PDS_VERSION_ID          = PDS3                                                
RECORD_TYPE             = STREAM                                              
                                                                              
OBJECT                  = TEXT                                                
   INTERCHANGE_FORMAT   = ASCII                                               
   PUBLICATION_DATE     = 2020-07-10
   NOTE                 = "This file describes the files in the               
                           EXTRAS/ORBNUM directory of this volume."           
END_OBJECT              = TEXT                                                
                                                                              
END                                                                           
                                                                              
                                                                              
Orbit number files for the Mars Express mission                               
===============================================                               
                                                                              
   This directory contains the orbit number file generated during the         
   mission using the NAIF's ORBNUM utility program for the final              
   merged spacecraft trajectory SPK files of the mission. The orbit           
   number file has the name ORMM_MERGED_vvvvv.ORB, where vvvvv is the         
   version number, that matches the version number of the most recent         
   SPK kernel available at the time the orbit number file was made.           
   The orbit number files are plain ASCII text files that have lines          
   terminated with a line feed character, LF (ASCII 10).                      
                                                                              
   The files included in this data set are the most recent files
   available at the moment of the compilation of each release of this
   data set, which should span at least the same time interval as all the
   SPK files included in the data set.
                                                                              
   They contain data that follow the "periapsis-to-periapsis" orbit           
   numbering scheme -- with the orbit number changing at periapsis.           
                                                                              
   The information contained in the orbit number files includes:              
                                                                              
    - Orbit number ("No".)                                                    
    - Periapsis or descending node UTC time ("Event UTC PERI")                
    - SCLK time ("Event SCLK PERI" )                                          
    - Apoapsis or ascending UTC time ("OP-Event UTC APO").                    
    - Sub-solar geodetic longitude and latitude (SolLon, SolLat), in
      the IAU_MARS reference frame.
    - Sub-spacecraft geodetic longitude and latitude (SC Lon, SC Lat), in
      the IAU_MARS reference frame.
    - Altitude of the vehicle above the primary body (Alt)                    
    - Inclination of the vehicle orbit (Inc)                                  
    - Eccentricity of the orbit plane about the primary body (Ecc)            
    - Longitude of the ascending node of the orbit (LonNode)                  
    - Argument of periapsis of the orbit (Arg Per)                            
    - Solar distance the time of the orbit event (Sol Dist)
    - Semimajor axis of the orbit (Semi Axis)                                 

   All longitudes and latitudes where computed using the IAU 2000 Mars
   rotation model.
                                                                              

Important Note Regarding Orbit Number Files
===========================================

   In the Mars Express orbit number files produced by NAIF's ORBNUM utility
   program each of the records contains the time of THAT orbit's pericenter
   and the time of the NEXT orbit's apocenter. For example, the line for
   orbit '3' provide UTC and SCLK of orbit '3' pericenter and UTC of orbit
   '4' apocenter.

   Since the project accepted orbit numbering scheme dictates the orbit number
   change to occur at apocenter, the time boundaries for a given orbit can be
   determined by taking the apocenter time from the PREVIOUS orbit record and
   the apocenter time from THIS orbit record.

   Orbit number 1 corresponds to the first mapping orbit, 2006 APR 20.

   All derived quantities provided on each record -- sub-solar lon/lat,
   sub-spacecraft lon/lat/alt, and orbital elements -- are computed for the
   time of pericenter.

Contact Information                                                           
===================                                                           
                                                                              
   Regarding Mars Express project specific information provided in this       
   data set and for general information about SPICE system, contact:          


      Alfredo Escalante Lopez
      +34 91 813 1429
      alfredo.escalante@esa.int

   , or

      Boris Semenov
      (818)-354-8136
      Boris.Semenov@jpl.nasa.gov