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Helge Moulding <[log in to unmask]> wrote:

>I wonder if the economics of conventional means were ever as clear as
>they are now. Zubrin talks about the economics in _Entering Space_. The
>current cost is in the thousands of dollars per pound of payload, partly
>due to the technological choices we're making. Zubrin seems to think
>that we could reduce the cost by a couple of orders of magnitude, even
>with conventional rockets. Back in 2000 David Smitherman (Space
>Elevators: An Advanced Earth-Space Infrastructure for the New
>Millennium) suggested the cost by elevator might be a couple bucks per
>pound. Smitherman also figured that it'd take maybe 50 years to build
>it. I gather some people are now, just 4 years later, saying we could do
>it in less than 20 years. What changed, besides Bush's proposed space
>initiative?
>--

Carbon nanotubes are what changed.  The space elevator, if built, will not be a super Eiffel Tower (although the required mass is considerably reduced if a 30-40 mile high supporting structure is built).  It will be a "ribbon" of extremely long carbon nanotubes, and it will be under tension.  If you tried to build it from steel cables, for instance, you run into something called the "taper factor".  For steel, this is ridiculous; the width at GEO has to be billions of times the width at the outer (counterweight) end.  With carbon nanotubes the taper factor is reduced to a thousand or so.

Regards,
M.R.F.

"As you struggle to save humanity be sure to avoid electrodes in your path" -- Robotron 2084


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