NOAA post-fit ("precise") GPS orbit data, computed by the
National Geodetic Survey, are available via anonymous ftp
from gracie.grdl.noaa.gov in the /dist/cignet/Ngsorbits 
directory.

The files are in UNIX-compressed format.  The file-naming
convention is as follows:

      ngsnnnnx.aaa,  where ngs = National Geodetic Survey
                           nnnn = GPS Week Number, e.g., 0745
                           x = day of week, Sunday = 0, ...,
                               Saturday = 6, weeklong = 7
                           aaa = file type, eph (SP3), sum, erp
                               (erp = earth rotation parameters)

The GPS orbits are provided in the format SP3 (ASCII) devised by  
NOAA's Dr. Benjamin Remondi and documented in two publications.
The publications are:

         NOAA Technical Report NOS 133 NGS 46, Extending the
          National Geodetic Survey Standard Orbit Formats,
          November 1989

         NGS Second Generation ASCII and Binary Formats and
          Associated Interpolation Studies, Proceedings,
          Twentieth General Assembly of the International Union
          of Geodesy and Geophysics, Vienna, Austria, August
          1991.
                                                               
These publications can be ordered for a nominal fee by telephone 
at 301-713-3242, or, alternatively, by <a href="/cgi-test/redirectNOAA.prl?u=ngs.infocenter">e-mail</a>