Relative Attitude Trajectory Tracking Using Line of Sight Measurements under Spacecraft Position Dynamics

This paper considers the problem of controlling relative attitude between two spacecrafts, so as to follow a smoothly time varying desired relative attitude trajectory. The spacecrafts are modelled as rigid bodies and attitudes are represented in non-linear state space of SO(3). The attitude control law proposed does not need relative attitude measurement and is determined from line of sight (LOS) unit vectors measured by spacecrafts to each other and from each spacecraft to a common object in respective body fixed frames. Unlike existing control laws using LOS measurements, positions of spacecrafts are not considered fixed. The state feedback laws proposed in this work guarantee almost global asymptotic tracking of the desired time varying attitude trajectory, when positions of spacecrafts do not become collinear or coincide. The simulation results of the proposed control law are also shown.