Talk:Space elevator/Archive 1
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Removed: NASA and the European Space Agencies should definitely start production of these space elevators if we are ever to exist as a race off of this planet, so that we dont put all of our eggs in one basket. Otherwise, this is great stuff! --MichaelTinkler
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Whups. I got some of the text off of a NASA web page, I guess I didn't edit it carefully enough. :) I'll check it some more for NPOV now.
To answer the next question I'm sure a lot of Wikipedians will now ask, yes, the text is pretty much verbatim from an external source, which is usually a big no-no. I can't find an explicit copyright statement on the pages. But the page in question is part of NASA's "project liftoff", which is a fully tax-funded educational project, and is hosted on nasa.gov, which is tax-funded site, and while NASA makes a bit of noise about being a semi-independent non-government entity, recent court decisions have made it clear that they are an agency of the government with regard to regulations covering agencies of the government (they are subject to FOIA, for example), so it appears that we are safe from copyright problems. --LDC
Please quote a link to the page used as the basis of the article. Paul Beardsell 12:13, 1 May 2004 (UTC)
- Good to hear a second opinion confirming my understanding of the situation. I did a bunch of editing on it as well, it'd be annoying to have it turn out to be illegal after all. :) -BD
How about using fibers made of synthetic spider silk protein? I heard spider silk is stronger than kevlar.
Unfortunately, I'd bet protein-based cables wouldn't hold up very well in the vaccum and hard radiation of space. Not to mention that spiderwebs have a high liquid-water content, necessary for their springyness and flexibility. A pity since it'd be really cool to string spiderwebs into space like that.
Shouldent this article contain some scepticism about space elevators e.g the potential downsides/risks/practical problems of a space elevators. This article reads like a space elevator promotion article at the moment G-Man 16:48 29 Jun 2003 (UTC)
- Added a section on failure modes, is that the sort of thing you were thinking of? Bryan
- The NASA report (http://flightprojects.msfc.nasa.gov/fd02_elev.html) (this link does not work) had a neutral discussion of the pros and cons. Astudent 05:19, 2003 Aug 16 (UTC)
"Artsutanov suggested using a geosynchronous satellite as the base from which to build the tower. By using a counterweight, a cable would be lowered from geosynchronous orbit to the surface of Earth while the counterweight was extended from the satellite away from Earth, keeping the center of mass of the cable motionless relative to Earth. Artsutanov published his idea in the sunday supplement of Komsomolskaya Pravda (Young Communist Pravda) in 1960."
Call me dumb, I can't seem to get the counterweight thing. Where would the opposing force (away from Earth) origin? I know some basic newtonean physics but this sounds weird unless there's some propulsion system (or another planet with sufficient gravity) to pull the (long!) extention towards space -- Rotem Dan
- The opposing force is centrifugal. By extending the counterweight outward from geosynchronous orbit using a cable, the counterweight is forced to keep moving at geosynchronous velocity despite the fact that an object orbiting at that radius would be moving slower. The counterweight is thus moving too fast for its orbit and wants to fly away from Earth, but the cable that hangs downward prevents this. Bryan
- Thanks, I think I got it (I was confused with the centripetal force but now it makes sense; <yeah I'll work on my physics on the next semesters>). This is a very interesting trick! also nice work on the failure points. Cheers -- Rotem Dan
Regarding cutting the space elevator at the anchor:
In Bradley Edwards' space elevator design, the ribbon is balanced so if it is cut at the anchor, it would not move. I found this quote from Newsweek: "What’s to keep the whole thing from flying out into space or crashing down to Earth? The upper half of the elevator gets thrown outward [by Earth’s rotation], and the bottom end is pulled down by gravity. Even if you cut it at the bottom, the ribbon would just float there." Going Up? - Newsweek Astudent
- That looks drastically oversimplified to me. If you have a space elevator that is exactly balanced, so that the weight of its lower portion is pulling downward with exactly the same force that the counterweight is pulling upward with, then as soon as you put any additional weight at all on the bottom end there will be more force downward than there is upward. The elevator will be pulled downward as a result. This would result in a catastrophic failure since moving the counterweight inward reduces the centripetal force, which accelerates the fall of the elevator. Without drastic measures such as cutting a large section of the lower end off to reduce the weight of the lower portion, the entire space elevator will fall down to Earth's surface. I suspect that Edwards is oversimplifying for MSNBC's benefit; he probably just means that if you cut the elevator it won't fall down to the ground. Bryan
- Thanks for your reply. I was wrong earlier about the exactly balanced ribbon. Your explanation is very good. Astudent
- No problem. Orbital dynamics aren't very intuitive even for conventional orbiting objects, let alone ones tied to the ground. :) Bryan
- True, but we were only talking about cutting it. You wouldn't put a cargo going up on a cut cable, as that would cause the whole thing to fall.
- Operationally, you'd need weights that you can move up and down on the out portion of the cable, so that you could lift cargo. You'd probably want some type of linear induction motor thingy, so you could just move weight up and down on that section, depending on whether you were lifting anything from earth's surface at that particular point in time. You're probably always want it slightly imbalanced pulling against the earth's gravity (long-term loss to earth's rotation and other problems not-withstanding), or a very fast response system, so that someone coming up and yanking on the cable doesn't cause it to crash.
- ~ender 2003-11-13 19:32:MST