The Skylon Spaceplane

British Aerospace company Reaction Engines Ltd is working on a design for a Single Stage To Orbit (SSTO) Spaceplane called Skylon that will take off and land horizontally from a runway, just like a normal plane. This concept has been studied several times already in the past, with projects such as the U.S.'s National Aerospace Plane (see my previous post) or the British HOTOL, but all encountered technological problems that they could not solve. 

The biggest challenge in such a spaceplane is to design an engine that can work both like a turbojet and a rocket. The Turbojet engine has the advantage of using the oxygen from the air as oxidizer (thus they are called 'air-breathing'), so the plane doesn't have to carry gigantic amounts of liquid oxygen, making it much lighter. But a conventional jet engine isn't capable of operating beyond ~Mach 3. So to reach the orbital speed of Mach 25, it needs to switch to rocket mode. You can't just have both a jet engine and a rocket engine because that would just be too heavy. You need to have one engine that can do both. And even then, you need to find a way to have the engine 'breathe the air' beyond Mach 3 to save enough weight.

Previous designs from the 1990's were looking into a hybrid Turbojet-Scramjet-Rocket engine. In Scramjet mode, incoming air would be compressed inside the inlet by the sheer speed of the aircraft, enabling to bypass the compressor stage of the turbojet and achieving greater speeds, up to Mach 15. 

The problem is that the air goes through the engine at supersonic speeds, so fast that the Hydrogen/Oxygen mix doesn't have time to fully burn before it exits the engine. They tried for years to come up with a fuel that burns faster, but never succeeded.

Another solution is to slow the incoming air to sub-sonic speeds before injecting it in the combustion chamber. The problem is that this heats the air to 1,000 degrees C, so much that it would melt the lightweight metals used in the engine, and using more heat-resistant materials would be too heavy.

The engineers at Reaction Engines managed to solve this problem by designing a revolutionary 'Pre-Cooler' system capable of cooling down the air from 1,000C to minus 150C in a few milliseconds. It passes the hot air through thousands of small tubes that are cooled down by the liquid hydrogen used as fuel, in a system reminiscent of the heat-exchangers used in homes in cold climate.

The SABRE engine

This would allow their SABRE engine to 'breath air' all the way to Mach 5.5. After that, the front conical inlet would close and the engine would switch to purely rocket mode, burning liquid Hydrogen and Oxygen.

Reaction Engines Ltd is planning an important test of their Pre-Cooler system this summer. If the test is successful, investors will lend $350 million to pursue the development of the engine and plane.

The Skylon spaceplane will have two of these engines, and will be able to deliver 12 tonnes to Low Earth Orbit, at a cost of $1,000 per kilogram, as opposed to $25,000 per kilo with current technologies. It is expected to be operational around 2020.

I believe this is exactly the kind of technology that we should be focusing on, instead of reinventing the wheel and sticking with 30 year-old apollo-style rocket and capsule designs.

Here is a nice video showing the Skylon in flight:

Via [space.com]