1. STScI
2. HST
3. Two Gyro Mode Handbook

	HST Two-Gyro Handbook

1.3 Guide Star Acquisitions

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There have been no losses of fine lock resulting from large pointing disturbances during any of the science observations obtained to date in two-gyro mode. Loss of lock has occurred during guide star acquisitions, but most of these failures have been traced to either bad guide stars or to minor problems during the process of entering fine lock from coarser pointing conditions. The former problem of bad guide stars existed for three-gyro acquisitions as well, and should be alleviated in part by the use of the new Guide Star Catalog 2. The remaining problems have been largely overcome with minor changes to the flight software. The acquisition success rate in two-gyro mode is roughly 96%, compared to 98% previously in three-gyro mode.