                                                                              
                                                                              
  VEX SCLK Files                                                              
  ==============                                                              
                                                                              
  This "aareadme.txt" file describes the contents of the kernels/sclk         
  directory of the VEX SPICE data server. It also provides the file naming    
  conventions used for the VEX SCLK kernels, and it provides identification   
  of the most current version of SCLK files.                                  
                                                                              
  SCLK files are created from the information contained in the ESOC's DDID    
  Time Correlation Packets, by the ADCS system located at ESAC.               
                                                                              
                                                                              
  The most detailed description of the data in an SCLK file is provided in    
  metadata included inside the description area of the file. This information 
  can be viewed using any text editor program.                                
                                                                              
  At least a basic knowledge of the SPICE system is needed in order to use    
  this kernel. The SPICE toolkit provides versions in Fortran (SPICELIB), C   
  (CSPICE), IDL (icy) and Matlab (mice), and the user can choose any one that 
  suits him/her.                                                              
                                                                              
  The SPICELIB routine FURNSH, CSPICE function furnsh_c, and icy and mice     
  routine cspice_furnsh load a kernel file into the kernel pool as shown      
  below.                                                                      
                                                                              
      CALL FURNSH ( 'kernel_name' )                                           
      furnsh_c    ( "kernel_name" );                                          
      cspice_furnsh, 'kernel_name'                                            
      cspice_furnsh( 'kernel_name' )                                          
                                                                              
  In the case when two or more files contain data overlapping in time for a   
  given object, for binary kernels, the file loaded last takes precedence.    
                                                                              
  If two (or more) text kernels assign value(s) using the '=' operator to     
  identical keywords, the data value(s) associated with the last loaded       
  occurrence of the keyword are used -all earlier values have been replaced   
  with the last loaded value(s).                                              
                                                                              
  All SCLK files (*.TSC) contained in this directory are unix text files.     
  These may be used in a non-compatible text environment by using the ASCII   
  mode of FTP to port the files.                                              
                                                                              
  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)   Issue C1 (VEX-ESC-IF-5003)   
       1 July 2005                                                            
                                                                              
    2. SCLK Required Reading (NAIF Document).                                 
                                                                              
    All the NAIF Documents are available at the NAIF web:                     
                                                                              
      http://naif.jpl.nasa.gov                                                
                                                                              
                                                                              
                                                                              
  Venus Express SCLK Directory Structure                                      
  =====================================                                       
                                                                              
     aareadme.txt         Text file describing the directory structure, the   
                          naming conventions for the SCLKs, and the current   
                          version(s) of each SCLK type.                       
                                                                              
     former_versions      Subdirectory that contains obsolete versions of the 
                          SCLK files that have been updated in the Current    
                          SCLK Kernels Set, and fake SCLK files used before   
                          the creation of real ones.                          
                                                                              
     VEX_YYMMDD_STEP.TSC  This file is a SPICE spacecraft clock (SCLK)
                          kernel containing information required for
                          the Venus Express spacecraft on-board clock
                          to UTC conversion. This file provides the
                          same time information that the Time
                          Correlation packets released via DDS, with
                          the exception of 60 seconds before the
                          starting time of each packet, during which
                          the clock rate was sightly adjusted to make
                          the correlation function continuous. The
                          validity time of the last time correlation
                          is given by YY-MM-DD.
                                                                              
                                                                              
                                                                              
-------------------                                                           
                                                                              
        This file was last modified on January 10th, 2020. (M. Costa)
