Friday, December 2, 2011

SDO Weekly Report for December 2, 2011

The FOT and Science Teams monitored Reaction Wheel speeds and instrument performance as the maximum wheel speeds on wheels 3 and 4 slowly rose above 850 RPM. Wheel speed predicts have indicated that the wheel speeds should soon begin reducing on their own, but this has not yet happened. A momentum unload has been scheduled for 12/7 and will be performed if the wheel speeds have not begun to reduce on their own by then.

On 12/1 the FOT began seeing sustained winds of approximately 45 mph at both SDO1 and SDO2 antennas. They contacted SDO personnel at WSC who indicated the latest forecast for overnight was for gusts up to 85 mph. The FOT alerted SSMO management and the Mission Director (MD). A teleconference was held with the SDO Project Scientist, the FOT, the MD and SSMO management to plan for the extreme wind event. It was decided to staff overnight in the MOC and at WSC. After winds at SDO2 exceeded 65 mph for 3 samples within a 5 minute period, SDO2 was automatically braked as of 02:35 GMT on 12/2. The highest wind speed recorded at SDO2 was 74 MPH. After the winds died down, SDO2 was brought back online as of 05:50 GMT with manual workarounds. The automatic recovery of SDO2 failed due to ACA faults, apparently caused by antenna motion while it was braked. SDO1 only experienced a few wind speed readings over 65 MPH and remained on point. However, due to the very high winds, there were Ka band dropouts at SDO1 while SDO2 was braked. There were also subsequent short periods of simultaneous data loss at both SDO1 and SDO2 because of the very high winds. Preliminary estimates put the data capture for 12/2, Day Of Year 336, at 94 percent. Lessons learned from this exceptional wind event will be discussed next week.