SOHO S/C Status SOHO S/C Status On Thursday, March 5th, the SOHO spacecraft returned to normal pointing mode and nominal operations after several unexpected spacecraft events.
On Tuesday, March 3, a spacecraft Warm Start Up occurred, the software onboard the spacecraft reconfigured and a SOHO Telecommunications Subsytem (COMS) Backup occurred. All Remote Terminal Units were reconfigured. The spacecraft clock was reset back to January 1958. Instruments remained on, but the instruments' onboard time could not be reset until the spacecraft clock was reset.
A little over 10 hours later during the Warm Start Up recovery procedures another anomaly occurred: The SOHO spacecraft entered into an Attitude Survival Mode or Emergency Sun Reacquisition (ESR). An ESR reconfigures the entire Attitude and Orbit Control System (AOCS) to the redundant units, and also reconfigures the RF system to the low data rate. Roughly 3.5 hours into recovery from the first ESR, a second ESR occurred. Rough estimates was that the spacecraft moved about 4 degrees in yaw and a bit less than 4 degress in pitch. Three momentum management burns were performed as part of the ESR recovery.
The spacecraft returned to normal pointing mode at the nominal SOHO observing position on Thursday, March 5 at 00:04 UT. The spacecraft emergency ended and no extra DSN support was required. An hour later, instrument commanding was enabled.
Later in early morning hours of March 5, submode patch upgrades were performed. Timeline of events follow below.
The SOHO Science Operations Coordinators
~ 09:02 UT Central Onboard Software (COBS) Warm startup occurred (meaning the software onboard the spacecraft reconfigured) and SOHO Telecommunications Subsytem (COMS) Backup All Remote Terminal Units have been reconfigured. The spacecraft clock has been reset back to January 1958. All instruments are on, but the time cannot be reset to them until the spacecraft clock is reset. ~ 09:31 UT Acquiring Low Rate Telemetry 12:51 UT Clock Adjustment Made 14:11 UT Clock Adjustment Made ~ 14:13 UT Acquiring Medium Rate Telemetry, in Submode #1 (Prelaunch) Have the 4 prelaunch values (Submodes 1,2,3,4) 14:41 UT Spacecraft clock reset to proper time within +/- 1 second. Adjustments will take place over the next few days to bring to within the +/- 20 millisecond specifications ~ 15:07 UT Getting High rate data (VC2) until 16:20 UT 15:09 UT OBT sent to CELIAS, CEPAC, SWAN, GOLF, MDI per OCD #694. 15:15 UT NRT enabled until 15:32 for MDI to resume structure and helioseismology program. MDI back to nominal operations. 18:49 UT Went into RMW mode (lost guide star) 18:51 UT Had an Emergency Sun Reacquistion (ESR) Initial estimates regarding the amount of movement are: ~ 4 degrees in yaw and less than 4 degrees in pitch. Back in Low Rate Telemetry. 20:41 UT NRT enabled briefly for CDS to warm up. (Getting colder faster than last time had an ESR) 22:50 UT Another Emergency Sun Reacquistion (ESR)DOY 063, Wednesday, March 4, 1998
01:15 UT ISA (Initial Sun Acquisition) Mode on ACU A
02:30 UT ISA on ACU B
02:52 UT IRU (Inertial Reference Unit) A stopped
03:25 UT FSA (Fine Sun-pointing Acquisition) mode
04:43 UT RMW (Roll Maneuver Wheels) mode, roll off by 66 degrees
11:07 UT Expect Medium Rate Telemetry and NRT within an hour.
12:14 UT Changed to Medium Rate Telemetry. Expect NRT available
in about 30 minutes.
12:36 UT OBT sent to CELIAS, CEPAC, SWAN, GOLF, MDI per OCD #694.
12:40 UT NRT enabled for 15 minutes. Onboard clock reset, MDI is
restarting structure program. May be some time before more
NRT available. Expect momentum mgt.
X - 14:57 UT 1st Momentum Management Activities Performed
13:35:51 UT, RMW --> CSP transition occured
14:08:08 UT CSP --> RMW transition occured
(Thruster Firings between 13:35 - 14:08 UT)
Fuel estimate low ~ 50 grams.
~14:57 UT NRT enabled briefly for UVCS to send commands to warm
themselves up.
15:47 UT OBT distribution sent to SUMER
16:39 UT Performing Roll back to nominal position.
NOTE:
As of this writing at ~ 16:41 UT, the spacecraft clock
is now +/- 134 milliseconds. The FOT will perform more
commands later today to get the clock to within +/- 20
milliseconds, THEN they will run the "PROC V_FL_SYNCHR"
procedure for VIRGO before 00:00 UT.
~ 18:00 UT Informed that another momentum management is needed
(will take place in roughly an hour or so..)
Relevant teams contacted. Fuel estimate low ~ 50 grams.
after 18:00 Contacted Walter Schmidt for SWAN (after previous
phone call discussions).
OCD written to perform additional/verification of -Z
sensor safing, prior to 2nd Momentum Management.
~ 19:25 UT 2nd Momentum Management
19:25:35 UT RMW --> CSP Transition
19:41:47 UT CSP --> RMW Transition
~ 21:26 UT NRT enabled briefly for LASCO prior to
3rd Momentum Management
~ 22:02 UT 3rd Momentum Management
22:02:11 UT RMW --> CSP Transition
22:19:53 UT CSP --> RMW Transition
~ 22:57 UT Clock Adjustment
~ 23:01 UT Starting FPSS procedure to move 3.3 arcminutes North
~ 23:06 UT FPSS offset procedure complete.
~ 23:42 UT Virgo procedure V_FL_SYNCHR performed.
DOY 064, Thursday, March 5, 1998
00:04 UT RMW to NM transition
00:45 UT S/C Emergency Ended. No longer need to request
extra DSN support.
~ 01:09 UT Running n_fl_llockout procedure for SWAN. (Unsafing).
01:40 UT Send delayed command file to recover CELIAS STOF
from safing prior to Momentum Managements.
~ 01:50 UT Brought VC2 online and NRT for instrument commanding.
(CDS, UVCS, and MDI).
03:07 UT Instrument teams done commanding and science resumed.
Begin Submode patches
Uplinked Submode #5
Uplinked Submode #2 patch upgrade
~03:37-03:41 UT Switched to Submode #5
Patched Submode #1 --> Submode #6
~03:53-03:56 UT Switched to Submode #6
Note: Submode #3 patch upgrade delayed, original
Submode #3 launch configuration onboard.
CDS --> 144 packets
LASCO/EIT --> 24 packets
03:57 UT Had to go to record due to DSN station problems
04:02 UT Quick successful LASCO commanding to get science going in
Submode #6, before LOS at 04:05
At roughly 04:05 UT, able to get a down-link only station,
however, cannot command recorder off. MDI notified.