The RB545 was an air-breathing rocket engine
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...

 that was proposed to propel a British space shuttle (see HOTOL
HOTOL, for Horizontal Take-Off and Landing, was a British air-breathing space shuttle effort by Rolls Royce and British Aerospace.Designed as a single-stage-to-orbit reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545 called the Swallow, to be...

) to orbit using a single stage. Rolls-Royce
Rolls-Royce plc
Rolls-Royce Group plc is a global power systems company headquartered in the City of Westminster, London, United Kingdom. It is the world’s second-largest maker of aircraft engines , and also has major businesses in the marine propulsion and energy sectors. Through its defence-related activities...

 was involved; while British Aerospace
British Aerospace
British Aerospace plc was a UK aircraft, munitions and defence-systems manufacturer. Its head office was in the Warwick House in the Farnborough Aerospace Centre in Farnborough, Hampshire...

 (BAe) worked on the vehicle.


The exact details of this engine are apparently covered by the UK's Official Secrets Act
Official Secrets Act
The Official Secrets Act is a stock short title used in the United Kingdom, Ireland, India and Malaysia and formerly in New Zealand for legislation that provides for the protection of state secrets and official information, mainly related to national security.-United Kingdom:*The Official Secrets...

 and there is consequently little public information about its operation.

Within the atmosphere, hydrogen fuel would be used in a heat exchanger to precool air entering a high overall pressure ratio turbojet-like engine cycle, before being burnt with the air in a rocket motor, to produce a very high velocity propulsive jet.

Once out of the atmosphere, the RB545 would be capable of burning the hydrogen with on-board liquid oxygen as a high efficiency hydrogen/oxygen rocket. The engine was given the Rolls Royce name of "Swallow".

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