Space plane SKYLON
We’ve been collaborating with Reaction Engines for the last 10 years, supplying components for the groundbreaking Skylon space plane.
“No one else has managed to create heat exchangers like this before, due in part to the fact that the specifications for the components are very demanding. There are a few other companies which can produce the kind of high tech tube we need but the Fine Tubes product is extremely high quality, meeting all the project specifications and we are very pleased with its performance.” Dr Robert Bond, Corporate Programmes Director, Reaction Engines.
Objective
Skylon is a revolutionary concept. This aircraft will be powered by a unique new propulsion system that combines jet and rocket engines in a single power plant enabling Skylon to take off and land on a runway, but also to exit Earth’s atmosphere. The result will be a reusable space plane operating at just two percent of the cost of existing rockets. The plane is being designed, developed and promoted by Reaction Engines Ltd. in Oxfordshire.
An essential component of Skylon’s Sabre engine is a high performance heat exchange system which cools air for the engine intake. Fine Tubes excels in the manufacture of the tiny tubing essential for heat exchangers (or pre-cooler systems) and has worked in partnership with Reaction Engines to come up with a breakthrough in aerospace heat exchanger design for the Sabre engine.
Approach
Key to developing the right solution for the project has been the highly effective working relationship between Fine Tubes and Reaction Engines. Reaction Engines has spent the last 20 years designing, producing and testing key areas of technology for Skylon, and for the last decade Fine Tubes has worked alongside the company developing and trialing various designs for Sabre’s pre-cooler system.
Challenges
Making heat exchangers of the size, scale and weight required presents a great technical challenge. The pre-cooler and its component parts need to be lightweight but also able to cope with temperatures around 1000°C, and very high pressure helium. They also need to withstand thermal expansions and the inertial and aerodynamic loads experienced during flight.
The project pushed our tube manufacturing process in a number of areas:
- The drawing of matrix tubes in heat-resisting nickel-based alloys, ensuring correct wall thickness and diameter
- Brazing heat exchanger tubes to headers
- Machining of heat exchanger tubes to give a profiled (non-constant) wall thickness to ensure good heat exchange properties without compromising physical strength
- Hole drilling
- Tube forming without ovalisation, wall thinning or buckling
- The assembly of large heat exchanger modules incorporating thousands of tubes
Solutions
Fine Tubes custom-made a high pressure tube for Reaction Engines which has a wall thickness of just 40 microns – that’s about half the diameter of a human hair. The tube itself is made from Inconel, a nickel alloy that is very resistant to temperature and well suited for use in extreme conditions. Each engine will use over 2,000km of tubing, so its walls have to be extremely thin to minimise weight and to act effectively as a heat exchanger, but also very strong because of the heat, pressure and forces involved.
Inconel is a difficult metal to shape and machine but it was essential that the tube retained its concentricity and overall straightness. Because the wall is so thin, it is also very susceptible to damage. So we installed specialist equipment at our tube mill to carry out the contract, including an apparatus capable of pumping cleaning fluid through the bore holes of such minute tubes.
Next steps
Reaction Engines is currently testing the feasibility of the pre-cooler; building and operating a prototype in a realistic environment in order to demonstrate its performance. The prototype pre-cooler consists of over 16,000 tubes, and needs to be capable of cooling air to around -150°C in a fraction of a second. It is now in testing.
This is one element of the Technology Demonstration Programme that Reaction Engines is running. The other two - testing the safety of combustion chamber cooling using liquid oxygen and air, and the operation of a specially designed pressure-compensating nozzle - are being run concurrently. When this demonstration phase is complete, it is hoped the Sabre engine will go into commercial production, leading to the first predicted Skylon flights in 2020.
In May 2011, the UK Space Agency (UKSA) asked the European Space Agency (ESA) for a technical assessment and evaluation of the design of the space craft. They concluded that there are no impediments to the further development of Skylon. The UKSA’s report also gave the thumbs-up to the next proposed stage in the development programme. Dr David Parker, Director of Technology, Science and Exploration at UKSA, said: “Both Sabre and Skylon are exciting new technologies that could transform access to space.”
In November 2011, Reaction Engines gave a presentation at the BIS Propulstion meeting held at RAF Cosford on the latest Skylon spaceplane developments. Alan Bond, Managing Director of Reaction Engines discussed the complexities in the manufacturing process of the very fine heat exchanger tubes for the pre-coolers forming part of the SABRe engine. Some of the biggest challenges in the seamless tube drawing process are to ensure the correct wall thickness and diameter of the seamless nickel-based alloy tubes are maintained, the brazing of heat exchangers tubes to headers, tube forming without ovalisation and wall thinning/buckling and much more. Please read more on http://www.reactionengines.co.uk/heatex_man.html.
Reaction Engines have also constructed a cryogenic wind tunnel facility at their Culham Science Centre which has been used to develop a frost control system for the 'air pre-cooler' heat exchanger of the SABRE engine. The pre-cooler is designed to cool the engine airflow (about 400kg/s) from intake recovered conditions (up to 1000°C at Mach 5) down to about -140°C prior to compression. At low altitudes atmospheric moisture will clog the matrix with frost within a few seconds unless preventive measures are taken. The wind tunnel has a test section where heat exchanger modules can be inserted and actual conditions in flight are simulated . Although the test matrix is much smaller than the real pre-cooler, it is built with the correct tube diameter, wall thickness and material. Read more on http://www.reactionengines.co.uk/heatex_frost.html.
About Reaction Engines Ltd
Reaction Engines Ltd was set up in 1989 to design and develop advanced space transport and propulsion systems. From its base at the Culham Science Centre in Oxfordshire, the company combines established physical principles with innovative engineering design to develop a range of products that will enable the commercial exploitation of space.
