Predictive centroiding for single and multiple FOVs star trackers
Additional Document Info
Star centroiding, locating the star image center in a CCD image, is a fundamental process for any star tracker. In this paper, the approximate location of the stars in successive image frames are predicted using the angular velocity as provided by the rate gyro, then the centroid is updated based upon local image processing. When the rate gyro data are not available, then the angular velocity is estimated using kinematics equation and successive attitude estimates from the Lost-In-Space Algorithm. Also of interest are the special features of non-circular star image shapes associated with optical tagging of starlight and/or image smear. And finally, an approach is presented to implement these ideas with recently introduced Active Pixel Sensors, allowing dynamic pixel access and selected subarray analog-to-digital conversion of the pixel information is feasible, with logic dictated by most recent image and the instantaneous angular velocity estimate. The resulting process predicts the CCD starlight locations and thus, we call the resulting algorithm predictive centroiding. The problem of the image smear is also treated, in which the relatively high angular velocity of the Spacecraft will affect the shape of the star images.