Trajectory Planning For Spacecraft Relative Motion Under Uncertainties

Relative motion trajectory planning is one of the key technologies for space missions such as on-orbit servicing,debris removal and close range reconnaissance.During actual missions,affected by uncertainties such as navigation,model and mechanism execution,the relative motion trajectory of the spacecraft will deviate from the pre-planned nominal trajectory,which will put forward higher requirements on guidance and control system and easily cause more propellant consumption.At the same time,with the increasing number of small targets such as space debris and micro-nano satellites,the task environment for the relative motion of spacecraft is also full of uncertainty due to the limitation of space target detection means.Therefore,it’s worthwhile to study the relative motion trajectory planning of spacecraft under uncertainties.This paper focuses on trajectory planning model,reachable domain analysis,robust trajectory planning and online trajectory planning of the spacecraft relative motion:(1)Based on the relative motion dynamics model,the constraints of the relative motion of spacecraft are summarized,and the general model of relative motion trajectory planning is established under the optimal control framework,which lays a foundation for subsequent research on trajectory planning method under uncertainties.(2)Aiming at the problem of the maximum reachable distance of the spacecraft with fixed terminal time,the mathematical expression of the maximum reach distance is derived by considering pulse and continuous thrust modes,and verified by numerical simulation.Considering the uncertainty of the initial state,the calculation method of the envelope of the relative reachable region of the spacecraft under the elliptic reference orbit is studied.Furthermore,a simplified solution strategy for the envelope of reachability domain is proposed and verified by numerical simulation.(3)For the relative motion robust trajectory planning problem under the influence of uncertainties such as navigation and model deviation,the main sources of uncertainty factors are summarized,and the corresponding mathematical description is given.The tensor product collocation method based on generalized polynomial chaos theory is used to analyze the influence of uncertainty on the task trajectory,the task trajectory robustness index is constructed,and the multi-objective evolutionary algorithm based on decomposition is used to solve the problem of robust trajectory planning under the framework of inner layer uncertainty analysis-outer multi-objective optimization.The Pareto front of robust trajectory planning problems is analyzed and the relationship between different performance indicators is analyzed to provide reference for engineering design.(4)For the relative motion collision avoidance trajectory planning under uncertain obstacle information,an online trajectory planning framework based on model predictive control is proposed.Based on the discrete trajectory planning model,the rotating hyperplane method is used to transform the nonlinear collision avoidance constraint into linear constraint,which improves the solving efficiency of online planning problem.Considering the shortcomings of traditional rotating hyperplane method in multi-obstacle scenario,an improved strategy based on rotating time window is proposed,and the determination of the length and position of rotating window is given.Furthermore,a three-dimensional collision avoidance constraint decomposition strategy is proposed,and the rotating hyperplane method is extended to the three-dimensional obstacle scenario.The feasibility and effectiveness of the proposed online planning method are verified by numerical simulation with uncertain information of obstacles.In conclusion,the paper focus on the relative motion trajectory planning of spacecraft under uncertainties,and some research results have been obtained in the relative motion reachable domain,the robust trajectory planning based on multi-objective optimization and the online trajectory planning method based on model predictive control,which can provide useful reference for reducing the influence of uncertainties on the spacecraft relative motion and improving the robustness of relative motion missions.