XPost: sci.space.policy, sci.physics   
   From: alain245@videotron.ca   
      
   On Jun/18/2018 at 2:45 PM, Sergio wrote :   
   > On 6/16/2018 8:54 AM, Alain Fournier wrote:   
   >> On Jun/15/2018 at 11:34 PM, Fred J. McCall wrote :   
   >>> JF Mezei  wrote on Fri, 15 Jun 2018   
   >>> 22:13:01 -0400:   
   >>>   
   >>>> On 2018-06-15 19:21, Alain Fournier wrote:   
   >>>>>   
   >>>>> Yes. But I think I am a little less optimistic than you about it   
   >>>>> becoming practical in the future. If we have fantastic materials in the   
   >>>>> future, maybe an elevator will become more practical,   
   >>>>>   
   >>>>   
   >>>> Apart from lifting geostationary satellites to just below orbit and then   
   >>>> let them use their own thrusters to position to their assigned   
   >>>> slot/longitude, what other use would a space elevator have ?   
   >>>>   
   >>>   
   >>> You go above the GEO point on the cable and get flung on   
   >>> interplanetary trajectories.   
   >>   
   >> Yes!   
   >>   
   >> You would also likely put at least one cable above GEO rotating in a   
   >> plane perpendicular to the main cable. So you can give an extra push for   
   >> interplanetary trajectories and to fine tune in which direction you   
   >> depart for said trajectories.   
   >>   
   >> You can also jump off at an altitude of about 15000 km (that figure is   
   >> from the top of my head, it might be more or might be less). From there   
   >> after a few passes of aero-braking you can reach LEO with very small   
   >> thrusters.   
   >>   
   >> For polar orbits, you use the rotating cable above GEO mentioned above.   
   >> But instead of using it for extra push you get off while it is   
   >> subtracting some speed but not quite in the direction of rotation of the   
   >> cable. So you subtract some speed in the direction of rotation of the   
   >> cable and give some speed in the north-south axis. You then use   
   >> aero-braking again to lower apogee, and a small thruster to raise   
   >> perigee. Note however that using the elevator to reach polar orbits in   
   >> this way isn't obvious. You would want a long and fast rotating cable   
   >> and you would want it far above GEO, it might not be practical to do so.   
   >>   
   >> Building an elevator, with current technologies, is outrageously   
   >> expensive. But if you have one, it can be very useful.   
   >>   
   >   
   > we don't have one, and never will.  It is a joke among Engineers.   
   >   
   > What would is the monthly insurance payment for it?  if it fell over ?   
      
   You put the cable on an east coast. You also put a system to cut the   
   cable at something like 10000 km high. If the cable breaks below that   
   10000 km the upper part doesn't fall it goes up, the bottom part falls   
   in the ocean, where it isn't likely to cause damage. If the cable breaks   
   higher than 10000 km, you cut it at 10000 km, the bottom 10000 km falls   
   once again in the ocean. The two other parts won't fall to the ground,   
   the lower part will probably be in an elliptical orbit, the higher part   
   might be in an escape trajectory. So the damage from a cable breaking   
   doesn't have to be high. It might be a little difficult to explain that   
   to an insurance company, but if you can pay for the cable, you should be   
   able to cover the damages.   
      
   > how many miles would the top swing back and forth ?   
      
   Why do you care?   
      
   > How much sideways force is pushed on it by a 20 mph wind ?   
      
   Why do you care?   
      
   > how much does one guy wire weigh ? (assume 20,000 km elevator height)   
      
   Why would you put a guy wire? Don't assume 20,000 km elevator height,   
   assume 70,000 km, you want the top of the cable to pull up the bottom of   
   the cable, so you have to go beyond GEO height.   
      
   > how much does one copper cable weigh if moving 200 amps ?   
      
   Don't put a copper cable. Send energy to the climber using some kind of   
   beamed energy. (A laser on the ground, maybe another one in   
   geosynchronous orbit, and photocells on the climber to convert back to   
   electricity. Or something of that kind.)   
      
   > What voltage is needed at the ground to feed the copper wires ?  assume   
   > 500 V AC needed at the top.   
   >   
   > How much does the tower weigh counting only the copper wires, main   
   > cable, and guy wires ?   
      
   The copper wires and guy wires are nonexistent and therefore weigh   
   nothing. As for the main cable, it weighs way too much. That is why I   
   said in the message to which you are replying that "Building an   
   elevator, with current technologies, is outrageously expensive." I don't   
   think we will ever have one.   
      
      
   Alain Fournier   
      
   --- SoupGate-Win32 v1.05   
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