Good news for spaceplane fanciers today, as a new report issued by the European Space Agency (ESA) says that "no impediments or critical items have been identified" which could block continuing development of the radical British-designed "Skylon" orbital craft.
Many Reg readers will be familiar with the Skylon, modern-day successor to the HOTOL proposal of the 1980s. The idea is to build a huge, superjumbo-sized robot aeroplane which would mainly be filled with fuel tanks containing cryogenic liquid hydrogen and oxygen. Fitted with radical SABRE engines, the Skylon would make a rolling takeoff from a runway, leaving its oxygen tanks untouched to begin with and using the surrounding air to burn its fuel.
As the aerospacecraft accelerated through Mach 6, it would have climbed to such heights that the air could no longer supply oxidiser and the SABREs would switch into rocket mode using onboard oxygen. The Skylon could achieve a low orbit above Earth without any need to throw away expensive fuel tanks or boosters, delivering as much as ten tonnes of cargo into space.
Having completed delivery, Skylon would then re-enter the atmosphere, its novel huge-but-lightweight aeroshell resisting the heat, and come in to land on a runway just as the space shuttle does. But getting it ready for another mission would be comparatively trivial: it wouldn't need to be lifted and hoisted into a vertical position and strapped onto an enormous disposable launch stack of tanks and boosters before being moved to a launch pad very slowly on a mighty crawler vehicle. Rather the Skylon would simply be refuelled, reloaded and rolled back out onto the runway - taking off again in just two days, according to designers Reaction Engines Ltd.
The new UK Space Agency last year asked the European Space Agency to "provide an independent assessment of the feasibility of the proposed design as well as to assess any areas of concern and provide recommendations for the future", and it is this ESA report which has now been released.
According to the Propulsion Engineering and Structures specialists of the ESA, there's nothing about the Skylon design as it stands which is impossible. The ESA report (pdf) says:
No impediments or critical items have been identified for either the SKYLON vehicle or the SABRE engine that are a block to further development.
But the report adds, in italics:
It is clear that the SABRE engine is critical for the successful development of the SKYLON vehicle.
The back end of the SABRE is a relatively conventional hydrogen-oxygen rocket, the most powerful type of chemically fuelled propulsion kit that can be built. If that were all SABRE was, however, Skylon could never work as it would have to carry much more liquid oxygen than it can.