Determination of a spacecraft attitude motion by measurements of four star sensors

The star sensor BOKZ-M60 allows to find parameters that define the attitude of its own coordinate system with respect to an inertial one by observing regions in the sky. We describe techniques for processing measurements of the set of four star sensors BOKZ-M60 located onboard the spacecraft Resurs-P2, and we give examples of processing the measurements obtained in the time interval of more than three orbit revolutions (19003s). The spacecraft was in orbital orientation at that time. Joint processing the measurements of four sensors allowed to associate with their set the universal coordinate system. This system agrees with the model of spacecraft attitude motion with root-mean-square errors less than 0.4$''$. The attitude of the universal system relative to the spacecraft device system was determined by measurements of the spacecraft angular rate. The root-mean-square errors of this determination on angles of rotation around the axes of the universal system are 0.044$^\circ$, 0.051$^\circ$ и 0.18$^\circ$. Low frequency (with frequencies less than 0.05 Hz) variations of star sensor own coordinate systems relative the universal system were not exceed 10$''$. These variations were seemed to be periodic with main frequency equal to the orbital frequency. Mean squared values of a high frequency component of those variations were not exceeded 18$''$.