ESA Science & Technology - No. 48 - Solar Flare Interacts with Rosetta

Apart for routine monitoring activities and the upload of a software patch to the Star Tracker B (on 8 September), a major unexpected event was a solar flare on 8 and 9 September, which hit the spacecraft at the beginning of the weekly non-coverage period. When the signal was acquired for the weekly contact on 15 September the spacecraft was found with the active Star Tracker crashed in INIT mode, and the second Star Tracker (not used for attitude control) in Standby mode.

AOCS had determined the attitude over a period of 6 days using gyroscopes only, and accumulated therefore a drift of about 0.7 degrees, of which 0.3 degrees offset in the High Gain Antenna pointing direction, small enough to allow the RF signal to be received on ground. The recovery activities took most of the ground station pass on 15 September. At the end both Star Trackers were back in Tracking mode and the nominal attitude reacquired.

No payload operations were carried out in the reporting period, and all instruments are switched off, except for SREM which is kept active in the background for radiation monitoring.

A total of 3 New Norcia passes of maximum 10 hours commanding duration were taken over the reporting period.

At the end of the reporting period (DOY 259) Rosetta was at 188.9 million km from the Earth (1.23 AU; one-way signal travel time was 8 minutes 7 seconds). The distance to the Sun was 245.5 million km (1.64 AU).