After nearly thirty years on the drawing board, a revolutionary British spaceplane has received approval for the next stage of development.
The Skylon vehicle would be able to take off from a runway and reach orbit in a single stage. The idea was derived from the Hotol spacecraft design from British Aerospace and Rolls Royce in the 1980s, which was later abandoned because of technical problems.
It would be capable of delivering payloads of up to 15 tonnes into low Earth orbit - around 200 miles - at about 1/50th of the cost of traditional expendable launch vehicles, such as rockets, says the UK Space Agency.
Its Sabre engines use liquid hydrogen combined with oxygen from the air at altitudes up to 26km and speeds of up to Mach 5, before switching over to on-board liquid oxygen for the final stage of ascent.
"Space has many things to offer humanity, but the sheer expense of rockets - which have served us well in the past - is inhibiting the growth of commercial activity in space," says Alan Bond, inventor of the Sabre engine and managing director of Reaction Engines.
"To take one example, Skylon promises to cut the cost of launching communication satellites, on which the digital revolution depends, by an order of magnitude."
And, finally, Skylon has received approval from a European Space Authority panel tasked with evaluating the design.
"No impediments or critical items have been identified for either the Skylon vehicle or the SABRE engine that are a block to further development," its report concludes.
"The consensus for the way forward is to proceed with the innovative development of the engine which in turn will enable the overall vehicle development."
The UK Space Agency says that Reaction Engines will carry out an important demonstration of the engine's key pre-cooler technology later this summer.