Research On Autonomous Proximity Sliding Mode Control For On Orbit Service Spacecraft

With the complication of space aerospace missions,the mission requirements of on-orbit service spacecraft have also become more diverse,and spacecraft have expanded from a single traditional aircraft to space robots and small space satellites.In the face of new mission requirements,such as on orbit maintenance,space garbage cleaning,fuel addition,no matter what kind of space mission,it is necessary to approach the served spacecraft in the next step,so autonomous docking technology is the key component technology.this paper mainly studies the guidance and control technology of autonomous docking of spacecraft in close range,including the studies of relative orbit and attitude sliding mode control method of relative motion spacecraft.Firstly,the paper analyzes the development of autonomous docking technology and the research status at home and abroad,and introduces the modeling process of the classical spacecraft relative motion model CW equation,spacecraft attitude kinematics equation and dynamics equation.Then,in the autonomous approach phase,based on the operational model of the spacecraft in the circular orbit,considering that the measurement of the distance sensor in the long distance is limited,a sliding mode observer is designed to observe the relative state of the serving spacecraft and the target spacecraft.At the same time,to further reduce the chattering of the observer,the saturation function is used instead of the observation matrix,the relative position sliding mode control law is designed based on the linear quadratic optimal theory.Secondly,aiming at the attitude motion of spacecraft in the final approach stage,the system model is decomposed into linear and nonlinear terms and considering the external uncertain disturbance torque,the model reference adaptive method is used to track the nonlinear term,and the relative attitude adaptive sliding mode control law that switching function only related to the linear term is designed.Finally,to address the synchronous control of spacecraft attitude and orbit,in order to reduce the singularity problems of attitude motion,modified Rodriguez parameters were used to describe the attitude motion,and a 6DOF model of spacecraft relative motion was established.Considering the uncertain external disturbance force and disturbance moment,the RBF neural network is used to approximate the non-linear target model,a sliding mode robust control law is designed that does not require exact model information.And a comparative simulation experiment is designed.The experimental results show that this control law has higher control accuracy than the second-order sliding mode control law.