SOHO in safe mode
21 December 1998At 17:49 UTC on 21 December, the SOHO Spacecraft went intoEmergencySun Reacquisition (ESR). Following a successful gyro calibrationmanoeuvre,prior to a planned orbit correction and momentum wheel managementactivities,the last of SOHO's gyros (Gyro B) failed to give the expected output.This occurred during transition from normal mode to momentum dumping mode,and resulted in the spacecraft transitioning into ESR-10.
The spacecraft is currently in ESR mode under open-loop real-time control from the ground. In this mode the spacecraft is sun-pointing and is stable from the power and thermal point of view. The payload remains switched on, but no science observations are being performed. This procedure was established and used successfully in the recovery phase. Current plans are to continue to control the spacecraft in this way, and reassess the situation in early January.