PDS_VERSION_ID                = PDS3                                          
                                                                              
RECORD_TYPE                   = STREAM                                        
RELEASE_ID                    = 0001                                          
REVISION_ID                   = 0000                                          
                                                                              
OBJECT                        = TEXT                                          
  PUBLICATION_DATE            = 2008-09-01                                    
  NOTE                        = "Description of the GEOMETRY directory        
                                 contents for the Venus Express ASPERA-4 /    
                                 ELS archive volume."                         
END_OBJECT                    = TEXT                                          
END                                                                           
                                                                              
                                                                              
                   GEOMETRY Directory Contents                                
                                                                              
The GEOMETRY directory contains ancillary geometry files for the Venus        
Express data within the ELS instrument dataset. The data includes             
spacecraft position and attitude in both EMEJ2000 and VSO coordinates system. 
The following files are found in this directory.                              
                                                                              
GEOMINFO.TXT -                The file you are reading.                       
                                                                              
ORB.FMT -                     Describes the format of the spacecraft          
                              orbit/attitude Table.                           
                              GEOMETRY data product refers to this file.      
                                                                              
                                                                              
The spacecraft geometry files have the following naming convention:           
                                                                              
ORB_yymmddhhmmss_ttttt.TAB  - A data table that contains spacecraft geometry  
                              information belonging to the time period as     
                              defined by the associated data product, where   
                              yymmddhhmmss is the beginning of observation    
                              and ttttt the duration in minutes.              
                              The data fields in this table include timing    
                              and position/attitude state of the spacecraft   
                              expressed in two coordinate frames: the J2000   
                              inertial frame centered on the target           
                              (typically Venus), and the Venus Solar Orbital  
                              (VSO) frame. Although both frames are centered  
                              on the target, the orientation of the frames    
                              differ. During the interplanetary cruise, the   
                              target is Earth and the J2000 coordinate system 
                              will be defined accordingly.                    
                              Geometry information are computed using various 
                              NAIF kernel files in addition to the orbit/     
                              attitude files retrieved from ESOC, and are     
                              sampled at equal time intervals of 60 sec.      
                              The data table is described below in detail:    
                              one data field (column) for the UTC time,       
                              one data field for each of the x, y, and z      
                              components of the spacecraft position expressed 
                              in the centered J2000 frame, 9 data fields      
                              in which are stored the elements of the 3       
                              orientation vectors defining the 3-axis         
                              spacecraft attitude referenced in the J2000     
                              coordinate system, followed by 3 and 9 data     
                              fields that incorporate respectively the        
                              position vector [3] and the 9 attitude          
                              parameters in VSO. The three components are     
                              always consecutive in x, y, z order.            
                                                                              
ORB_yymmddhhmmss_ttttt.LBL  - PDS label for ORB_yymmddhhmmss_ttttt.TAB.       
                                                                              
                                                                              
These spacecraft attitude and position data files are part of the ASPERA-4    
archive. These files are provided here to improve the usability of the Level  
1B ELS data on this disk.                                                     
                                                                              
The SPICE kernels related to the VEX mission may be obtained using anonymous  
ftp to the following NAIF or ESA server:                                      
ftp://naif.jpl.nasa.gov/pub/naif/VEX/kernels                                  
ftp://ssols01.esac.esa.int/pub/data/SPICE/VEX/kernels                         
                                                                              
Each of these kernels is dynamic and is subject to updates with               
time. The official archive of all SPICE products is maintained by the         
Navigation and Ancillary Information Facility (NAIF) at the Jet               
Propulsion Laboratory (JPL) in Pasadena, CA.                                  
                                                                              
In addition to being the PDS archive site for the SPICE kernels, NAIF         
provides and maintains a software toolkit (SPICELIB) for accessing            
the kernels. For more information about NAIF or SPICELIB please visit         
the NAIF website (http://pds.jpl.nasa.gov/naif.html).