Re: Towers to the Stars

From: Robert J. Bradbury (
Date: Wed Mar 01 2000 - 04:59:50 MST

On Tue, 29 Feb 2000, Spike Jones wrote:

> Robert, I got to the same point Landis did in my 1993 paper. I will snail
> mail you a copy if you wish, or better yet, I will scan and email it.

It would be nice to get it, I'll add it to the database and link it to the
Landis paper.

[I wonder how much progress will speed up when engineers can stop
reinventing things invented by someone else???]

> I did the same thing Landis did: numerical integration. {8-[
> I used excel for that purpose.

I suspect that if Mathematica can't integrate it then it can't be done.
Fortunately, the computers are so fast now, numerical integration does
a fine job for most stuff.

Interestingly enough, I converted one of Matloff's early papers on Solar
sails the a couple of days ago and he mentions doing the calculations
on a TI SR-52... remember those??? Things are so much simpler today,
but you need a full semester course to really learn to use Excel or
Mathematica well.

> I wonder if anyone has managed to perform that integral and get a closed
> form solution for the mass of a skyhook in terms of specific strength of
> the material and the mass and rotation rate of the planet about which it
> orbits. Have you heard of such a solution?

Nope. Send it off to Wolfram as a bug they need to fix. :-)

> When I did my paper, I mentioned spider silk, but not diamond. I didnt
> have a theoretical tensile strength of diamond. Do you have that?

Pg. 386 of NM says the Young's Modulus is ~400 GPa for saphire and 1050 GPa
for diamond. But what we really need are some comparisons between the
compressive and tensile strength. Since it isn't in the Structural Materials
sheet from my Physical Properties workbook, I doubt I've run across it in
any of the books I currently have. "Honey, can I see your diamond for
a minute?", "Why?", "Oh, the school won't give me the funds to do
a compression test on one, so I figured I'd use yours....".

> Also, I think someone mentioned a isosynchronous cable on Mars.
> I concluded in 1993 that it is faaar more feasible there than on Earth.

Naturally. Mercury would be even better because the rotational speed
is much lower. I'm wondering though if you or Landis took into account
the strength requirements for gale force winds buffeting the tower???
With that much surface area you really have to do that.


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