Blighty's Skylon spaceplane faces key tech test in June
Helium pre-cooler vital for SABRE airbreather rocket
A British firm seeking to build a radical spaceplane – the Skylon – able to fly to orbit from a runway takeoff without any jettisoning of fuel tanks or boosters says that it will test its main technical special sauce this year.
The announcement was made at a spaceplanes conference in California last week. Roger Longstaff, engineer at Reaction Engines Ltd, said that the company intends to test its amazing "pre-cooler" technology in June.
The pre-cooler is the key to REL's amazing SABRE engines, which are themselves perhaps the primary factor permitting a single-stage-to-orbit space plane.
The company describes the SABRE engine as being a rocket furnished with and additional pre-cooled turbocompressor. Air is taken in at the front of the SABRE and almost instantly cooled down to the point at which it is almost liquid, using terrifically powerful freezer kit employing a liquid-helium loop. The supercold air takes the place of liquid oxygen in the combustion chamber, reacting with liquid-hydrogen fuel to produce thrust in much the same way as the space shuttle main engines. Heat sucked from the intake air is dumped into the fuel.
This use of air instead of liquid oxygen for takeoff and the early part of the flight up to orbit means that the Skylon doesn't need to carry nearly as much liquid oxygen as the Shuttle does, and thus that it can carry a cargo to orbit without needing to throw large parts of itself away. It can also make a runway takeoff, so avoiding the costly and troublesome need to point itself vertically into the sky for launch.
We here on the Reg spaceplane desk spoke to REL technical director Richard Varvill last year , and he said that the company is expecting to test a SABRE on the ground as soon as 2013 or 2014. However, before REL's backers will fund the building of a complete SABRE, it seems that they need to see the pre-cooler working. It is this which will be trialled in June.
"[The pre-cooler] is the only brand-new piece of technology," Longstaff told  InnovationNewsDaily.com last week.
Varvill had previously said that REL has a 10-year roadmap to actual Skylon flights, with costs during that time of maybe $15bn. The plan works like a snowball: at first, comparatively small investments lead to comparatively minor tests and trials, which then unlock bigger sums allowing bigger building blocks to be built and validated and so on – until in the final years, big cheques get signed and actual Skylons get built.
The amazing spaceplane is expected to be able to repay those big investment cheques, as it will be able to deliver payloads – admittedly, at first quite small ones of only 10 tonnes or so compared to its own substantial mass of 275+ tonnes – at low cost. The whole Skylon is reusable, and re-using it is a comparatively simple matter of refuelling it, loading it up again and taxiing it back out onto the runway as opposed to strapping on a brand new set of tanks and boosters and standing it on end next to a launch gantry.
All that said, there will still be some major obstacles to get over even after the pre-cooler and the entire SABRE have been tested. REL's engineers have been compelled to shave everything to the limit to produce a design which seems to show that SABREs and the fuel they need to reach orbit can fit into a re-entry-capable airframe along with some cargo.
The ceramic aeroshell is to be just 0.5mm thick. The undercarriage has had to be lightened too, so that a Skylon won't be able to land on just any runway – it will need a special reinforced one able to cope with heavily loaded wheels moving rather fast. If the craft itself should gain just a few per cent in fuelled-up weight during the development process, this would wipe out its entire payload margin.
There are those who would argue that operations using liquid hydrogen fuel will simply never be economical: the stuff takes up so much room that hydrogen aircraft – including the Skylon – are always made up mainly of fuel tanks. It is so troublesome, potentially dangerous and expensive to handle that it will infallibly destroy any business model based on it other than that of government-funded military or scientific projects.
This has led other pioneering space companies such as Elon Musk's famous firm SpaceX to use kerosene fuel instead, sacrificing the greater power of hydrogen rockets for denser fuel that doesn't require such huge tanks and needn't be handled at cryogenic temperatures.
But Musk's rockets are necessarily multistage vertical-launch affairs which must throw away huge amounts of expensive technology on every flight. The Skylon concept at least holds out the prospect of being able to reuse the entire craft.
It remains to be seen who is right in the long run. In the short run, though, while Musk and the other rocket men aren't in a simple business, they definitely have fewer technical hurdles to overcome.
Even if this summer's precooler test goes well, the Skylon engineers would be the first to admit that it will still be a long time until their huge, black robot spaceplane takes to the sky. ®