Safe Proximity Control Method Under Complex Shape Constraints Of Two Spacecraft

On-orbit operations are the primary way to save retired spacecraft or remove orbital debris.The prerequisite for completing on-orbit operations is to achieve a safe approach to the retired target.Space retired targets usually have complex appearance features and may rotate,which increases the risk of collision and the difficulty of approaching.Therefore,the research background of this paper is the on-orbit operation of the retired target,and the research object is the safe approach of the spacecraft under the constraints of the complex shape of the two spacecraft(servicing spacecraft and target).Research is carried out on the construction method of the two spacecraft’s complex shape collision avoidance constraint,the trajectory planning method under the action of multiple constraints of the spacecraft,and the attitude and trajectory tracking control method.Firstly,the non-collision constraint construction method that combines the complex shape and the line-of-sight is studied.By solving the critical geometric relationship between the complex shapes of two spacecraft,a critical safety curve(CSC)is constructed,which is a novel keep-out-zone(KOZ)that can integrate the complex shapes of two spacecraft with the relative attitude.The idea of dimensionality reduction based on projection transformation is further proposed,and CSC is extended to three-dimensional scenes.Secondly,the method of close-range safe approach trajectory planning under the constraints of the complex shape of the two spacecraft is studied.The KOZ formed by CSC is used as an obstacle to be avoided in trajectory planning,and the disturbed fluid method(DFM)is used for trajectory planning.The current trajectory planning methods have three significant difficulties when dealing with the complex problems in this article: unlawful avoidance of non-convex obstacles,no integration with orbital dynamics,no consideration of the requirements of space missions for thruster performance.The DFM is improved,and a speed planning method is proposed under the initial and terminal constraints,the chaser thruster performance constraints,and the optimal time constraints.The simulation data shows that the improved disturbed fluid method(IDFM)can realize the short-range safe approach trajectory planning under multiple constraints,such as the complex shape of the double spacecraft.Finally,the offline and real-time attitude and orbit tracking control methods for non-rotating or rotating targets are studied.Aiming at the safe proximity trajectory and attitude planned by the IDFM offline or online,PD control,explicit Model Predictive Control(e MPC),and Model Predictive Control(MPC)is used for tracking.The results show that for offline planning,the e MPC tracking error is small,and the calculation speed is fast.Real-time online planning and control are further considered for the rotating target,and a real-time attitude orbit tracking controller combining PD feedback control and MPC is proposed.The simulation results show that the controller can realize the real-time online trajectory planning of the rotating target while ensuring stability.This paper focuses on the planning and control of the short-range safe approach process.Based on theoretical analysis and numerical verification,three aspects of collision avoidance constraints,trajectory planning,and attitude control are carried out under the constraints of the complex shape of the two spacecraft.The research in this paper can theoretically expand the evolution law of relative motion,collision avoidance processing,and control methods at very close distances,which can provide technical prerequisites for on-orbit operations under complex conditions in the application.