BLOGS: Commissioning updates of new gyroless operation mode (24 September 1999 - 5 October 1999)

On September 24, the SOHO spacecraft underwent a period of software uploads and maneuvers to commission a new gyroless operating mode.

Many of SOHO's instruments were placed into a safe configuration until these activities end. Most instruments were not providing real-time images during this period.

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 CRP mode.

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 triggers.

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.