The Skylon, a concept spaceplane that (theoretically) could go from a standing start to orbit and back without disposing of any rocket stages, took another big step forward today as tests independently audited by the European Space Agency confirmed that the Sabre engine underpinning it is conceptually sound. It’s the second key endorsement from the ESA that Skylon and the Sabre engine have picked up in the past two years--giving Sabre-maker Reaction Engines cause to call its technology the biggest engine breakthrough since the jet.
That’s big talk for a small aerospace firm, but then Skylon is a really big idea. The Sabre engine, if successful, should be able to double the normal top speed of conventional jet engines from 2.5 times the speed of sound to 5 times the speed of sound, and it should be able to do so using atmospheric air (rather than tanked oxygen, like a rocket). At that speed Skylon could climb to more than 15 miles up. Once up there amid the much thinner air, its hybrid propulsion system would switch to rocket mode to climb the rest of the way into space.
Other scramjet-style vehicles like the U.S. Air Force Waverider or DARPA’s HTV-2 have similarly used atmospheric air to generate huge amounts of thrust, but these vehicles have to be carried to very high speeds by either rockets or other aircraft before their powerful propulsion systems can engage. Sabre’s breakthrough is that it can (again, theoretically) flirt with hypersonic speeds after starting from a full stop on a conventional runway, without the need for multiple rocket stages or carrier aircraft.