08-15-2009, 10:10 PM | #1 |
Join Date: May 2005
Location: Oz
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Orbital elevators and long, long days
My algorithm for determining what planets in my SF setting ought to have tower facilities (a.k.a. orbital elevators, a.k.a. beanstalks) takes into account economic volume and tech level, but not the cost of building the elevator. Now that I am using (modified) GURPS Space to generate more realistic star systems I am getting quite a lot with much, much longer days. And that means longer, more massive, more expensive elevators.
So what's the story? In the case of a planet that is tide-locked to one of its moons the geostationary orbit is at the moon's altitude, which means that the options are to build an elevator to the moon (allowing somehow for variations in its length and orientation if the moon's orbit is at all eccentric) or to build an elevator to L1, L3, L4, or L5. (In the case of a tide-locked habitable moon L1, L2, L4, and L5 are available.) In the case of a planet the solar L1, L2, L4, and L5 points are the only possible places for the centre of mass of an orbital elevator. Intuition suggests to me that elevators to moons or to the Lagrange points, and especially to solar Lagrange points would be prohibitively expensive, and possibly impractical, perhaps even impossible at TL10. But intuition is notoriously unreliable. Has anyone seen studies?
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Decay is inherent in all composite things. Nod head. Get treat. |
08-16-2009, 02:58 AM | #2 |
Join Date: Jun 2005
Location: Here on the perimeter, there are no stars
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Re: Orbital elevators and long, long days
My understanding is that under current science and on Earth, a beanstalk would have to be made of unobtanium. Specifically, it needs to be both stronger and lighter than carbon nanotubes, even disregarding the current production problems with attempts to grow nanotubes to any reasonable size. Apparently the distance is such that the weight of the cable alone is prohibitive.
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08-16-2009, 03:30 AM | #3 | |
Join Date: May 2008
Location: CA
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Re: Orbital elevators and long, long days
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08-16-2009, 06:51 AM | #4 |
Join Date: Aug 2004
Location: Austin, TX
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Re: Orbital elevators and long, long days
Pinwheels can be built in highly elliptical orbits, but otherwise have similar engineering issues and solutions to beanstalks. Maybe they would be the preferred lift solution on your tide locked planets?
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08-16-2009, 07:38 AM | #5 |
Join Date: May 2005
Location: Oz
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Re: Orbital elevators and long, long days
Are those the things I call "rotovators", or something else? Rotovators are a very likely alternative to elevators.
__________________
Decay is inherent in all composite things. Nod head. Get treat. |
08-16-2009, 08:03 AM | #6 | |
Join Date: Aug 2007
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Re: Orbital elevators and long, long days
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You may also be exaggerating the habitability of planets with extremely long days. It may depend on what you're calling "much, much longer" but there probably are day lengths that will result in too much temperature swing to be viable. I don't remember my exact criteria, but back when I was trying to determine how common Earth-like planets would be according to the assumptions of Gurps Space I simply kicked planets with excessive day length out of the results. Too long and you might not even get a really Earth-like atmosphere. Plants have to subsist on stored energy during the night cycle and algae-analogies are very likely to come before macroflora. A cycle that had many, many hours of light followed by many, many hours of darkness might be too much of a stretch for early microflora.
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Fred Brackin |
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08-16-2009, 08:28 AM | #7 | |
Join Date: May 2005
Location: Oz
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Re: Orbital elevators and long, long days
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I have been doing a write-up of a planet that the starsystem generation sequence gave me as Affinity 8. Its days are 317.5 hours long. Which has no effect on the Habitability calculation--and neither does the temperature range induced by the absurd orbital eccentricity, nor the obliquity of 37°.
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Decay is inherent in all composite things. Nod head. Get treat. |
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08-16-2009, 08:56 AM | #8 | |
Join Date: Jun 2005
Location: Lawrence, KS
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Re: Orbital elevators and long, long days
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I think it's probably safe to say that the temperature extremes for a 3:2 resonance would not be greater than those for a tide-locked world. See p. 125 of Space for all this. Bill Stoddard |
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08-16-2009, 10:17 AM | #9 | |
Join Date: Dec 2007
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Re: Orbital elevators and long, long days
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08-16-2009, 11:09 AM | #10 | |
Join Date: Aug 2007
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Re: Orbital elevators and long, long days
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You've got to have photosynthesis or there will be no atmospheric oxygen. That's what I was getting at.
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Fred Brackin |
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Tags |
beanstalk, non-rocket spacelaunch, orbital elevator, orbital facilities, space, space elevator, ultra-tech |
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