Wide Field and Planetary Camera 2 Instrument Handbook Update for Cycle 15

1.1 WFPC2 and Two-Gyro Mode

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Two-gyro mode is expected to have no impact whatsoever on WFPC2 imaging performance. This expectation is based largely on extensive on-orbit imaging tests carried out with both ACS and WFPC2 in February 2005. The gyro set and implementation details will be somewhat different between the February 2005 test and GO observing, so there is some remote possibility of unexpected effects. Additional tests are planned in August 2005 to address these concerns.

There are, however, significant impacts from two-gyro mode on target scheduling. These are discussed in the HST Two-Gyro Handbook and are implemented in the APT planning tools.

HST fine-pointing and instrument performance in two-gyro mode is expected to be indistinguishable from the performance observed in three-gyro mode.