Skylon, in development by the British company Reaction Engines, would be the Holy-Grail-meets-cold-fusion of space travel, a single-stage-to-orbit spaceplane powered by the Sabre engine, which is both a jet and a rocket. While typical Skylon spaceports still belong to a hazy future, a recent test of the Sabre engine has put us a fraction closer to cheap hypersonic travel.
The Sabre engine is fiendishly complicated, so much so that it borders on the impossible. It would have to work as a jet engine all the way to the upper reaches of the atmosphere where it would switch to rocket mode and send the slender Skylon into space.
There are issues, and the latest test performed by Reaction Engines addresses only one of many: How to cool the 1,000-degree intake gases the engine would encounter at high speed to -220 °F in 10 milliseconds? This is slightly more complicated than performing a hot lap in a Toyota GT86.