Adaptive tracking control of spacecraft relative motion with mass and thruster uncertainties

This study presents adaptive tracking controls of relative position between two spacecraft in the presence of uncertainties in the thrust alignments and gains, and the active spacecraft's mass. The proposed methods are based on the equations of motion expressed in the general second-order form with trajectory-controllable Hamiltonian systems, which makes it possible to use some useful physical properties in the control law design. Unlike most of the previous works, the control laws are presented not only for the Cartesian coordinates, but also for the spherical coordinates in Keplerian orbits whose dynamic equation is highly complicated but reflects the actual measurement environment (laser/microwave based) and thus is more suitable in real applications. The proposed adaptive algorithms are developed utilizing the smooth-projection algorithm in order to deal with the uncertainties in the actuator model. Numerical simulations show that the proposed adaptive scheme successfully achieves the relative position tracking within a small level of error in the whole process, compared with the non-adaptive scheme.