From: jrfrank@ibm-pc.borg.retro.com   
      
   Hop David  wrote in   
   news:40B4D203.2060905@tabletoptelephone.com:   
      
   > Henry Spencer wrote:   
   >   
   >> Essentially nothing on rendezvous, or relative motion in general.   
   >> Nothing on multi-body dynamics.  Almost nothing on perturbations.   
   >> The stuff on numerical methods can be described politely as "dated".   
   >> Half a page on geostationary orbit.  No bielliptic or other   
   >> generalized transfers, no gravity assists.   
   >   
   > Hmmm. Perturbations and gravity assists seem to be increasingly   
   > important in scenarios I'm playing with.   
   >   
   > Bielliptic meaning a transfer from one elliptical orbit to another   
   > elliptical orbit? That's something else I hunger to study.   
      
   Not quite. A bielliptic transfer is a transfer between two circular orbits   
   using two elliptical transfer orbits (and three burns), rather than the   
   single elliptical transfer (and two burns) used by the Hohmann transfer.   
   The first burn boosts apogee much higher than either the initial or final   
   orbits. The second burn, at apogee, changes perigee to the final orbit. The   
   third burn, at the new perigee, circularizes at the final orbit.   
      
   Somewhat counterintuitively, the bielliptic transfer can be more   
   propellant-efficient than the Hohmann transfer if the ratio between the   
   initial and final orbit heights is high enough (normally LEO to GEO isn't   
   enough). It can be especially efficient if there is a large plane change   
   involved. It has the disadvantage of requiring much more transfer time.   
      
      
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   JRF   
      
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