UK engineers developing a novel propulsion system say their technology has passed another key milestone.

The Sabre air-breathing rocket engine is designed to drive space planes to orbit and take airliners around the world in just a few hours. To work, it needs to manage very high temperature airflows, and the team at Reaction Engines Ltd has developed a heat-exchanger for the purpose. This key element has just demonstrated an impressive level of performance.

REL's CEO Mark Thomas spoke with our science correspondent Jonathan Amos.