Re: shuttle disaster (space elevators)
On Thu, Feb 06, 2003 at 07:11:46PM -0600, 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. )...
>
> 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.
There would have to be a tension at the base greater than the weight
of the heaviest load you expected to send up. Otherwise when it
started climbing the cable, it would simply pull the whole thing down...
You'd also have to make an allowance for the tension created by the
wind blowing it sideways; that might be rather large. The base would
still be the point of minimum tension though.
> > ...the mass-per-unit-length (kg/m) that is assumed for the ribbon.
>
> Which must be tapered, of course.
>
> > The last time I checked, there was not a material having a suitable
> > combintation of kg/m and tensile strength.
>
> Theoretically any material will work, but the dimensions get out of hand
> when using wet spaghetti. In practice carbon nanotubes are strong enough.
So spaghetti's no good, but macaroni is OK. :-)
Pigeon
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