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ESA review finds 'no impediments' for SKYLON spaceplane development


June 26, 2011

Skylon spaceplane

Skylon spaceplane

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After nearly 30 years of service, the Space Shuttle fleet is due to enter retirement with the last ever mission scheduled for takeoff on July 8, 2011. In its lifetime, the world's first Reusable Launch Vehicle (RLV) has provided information that will prove invaluable for the next generation of spacecraft that will succeed it. One such craft is the Skylon, an unpiloted, single-stage, reusable spaceplane currently under development by UK-based Reaction Engines Ltd. (REL). The Skylon got a shot in the arm last month with the release of a technical review of Skylon carried out by the European Space Agency (ESA) that concluded there are "no impediments" that would prevent the continued development of the Skylon and its SABRE engine.

The Skylon design, which grew out of the HOTOL (Horizontal Take-Off and Landing) program by Rolls Royce and British Aerospace that was terminated in 1988, consists of a slender fuselage containing propellant tankage and payload bay, with delta wings attached midway along the fuselage carrying the SABRE engines in axismmetric nacelles on the wingtips.

With a payload bay measuring 4.6 m (15 ft) in diameter and 12.3 m (40 ft) long, Skylon is designed to transport up to 15 tons of cargo into Low Earth Orbit (LEO, approx. 300 km /186 mile) at about 1/50th of the cost of traditional expendable launch vehicles, such as rockets. It could also carry 10.5 tons to a 460 km (286 mile) equatorial space station, or 9.5 tons to a 460 km x 28.5 degree space station, when operating from an equatorial site.

Skylon's fuselage and wing load bearing structure would be made from carbon fiber reinforced plastic, with the aluminum propellant tankage suspended within that is free to move under thermal and pressurization displacements. The external shell would be made from a 0.5 mm thin fiber reinforced ceramic that is corrugated for stiffness and free to move under thermal expansion. During re-entry, heat is radiated away from the hot aeroshell and prevented from entering the vehicle by layers of reflective foil and low conductivity shell support posts.

Unlike the Space Shuttles, which launch vertically with the majority of thrust provided by two solid rocket boosters that are jettisoned two minutes after liftoff, the Skylon takes off and lands horizontally on a (heavily reinforced) conventional runway courtesy of its SABRE (Synergistic Air-Breathing Rocket Engine) engines, which have a dual mode capability.

SABRE is not a scramjet like that being used in the X-51A Waverider, but rather a jet engine running combined cycles of a pre-cooled jet engine, rocket engine and ramjet. In air-breathing mode, which is employed from takeoff to when the spacecraft reaches Mach 5, the SABRE engines use atmospheric oxygen in place of liquid oxygen in the combustion process with stored liquid hydrogen. This reduces the quantity of oxidizer that a vehicle is required to carry, thereby enabling a single-stage to orbit (SSTO) spacecraft.

Once Skylon hits Mach 5 at 93,500 ft, the engine switches to a closed cycle using stored liquid oxygen and liquid hydrogen from the on-board fuel tanks. Under this pure rocket propulsion, Skylon is able to reach orbital velocity of around Mach 25.

REL's ambitious aim of 10 years development time for the Skylon received a shot in the arm last month when the UK Space Agency's technical assessment on the Skylon, for which the ESA was commissioned, was released. The report stated that the SABRE engine and Skylon vehicle can be developed with "today's current technology," and that, "no impediments or critical items have been identified for either the Skylon vehicle or the SABRE engine that are a block to further developments".

The technical assessment process comprised two parts. The first was a series of visits by ESA technical teams to review designs and tests of component performance, while the second was a Skylon System Requirement Review that saw almost 100 international aerospace experts pose questions and make comments on the proposed spacecraft's technical and economic feasibility.

Calling the review a success, REL is looking to demonstrate its heat exchanger technology later this year before moving onto Phase III of the program. The total cost of the program is about US$10 billion, but REL says Skylon will be able to repay its development costs, meet its servicing and operating costs and turn a profit for its operators whilst being an order of magnitude cheaper to customers than current space transportation systems.

