Skylon is a single-stage-to-orbit (SSTO) space plane that uses a convertible jet engine. The engine converts in flight from a conventional jet engine to a ramjet, somewhat similar to the SR-71 Blackbird, and then to a rocket engine. It burns hydrogen with air, then switches to hydrogen with liquid oxygen. The plane's fuselage is mostly comprised of two hydrogen storage tanks.
The concept has been in development since the early 80's. The problem was that there was no efficient way to cool the intake air enough at high speeds to make combustion efficient. But now Reaction Engines Ltd. has developed a lightweight heat exchanger that uses 1mm tubes with 27-micron thick walls. It cools the incoming air from 1000*C to -150*C in 1/100 second, and it does it without creating frost on the tubes. (That's 1832*F cooled to -238*F.) Chilled helium transfers the heat to a nitrogen boiler in the test models. The nitrogen is replaced with liquid hydrogen in the Skylon jet.
The heat exchanger concept for jet engines has been in development since the 70's.