Fancy the idea of taking off from Heathrow at 12 noon and landing in Sydney at 4pm? That's what the Skylon space-plane should be able to do assuming the £60m the British Government has just chucked at the developers, a company called Reaction Engines Ltd. (check out their promo video below), bears fruit. Actually the money will be used to develop the Skylon's Sabre (Synergetic Air-Breathing Rocket Engines) engines which is the key to the project. Space planes are easy to build, it's the engines and more importantly fuel that cause the headaches.
Spaceplanes are what engineers call single-stage-to-orbit vehicles, or fully reusable planes that can get into orbit by taking off and landing from a traditional runway. This is exactly what the Rolls-Royce/British Aerospace HOTOL (Horizontal Take-Off and Landing) was hoped to do before the UK Government pulled the funding in 1988. Bar-room experts will tell you this was because the Government was being cheap and incompetent. Rubbish, bits of HOTOL simply didn't work and nor where they ever likely to.
The reusable spaceplane still has its attractions though. By using reusable vehicles the cost of reaching orbit could be reduced to 5% current levels which makes spaceplanes a game changer both for taking astronauts into space, deploying satellites and getting people and stuff from one side of the planet to the other very, very quickly.
The problem with any ground-launched rocket is that most of the weight is either fuel or the oxidising agent needed to make it burn, usually oxygen, which is stored as liquid in separate tanks. Spaceplanes do away with the need for carrying most of the oxidiser by using air from the atmosphere during the initial stages of their flight. That's why an air-breathing rocket motor is the Holy Grail of cheap spaceflight.
That is also pretty much how a traditional jet engine works and why most of a Space Shuttle launcher is fuel while most of a full-laden Boeing 747 isn't. To reach low-orbit orbit, Skylon will use the Sabre engine to reach Mach 5 then it will then close its air intakes and use a small amount of onboard oxidiser to turn the jets into rockets and boost itself to Mach 22. At this speed the craft will reach low earth orbit.
If it works - fingers crossed the first test flights will take place in 2019 - the Sabre motor could herald a new era a cheap space access and very quick intercontinental travel. But keep in mind we were saying the same things about HOTOL back in the early 1980s.