#21
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Beanstalks...
So, what are the arguments pro and con for having
the high end of the beanstalk anchored to some Big Honking Rock ... or just a garden variety space station, as the far point anchor, given that the beanstalk's stationkeeping I'm of the "big honking rock" fan club. The big honking rock doesn't need to be rock - it can be a metallic asteroid or some other valuable asteroid. If travel on the orbital elevator gets cheap enough, it might be worthwhile to deliver ore (or refined metals) from the anchor rock to Earth. As for making up momentum, putting the anchor rock beyond geosynchronous should result in the Earth's rotation replacing any momentum lost by the beanstalk. Mike Miller |
#22
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Beanstalks...
"delt0r" wrote:
There will almost certainly be a sizable counterweight and it only really makes sense when its quite a nit past GEO. The first reason to have a counterweight is dynamic stability, to keep everything from shaking itself apart. Its huge so destructive resonate modes will be measured in hours. Hmm, as with Niven's _Ringworld_, a beanstalk may need active countermeasures to keep it from yanking itself out of orbit. Would the much mentioned concept of using the earth's electromagnetic fields for marching satellites around also work for a beanstalk, so that lengths of powered cable up and down it's length could be tuned to counter and thus damp the resonances? xanthian. Fun off-topic factoid: about 32 years ago, I was driving a research ship to support el Nino research by putting down and picking up deep ocean buoys in 4000 meters of water. A "many metric tons"-stressed Kevlar(tm) cable that long is a very low period musical instrument, in the passing tidal current flows my passengers were studying. The deep infrasound it created turned out to attract huge schools of huge tuna, visible through the clear water 100 meters down as if they were fleets of trucks doing synchronized maneuvers, which infrasound-tropic fish the crew then gleefully harvested with hook and line, to barbecue on deck for lunch. Think of that next time you hear some stranger humming, or a cellist getting in tune. -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
#23
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Beanstalks...
delt0r wrote: Iain McClatchie wrote: Someone must have looked at having the base of the elevator up above the atmosphere by now. You could have the base moving at 1000 m/s relative to the equator, at a few hundred km altitude, which would make a pretty reasonable target for a 767 with rocket assist. Yes, the are often called LEO elevators IIRC, but 767 with rocket assist?. Unfortunatly they still require quite good materials anyway to get a decently low speed (orbit velocity does not go down that quikly with height). You could run a GEO (GEO as in period and inclination) space elevator were the end still sits 1000km up or a little more. This could a simpler way to avoid debris, while the dV is still very modest for a rocket. Zubrin refers to it as a hypersonic skyhook. The important characteristic for a material is "characteristic velocity, U = SQRT(Strength / Density). http://www.islandone.org/LEOBiblio/SPBI1MA.HTM has a table. Kevlar has a U of 2.2km/s, and nanotubes in theory 15km/s according to this. According to Zubrin, kevlar is 1.2 to 1.6. A skyhook with a material with U of 2km/s, and tip velocity relative to Earth of 5km/s would have to mass 11 times its payload. The only thing that is a bit niceer on the specific strength of materials it rotavators. A problem with elevators and skyhooks is the need for an elevator with power source. This means that cargos would have to spend days travelling through the radiation belts. Rotovators get round this problem by flinging cargos through the radiaton belts in a matter of 10s of minutes. They also need no elevator mechanism, and can be lighter than an equivelant skyhook. |
#24
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Beanstalks...
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#25
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Beanstalks...
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#26
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Beanstalks...
Ian Stirling wrote:
A non-tapered beanstalk on earth is not possible with any known material. That's not actually true. Blaise Gassend has shown that a non-tapered beanstalk is possible with nanotube material strength of about 65 GPa (which is the same target strength needed for a conventional beanstalk). A non tapered beanstalk has much less capacity though. But there is a big advantage during construction of a non tapered beanstalk- it's actually possible to create a loop out beyond GEO and back to the ground and spin it using a motor on the ground using untapered fiber. It turns out that construction is faster than the normal construction approach using laser powered climbers. You can exponentially increase the cable thickness from the ground; so basically you would be using carbon nanotube to lift more carbon nanotube, and with efficient/cheap mechanical power supply from the ground. |
#27
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Beanstalks...
on Wed, 15 Mar 2006 19:40:25 -0000, Ian Woollard sez:
` Ian Stirling wrote: ` A non-tapered beanstalk on earth is not possible with any known material. ` That's not actually true. Blaise Gassend has shown that a non-tapered ` beanstalk is possible with nanotube material strength of about 65 GPa ` (which is the same target strength needed for a conventional ` beanstalk). A non tapered beanstalk has much less capacity though. Well, if "known material" is read as "known to be manufacturable to the required length" then AFAIK the statement is true. ` But there is a big advantage during construction of a non tapered ` beanstalk- it's actually possible to create a loop out beyond GEO and ` back to the ground and spin it using a motor on the ground using ` untapered fiber. It turns out that construction is faster than the ` normal construction approach using laser powered climbers. You can ` exponentially increase the cable thickness from the ground; so ` basically you would be using carbon nanotube to lift more carbon ` nanotube, and with efficient/cheap mechanical power supply from the ` ground. I'm trying to visualize what you are describing here. A pair of cable ends at the earth mounted next to each other and rotated about a common centre? Or a cable pulled through a pulley like a hoist? I assume the latter as the former doesn't make any sense to me, though "spin" doesn't quite seem like the right word for that - it would be parallel lines rather than a ring. -- ================================================== ======================== Pete Vincent Disclaimer: all I know I learned from reading Usenet. |
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