Skylon Spacecraft's Engines Passes Critical Test

Reaction Engines Ltd. on Wednesday, November 28, 2012 announced the completion of a critical round of testing the precooler system its Sabre machine. Sabre is a radical type of hybrid jet/rocket engine that can propelling a spacecraft into orbit or flight in the atmosphere, at speed of Mach 5 (3,800 mph, 3,300 knots, 6,115 kph).

This machine will be used for Reaction Engines's Skylon spacecraft and LAPCAT A2 hypersonic aircraft.

The unconventional Skylon rocketplane could be the next generation space shuttle. (Picture from: http://randommization.com/)

The Lapcat A2 hypersonic aircraft. (Picture from: http://www.reactionengines.co.uk/)

The Company has conducted its own tests earlier this year at its facility in Oxfordshire, England, and the series was conducted under the supervision of the European Space Agency (ESA) on behalf of the UK Space Agency to provide official validation of the technology. According to Reaction Engines press release, "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."

Skylon in flight. (Picture from: http://www.gizmag.com/)

Skylon was Single Stage To Orbit (SSTO) spacecraft designed to take off and land at a conventional airport. Unlike hypersonic aircraft in general, Skylon will take off and accelerate to hypersonic speeds under its own power using Sabre engine, without requiring the rocket boosters. The engine is thermodynamically simple, but very complex in engineering. It is designed to be extremely light, with the skin of some components being thinner than a human hair.

A rendering of Skylon in flight, showing the Sabre engine. (Picture from: http://www.gizmag.com/)

According to the makers of Skylon, the engines are possible to be built with current technology. It can take about 15 tons of cargo into space, and since it is reusable, it can greatly reduce the costs involved. Since the spacecraft does not have have to throw away high-tech equipment on each flight, the costs involved are further reduced. It is estimated that flights of Skylon would cost U.S. $40 million, which is much cheaper than numerous other options available.

Skylon's internal layout. (Picture from: http://www.gizmag.com/)

The SSTO rocket is designed to return to Earth, the payload is even smaller. Skylon's Sabre engine reduces the need for carrying so much oxygen by using air like a jet plane, to burn its fuel for part of the ascent. Sabre is basically a rocket engine that uses a precooled compressor for part of the ascent. It acts as an air-breathing jet until it reaches Mach 5 and a height of 25 kilometers (15,53 miles). At this time, it had 20 percent on its way to space. For the other 80 percent, Sabre convert to a pure rocket mode using the onboard storage of liquid oxygen instead of air to reach into orbit at a speed of Mach 25 (19,000 mph, 16,500 knots, 30,600 kph).

Cutaway of the Sabre engine with notes. (Picture from: http://www.gizmag.com/)

The Sabre engine requires the incoming air to be compressed to 140 atmospheres. This compression makes the air so hot that it would melt any known material, so the incoming air needs to be pre-cooled to nearly liquid. In previous experimental engine that uses cryogenic hydrogen fuel to cool the heat exchanger, but the engine is wasteful of fuel and causing all sorts of problems, such as making the metal brittle.

The Sabre engine in air-breathing mode. (Picture from: http://www.gizmag.com/)

The Sabre get around this by using a closed-loop helium cycle. It is designed to cool the incoming air flow from over than 1,000ºC (1,832ºF) to -150ºC (-238ºF) in less than 1/100th of a second without blocking with frost. It's not waste the use of hydrogen, which keeps helium loop cold and avoids hydrogen brittling, making it more heat-resistant materials may be used. After cooling, a "relatively conventional" turbo compressor using jet engine technology can be used to compress the air to the required pressure - "relatively" being the word for a machine designed to go into space.

Reaction Engines still requires one year completed engine and the construction Skylon aircraft was a year after that, though the company remains optimistic and is currently seeking additional funding to continue the development of this spacecraft. *** [GIZMAG  | REACTION ENGINE | FROM VARIOUS SOURCES | EKA]

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