[extropy-chat] Re: Space Elevators

[Mike Lorrey]

--- Bret Kulakovich <bret at bonfireproductions.com> wrote:

> 
> uhm, After a while, you are going away from the Earth at a comperable
>  speed to the mass you are repelling away from you?
> 
> Something doesn't click here... Without station keeping thrust, your 
> mass changes and you are going to gain/lose altitude as you spool out
> the cable. And as it gets closer to the Earth (inserting previous  
> gripe:) it starts to build an electrical differential with you on
> orbit?

Not quite. While you are moving away from the earth in reaction to
spooling the cable out, you are still attached to it, so you are all
one orbiting mass, orbiting at the velocity of your original orbit. As
the cable is fed out, the end of that cable is travelling at less than
the orbital velocity for that lower orbit, so it is gravitationally
attracted toward the earth. 

This is the tide. So long as the common center of gravity remains
inside your ship, all is well and the cable remains taut. As soon as
the common center of gravity is somewhere along the cable, then you are
going to have bunching problems, because the center of gravity will be
moving slower than your rate of feed. 

Because of this, it is at this point you should start feeding out your
counterbalance in the opposite direction, outward. As it is now
orbiting at a higher altitude, but at the orbital velocity of the point
of the common center of gravity, it experiences a centrifugal force
outward, and is drawn outward.

Electrical potential can be built along the length of the cable because
as a wire travelling through the electromagnetic field of earth, it
will do so. The question to ask is whether that field itself rotates in
a 24 hour period as well. If so, then there should be little or no
potential built for this reason. Tethers in LEO build potentials
because they orbit much faster than the 24 hour rotation time of earth.

Now, if there is a potential, then while drawing that potential out
will lower your altitude (because you are doing work by drawing that
potential out), if you feed current into the cable, you will raise your
orbit, so having a nuke reactor and/or solar panels on your cable feed
station will help to stabilize the system.

> 
> 
> Just thinking out loud.
> 
> 
> ]3
> 
> 
> On Aug 3, 2005, at 4:44 PM, Damien Broderick wrote:
> 
> >  Mysteriously, it's going straight away from me toward the surface.
>  
> > After a while, the far end is hovering one inch above the ground.
> 
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> 


Mike Lorrey
Vice-Chair, 2nd District, Libertarian Party of NH
"Necessity is the plea for every infringement of human freedom.
It is the argument of tyrants; it is the creed of slaves."
                                      -William Pitt (1759-1806) 
Blog: http://intlib.blogspot.com


		
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