ESA Prepares Revolutionary Air Breathing Rocket Engine

If new rocket engines being developed by the European Space Agency (ESA) are successful, they could revolutionize rocket technology and change the way we get to space. The engine, called the Synergistic Air-Breathing Rocket Engine (SABRE), is designed to use atmospheric air in the early flight stages, before switching to conventional rocket mode for the final ascent to space. If all goes well, this new air-breathing rocket could be ready for test firings in about four years.

Conventional rockets have to carry an on-board oxidizer such as liquid oxygen, which is combined with fuel in the rocket’s combustion chamber. This means rockets can require in excess of 250 tons of liquid oxygen in order to function. Once this oxygen is consumed in the first stages, these used up stages are discarded, creating massive waste and expense. (Companies like SpaceX and Blue Origin are developing re-usable rockets to help circumvent this problem, but they’re still conventional rockets.)

Conventional rockets carry their own oxygen because its temperature and pressure can be controlled. This guarantees the performance of the rocket, but requires complicated systems to do so. SABRE will eliminate the need for carrying most on-board oxygen, but this is not easy to do.

SABRE’s challenge is to compress the atmospheric oxygen to about 140 atmospheres before introducing it into the engine’s combustion chambers. But compressing the oxygen to that degree raises its temperature so much that it would melt the engines. The solution to that is to cool the air with a pre-cooling heat exchanger, to the point where it’s almost a liquid. At that point, a turbine based on standard jet engine technology can compress the air to the required operating temperature.

This means that while SABRE is in Earth’s atmosphere, it uses air to burn its hydrogen fuel, rather than liquid oxygen. This gives it an 8 x improvement in propellant consumption. Once SABRE has reached about 25 km in altitude, where the air is thinner, it switches modes and operates as a standard rocket. By the time it switches modes, it’s already about 20% of the way into Earth orbit.

Like a lot of engineering challenges, understanding what needs to be done is not the hard part. Actually developing these technologies is extremely difficult, even though many people just assume engineers will be successful. The key for Reaction Engines Ltd, the company developing SABRE, is to develop the light weight heat exchangers at the heart of the engine.

Heat exchangers are common in industry, but these heat exchangers have to cool incoming air from 1000 Celsius to -150 Celsius in less than 1/100th of a second, and they have to do it while preventing frost from forming. They are extremely light, at about 100 times lighter than current technology, which will allow them to be used in aerospace for the first time. Some of the lightness factor of these new heat exchanges stems from the wall thickness of the tubing, which is less than 30 microns. That’s less than the thickness of a human hair.

Reaction Engines Limited says that these heat exchangers will have the same impact on aerospace propulsion systems that silicone chips had on computing.

A new funding agreement with the ESA will provide Reaction Engines with 10 million Euros for continued development of SABRE. This will add to the 50 million Pounds that the UK Space Agency has already contributed. That 50 million Pound investment was the result of a favorable viability review of SABRE that the ESA performed in 2010.

In 2012 the pre-cooler, a vital component of SABRE, was successfully tested at Reaction Engines facility in Oxfordshire, UK. Image: ESA/Reaction Engines
In 2012 the pre-cooler, a vital component of SABRE, was successfully tested at Reaction Engines facility in Oxfordshire, UK. Image: ESA/Reaction Engines

IN 2012, the pre-cooler and the heat exchangers were tested. After that came more R&D, including the development of altitude-compensating rocket nozzles, thrust chamber cooling, and air intakes.

Now that the feasibility of SABRE has been strengthened, Reaction Engines wants to build a ground demonstrator engine by 2020. If the continued development of SABRE goes well, and if testing by 2020 is successful, then these Air Breathing rocket engines will be in a position to truly revolutionize access to space.

In ESA’s words, “ESA are confident that a ground test of a sub-scale engine can be successfully performed to demonstrate the flight regime and cycle and will be a critical milestone in the development of this program and a major breakthrough in propulsion worldwide.”

Bring it on.

