--- Erik Reuter <[EMAIL PROTECTED]> wrote: <snip> > I derived the applicable formulas for a > space elevator and > posted them to Brin-L several years ago. I've > appended that to my post > here if you want to try some numbers. I also > included another article > that talks about space elevators and gives a few > useful numbers. <snipped rest>
Thanks for the re-post -- I'm afraid the math was over my head, but the other articles were interesting. Having read somewhere that "spider silk has greater tensile strength than steel," I looked up a few articles. It seems that the properties of spider silk that allow it to be both strong and resilient/elastic, while still not understood, involve sheets of 'stiff' alanine chains coupled with more flexible/elastic protein sequences, twined together in different ways for different types/uses of the silk. It is comparable to Kevlar (one article said 'tougher'), but much lighter. This article, about stress-strain curves and Young's modulus of elasticity, gave some numbers I hope someone else can play with (hint hint! :} ): http://www.tiem.utk.edu/~mbeals/spider.html "...From the stress-strain graph we can see that the spiral's mean extensibility, which is the maximum strain (or stretch) before breaking, was 476%, as compared to the radii's mean extensibility of 39.4% (data from K�hler & Vollrath not shown). The tensile strength of the capture spiral is 1,338 MPa, while the tensile strength of the radial thread is 1,154 MPa. For comparison, the tensile strength of "mild" steel is 400 MPa (in Vogel 1988, p. 185). The capture spiral must absorb most of the kinetic energy from an insect's initial impact, while the radial threads serve primarily as scaffolding for the spiral..." [radial silk is closer to dragline silk in properties - DH] http://www.discover.com/sept_01/featbiology.html "...More research has been done on the dragline silk of Nephila than on any other kind. But it is a long way from being understood. A single thread of that silk is perhaps three to five micrometers across. When Vollrath started looking into it, people thought dragline silk was a relatively simple composite material, like fiberglass, consisting of stiff sheets of crystallized protein floating in an elastic rubbery matrix. But that, Vollrath has found, is not the structure of the whole thread; it's the structure of a single filament inside the thread� and there may be thousands of such filaments, each only a few nanometers across, too small to be seen with a typical microscope, and perhaps bundled in some way that has yet to be discerned. "That's what gives it this incredible tensile strength, this whole microstructure," Vollrath says. "If you're jumping off a bridge, would you prefer I gave you a single rubber band or a thousand rubber bands with the same total diameter? It's intuitive� if you have a thousand, a few can snap and there are still enough to hold you." The spider's dragline is made even more snap-resistant, Vollrath thinks, by long, fluid-filled channels that are interspersed among the tightly packed filaments. Those channels may help distribute the tensile forces and so stop a nascent crack from ripping right across the thread..." Dragline silk is being studied by the Army: http://www.sciencedaily.com/releases/2002/06/020618072100.htm "...And why is the U.S. Army interested in this material? "The major interest is to use it as material for bulletproof vests, armor and tethers; there are many possibilities," said first author Emin Oroudjev, a researcher at UC Santa Barbara. "At UC Santa Barbara, the focus is on the basic research of learning how the protein folds and how it is organized in the silk fiber. Using atomic force microscopy and a molecular puller, the researchers are getting clues from imaging and pulling the protein. These observations help the researchers to model what is happening in the silk gland when silk proteins are assembling into spider dragline silk fibers..." Quite a few links are defunct, so I'm not sure the GM goats that were supposed to mass-produce spider silk in their milk (I am NOT making this up!) are still being experimented with...medical applications would exist too: http://news.nationalgeographic.com/news/2002/01/0117_020117TVspidermammals.html Nexia (the goat-folk) was still around in Jan 2002: http://www.eurekalert.org/pub_releases/2002-01/nbi-nau011102.php So, could the structure and properties of dragline silk be helpful in the design of carbon nanotubules for a space elevator? (Of course, I'm guessing you wouldn't want it to be that elastic, but the structure is intriguing. Here are some graphics:) http://www.chm.bris.ac.uk/motm/spider/page3h.htm http://www.imb-jena.de/www_elmi/molcyto_spid.html http://www.amonline.net.au/spiders/toolkit/silk/structure.htm The latter site is part of an entire spider info fest (fun!). Debbi Charlotte's Web Maru :) __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
