A cryogenic rocket engine is a rocket engine that uses a cryogenic fuel or oxidizer, that is, its fuel or oxidizer (or both) are gases liquefied and stored at very low temperatures.[1] Notably, these engines were one of the main factors of the ultimate success in reaching the Moon by the Saturn V rocket.[1]
http://en.wikipedia.org/wiki/Cryogenic_rocket_engine
Our very own have thier boot on our throats allowing others to corner the market in almost every field.
The nice thing about cryogenic rocket engines is that you can turn them off.