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Krowser
2009-Nov-25, 06:49 PM
What happens if you attach a cable on the ground of the moon and bring it all the way back to the Earth?

I figure since the moon isint geostationary that cable is going to go wild but it wont wind (winde? As in rewind) away since we always see the same face of the moon.

George
2009-Nov-25, 07:11 PM
In a sense, the Earth's gravitational tide acting on the Moon has caused the tidal lock we see (one side only). But the Moon takes almost a month to go around the Earth whereas the Earth rotates once around in one day. Thus, if the cable were sufficently slack, it would wind once around the Earth in a little more than one day's time. [The movement of the Moon requires the Earth to rotate further to catch up to the Moon each day.]

Krowser
2009-Nov-25, 08:02 PM
Ok, what if it wasnt attached to the earth? Would it fly off into space?

What if you attached something heavy enough to keep it under the Earth's atmosphere?

AndreasJ
2009-Nov-25, 08:30 PM
The Moon's orbital excentricity would make it swing back and forth, in and out of Earth's atmosphere, unless the counterweight was heavy enough to substantially alter the dynamics of the Earth-Moon system.

Cookie
2009-Nov-25, 08:31 PM
What if you attached something heavy enough to keep it under the Earth's atmosphere?It would probably be one heck of a wrecking ball !

Hop_David
2009-Nov-25, 09:00 PM
The August, 2004 issue of Scientific American had an interesting article on tethers. If I remember right, one of the tethers they discussed always pointed outward, that is it was aligned radially from earth's center.

This was thought to be stable. Basicly a small, elongated tide locked moon. As you moved earthward, gravity would overwhelm (so called) centrifigal force and thus you had some gravity at the near earth end. Outwards, centrifugal force overwhelms gravity and occupants at the outer end would feel "gravity" and thus could enjoy things like flushing toilets or setting their plates on a table.

I believe what you're talking about would remain stable so long as the earth end didn't penetrate too far into the atmosphere. Passengers on the cable would experience weightlessness at the Earth Moon L 1 point (EML1). As they either moonward or earthward from EML1, they would feel increasing gravity.

The tether stress would be increasingly enormous as you moved earthward. I don't think even bucky tubes would enable extending the tether end to just above the earth's atmosphere.

A bean stalk from EML1 to the moon's surface is interesting. I believe Geoffrey Landis as well as others have discussed this.

AndreasJ
2009-Nov-25, 10:51 PM
I believe what you're talking about would remain stable so long as the earth end didn't penetrate too far into the atmosphere.
Lunar libration (http://en.wikipedia.org/wiki/Libration) would make the cable oscillate.

neilzero
2009-Nov-25, 11:32 PM
My guess is swinging in and out of Earth's atmospheres, with an average air speed of almost 1000 miles per hour, so it would produce a sonic boom all the way around the equator, except it would occasionally swing into the temperate zones, rarely touching the surface, unless it had 30 thousand miles of excess length and a wrecking ball on the earth end. The moon's orbit is not very circular. Various transients would cause random movements and lots of stress on the tether. Even using CNT = carbon nanotubes with optimistic specs, it would have a mass of millions of tons = large taper to survive the stress, for even one month. An Edwards type climber could make repairs above Earth's atmosphere, perhaps also in the upper atmosphere. The tether would be damaged by space junk, micrometeorites, lightening strikes and atomic oxygen. It cannot be attached at both the moon end and earth end, due to Earth's rotation. Neil

Hop_David
2009-Nov-26, 02:03 AM
Lunar libration (http://en.wikipedia.org/wiki/Libration) would make the cable oscillate.

Yes, that's true.

Jens
2009-Nov-26, 02:13 AM
It would probably be one heck of a wrecking ball !

And I suspect even Tarzan would have a hard time grabbing onto it!