                                                                              
                                                                              
  VEX SPK Files                                                               
  =============                                                               
                                                                              
  This "aareadme.txt" file describes the contents of the kernels/spk directory
  of the VEX SPICE data server.  It also provides the file naming conventions 
  used for the VEX 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 Service.
                                                                              
  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 Service       esa_spice@sciops.esa.int
                                                                              
  , or                                                                        
                                                                              
    Marc Costa Sitja     marc.costa@esa.int
                                                                              
  if you have any questions.                                                  
                                                                              
                                                                              
                                                                              
                                                                              
  References                                                                  
  ==========                                                                  
                                                                              
                                                                              
    1. Data Delivery Interface Document (DDID)       Appendix H - FD          
       products Issue 3.0 (VEX-ESC-IF-5003)                                   
                                                                              
    2. SPK Required Reading (NAIF Document).                                  
                                                                              
    All the NAIF Documents are available at the NAIF web:                     
                                                                              
      http://naif.jpl.nasa.gov                                                
                                                                              
                                                                              
                                                                              
  Venus 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.   
                                                                              
    DE405.BSP                       SPICE kernel containing ephemeris data
                                    for planet barycenters, and for the sun,
                                    earth and moon mass centers. Spans the
                                    entire VEX mission.
                                                                              
    EARTHSTNS_FX_YYMMDD.BSP         SPICE kernel containing 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     SPICE kernel containing ephemeris data
                                    for NASA DSN stations relative to the
                                    terrestrial reference frame label 'ITR93'.
                                    This file was released on YY-MM-DD.

    ESTRACK_Vvv.BSP                 This kernel defines the position for each
                                    of the ESA ESTRACK ground stations relative
                                    to the center of the Earth. 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'.

    OUTERPLANETS_Vvvvv.BSP          Ephemeris information for the outer planets
                                    of the solar system: Jupiter, Saturn,
                                    Uranus and Neptune. It is meant to
                                    complement DE405.BSP, which contains
                                    information for their barycenters, but not
                                    the bodies themselves.

    VEX_STRUCT_Vvv.BSP              SPICE kernel containing the location of
                                    various Venus Express instruments and
                                    structures.
                                                                              
    ORHV_T19___________xxxxx.BSP    SPICE kernel containing VEX spacecraft
                                    reconstructed cruise ephemeris. This
                                    ephemeris corresponds to the ESOC orbit
                                    file named:
                                                                              
                                    ORHV_FDLMMA_DA______________xxxxx.VEX
                                                                              
                                    where xxxxx designates the version number.
                                                                              
    ORVF_______________xxxxx.BSP    SPICE kernel containing VEX spacecraft
                                    long term planning operational Venus
                                    centric ephemeris. This ephemeris
                                    corresponds to the ESOC orbit file named:
                                                                              
                                    ORVF_FDLMMA_DA______________xxxxx.VEX
                                                                              
                                    where xxxxx designates the version number.
                                    This is the file that should be used for  
                                    planning. For data analysis you have to   
                                    use the ORVV files below.                 
                                                                              
    ORVV_T19_YYMMDD000000_xxxxx.BSP SPICE kernel containing VEX reconstructed
                                    ephemeris after orbit insertion, starting
                                    from 20YY-MM-DD. This ephemeris corresponds
                                    to the ESOC orbit file named:

                                    ORVV_FDLMMA_DA_YYMMDD000000_xxxxx.VEX

                                    where xxxxx designates the version number.
                                    These are the files that should be used
                                    for data analysis.
    
    ORVM_______________xxxxx.BSP    SPICE kernel containing the latest VEX
                                    reconstructed ephemeris for both cruise
                                    and after orbit insertion and until End
                                    of Mission. This ephemeris corresponds
                                    to the final ESOC orbit file named:
					
				                    VOEM_150721OAS_PREDICT__0001.CR.gz.txt

				                    This is the file that should be used for
				                    data analysis after the End of Mission.

    ORVM_T19___________xxxxx.BSP    SPICE kernel containing the latest VEX
                                    reconstructed ephemeris for both cruise
                                    and after orbit insertion and until End
                                    of Mission. This ephemeris corresponds
                                    to the final ESOC orbit file named:

                                    VOEM_150721OAS_PREDICT__0001.CR.gz.txt

                                    This is the file that should be used for
                                    data analysis after the End of Mission.
                                                                              
  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).                                                            
                                                                              
                                                                              
-------------------                                                           
                                                                              
        This file was last modified on January 21st, 2020. (A. Escalante)
