uses electrically driven reaction wheels to perform all slewing required for guide star acquisition and pointing control. A separate set of rate gyroscopes provides attitude information to the pointing control system (PCS). The slew rate of HST
is limited to approximately 6° per minute of time. Consequently, about one hour is needed to go full circle in pitch, yaw, or roll. After the telescope arrives at the new target, attitude updates and guide star acquisitions take an additional 13 minutes.
As a result, large maneuvers are costly in time and are generally scheduled during Earth occultation or while crossing the SAA (see Section 2.2.2