In reply to Jed Rothwell's message of Sat, 17 Jan 2015 17:47:23 -0500: Hi, [snip] ><[email protected]> wrote: > > >> Actually what I had in mind was more something with just jet engines iso >> rocket >> engines, not something carried into the air on the back of a jet. >> > >What is the typo "iso" supposed to be? Instead of? Inside of? > >Anyway, you need both. The jet engines no longer work at high altitudes. >The piggyback method is used so that you can leave the jet engines behind >when they become useless for lack of air. > > > >> Space elevators should never be built. Far too dangerous (read "Red >> Mars"?) and >> unstable (wind problems). >> > >I read "Red Mars." That is an incorrect portrayal of the way a space >elevator would work, at least in the first implementation for the next >century or so. If you cut one at that ground it would simply drift up and >away. If you cut one at the space station terminal, or halfway down, it >would fall to earth with approximately as much force as a falling >newspaper, according to Edwards and Westling ("The Space Elevator.") The >cable is about as thick as a piece of paper and about a 20 cm wide at the >widest point, as I recall. It is 200 layers each 1 micron thick (0.2 mm). >This would support 20 tons: > >http://www.thespacereview.com/article/47/2
The weakness in this as near as I can tell is that the strength of the ribbon is only the same as that of individual nano-tubes if they can be attached to one another effectively and with the strength of the bond equal to the strength of individual tubes. Either that, or individual tubes need to be 35000 km long. Furthermore, I get the impression from the article that the given strength of 300 GPa, is only calculated, not necessarily measured. However if the problem(s) can be overcome, then I take back my claim that space-elevators would never be built. > >Of course if there were a 20-ton climber on the cable below where you cut >the cable, the climber would come crashing back to earth. This is actually the most likely scenario, because the tension on the cable increases with altitude, so it is maximal at the top, and hence that is also where it is most likely to break. However a single climber would most likely crash in the ocean, and is unlikely to do any significant damage. > >Wind is not a problem. The thing can stand up to far greater forces than >that. The total exposed surface in the atmosphere is smaller than the face >of a large building. I was thinking of resonance (think violin string, loaded with a climber). If this turns out to be a real problem, then the whole project might end up being very short lived. > >- Jed Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
