Spacecraft Maintenance & Status Information
Starting on September 24, the SOHO spacecraft will undergo
a week-long period of software uploads and maneuvers to
commission a new gyroless operating mode.
Many of SOHO's instruments will be placed into a safe
configuration until these activities end (anticipated
October 4, 1999). Most instruments will not be providing
real-time images during this period.
Story on ESA Science News:
new software works perfectly -scientists and engineers overjoyed.
October 4/5, 1999
A guide star release and recovery test was performed on October 4
in normal pointing mode, concluding successfully the implementation
of the gyroless SOHO software system. The post operations meeting
confirmed the readiness of the spacecraft to resume normal science
operations. SOHO is now in a more robust condition
for the future.
Instrument recovery operations to prepare for normal operations
were initiated on October 4, and will continue through October 5.
October 2, 1999
The momentum management, station keeping, and reaction wheel #4
maintenance activities were performed as planned, and SOHO was
placed in normal pointing mode for the night.
No spacecraft operations are scheduled for Sunday October
3. Operations planned for Monday October 4 include a number of
instrument recovery activities to prepare for normal operations.
October 1, 1999
The star sensor unit patch was uploaded as planned while
SOHO was in Coarse Roll Pointing (CRP) mode. The new CRP
mode continued to function very satisfactorily:
During last night the CRP mode was run for 15 hours with drift
compensation; the residual drift was -0.03 degrees.
The spacecraft was placed in Roll Maneuver Wheels (RMW)
mode, and movements in pitch, roll, and yaw were
performed. These tests verified the functioning of the
modified RMW mode. The spacecraft was then restored to
nominal pointing. SOHO was left in Roll Maneuver Wheels
(RMW) mode for the night.
September 30, 1999
Yesterday's roll maneuver was continued in steps of
about 90 degrees at a time, to test the Coarse Roll Pointing
(CRP) mode stability in all four quadrants. By the end of the day,
SOHO had completed a full turn, returning to its nominal orientation,
and will spend the night in CRP mode.
September 29, 1999
SOHO was placed in Coarse Roll Pointing (CRP) mode and moved
in pitch, yaw and roll to exercise and verify the functioning
of the attitude control system in CRP mode. The spacecraft
was then moved through -74 degrees in roll (from +2 to -72
degrees) and left at that position for the night, still in
September 28, 1999
The experiment off-pointing test verified that all 4 instruments
groups set to receive the off-pointing flag reacted as expected
(LASCO/EIT, UVCS, MDI, SUMER).
The spacecraft was moved in pitch, roll and yaw while in normal
pointing mode to exercise and verify the functioning of the new
attitude control system. Other tests performed during the day
included thruster monitoring and reaction wheel speed monitoring
Momentum management burns in preparation for roll maneuver tomorrow
were completed before placing the spacecraft in normal pointing
mode for the night.
September 27, 1999
The remainder of the Gyroless on-board software was uplinked
and verified successfully. Several spacecraft transitions
were successfully made into and out of the new Coarse Roll Pointing
(CRP) mode. The spacecraft was placed into its normal pointing mode
at the end of the day.
September 24, 1999
The first portion of the Gyroless on-board software was successfully
uplinked to an unused memory section.
Last modification: June 28, 2004
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