If the idea is to launch from a higher altitude and use inflatables for a building as part of the process, why not just build a blimp or dirigible that would lift the vehicle to altitude and then let it fly from the elevated position of the blimp? Why build a permanent structure for this? With blimp or dirigible, one could launch from nearly anywhere on Earth so get a good range of orbits, etc. Yes, I guess one needs to have a way to get up to a bit of speed for stability, but I don¹t see the value of a structure given all the complications.
Mike On 8/20/15, 3:40 PM, "Andrew Lockley" <[email protected]> wrote: > He's partially right about the fuel savings. In fact, he fails to discuss that > almost all of the drag losses are incurred in early stage flight, so there's a > bonus for him. What he's ignoring is that you can't approximate a launch from > a standing start at 20km with a vehicle that's been accelerating at 13g for > 20km. Speed matters! > > The foundations are nothing really to do with resisting torque, as it doesn't > only happen at the end. If it's a straight tower subjected to wind shear, the > bending moment in the bottom km of the tower is going to be insane, and it > doesn't have to buckle at the footings - anywhere will do. This is a feat not > dissimilar to balancing a hair on its end. All the stiff footings you'd care > to build won't get rid of that buckling risk, and I'd be very surprised if it > the tower structure came anywhere near to resisting it. Far easier to use > tethers (just like a TV mast), but you'd struggle to mount these at the top, > due to the free breaking length of the cables. Even mounting them half way up > likely won't solve the problem, as you'd still have a 10km tower wobbling away > like Jell-O on top. > > Active damping is great at removing vibrational distortion. But all the active > damping in the world won't solve the problem of a steady bending load. I think > the wind will huff and puff and blow the tower down. > > A > > On 20 Aug 2015 20:18, "Julia Calderone" <[email protected]> wrote: >> Hi all, >> >> Brendan Quine, the inventor of the space tower, has followed up with some >> responses to a few of your thoughts (his responses are bolded below). I have >> included his statements in an updated version of the story: >> http://www.techinsider.io/thoth-12-mile-space-tower-elevator-astronauts-trave >> l-major-flaws-2015-8 >> >> If anyone has any thoughts or responses to his comments, please feel free to >> shoot me a response here. >> >> Thanks again. >> >> Best, >> Julia >> >>> *External forces* would be an issue: >>> >>> ³This 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 [twisting force] at the base will be enormous. It's >>> just not clear how it will actually stay up.² >> >> We agree that the tower will require very substantial foundation however this >> requirement is similar to that of existing massive steel and concrete >> construction structures. The patent describes a harmonic control strategy and >> actively guided structure concept where the attitude of the building is >> constantly monitored and its vibration modes controlled (see FIG. 4 a >> schematic diagram showing active stabilization control of the elevator core >> structure, US9085897). >> >>> ³Thunderstorms and icing would be a big problem. Construct[ing] a tower to >>> take wind gusts and turbulence arising from deep tropical convection looks >>> very problematic to me.² >>> >>> Ice build-up hampers proper functioning of planes and drones at such high >>> altitudes. Unlike aircraft that can fly, a giant tower wouldn¹t be able to >>> navigate around those regions. >> >> The structure may require de-icing in the same way that aircraft wings are >> sprayed with antifreeze during operation in winter. This function can be >> facilitated within the elevator structure however it is likely that icing >> will be occasional as event will be isolated and the solar radiation >> environment will rapidly heat and melt ice buildup during the day. It is >> likely that the elevators would be equipped with a de-icing capability also >> cleaning the outer surface as the pass up and down the core. There is some >> significant research developments in materials finishes that prevent ice >> build-up that could also be deployed in lower structural sections. It is >> unlikely that the mass of any ice buildup would be significant by comparison >> to the overall mass of the structure. >> >> The structure is designed to withstand a Category 5 hurricane with wind speed >> of 