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Revolutionary spaceplane engine concept achieves key milestone

28 November 2012

The UK-based company developing an engine for a new type of spaceplane says it has successfully demonstrated the power unit's revolutionary technology. Reaction Engines Ltd (REL) of Culham, Oxfordshire, ran a series of tests on key pre-cooler elements of its Sabre propulsion system under European Space Agency (ESA) observation, which confirmed that all the demonstration objectives were met. 

The revolutionary Sabre engine would power the Skylon spaceplane and would breathe oxygen at low altitude and switch to rocket propulsion  higher up
The revolutionary Sabre engine would power the Skylon spaceplane and would breathe oxygen at low altitude and switch to rocket propulsion higher up

The company claims the major technical obstacle to its concept has now been removed.

REL is developing the engine for an 84 metre-long vehicle called Skylon. This spaceplane would take off and land on a conventional runway but could achieve low-space orbit, as well as fly at Mach-5 between cities, reducing the duration of a flight between London and Sydney to four hours. 

The vehicle would burn a mixture of hydrogen and oxygen, but in lower atmospheric levels the oxygen would be taken from the air, like a jet engine.

"This is a big moment; it really is quite a big step forward in propulsion," said Alan Bond, the driving force behind the Sabre engine concept.

The pre-cooler demonstration was a critical step in proving the Skylon concept. Only once it had achieved very high speeds would Skylon switch to full rocket mode, burning onboard fuel supplies.

Taking its oxygen from the air in the initial flight phase would mean Skylon could fly lighter from the outset with a higher thrust-to-weight ratio, enabling it to make a single leap to orbit, rather than using and dumping propellant stages on the ascent - as is the case with current expendable rockets.

If such a vehicle could be made to work, its reusability should transform the costs of accessing space.

But success depends on the Sabre engine's ability to manage the very hot air entering its intakes at high speed with the gases having to be cooled prior to being compressed and burnt with the onboard hydrogen.

REL's solution is a module containing arrays of extremely fine piping that can extract the heat and plunge the incoming air to minus 140C in just 1/100th of a second.

Ordinarily, the moisture in the air would be expected to freeze out rapidly, covering the piping in a blanket of frost and dislocating their operation. But the company's engineers have also devised a means to control the frosting, permitting the Sabre engine to run in jet mode for as long as is needed before making the transition to full rocket mode to take the Skylon spaceplane into orbit.

It is the innovative helium cooling loop with its pre-cooler heat-exchanger that REL has been validating on an experimental rig. "We completed the programme by getting down to -150C, running for 10 minutes," said Mr Bond. "We've demonstrated that the pre-cooler is behaving absolutely as predicted."

"With this now successfully demonstrated by REL, there are currently no technical reasons why the Sabre engine programme cannot move forward into the next stage of development."

The next phase is a three-and-a-half-year project. It would see a smaller version of Sabre being built on a test rig. The demonstrator would not have the exact same configuration as the eventual engine but it would allow REL to prove Sabre's performance across its air-breathing and rocket modes.

The company must now raise the £250m needed to complete the next phase of development which would essentially take the project to the final designs that could be handed to a manufacturer. 

"The project to date has been more than 90% privately funded, and we intend to continue with that type of structure," explained Tim Hayter, the CEO of REL.

The UK government is currently assessing what shape any involvement it should have in the next phase of Skylon/Sabre.

In addition, ESA is keen to do some study work with REL. Although it is currently working on new versions of its Ariane rocket - a classic expendable vehicle - the agency also wants keep an eye on future launcher technologies.

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