> > 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.

As I said " ... at least that far ...".
In fact a practical elevator will almost certainly taper - wider as you go
up* - at least until your technology and resources are so advanced that you
don't care about cost. So it's not liable to have constant mass per length.

* Imagine a cable that "just" hangs in place without any ground support. The
point 100 metres up only has to support the mass below it. The point 200
metres up has to support twice as much and so on. Gets more complex than
that but that shows why tapering makes sense.

> > 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?

Yes. There are of course many suggestions on how to do this (talk is cheap
when there is no capability :-) ) but some involve eg an asteroid anchor not
too far past geosync. This is being "flung" outwards as a balance weight.
The need is to keep a tension on the 'cable' and this is one way of
achieving it.

If you do make the beanstalk long enough you can simply take things up to
the top (or highish points) and let them go and they fly away all by
themselves :-). Do it at the right time/place and you have a free delivery
system. The earth slows down very very ... very slightly each time.


> > Such an elevator is the ultimate logical target for terrorists. A small
nuke ...

> I think such an elevator is most vulnerable at the bottom, where it is
> attached to the earth anchor.

Maybe. But it depends what you are trying to achieve. If its ultimate terror
then wrapping the super techo whizz bang cable right around the earth is a
pretty fair aim.

> 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.

It would have to be pretty good to make it nuke safe. And nukes can be
extremely small. Much more so than may be appreciated by most if you have
enough technology. But given the size of probable upgoing payloads even a
more "normal" one would be doable. For the first year the inspectors are
death incarnate. For the 1st 5 years they are very keen. After about 10
years of boring incident free day in day out inspection they should be about
ripe to let a nuke slip through. Terrorists are often not in a particular
hurry. And missiles must be considered. One can be pretty sure that any sort
of aircraft wouldn't have a show. This would be a no fly zone from a vast
distance away.



        RM

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