When it comes to the future of space exploration, the name of the game is “save money”. To do this, space agencies and aerospace companies around the world are investing in things like reusable rockets, single-stage-to-orbit (SSTO) rockets, and reusable space planes. This last concept builds on the tradition established by the Space Shuttle and Buran spacecraft, two reusable vehicles designed to make space launches more affordable.

The one drawback of these spacecraft was the fact that it still took two rocket boosters and a huge external fuel tank to put them into orbit. This is where the Synergetic Air Breathing Rocket Engine (SABRE) comes into play. With the help of the European Space Agency (ESA) and the UK Space Agency (UKSA), this revolutionary hypersonic engine recently took a big step towards fruition.

The idea behind the SABRE engine is both elegant and straightforward. During take-off and ascent, the engine scoops up atmosphere and uses it to generate thrust (reaching speeds up to Mach 5.4). After reaching an altitude of about 25 km (15.5 mi), it switches to rocket mode and accelerates to Mach 25 to achieve orbit and flight in space.

The engine is the brainchild of UK-based aerospace manufacturer Reaction Engines, who originally proposed it as part of their Skylon space plane concept. The company was founded in 1989 with the purpose of developing the technologies necessary to create a hypersonic engine that could combined the fuel efficiency of a jet with the power and high-speed capability of a rocket.

Together with the UKSA, the ESA recently reviewed the preliminary design of the engine demonstrator’s core, thus bringing the full-scale engine one step closer to realization. As Mark Ford, the head of the ESA’s Propulsion Engineering section, indicated in a recent ESA press release:

“The positive conclusion of our preliminary design review marks a major milestone in SABRE development. It confirms the test version of this revolutionary new class of engine is ready for implementation.”

This represents the latest step in the joint effort by the ESA and Reaction Engines to develop the SABRE engine. Back in 2010, the ESA became officially involved after conducting an independent review of the engine’s viability, which opened the door for the British government to invest on behalf of the UKSA.

Testing the precooler design for the SABRE engine at the Reaction Engines’ site in Oxfordshire (overseen by the ESA) in November of 2012. Credit: Reaction Engines Ltd

This was followed in 2012 by the ESA and Reaction Engines collaborating on the testing of the engine precooler. This element, which is essential to the SABRE, ensures that the hot airstream entering at hypersonic speeds is kept at a consistent temperatures. These tests fully-validated the precooler, showing that it performed well at ambient air temperatures.

According to Richard Varvill, the Chief Technology Officer of Reaction Engines, this step-by-step validation process is one of the things that sets the SABRE apart:

“One of the great advantages of the SABRE propulsion concept is that it is totally modular from both design and operational perspectives. Therefore it is possible to subject each of the key components of the engine to rigorous ground testing, which fully mimic the operational conditions the engine will face up to Mach 5 flight at 25km altitude.”

Development of the engine core began in October of 2016 when the company decided to create the central element of the SABRE. When tested, Reaction Engines and the ESA will be seeking to validate the engine’s heat exchanges, turbomachinery modules, and ability to mix air and liquid hydrogen to generate combustion.

The testing of the core demonstrator will take place at the company’s dedicated test facility in Westcott Venture Park, Buckinghamshire (which is currently being built). This site has a rich history when it comes to testing British rockets, as it was was where the historic Blue Streak and Black Arrow rockets were first launched.

As Chris Castelli, the Director of Programs at the UK Space Agency, said:

“As the home of the jet engine, the UK has a rich aerospace heritage and world-renowned skills and expertise. This is an exciting landmark for Reaction Engines in the development of its SABRE engine, which could revolutionize both access to space and international travel by powering aircraft to five times the speed of sound.

“The government’s modern industrial strategy is putting the UK at the forefront of pioneering aerospace technologies and ensuring we thrive in the new commercial space age. Our £60m investment in SABRE is a great example of how we are backing the businesses of tomorrow.”

According to statements made by Reaction Engine officials, this latest review opens the door to several testing milestones that the company will undertake during the next 18 months. These will culminate in the first full-scale test of the completed engine, which (if successful) could revolutionize space flight as we know it.

As with the progress made in the retrieval and relaunching of rockets in recent years, the prospect of reusable space planes that do not require external rocket boosters or fuel tanks to get to space will mean drastic reductions in the cost of individual launches. It will also offer a specialized type of launch service that could facilitate the deployment of satellites, small payloads and crews to orbit.

And that’s not even including the way that this engine could spur developments in the space tourism industry. In the end, space planes that are capable of taking off, reaching space, and landing without any additional help will be an all-around game-changer!

Further Reading: ESA