SOHO enters – and recovers from ESR (safe) mode

July 30, 2001

Update of plans as of 01:00 UT:

Only one of the burns of the momentum management will take place before 02:00 UT. Then the DSN coverage will be returned back to Wind. After 08:30 UT, the other two segments will be run. Also, the launch of Genesis has been already postponed for 24 hours, so there is a chance for doing the station keeping later today if we get enough DSN time and the input from FDF. The decission will be taken whenever these two conditions are resolved, and not by the 1 PM EDT time mentioned yesterday.

Status of the spacecraft as of 13:00 UT:

SOHO is in RMW mode. The remaining two segments of the momentum management were completed this morning by 10:45 UT. At about 14:00 UT there will be a roll trim and later today the spacecraft will be brought to Normal Mode. The DSN coverage has changed: If FDF has an orbit solution, the station keeping maneuver will take place tomorrow after 12:00 UT. Otherwise, on the night (EDT) from Wednesday to Thursday.

Status of the spacecraft as of 15:00 UT:

SOHO is back in normal mode.

July 29, 2001

SOHO is, since 03:35 UT, in Coarse Roll Pointing mode. The emergency declared to secure additional DSN coverage was lifted two minutes afterwards, at 03:37 UT. There will not be any additional recovery activities until 15:00 UT at the very earliest.

Status of the spacecraft as of 14:00 UT:

All instruments are safe, and SOHO is in CRP mode with a roll attitude of +162.3 degrees. Target roll attitude is +4.59 degrees, so there will be a roll of some -158 degrees later today. Current plans are: Transition to medium rate telemetry (2 hours), roll back to nominal attitude (5 hours), and momentum management (2 hours thruster burn). Later on, still not scheduled, there will be an station keeping maneuver which will push the need for the regular one from early October to December or perhaps even later. Another review of the spacecraft status will take place this evening (EDT). Note: There will be difficulties in obtaining additional DSN support tomorrow, beyond what is already scheduled, because of GOES operations, the Genesis launch, and the MAP lunar swingby, so some activities might be postponed to later in the week.

Status of the spacecraft as of 23:00 UT:

At 16:33 UT SOHO transitioned from low rate to medium rate telemetry, submode 6. Then the roll back to nominal attitude was started and some instrument teams were already able to upload commands. The roll maneuver was completed at 22:45 UT. The current plan is to load the SSU patch and then run a three segment momentum management, which will be two hours long. Further plans will depend on the launch of Genesis tomorrow. If the launch goes ahead as scheduled, the station keeping maneuver will be postponed until Wednesday. Otherwise, it will be attempted tomorrow if we obtain enough DSN time and FDF has by then an orbit solution. The course of action will be decided tomorrow at 1 PM EDT.

July 28, 2001

SOHO entered ESR (safe) mode after an attitude control unit (ACU) reset at 20:16 UT. At the time, there was contact with the spacecraft by means of D27. Because of the communications restrictions with D27, an spacecraft emergency was declared at 20:33 UT in order to secure another DSN station, which was brought up at 21:00 UT.

Two thruster firings were used to reduce the roll rate of the spacecraft.

The current plan calls for transitioning to CRP mode tonight. Tomorrow morning Eastern time there will be a status meeting with FDF to discuss the recovery timeline.