Non-contact debris removal methods are fuel-efficient in a single operation compared to contact-based strategies as spacecraft don’t need to match debris velocity. To comprehensively analyze this scheme, maneuvering schemes for maximum debris removal with minimum fuel consumption, including task assignment, sequence planning, and trajectory planning, must be formulated. The coupling between variables’ dimensions and optimization results in task assignment poses challenges, as debris removal is repetitive and uncertain, leading to a vast search space. This paper proposes a novel Greedy Randomized Adaptive Search Procedure with Large Neighborhood and Crossover Mechanisms (GRASP-LNCM) to address this problem. The hybrid dynamic iteration mechanism improves computational efficiency and enhances the optimality of results. The model innovatively considers unsuccessful single removal by using a quantitative method to assess removal percentage. In addition, to improve the efficiency of sequence and trajectory planning, a Suboptimal Search Algorithm (SSA) based on the Lambert property and accelerated Multi-Revolution Lambert Problem (MRLP) solving strategy is established. Finally, a real Iridium-33 debris removal mission is studied. The simulation demonstrates that the proposed algorithm achieves state-of-the-art performance in several typical scenarios. Compared to the contact-based scheme, the new one is simpler, saving more fuel under certain conditions.

This paper proposes a novel distributed control method for surrounding a noncooperative target that has maneuverability by spacecraft formation. A relative orbit error dynamic model between the target and the formation is established dependent on a reference spacecraft under the 2-body assumption. To estimate and compensate for the target’s control input rapidly, a novel finite-time extended state observer is developed. It is stable in the sense of fast finite-time uniformly ultimately bounded stability. A fast terminal sliding mode controller is proposed for finite-time convergence of the system. Simulation examples are implemented to show the effectiveness of proposed algorithm.

Focusing on the non-concave trajectory constraint, a sliding-mode-based nonsingular feedback fast fixed-time three-dimensional terminal guidance of rotor unmanned aerial vehicle landing, planetary landing and spacecraft rendezvous and docking terminal phase with external disturbance is investigated in this paper. Firstly, a fixed-time observer based on real-time differentiator is developed to compensate for the external disturbance, whose estimation error can converge to zero after a time independent of the initial state. Then, a sliding surface ensuring fixed-time convergence is presented. This sliding surface can guarantee that the vehicle achieves a non-concave trajectory, which is better for avoiding collision and maintaining the visibility of the landing site or docking port. Next, the nonsingular guidance ensuring the fixed-time convergence of the sliding surface is proposed, which is continuous and chatter free. At last, three numerical simulations of Mars landing are performed to validate the effectiveness and correctness of the designed scheme.