From: jorj.strumolo@chowda.com (Jorj Strumolo) Newsgroups: rec.arts.sf.science Subject: Re: beanstalk cable Date: Sun, 29 Dec 1996 11:38:00 GMT Message-ID: <9612291800165611@chowda.com> Organization: Chowdanet BBS - 401-331-2604 Distribution: world References: <5a296e$4i8@nntp.seflin.lib.fl.us> Lines: 40 > p008536b@pbfreenet.seflin.lib.fl.us (Greg Muir) writes: GM> What would be the best material for a beanstalk's cable? [etc.] From an old article by Charles Sheffield, "How to Build a Beanstalk". It gives this table on materials and their support lengths: Tensile Strength Density Support length Material (kg/sq.cm.) (g/cc) (kilometers) ---------------------------------------------------------------------- carbon steel 7,000 7.8 9 manganese steel 16,000 7.8 21 drawn tungsten 35,000 19.3 18 drawn steel wire 42,000 7.8 54 iron whisker 126,000 7.8 161 silicon whisker (SiC) 210,000 3.2 660 graphite whisker 210,000 2.0 1,050 *fictionite 2,000,000 2.0 10,000 ---------------------------------------------------------------------- The support lengths assume no tapering. He figures tapering would be used, but a safety margin is also required, so they cancel out. The necessary support length for a Terran beanstalk is about 4,940 km. He mentions that graphite whisker is already strong enough for a Martian beanstalk, where the support length is 975 km. Sheffield believes material technology will advance, and Terran beanstalks will one day be feasible. He even says he wouldn't be surprised if there were a working prototype by 2050 (the article was written in 1979). GM> What would be the dimensions of a DM cable 28,000 miles > long capable of supporting its own weight plus cargo? That's a function of tensile strength and density. Unless you estimate those variables, you can't say. The support lengths given in the chart are for just the cable, with no cargo. We don't have any material yet that can manage it. -+- Jorj.Strumolo@chowda.com * Fido 1:323/140 * jorj@wsii.com