VEX CK SPICE Kernels                                                        
  ====================                                                        
                                                                              
                                                                              
  This "aareadme.txt" file describes the contents of the kernels/ck directory 
  of the VEX SPICE data server. It also provides the file naming conventions  
  used for the VEX CK files.                                                  
                                                                              
  The CK in this subdirectory provide information on:                         
                                                                              
    - predicted and reconstructed spacecraft orientation CKs,                 
                                                                              
    - "planning" spacecraft CKs,                                              
                                                                              
    - orientation CKs for instruments with moving parts.                      
                                                                              
    - orientation for the Solar Arrays.                                       
                                                                              
  Each kernel file provides information of only one of the types above.       
                                                                              
  * Predicted spacecraft orientation CK files are produced by an automated    
    system located at ESAC, operated by the ESA SPICE Team.                   
                                                                              
  * "Planning" CK files are also produced using ADCS. These files contain the 
    spacecraft orientation requested by the VEX Project Science Team through  
    the Pointing Timeline Request (PTR) files. Each of these files is produced
    at the end of a medium term planning cycle. They should only be used in   
    support of the planning activity and NEVER for data analysis since the    
    pointing may change before being implemented on the spacecraft during the 
    short term planning activities.                                           
                                                                              
  * The third kind of spacecraft orientation CK files contain RECONSTRUCTED   
    data. There shall be only one kernel of this type (if any), with the      
    orientation of the spacecraft for all the time periods for which the      
    predicted attitude was not accurate enough; for these periods, a          
    recostruction of the attitude was requested to ESOC, and stored in this   
    kernel.                                                                   
                                                                              
  * The instrument CKs are generated by the instrument teams, and contain     
    orientation of the moving parts for each instrument.                      
                                                                              
  * The CKs for the Solar Arrays contain information about their orientation, 
    with respect to the spacecraft reference frame.                           
                                                                              
                                                                              
  The contents and time span covered by any CK file may be easily determined  
  using the "ckbrief" utility program available in all copies of the          
  SPICE Toolkit. Examples of usage:                                           
                                                                              
    %ckbrief  <ck_file_name> <sclk_file_name> <lsk_file_name>                 
                                                                              
                                                                              
  This utility requires a SPICE sclk file and an lsk file in addition to the  
  CK file; use the latest versions of these files.                            
                                                                              
  Descriptive information about how/why/when an CK 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 <ck_file_name>                                                 
                                                                              
                                                                              
  All binary CK files (*.BC) 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).                                                            
                                                                              
  For information on the content of this folder or information in general on  
  SPICE for VEX, contact                                                      
                                                                              
        ESA SPICE Team,           esa_spice@sciops.esa.int                    
                                                                              
  , or                                                                        
                                                                              
        Jose Luis VAzquez,        jlvazquez@sciops.esa.int                    
                                                                              
                                                                              
                                                                              
  References                                                                  
  ==========                                                                  
                                                                              
    1. Data Delivery Interface Document (DDID), Appendix H - FD  products     
       Issue 3.0 (VEX-ESC-IF-5003)                                            
                                                                              
    2. CK Required Reading (NAIF Document).                                   
                                                                              
    3. NAIF IDs Required Reading (NAIF Document).                             
                                                                              
    4. Venus Express Frames Definition Kernel (FK), latest version.           
                                                                              
                                                                              
  All the NAIF Documents are available at the NAIF web:                       
                                                                              
    http://naif.jpl.nasa.gov                                                  
                                                                              
                                                                              
                                                                              
  Venus Express CK Directory Structure                                        
  ====================================                                        
                                                                              
    aareadme.txt                  This file.                                  
                                                                              
    former_versions               Subdirectory that contains obsolete         
                                  versions of the CK files that have been     
                                  updated in the Current CK Kernels Set.      
                                                                              
    ATNV_PYYMMDDhhmmss_xxxxx.BC   Contains Venus Express predicted attitude   
                                  information covering the time span          
                                  starting at the date YYMMDDhhmmss. This     
                                  attitude information corresponds to the     
                                  ESOC attitude file named:                   
                                                                              
                                  ATNV_FDLMMA_DAPYYMMDDhhmmss_xxxxx.VEX       
                                                                              
                                  where xxxxx designates the version number.  
                                                                              
    ATPV_Pvvvvv_YYMMDD_xxxxx.BC   Contains Venus Express medium term planning 
                                  predicted attitude information covering the 
                                  time span starting at the date YYMMDD. This 
                                  attitude information corresponds to the ESOC
                                  attitude file named:                        
                                                                              
                                   ATPV_FDLVMA_DAPvvvvv_YYMMDD_xxxxx.VEX      
                                                                              
                                  where xxxxx designates the version number.  
                                  This attitude information corresponds to the
                                  PTR file version vvvvv delivered from VSOC  
                                  to ESOC and it is intended for the Teams to 
                                  check the pointings. The final attitude file
                                  is fixed after iterating the PTR and it may 
                                  differ from this "planning C-Kernel." (*)   

    ATPV_PxNyHz_YYMMDD_xxxxx.BC   Planning attitude kernels used during 
                                  quadrature. These files correspond to the
                                  ESOC files 
    
                                   ATPV_FDRVMA_DAPxNyHz_YYMMDD_xxxxx.VEX

                                  x - ecliptic flag
                                  y - north flag
                                  z - HGA flag
 
                                  xxxxx - version of the file


    ATPV_PExHG1_YYMMDD_xxxxx.BC   Same as above, but with an older naming 
                                  scheme
                                                                              
    ATNV_RECONSTITUTED_xxxxx.BC   Contains Venus Express RECONSTITUTED        
                                  attitude information. This attitude         
                                  information corresponds to all reconstituted
                                  attitude files delivered from ESOC to PST.  
                                  This file is updated every time new         
                                  reconstituted data are available. The file  
                                  contains gaps between data segments.        
                                  Extensive documentation specifying valid    
                                  interpolation intervals (periods with no    
                                  data gaps) is provided in the comment area. 
                                  Please refer to text above for information  
                                  about using the COMMNT utility.
                                               
    ATNV_MEASURED_Vvv.BC          Contains Venus Express MEASURED attitude,
                                  provided by the onboard AOCS system. The 
                                  coverage is not coninuous; instead, periods
                                  with measured attitude are added to this
                                  kernel as requested by the Teams.
                                                                              
    VEX_BOOM_vxx.BC               This file contains orientation of the Venus 
                                  Express Magnetometer's Boom frame           
                                  ('VEX_MAG_MAGB' frame) relative to the      
                                  Magnetometer's Boom hinge frame             
                                  ('VEX_MAG_MAGB-H' frame).                   
                                                                              
    VEX_SA_YYYYVvvvv.BC           Contains orientation for the Solar Arrays,  
                                  for the year YYYY. vvvv is the version      
                                  number, and it is increased when new data is
                                  added to the file.                          
                                                                              
                                                                              
-------------------                                                           
                                                                              
        This file was last modified on March 17th, 2009. (J. Vazquez)