| Description: The commanded lock of the Fine Guidance Sensor during the observation. For HST data files, this is the value of FITS keyword FGSLOCK. Common values are: - FINE: Fine lock on guide stars using two Fine Guidance Sensors. This is the most accurate pointing option, within 0.2 to 1 arcsec. - COARSE: Until new flight software (version 9.6) came online in September 1995, if the guide star acquisition failed, the guiding dropped to COARSE track. - GYRO: This mode produces the least accurate absolute and relative pointing. Absolute pointing accuracy is about 2-50 arcsec and drift is 1-5 mas/sec. - FINE/GYRO: Fine lock on a guide star using one FGS to control the pitch/yaw of the spacecraft, while roll control is handled by the gyros. Absolute accuracies can range from 0.5-5 arcseconds, while error due to roll drift about the guide star would be ~ 1-2 mas/sec. - UNKNOWN: Check the jitter files to find out what happened during the observation. |