Space Plane Tech Could Power Aircraft for US Military

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Engine technology being developed for a British space plane could also find its way into hypersonic aircraft built by the U.S. military.

The U.S. Air Force Research Laboratory is studying hypersonic vehicles that would use the Synergetic Air-Breathing Rocket Engine (SABRE), which the English company Reaction Engines Ltd. is working on to power the Skylon space plane, AFRL officials said.

"AFRL is formulating plans to look at advanced vehicle concepts based on Reaction Engine's heat-exchanger technology and SABRE engine concept," officials with AFRL, which is based in Ohio, told Space.com via email last month. [The Skylon Space Plane (Images)]

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Courtesy of Sir Richard Branson

A bold British space plane concept

SABRE and Skylon were invented by Alan Bond and his team of engineers at the Abingdon, England-based Reaction Engines.

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SABRE burns hydrogen and oxygen. It acts like a jet engine in Earth's thick lower atmosphere, taking in oxygen to combust with onboard liquid hydrogen. When SABRE reaches an altitude of 16 miles (26 kilometers) and five times the speed of sound (Mach 5), however, it switches over to Skylon's onboard liquid oxygen tank to reach orbit. (Hypersonic flight is generally defined as anything that reaches at least Mach 5.)

Two SABREs will power the Skylon space plane — a privately funded, single-stage-to-orbit concept vehicle that is 276 feet (84 meters) long. At takeoff, the plane will weigh about 303 tons (275,000 kilograms).

The SABRE heat exchanger is also known as a pre-cooler. It will cool the air entering Skylon's engines from more than 1,832 degrees Fahrenheit (1,000 degrees Celsius) down to minus 238 degrees Fahrenheit (minus 150 degrees C) in one one-hundredth of a second. The oxygen in the chilled air will become liquid in the process. [Skylon's Many Possible Missions (Video)]

"The [pre-cooler] performance has always been pretty much what we predicted," Bond explained in an interview with Space.com at the Farnborough International Airshow in England on July 16. "We've now done over 700 actual tests. It's now done as much service as a pre-cooler would in a real engine."

Bond's team has also successfully tested the pre-cooler for a problem aviation jet engines have to deal with: foreign objects being sucked in.

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"We know it [the pre-cooler] can take debris, insects, leaves," Bond said.

Working with the U.S. military

Bond estimates that the pre-cooler is now at a technology readiness level (TRL) of about 5. NASA and AFRL use a 1-to-9 TRL scale to describe a technology's stage of development. According to NASA's TRL descriptions, 5 represents "thorough testing" of a prototype in a "representative environment."

The AFRL work is being carried out under a Cooperative Research and Development Agreement (CRADA) with Reaction Engines that was announced in January. AFRL officials told Space.com that they are using computers to model SABRE.

"The Air Force research laboratories in the States have carried out some modeling to verify that the SABRE does actually work, that it is a real engine, and so I am hoping they are going to confirm that very soon," Bond said.

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"This is obviously opening doors in the United States, and again, I can't say a great deal about that, but we have very good dialogue going across the Atlantic," he added. "In the next couple of years, it's going to be quite exciting."

Bond declined to confirm rumors of organized support within the U.S. aerospace community that involves former senior program managers of the U.S. military's most high-profile defense projects.

Bond sees Skylon as an international project that would include the U.S. and Europe.

"We're in dialogue with people across Europe in regard to supplying [rocket engine components]. We don't want to reinvent the wheel; we'd like to be the engine integrator and put it on our test facilities and run it," he explained.