Finite-Time Human-Machine Shared Control for Output-Constrained Manned Spacecraft Closed-Range Rendezvous Missions

This paper studies a safety-oriented shared control problem for close-range manned spacecraft rendezvous and docking under coupled pose constraints. To explicitly describe the docking corridor, time-varying inequality constraints defining the safety corridor are established within the line-of-sight coordinate system. Based on the resulting constrained dynamics, a constrained control strategy using non-singular terminal sliding mode is developed by combining projected safe references, logarithmic coordinate transformation, and finite-time sliding-mode analysis. Results show that the transformed sliding mode variables can converge to any small neighborhood of the sliding surface within a finite time, thus ensuring finite-time convergence of the system state error to a residual set on the sliding surface. A shared-control mechanism is further introduced to coordinate human commands and autonomous safety corrections according to the current safety condition, and the closed-loop system preserves admissibility while retaining the human command in the overall safe operating region. In addition, an actuator-level control allocation problem is formulated for a twelve-actuator configuration so that the generalized force-torque command can be distributed to the underlying actuators in a physically implementable manner. Finally, the uniform boundedness of the system state was analyzed based on Lyapunov stability theory, and the effectiveness of the proposed method was verified by comparative simulation. Note to Practitioners - Close-range manned spacecraft rendezvous and docking missions are safety-critical operations that require astronauts and onboard autonomous systems to cooperatively accomplish precise docking tasks under strict safety constraints. In practical missions, unsafe piloting commands, coupled pose constraints, and actuator limitations may cause corridor violations or even collision risks during proximity operations. Existing constrained control approaches often focus on autonomous docking scenarios and may not explicitly address the coordination between human operational intention and safety-preserving autonomous intervention under complex docking constraints. This paper presents a safety-oriented shared control framework for close-range spacecraft rendezvous and docking under docking corridor constraints. The proposed method enables the autonomous system to continuously monitor the current safety condition and provide corrective assistance only when necessary, thereby preserving human operational authority within the allowable safe region. In addition, the control strategy explicitly incorporates coupled pose constraints and actuator allocation requirements, making the generated control commands physically implementable for practical spacecraft platforms. Compared with conventional constrained docking approaches, the proposed framework improves operational safety while maintaining smooth human-machine cooperation and real-time applicability. The proposed approach is particularly suitable for future crewed on-orbit servicing, space station assembly, and safety-critical docking missions where both operational flexibility and collision avoidance capability are required. Future work will further investigate shared control with parameter uncertainty under fixed time and corresponding simulation verification.