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This study is mainly focusing on the problem of spacecraft close-range proximity with obstacle avoidance in the presence of complex shape. A novel Gaussian mixture model–based nonsingular terminal sliding mode control (GMM-NTSMC) is proposed. This is achieved by developing GMM-based potential function with a switching surface of NTSMC. It is theoretically proved that the closed-loop system is globally stable. The main contribution of this study is that the GMM-based avoiding strategies, which include the GMM-based terminal sliding mode control (GMM-TSMC) and GMM-NTSMC, can solve the collision avoidance problem considering complex shape while the artificial potential function–based terminal sliding model control (APF-TSMC) fails. Moreover, the GMM-NTSMC and the GMM-TSMC require less energy with respect to the APF-TSMC. Furthermore, the GMM-NTSMC retains the advantage of the NTSMC and can avoid singularity problem while GMM-TSMC cannot. Finally, numerical simulations are performed to verify the effectiveness and superiority of the proposed GMM-NTSMC. [ABSTRACT FROM AUTHOR]

In terms of the motion planning problem of spacecraft proximity operations with obstacle avoidance under low uncertainty, the improved equal-collision-probability-curve and improved linear quadratic regulator (IECPC-ILQR) strategy is proposed. Firstly, the novel function of the IECPC algorithm is developed to generate the avoidance control impulse. Subsequently, the ILQR is designed to track the reference trajectory. Furthermore, combining the improved ECPC algorithm with the ILQR controller, the composite controller of the IECPC-ILQR strategy is obtained and is implemented on the chaser spacecraft. Compared with the traditional ECPC algorithm, the IECPC-ILQR strategy can avoid collision in the presence of low uncertainty. Furthermore, the proposed avoidance strategy can obtain higher control precision while requiring the same fuel. Finally, numerical simulations verify the effectiveness of the proposed IECPC-ILQR strategy. [ABSTRACT FROM AUTHOR]

In this paper, the problem of autonomous rendezvous and docking with a non-cooperative target spacecraft is studied. A coupled translational and rotational dynamics of the spacecraft is used, where the rotation matrix is used to represent the attitude of spacecraft to overcome the drawbacks related to the unwinding. An asymptotically stable autonomous rendezvous and docking collision-free controller is proposed based on a novel designed sliding surface. Then, a new nonsingular terminal sliding surface is given, based on which the developed autonomous rendezvous and docking collision-free controller can make the tracking errors converge into a small bounded area near the origin in a finite time. Using artificial potential function and virtual obstacles model established based on cissoid, both controllers ensure the chaser spacecraft strictly remains in the safety area to avoid the collision with the target spacecraft. The effectiveness of the proposed controllers is demonstrated by numerical simulation. [ABSTRACT FROM AUTHOR]

A novel guidance strategy is developed based on the artificial potential function for a chaser spacecraft to autonomously approach a freely tumbling target in the on-orbit servicing missions, which can generate the desired velocity instruction for the chaser spacecraft. Considering the collision avoidance constraints, the motion of the tumbling target is classified into three cases. The tumbling axis of the target is perpendicular to its docking port axis in Case 1, and the two axes are nonorthogonal in Case 2, and the two axes are in line in Case 3. Different safe boundaries are established for Case 1 and Case 2, and the desired velocity instruction is determined using the novel guidance strategy, respectively. The method for Case 3 is similar to Case 2. A sliding model controller is designed to control the chaser spacecraft to satisfy the desired velocity instruction. Numerical simulations are performed, and the results show that the developed guidance strategy is an effective method to solve the problem of autonomously approaching a tumbling target. [ABSTRACT FROM AUTHOR]