I’m sure you’ve heard the one:what do you get if you cross a sheep and a spacecraft?Or what about:what do you get if you cross a plane and a spaceship?Well to see if you come up with the same answers as me, read on…

Over the years comic book illustrators and movie makers have imagined the most fantastic and often impossible vehicles for their characters or superheroes to be seen in.Years later, as our technology has greatly improved, by the most bizarre coincidences we often see a parallel between these old designs and new vehicles that have become a reality.Evolving from an undeveloped craft called Hotol from the 1980s, one such project that looks to be shaping up in this direction is today known as Skylon.

image of skylon side-on

Skylon in profile (Image credit:GW Simulations)

Early charcoal-coloured concept designs look like something Batman would keep in his Batcave.The Skylon is essentially a large missile-shaped fuselage with a couple of nose fins, tail fins, and small wing-like projections half-way along its length. They carry two sleek engines, fixed close to the body of the plane. Skylon’s components are not however being built in the cellars of Bruce Wayne’s mansion, but on the premises of Reaction Engines Limited, in Oxfordshire.

Known as an SSTO or ‘Single Stage to Orbit’ vehicle, this revolutionary plane will take off conventionally from an airport runway, then head vertically up, into space in one fell swoop.Its most likely function in the spaceflight market would be as a fast transport vehicle for depositing satellites outside the Earth’s atmosphere before returning to Earth and landing on a conventional runway.If successful, this British concept would obviously have great commercial potential, perhaps paving the way for many to fulfil a lifelong dream.The dream of entering space.


Image of Skylon and shuttle comparison

The sharply-pointed nose, tiny wings and engines on wingtips give Skylon an astonishing retro look.(Compare it to the unbuilt Lockheed CL-400 Suntan and Avro 730.) Skylon’s sleek profile is a sharp contrast with that of the chunky Space Shuttle. (Image credit: Armagh Planetarium based on original graphics from GW Simulations and NASA)


This futuristic plane’s unique ability to straddle two very different flights zones, the skies and outer space, is essentially down to one component. Its Sabre engines. In technological terms, this cutting edge engineering possesses a ‘heat exchanger’ that can not only super-cool scorching engine air temperatures enabling the space plane to travel five times faster than the speed of sound, but also can use the oxygen content of passing air while it flies in Earth’s atmosphere. This of course removes the need for the space-bound vehicle to carry a fuel load of liquid oxygen in an external tank like earlier designs. Remove the need for vertical take-off, and we could dispense with the expensive launchpad, so ingrained into our mind’s eye when we think about space flight.

It’s hard not to imagine some superhero sitting in the cockpit pushing a red button when we learn that on reaching the highest boundaries of Earth’s atmosphere, Skylon’s Sabre engines go into ‘rocket mode’, taking the plane’s occupant on into space. The Sabre engine’s landmark achievement is not only that it will be able to take a plane straight into space, but if Skylon becomes a reality, the world also will become a smaller place as flight times to anywhere would be reduced to four hours.

Although the plan has not as yet received the official stamp of approval, an ESA/UK government testing program could not find any major engineering difficulties with the design.Skylon developer Alan Bond who has been pursuing the concept since the 80’s, is confident that the project will come to fruition and make space travel easier.

So finally, to return to the start:what do you get if you cross a sheep and a spacecraft?The answer of course is:Apollo neck (try saying it out loud). And then, in answer to the second question: what do you get if you cross a plane and a spaceship? Well we both know the answer to this one. Without a doubt it is Skylon.

(The history of spaceplanes – winged spacecraft – is summarised in Space.com’s infographic)
See how engineers turned the dream of winged spaceship into reality with NASA's space shuttle in this SPACE.com infographic.
Source SPACE.com: All about our solar system, outer space and exploration

(Article by Nick Parke, Education Support Officer)


Wes · July 20, 2015 at 18:16

I am from the USA and don’t think heard anything about the Skylon plane before so I assume a possibility that by now something came up wrong. It seem to be the operational margins were slim meaning the complexity of the propulsion system. I am not an engineer but think using one or a single rocket engine (s) fire into Earth orbit requires the most ISP Instead use three on/off rocket engine (s) burns into Earth orbit I believe for the least ISP. Thank you, Wes D.

Mike · August 30, 2012 at 20:02

Although I am not an engineer nor do I have any connections with the aviation sector, I do feel proud that the UK might soon take it’s place in the history of space exploration. On the other hand I am concerned that, like so many projects of the past, Skylon may yet become another British aerospace failure and our transatlantic friends will once again smile in the knowledge that American “know-how” will continue to lead the way into space.

Andrew W · August 17, 2012 at 23:38

A post I made a little over a year ago, it might be a little dated now, but I think the basic argument remains valid: Skylon is supposed to have a huge physical size (about the size of an A380) but have a dry mass (excluding the respective engine masses) only a tenth that of an A380:

After running through the mass numbers for Skylon that Reaction Engines offers, I’m left believing that they’ve got an engine that will theoretically get them to orbit in one stage, but only by them making unrealistic assumptions about the structural weight of the rest of the vehicle, total dry mass 53 tonnes, engine thrust 270 tonnes, engine T/W 14 therefore mass of engines ~19 tonnes, therefore mass of the rest of the vehicle ~34 tonnes. 34 tonnes for a winged vehicle that’s 83 meters long, carries all its landing gear to orbit, it has a propellant volume around 1400^3 meters, it uses cryogenic propellants and it has to endure re-entry. I know they’re promoting Skylon as having revolutionary construction materials and methods, but it seems to me they’ve had to make some excessively optimistic assumptions about the structural weight to get the numbers to come together so they can continue with their pet project – the engines.

Looking at it another way: The combined propellant tank volume by my math (with a few assumptions on the current LH2:LOX ratio) would have enough volume to hold 500 tonnes of LH2/LOX at a 1:6 ratio, lets allow structural weight growth of 20% for the heavier take-off weight making structural wt 40.8 tonnes, 2 SSME’s (or easily maintained equivalent) is + 6.4 tonnes, so total unladen weight is 47.2 tonnes, add a P/L of 15 tonnes and also the 500 tonnes LOX/LH2 and you get a take-off weight of 562.2 tonnes, at engine shut off weight is 62.2. Mo/M1 is 9.03, delta V at Ve 4500 m/s is 9907m/s.

9.2 km/s is about all you need to get into orbit.

    admin · August 20, 2012 at 09:32

    That’s an interesting analysis which I can’t fault. I get the distinct impression that reuseable launch vehicle promoters are super-optimistic when their vehicle is at the vapourware stage, assuming that a miracle or two will occur doing the development process. I would love Skylon or something like it to fly, but I can’t see it happening.

    What amazes me is that a tiny company like Reaction Engines hopes to build, with private finance, a vehicle with revolutionary powerplant and structure and a performance beyond any X-plane, when it takes the giants of aerospace decades (with government support) to create far more mundane aircraft like the A380, F-35 or Typhoon. They certainly seem serious and I guess we ought to admire their optimism.

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