Fly Joburg to London in two hours

Hypersonic air travel and cut-price satellite launches will move a step closer when British defence giant BAE Systems buys a stake in a company developing engines able to power aircraft at 4000km/h and into space. The new engines combine jet and rocket technology and the boost of BAE's engineering talent and financial resources could speed up development of technology that could revolutionise air travel and space flight.

BAE is to purchase 20% of UK-based Reaction Engines for £20.6-million.

"The potential for this engine is incredible," said Nigel Whitehead, managing director at BAE. "I feel like we're in the same position as the people who were the first to consider putting a propeller on an internal combustion engine. We understand that there are amazing possibilities but don't fully understand what they are. It could be very high-speed flight, low-cost launches to orbit or other fantastic achievements."

For 20 years Reaction Engines has been developing its Synergetic Air-Breathing Rocket Engine (Sabre), which works like a normal jet engine while in the Earth's atmosphere, sucking in air to burn with its hydrogen fuel. Once it hits five times the speed of sound - about 4000km/h at very high altitude - and is close to leaving the atmosphere where there is no air, it switches to being a conventional rocket engine, burning the liquefied oxygen it carries along with its fuel.

The ability to switch modes means the system is lighter than conventional rockets, which have to carry much more oxygen for launches but are then jettisoned.

Reaction Engines has developed a heat exchanger, which cools air going into the engine to a level at which it is almost liquid before it is ignited, allowing the Sabre engine to swap modes. This device can cool air from more than 1000C to minus 150C in less than 1/100th of a second.

Aircraft equipped with Sabre engines will be able to take off from a runway like a normal plane before accelerating to as much as 20 times the speed of sound. At this speed, travelling between Britain and Australia could take just four hours.

Mark Thomas, managing director of Reaction Engines, said though the physics of the concept are well understood, his company has been the only one to develop components that make the system viable.

"This investment will allow us to transition from being a research operation to a development one."

BAE's backing means the project, which is in the final stages of winning a £60-million government investment, should have a completed engine ready for ground testing by the end of the decade.

Flight tests will start in the early 2020s.

If the engine proves successful it is likely to be used for low-cost satellite launches first, with Sabre-powered passenger jets coming much later.