Skylon spaceplane approaches decision time
It is one of those projects that has the potential to put the "great" back into Britain.
Each Skylon vehicle is expected to have an operational life of some 200 flights
The Skylon spaceplane concept has quietly been gaining momentum ever since the UK government withdrew its support from a previous incarnation of the vehicle, known as Hotol, at the back end of the 1980s.
The flaws that hobbled that earlier venture have now been fixed, its designers believe; and Skylon will very soon be at a state of technical readiness where investors have to decide whether to put their full weight behind the endeavour.
For those not familiar with Skylon or who have only a vague recollection of Hotol, let me reprise briefly what is on the table.
The autonomous, unmanned Skylon is being developed by Reaction Engines, a small company formed out of the Hotol experience.
Their 84m-long, single-stage-to-orbit spaceplane would take off from a runway, deploy its 15-tonne payload in low-Earth orbit and then return to land at the same runway.
That 15-tonne payload could include a retrievable upper-stage capable of pushing the biggest telecommunications satellites into geostationary transfer orbit some 36,000km above the planet.
The concept is very different from today's expendable rockets which dump stages as they ascend to orbit; or indeed the space shuttle, which as an entire system is only partially re-usable.
Skylon's disruptive technology is its Sabre propulsion unit. It is part jet-engine, part rocket-engine.
It burns hydrogen and oxygen to provide thrust - but in the lower atmosphere, this oxygen is taken straight from the atmosphere. This is extremely tricky.
The pre-cooler is made from a network of very fine pipes that rapidly extract the heat in the air
At high speeds, the air entering the Sabre intakes would be 1,000C, but to burn efficiently with the hydrogen it must be cooled prior to being compressed.
The "breakthrough" is a remarkable pre-cooler heat-exchanger. Arrays of extremely fine piping plunge the hot intake gases to about -140C in just milliseconds.
Sabre allows Skylon to carry less propellant, enabling the spaceplane to make that single leap to orbit with a payload that is much larger, relative to the vehicle's overall launch mass, than is currently the norm.
This, along with its airliner-like reusability, should lower the cost of access to space - dramatically. By an order of magnitude, maybe more.
If it can be made to work, it is a "game-changer".
The UK Space Agency has called a workshop this week to review the project and its prospects.
Is it really technically possible or have some showstoppers been overlooked? How much would it cost to develop (probably $9-12bn) and how would the UK make it happen - with European partners or with a wider international consortium?
First things first, the critical technology has to be proven.
A major event will occur next summer when a full version of the pre-cooler heat-exchanger will be demonstrated on an experimental rig at Culham in Oxfordshire.
A Viper engine will suck air through the pre-cooler, whereupon it will dive instantly to sub-zero temperatures. Ordinarily, the moisture in the air would be expected to freeze out rapidly, covering the network of fine piping in a blanket of frost that dislocates the whole system.
Except, Reaction Engines say they have developed an anti-frost solution that will allow the heat exchangers to run and run.
The vehicle would weigh a little over 300 tonnes, fuel included, as it went down the runway
So, assuming that all works, where does Skylon go next?
The project is envisaged as a commercial enterprise, one where investors could be expected to see a full return on the development costs and make a handsome profit.
The independent assessment recently carried out by the London Economics consultancy certainly makes Skylon look attractive, even using sceptical treasury appraisal methods.
Skylon would operate like a transport plane
It suggests that in a mature market, if you were to produce about 90 vehicles, unit costs could come down to about $650m per spaceplane, each of which would be designed to fly perhaps 200 missions.
However, as we all know, this is a game of uncertainties, and the space business is a strange beast where normal economics don't always apply.
National prestige demands certain satellites fly on particular rockets whatever the cost.
And trade barriers erected in the name of "national security" will prevent some satellite operators from using the cheapest rockets whatever their wishes.
Even if a British government does not itself invest heavily in Skylon, it will absolutely have to take a front-seat role in helping to smooth the political and regulatory barriers that will inevitably confront Skylon's introduction.
Alan Bond is the MD at Reaction Engines. He has doggedly pursued this project through its up and downs, and remains confident the project can be brought to fruition by the end of this decade. He told me this week:
"What I would really like to think is that a year from now there is a project that is growing - a British project predominantly, probably pulling in large parts of European industry, a little bit of government involvement and a large part of private finance. And that would, I think, give Europe and Britain a really strong hold on these technologies in the world. There are other people out there watching what we're doing - the Americans, the Russians, the Japanese. If we don't do it, sooner or later one of them will; and then we will have lost out again on something that could help transform the British economy."
You can hear my extended interview with Alan Bond by clicking on the audio below.
I have also been chatting with Charlotte Duke from London Economics about the assessment her consultancy completed on Skylon.
David Parker from the UK Space Agency explains its role in the Skylon review process.
And because I know there are a great many Skylon fans out there, I had a brief conversation also with Mark Hempsell at Reaction Engines. He has been working on the latest iteration of the Skylon concept, known as the D1. This is a rescaling of the current C1 concept and is being designed to cope with the expected increase in mass of the next generation of large telecommunications satellites.