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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
 Posted - 10/15/2005 : 13:30:57 [Permalink]
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quote:
Originally posted by markie
Essentially the angular momentum of the earth' rotation itself is providing the force of 20 tons on the line. And there's a *lot* of energy tucked away in the angular momentum of the earth, so it's not going to drain away any time soon.
It looks to me as if you were reasoning that having this space-station tethered outside geosynchronus orbit would have a constant drain on Earth's angular momentum. This is not true. The beanstalk and the orbital station will be a part of Earth momentum-wise as long as it's attached.
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markie
Skeptic Friend
Canada
356 Posts |
Posted - 10/15/2005 : 14:31:38 [Permalink]
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quote:
Originally posted by Dr. Mabuse
quote:
Originally posted by markie
Essentially the angular momentum of the earth' rotation itself is providing the force of 20 tons on the line. And there's a *lot* of energy tucked away in the angular momentum of the earth, so it's not going to drain away any time soon.
It looks to me as if you were reasoning that having this space-station tethered outside geosynchronus orbit would have a constant drain on Earth's angular momentum. This is not true. The beanstalk and the orbital station will be a part of Earth momentum-wise as long as it's attached.
It is indeed all part of the earth's momentum system, so i see what you are saying. On the other hand I figure that the 20 tons of force which the line is exerting on the earth, pulling it upwards, has to be coming from *somewhere*. Oh oh, since work is force times distance, and nothing's moving, then no work is being done, and thus, as you say, there is no drain on the earth's momentum energy. I think you're right.
Mark
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 10/15/2005 : 14:56:37 [Permalink]
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Actually, there is the issue of angular momentum.
An ice-skater's arms are "all part of the [skater's] momentum system," but by moving his arms toward or away from his body, he can adjust the speed at which he spins.
The numerous hydroelectric dams in the Northern hemisphere of the planet have actually confined enough water closer to the Earth's axis to make it spin faster than it otherwise would. Not much faster, but the speed difference exists. If I remember correctly, it's on the order of a second per million years that'll be lost when comparing a clock to the position of the Sun in the sky.
Likewise, tethered masses out beyond geosynchronous orbit will indeed slow the Earth's spin. By less than the dams affect us, but the angular momentum of the tiny masses (compared to the Earth itself) must be conserved. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 10/15/2005 : 16:45:17 [Permalink]
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Yes, as the station is locked into its place, the rotational speed of earth will slow down.
Or will it?
If the majority of the stations building material is transported up the tether, then yes it will.
If shuttles carry up the bulk of the station, then it is placed in orbit without affecting the angular momentum of Earth. |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 10/15/2005 : 17:26:24 [Permalink]
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| Things taken up into orbit by Shuttle still have angular momentum. Otherwise, we could increase the speed of the Earth so that the Sun rises every hour simply by taking big masses up to orbit by shuttle, and then having them crawl down the tether. Each time would necessarily increase the angular speed of the Earth, if taking mass up by shuttle didn't decrease it. We'd just need to move one mass around, millions of times: shuttle up (no change), tether down (speed up the spin a little). Or, if we wanted to slow the Earth, we could reverse the cycle (mass goes up the tether, and comes back down via shuttle). |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
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R.Wreck
SFN Regular
USA
1191 Posts |
Posted - 10/15/2005 : 17:26:52 [Permalink]
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quote:
Originally posted by Dr. Mabuse:
Yes, as the station is locked into its place, the rotational speed of earth will slow down.
Or will it?
If the majority of the stations building material is transported up the tether, then yes it will.
If shuttles carry up the bulk of the station, then it is placed in orbit without affecting the angular momentum of Earth.
Either way, the mass of the station is removed from the mass of the Earth, then positioned in orbit with the tether anchoring it. Why would it matter what the mode of transport was? The final configuration is the same, so I think the affects on the Earth's rotation would be the same.
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The foundation of morality is to . . . give up pretending to believe that for which there is no evidence, and repeating unintelligible propositions about things beyond the possibliities of knowledge.
