From: henry@spsystems.net   
      
   In article ,   
   Monte Davis   wrote:   
   >Dumb question: If one were in circular LEO and crazy enough to want a   
   >90-degree change of inclination, what's the cost in delta-v? Is it, as   
   >intuition is telling me, equivalent to throwing away all your ~9 kps   
   >and re-acquiring it all?   
      
   Not that bad, because there's a different strategy you've missed.  You can   
   do *any* LEO plane change with about 6.6km/s.  The first 3.3km/s turns the   
   orbit into a very elliptical one with an extremely high apogee.  Coast up   
   to apogee.  Orbital velocity there is negligible, so a negligible burn can   
   accomplish *any* plane change there.  Coast back down.  The other 3.3km/s   
   converts the elliptical orbit back into a circular one.   
      
   Add a little if you're impatient and prefer a somewhat less extreme apogee   
   (you save almost nothing on the two big burns, and the actual plane change   
   costs a bit more).  Subtract some if you can use a lunar flyby to do the   
   plane change.  Subtract a whole bunch if you use aerobraking to do most of   
   the final apogee lowering (but be warned that if you do it gradually, it   
   takes a long time and you'll make many passes through the Van Allen belts).   
   --   
   "Think outside the box -- the box isn't our friend."    |   Henry Spencer   
                                   -- George Herbert       | henry@spsystems.net   
      
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