=============================================================================
MEX SPK Files
=============================================================================

  Last update:  22 NOV 2005  

  This "aareadme.txt" file describes the contents of the KERNELS/SPK
  directory of the MEX SPICE data server.  It also provides the file 
  naming conventions used for the MEX SPK kernels, and it provides
  identification of the most current version of each kind of SPK file.

  Some of these SPK files are produced by an automated system located
  at ESTEC, operated by the MEX Project Science Team (PST). For these we
  have chosen to use the ESOC naming convention for SPK files, which are
  converted from ESOC's DDID Orbit files. Although this convention doesn't
  seem very descriptive and holds some redundant information, it could be
  useful to use the same name style for the sake of consistency. Also, data
  handling performed by the PST automated system will be easier and faster.

  The contents and time span covered by any SPK file may be easily determined
  using the "brief" utility program available in all copies of the
  SPICE Toolkit. Examples of usage:  
     %brief  <spk_file_name>
     %brief  <*.bsp>
     %brief  <xxx*.bsp>

  Descriptive information about how/why/when an SPK file was created is
  usually available in the "comment area" of the file. This may be viewed
  using the "commnt" utility program available in all copies of the
  SPICE Toolkit. Use the "-r" option to read the comments. Example:
    %commnt -r <spk_file_name>

  All binary SPK files (*.BSP) contained in this directory are unix binary
  files. These may be used as is (without format conversion) in a non-unix
  environment when using any recent version of the SPICE Toolkit (Version
  N0052 or later).  [Ref 3b]

  Contact Jorge Diaz del Rio (jdiaz@rssd.esa.int) or Joe Zender 
  (Joe.Zender@esa.int) if you have any questions.


=============================================================================
References
=============================================================================
    1. Data Delivery Interface Document (DDID)       Appendix H - FD 
       products Issue 3.0 (MEX-ESC-IF-5003)

    2. SPK Required Reading. NAIF Document No. 168.10  05 Sep 2002

    3. Selected SPICE Tutorials from the NAIF server:  
ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/Tutorials/office/individual_docs/

       a) SPK Tutorial                14_spk.ppt
       b) Porting Kernels Tutorial    09_porting_kernels.ppt

    4. ``Astrometric Observations of Phobos and Deimos with the SRC on 
       Mars Express'', Oberst, J. et al. Astronomy and Astrophysics. Accepted
       07-Oct-2005
  
=============================================================================
Mars Express SPK Directory Structure
=============================================================================
 aareadme.txt         Text file describing the directory structure, the naming
                      conventions for the SPKs, and the current version(s) of
                      each SPK type.

 former_versions      Subdirectory that contains obsolete versions of the 
                      SPK files that have been updated in the Current SPK
                      Kernels Set.




=============================================================================
MEX Spacecraft SPK Naming Conventions          ffff__YYMMDDhhmmss_vvvvv.BSP
=============================================================================


          token           description
          ------------    --------------------------------------------
          ffff            Source Product Type Identifier: 
                             ORHM -- S/C Orbit, cruise, heliocentric
                             ORMF -- S/C Orbit, Mars centric. Long 
                                     Term Planning
                             ORMM -- S/C Orbit, operational, Mars
                                     centric.
                      
          YYMMDDhhmmss    Coverage start time of the data contained
                          in the ORMM file. In ORMF and ORHM files this
                          token is replaced by twelve "_".
          vvvv            version number

=============================================================================
DSN Stations SPK  Naming Convention         EARTH_[spec]_yymmdd.BSP
=============================================================================

      token           description
      ---------       -------------------------------------------------------
      [spec]          Reference frame label:
                        FX:     EARTH_FIXED alias used.
                        ITRF93: ITRF93 label used.
      yymmdd          Release date.



=============================================================================
Planet and Satellite Ephemeris SPK Naming Convention
=============================================================================
 Use original names assigned by NAIF, in uppercase. For example:

          DE405.BSP      Planetary ephemeris
          MAR033.BSP     Mars satellite ephemeris (Phobos and Deimos)


 
=============================================================================
Current SPK Kernels Set
=============================================================================

Note: There may be several files of a given type, each one having a different
time span (e.g. the ORMM family). 

Note: Files EARTHSTNS_FX_yymmdd.BSP and EARTHSTNS_ITRF93_yymmdd.BSP contain
the same data. These files only differ in that the second one use the
reference frame label 'ITR93' instead of 'EARTH_FIXED'. 'EARTH_FIXED' alias
must be map to either 'ITR93' or 'IAU_EARTH' before using the file. For high
accuracy work, the EARTHSTNS_ITRF93_yymmdd.BSP is recommended (on the basis
of ease of use).


 Name                               Comments
 ---------------------------------  -----------------------------------------
 BEAGLE2_SAMPLE_Vx.BSP              Contains ephemeris data for the
                                    Beagle-2 lander (location relative to
                                    the center of Mars, in Mars
                                    body-fixed rotating frame.)

