Skylon: What is it, and why is it so cool?

skylon whiteIf you’re an ubergeek then you probably already know about Skylon and its potential to revolutionize the aerospace industry. If, on the other hand, you’re just an ordinary science fiction fan like me, you might be forgiven for assuming it has something to do with the sentient and somewhat preachy robots from the Battlestar Galactica franchise.

For the benefit of those of you who are scratching your heads and/or arses right now, Skylon is in fact a design for an experimental new space-plane. Not only is this new spacecraft design super cool, remarkably practical, and a little bit sci-fi (adding to the super-coolness factor), it might just be the future of human space flight.


The trouble with space travel has always been the difficulty and expense of actually getting into outer space. That, and the problem of how to get back home once you’re there. Of course, we’ve been able to do this for quite some time now, but not particularly very well. While many people might think we’ve got the whole launch and landing thing pretty much licked, we science fiction fans recognize that our efforts have only just begun. From a science fiction point of view, conventional rockets are a little bit crude, a little bit inconvenient, and a little bit old hat. From the practical point of view taken by most ordinary people, rockets are also just a little bit too expensive and somewhat wasteful.

The big problem with rockets is that they require huge amounts of fuel. This means that they also have to be excessively large. Much of this extra rocket also ends up going to waste, being jettisoned immediately after launch to burn up in the Earth’s atmosphere. After all that fuel burning and all that jettisoning, only a tiny capsule survives to return to Earth, and that usually goes to waste soon after (usually ending up in a museum somewhere). Of course, the Space Shuttle did solve some of these issues, but alas, they are no more.

skylonIt’s time for something new, something better.

As a successor to the Space Shuttle, the Skylon spaceplane has been envisioned as a 100% reusable launch vehicle. It will be more efficient and cheaper to operate  and it will be capable of carrying payloads similar to that of the Space Shuttle. Skylon will be slightly larger than the Space Shuttle, but as a single-stage-to-orbit vehicle, no part of spacecraft will need to be jettisoned.

Skylon will be a true spaceplane, able to function within the atmosphere and to reach a high orbit. It will be able to take off and land using an ordinary runway, and it will require only two days of maintenance between missions.

How is Skylon able to do all of these things? Well, it’s largely due to a new type of rocket engine known as SABRE, which is currently in development. It’s also due to lessons learned from the design, extended use, and ultimate failure of the Space Shuttle. Because it will be larger and lighter than the Space Shuttle was, Skylon will be slowed at a higher altitudes and will not be subjected to as much heat during re-entry. This will solve the heat shielding problem experienced by its predecessor.

Why is Skylon so cool? Because if the project is successful, it will deliver the kind of multi-purpose, multi-use, single stage launch and re-entry spaceship that science fiction has been dreaming about for the past century. Such craft are a staple of the genre, and their real-life development is essential to the future of manned space exploration, space tourism, and other attainable sci-fi dreams-come-true.

SABRE Engines

The experimental SABRE engine is key to the design of the Skylon spacecraft, allowing it to fly intra-atmosphere like a conventional aircraft while requiring considerably less fuel than a conventional rocket engine. While this revolutionary hybrid rocket-jet engine was originally conceived as long ago as 1955, modern technology is only now making the design feasible. How does it work? Here’s a ridiculously over-simplified explanation…

The best way to describe the SABRE engine concept to an idiot is to tell them that a rocket and a jet engine had a baby. Another way to wrap your head around the idea is to imagine a hydrogen fueled jet engine, or a rocket with an air intake.

Rocket engines work on the simple formula Hydrogen + Oxygen = BOOM, literally burning hydrogen as one burns any combustible fuel.

Aside from using the powerful and unstable element hydrogen as a fuel source, conventional rocket engines actually work in a very similar way to aircraft jet engines, forcing compressed fuel and air into a combustion chamber, where it is ignited. The major difference has always been that air-breathing jet engines are able to utilize atmospheric oxygen (taken from the air), while rockets require pressurized liquid oxygen.

