PDS_VERSION_ID          = PDS3
RECORD_TYPE             = STREAM

OBJECT                  = TEXT
   INTERCHANGE_FORMAT   = ASCII
   PUBLICATION_DATE     = 2007-03-05
   NOTE                 = "This file describes the files in the 
                           extras/orbnum directory of this volume."
END_OBJECT              = TEXT

END


Orbit number files for the Mars Global Surveyor mission
=======================================================

   This directory contains the orbit number files generated during the
   mission using the NAIF's ORBNUM utility program for some the final
   merged spacecraft trajectory SPK files for the orbital phases of the
   mission. The orbit number files have the same names as the
   corresponding SPK files but with the extension ".bsp" replaced by
   ".orb" or ".nrb". The only exception are the "mgs_ext25_v2.nrb" and
   "mgs_ext26_v2.nrb" file that do not have matching SPKs. These files
   supersede the "mgs_ext25.nrb" and "mgs_ext26.nrb" files, also
   included in this directory for the record, the orbit numbers in
   which were off by one due to a bug in the version of the ORBNUM
   program used to generate them.

   The orbit number files are plain ASCII text files that have lines
   terminated with a line feed character, LF (ASCII 10).
 
   The orbit number files with the ".orb" extension contain data that
   follow the "periapsis-to-periapsis" orbit numbering scheme -- with
   the orbit number changing at periapsis.
 
   The orbit number files with the ".nrb" extension contain data that
   follow the "node-to-node" orbit numbering scheme -- with the orbit
   number changing at the descending node.
 
   The information contained in the orbit number files includes the
   orbit number ("No."), periapsis or descending node UTC time
   ("Periapsis UTC" or "Desc-Node UTC") and SCLK time ("Periapsis SCLK"
   or "Node SCLK" ), apoapsis or ascending UTC time ("Apoapsis UTC" or
   "Asc-Node UTC"). It also includes a few additional items computed at
   the time of periapsis or descending node such as planetocentric
   subsolar longitude and latitude ("SolLon" and "SolLat") in the Mars
   body-fixed frame based on the IAU 1994 Mars rotation model,
   planetocentric subspacecraft longitude and latitude ("SC Lon" and
   "SC Lat") in the Mars body-fixed frame based on the IAU 1994 Mars
   rotation model, spacecraft altitude above Mars ("Alt") relative to
   the IAU 1994 Mars ellipsoid, and Sun-Mars distance ("Sol Dist").


Contact Information 
===================

   Regarding Mars Global Surveyor project specific information provided
   in this data set and for general information about SPICE system,
   contact:
   
      Boris Semenov 
      (818)-354-8136 
      Boris.Semenov@jpl.nasa.gov
      
   address:
   
      Navigation and Ancillary Information Facility (NAIF)
      Jet Propulsion Laboratory
      MS 301-125L
      4800 Oak Grove Drive
      Pasadena CA 91109 USA