FY-4 Imager: Visible Channel Star Sensing

FY-4 geostationary operational environmental three-axis stabilized satellite imager visible channel has a 16-channel visible detector array. This visible array performs earth-observing and star sensing. At intervals of approximately 30 minutes, the earth-observing operation is interrupted and the sensor transitions into starsense mode. In this mode, the sensor is commanded to observe four preselected stars, preferably in the corners of its 23° by 21° field of regard. Differences between predicted and actual star positions are used to determine the spacecraft payload attitude and to compensate for radiometer pointing errors due to orbit, attitude drift and thermal distortion. Star sense uses two-axis scan mirror, optical system and visible channel electronics of the imager.