XPost: sci.space.policy, sci.physics, sci.astro   
   From: alain245@videotron.ca   
      
   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.   
      
      
   Alain Fournier   
      
   --- SoupGate-Win32 v1.05   
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