SKYLON is a spaceplane currently under development by Reaction Engines, Limited, of the UK. The vehicle is intended to be an aircraft that can reach orbit. Skylon would be able to take off from a conventional runway.
Testing of the key technologies was completed in November 2012, and the project has been awarded $350 million of funding contingent on a test of the engine's precooler technology being successful. The company is seeking an additional £250 million over the next ten years to continue development, and estimates the total cost of the program will be £7.1 billion. Projected unit cost is £190 million.
The core technology of Skylon are its SABRE engines, which is a combination of a precooled jet engine, rocket engine and ramjet. After taking off from a conventional runway, the craft is designed to accelerate to Mach 5.5 using a jet engine, at which point its air intake closes and it switches to rocket mode, which takes it to orbit.
When the project was begun around 2000, the key technology for this type of precooled jet engine did not exist as it required a heat exchanger that was ten times lighter than the state of the art. Research conducted since then has achieved the necessary performance.
- Technical Documents at Reaction Engines website