14 Replies to “ESA Prepares Revolutionary Air Breathing Rocket Engine”

  1. I read somewhere that they had overcome the frosting problem by pre-mixing intake air with alcohol, hopefully the weight of the alcohol is less than the oxidiser saved. Thank goodness the UK’s involvement in ESA and the funding is not dependent on EU membership otherwise this truly promising project would end up the same way as HOTUL in the 1980s

    1. “But a new report from the House of Commons says the government should not rest on the laurels of its astronaut but should seize on the public enthusiasm for his return to support an expansion of Britain’s role in space with a separate national program to address the skills shortage in technical fields.”

      “The UK has, however, signaled support for cutting-edge propulsion technologies that could lead to an indigenous launch capability, notably the Sabre powerplant in development at Reaction Engines Ltd. (REL), a UK start-up with a long-term plan to produce a single-stage-to-orbit launch vehicle dubbed Skylon.

      However, the committee says that as of February, the UK government’s £60 million promise to invest in REL had not yet materialized.

      “This was a bold decision, but it has not been followed by solid action,” the report says of the UK investment announced in 2014. “The government seems to have fallen short of the professional standards of investment that we would expect.”

      The report also chides Britain’s lack of appetite for risk. Aside from Richard Branson of Virgin Galactic, the UK lacks the start-up culture of SpaceX and Blue Origin, companies that are pioneering new business models and technological developments in the U.S. space sector.”

      [ ]

      At a guess, UK government has abandoned REL in order to make ESA take the burden. That may be a lost game, and if not simply delaying SABRE it should doom it.

      1. It’s all very depresssing, the only science they are interested in is the Black-Scholes equation and look how that worked out

  2. My grandmother had a scifi about a century old, where the hero had a ground-to-orbit-to-ground plane like this. It is cool that they can do it of course, even if they cheat with minimal thrust on the way back to save launch mass.

    The problem should be that the new reusable launch technologies, if they work as advertised which is not a closed case yet, are way cheaper. The penalty of lugging two engine sets and no stages is just mooted by intake of oxidiser part of the way up.

    It reminds me of the old airship technology. Some transport expert made a scale comparison with modern technology, and despite airships being environmentally friendly they were a waste of resources.

    To be fair, I think the pre-cooler technology could be used for hotspots in supersonic planes and possibly in aerobraking orbit-to-ground landers.

  3. Being pedantic, it’s inaccurate to describe these engines as being ‘developed by the ESA’. They’re developed by Reaction Engines, a UK company, and get some grants from the ESA.

  4. Is this more cost efficient than Paul Allen´s project to carry the rockets to at least a 30 thousand feet altitude with an aircraft??
    This is going to be interesting.
    The Paul Allen approach does not require such exotic and costly engineering.

    1. Every time an effort to expand human knowledge occurs, it is not a waste of effort.

  5. This is not a new idea. Go Check out GQM 163 target rocket. It is built by Orbital ATK. It is an air breathing solid fuel rocket.

  6. The time it’s taken to develop this new engine is indicative of it’s complexity. I hope they can conquer all the problems involved but feel that due to the exotic nature of the materials and the number of moving parts, it may be another 10 years before it is perfected?

    I’ve got ‘high hopes’ for this project…

    1. Back! Something to think about? Foamed metals forged in zero gravity orbital plasma chambers and other materials advances made in micro-gravity may be key? Think BIG carrot on a stick.

  7. This may not be a completely “new news”; however, the funds have finally been released to the company and now, hopefully, they will be able to make some progress toward the sub-scale ground based demonstrator. A full scale engine may follow a decade after that and the full space vehicle maybe a few years later…

  8. Been following this really exciting project since the 90’s. The article doesn’t make clear that the main problem between jet engines and rocket engines is the different pressures that each require to operate efficiently so making a hybrid engine is an engineering challenge to say the least.
    This project has been operating on a shoestring for years and it shows how UK governments are 1. risk averse and 2. Since Thatcher became PM how visionary science and engineering lost it’s influence at the top.
    I am pleased that the money is beginning to flow in adequate amounts and I would dearly love to see Skylon fly before I die.
    Look at the REL website for the design detail. It looks the business compared to the hyperbollically named Virgin galactic.

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