Skylon is a series of designs for a single-stage-to-orbitspaceplane by the British company Reaction Engines Limited (REL), using SABRE, a combined-cycle, air-breathingrocket propulsion system. The vehicle design is for a hydrogen-fuelled aircraft that would take off from a purpose-built runway, and accelerate to Mach 5.4 at 26 kilometres (85,000 ft) altitude (compared to typical airliners' 9–13 kilometres or 30,000–40,000 feet) using the atmosphere's oxygen before switching the engines to use the internal liquid oxygen (LOX) supply to take it into orbit. It could carry 17 tonnes (37,000 lb) of cargo to an equatorial low Earth orbit (LEO); up to 11 tonnes (24,000 lb) to the International Space Station, almost 45% more than the capacity of the European Space Agency's Automated Transfer Vehicle; or 7.3 tonnes; 7,300 kilograms (16,000 lb) to Geosynchronous Transfer Orbit (GTO), over 24% more than SpaceXFalcon 9 launch vehicle in reusable mode (As of 2018[update].) The relatively light vehicle would then re-enter the atmosphere and land on a runway, being protected from the conditions of re-entry by a ceramic composite skin. When on the ground, it would undergo inspection and necessary maintenance, with a turnaround time of approximately two days, and be able to complete at least 200 orbital flights per vehicle.
