From: vince@offshore.ai (Vincent Cate) Newsgroups: sci.physics,sci.astro,sci.space.policy,sci.materials,sci.energy Subject: Re: beanstalks (was Re: Metallic hydrogen ...) References: <40C0B48F.F477E3F7@mchsi.com> <9186edb5.0406070549.44aacf7e@posting.google.com> NNTP-Posting-Host: 207.42.133.252 Message-ID: <9186edb5.0406080608.4793394c@posting.google.com> henry@spsystems.net (Henry Spencer) wrote in message news:... > Ten years ago, it was all very hypothetical, with some laboratory-specimen > fibers not *too* far below the necessary strength, and little realistic > hope of practical materials using them. Now, fairly suddenly, the fibers > have *twice* the required strength, making them in quantity is looking > feasible, and the one major remaining unknown is making a practical > material with them. About 48 years ago they discovered "graphite whiskers" with a tensile strength of 20 Gpa. These are like a layer of graphite rolled up like a scroll. Carbon nanotubes are like a layer of graphite rolled up into a tube and connected to itself. The graphite whiskers leave an edge for glues to bond to. Still 48 years later we don't know how to glue graphite whiskers into a rope with near the strength of the graphite whiskers. In 1981 Moravec and Forward talked about graphite whiskers said: "Graphite fiber technology is developing so rapidly that a rotating space cable will soon be feasible. Shortly after that, we may be able to make cables strong enough to weave a stationary skyhook." Carbon-nanotubes do not have an open edge to bond to like graphite whiskers. So they are more slippery than graphite whiskers. Making fibers twice as strong is not getting us any closer to solving the really hard problem of how to glue them together into a rope. In another 48 years we might have a glue, but we might not. -- Vince History of Graphite Whiskers: http://pubs.acs.org/cen/NCW/8142acsn.html Moravec and Forward http://www.frc.ri.cmu.edu/~hpm/project.archive/general.articles/1981/high.wire/high.wire.html Graphite Whiskers / Nanotubes: http://members.tripod.com/marosso/nanotube.pdf ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vincent Cate Space Tether Enthusiast vince@offshore.ai http://spacetethers.com/ Anguilla, East Caribbean http://offshore.ai/vince ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You have to take life as it happens, but you should try to make it happen the way you want to take it. - German Proverb