Space elevator feasibility; split from: NASA Announces New Launch Vehicle and CEV

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  • #51
DaveC426913
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HitSquad: can you please elaborate on this pole-anchored space elevator?

AFAIK, ribbon-type space elevators must have their centre of mass in a geostationary orbit so that it does not move wrt its anchor on Earth.


If you were to build a space elevator similar to that tetherball, what angle(s) would your elevator shaft be wrt the Earth's surface? Do forces balance and create a stable configuration?
 
  • #52
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This is not the case for orbiting bodies which are tethered.
images.google.com/images?q=tetherball
Ok, theoretically, that COULD work. However, the anchor would have to be ACTIVELY swung at a VERY high rotational rate requiring ENORMOUS amounts of energy to keep it spinning.

However, this is what I like to call the difference between where physicists live, and where engineers live. Why do it at a pole where energy input and an angular momentum imparter are required when it can be done without either of those at the equator, thus somewhat simplifying an already mind-boggling problem.

Cheers...
 
  • #53
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The playground physics of space-elevators, continued

DaveC426913 said:
can you please elaborate on this pole-anchored space elevator?
Actually, a tethering at an exact pole would not be feasible since the ribbon would be draped across the terrain at least until the point where the satellite was visible at the horizon. To tether at a pole, you would need a tower in order for the tether to clear the horizon. Also, I think a tether would droop as it was moved away from the equator and therefore the farthest distance from the equator that one could tether would be even more limited than by what might be suggested by the horizon.


ribbon-type space elevators must have their centre of mass in a geostationary orbit so that it does not move wrt its anchor on Earth.
I have been describing tethered geostationary orbits, though there are ways around the geostationary prerequisite which I have not yet described.


If you were to build a space elevator similar to that tetherball, what angle(s) would your elevator shaft be wrt the Earth's surface?
Less than 90 degrees. Tethers at the equator would be 90 degrees, and tethers placed progressively farther from the equator would have progressively smaller tether angles. 10 miles on either side of the equator would create tether angles just a bit less than 90 degrees.


Do forces balance and create a stable configuration?
Yes. A tetherball sent into orbit is stable. Try it at a playground near you.
 
  • #54
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Challenging the equatorial imperative

LunchBox said:
hitssquad said:
This is not the case for orbiting bodies which are tethered.
images.google.com/images?q=tetherball
the anchor would have to be ACTIVELY swung at a VERY high rotational rate
The non-equatorial tethered anchor is geostationary and therefore its orbital period is 24 hours.


Why do it at a pole [...] when it can be done [...] at the equator
One reason to do it in the continental United States is that most Americans do not live at the equator. It might be convenient to visit Space Hilton 1 without requiring a passport.
 
  • #55
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SkepticJ said:
Good point. I'll see if I can find that technical paper. Google searches aren't finding anything, but I'll keep trying to get it.

No, not that link; the link in post #18's bottom. It doesn't work for me.

Shouldn't be hard at all. For one thing, the pipe could be very narrow in diameter; which means less air inside. For another thing, the vacuum pump isn't fighting against gravity. If you had a pipe as tall as this, connected even just a small vacuum pump, it could eventually suck all the air out. "Eventually" wouldn't do, so something like a 777's jet engine powered vacuum pump would do nicely. It'd probably be able to suck the pipe to a vacuum in several hours to a day. Since the top of the pipe is above the atmosphere no more, or very, very little and slowly, will get in again that way. Going through the pipe material itself, hydrogen and helium are the only gases I know of that can squeeze through metal. There's not much of either gas in Earth's atmosphere, because they rise to the top of the atmosphere and are blown away by Sol's solar wind.

Adding to this post:

The vacuum pipe need not be steel. Materials such as aramid, carbon fiber, fiber glass, synthetic spider silk(still being worked on, but the transgenic "spider goats" are really helping) and carbon nanotubes(ditto) would work far better.

Another way for a space elevator, gone into in much detail, are Jacob's Ladders
here
The supra planets on there I'm very fond of as well. They're quite a bit in the future due to the lack of extreme need for such amounts of living space, the lack of getting to space cheaply etc. I, unlike Birch, don't see such things being built for several hundred years at least however.
 
  • #56
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Did I kill this thread, or there's just no more to say? :confused: :shy:
 
  • #57
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eh, nothing more to say
 
  • #58
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Ki Man said:
eh, nothing more to say
How about I thought of another way to support the mass stream's vacuum pipe?: The pipe segments exert magnetic drag on the mass stream, stealing some of its inertia, to hold the vacuum pipe up. This is probably how it's supposed to work in the original idea. If not, then how would many thousands of kilometer high towers function without nanotube pipes under huge tensile load from the top? How would any of the hanging structure? Nanotubes weren't even discovered yet when the space fountain idea came about.
I don't think any length of the tower would have to hang from another part(within reason), it'd all be supported right on the spot by the internal mass stream.
 
  • #60
Mech_Engineer
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Holy old thread Batman!
 

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