... Unless requested, all observations will be scheduled with FINE LOCK guiding, which may be one or two guide stars (dominant and roll). ... If the acquisition of the second guide star fails, the spacecraft guidance, GUIDEACT, may drop from FINE LOCK to FINE LOCK/GYRO, or even to GYRO, which may result in a target rolling out of an aperture. ... The jitter values will be increased because FINE LOCK was not used. ... Observations are scheduled with FINE LOCK acquisition, i.e., with two or one guide...