[extropy-chat] Space Pulleys (was Name that system)

Keith Henson hkhenson at rogers.com
Thu Dec 21 01:05:36 UTC 2006

At 02:43 PM 12/20/2006 -0800, you wrote:

>--- Keith Henson <hkhenson at rogers.com> wrote:
> >  But
> > (because the original
> > concepts required taper, people thought they had to
> > go up the elevator with
> > a climber.
>I do not think taper is necessary nor desirable in a
>space elevator. The part that is to be tapered, the
>distal portion, is actually the part that would weigh
>the least tapered or not, due to its position in the
>gravitational field. It would also be near the part
>that is subjected to the most strain. Therefore
>tensile strength by increased cross-section here would
>be preferable. So rather than a taper, I would want a
>flair toward the distal end.

It's the same thing.  The thickness of the cable at any altitude is an 
exact mathematical expression given here:


> > This led to Rube Goldberg concepts of electric
> > motors and lasers beaming up
> > power for the motors.  Plus going up slowly--which
> > you have to do because
> > of power and weight problems with motors--loads the
> > cable much more than
> > going up fast, not to mention that it subjects you
> > to a long time in the
> > Van Allen belt.  Projected efficiencies are in the
> > 1-2% range.
>I agree that most of the designs for the climber are
>inefficient. GEO is still within the upper layers of
>the Van Allen belts so you are going to need shielding

Unless you drain the Van Allen belt.

> > So I was working on a book which included space
> > elevators/solar power
> > satellites last summer and came up with a way to
> > effectively get step taper
> > from a constant cross section cable with a mess of
> > pulleys.
>I am not sure what "step-taper" is supposed to
>accomplish. See above for argument against tapering. I
>think a constant cross-section cable with a space
>pulley is an interesting idea. It would, amongst other
>things allow for maintenance of worn cable by allowing
>different sections to be rotated to ground and

In fact, the whole cable goes back to ground in perhaps 50-100 days.

>One thing you would have to figure out is how to
>balance the torque of the distal pulley. How would you
>keep the "motors" from rotating the entire housing
>rather than the axle of the pulley.

The cables are under mega tension.  Use an idler pulley on a lever to 
counter the torque.

> > Not surprising the concept gets ignored to
> > denigrated by the
> > "establishment."  :-)
>I find the fact that there is an "establishment"
>devoted to an unestablished technology to be
>hillariously sad.

It's not as fatal (or maybe it is) as getting the EP model of why wars 
happen accepted.

Though that model leads to some bizarre proposals, like swapping out the 
Iraqi population with Texans to end the war.

Keith Henson

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