Derivation of angular velocities of the GRACE satellite formation from the star camera data

The presentation discusses possibilites to derive common frame angular velocities from the star cameras in the GRACE system. Generally the star cameras measure the rotation of each satellite independently from the other satellite. However, common frame rotations are also needed for various applications. Specifically in this presentation we discuss the application to a variant of the differential gravimetry approach. In this, angular rates around the crosstrack component of the so-called instantaneous relative reference frame are needed. The latter is a common reference frame formed by the inter-satellite connection of the two GRACE satellites. We will quantify the accuracy demands on the derivation of the angular velocities and discuss the possibilites to meet these demands with existing star camera observations. We will also give an outlook on new possibilites in the determination of the orientation and the derivation of angular velocities offered by the laser ranging instrument which will be used in the GRACE Follow-On mission.