On this issue of icing, while the situation would vary depending on what it is constructed of, the structure will be able to radiate heat away far more effectively than the air can radiate. Thus the building surface will cool with respect to the air. The air temperature at upper troposphere/lower stratosphere levels is 40 C or below, being maintained at this level by heat from convection that maintains the lapse rate through the tropsophere. I would think the building surface would cool to lower than that and so the skin temperature would be well below the temperature at which one would expect water vapor to be freezing out. This doesn¹t happen on an airplane because its interior is kept warm and this must make the plane¹s exterior pretty warm compared to what could happen to a building that just sits there. So, given the different IR emmissivities of the building surface and the air mass, I¹d be quite careful of the analysis. True that there is not much water vapor in air near highest altitudes, but the analysis would need to be done at each level, etc.
Mike On 8/20/15, 2:58 PM, "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-travel > -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-trave >> l-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.
