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

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

Date: Sat, 26 Jun 2004 23:04:31 -0700

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.

> However, if you lower the payload mass a tad, you can have many cars on
> the elevator at once. Once you hit an altitude of some 2400Km, G has
halved,
> and continues to reduce.
>
> > support on the climb. And the anchor will need to supply
"circumferential"
> > momentum, to minimize displacement of the tether. Especially if
thrusters
> > (and their fuel) are not provided for use in the design.
> >
> > I ask again, "How does the mass of this 'tiny "rock" ', compare to a
single
> > elevator + payload?" What kind of loads are we considering to pay for
this
> > massive engineering and maintenance effort? Are we sending up one atom
at
> > a time?
>
> 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.

David A. Smith

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