 routine writes an SPK type 3 data segment to the designated 
   SPK file, according to the format described in the SPK Required 
   Reading. 
 
   Each segment can contain data for only one target, central body, 
   and reference frame.  The Chebyshev polynomial degree and length 
   of time covered by each logical record are also fixed.  However, 
   an arbitrary number of logical records of Chebyshev polynomial 
   coefficients can be written in each segment.  Minimizing the 
   number of segments in an 