Saturday, September 14, 2013

Is the Skylon scalable?

Just 23 pounds for each pound of cargo.  For comparison, the Shuttle took 84 pounds for each pound of cargo.

What if you wanted a specialized vehicle, that was reusable, and only delivered a crew of 2 to LEO?  The Shuttle was reusable, but it only came in 1 size.  If it were scalable, and if you could use that number of 84 pounds per pound, and if you could use the number of 7000 pounds for the crew compartment as cargo, then it would take 590,000 pounds of mini Shuttle to get to LEO.

But we cannot do that with the Shuttle.  It is history.  But what about the Skylon?   Could you scale it down from the current planned size that is slated to carry up to 33,000 pounds to LEO?  If so, it would mean a bird that would only mass at 161,000 pounds.  The current planned size at 23 pounds for each of the 33,000 pounds gives a bird of 760,000 pounds,

Even if the Skylon required more mass at lower capacities, it could do better than the Shuttle, one would think.  That would mean less than 590,000 pounds at liftoff.

A comparison with another craft, the VentureStar, suggests that it may not be scalable to smaller sizes.  The scaled down version of the VentureStar, the X-33, could not reach orbit at all, and massed at 285,000 pounds.  It could only get about half the velocity needed for orbit and zero payload.  However, the fully configured VentureStar was better at payload fraction, taking only 49 pounds to LEO v 84 to LEO for the Shuttle.

The Skylon will have limited scalability, as with any launch platform.  Less mass means less fuel, but the hardware doesn't change.  If you could change it to a smaller version, would it be worth it?

I suppose the answer should be one goal at a time.  The VentureStar may have flown, but was canceled.  The cancellation may have been politically motivated.  Composite tanks failure was the reason given, but it sounded to me to be more like an excuse.



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