Reaction Engines is a British aerospace company with big ambitions. The SABRE engine is their unique combination of jet and rocket engine technology, which creates a reusable, fuel-efficient propulsion system capable of reaching space.
The SABRE engine
SABRE (Synergetic Air-Breathing Rocket Engine) is currently in development and is very experimental. Using liquid hydrogen as its fuel, it is designed with two modes of operation. In air breathing mode, it sucks in air like a conventional jet engine, with a capability of going 5.4 times the speed of sound (almost twice as fast as conventional jet engines). In rocket mode, it will switch to using liquid oxygen as a propellant (instead of the oxygen in the air) producing speeds of up to 25 times the speed of sound and unlocking access to space.
SABRE will be able to attain higher speeds than a conventional jet engine is thanks to its innovative pre-cooler. As air is drawn into a jet engine it is compressed. This compression causes it to heat up to temperatures that would destroy the light weight materials necessary for a spacecraft to reach orbit. SABRE has a system of extremely fine tubing, through which helium (that has been cooled by the engine’s extremely cold hydrogen fuel) is pumped. Due to the enormous surface area of the fine tubes, the heat from the compressed gas can transfer into the helium coolant, allowing a drop in temperature of 1000 degrees celsius in less than 1/25 of a second.
Once the engines have been tested and proven, the next step will be to integrate these into a fully functional spacecraft. Reaction Engines are currently working on the Skylon concept (pictured in the headline image) to pioneer the use of their supercooled, air breathing, hybrid engines.