ESA: British Skylon spaceplane seems perfectly possible

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It gets you into orbit, but not big-payola orbit

This means that Skylon needs not only to cover its operating costs but pay back its development costs reasonably swiftly. This would mean that such things as the suggested two-day turnaround time and the number of flights a SABRE engine could endure before needing major maintenance would become very important - and these things are as yet unconfirmed. The costs of safely handling and storing large tonnages of explosive liquid hydrogen on the ground could be a major issue, as they have been in ordinary rocket programmes to date.

Skylon during ascent. Credit: REL

It's definitely got class.

Then, Reaction Engines has its sight set firmly on the lucrative commsat market, where most commercial space money is to be made. Unfortunately communications satellites mainly need to go into a high geostationary orbit: and Skylon itself cannot get to geostationary orbit.

Possible solutions to this include a "Skylon Upper Stage", in which a Skylon would deploy a geostationary satellite attached to a small rocket which would take it to its destination orbit. Reaction Engines nowadays prefers to discuss its proposed Fluyt vehicle, a small reusable robot ship which would remain in space, ferrying many Skylon-delivered satellites from low to geostationary orbit and also refuelling from Skylons as required.

The ESA analysts considered that the low-to-geostationary problem will have to be sorted out one way or another, as Skylon alone may never pay its way:

ESA considers that the SKYLON Upper Stage (SUS) which is potentially required for GTO missions may need to be included in the overall development costs. This is because if telecoms spacecraft customers have to pay to develop a GTO stage on top of the launch price then this may push the cost to orbit to a point where the SKYLON becomes less competitive. ESA recommends that the development cost model of the vehicle be re-assessed to account for the additional cost of developing the SUS.

Based on the existing satellite market, Reaction Engines thinks that a Skylon flight might have a true cost of $40m - comfortably beating the cheapest commercial launch provider right now, famous rocket company SpaceX, which quotes $54-60m per launch for its Falcon 9 vehicle.

But Falcon 9 is flying now, and it can carry nearly five tonnes to geosynchronous orbit already - it doesn't need extra upper stage equipment to get there.

Reaction Engines notes, however, that true costs don't normally bear much relation to prices charged in the space launch business. The company would argue that unseen subsidies to existing rocket firms, coming in large part from military missile infrastructure and other national sources, enable companies like SpaceX and its US and European competitors to charge unrealistically low amounts compared to what their technology actually costs to operate.

Assuming that Skylon benefited from the same kind of help - as have previous European megaprojects of the same kind of size, for instance Concorde, the Airbus A380, Ariane V - a Skylon launch might cost less than $10m. This could represent a serious shift in the costs of going to space, to the point where a tourist visiting an orbiting station could pay as little as $100k for a return flight - as opposed to north of $20m as has been seen in recent times. Whether this view of the hidden subsidies of space launch would apply to Skylon (much more different from a nuclear missile than most launchers are) is unclear.

What is also a bit worrying about Skylon is that weight growth of just a few per cent as it moved off the drawing board and into reality - not at all unlikely, especially with a very radical design in which weight has already been squeezed hard - would wipe out its ability to carry payload altogether.

For now though, as the ESA says, the primary concern is surely to see if the engines will really work. It's also true that such engines would be a new thing in the world, potentially very useful even if Skylon itself can never be built (for instance modified versions might offer hypersonic airliners or military aircraft).

Thus the next thing to focus on is the ongoing SABRE ground tests, and down the road, possible flights of the Nacelle Test Vehicle. And today's positive assessment of Skylon from the ESA is cheerful news for the company and its many fans no matter what. ®

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