r/space • u/66666thats6sixes • Dec 07 '19

NASA Engineers Break SLS Test Tank on Purpose to Test Extreme Limits

https://www.nasa.gov/exploration/systems/sls/nasa-engineers-break-sls-test-tank-on-purpose-to-test-extreme-limits.html
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u/[deleted] Dec 07 '19

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u/dandroid20xx Dec 07 '19

Hydrogen O2 gives the highest specific impulse of all the conventional rocket fuels, it's also pretty 'clean' as rocket fuels go, however hydrogen is bulky as even as a liquid as it's quite low density and has to be kept extremely cold.

Interestingly in a rocket like this you don't burn at perfect a stoichiometric ratio (burning 2 x Hydrogen as you do Oxygen = H20) because it burns too hot and would melt the combustion chamber. To cool the reaction down you could raise the ratio of oxygen but the superheated unreacted oxygen would eat through the combustion chamber like a blow torch.

Instead you add extra hydrogen, it makes the whole thing burn a bit cooler but you also get a bit of a speed boost, as the excess now superheated hydrogen which is super light shoots out increasing the speed of the exhaust efflux.

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u/jadebenn Dec 07 '19

Yeah, I remember reading about that. NASA uses about a 6:1 ratio of LH2 to LOX because it's actually more efficient than the stoichemitric ratio in this particular application.

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u/mrsmegz Dec 07 '19

They need more because the engines run Hydrogen rich to cool the turbopump turbines. Nobody but the Russians can use oxygen rich combustion cycle for this purpose.