Major governments seem to have given up on single-stage-to-orbit spaceplanes in favor of simple and reliable (but way less cool) rockets. That's perfectly fine with U.K.-based Reaction Engines, which is working on a spaceplane of its own. The company looks to have the trickiest problem licked. Next stop, orbit.
Earlier this month, Reaction Engines performed a test of the cooling system that will allow its Sabre engine to breathe air. Breathing air is important, because it means that the Skylon spaceplane (which will be powered by a pair of Sabre engines) can take off from a runway and power itself up to Mach 5.5 and 18 miles up without having to rely on giant tanks of oxidizer like rockets do. All of that space and weight can then be given over to payload, making getting to space on the Skylon 10x cheaper and 400x more reliable. And after the spaceplane gets high enough that there's not enough oxygen for the engines, it uses on-board oxidizer to fuel a conventional rocket engine to take it the rest of the way into space.
All of this is based on existing technology, except for Sabre's method of precooling incoming air down to keep it from melting the engine compressor. Here's how amazing this cooler is: air comes flying in at Mach 5 and gets compressed in the engine inlet, heating up to almost 2,000 degrees F. It then passes through the precooler, which manages to take it down to -238 degrees F in the space of 1/100th of one second. As if that's not amazing enough on its own, it does this without causing any water vapor to precipitate out of the (now well below freezing) air and freeze onto the precooler itself, which would cause it to stop working. This last bit is Reaction Engine's real secret, and the company's engineers are not telling anyone how they've gotten it to work, but they have.
The precooler is made up of a complicated array of tiny pipes containing liquid helium at -452 degrees F that suck all the heat out of the air as it flies past. The helium takes that heat away and then dumps it all into the liquid hydrogen fuel, which is at −423 F, and goes back into the precooler. The fuel warms up, but that's not a problem, since it all gets burned off as gas anyway. Reaction Engines has just tested this technology with the supervision of the European Space Agency, which declared "with this now successfully demonstrated by REL, there are currently no technical reasons why the Sabre engine programme cannot move forward into the next stage of development."
In addition to powering a spaceplane, Sabre engines could power a more conventional 300 seat Mach 5.5 passenger aircraft. Mach 5.5 works out to be nearly 4,200 mph, which will get you from Bali to San Francisco in under two hours instead of the 14 it took me last weekend.
To make all of this happen, Reaction Engines just needs $400 million or so for the next phase of development (building a complete test engine), most of which it's hoping to score from private investors.