This is where the simple genius of SABRE comes in. SABRE engines feature a forward air intake with an incredibly efficient heat exchange immediately behind. This heat exchange cools and compresses the oxygen before feeding it into the combustion chamber. While in the atmosphere, the SABRE engine functions like a highly efficient jet engine, using the atmospheric oxygen around. When in space, this air intake is turned off and the engine switches to a supply of liquid oxygen stored aboard the spacecraft, just like an ordinary rocket.

The advantage of the SABRE engine over conventional rockets is that it takes advantage of a naturally occurring fuel source in the form of atmospheric oxygen, meaning that a spacecraft is required to carry less liquid oxygen fuel. By doing so, it also makes the rocket engine a viable method of propulsion for intra-atmosphere flight as well as space flight, and successfully combines the two.

Safer Re-Entry

While the launch of the Skylon spaceplane will rely on the development of the SABRE rocket engine, the safe return of the vehicle to Earth will be the result of its simple fuselage design.

The heat-shielding of the Space Shuttle turned out to be its Achilles heel, but Skylon is unlikely to have this problem. Because the spaceplane will be both large and light, it will have an advantage during atmospheric re-entry compared to its predecessors due to a low ballistic coefficient. Because of the low ballistic coefficient, Skylon would be slowed at higher altitudes where the air is thinner. As a result, the skin of the vehicle would only reach 1,100 Kelvin (in contrast, the smaller Space Shuttle was heated to 2,000 K) and require considerably less heat-shielding.

While the tiles used to protect the Space Shuttle during re-entry were notoriously fragile and expensive to maintain, Skylon will instead opt for a simple and durable reinforced ceramic skin.

skylon whiteDevelopment

Skylon is currently still on the drawing board pending the development of the SABRE rocket engines, which are currently undergoing prototype testing. Let’s keep our fingers crossed that this incredible machine makes it into the skies someday soon.


This article was written by Mark Ball.

  • http://orionarm.proboards.com Josh G

    This is the greatest news I’ve seen all year. I could’ve waited on the Higgs Boson to hear of this remarkable innovation!

  • http://wideawakebutdreaming.wordpress.com/ Cassidy Frazee

    I remember this from when it was the HOTOL project. While I’m still waiting for that SSTO craft that will truly open up LEO, Skylon seems more a proof of concept that something that’s going to solve everything. Fifteen tones to just under two hundred kilometers is keeping us in the Space Shuttle phase of “exploration”; we really need to develop a heavy lift booster that can whack a hundred tones into the three hundred to five hundred kilometer range. Keep my fingers crossed that I’ll see something remarkable happen in this area before I die.

  • rheaherherherrsh

    this is the best hope for increasing man’s presence in space. i believe it was heinlein who said “low earth orbit is halfway to anywhere” and as far as delta-v goes, it is. in a lecture, on youtube somewhere, by one of the geniuses behind this project (alan bond) the boss of reaction engines says something along the lines of “this will making getting to space boring, and that’s a good thing”. sure enough it is, one space access is easy then exploring the depths of space becomes a much cheaper and simpler task. when one no longer has to stress about the astronomical cost of multi-stage non-reusable rocket launches then manned interplanetary ships can be built in orbit, huge spinning (for artificial gravity) space stations can be built in orbit, tens of robotic interplanetary probes can be launched cheaply by one launch vehicle, space mining makes economic sense, space telescopes become common and space tourism becomes viable. in terms of the changes it can bring about skylon is the most important project currently being developed in any field of space technology, i wish them luck and wish more people would see that this is one of the projects that really needs funding.

    as a note this is a direct continuation of HOTOL, same group of engineers, same engine concept. the key difference is the engines wings an fuel tanks have been repositioned to reduce problems that the old hotol had with it’s centre of mass and that skylon has reached the stage of actually building many of the critical components (the heat exchanger is one of the most important as it is needed to cool the incoming air so that it can be reacted with hydrogen during the airbreathing phase of the ascent).

    as a second note, in the far future this is exactly the sort of thing you want to carry along with your interplanetary/interstellar ship, you can use this sort of craft to descend from orbit then return to your space-based craft.