Re: beanstalks (was Re: Metallic hydrogen ...)

From: N:dlzc D:aol T:com \(dlzc\) (net_at_nospam.com)
Date: 06/27/04 

Date: Sun, 27 Jun 2004 15:51:32 -0700

Dear Ian Stirling:

"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:40def21f$0$12769$ed2619ec@ptn-nntp-reader02.plus.net...
> In sci.physics "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox
T:net@nospam.com> wrote:
> > Dear Ian Stirling:
> >
> > "Ian Stirling" <root@mauve.demon.co.uk> wrote in message
> > news:40de07ae$0$9698$ed2619ec@ptn-nntp-reader02.plus.net...
> >> In sci.space.policy "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox
> > T:net@nospam.com> wrote:
> >> > Dear Ian Stirling:
> >> >
> >> > "Ian Stirling" <root@mauve.demon.co.uk> wrote in message
> >> > news:40dde11c$0$8790$ed2619ec@ptn-nntp-reader02.plus.net...
> >> >> It depends on where you terminate the tether.
> >> >> For example a 50GPa 1.3 density nanotube rope made into a tether.
> >> >> If the tension at the base is 1Kg, then up to 48300Km (from the
center
> > of
> >> > the
> >> >> earth), the mass is 27Kg.
> >> >> The tension is 30N, and the accelleration is .1m/s^2.
> >> >> If you terminate here, you need a mass of 300Kg, for an overall
mass
> >> >> of 327Kg.
> >> >> At 191000Km, the accelleration is 1m/s^2, and the tension is 4N,
with
> > the
> >> >> tether mass being 84.4Kg below this. The counterweight only adds
4Kg,
> >> >> for an overall mass of 87Kg.
> >> >> Taking it right out to where the tension is 1/1000N, the mass is
half
> >> >> a gram, and the total 88Kg.
> >> >
> >> > You've descibed a tether system that can just support itself, with
no
> >> > elevator, no load. Each lofted kilogram will require
slowly-decreasing
> >>
> >> Not quite.
> >> The payload is the same as the tension.
> >> When you put a payload on the bottom, the tension falls to near zero.
> >
> > The tension where? The tension at the anchor, as you've described the
> > tether is simply supporting the tether. As you add an elevator, the
net
> > tension increases. As you add payload to the elevator, the tension
> > increases again. The tension at the Earth end is not at issue.
>
> Nope.
> There is a preload of somewhat above the mass of the payload on the
cable.
> Say this is 2 tons.
> If you put a car of 1.5 tons on the cable, then the tension at the earth
> end drops to 0.5 tons, and gradually rises back to the 2 tons figure as
> the car climbs.

More useful than the "30N" force you quoted before...

> <snip>
> >> It depends on the average strength/density of the tether.
> >> For the above tether, the mass of each car is some 1% of the total
mass
> >> of the system.
> >> Payload maybe 0.5% or so per.
> >
> > So we can take up 0.5% of 327 kg per load (including the elevator)?
That
> > is a whopping 1.5 kilos... no room for batteries, drive motor, really
not
> > much of anything.
>
> No, .5% of 88Kg, so 500g or so payload and 500g car, for a 1Kg
> tether.
>
> I'd hoped it was obvious that the 1Kg payload tether was only an example,
> and the math is exactly the same for 1 ton, or 1000 tons.

I'd hoped I'd get an answer, rather than a guessing game. Apparently 0.5%
(elevator+payload/anchor) is the answer for the question asked "How does
the mass of this 'tiny "rock" ', compare to a single elevator + payload?"

David A. Smith

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