This brief is devoted to the fixed-time six-DOF tracking control problem for noncooperative spacecraft fly-around mission in the presence of the parameters uncertainties and disturbances. First, a new and coupled six-DOF relative motion dynamic model without using any target orbital information is established. Subsequently, a novel nonsingular fixed-time terminal sliding mode (NFTSM) with bounded convergence time in regardless of the initial states is designed, which not only can circumvent the singularity problem, but also has faster convergence performance than fast terminal sliding mode. By employing the designed NFTSM and the adaptive technique, a continuous adaptive nonsingular fixed-time fast terminal sliding mode control strategy with no information of the mass, inertia matrix, and disturbances is proposed, which can eliminate the chattering phenomenon and guarantee the fixed-time reachability of the relative position and attitude tracking errors into the small regions containing the origin. Finally, the performance of the proposed control schemes is demonstrated by numerical simulations.

This paper is devoted to the fixed‐time consensus tracking control for second‐order multi‐agent systems with bounded input uncertainties under a weighted directed topology. Firstly, a novel non‐singular fixed‐time fast terminal sliding mode (NFFTSM) surface with bounded convergence time in regardless of the initial states is designed, and the explicit expression of the settling time is provided. Fair and unprejudiced comparisons show that the proposed NFFTSM has faster convergence performance than most typical terminal sliding modes in the existed results. Subsequently, by employing the proposed NFFTSM, a non‐singular fixed‐time distributed control protocol for second‐order multi‐agent systems is designed, which only requires one‐hop information of the neighbours without the global topology information and has the advantage of fast convergence performance both in the reaching phase and sliding phase. Rigorous proofs show that the fixed‐time consensus tracking control for second‐order multi‐agent systems can be guaranteed by the proposed distributed control protocol. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed control scheme.

An adaptive finite-time control scheme is developed for noncooperative spacecraft fly-around subject to input saturation, full-state constraints, dynamic couplings, parameter uncertainties, and disturbances. Different from traditional fly-around model based on C-W equation, the derived 6-DOF spacecraft fly-around model can be suitable for noncooperative case in close proximity. By using the backstepping control technique, an integrated adaptive finite-time control law is designed, in which the tan-type barrier Lyapunov function (BLF) is incorporated to handle the full-state constraints. Meanwhile, the unknown dynamic couplings, parameter uncertainties, and disturbances are attenuated effectively by using adaptive estimation technique and the adverse effects raised from input saturation are reduced by the designed saturation compensator. Based on the constructed BLF, it is shown that the designed adaptive finite-time controller can guarantee that full-state constraints are not breached, but also can drive relative position and attitude tracking errors into the accurate convergent regions with finite-time convergence. Finally, the performance and advantage of the designed adaptive finite-time control scheme are demonstrated by numerical simulations.