***** 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