessel. But just for the sake of mental imagery...)
The BOTE numbers don't seem to indicate that the size in SS would be wildly out of whack. There's a square-cube relationship there with area-volume, but over the size range of interest, it doesn't look like it's running away quite yet.
As for thrust, 550 times the mass flow should mean 550x the thrust. So, 825M pounds of thrust. But the Saturn V weighed 3000 metric tons, so our comparison ships are only 120-190x as massive, or <600x the mass when scaled to SM+15. Even with only 1 RBF-1* engine, that's still about half a G of acceleration. Which seems to fall into line with the Saturn V, recalling that it had five engines in the first stage.
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* Really Big F-1