The coupled and decoupled relative navigation algorithms for rendezvous and docking of a malfunctioned spacecraft

It is important to estimate relative states including translational and rotational parameters in robotic on-orbit service. Coupled and decoupled relative navigation algorithms are proposed to estimate relative position and velocity, attitude and angular velocity of a target satellite by using a binocular stereo-vision system. The coupled navigation algorithm estimates the translational and rotational parameters simultaneously by using an EKF tool. The CW equations and attitude dynamics equations are combined together as the state equations, and the measurement equations are derived according to the relationship between the image point coordinates and the states. Compared to the coupled algorithm, a preprocessing method is proposed to divide the coupled model into two parts: a translational part and a rotational part. The two algorithms are evaluated by executing mathematical simulations, and the results show that both algorithms can estimate the states effectively and the two algorithms have different performances: the convergence time of the decoupled algorithm is shorter and the estimation accuracy of the coupled algorithm is better.