Research On Trajectory Planning And Control For Safely Approaching A Space Tumbling Target

The on-orbit servicing technology is the basis for realizing the high-efficiency and low-cost development and utilization of outer space,and it has important economic and military significance.However,there are many technical problems in implementing on-orbit servicing.One of the key technologies is to safely approach a space tumbling target,which is an important prerequisite for the subsequent on-orbit servicing operation.In this paper,the trajectory planning and control methods for safely approaching a space tumbling target are studied.Firstly,the relative motion model of two spacecrafts in the central gravity of the earth is established.The linearized relative motion equations of the circular reference orbit and the elliptical reference orbit are derived respectively,and the analytical solutions of the two equations are given.The tumbling motion of the target spacecraft is analyzed using the theory of rigid body free rotation,and is divided into three cases according to the spatial relationship of the target's tumbling axis and its docking axis.Secondly,the task process of approaching space tumbling target is divided into two pahses: the transition approaching pahse and the final approaching phase.An optimal trajectory planning method based on inverse dynamics is proposed for the transition approaching phase,and the trajectory of the service spacecraft is parameterized by the inverse dynamics.Then,the trajectory optimization is to minimize the energy consumption and the constraints of active collision avoidance,thrust limit and passive safety should be satisfied.The direct method is used to discretize the optimization problem and all the constraints,and the discretized problem is solved using the nonlinear programming algorithm.Thirdly,a trajectory planning method based on the artificial potential field and the safe boundary constraint is proposed for the final approaching phase.Considering target spacecraft's different cases of tumbling motions and its geometric shape,different safe boundary constraints are established respectively.Then the desired relative velocity instructions are determined,and the sliding mode control is designed to control the service spacecraft to follow the instructions and safely approach the space tumbling target without collision.Finally,the trajectory planning and control methods in the transition approaching phase and the final approaching phase of approaching the space tumbling target are simulated and analyzed.The results show that the proposed methods can give a safe trajectory to the service spacecraft,and satisfy the requirements of security and other constraints at both approaching pahses.In addition,the simulation results of the transition approaching phase show that it is necessary to take into account the passive safety constrint.