MEX SPK Files                                                               
  =============                                                               
                                                                              
  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 ESAC, operated by the ESA SPICE Team.                                    
                                                                              
  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. Example of usage:                                            
                                                                              
    $ brief  <spk_file_name>                                                  
                                                                              
  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).                                                            
                                                                              
  Contact                                                                     
                                                                              
        ESA SPICE Team       esa_spice@sciops.esa.int                                
                                                                              
  , or                                                                        
                                                                              
    Jose Luis Vazquez    jlvazquez@sciops.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).                                  
                                                                              
    3. "Astrometric Observations of Phobos and Deimos with the SRC on         
       Mars Express", Oberst, J. et al. Astronomy and Astrophysics. Accepted  
       07-Oct-2005                                                            
                                                                              
    All the NAIF Documents are available at the NAIF web:                     
                                                                              
      http://naif.jpl.nasa.gov                                                
                                                                              
                                                                              
                                                                              
  Mars Express SPK Directory Structure                                        
  ====================================                                        
                                                                              
                                                                              
    aareadme.txt                    This file.                                
                                                                              
    former_versions                 Subdirectory that contains obsolete       
                                    versions of the SPK files that have been  
                                    updated in the Current SPK Kernels Set.   
                                                                              
    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.) 
                                                                              
    DE405.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.      
                                                                              
    MAR063.BSP                      Contains the mar063 ephemeris data from   
                                    JPL, for Phobos and Deimos, for the entire
                                    mission. Note that this is the baseline   
                                    kernel used for planning.                 
                                                                              
    MAR080.BSP                      Contains a slightly improvement over      
                                    MAR063.BSP, using Mars Express            
                                    observations.                             
                                                                              
    MARSAT_ESA_yymmdd_Vxx.BSP       Contains ESOC ephemeris data for Phobos   
                                    and Deimos starting from 20yy-mm-dd.      
                                                                              
    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.                       
                                                                              
    MEX_ROB_YYMMDD_yymmdd_vvv.BSP   High precision SPK kernels for Mars       
                                    Express, created by the Royal Observatory 
                                    of Belgium. The kernels cover MEX position
                                    from YY-MM-DD to yy-mm-dd; vvv is the     
                                    version number.                           
                                                                              
    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 planning
                                    operational Mars centric ephemeris. This  
                                    ephemeris corresponds to the ESOC orbit   
                                    file named:                               
                                                                              
                                      ORMF_FDLMMA_DA______________xxxxx.MEX   
                                                                              
                                    where xxxxx designates the version number.
                                    This is the file that should be used for  
                                    planning. For data analysis you have to   
                                    use the ORMM files below.                 
                                                                              
    ORMC_FD_xxxxxxxxxxxxxxxx.BSP    Contains MEX spacecraft long term         
                                    operational Mars centric ephemeris. This  
                                    files are used as candidate orbits in     
                                    order to analyse different options before 
                                    implementing the long term operational    
                                    orbit (ORMF).                             
                                                                              
    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.
                                    These are the files that should be used   
                                    for data analysis.                        
                                                                              
  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).                                                            
                                                                              
                                                                              
                                                                              
  About Phobos and Deimos ephemeris                                           
  =================================                                           
                                                                              
  The current Mars Express SPICE data set contains five SPKs giving ephemeris 
  data for both Phobos and Deimos. Four out of the five 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.                                                                      
                                                                              
  The fourth file, MAR063.BSP is the official ephemeris from JPL, using MRO   
  observations. This is the baseline kernel used for planning.                
                                                                              
  The fifth solution, MAR080.BSP, is a slightly improvement over the previous 
  one, using Mars Express data.                                               
                                                                              
                                                                              
-------------------                                                           
                                                                              
        This file was last modified on March 4th, 2009. (J. Vazquez)