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Revolutionary rocket engine passes U.S. Air Force feasibility test

Charles Black, Founder and CEO of Sen
Apr 16, 2015, 15:55 UTC

Sen—A revolutionary engine concept developed by a UK company, Reaction Engines Limited, has passed a feasibility test conducted by the U.S. Air Force Research Laboratory.

The engine, known as SABRE—which stands for Synergetic Air-Breathing Rocket Engine—could be used to power a spaceplane from a runway to orbit in a single stage.

The engine is designed to reach Mach 5.5 (4,500 mph) whilst in air-breathing mode in the atmosphere (about twice as fast as a jet engine) and then transition to "rocket mode" accelerating to orbital velocity of about Mach 25.

The key component of the engine is its heat exchanger technology which can cool the air it sucks in from 1,000°C to minus 150°C in one hundredth of a second, without frosting up. The team at Reaction Engines, led by Chief Engineer Alan Bond, have spent over two decades developing the technology.

Because the engine "breathes" air it avoids the need to launch with heavy fuel loads. The weight saving would enhance a vehicle's launch capabilities, and the engines could be used to power a reusable spaceplane with the ability to take-off and land on a runway, increasing operational efficiencies and reducing launch costs.

Reaction Engines entered into the Cooperative Research and Development Agreement (CRADA) with the U.S. Air Force Research Laboratory's Aerospace Systems Directorate (AFRL) back in Jan. 2014, as reported by Sen.

Reaction Engines and AFRL will now collaborate to consider vehicle concepts which could be powered by a SABRE propulsion system. For example, the engine could be used to power a horizontal take-off single stage or two-stage-to-orbit spaceplane. It could also be used to empower an aircraft to fly at hypersonic speed—five times the speed of sound—from one side of Earth to the other in under four hours.

Reaction Engines, however, is not planning to build a spaceplane or aircraft, but rather develop the engine and supply them to aerospace companies who choose to use the technology. 

Barry Hellman, program manager at the U.S. Air Force Research Laboratory, said in a statement: "The activities under the CRADA [research and development agreement] have allowed AFRL to understand the SABRE engine concept, its pre-cooler heat exchanger technology, and its cycle in more detail. Our analysis has confirmed the feasibility and potential performance of the SABRE engine cycle.

"While development of the SABRE represents a substantial engineering challenge, the engine cycle is a very innovative approach and warrants further investigation. The question to answer next is what benefit the SABRE could bring to high speed aerospace vehicles compared to other propulsion systems.

"Although application of the SABRE for single-stage-to-orbit space access remains technically very risky as a first application, the SABRE may provide some unique advantages in more manageable two-stage-to-orbit configurations. Furthermore, the heat exchanger technology also warrants further investigation for applications across the aerospace domain."

Previous test results for the SABRE technology have also been validated by the European Space Agency (ESA) following a request from the UK government.

However, a finished engine is still a long way off—if development all goes to plan it will be four to five years before a prototype SABRE engine is ready to be fully tested. The testing would measure its fuel consumption and thrust to weight ratio. If the testing proves successful, the next step would be installing the engines into a vehicle for flight testing.

Earlier this year in an exclusive interview with Sen, Alan Bond told us: “If we manage to pull this off, then by the time we get to 2030, access to space will be more like you see in science fiction films than the way it is today.  

“So regular vehicles flying into orbit and back again on a daily basis, and all that sort of stuff, carrying out all sorts of useful tasks. That will actually be with us and that is something pretty exciting to look forward to.” 

Sam Hutchison, Director of Corporate Development at Reaction Engines Ltd said in a statement: “The confirmation by AFRL of the feasibility of the SABRE engine cycle has further validated our team’s own assessment and conviction that the SABRE engine represents a potential breakthrough in propulsion that could lead to game-changing space access and high speed flight capability. We look forward to continued collaboration with AFRL.”

Although Reaction Engines is a private company and completed a further investment round in 2014, the company's SABRE development program is receiving funding from the European Space Agency. The company also received a boost from the UK government which has provided a research and development grant worth £60 million ($88 million).

The company recently announced that Mark Thomas, who has been working at Rolls-Royce as Chief Engineer for Technology and Future Programmes, is joining Reaction Engines as Managing Director on May 25.

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Cutaway illustration of SABRE. Image credit: Reaction Engines Limited

SKYLON SABRE Heatex from Reaction Engines Ltd on Vimeo.