British engineers have successfully tested a key component of an engine that could power a spaceplane from London to Sydney in under four hours. The engineers have hailed it as the biggest breakthrough in aerospace propulsion "since the invention of the jet engine". Oxfordshire-based Reaction Engines hope to build a rocket plane called Lapcat that would take off from an ordinary runway, reach speeds of around 19,000mph in the upper atmosphere and then land like a normal jet aircraft. While still in the atmosphere, the plane's Sabre engine would combine on-board hydrogen fuel with oxygen that it "breathes" from the air. But the air needs to be super-cooled for the engine to work.