Spacecraft oscillations for GOLF

SOHO COMMISSIONING PHASE TEST SHEET

1. TEST IDENTIFICATION
   Spacecraft attitude periodic oscillations to checkout instrument(s).

2. TEST PURPOSE
   The purpose of this test is to participate in the determination of the susceptibility to spacecraft off-pointing for GOLF and possibly other instruments.

3. APPLICABLE PHASE
   Cruise.

4. SCHEDULE
   Three different periods are proposed. All shall be after the outgassing minimum recommended security period of 30 days.
   In order to decrease the impact of the generated disturbance on other investigations, the first two ones shall preferably be as early as spacecraft/instruments early operation allows. Earlist suggestion is Days 30, 31 and 32 for GOLF channel A, Days 39, 40 and 41 for GOLF channel B.
   As it requires the spacecraft to be rotated 90 degrees from nominal roll attitude, third period shall preferably be in conjonction with another specific cruise phase activity involving a number of instruments : "Roll maneuver to chekout instruments", i.e. preliminarily Days 100, 101 and 102 to allow participation of CDS, EIT, LASCO, MDI, SUMER and VIRGO.
   Dates can be shifted but it is prefered to have 3 consecutive days for each channel testing. About one week is necessary to obtain full stability after any GOLF channel change.

5. TYPE OF MEASUREMENT
   Instruments perform solar observations while the spacecraft attitude is oscillated. Nominal accuracy time-tagged Fine Pointing Sun Sensor and Roll measurements (Star Sensor Unit or Inertial Reference Unit) are included in telemetry.

6. SUCCESS CRITERIA AND/OR EXPECTED OUTPUT
   The expected output is the determination (off-line) of instrument(s) susceptibility to small amplitude off-pointing (this susceptibility being strongly dependant on solar structure and rotation, its observation with proper accuracy is not achievable from/on ground).

7. METHOD / DURATION
   Each of three days of a series, the spacecraft shall be oscillated around one of its three reference axes (pitch, yaw and roll) with a same period of 800 seconds maintained during as long as daily real-time operation allows (close to 20 hours). Oscillations shall be generated by use of inertia wheels.
   If applicable used wheels shall be selected in such a way as to maintain attitute as close as possible to nominal one around two other axes.

8. PROCEDURE REFERENCE
   The procedure being the same for each series of three days/three axes, only one such series shall be described/specified in full detail hereafter. Others shall derive from it as indicated.

   DAY 23

   If not already done, switch GOLF channel A ON by use of proper STOLs :
   • run "x_exp_prep_on" STOL (TBC by FOT),
   • switch GOLF non-op heaters OFF,
   • run "g_pwron_m" STOL,
   • run "g_observe_m" STOL,
   Select operational heaters fine tuning parameters (a few minutes per day NRT commanding is foreseen until Day 29).

   DAY 30

   at beginning of real-time long pass :
   GOLF remaining unchanged, initiate Pitch oscillations :
   
   • at To : rotate spacecraft in pitch one +15 arcsec step,
   • at To + 400sec : rotate S/C in pitch one -30" step,
   • at To + 800sec : rotate S/C in pitch one +30" step,
   • at To + 1200sec : rotate S/C in pitch one -30" step,
   • at To + 1600sec : rotate S/C in pitch one +30" step,
   Continue having alternately 1 step of + then -30" amplitude each 400 seconds.
   At end of day oscillated dedicated time return spacecraft to nominal pointing mode (one 15 arcsec step)..

   DAY 31

   at beginning of real-time long pass :
   Repeat exactly the same off-pointing sequence (same amplitudes and same timing) as for Day 30 but for Yaw axis.

   DAY 32

   at beginning of real-time long pass :
   Repeat exactly the same as previous two days, but this time oscillating in Roll and with steps individual amplitude of 90 arcsec, (45 arcsec for the first step of the day and the last one) keeping the same duration of 400 seconds between steps, in order to maintain the same full cycle 800 seconds period.

   At the end of third day long pass (or at beginning of fourth day long pass) : Switch GOLF Channel A OFF by use of dedicated STOL : "g_pwroff_m".

   DAY 32 or 33

   Start channel B testing as for A one, beginning again already described sequence starting as from DAY 23.

   DAY 39

   Perform Pitch oscillations as per DAY 30

   DAY 40

   Perform Yaw oscillations as per DAY 31

   DAY 41

   Perform Roll oscillations as per DAY 32

   Third period of test only difference with already performed ones is that :

   • Spacecraft shall be rotated 90 degrees from nominal attitude in Roll prior to start oscillations susceptibility sequence as described earlier.
   • Testing of only GOLF Prime observation channel is foreseen, the two first off-pointing oscillation tests result being one element of selection (among others) for this Prime channel selection.

   DAY 93 if not done earlier

   Start selected GOLF channel testing, beginning again already described sequence starting as from DAY 23.

   DAY 99

   Rotate spacecraft at 90 degrees from nominal Roll attitude and perform CDS and other instruments specific activities.

   DAY 100

   Perform Pitch oscillations as per DAY 30

   DAY 101

   Perform Yaw oscillations as per DAY 31

   DAY 102

   Perform Roll oscillations as per DAY 32

   DAY 103

   Perform CDS and other instruments specific activities and roll back spacecraft to nominal Roll attitude.

9. CONSTRAINTS / PREREQUISITES
   Stabilisation during a few days, up to a week, is necessary for GOLF to reach full instrument sensitivity (duration could be reviewed after real evolution better knowledge has been obtained during instrument early operations performance).
   Activities (other than those here described) affecting spacecraft pointing should be avoided for these tests duration.
   GOLF prior to MCC2 early operations should have been preferably performed.

10. SPECIFIC REQUIREMENTS
    

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    Jacques Charra
    Last modification: 29 May, 1995