Arthur C. Clarke's, "Fountains of Paradise" had some of the math worked out
and dealt with the design problems of exactly such a system. Also see this
link http://science.nasa.gov/headlines/y2000/ast07sep_1.htm from NASAs site.
Madhu

>-----Original Message-----
>
>Russell McMahon <apptech@PARADISE.NET.NZ> wrote:
>> Geosynchronous orbit is at about 22,236 miles.
>
>Yes.
>
>> A space elevator that is earth anchored must reach at least that far and
>> in practice somewhat more.
>
>Actually quite a lot more. The 22k mile cable itself is by far the heaviest
>part of such a system. Its center of mass must be at the 22K mile orbit,
>and the simplest and most cost-effective way to do this is to make it
>44.472K miles long.
>
>> Earth circumference is about 24,000 miles. If you cut the elevator below
>> its anchor point it will fall.
>
>What "anchor point"? Are you imagining some sort of massive object (many
>times more massive than the cable itself) in the geosynchronous orbit?
>
>> Such an elevator is the ultimate logical target for terrorists. A small
>> nuke somewhere near the top is liable to be enough. Stopping anyone
>> getting one there could be an interesting task if large amounts of
>> freight and people are travelling up it constantly (as they would have
>> to be).
>
>I think such an elevator is most vulnerable at the bottom, where it is
>attached to the earth anchor. There's just enough tension at this point to
>make the cable stiff enough to use and to provide a margin for any minor
>orbital anomalies. If it gets separated at that point, the whole system
>will just slowly drift away.
>
>Protecting the rest of the cable shouldn't be all that difficult. The
>cargo containers can be held at some distance from the cable itself,
>and energy-absorbing/deflecting shielding materials can be placed in
>between.
>
>-- Dave Tweed
>

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