T. H. Huxley
The Cattle Prod of Enlightened Compassion
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 10/16/2005 : 13:25:57 [Permalink]
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quote:
Originally posted by Dave W.
Things taken up into orbit by Shuttle still have angular momentum.
Yeah, but it's the shuttle's thruster that is providing the angular speed (and thus momentum) |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 10/20/2005 : 21:16:29 [Permalink]
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quote:
Originally posted by Dr. Mabuse
Yeah, but it's the shuttle's thruster that is providing the angular speed (and thus momentum)
No, the Shuttle provides more momentum in order to get an object into a 90-minute orbit. Anything which would be hauled to an elevator would necessarily have the exact same 360°/day angular velocity as the surface of the Earth. Since the angular velocity cannot change, the angular momentum must change, and it must do so at the same rate it would if it were lifted off the Earth on the elevator, because otherwise we get ridiculous physics in which we could use the elevator to speed up the Earth (and maintain the speed change after demolishing the elevators). |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 10/21/2005 : 09:50:50 [Permalink]
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| Hey, theres no reason we cant speed up the Earth. It would just be really hard and expensive. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 10/21/2005 : 10:57:08 [Permalink]
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| No, BPS, there's no reason we can't speed up the Earth. We just can't do it through the method described (repeatedly launching a mass up into orbit, and then winching it back down to the surface). A zillion big rockets around the equator would do it. So would damming more rivers up North. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 10/21/2005 : 11:03:23 [Permalink]
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| http://www.msnbc.msn.com/id/9763307/ Space elevator contest 1.0, testing ribbons and climbers. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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ronnywhite
SFN Regular
501 Posts |
Posted - 10/21/2005 : 16:19:17 [Permalink]
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| Seems to me the teather issue's irrelevant as opposed to just having any ole' mass orbiting the Earth RE effect on angular velocity. Accomplish same speeding/slowing by just launching a bunch of massive satellites into orbit (which isn't much.) Gravitational pull holds them to Earth's mass, tangential part of gradient slows Earth (ever so little.) Energy to slow Earth comes from energy expelled by rockets against gravitational pull to take it into orbit (just like ice skater- work to make spin faster done by arm muscles pulling in.) Conservation of energy- putting a satellite 60 or 100 miles up into orbit's like having a bunch of 747's simultaneously ascend to 40K feet or about 8 miles. But no more than exploding the same amount of jet or rocket fuel otherwise (say, as a bomb in a low orbit) effects Earths ephemeris. Either satellites or the teather will also alternately accelerate and deaccelerate the Earth a little during each orbit due to torque from solar radiation hitting the satellite (or cable) surface, how much depending on solar flares etc. You could calculate how much, but I think it would be under a second over the lifetime of the Universe (a guess.) |
Ron White |
| Edited by - ronnywhite on 10/21/2005 16:23:59 |
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pleco
SFN Addict
USA
2998 Posts |
Posted - 10/21/2005 : 16:20:36 [Permalink]
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| I'm sure brainbreak probably has some interesting ideas on this topic. |
by Filthy
The neo-con methane machine will soon be running at full fart. |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 10/21/2005 : 18:24:39 [Permalink]
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quote:
Originally posted by BigPapaSmurf
http://www.msnbc.msn.com/id/9763307/ Space elevator contest 1.0, testing ribbons and climbers.
Wow...
Using sterling engines was an innovative sollution. I'm impressed. |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 10/21/2005 : 18:40:02 [Permalink]
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When building the beanstalk from the ground, how much would it swing in bad weather when it gets tall? Will it eventually bend like a long bamboo?
Wouldn't it be better to manufacture the nanotube in space and lower it down from orbit, down to where ever the ground-station will be?
If a cargo container would be a few tonnes, how will it propel itself up the bean-stalk? I guess some kind of cog-wheel for atmospheric ascention, and once the gravity effect lessens enough, some kind of wheels or mag-lev propulsion... |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
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