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4.5 Maneuvers

With the original three-gyro operating system, the telescope could be slewed only along one axis (i.e. pitch, yaw, or roll) at a time when moving from one target to another. The two-gyro/FSS control system permits pitch slews (changing Beta) and "sunline" slews (a rotation at a constant Beta, a combination of yaw and roll motion). The sunline slews increase the efficiency of many maneuvers at lower Beta angles, when compared to those under the three-gyro control system. Normal slew rates are in the range of 3 to 6 degrees per minute. However, in order to maintain accurate attitude control and adequate power, the solar panels must remain optimally oriented toward the sun to within fairly narrow limits. These constraints on solar panel orientation may require maneuvers longer than expected, if only the great-circle distance between two targets is considered. Additional information is given in Section 2.4.

Maneuvers normally require 3 to 5 minutes for calculation and proper configuration of the spacecraft for the maneuver. A typical maneuver requires 30 minutes to perform, although careful choice of targets can keep this overhead to a minimum. Some functions, such as camera preparations, can be performed during the slew. After the maneuver, 15-20 minutes are normally needed to identify the target, trim the gyros, move the telescope so that the target is in the aperture, locate a guide star, and begin the exposure.

Last updated: 11 June 1997