Reaction Engines Ltd., today announces the signing of a €10m European Space Agency (ESA) contract which will enable the development of a ground based demonstrator of SABRE, a new class of aerospace engine which is highly scalable with multiple potential applications in hypersonic travel and space access.
SABRE is at heart a rocket engine designed to power aircraft directly into space (single-stage to orbit) to allow reliable, responsive and cost effective space access, and in a different configuration to allow aircraft to cruise at high speeds (five times the speed of sound) within the atmosphere.
In the past, attempts to design single stage to orbit propulsion systems have been unsuccessful largely due to the weight of an on-board oxidiser such as liquid oxygen, needed by conventional rocket engines. One possible solution to reduce the quantity of on-board oxidizer required is by using oxygen already present in the atmosphere in the combustion process just like an ordinary jet engine. This weight saving would enable the transition from single-use multi-stage launch vehicles to multi-use single stage launch vehicles.
SABRE is the first engine to achieve this goal by operating in two rocket modes: initially in air-breathing mode and subsequently in conventional rocket mode:
- Air breathing mode - the rocket engine sucks in atmospheric air as a source of oxygen (as in a typical jet engine) to burn with its liquid hydrogen fuel in the rocket combustion chamber
- Conventional rocket mode - the engine is above the atmosphere and transitions to using conventional on-board liquid oxygen.
In both modes the thrust is generated using the rocket combustion chamber and nozzles. This is made possible through a synthesis of elements from rocket and gas turbine technology.
This approach enables SABRE-powered vehicles to save carrying over 250 tons of on-board oxidant on their way to orbit, and removes the necessity for massive throw-away first stages that are jettisoned once the oxidant they contain has been used up, allowing the development of the first fully re-usable space access vehicles such as SKYLON.
While this sounds simple, the problem is that in air-breathing mode, the air must be compressed to around 140 atmospheres before injection into the combustion chambers which raises its temperature so high that it would melt any known material. SABRE avoids this by first cooling the air using a Pre-cooler heat exchanger until it is almost a liquid. Then a relatively conventional turbo compressor using jet engine technology can be used to compress the air to the required pressure.
This means when SABRE is in the Earth's atmosphere the engine can use air to burn with the hydrogen fuel rather than the liquid oxygen used when in rocket mode, which gives an 8 fold improvement in propellant consumption. The air-breathing mode can be used until the engine has reached over 5 times the speed of sound and an altitude of 25 kilometers which is 20% of the speed and 20% of the altitude needed to reach orbit. The remaining 80% can be achieved using the SABRE engines in rocket mode.
For space access, the thrust during air-breathing ascent is variable but around 200 tonnes per engine. During rocket ascent this rises to 300 tonnes but is then throttled down towards the end of the ascent to limit the longitudinal acceleration to 3.0g.
Today’s signing represents the final piece of the British Government’s £60 million commitment of grant funding towards the SABRE programme. Within this commitment, €10m is being administered by ESA’s Technology Centre (ESTEC), alongside £50 million directly through the UK Space Agency. The terms of the UK Space Agency grant funding were agreed in late December 2015. In November 2015, BAE Systems invested £20.6 million in Reaction Engines to acquire 20 per cent of its share capital and agreed to provide industrial, technology development and project management expertise to support Reaction Engines during its development phase.
The agreements now in place between Reaction Engines, ESA and the UK Space Agency, together with the working partnership with BAE Systems, set the framework for Reaction Engines to deliver the world’s first SABRE ground demonstrator engine by the end of the decade.
SOURCES - Reaction Engines, Vimeo