XPost: sci.space.policy, sci.physics   
   From: invalid@invalid.com   
      
   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 ?   
      
   how many miles would the top swing back and forth ?   
      
   How much sideways force is pushed on it by a 20 mph wind ?   
      
   how much does one guy wire weigh ? (assume 20,000 km elevator height)   
      
   how much does one copper cable weigh if moving 200 amps ?   
      
   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 ?   
      
   >   
   > Alain Fournier   
      
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