It IS rocket science - air-breathing rocket engine for plane and space travel

Materials World magazine
2 Jan 2014

Commercial space travel and speedy long-haul flights are moving a step closer. Alan Bond, of Reaction Engines, spoke about the potential of SABRE engines to a rapt crowd at the Institution of Mechanical Engineers, in London, UK. Eoin Redahan reports.

What type of engine is being developed?
The Oxfordshire-based company is developing the Synergetic Air-Breathing Rocket Engine (SABRE), which could cut the cost of space travel and dramatically reduce the time of long-distance flights.

How will the engine work?
The SABRE engine is a closed-cycle rocket engine with a pre-cooled turbo-compressor that provides high-pressure air supply to the combustion chamber. The engine uses the oxygen present in the atmosphere to burn with the liquid hydrogen fuel in the combustion chamber instead of on-board liquid oxygen, which is only used when the engine is above the atmosphere. The system could remove the need to carry 250 tonnes of on-board oxidant on the way to orbit. Bond’s company claims the weight saving will enable the transition from ‘single-use, multi-stage launch vehicles to multi-use, single-stage vehicles’.

Why is the pre-cooler essential?
In the engine’s air-breathing mode, the air must be compressed before it is injected into the combustion chambers. However, this raises the temperature to such a point that it would melt any known material. The SABRE engine counteracts this by employing a pre-cooler heat exchanger to cool the air until it is almost liquefied. The air can then be compressed to the required pressure.

What could this mean for space travel?
In theory, this could increase launch volumes by up to 15 times. Once grounded, the craft could be back up in space within two days.

And what about aerospace?
Using this technology, aircraft could cruise at five times the speed of sound within the atmosphere. With that in mind, the engine will be adapted for use in commercial air travel. Travelling at a Mach 5 speed, the plane could complete the 18,732km journey from Brussels to Sydney in less than one hour 45 minutes, with 300 passengers onboard. Bond says, ‘In terms of economics, the cost of this would be the same as first class or business class in a commercial aircraft’.

How much will it cost?
Development of the SABRE engine – and the Skylon space plane that will house it – will cost £10bln. About 85% of this will be privately funded.

In what other applications could the technology be used?
The technology could also be used in the aero gas turbine market (to improve fuel burns by 5–10%) and to improve the multi-stage flash technology used in desalination.

For how long will the project last?
The project runs until October 2024.

For more information on the SABRE technology, visit

Skylon’s the limit
Reaction Engines is also developing the Skylon – a single-stage-to-orbit space plane that will incorporate the SABRE engines. The plane’s fuselage and wing loadbearing structure will be made from carbon fibre-reinforced plastic, and the external shell will consist of a 0.5mm-thick fibre-reinforced ceramic that is corrugated for stiffness. Drive turbine and regenerators Heat shield Helium circulator Pre-burner and re-heater The main pre-cooler heat exchanger Two shock axisymetric intake Air turbocompressor Spill duct Spill duct ramjet burners Four bell nozzle thrust chambers Lox pump Movable centrebody Hydrogen pump