BBC: The UK’s Reaction Engines Ltd (REL) has run successful tests on key parts of its experimental Synergistic Air-Breathing Rocket Engine (SABRE). SABRE is designed as the engine for Skylon, a horizontal take-off and landing spacecraft. At low altitudes, the engine will operate like a jet, taking in oxygen as fuel from the air. Thus Skylon can launch with much less fuel onboard than traditional spacecraft. During the tests, REL demonstrated an innovative system for rapidly cooling the intake air, which will let the engine operate in air-breathing mode for as long as necessary. The cooling system uses an array of small pipes, through which helium passes. The helium extracts the heat from the air and drops the air temperature to -140 °C in 1/100th of a second. The flowing helium also prevents the buildup of ice on the surface of the pipes, which would reduce the effectiveness of the cooling. The European Space Agency served as an independent observer and confirmed the success of the testing. REL is primarily privately funded and will need to raise £250 million ($400 million) for the next stage of development of SABRE, a version of the engine which will show the viability of the engine in both air-breathing and traditional rocket modes.