General information about SPICE SCL-kernels                                   
===========================================                                   
                                                                              
   In the SPICE system, the Spacecraft Clock (or SCL) kernel contains
   information required to perform a mapping between Ephemeris time
   (ET, also called Barycentric Dynamic Time, or TDB) and spacecraft
   on-board time (SCLK).

   The spacecraft clock coefficient information contained in an SCLK
   file can be manipulated by a collection of subroutines to provide a
   transformation between Ephemeris and spacecraft on-board times.
   These subroutines are part of the SPICE library, the major component
   of the SPICE Toolkit. The routines needed are integrated into a
   user's application programs. For information on the SPICE Toolkit
   and/or how to obtain it, please consult SPICE_INST.CAT and SOFT.CAT.

   Refer to the SCLK.REQ document provided with the Toolkit to get more
   information about conversion between ET and spacecraft clock times.        


Venus Express SCLK Files                                                      
========================                                                      
                                                                              
   This file describes the contents of the DATA/SCLK directory of the         
   Venus Express SPICE data set.
                                                                              
   SCLK files are created from the information contained in the ESOC's        
   DDID Time Correlation Packets.                                             
                                                                              
   All SCLK files (*.TSC) contained in this directory are UNIX text files
   with lines terminated by <LF> only.
                                                                              
                                                                              
Venus Express SCL-Kernels Contained in this Data Set                          
====================================================

   The following SCL-kernels are provided in this data set:
                                                                              
       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.

   Note that when several SCLK kernels are provided in the data set, the
   most recent one supersedes all the others.


Kernel File Details
===================

   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 these kernels. The SPICE Toolkit provides versions in Fortran
   (SPICELIB), C (CSPICE), IDL (icy), Matlab (Mice), and Java
   (JNISpice) and the user can choose any one that suits him/her.

   The SPICE routine FURNSH can be used to load a kernel file into a
   SPICE-based application to make kernel data usable with SPICE
   APIs.

   If two (or more) text SCLK 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).