***** File ATTCPGIO.DOC                                                       
                                                                              
Giotto Cruise Phase Attitude History File                                     
-----------------------------------------                                     
                                                                              
1. Introduction                                                               
                                                                              
   This note provides details on the Giotto cruise phase attitude             
history file (GEXCPAHF). The full file was provided to the experimenters      
via a standard magnetic tape. The file format of GEXCPAHF is given in         
section 2.1. A printout of the attitude history file, covering the            
period 5 - 17 March 1986 is given in section 2.2.                             
                                                                              
2.1 File Details                                                              
                                                                              
   The experimenter cruise phase attitude history file contains records       
according to the content and format described in the Giotto Software          
Design Document, Annex C. It was intended that records would be provided      
only between two consecutive manoeuvres. However, it was decided to           
include additional records corresponding to fine attitude determination       
using the Giotto star mapper operating in star mode. Thus, in any period      
between two manoeuvres there could in general be more than one record         
containing the attitude details during free drift. Hence the GEXCPAHF         
provides a more finely sampled representation of the attitude history         
of Giotto.                                                                    
                                                                              
   The updated record format is given in Fig. 2.1                             
                                                                              
Notes:                                                                        
                                                                              
1) The start and stop times are UTC ground receive time.                      
                                                                              
2) The attitude is provided with respect to the spacecraft -z axis            
   (+ve spin-axis) in the mean equatorial system of B1950.                    
                                                                              
3) In any single given record the attitude refers to the attitude at          
   the start time specified in that record. Similarly, the spin-rate          
   provided also corresponds to the record start time.                        
                                                                              
4) It may be assumed that if the delta-V is exactly zero, and if              
   indicator flags F2 and F3 are both set to zero, then the attitude          
   etc. provided for that record corresponds to a period of free              
   drift, i.e. no manoeuvres have occurred.                                   
                                                                              
5) Default values of indicator flags F1, F2, F3 are zero.                     
                                                                              
6) During 5 - 17 March 1986, Giotto's geocentric distance increased           
   from about 139 million km to about 145 million km. The one-way             
   light time correspondingly increased from 7 mins 44 secs to                
   8 mins 04 secs. The event time on-board can be calculated by               
   subtracting the one-way light time from the ground receive time.           
   The spacecraft's geocentric distance, and hence light time, is             
   easily calculated from the orbital data.                                   
                                                                              
Fig 2.1  Format of the attitude records                                       
                                                                              
 !---------!------------!----------------------------------------------------!
 !   BYTE  !   FORMAT   !             DESCRIPTION                            !
 !---------!------------!----------------------------------------------------!
 !         !            !                                                    !
 !  1 -  3 !   I2,1X    !  YEAR                   START                      !
 !  4 -  7 !   I3,1X    !  DAY IN YEAR            TIME                       !
 !  8 - 10 !   I2,1X    !  HOUR                   OF                         !
 ! 11 - 13 !   I2,1X    !  MIN                    VALIDITY.                  !
 ! 14 - 16 !   I2,1X    !  SEC                                               !
 ! 17 - 20 !    4X      !  BLANK SPACE PADDING                               !
 ! 21 - 23 !   I2,1X    !  YEAR                   STOP                       !
 ! 24 - 27 !   I3,1X    !  DAY IN YEAR            TIME                       !
 ! 28 - 30 !   I2,1X    !  HOUR                   OF                         !
 ! 31 - 33 !   I2,1X    !  MIN                    VALIDITY.                  !
 ! 34 - 36 !   I2,1X    !  SEC                                               !
 ! 37 - 40 !    4X      !  BLANK SPACE PADDING                               !
 ! 41 - 48 ! F6.2,2X    !  ATTITUDE RIGHT ASCENSION (DEG)                    !
 ! 49 - 56 ! F6.2,2X    !  ATTITUDE DECLINATION (DEG)                        !
 ! 57 - 63 ! F6.3,1X    !  INSTANTANEOUS SPIN RATE (RPM)                     !
 ! 64 - 66 !    3X      !  BLANK SPACE PADDING                               !
 ! 67 - 74 ! F7.4,1X    !  VELOCITY INCREMENT/ DELTA-V (DV) (M/S)            !
 ! 75 - 76 !    2X      !  BLANK SPACE PADDING                               !
 ! 77      !    I1      !  INDICATOR FLAG F1 : F1=1 IF ATT.IS A PREDICTION   !
 ! 78      !    I1      !  INDICATOR FLAG F2 : F2=1 IF DV IS INACCURATE      !
 ! 79      !    I1      !  INDICATOR FLAG F3 : F3=1 IF DV NOT PROVIDED       !
 ! 80      !    1X      !  BLANK SPACE PADDING.                              !
 !         !            !                                                    !
 !---------!------------!----------------------------------------------------!
                                                                              
N.B. The delta-V applies to a manoeuvre starting at the stop time of          
     validity and ending at the start time of the next record.                
                                                                              
2.2 Printout of GEXCPAHF                                                      
                                                                              
    A printout of GEXCPAHF is appended. Note the following:-                  
                                                                              
   1) At the encounter, i.e. over days 072/073, the Giotto attitude was       
      lost (due to loss of useful star mapper datation no attitude            
      determination was possible) shortly before the point of closest         
      approach to the comet and not recovered until several hours past        
      this point. The GEXCPAHF therefore contains the determined              
      attitude shortly before closest approach and then when the              
      spacecraft attitude was re-determinable.                                
                                                                              
   2) For further information during days 072/073, refer to the other         
      files provided dealing specifically with the encounter period.          
                                                                              
86 064 00 00 00    86 064 05 34 19     325.34    5.71  14.991     0.0254   000
86 064 05 35 15    86 065 03 03 06     326.60    5.62  14.991     0.0254   000
86 065 03 04 11    86 066 05 02 51     327.83    5.49  14.991     0.0254   000
86 066 05 03 55    86 067 02 40 09     329.03    5.22  14.991     0.0254   000
86 067 02 41 05    86 068 04 22 15     330.26    5.10  14.991     0.0273   000
86 068 04 23 19    86 069 05 16 16     331.56    4.84  14.992     0.0254   000
86 069 05 17 12    86 070 05 06 22     332.78    4.70  14.992     0.0273   000
86 070 05 07 26    86 071 01 09 24     334.06    4.41  14.993     2.4709   000
86 071 01 42 46    86 071 03 19 29     334.53    4.36  14.622     0.0030   000
86 071 03 19 40    86 071 04 48 30     334.52    4.36  15.007     0.0175   000
86 071 04 49 11    86 072 04 36 50     335.36    4.15  15.008     0.0755   000
86 072 04 39 38    86 072 19 15 00     338.19    1.92  15.008     0.0000   000
86 072 19 15 00    86 072 23 30 00     338.18    1.95  15.008     0.0000   000
86 073 05 40 00    86 073 18 45 00     338.95    2.73  14.958     0.0000   000
86 073 18 45 00    86 074 04 36 58     338.94    2.75  14.958     0.0158   000
86 074 04 37 38    86 075 03 11 05     339.56    3.19  14.960     0.1055   000
86 075 03 15 01    86 075 11 17 31     336.68    7.55  14.960     0.0176   000
86 075 11 18 19    86 076 00 00 00     337.34    8.13  14.960     0.0000   000