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Moving Target Observations in Two Gyro Mode
There will be very few restrictions on Moving Target observations in Two Gyro mode. These targets will be subject to the same reduction in overall scheduling flexibility as are fixed targets.Operations in Three Gyro mode provided for a 2 degree radius cap around the anti-sun direction in which observations at any roll orientation can take place. This had occasionally been useful for observations of planets at opposition. The radius of this cap is reduced to 1 degree in Two Gyro mode.
There are several pointing control options previously available that will not be available in Two Gyro mode. These have been used rarely in recent cycles. Options no longer possible are:
- observing in Gyro-only mode, as the pointing errors in the equivalent mode will be degrees, rather than arc-seconds.
- starting observations under FGS control and transfer to Gyro-only mode as the guide stars leave the FGS field-of-view.
- starting observations under FGS control and "hand-off" to a second pair of guide stars as the observations proceed.
The Two Gyro Science Mode web site can be found at: http://www.stsci.edu/hst/HST_overview/TwoGyroMode