<h2>AAS 95-340</h2><h2>Refinement of a Sun-Synchronous, Critically Inclined Orbit for a Global Personal Communications System</h2><h4>J.  Draim, Constellation Design, Mobile Communications Holdings, Inc., C. Sabol, Phillips Laboratory,Kirtland AFB, NM., P. J. Cefola, Draper Lab. , Cambridge, MA</h4><h2> Abstract </h2>A sun-synchronous, critically inclined orbit with mean motion of eight  revs per day was studied by the authors for use in the EllipsoTM Big-LEO personal communications system.  The original version experienced moderately high atmospheric drag near the 520 km perigee; further, the one day repeat cycle caused significant  Tesseral resonance.  A convenient strategy for reducing these adverse effects has been found:  (1) Tesseral effects are alleviated by increasing the repeat cycle from one day (with eight orbits) to ten days (with eighty-one orbits) and (2) Eccentricity and semi-major axis adjustments to maintain sun-synchronism also raise the perigee and thus reduce drag.  The new, optimized, orbit reduces the maneuvering fuel required; the time interval between corrective maneuvers is increased.<br><br>