Author Topic: Space elevator trips could be agonizingly slow - New Scientist  (Read 8308 times)

Offline A_M_Swallow

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Unfortunately we have only measured carbon nanotubes 63 times as strong as steel, and that was a single thread.
http://en.wikipedia.org/wiki/Carbon_nanotube

Offline KelvinZero

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How about a space bungie? :)
« Reply #21 on: 12/28/2008 05:48 pm »
What you want isnt a constant speed but a constant acceleration.

You could possibly do this with a flexible material, but perhap another way is for the orbiting counterweight to be both higher and with a slower orbital period than geostationary.

The goal isnt to transport the ascending cargo up to geostationary orbit. After a period of acceleration the cargo has gained at least orbital velocity and it can let go of the cable.


Im a bit hazy about how you pull the business end back to earth afterwards. Perhaps the cable expands or shrinks. If the whole thing is  more than thirty thousand km high then even ten percent contraction would be sufficient I think. Possibly thermal expansion? In which case it could be directly solar powered by rotating the ribbon towards or away from the sun. Another possibility is sending cargo down the ribbon. A third is an eliptical orbit and a bucket that anchors itself in the ocean by filling with sea water ballast.

hehe.. this idea is sounding flakier and flakier as I think it over.

Offline ANTIcarrot

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Unfortunately we have only measured carbon nanotubes 63 times as strong as steel, and that was a single thread.

Yes, and we've also only spent a few thousand dollars on any given elevator design. However way you look at it there is significant room for improvement.
What you want isnt a constant speed but a constant acceleration.

The problem is that wheels can only go so fast before they fly apart. Linear induction could do the job if magnets were incorporated into the elevator itself, and the car did the grunt work, but that's a real increase in power levels and complexity, and power switching requirements get rather horrid at 10kmps+. As would the construction of the elevator itself; good luck making it magnetic without adding all sorts of other problems.
« Last Edit: 12/29/2008 03:35 pm by ANTIcarrot »

Offline mlorrey

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Unfortunately we have only measured carbon nanotubes 63 times as strong as steel, and that was a single thread.

Yes, and we've also only spent a few thousand dollars on any given elevator design. However way you look at it there is significant room for improvement.
What you want isnt a constant speed but a constant acceleration.

The problem is that wheels can only go so fast before they fly apart. Linear induction could do the job if magnets were incorporated into the elevator itself, and the car did the grunt work, but that's a real increase in power levels and complexity, and power switching requirements get rather horrid at 10kmps+. As would the construction of the elevator itself; good luck making it magnetic without adding all sorts of other problems.

How conductive is a carbon nanotube cable? Given the cable will go through the van allen belts, there will be significant differentials in charges in the various locales the cable exists in, both at ground level, in the ionosphere, through the belts up to geosynchronous orbit. With such charge differences I expect we will also see significant electrical currents flowing, and as a result, electric fields around the cable due to these currents. This should allow for  some degree of magnetic stabilization at the least if the lifter is able to accelerate at over 1 g, if not use the field as a means of magnetic traction. Not sure though, what do the experts say on this?
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Offline KelvinZero

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What you want isnt a constant speed but a constant acceleration.

The problem is that wheels can only go so fast before they fly apart. Linear induction could do the job if magnets were incorporated into the elevator itself, and the car did the grunt work, but that's a real increase in power levels and complexity, and power switching requirements get rather horrid at 10kmps+. As would the construction of the elevator itself; good luck making it magnetic without adding all sorts of other problems.

You didnt read my post.

My idea was pretty silly, but there are clearly no wheels involved. With a bungie cable you just hold onto the bottom and scream.

Offline mlorrey

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What you want isnt a constant speed but a constant acceleration.

The problem is that wheels can only go so fast before they fly apart. Linear induction could do the job if magnets were incorporated into the elevator itself, and the car did the grunt work, but that's a real increase in power levels and complexity, and power switching requirements get rather horrid at 10kmps+. As would the construction of the elevator itself; good luck making it magnetic without adding all sorts of other problems.

You didnt read my post.

My idea was pretty silly, but there are clearly no wheels involved. With a bungie cable you just hold onto the bottom and scream.

Ah an elastic inchworm? Didn't Wil E. Coyote do that trick once or twice?

But ya, should have plenty of strength over 50 meters or so to stretch out a bungee, release it, then the grip on the skyhook cable. It would IMHO be a very bouncy ride tho.
VP of International Spaceflight Museum - http://ismuseum.org
Founder, Lorrey Aerospace, B&T Holdings, ACE Exchange, and Hypersonic Systems. Currently I am a venture recruiter for Family Office Venture Capital.

Offline KelvinZero

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That wasnt quite what I meant :)

But Wile E. Coyote would still be proud ;)

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