Space Elevator

Discussion in 'General Science & Technology' started by Deena, Aug 23, 2002.

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1. AgesilausRegistered Senior Member

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Since only the end tethered at geosynchronous orbit would have orbital velocity I don't see anyway that it could do anything other than fall down. Everything below that would be moving at suborbital velocity.

3. postoakRegistered Senior Member

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If something cut one of these in two, I believe the way it works is the upper half would fly off into space since it's center of gravity would (then) be above the GEO point and yet it would be going faster than orbital speed. In the same way, the lower piece would fall to earth. How much damage the lower piece did would depend on how long it was. The break could happen 10 feet above the earth's surface, in which case the damage wouldn't be too much.

5. AgesilausRegistered Senior Member

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Every point on the elevator is moving at less than orbital velocity except the terminal GEO end. At the surface it would be moving at about 1000 mph but orbital velocity is over 18,000 mph at the surface. The difference in actual velocity and orbital velocity decrease all the way up to the terminus.

How could the center of gravity ever be above the orbital teminus, all the mass is below the terminus and for a linear object that means that the COG has to fall on the object somewhere in between the two ends.

7. BatMMember At LargeRegistered Senior Member

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In the hammer-throw, when you release the hammer, where does it go? It doesn't hit you on the head... :bugeye:

8. postoakRegistered Senior Member

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Agesilaus - well there is more than one proposed version of this thing. The one I like best, and therefore was talking about, was one that was twice the length of the distance from the earth's surface to the GEO distance. So, for every unit of mass below GEO, there is one above balancing it, unless the thing was cut. But even on the other model, there is a huge mass at the upper end to counter-balance the mass of the elevator hanging down. In either design, the center of gravity is right at the GEO.

9. AgesilausRegistered Senior Member

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Huh? Have you ever done center of mass aka center of gravity calculations? It is mathematically impossible for the COM to be at the terminus unless the elevator section is massless. I don't know of any super-strong weightless engineering materials but perhaps you do. The COM is that point where all the vectors sum to zero, the balence point. In a homogeneous object like a meterstick is is at the center of the the stick. But in a heterogenous struction made up of different density sections you have to integrate all the various sections to come up with a COM. Its hard to describe since its not too easy to show integrals here.

I also am confused by your "twice the length" comment, the length of a space elevator is fixed at 23,500 miles on earth, geosynchronous orbit distance. Any other distance would require the vertical column to accelerate the entire structure, this would increase the stress on the object unimaginably. It would be like constructing a building x miles high where x is whatever distance you imagine this to be. A 200 mile high building for instance. That would negate the attraction of the elevator.

10. FrencheneeszAmazing MemberRegistered Senior Member

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I don't know about the rest of you, but its kinda annoying when you just quote someones whole response. We already read it, right? If you take out the part that is relevant to what you are saying, it would waste much less space.

Also, you sound like you think you know something talking about coms and integrals, but Im suspicious. It would be incompletely possible to balance each side of the GEO sync. orbit to produce an average COM.

When he was saying "twice the distance" he was talking about putting weight on the far end of the orbit of the actual station to balance out the pulling effect of the line and elevator below the orbit. Personally, I don't think this is very hard to understand. The weight counter could be made mechenized to flux the counter weight to compensate for added and subtracted weight inside orbit. Even so, the counter would never be perfect and this is why all space stations have orbit correcting thrusters to keep them going good.

I hope you can understand how that would work, although I do think that building one would be a huge waste of money.

11. AgesilausRegistered Senior Member

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Well I finally went out on the web and found a description of what you are talking about, the total cable length is 100,000 or so km extending well beyond the geosynchronous 38,500 km point. That makes the GEO point the COM and I was just plain wrong. I was visualizing a single cable down from GEO to the surface.

12. FrencheneeszAmazing MemberRegistered Senior Member

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"I was just plain wrong. "

I admire it when people admit they are wrong. I find that so many people in these forums seem to be set in their ways without reason. My hat's off to you.

13. AgesilausRegistered Senior Member

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Life would be so boring without the occasional idiotic mistake. No reason not to 'fess up' tho

14. ClockwoodYou Forgot PolandRegistered Senior Member

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One end actually would be slightly beyond orbital distance. This would caues it to be kept taught.

Remember, That much cable weighs a LOT. You need that extra bit of centrifical force to keep it from being pulled out of orbit.

15. >_ORegistered Senior Member

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I agree with the Frenchie, granted unless we all become sterile from our microwaves and curb the population problem it will be neccessary to move into off planet alternatives, but this is hardly worth its effort, interesting idea but still SO0o ridicules

16. goofyfishAnalog By Birth, Digital By DesignValued Senior Member

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It was once thought ridiculous that we would
build an airplane, break the sound "barrier" or get
to the moon. An open mind is a powerful tool.

Peace.

17. >_ORegistered Senior Member

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ah true but a sensible mind will find a better way than building some geeky space elevator

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19. EvilPoetI am what I amRegistered Senior Member

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"Keeping an open mind is a virture---but, as the
space engineer James Oberg once said, not so
open that your brains fall out."
-Carl Sagan, The Demon-Haunted World

20. FrencheneeszAmazing MemberRegistered Senior Member

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"It was once thought ridiculous that we would
build an airplane, break the sound "barrier" or get
to the moon."

I don't doubt that we COULD build a space elevator. But who would want to build an airplane if we could get to New York from Britain in less time for less money?

The thing would probably fall apart before it paid off its expense.

21. ClockwoodYou Forgot PolandRegistered Senior Member

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Well, if we ever get the first von noimen machines working we could do whatever our hearts desired (within the laws of physics).

Tell them what to build and they would build it. Stick on a good AI and you wouldn't even have to do that.

22. BatMMember At LargeRegistered Senior Member

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Do you mean "Von Neumann"? I thought all our current computers were based upon the Von Neumann architecture.

23. FrencheneeszAmazing MemberRegistered Senior Member

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I might be wrong, but arent von neumann machines the nano-bots that can reproduce and repair themselves? I think the hype about them is that they could build anything for us and we wouldn't have to worry about getting them energy, materials, or instructions.