156 mph with significant safety margin and so the sheer and turbulent >> forces of a thunder storm are within this design envelope. >> >> >>> Problem with *buckling* under it's own weight: >>> >>> "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. When one part of the internal cell starts to buckle, >>> the volume of the gas inside does not change, which means that it would not >>> resist the collapsing action" >> >> The problem of structural wrinkling (the onset to buckling) has been >> addressed by previous research (see Experimental investigation of inflatable >> cylindrical cantilevered beams ZH Zhu, RK Seth, BM Quine, S Okubo, K Fukui, Q >> Yang, T Ochi, JP Journal of Solids and Structures 2 (2), 95-110, 2008). In >> fact there is a volume change during the buckling event. Also the commentator >> may be assuming that the core is comprised of a single gass cell the diameter >> of the structure however the structure is comprise of many cells arrange in a >> torus and there is a significant volume change between the sides of the >> structure during buckling. The research paper lays out experimentally derived >> guidelines for pneumatic structures to avoid the onset of wrinkling which we >> have adopted in our design. >> >>> *Material and cost* limitations: >>> >>> The most feasible type of tower that could reach such heights is a >>> cylindrical tower made out of plastics reinforced with carbon fibers, >>> called Carbon Fibre Reinforced Plastic, or CFRP, which would cost about >>> $500 billion and need 250 million tons of the carbon material. Of course >>> new materials may become available, but nothing much is on the horizon that >>> is substantially better than CFRP." >> >> Our patent proposes the use of polyethylene reinforced with Kelvar 49 (both >> widely available in industrial quantity). We agree that there would be a need >> for a significant increase in industrial manufacturing capability of these >> materials and consequently we are proposing the a 1.5 km demonstrator be >> constructed first in order to grow production capacity before embarking on >> the 20 km tower. >> >>> Not much fuel savings: >>> >>> "Less than 1% of the energy required for orbit is saved by launching from a >>> height of 20km. There doesn't seem to be much benefit." >> >> As we describe in A free-standing space elevator structure: a practical >> alternative to the space tether BM Quine, RK Seth, ZH Zhu Acta Astronautica >> 65 (3), 365-375, 2009, rockets consume approximately 30% of their fuel during >> the initial ascent phase to 20 km. The reduction in fuel usage comes with a >> corresponding benefit in the number of stages needed to reach orbit (only one >> stage is required for a launch at 20 km versus 3 or 4 for conventional >> launch). The 1% energy estimate claim does not take into account the staging >> aspect of rocketry (the rocket is extremely heavy with stages and fuel at >> launch and very light by orbit). Rocketry is extremely energy inefficient >> with only about 3% of the chemical energy going into raising to payload to >> orbit. Thus massive amounts of fuel and hardware must be raised initially to >> have enough left to propel the final injection stage. Electrical elevators >> are %50-%60 efficient leading to a significant fuel saving advantage that >> enables single stage to orbit space planes to fly from the top of the tower. >> These planes can also be completely reusable like a passenger jet as opposed >> to being single use like current rockets. This reaps the a very significant >> hardware cost advantage which will dramatically reduce the cost of space >> access. >> >> On Thu, Aug 20, 2015 at 12:11 PM, Julia Calderone <[email protected]> >> wrote: >>> Hi all, >>> >>> Thanks to everyone for your extremely helpful responses. I have included >>> quite a few of them into my article. >>> >>> http://www.techinsider.io/thoth-12-mile-space-tower-elevator-astronauts-trav >>> el-major-flaws-2015-8 >>> >>> Take a gander, and please let me know if you see any glaring errors or >>> issues! Hope you enjoy it. >>> >>> Thanks again for everyone's help. >>> >>> My best, >>> Julia Calderone >>> >>> On Wed, Aug 19, 2015 at 12:30 PM, David Appell <[email protected]> >>> wrote: >>>> >>>> >>>> Greg Rau wrote: >>>> "Anyway, couple of thoughts. If the tether is made of carbon, that's more >>>> than a few dollars worth of carbon sequestration..." >>>> >>>> Except the mass of a space elevator is only ~10^5 kg. >>>> >>>> David >>>> >>>> -- 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.
