Several pointings were used for the observations on the Mars Express          
spacecraft. The pointings refered in this description file are used           
in data product labels as values of the keyword                               
    SPACECRAFT_POINTING_MODE.                                                 
The values that can be used are indicated in CAPITALS in this file.           
                                                                              
                                                                              
The INERT pointing is used to point the instrument platform towards a fixed   
direction in right ascension and declination.                                 
                                                                              
                                                                              
The NADIR pointing mode is used for science observations nominally around     
the pericentre. In this pointing mode the Z-axis of the spacecraft points     
towards the centre of Mars and the X-axis perpendicular to the ground track.  
                                                                              
The ACROSSTRACK pointing mode is a derivative of the NADIR pointing mode      
using a constant offset perpendicular to the flight direction of the          
spacecraft. The angle for this observation is measured degrees and shall      
be specified in the data product label file.                                  
                                                                              
The ALONGTRACK pointing mode is a derivative of the NADIR pointing mode       
using a constant offset in the flight direction of a spacecraft.              
The angle is measured in degrees and shall be specified in the data product   
label file.