ration) at the epoch
      %  July 4, 2003 11:00 AM PST.
      %
      target   = 'Mars';
      epoch    = 'July 4, 2003 11:00 AM PST';
      frame    = 'J2000';
      abcorr   = 'LT+S';
      observer = 'Earth';

      %
      %  Convert the epoch to ephemeris time.
      %
      et = <a href="cspice_str2et.html">cspice_str2et</a>( epoch );

      %
      %  Look-up the position for the defined parameters.
      %
      [ pos, ltime ] = <b>cspice_spkpos</b>( target, et, frame, ...
                         