The plane, which is designed to give low-cost access to space, has a 275t gross take-off weight but needs to carry 220t of propellant. Engineers are currently investigating technologies that will help to increase its 12t payload and make it a more viable commercial proposition.

For example, Skylon's Sabre engine, which delivers air breathing thrust at take off and reverts to a high specific impulse rocket engine in space, employs its rocket combustion chamber, nozzle and pumps in both propulsion modes, in order to avoid the weight penalty of a separate air-breathing engine.

This innovation required the design of unique, high-power heat exchangers.

The pre-cooler is a counter-flow design that consists of many thousands of small-bore, thin-walled tubes. Its manufacture required 2,000km of tube and 1.2 million drilled holes. Much of the development work has focused on header machining and heat exchanger brazing - which is where Poeton became involved.

The company's Apticote 400 coating process is applied to areas where the tubes - each 1mm diameter with a wall thickness of just 25 microns - are brazed to the main feed tube.

Explaining the process, Poeton's technical manager Roger Walker says that following extremely complicated masking the coating is applied selectively to an area of the tube inside and out before brazing. The assembly is then placed in a vacuum furnace at 900infinityC, at which point the Apticote 400 melts, forming a fillet that creates a perfect seal.

www.poeton.co.uk