HST Two-Gyro Handbook Update for Cycle 14 Phase II Proposals
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1.1 Introduction
The HST Two-Gyro Handbook is the primary reference for issues related to Hubble Space Telescope observations conducted with an attitude control system relying upon just two gyroscopes. This update to the HST Two-Gyro Handbook summarizes recent progress in understanding the telescope pointing and instrument performance while HST is operating in two-gyro mode. In this mode, two gyros are used in combination with the Fine Guidance Sensors to provide fine-pointing information while science observations are being conducted.
On-orbit tests of the HST two-gyro fine guiding mode and its impact on science instrument performance were carried out on 20-23 February 2005. Gyro #1 was removed from the pointing control loop, and Gyros #2 and #4 were used with the FGS to control the HST attitude during all science observations. The control law used during the test was the same as the one that will be used when HST enters two-gyro mode (either deliberately or as a result of gyro failure). More than 450 science exposures were obtained with the Advanced Camera for Surveys (ACS), the Near Infrared and Multi-Object Spectrograph (NICMOS), and the Fine Guidance Sensors during the three day test.
The ACS, NICMOS, and FGS instrument teams are analyzing the data from these tests. Early analyses of those data indicate that the HST instrument performance is excellent. A series of detailed Instrument Science Reports will document the results from these tests, which are summarized briefly below.
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