GOLF Operation - Operation Chronology

Here we aim to list the significant events which modify or interrupt an otherwise stable and continuous observing routine. These are listed in inverse order, with the latest events and news at the start.
Before listing in details the events which have occured during GOLF operations, we list the consequences of these events on the timing of the measurements performed by the instrument. The exact time corresponding to the first measurement of the day (first point of the daily intensity files available in the SoHO archive) is given here.

  • Return to nominal operations on 18th November 2002

    We switched back to the blue-wing configuration.

  • Return to quasi “nominal” operations on 4th March 1999

    With stabilisation of the nominal roll position, the GOLF data is now of good quality. We are still on the red-wing of the profile and have postponed for the moment a decision on whether to stay there, or when to switch over.

  • Partial recovery on 2nd February 1999

    SoHO is in "normal" mode, which means that GOLF data is received. The roll orientation is still being re-configured and is not maintained in the nominal position, so that the data quality is not optimum. However GOLF is not very susceptible to roll offset and the data should still be useable.

  • New SoHO problems starting 21 December 1998

    Following an apparent loss of functionality in the 3rd and last gyro, the spacecraft has been put into a "safe" mode. It will stay in this mode until the project developes a fully qualified procedure for operating SoHO without gyros. This is expected to take 1 to 2 months. In this mode, GOLF is pointed at the Sun centre and rotating slowly about this axis. No science data is being received. It is possible that the GOLF data in this mode would be only slightly degraded. GOLF has asked the project to examine the possibility of receiving the science data, whilst in this safe mode. We are awaiting a response from the project to this suggestion.

  • Strategy adopted in December 1998

    After a discussion on the relative scientific merits of the blue and red wings, a decision has been taken to leave GOLF on the red wing until April 1999, in order to learn how important the seasonal effect will be. This effect causes the red wing point to move deeper in the absorption line profile, which means higher in the solar atmosphere. It is at a maximum in March and should result in a significant reduction in the solar velocity noise background. Depending on the observed magnitude, we will decide whether to switch in April to the blue wing for a new long data set (2 years ?) leading up towards the solar maximum.

  • The situation following recovery in October 1998

    Following the switch-on, the quarter-wave mechanism was found to be rotated by an arbitrary angle from its previous position in June. This may be due to the unforeseen manoeuvres of SoHO, but is more likely due to the switch-on sequence. The performance of the mechanisms was no worse, but also no better than in the past. It therefore took 5 hours of painstaking commands by Jacques Charra to turn the QW to the next valid position at 90 deg. This was all that was possible within the dedicated day allocated to GOLF switch-on. GOLF was then functioning correctly, but in the red-wing mode. This is giving good oscillation data, somewhat limited in quality by the lack of spacecraft thermal stability in its present re-commissioning phase. We are now discussing the option of leaving it in this mode, or returning to the blue- wing only mode. The red wing may have some advantage by looking higher in the solar atmosphere, but is expected to be more sensitive to disturbances from active regions. As we are approaching the maximum of solar activity, this may be unwise. If we decide to change, we will try to do this in the next few weeks, so that we can rapidly resume a new long data-set.

  • The loss of SoHO, June - September 1998

    Data was lost on June 25 1998, when contact was lost with SoHO. Following the re-acquisition and gradual resumption of control, GOLF was switched on October 8 1998. It would appear that all systems are functioning as they were in June.

  • First extended data set, April 1996 - June 1998

    Starting April 11 1996, an extended sequence of observations has been obtained in the blue-wing only mode. On Sept 11 1996, for unexplained reasons, GOLF performed an automatic reset, during which the cell was inadvertently switched off. Although this was rapidly corrected manually, the resulting thermal disturbance takes time to recover. For highly critical work, it may be advisable to reject 2 or 3 days of data following this incident. Otherwise there are no interruptions of comparable duration. On March 3 1998, a spacecraft incident resulted in the loss of some 12 hours of data and a small displacement of our daily timing pulse. This means a shift, as of this date, in the start time of each daily file by 22 seconds, although the absolute timing indicated in the data files remains valid. In spite of these two incidents, we now have a data set of some 804 days, with over 99 % continuity!

  • Limited data set in pre-planned mode, February - March 1996

    The data set from January 18 1996 to February 12 1996 is the only useful data recorder in the full pre-planned mode, which enables the analysis in terms of the global solar magnetic field. From here until the end of March 1996, we lose the magnetic field possibilities, but continue to record data from both the blue and red wings of the solar line profile.

  • Mechanism problems, January 1996 - April 1996

    Some malfunctions of the rotating mechanisms for the polariser and quarter-wave plates began to appear in January 1996 and became progressively worse. The quarter-wave mechanism was stopped on February 12 1998. It was decided finally that it would be better to stop both mechanisms in an optimum position, rather than risk continual perturbations to the regularity of our observations. On April 11 1996, this was accomplished, with the mechanisms correctly set for the blue-wing observing mode

  • Initial Commissioning Period, December 1995 - March 1996

    During this period, the redundant Channel A was commissioned and calibrated. Channel B was exercised only briefly, to ensure that it was fully functional. All sub-systems were commissioned, the temperature of the entrance filter adjusted for optimum stable performance and the optimum cell temperature attained. Tests were carried out on the sensitivity of the measurements to offset pointing, in order to ensure that no trace of the spacecraft residual jitter would appear in the science data. This test were very reassuring. The normal pre-planned mode of operation was started on January 18 1996, although this was later interrupted for further tests.