The UK Space Agency's Skylon technical assessment produced by the ESA can be downloaded here.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

Great. With 9.5t payload to reach the ISS the Skylon should be able to transport a kind of manned pressurised payload to transport personal to the Spacestation so that we don\'t have to rely on the Russians. Maybe even a kind of hull that makes ist possible to leave the Skylon in orbit to repair a sat. But needless to say. ESA ist not NASA. They don\'t have any ideology other than to make money and from their point of view, there is no money to make in manned space travel. Shame on us.


Unfortunately, NASA is not what NASA was- like so much today.

Unless there is IMMEDIATE tangible profit at hand, much creativity is ignored.

Man is choking on greed while he ruins the world.

Atlas still shrugs in perplexity...


This has potential - conventional take-off spacecraft can potentially be much more efficient than vertical take-off launches, especially with a mothership and parasite launch concept, but the X-15, space ship 1 etc have just never boosted high enough and were never intended to orbit, they\'re built on too small a scale. I also puzzle at how this configuration can re-enter safely.

Also, I agree with the previous comment - sadly, it will take some very progressive governments to put forward funding for such a project, and then the bickering will ensue over who gets to build which part, and where it will be assembled.


Check out the Junkers RT 8-1-01 \"Raumtransporter,\" 1960s design. It might work with today\'s materials and technology.

William Lanteigne

This is exactly what we need.

Unfortunately the present international space station program will end by the time this is operational.

Very nice.


Ten years?? This seems like a long time to wait for the delivery van to arrive with the groceries and spare parts!!

Especially with the termination of the Space Shuttle

George Leavitt

Getting away from vertical launch is a major step forward. It massively reduces the required thrust for takeoff.

Progressive governments are the problem with space exploration. The extended tank X-15A was never used for a straight up maximum altitude test, and its successor the X-15B that was designed to reach orbit was killed in favor of disintegrating totem poles.

The greatest triumph of putting a man on the moon and returning him safely to earth was achieved by building rockets that not even the USofA could afford to operate for long.

Making a cheep to operate unmanned launch system is the first step. If they make it cost the equivalent of 2oz of gold or less to put a ton into orbit, with reasonable reliability, it will not stay unmanned for long.


Looks like a clipped wing YF-12A. ;) It\'s also black and has corrugated parts to control thermal expansion, like the YF-12A and SR-71.

Gregg Eshelman

especially for a cargo frieghter, the use of a mechanical or magnetic slingshot could further reduce onboard fuel storage needs and perhaps increase payload capacities. An even better idea would be a laser powered space elevator.


Alan Bond from Reaction engines gave a pretty fascinating lecture about this at the university of Strathclyde. Air breathing engines bring down the mass ratio (weight of rocket with propellant vs without) or more obviously they use less propellant because they can get some of it as they fly (from the air) whereas rockets have to carry tanks of oxygen all the way.

It\'s very challenging to make air breathing engines that work above mach 5, however, and you already have most of the benefit that can be obtained by the time you reach this speed. Some designs have a jet engine and a rocket engine and swap over but this makes the craft heavy. Skylon\'s innovation is to use only a rocket engine which needs to be supplied with liquid oxygen and to get that by liquifying air as it comes into the engine. In other words the rocket thinks it\'s always a rocket even though it starts off getting air from the atmosphere. After Mach 5 the engine closes off and oxygen comes from internal tanks. The cooling is done by using the hydrogen fuel to cool incoming air.

This is also not a completely new technology (Liquid Air Cycle Engine - LACE) but the SABRE engine in Skylon is particularly good and does it\'s job very efficiently because of the way the cooling system for incoming air works. The precooler is the big technology item.

The lecture can be seen here: http://www.youtube.com/watch?v=2G-HPHNrrLQ

There\'s also a good discussion and lots of technical info in the Nasa spaceflight forum about Skylon: http://forum.nasaspaceflight.com/index.php?topic=24621.0

Timothy Murphy
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