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Re: shuttle disaster (space elevators)



John Hasler wrote:

>Paul E Condon writes:
>> It is not hard to compute the tension in a space elevator ribbon. (It
>> would be a fair question for a final exam in an undergraduate mechanics
>> course.)  It depends on position along the ribbon, on the Earth
>> parameters (size, rate of rotation, etc. )...

Of course, 2Pi*r/24hrs at the CG must be the rate of rotation.  In other
words it must be in geosynchronous orbit.

>In particular there is no reason for there to be any significant tension is
>the cable at the base.  With proper controls such a cable should just hang
>there if severed at or near ground level.  A fail-safe design would make
>the connection to the bottom anchor the weakest point so that an
>over-tension event would not result in a cable fall.  The real risk comes
>from an impact high up on the cable.

Not just impact.  The tension at the CG will be incredible-- the
integral from r(at CG) to r(at surface) of M(a[gravity]- a[angular])dr.
If the elevator should part at the CG, 23,500 miles of material would
fall to the East, nearly circumnavigating the globe.

If I don't have this quite right, I claim 40 yrs of opportunity to
forget integral calc. :)

>> ...the mass-per-unit-length (kg/m) that is assumed for the ribbon.
>
>Which must be tapered, of course.

That would be more efficient, but is not *required*.  The idea of
"ribbons" seems a bad idea.  Think of the vibratory forces.  Resonances
would exist in every section at umpteen harmonics, and don't even think
about the odd order heterodynes.  

[...]

I'm surprised no one has mentioned Robert A. Heinlein.  He used the idea
(space elevators--including construction and installation details) in
several short stories and at least one novel, going back to at least the
60's, maybe earlier.  This is the guy who, in the late 30's, described
the physics and practical application of the nuclear pile.  More
importantly, he is credited with the invention of the water bed.  What a
mind. :)
--
gt                  kk5st@sbcglobal.net
 If someone tells you---
 "I have a sense of humor, but that's not funny." 
                                  ---they don't.



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