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While airplane engines have become quite efficient over recent decades, rocket engine technology has not progressed significantly in 70 years. Reaction Engines is a company looking to push both types of propulsion technology forward by merging an airplane engine and a rocket engine in one system to create a hybrid hypersonic engine. The result is a light, powerful system called the Synergetic Air-Breathing Rocket Engine (SABRE), which could open the door to more sustainable aviation.
In October 2019, Reaction Engines hit a major objective with the successful testing of SABRE’s essential pre-cooling technology.
As the propulsion system in a "space plane", SABRE would enable supersonic commercial flight, which has not been available since the Concorde was grounded in 2003. Whereas Concorde used a conventional aero engine, SABRE can change from one that consumes oxygen from the atmosphere to one that can operate in the vacuum of space.
Cleaner Hypersonic Flight Technology with the Synergetic Air-Breathing Rocket Engine
SABRE is designed to enable hypersonic travel, which is more than five times the speed of sound. These speeds are very difficult to achieve with a standard airplane engine. This is because moving at such a high rate creates enough heat to melt the engine. Military fighter jets can achieve hypersonic speed via an intricate cooling system, but engines are costly and inefficient.
The hybrid hypersonic engine from Reaction Engines involves two different modes. In “air-breathing mode”, the craft is capable of Mach 5 (hypersonic travel) and, in spaceflight mode, it is capable of Mach 25. According to the company, SABRE would be the first air-breathing rocket engine, as conventional rocket engines use on-board liquefied oxygen.
Ideally, SABRE would allow for single-stage-to-orbit rockets, as opposed to the US Space Shuttle model of solid-fuel booster rockets and a massive liquefied fuel tank. With less waste, SABRE may be a cheaper and easier mode of travel.
To achieve such high speeds, it is essential to pre-cool air that is going into the engine because the friction and the compression of air at supersonic speeds causes extreme temperatures of around 1000 °C (1800 °F). While the Concorde used variable ramps to slow down incoming air for its engines, the precooler in the hybrid hypersonic engine uses 16,800 tubes filled with supercooled helium. Hot air entering the system contacts these cold pipes and heat from the air is then transferred into helium.
After the air has been cooled, it is passed through a compressor and channelled into a combustion engine, where it mixes with nitrogen fuel. The heat captured from the pre-cooling system is utilized in various ways, including in an afterburner system seen on military jets.
What Applications Could the SABRE Engine be Used in?
In addition to being useful on the SABRE system, the precooler technology developed by Reaction Engines is expected to have many other possible uses, including in areas such as motor sport, industrial operations and the oil industry.
According to Reaction Engines, test evaluations of the engine core is expected to begin in 2020 and flight trials are projected for about a decade from now. Company officials have said their system is sound from a scientific point of view, and it is time to move on to the physical testing phase. The company successfully tested the pre-cooling system at its Colorado testing facility, operating at 420 °C , which is associated with travel at Mach 3.3. Reaction Engines is currently building a new test centre in the UK.
Reaction Engines was founded in 1989 with the goal of hypersonic commercial travel. In 2012, the company announced successful trials of the technology behind the pre-cooling system, and in 2013, Reaction Engines received £60 million in funding from the UK government to develop SABRE.
The company also recently received financial backing from the US Defense Advanced Research Projects Agency (DARPA), European Space Agency, as well as BAE Systems, Rolls-Royce and Boeing’s venture capital division HorizonX.
Making Global Travel Faster and Greener with a Hypersonic Aircraft Engine
According to experts, the SABRE system could enable travel from the UK to Australia in less than four hours, and travel from New York to London in slightly more than an hour. The fastest UK-Australia flight currently lasts around 18 hours.
An aircraft utilizing the SABRE engine for commercial travel would take off horizontally, potentially switching to ‘rocket-mode’ for long intercontinental trips. Reaction Engines said the SABRE system could also be used in automotive applications.
The system enables a more sustainable aviation approach than using a vertically launched rocket. A rocket needs a large amount of fuel to lift an aircraft and its cargo into orbit, and the more fuel it needs, the heavier the rocket is. This means even more fuel is needed. Essentially, it’s a feedback loop of unsustainability.
HTX Mach 5 test results - interviews - October 2019
Video Source: Reaction Engines/YouTube.com
Space Planes for More Sustainable Aviation
Many other organizations are also pursuing aeronautics technologies that would enable flight in the Earth’s atmosphere and in space, including SpaceX and the US Air Force.
According to reports and press releases from the company, SpaceX is currently developing its BFR rocket-ship combination system to take passengers halfway around the globe in under an hour. BFR would achieve this by launching into space like a typical rocket and releasing the rocket booster once the craft is above the Earth’s atmosphere, allowing the BFR craft to land on a landing pad similar to the way the company’s reusable rockets land back on Earth. The system enables sustainable aviation by using a booster that is also recovered and reused.
Shrouded in mystery as a classified project, the US Air Force’s Boeing X-37B space plane recently completed a 780-day mission in orbit. Experts have said the plane is radiation-hardened and automated to make it both robust and reusable.
Like the SpaceX system, the Boeing X-37B launches as a rocket, but flies like a plane. Unlike the SpaceX system, the Boeing X-37B lands on a runway as a plane.
References and Further Reading
Brit rocket boffins Reaction Engines notch up first supersonic precooler test. The Register.https://www.theregister.co.uk/2019/04/08/brit_rocketeers_notch_up_first_supersonic_precooler_test/
Reaction Engines mach 5 engine is just the tip of the new aerospace boom. Tech Crunch.https://techcrunch.com/2019/11/01/reaction-engines-mach-5-engine-is-just-the-tip-of-the-new-aerospace-boom/
SpaceX plans to use spaceships for earth passenger transit. Tech Crunch. https://techcrunch.com/2017/09/28/spacex-plans-to-use-spaceships-for-earth-passenger-transit/
New hypersonic engine poised to cut London-Sydney flight times to just four hours by 2030s. The Telgraph. https://www.telegraph.co.uk/news/2019/09/24/british-tourists-will-able-fly-australia-4-hours-2030-uk-space/