On 29 Feb 2000, Anders Sandberg wrote:
>
> > Clarke's skyhook was built from the bottom up ANd from the top down...
> > joined in the middle I think...
> Sounds wrong. The problem with building a tower is that you need
> materials with very high compression strength, and I seem to recall
> there are no such materials that would give a working tapering ratio -
> with enough tapering you could do it, but the result of the "how high
> tower could we possibly build" thread here or on rec.arts.sf.science
> concluded it needed several thousand kilometers of base to reach
> orbit, clearly infeasible.
It seems that those conversations may have been in error.
Landis says a standard 2240 km high, compression tower built out of
boron/epoxy (supporting a Shuttle payload) would have a diameter of
1 cm at the top and 9 meters at the bottom.
A pressurized 1 atm tower from PBO fibre, would be 2.21 m at the top and
138 meters at the base. I can build a 138m platform in the ocean easily
it draws about the mass of an oil tanker.
> Beanstalks "work" because high tensile strengths are possible and most
> parts of the structure are outside the strong gravitational field near
> the earth and hence do not contribute much to the tension.
It turns out that a sky hook cable masses more than the equivalent tower
because it has to support more weight in the high gravitational field.
But the differences the lower compression strength in a non-pressurized
tower vs. the tensile strength of a sky hook make the masses come out
in the same general neighborhood.
If the Landis estimates for Alumina wiskers are close to diamond, it
looks like nanotech should be able to build a tower massing 4-5 times
less (about 40,000 tons). Thats about an order of magnitude less material
than is in the Empire State Building.
Robert
This archive was generated by hypermail 2b29 : Thu Jul 27 2000 - 14:04:21 MDT