Line-of-sight based formation keeping and attitude control of two spacecraft

We consider coupled attitude and position control of two spacecraft where absolute attitudes are not available. The objective is to attain a formation requiring a desired distance between two spacecraft and alignment of attitudes along the inertial line-of-sight (LOS) direction between the center of masses of the spacecraft. A relative attitude and position control scheme is developed using LOS vectors measured in each spacecraft's body frame. The current work differs from past research in the sense that the relative positions of the two spacecraft are not assumed to be fixed and all control laws are obtained in respective body fixed frames. The state feedback laws put forth in this work guarantee almost semi-global asymptotic stability of the desired closed-loop equilibrium configuration.