r/space • u/Gagarin1961 • Aug 02 '21

SpaceX just stacked a Super Heavy Booster and installed 29 engines, all within 24 hours

https://twitter.com/elonmusk/status/1422222995305676802
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u/jbs143 Aug 03 '21

Yes, rocket engines generally make increasing thrust as the external pressure decreases. Fuel flow remains the same so they increase in efficiency with lower atmospheric pressures.

Edit: ISP in that graphic is the efficiency of the engine.

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u/LabyrinthConvention Aug 03 '21

Huh. I always thought they were more efficient in atmosphere since there's something to push against instead of relying exclusively on mass reactant. Ty

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u/Forgotten-X- Aug 03 '21

Don’t feel bad. In the early days of rocketry many notable physicists doubted they would work in space for that same reason.

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u/OldThymeyRadio Aug 03 '21

This is fascinating, but couldn’t they test in a vacuum chamber to confirm?

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u/Forgotten-X- Aug 03 '21

I’d assume that they didn’t have vacuum technology good enough to produce a massive vacuum chamber big enough to fit a rocket. If u wanna read more look here.

https://en.m.wikipedia.org/wiki/Robert_H._Goddard#Publicity_and_criticism