Research On On-orbit Servicing Spacecraft Integrated Orbit And Attitude Control

With the increasing diversity and complexity of space missions,the autonomous on-orbit service technology has become an inevitable trend of future space technology development with the advantages of low-cost,high-efficiency,strong flexibility and good imperceptibility.As the basis of the close operation of servicing spacecrafts,the space rendezvous and docking technology has drawn widely attention with its important strategic significance.The rendezvous and docking technology aimed at cooperative spacecraft in the traditional space missions has been mature and perfect,while the technology of rendezvous,flying-around and approaching is still at a stage of rapid development,and it also puts forward new requirements for the technology of on-orbit servicing spacecraft integrated orbit and attitude modeling and control.This paper is based on the actual mission background,and focuses on the modeling and control of spacecraft integrated orbit and attitude,and highlights the two critical questions,which are fast flying-around and approaching and tracking to the target.The main research contents are presented as follows:For the problem of integrated modeling of on-orbit servicing spacecraft orbit and attitude,and according to the mission requirements of different stages,the dynamic model of fast flying-around and final-approaching considering natural coupling and control input coupling are established based on line of sight coordinate system,respectively.And the dynamics are the foundation of system analysis and controller design of subsequent chapters.For the control problem of fast flying-around and pointing from servicing spacecraft to the non-coorperative target,the relations between the velocity increment and the flying radius,flying period and orbital altitude under the circumstances of flying in the orbital plane and the horizontal plane have been deeply researched from the relative motion based on line of sight coordinate system.The problen of fast flying-around and pointing control is translated into the problem of tracking control of the desired states through designing the norminal flying-around trajectory and calculating the desired attitude pointing directions,and the error dynamics of the flying-around stage is established.And then,considering that the upper bound of the compound disturbances in the system is unknown and hard to estimate,and in order to improve the rapidity and robustness,a fast flying-around and pointing control algorithm based on second-order sliding mode disturbance observer has been proposed,and the stabilities of the close-loop systems are proved by the finite time Lyapunov stability theorem.For the control problem of approaching and tracking from servicing spacecraft to the non-coorperative target,firstly,the error dynamics of the approaching stage is established.Considering the state constraints existed in the actual system,a full-state constraint final approaching control algorithm is put forward based on Barrier Lyapunov function.A detailed comparision and analysis between Barrier Lyapunov function and traditional quadric Lyapunov is made.Next,an adaptive method is ultilized to estimate the upper bound of the disturbance and saturation difference,and a full-state constraint final approaching control algorithm is proposed considering the input saturation.Due to the limitations of the former method,a modified full-state constraint final approaching control algorithm based on Anti-windup compensator is designed.Numerical simulation is carried out to validate the effectiveness of the proposed algorithms.