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Regarding the Space Elevator/Cable Concept

10/16/2006 2:04 PM

Why can't a monofilament (fishing) line be sent aloft by balloon, then transferred to a jet hook/link and taken higher, then picked up by a shuttle, and hooked to a geo-stationary object outside the earth's orbit . The way I see it, that would put possitive force on the line, and hold it in place. With a pulley at the end in space, drop down a small weight, and let gravity take up a larger line, and then a larger line, and so on, until the centripetal force effectively holds a strong enough cable in place to effectively transport an 'elevator' that would ride the cable. Is there something wrong with the physics in this? I would think that starting with a small light monofilament line would allow the link to a geostationary object to be established, then effectively fishing up a bigger one, one process at a time, would work?

Eric

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#1

Re: Regarding the space elevator/cable concept

10/16/2006 2:28 PM

"Why can't a monofilament (fishing) line be sent aloft by balloon, then transferred to a jet hook/link and taken higher, then picked up by a shuttle, and hooked to a geo-stationary object outside the earth's orbit."

Did you give any thought to the tensile strength the monofilament line would need to support its own weight? This is where the technology doesn't exist (yet).

There was a thread about this not to long ago ("space elevator", I think). Search for it on the Forum search and check it out.

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#2
In reply to #1

Re: Regarding the space elevator/cable concept

10/16/2006 2:53 PM

Thanks for your quick reply. I understand they already use a monofilament to hold balloons at huge altitudes for atmospheric measurements. So that may not be a factor. The last I heard, things put in space also have no 'weight'. So, why do scientists discount these things without at least trying them?

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#3

Re: Regarding the Space Elevator/Cable Concept

10/16/2006 3:19 PM

If this could be done would it change the earths orbit ? also would it short out the atmosphere ?

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#4

Re: Regarding the Space Elevator/Cable Concept

10/17/2006 12:07 AM

The longest self supporting length of a tapered filament is currently on the order of 40-50 miles. This tapers down to a fine thread at the bottom and can carry no weight.

The concept was first put forth by a Russian.

lots more here

http://en.wikipedia.org/wiki/Space_elevator

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#5

Re: Regarding the Space Elevator/Cable Concept

10/17/2006 12:50 AM

Disregarding the tensile strength of the line, there are several problems with the physics. Assuming you can get the first line to the satelite, once you connect it you are increasing the mass of the satelite several times. A large part of that mass is closer to the earth thus affected more by gravity. The obit would degrade rapidly, essentially fall out of the sky unless you have very powerful rockets aboard to boost the whole thing into a higher orbit. Once you overcome that obstacle and everything is orbiting nicely, how the heck do you "drop down a small weight"? Anything released from the satelite will also be in orbit. Even if you could just drop a weight, it wouldn't be a small one. It would need to be about twice the weight of the cable lifted so far. The idea is not without merit however. Especially the baloon portion. If you raised the line so a reasonable sized baloon carried up a portion of the line, then attach another baloon to carry the next length, and so on. You end up with a line supported every few meters along its length so that no one portion of the line needs to carry the whole weight of the line.

To raise further strands you could use a technique I would call rope jacking. At the lead end of the new line attach a small rope climbing robot. Essentally a couple pulleys and a motor. Did I mention that the first line was 2 strands of conductive carbon fiber to power the bot? The bot is not strong enough to pull the whole cable, that would be too heavy, but it is strong enough to hold it in position. Activate the climber bot at the same time as a huge ground winch pulls the first line down several feet. So the new line basically stayed where it was. But the head of the new line is now attached to a point further up the original line. Now release the original line with the baloons to lift both lines back up those couple feet lost to the winch.

slo

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#6
In reply to #5

Re: Regarding the Space Elevator/Cable Concept

10/17/2006 1:31 AM

I did a similar experiment years ago, except I used kites. I had 5 kites attached to each other about 500 feet apart. A kite with too much string ends up far away at a low altitude, due to the weight of the string and the wind velocity hitting the string, however 5 in a row, makes them all almost vertical, because they lift each other. You may have a similar positive result with the balloons?

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#7

Re: Regarding the Space Elevator/Cable Concept

10/17/2006 3:34 AM

The last time this came up I did a quick spread sheet to prove it was impossible. I was surprised: ignoring the fact that the top of the cable is in orbit and therefore lighter, and, without tapering the cable towards the bottom:

Using carbon nanotube with a density of 2.6 grams per cubic cm.

A 1 square metre cable 36000 km long weighs about 1.38 Giga Newtons, and, apparently has a strength of 1.5 Giga Newtons.

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#8

Re: Regarding the Space Elevator/Cable Concept

10/17/2006 3:37 AM

Now we're getting somewhere! You see, a few good ideas, strung together....

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#9
In reply to #8

Re: Regarding the Space Elevator/Cable Concept

10/17/2006 5:55 PM

Gentlemen and [ladies] if present or in the future; In my way of thinking, the way I see it, the space elevator has just NOW become a reality.

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