This study presents a tracking control strategy for spacecraft proximity operations subjected to kinematic couplings, input saturation, modeling uncertainties, and external disturbances. First, a coupled six degrees of freedom dynamics is modeled to depict the relative motion between the pursuer and target spacecrafts. To address the input saturation problem, a dead-zone operator-based model is introduced. Subsequently, a finite-time controller is proposed by exploiting the non-singular integral terminal sliding mode method. By employing the adaptive technique, the proposed control strategy enjoys the feature that it can avoid requiring the prior knowledge of the lumped uncertainty's bounds. Using the Lyapunov theory, the designed controller is proved to guarantee that the translational and rotational tracking errors can converge to the origin within finite time. Finally, numerical simulations are performed to illustrate that the developed control scheme possesses a strong robustness, a fast convergence rate, input saturation elimination as well as chattering suppression.
K E Y W O R D Sadaptive finite-time control, input saturation, non-singular integral terminal sliding mode control, spacecraft proximity operations
INTRODUCTIONThe technology of autonomous rendezvous and docking has aroused considerable attention due to its wide application. [1][2][3] The whole phases include the homing phase, closing phase, translation phase, and proximity operation. The last two phases are quite crucial because two spacecrafts could suffer from collision 4 during the docking procedure. The proximity phase is to force the pursuer along a predetermined orbit toward the docking port. Generally, the key difficulty of the proximity phase is to develop special strategies for synchronously controlling the relative position and attitude between two spacecrafts. This work investigates a robust controller for spacecraft proximity operations (SPO) to gain the prerequisite for the propitious rendezvous and docking. Still, the dynamic modeling and controller design for the SPO problem is very important. First, linearized Clohessy-Wiltshire equations 5 were used to describe the relative translation for circular reference orbits. Afterwards, a multitude of variants 6,7 on the nonlinear models was reported for the arbitrary orbital eccentricity.