Space Plane Tech Could Power Hypersonic Aircraft​ for US Military

This artist's illustration depicts the Skylon concept vehicle.

Credit: Adrian Mann

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 reporters.

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

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.

Two SABREs will power the Skylon space plane, a privately funded, single-stage-to-orbit concept vehicle t-hat 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.

"The [pre-cooler] performance has always been pretty much what we predicted," Bond explained to reporters 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.

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

ESA test opens way to UK spaceplane engine investment

The Synergistic Air-Breathing Rocket Engine, or SABRE, seen in place on a Skylon spaceplane. 

Designed by UK company Reaction Engines Ltd, this unique engine will use atmospheric air in the early part of the flight before switching to rocket mode for the final ascent to orbit. 

The concept paves the way for true spaceplanes - lighter, reusable and able to fly from conventional runways. 

Reaction Engines plan for SABRE to power a 84 m-long pilotless vehicle called Skylon, which would do the same job as today's rockets while operating like an aeroplane, potentially revolutionising access to space. 

Image courtesy Reaction Engines Ltd.

Reaction Engines plans for SABRE to power a 84 m-long pilotless vehicle called Skylon, which would do the same job as today's rockets while operating like an aeroplane, potentially revolutionising access to space.

The investment decision followed the success of ESA-managed tests of a key element of the SABRE design, a precooler to chill the hot air entering the engine at hypersonic speed, in Reaction Engines' Oxfordshire headquarters back in November 2012.

"Ambient air comes in and is cooled down to below freezing in a fraction of a second," explained Mark Ford, head of ESA's propulsion section. "These types of heat exchangers exist in the real world but they're the size of a factory.

"The key part of this is that Reaction Engines has produced something sufficiently light and compact that it can be flown.

"The idea behind the engine is that the vehicle flies to about Mach 5 in the lower atmosphere using airbreathing before it switches internal liquid oxygen for the rest of its flight to orbit.

"At that speed, the air is coming in extremely fast. You need to slow it down in order to burn it in the engine, and doing so will raise the temperature of the air to about a thousand degrees, which can exceed engine material temperature limits.

"Hence the concept of the precooler is to cool the air down to a temperature that is then usable by the engine."

"The idea has been around since the 1950s but this is the first time anyone has managed to achieve a working system. Nobody else has this technology, so Europe has a real technological lead here."

SABRE Engine: Skylon spaceplane's revolutionary engine passes key milestone

Illustration of the Skylon spaceplane powered by SABRE engines. 

Credit: REL/Adrian Mann

A revolutionary new air-breathing rocket engine designed to propel a spacecraft to orbit in a single stage has passed a critical milestone.

The engine could also revolutionise air travel, reducing journey times around the planet to under 4 hours.

The engine, called SABRE, is a hybrid of a jet engine and a rocket engine. An aircraft fitted with the engines could fly to other side of the planet in under 4 hours travelling at Mach 5.5. more than five times the speed of sound, whilst a spaceplane such as Skylon could be propelled into orbit in a single stage.

The engines breathe in air as they pass through the atmosphere, meaning the spaceship could launch without a fully laden fuel load.

However, the challenge of the design has been how to cool the huge amount of air it continuously breathes in without the engine freezing up.

The testing has proved that SABRE's pre-cooler heat exchangers can cool air from over 1,000⁰C to minus 150⁰C in less than 1/100th of a second without the engine frosting up.

The UK company which invented the new propulsion technology, Reaction Engines Limited (REL) described the successful testing as "the biggest breakthrough in aerospace propulsion technology since the invention of the jet engine".

REL has also devised a spaceplane called Skylon that would be fitted with the SABRE engines. Skylon would take off and land on runways, and would not require any part of the craft to be jettisoned during its journey to orbit.

This would make it a completely reusable spacecraft which could reduce the time and cost of launching payload into space.

REL believe the cost of launching satellites could be cut by 90% if the SABRE powered Skylon entered service.



The UK Space Agency asked experts from the European Space Agency (ESA) to validate the pre-cooler heat exchanger test results

ESA experts who reviewed the testing concluded "The pre-cooler test objectives have all been successfully met and ESA are satisfied that the tests demonstrate the technology required for the SABRE engine development."

The SABRE engine has the potential to revolutionise our lives in the 21st century in the way the jet engine did in the 20th Century. This is the proudest moment of my life. Alan Bond, REL

Illustration of the SABRE engine with the location of the pre-cooler heat exchanger highlighted in blue. Credit: REL/Adrian Mann

SABRE Engine: The Biggest Breakthrough In Propulsion Since The Jet Engine

The SABRE engine has the potential to revolutionise lives in the 21st century in the way the jet engine did in the 20th Century.

Reaction Engines can announce the biggest breakthrough in aerospace propulsion technology since the invention of the jet engine.

Critical tests have been successfully completed on the key technology for SABRE, an engine which will enable aircraft to reach the opposite side of the world in under 4 hours, or to fly directly into orbit and return in a single stage, taking off and landing on a runway.

SABRE, an air-breathing rocket engine, utilises both jet turbine and rocket technology. Its innovative pre-cooler technology is designed to cool the incoming airstream from over 1,000C to minus 150C in less than 1/100th of a second (six times faster than the blink of an eye) without blocking with frost.

The recent tests have proven the cooling technology to be frost-free at the crucial low temperature of -150C.

The European Space Agency (ESA) has evaluated the SABRE engine's pre-cooler heat exchanger on behalf of the UK Space Agency, and has given official validation to the test results: "The pre-cooler test objectives have all been successfully met and ESA are satisfied that the tests demonstrate the technology required for the SABRE engine development."

Minister for Universities and Science, David Willetts said: "This is a remarkable achievement for a remarkable company.

Building on years of unique engineering know-how, Reaction Engines has shown the world that Britain remains at the forefront of technological innovation and can get ahead in the global race. This technology could revolutionise the future of air and space travel."

Well over 100 test runs, undertaken at Reaction Engines Ltd's facility in Oxfordshire, integrated the ground-breaking flight-weight cooling technology and frost control system with a jet engine and a novel helium cooling loop, demonstrating the new technologies in the SABRE engine that drive its highly innovative and efficient thermodynamic cycle.

This success adds to a series of other SABRE technology demonstrations undertaken by the company including contra-rotating turbines, combustion chambers, rocket nozzles, and air intakes and marks a major advance towards the creation of vehicles like SKYLON - a new type of reusable space vehicle that will be powered by SABRE engines, designed primarily to transport satellites and cargo into space.

Alan Bond, who founded Reaction Engines to re-build the UK's rocket propulsion industry and has led the research from the start, said: "These successful tests represent a fundamental breakthrough in propulsion technology.

Reaction Engines' lightweight heat exchangers are going to force a radical re-think of the design of the underlying thermodynamic cycles of aerospace engines.

These new cycles will open up completely different operational characteristics such as high Mach cruise and low cost, re-usable space access, as the European Space Agency's validation of Reaction Engines' SABRE engine has confirmed.

The REL team has been trying to solve this problem for over 30 years and we've finally done it. Innovation doesn't happen overnight. Independent experts have confirmed that the full engine can now be demonstrated.

The SABRE engine has the potential to revolutionise our lives in the 21st century in the way the jet engine did in the 20th Century. This is the proudest moment of my life."

Dr Mark Ford, ESA's Head of Propulsion Engineering, said: "One of the major obstacles to developing air-breathing engines for launch vehicles is the development of lightweight high-performance heat exchangers.

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