Estimating the Accuracy in Determining Orientation Parameters by the BOKZ-M60 Star Tracker

Resumo

We investigate the precision in the readings of the star tracker BOKZ-M60 obtained in the dynamic field testbed of the Space Research Institute of the Russian Academy of Sciences (SRI RAS). The testbed features a mobile platform, on which a star tracker is mounted, which scans the starry sky. The platform movement is controlled by a PC, however, the values of the rotation angles in the platform hinges are not known with the desired degree of accuracy. In testing star trackers, the error in the known platform orientation must be around 1″, which corresponds to an error in determining the linear coordinates of the platform reference points of less than 3 μm. It is difficult and expensive to organize outside measurements of the movement of a mobile object with such accuracy. For this reason, the following accuracy estimation scheme is used. We consider comparatively long series of the determined orientation parameters obtained by the tracker in the testbed. With the help of a suitable mathematical model, a detailed reconstruction of the actual rotational motion of the tracker is performed based on these measurements. In this reconstruction, the residuals in the tracker readings are calculated. Based on the analysis of the residuals, conclusions are drawn about the accuracy of the tracker. As it turns out, the accuracy of determining the optical axis of the tracker lens depends on the angular velocity of the platform and lies in the range from 2″ to 25″