Reply to post: Re: Why super-cooled fuel?

SpaceX Falcon 9 grounded by 'sledgehammer' winds

Cuddles

Re: Why super-cooled fuel?

"Anyone know what is the rationale for supercooled fuel? Obviously you get a higher density, so more energy packed in a given size of tank. But it adds complexity and trouble. Why not increase the diameter of the rocket instead?"

Using liquid oxygen means you don't need a pressure vessel - liquids aren't really compressible, so everything is kept at standard atmospheric pressure (and this part doesn't make it into space, so you don't need to worry about even dealing with a 1 atmos difference). In order to compress the same amount of oxygen into the same space just by pressurising it without cooling it, you'd need a massively heavy vessel that would basically mean you could never launch a rocket at all.

To give some numbers - LOX is compressed by a factor of 861 relative to stp. High pressure oxygen tanks have a compression factor of around 130, and need tanks that weigh many times more than the actual stored oxygen. So you end up with fuel tanks that not only weigh much more, but also have to be several times larger. Cryogenic systems may be awkward to work with, but the alternative is basically not being able to build rockets at all because they'd be too big and heavy.

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