PDS_VERSION_ID       = PDS3                                                   
RECORD_TYPE          = STREAM                                                 
OBJECT               = TEXT                                                   
  PUBLICATION_DATE     = 2000-04-10                                           
  NOTE                 = "PLS sector description."                            
END_OBJECT           = TEXT                                                   
END                                                                           
                                                                              
                                                                              
                                                                              
                                                                              
                          Table 7.                                            
                                                                              
                                                                              
                       AACS Sector ID                                         
                                                                              
                                                                              
                                                                              
   Sectoring mode                  AACS Sector values                         
--------------------      -------------------------------------               
                                                                              
 Quadrants (4/spin)          0, 64, 128, 192                                  
                                                                              
  Octants  (8/spin)          0, 32, 64, 96, 128, 160, 192, 224                
                                                                              
                                                                              
                                                                              
    The AACS rotor spin angle is an integer number in the range 0-255.  It    
    is zero when the spacecraft X-axis is pointed at (or near) the south      
    ecliptic pole and increases as the spacecraft rotates.  The rotor spin    
    angle may be converted to an angle in the range 0-360 degrees with the    
    equation:                                                                 
                                                                              
                      angle = (AACS rotor spin angle) * (360/256)             
                                                                              
    The fields-of-view of the PLS detectors are offset by 45 degrees from     
    the spacecraft X-axis in the X-Y plane.  So when the rotor spin angle     
    is zero (0) the fields-of-view are making a +45 degree angle with         
    respect to the X-axis in the X-Y plane. This 45 degree offset is not      
    included in the AACS rotor spin angle provided in the RDR data files.     
                                                                              
    To compute the rotational angle from the north ecliptic pole to the       
    velocity vector of the plasma particles entering the PLS field-of-view:   
                                                                              
         velocity angle = 45 + [ (AACS rotor spin angle) * (360/256) ]        
                                                                              
    A significant challenge to the PLS flight software was decoupling data    
    collection from data transmission. Plasma measurements need strong        
    control of, and repeatability in, the angular sampling.  A very           
    conscious trade was  made by the PLS team to relax the time knowledge     
    in favor of tightening the angular knowledge. This means that the PLS     
    data can not be directly compared to the spacecraft attitude (AACS)       
    data set based solely on the time word. PLS uses the AACS CLOCK data      
    distributed onboard the spacecraft to determine when to begin             
    accumulating sensor data.  Depending on the modes of operation PLS may    
    begin, for example, on quadrant or octant sector boundaries.  Within      
    each sector the instrument uses a fixed  accumulation time for each       
    sample.  Thus within each sector successive samples (successive energy    
    steps) start at successively larger angles as the spacecraft rotates at   
    ~18.9 degrees/second.                                                     
                                                                              
    The time assigned to each measurement in an RDR file is the time that     
    data collection was initiated for that particular mode.  Thus, data       
    collected over approximately one spin of the spacecraft will all have     
    the same SCLK time in the file.  And since the actual data collection     
    begins on a sector boundary, the actual time of the first data may be     
    up to one sector later than the initiation time.