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How do the Space Shuttle main engines work? The three Space Shuttle main engines are located on the back end of the orbiter, and they provide the orbiter with most of its thrust during the ascent, the other coming initially from the Solid Rocket Boosters. The main engines are really incredible pieces of technology. The liquid hydrogen and liquid oxygen we use are fed in from the External Tank. Now the liquid hydrogen, at minus 423 degrees Fahrenheit, is the second-coldest liquid in the universe. And when you combine that with liquid oxygen in the combustion chamber, the temperature there can exceed 6,000 degrees Fahrenheit. That's hotter than the boiling point -- not the melting point, but the boiling point -- of iron. Iron would be a gas at that temperature. And so the obvious question is: well, why doesn't the engine bell melt under that temperature? The reason being, if you look at the engine bell, it's made of hundreds of tubes welded together. And before the liquid hydrogen is sent into the combustion chamber, we flow it through all those tubes, thus cooling the engine bell down. The other amazing thing about the pumps on the main engines: if we were to use them to pump water instead of the liquid hydrogen and oxygen, we could drain an average-size swimming pool in about 25 seconds. And that's how the Space Shuttle main engines work.