 DE405S.BSP                         Contains ephemeris data for planet
                                    barycenters, and for the sun, earth
                                    and moon mass centers. Spans the
                                    entire MEX mission.

 EARTHSTNS_FX_yymmdd.BSP            Contains ephemeris data for NASA
                                    DSN stations relative to the terrestrial
                                    reference frame ITR93. In the interest of
                                    flexibility, in this file the reference
                                    frame is labeled with the alias
                                    'EARTH_FIXED'. Any application using this
                                    file must map the alias 'EARTH_FIXED' to
                                    either 'ITR93' or 'IAU_EARTH'. This file
                                    was released on yy-mm-dd.

 EARTHSTNS_ITRF93_yymmdd.BSP        Contains ephemeris data for NASA
                                    DSN stations relative to the terrestrial
                                    reference frame label 'ITR93'. This file
                                    was released on yy-mm-dd.

 NEW_NORCIA.BSP                     Contains ephemeris data for the
                                    ESA New Norcia station.

 MAR033_2000-2025.BSP               Contains JPL ephemeris data for Phobos
                                    and Deimos. Spans the entire MEX mission.
 
 MAR033_HRSC_V03.BSP                Contains time-shifted JPL ephemeris data
                                    for Phobos and Deimos. Spans the entire MEX
                                    mission. For further explanation, please
                                    check the "About Phobos and Deimos
                                    ephemeris" chapter in this aareadme file
                                    and the comment area of this kernel.

 MARSAT_ESA_040101_V01.BSP          Contains ESOC ephemeris data for Phobos
                                    and Deimos. Spans from 2004-01-01 to
                                    2006-01-01.

 MEX_ASPERA_STRUCT_Vxx.BSP          Contains relative locations of the ASPERA 
                                    structures with respect to the spacecraft
                                    bus and each other. This SPK spans the
                                    entire MEX mission.
                        
 ORHM_______________xxxxx.BSP       Contains MEX spacecraft reconstructed
                                    cruise ephemeris. This ephemeris 
                                    corresponds to the ESOC orbit file named:
                                    ORHM_FDLMMA_DA______________xxxxx.MEX
                                    where xxxxx designates the version number.

 ORMF_______________xxxxx.BSP       Contains MEX spacecraft long term
                                    operational Mars centric ephemeris. This
                                    ephemeris is an approximation to that
                                    provided by an corresponds to the ESOC
                                    orbit file named:
                                    ORMF_FDLMMA_DA______________xxxxx.MEX
                                    where xxxxx designates the version number.

 ORMM__yymmdd000000_xxxxx.BSP       Contains a MEX predicted and reconstructed
                                    ephemeris after orbit insertion, starting
                                    from 20yy-mm-dd. This ephemeris corresponds
                                    to the ESOC orbit file named:
                                    ORMM_FDLMMA_DA_yymmdd000000_xxxxx.MEX
                                    where xxxxx designates the version number.

=============================================================================
About Phobos and Deimos ephemeris
=============================================================================

 The current Mars Express SPICE data set contains three SPKs giving ephemeris
 data for both Phobos and Deimos. Two out of the three files correspond to
 the JPL orbit solutions for both Mars' moons, and the third one to the ESOC
 orbit solutions. 

 The official JPL SPK file, provided by NAIF and named MAR033_2000-2025, 
 was used in the data analysis of HRSC/SRC images [Ref. 4]. In this analysis,
 the measured Phobos and Deimos positions have been compared with the JPL
 predictions. This comparison has shown that Phobos has advanced by approx.
 12 km with respect to the JPL model, while the predicted Phobos positions
 in the across-track directions are off by only small amounts (+/- 1 km).
 Deimos observations show that this satellite has advanced by approx. 50 km,
 and is also off across-track by less than 1 km.

 The down-track offsets of 12 km and 50 km of the satellites' position
 can be removed by shifting in time the Phobos and Deimos ephemeris. This
 solution has been implemented and a new SPK kernel produced: 

   MAR033_HRSC_V03.BSP

 This file solves the down-track offsets but there are still some across-track
 inconsistencies that remain, until a new orbit solution, more accurate, is
 provided.

 The third file, named MARSAT_ESA_040101_V01.BSP, was also used in the
 analysis of HRSC/SRC images [Ref. 4]. In this analysis, the measured Phobos
 and Deimos positions have been also compared with the ESOC predictions and
 the results are the following:

    Phobos' predicted position is 2 km ahead of the measured position,
    and it is off by +/- 8 km cross-track.

    Deimos' predicted position is 5 km ahead of the measured position,
    and it is off by +/-18 km cross-track.

 A comparison of official the ESOC and JPL orbit solutions of Phobos for
 epochs in 1989 show position differences over one Phobos orbital revolution
 ranging from 3 km to 7.5 km. These differences are mainly periodic.
 At the time frame of the ESOC file, 2004-2006, the same comparisons show
 larger differences over a Phobos orbital revolution, ranging from 6km to
 22 km.

 It is recommended therefore to use the HRSC/JPL solution since it's the
 one providing more accurate values.