“Air-breathing” rocket engine
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Sabre is an experimental air-breathing rocket engine, designed to power a craft from standstill on a runway to hypersonic flight at over Mach 5 (6,300km/h), before switching over to rocket mode to reach Mach 25
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Concept space plane

Sabre: Synergetic Air Breathing Rocket Engine 

Air-breathing mode: Burns liquid hydrogen in atmospheric oxygen

Rocket mode: Uses on-board liquid oxygen

Heat is generated by compression of air in engine’s intake. Concorde’s engines dealt with temperatures of about 160oC at Mach 2 (2,140km/h)
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1 Air intake: Air must be slowed to subsonic speed. At Mach 5.14 temperature of air can reach 1,000oC

2 Pre-cooler: Air is chilled from 1,000°C to -120°C by super-cold, liquid helium pumped through thin-walled pipes

3 Compressor: Helium turbine, which uses heat absorbed by pre-cooler, compresses air to 150 bar (153kg/cm2)

4 Rocket engines Compressed air and liquid hydrogen ignited in combustion chambers, producing thrust

5 Rocket mode: Air intake is closed and compressor stops. Liquid oxygen used

Ramjets Excess air and hydrogen burn to provide additional thrust

Excess air

16,800 pipes made of Inconel 718 alloy. Wall thickness of 40 microns
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Sources: Aviation Week & Space Technology, Reaction Engines © GRAPHIC NEWS