Establishing spacecraft's relative orbit and attitude coupling dynamics model based on screw theory

Considering the strong coupling between the orbit and attitude of two spacecraft in relative motion, based on the assumption of rigid body dynamics and the screw theory, we deduce and establish their orbit and attitude coupling dynamics model and analyze the orbit and attitude coupling effect. Considering that the dynamics model is strongly coupled and nonlinear, we design its nonlinear feedforward control law, which has a good control precision and stability and is suitable for the short-distance and in-orbit operations that have time constrains. We simulate the effectiveness of the orbit and attitude coupling dynamics model and the nonlinear feedforward control law; the simulation results, given in Fig. 1 through 6, and their analysis show preliminarily that: (1) both the relative speed and angular speed of the two spacecraft converge to zero, there being no change in their relative position and attitude and the whole control process reaching the desired value within 200 seconds; (2) the orbit and attitude coupling model we thus designed can be used for spacecraft's short-range randezvous and the nonlinear feedforward control law can satisfy the precision requirements for in-orbit operations.