XPost: sci.space.policy, sci.physics   
   From: alain245@videotron.ca   
      
   On Jun/19/2018 at 10:12 PM, JF Mezei wrote :   
   > On 2018-06-19 19:45, Alain Fournier wrote:   
   >   
   >   
   >> at first in the rotating reference frame of the ground it is just going   
   >> down. When you tighten up something that is rotating, like a figure   
   >> skater pulling in their arms, that increases the rotation rate. So the   
   >> cable will be going eastward faster than Earth.   
   >   
   > Would such a system be planned with enough "counterweight" above   
   > geostationary orbit to pull the cable up enough such that its weight at   
   > altitude 0 would be 0 ?   
      
   A little more counterweight than that. You want the cable to be taut.   
      
   > Does this mean tensile stress would max out at geostationary altitude   
   > where a force equal to the total weight of the cable below it would be felt?   
      
   The tensile stress has to max out at geostationary altitude. Everything   
   higher pulls up, everything lower pulls down. The stress at   
   geostationary altitude is a little more than the "weight" of the cable   
   below because you want the cable to be taut. That is if you use a   
   definition of "weight" that takes into account the centrifugal force,   
   that is mass multiplied by local gravitational force minus r   
   (pi/953882)^2, where r is the distance to the centre of Earth, the   
   pi/953882 part is Earth's rotation (sidereal) rate in radian/s. If you   
   compute the "weight" above geostationary altitude (it will be negative,   
   the centrifugal force being stronger than gravity) you will get the   
   maximal tensile stress (this time you don't have to add a little because   
   you want the cable to be taut, the small difference between the forces   
   above and below and above geostationary altitude is what keeps the cable   
   taut).   
      
   > In just a case, would the most likely break point be at geostationalry   
   > orbit, allowing nearly 36,000km of cable to fall down?   
      
   No. The cable is tapered, so it is stronger at geostationary altitude.   
   The most likely reason for the cable to break is if it is hit by   
   something. The cable being very big at geostationary altitude (and most   
   likely multi-stranded) it is probably more likely to survive a hit there.   
      
   > Considering the top most portion of the falling cable was going at   
   > 9369km/h and that it would further accelerate as it drops altitude,   
   > woudln't there a great big force to pull the whole cable eastward,   
   > causing portions already on ground to drag?   
   >   
   > I assume that as more and more cable drags on ground, the drag force   
   > would eventually exceed cable strength and cable would snap, allowing   
   > the still" flyinG" cab;le to move forward some and stary layiong cable   
   > on ground and drag it until that force again exceed the cable strength   
   > (lather, rinse repeat) ?   
   >   
   >   
   > Would the portions of cable at near geostationary orbit accelerate   
   > enough as it falls that upon reaching entry interface, would burn up?   
      
   That depends on the physical properties of the cable. We don't know what   
   are the physical properties of a cable made of an unknown material. But,   
   as I said in another post, I think they would put some kind of mechanism   
   to cut the cable in case of an emergency. If you do so only a relatively   
   small portion of the cable would fall to the ground.   
      
   If you don't cut the cable and most of it comes down, as I said the   
   outcome depends on the physical properties of the cable, but burning up   
   in the atmosphere seems to me as a reasonable outcome, especially if it   
   is multi-stranded. As for dragging and snapping, maybe it would snap at   
   or near the attach point to the anchor (where the cable is thinnest) but   
   after that, I wouldn't think so. It must be a very strong cable. But   
   once again this is just speculation on my part, I don't know how would   
   behave a cable of unknown material.   
      
      
   Alain Fournier   
      
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