1. STScI
2. HST
3. Two Gyro Mode Handbook

	HST Two-Gyro Handbook

2.4 Two-Gyro Orbit Calculations for Phase I

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The visibility period for two-gyro observations should make use of the two-gyro visibility periods from the plots and tables described in this chapter. The tools for creating these plots and tables are available on the Two-Gyro Science Mode web site. Exposure times for two-gyro observations should be calculated with the appropriate two-gyro exposure time calculators (ETCs) for each instrument. In most cases, these are the same ETCs as were used for three-gyro mode since the instrument performance in both cases is nearly indistinguishable. Links to these ETCs can be found on the main web page for each instrument.