[extropy-chat] Re: Space Elevators

[Mike Lorrey]

--- Damien Broderick <thespike at satx.rr.com> wrote:

> At 02:23 PM 8/3/2005 -0700, Adrian Tymes wrote:
> 
> >Rotation...assuming you adjust your angular velocity accordingly
> while
> >spooling out the cable (an easy trick to do, especially if you're
> >careful to spool out an exact same amount straight away from the
> >surface at the same time).
> 
> This don't make no lick o' sense to me, bubba.
> 
> Starting at the hind end -- I reckon you need to spool out a damned
> sight more from the farside spigot, on account o' the gravitational
> gradient weakening. Just a detail.
> 
> Now as for rotating -- what Mike called " tidally locked", although
> that's not what it is, just what it emulates 

Uh, no, that IS what allows you to spool the cable out at all, unless
you electrically charge it. Tide is a difference of gravitational
potential exerting different amounts of force on an object at different
points on that object. 

The difference of gravitational potential is expressed orbitally as a
difference in required orbital velocities at different altitudes. While
LEO orbital velocity is mach 25, GEO orbital velocity is far less, only
a few thousand mph AFAIKR (which makes sense, as its orbital
circumference is 2xRx3.14159263 or thereabouts, in a 24 hour orbit,
orbital velocity should be about 6,000 mph).

Nor, as was asked previously, do you NEED to spool out cable above the
GEO point, that is just an added feature if you want to extract earth's
rotational energy to propel spacecraft across the solar system. You can
just as easily have a space station several times heavier than the
cable a short distance above the GEO point counterbalancing the cables
mass. You could still have an outer sling of some size, so long as its
mass is counted in the euqation and the whole systems center of mass is
at the GEO point. As you can see this is a very fragile balancing trick
that could induce dangerous harmonics in either cable, especially if
the cargoes transported are not an immensly small fraction of the total
system mass, and/or so long as an active counterweight system is not
used to adjust for shifts in center of mass. 

Ideally you'd build the cable as a loop and pully with multiple cars on
it, and so long as you send up about the same amount of mass as is sent
down, it will remain stable.

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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