The Synergistic Air-Breathing Rocket Engine, or SABRE, seen in place on a Skylon spaceplane. Designed by UK company Reaction Engines Ltd, this unique engine will use atmospheric air in the early part of the flight before switching to rocket mode for the final ascent to orbit. The concept paves the way for true spaceplanes – lighter, reusable and able to fly from conventional runways. Reaction Engines plan for SABRE to power a 84 m-long pilotless vehicle called Skylon, which would do the same job as today’s rockets while operating like an aeroplane, potentially revolutionising access to space.