SOHO recovery actions continue
1 December 1999On Tuesday 1 December at 18:46 UT another SOHO spacecraftemergency was declared in order to secure Deep Space Network (DSN) contact with 34-metre antennas, after amanual triggering of the Emergency Sun Reacquisition (ESR) mode at about 18:40 UT.At about 18:10 UT, SOHO was in the middle of astationkeeping (orbit trim) manoeuvreRoll Pointing (CRP) mode was invoked automatically and the thruster burns were aborted. The cause of this anomaly is yet to be determined.
The ESR mode was triggered because the spacecraft was rolling while in CRP mode using the High Gain Antenna (HGA). The HGA has a narrow beam width which needs to be accurately pointed towards the Earth. A significant, unplanned roll excursion causes the HGA to be mispointed, with loss of signal as a result.
The ESR mode was triggered to ensure low rate telemetry through the low gain antenna which has a much wider beam.
Low rate telemetry was acquired from the spacecraft at 19:18 UT through the Goldstone DSN station, and analysis of the telemetry is ongoing to determine the cause of the anomaly and the course of action to be taken.