In contrast to towers, what about this?: "A space elevator is a proposed type of space transportation system.[1] Its main component is a ribbon-like cable (also called a tether) anchored to the surface and extending into space. It is designed to permit vehicle transport along the cable from a planetary surface, such as the Earth's, directly into space or orbit, without the use of large rockets. An Earth-based space elevator would consist of a cable with one end attached to the surface near the equator and the other end in space beyond geostationary orbit (35,800 km altitude). The competing forces of gravity, which is stronger at the lower end, and the outward/upward centrifugal force, which is stronger at the upper end, would result in the cable being held up, under tension, and stationary over a single position on Earth. Once the tether is deployed, climbers would repeatedly climb the tether to space by mechanical means, releasing their cargo to orbit. Climbers would also descend the tether to return cargo to the surface from orbit.[2] " https://en.wikipedia.org/wiki/Space_elevator
Greg -------------------------------------------- On Tue, 8/18/15, Chris Burgoyne <[email protected]> wrote: Subject: Re: [geo] space elevator To: [email protected] Cc: "Peter Davidson" <[email protected]>, "Hugh Hunt" <[email protected]> Date: Tuesday, August 18, 2015, 9:57 AM We considered towers quite seriously as part of the SPICE project for delivering particles to the stratosphere. See the full paper Davidson P, Burgoyne C.J., Hunt H.E.M. and Causier M.L.T.C., Lifting options for Stratospheric Aerosol Geoengineering: Advantages of Tethered Balloon System. Proc Roy. Soc A. 370/1974 4263-4300, Sep 2012. doi:10.1098/rsta.2011.0639. http://www-civ.eng.cam.ac.uk/cjb/papers/p77.pdf and a shorter version Burgoyne C.J., Hunt H.E.M., Davidson P. and Causier M.L.T, Structures for Stratospheric Particle Injection, Paper P-0047 IASS-IABSE Symposium “Taller, Longer, Lighter”, London Sept 2011. http://www-civ.eng.cam.ac.uk/cjb/papers/cp94.pdf The issue for tall towers is not strength but stiffness. They would buckle under their own weight unless made very wide. We showed in the second paper (equation 2) that the critical buckling length is governed by a material property (the ratio (E/rho.g) where E is the Young's Modulus and rho is the density; g is gravity) and a geometric property (the ratio of the radius of gyration to the length). These are multiplied by a number that depends on how the tower tapers to the top but that need not bother us here. The important point is that you don't get much choice about these ratios. About the highest material ratio is given by Carbon Fibre Reinforced Plastic (CFRP) which has a similar stiffness to steel but a quarter of the density. Almost all other engineering materials fall within these two extremes. What you really want to do is to maximise Youngs Modulus and minimise density. But it should be noted that even the most exotic materials only have a stiffness that is about twice that of CFRP (because they are limited by the STIFFNESS (not strength) of the C-C bond), and very few engineering materials have a much lower density. In addition, the geometric ratio can't change much. The radius of gyration of a solid circle of radius R is R/2. For a thin circular tube it is R/SQRT(2) (and interestingly independent of the thickness). No matter how you play with the internal structure of the tube you are going to be somewhere within this range. We based our SPICE work on the assumption that the best you could do was to use CFRP as a thin tube, which is about as good as you can get with any material we currently know about. What about the inflated tube? The problem with this, assuming you could design one that you could actually build, is that it would be subject to the same problems of self-weight buckling. The internal pressure is a self-equilibrating system; when the tube starts to buckle globally the internal volume does not change, so no work is done on the internal air and thus it does not help to resist the buckling action. The inflation might help to resist local buckling (dimpling of the external surface) but that isn't the issue. For the SPICE project we decided that the tower should be ruled out on the basis of this simple analysis alone, so we did not go on to consider the effects of lateral wind loads (or the Coriolis forces you would generate on a moving lift). These would have the effect of moving the tower sideways so it would be as though you had built a non-straight tower. These initial imperfections would dramatically reduce the tower's capacity to resist buckling which would make the situation even worse. It is possible to make quite impressive blow up towers at laboratory scale, because at this scale it is local buckling that dominates the behaviour, but not at the scale needed for geoengineering (or to get into space) where global behaviour matters. As most readers probably know, we ended up proposing a balloon supporting a pipe up which "stuff" (undefined) could be pumped. We were initially quite surprised how expensive the tower was and how cheap the balloon. The difference is that the balloon system is completely in tension (which lightweight materials like) rather than in compression, which they don't. See the concluding page of the second paper. Chris Burgoyne Prof of Structural Engineering University of Cambridge On 18/08/2015 16:14, Andrew Lockley wrote: Traditional space elevators are under tension. It's just a taut wire you go up and down (hence very narrow, and thus resistant to wind shear) . This is a big fat tower, and it's under compression . The graphics don't show any tethers or taper, and the sides are not obviously wind permeable. This means the torque at the base will be enormous. It's just not clear how it will actually stay up. A On 18 Aug 2015 16:04, "Julia Calderone" <[email protected]> wrote: Hi All, I'm a science science journalist at Tech Insider and am writing about the space elevator that Dr. Boucher dropped in here yesterday. I am looking for some expert commentary on the feasibility of this tower. What distinguishes this one from other "space elevators" proposed in the past? How likely is it to work? Are the designs and engineering scientifically sound? If anyone would like to chime on, please drop me a line — I'd greatly appreciate the help. Thank you very much! My best, Julia Calderone On Mon, Aug 17, 2015 at 7:20 PM, Alan Robock <[email protected]> wrote: Dear Olivier, I discussed this option in: Robock, Alan, Allison B. Marquardt, Ben Kravitz, and Georgiy Stenchikov, 2009: The benefits, risks, and costs of stratospheric geoengineering. Geophys. Res. Lett., 36, L19703, doi:10.1029/2009GL039209. http://climate.envsci.rutgers.edu/pdf/2009GL039209.pdf You'll see the tower in Figs. 1 and 3. See Section 4.4 for discussion of this option. Figure 1. Proposed methods of stratospheric aerosol injection. A mountain top location would require less energy for lofting to stratosphere. Drawing by Brian West. Alan Alan Robock, Distinguished Professor Editor, Reviews of Geophysics Department of Environmental Sciences Phone: +1-848-932-5751 Rutgers University Fax: +1-732-932-8644 14 College Farm Road E-mail: [email protected] New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock http://twitter.com/AlanRobock Watch my 18 min TEDx talk at http://www.youtube.com/watch?v=qsrEk1oZ-54 On 8/17/15 1:26 PM, Olivier Boucher wrote: Hello, this is relevant to SRM by stratospheric particles http://www.independent.co.uk/news/science/a-canadian-company-is-planning-to-build-a-tower-thats-20km-high-and-could-making-flying-to-space-like-taking-a-passenger-jet-10459058.html http://thothx.com/news-2/ although I don't know how realistic and advanced the plans are... Regards, Olivier -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout. -- Julia Calderone Science Writer Cell: (818) 209-0926 Email: [email protected] Web: www.juliacalderone.com Twitter: @juliacalderone -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
