                                                                              
                                                                              
  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 Service.
                                                                              
  * "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 Service,           esa_spice@sciops.esa.int
                                                                              
  , or                                                                        
                                                                              
        Marc Costa Sitja,         mcosta@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   SPICE kernel containing 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.

    ATNV_T6_PYYMMDDhhmmss_xxxxx.BC

                                  SPICE kernel containing Venus Express
                                  predicted attitude information covering
                                  the time span starting at the date
                                  YYMMDDhhmmss. This product is a Type 6 CK
                                  kernel and requires at least the SPICE
                                  Toolkit N0065 to be used. 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   SPICE kernel containing 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_MEASURED_Vvv.BC          SPICE kernel containing Venus Express
                                  MEASURED attitude, provided by the onboard
                                  AOCS system. The coverage is not continuous;
                                  instead, periods with measured attitude are
                                  added to this kernel as requested by the
                                  Teams.

    ATNV_MEASURED_YYYY_Vvv.BC     SPICE kernel containing Venus Express
                                  MEASURED attitude, provided by the onboard
                                  AOCS system. The coverage is for the year
                                  indicated by YYYY.

    VEX_ASPERA_SAF_YYMMDD_vv.BC   SPICE kernel containing data describing the
                                  ASPERA scanner motion from the telemetry.
                                  It is provided by the ASPERA Team.
                                                                              
    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_VIRTIS_YYYY_Vvv.BC        SPICE kernel containing the optical angles
                                  of the VIRTIS scanning mirror orientation,
                                  which correspond to the actual direction of
                                  pointing of each acquisition with respect
                                  to the instrument's boresight.
                                                                              
    VEX_SA_YYYY_Vvvvv.BC          SPICE kernel containing 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 January 20th, 2020. (A. Escalante)
