SOHO Status Report - February 2005
10 March 2005 15:11Mission Status
The spacecraft status is nominal, with the High Gain Antenna (HGA) Z-axis in a fixed position. On 8 December 2004 the spacecraft transitioned into Emergency Sun Re-acquisition mode (ESR-24). The reason was a false trigger of the Coarse Sun Pointing Attitude Anomaly Detector (CSPAAD), most likely caused by a particle crossing the CSPAAD field-of-view. The particle probably came from the Fine Sun Pointing Attitude Anomaly Detector (FSPAAD), which was obstructed since April 2004 (cause of three ESRs) and is now clear.
On 21 December a nominal manoeuvre (station keeping, momentum management and roll) was performed. 0.3808 kg of fuel was used. The delta-V shortfall was a mere 0.00006 ms-1. The remaining hydrazine is 118.8 kg. The solar array degradation after 108 months of flight is 16.51%, which corresponds to 1.83% per year. The spacecraft downlink was affected by RFI from the P92-3 USAF Satellite on 22 and 24 October and 1, 2, 3, 6, 7 and 12 November for duration of a few minutes each. In order to better prepare for such RFI's, ESOC, together with the US Department of Defence, is investigating the possibility of getting information ahead of time.
On 26 December 2004, the Solid State Recorder (SSR) memory unit number 12 switched itself off (over-current trigger mechanism). The unit is remaining switched off while an investigation is ongoing. This was the second occurrence of a memory unit self switch-off. The first occurred in September 2000. That unit was re-activated later without any problems. One of two (redundant) detectors in the SUMER UV spectrograph is showing signs of degradation to the point that the PI has instituted end-of-life observing plans (observing bright sources to use remaining photon sensitivity before loss of entire detector). All science objectives are still achievable with the other detector.
Operations and Archiving
All other instruments are nominal and SOHO science operations are progressing smoothly. The use of the on-board patch for intermittent recording of selected packets was an unambiguous success for the winter keyhole. VIRGO, GOLF, and MDI low-bandwidth data was captured continuously through the whole period. LASCO telemetry was also recorded for parts of the keyhole. Links to the SOHO archives (including mirrors) are accessible at http://soho.estec.esa.nl/data/.
A joint RHESSI, SOHO, TRACE workshop was held on 8-11 December 2004 in Sonoma, California, on the topic "Coordinated Observations of Flares and CMEs". The workshop was attended by over 140 participants. It was oriented towards the synthesis of data from the three space missions and ground-based data. With the emphasis of the workshop being on actual research work, there were no set presentations other than four introductory talks. To maximize the exchange of ideas and foster new research arrangements, the workshop was organized around seven parallel working groups.