SABRE (rocket Engine)

SABRE (rocket Engine)

SABRE (Synergistic Air-Breathing Rocket Engine) is a concept under development by Reaction Engines Limited for a hypersonic precooled hybrid air breathing rocket engine. The engine has been designed to achieve single-stage-to-orbit capability, propelling the proposed Skylon launch vehicle. SABRE is an evolution of Alan Bond's series of liquid air cycle engine (LACE) and LACE-like designs that started in the early/mid-1980s for the HOTOL project.

The design comprises a single combined cycle rocket engine with two modes of operation. The air breathing mode combines a turbo-compressor with a lightweight air precooler positioned just behind the inlet cone. At high speeds this precooler cools the hot, ram compressed air leading to an unusually high pressure ratio within the engine. The compressed air is subsequently fed into the rocket combustion chamber where it is ignited with stored liquid hydrogen. The high pressure ratio allows the engine to continue to provide high thrust at very high speeds and altitudes. The low temperature of the air permits light alloy construction to be employed which gives a very lightweight engine — essential for reaching orbit. In addition, unlike the LACE concept that preceded it, SABRE’s precooler does not liquefy the air letting it run more efficiently.

After shutting the inlet cone off at Mach 5.14, 28.5 km altitude, the system continues as a closed cycle high performance rocket engine burning liquid oxygen and liquid hydrogen from on-board fuel tanks allowing Skylon to reach orbital velocity after leaving the atmosphere on a steep climb.

An engine derived from the SABRE concept called Scimitar has been designed for the company’s A2 hypersonic passenger jet proposal for the European Union-funded LAPCAT study.

In November of 2012, Reaction Engines announced it had successfully concluded a series of tests that prove the cooling technology of the engine, one of the main obstacles towards the completion of the project. The European Space Agency (ESA) has evaluated the SABRE engine's pre-cooler heat exchanger, and believes the technologies required to proceed with the engine's development have been fully demonstrated.