Close-proximity Relative Dynamics And Control For On-orbit Servicing

Spacecraft on-orbit servicing has become one of important trends in the development of space technology.On-orbit servicing tasks such as propellant supplement,component replacement and function upgrade of spacecraft,maintenance of fault spacecraft,and utilization and remanufacturing of scrapped spaceraft are significant for the sustainable development and utilization of space resources.In the process of autonomous on-orbit servicing,a core stage is that the servicing spacecraft keeps in a close range with the target.This stage mainly performs close-range observation and on-orbit operation for the target.This thesis systematically studies the basic motion problems such as relative motion dynamics,trajectory planning of fast fly-around flying and relative state transition,and motion control using space environment force.The key technologies involved in the observation mission and the arrest mission for uncontrolled rolling target are studied,aiming to lay a theoretical and technical foundation for the engineering realization of autonomous on-orbit servicing.Firstly,the relative motion dynamics of on-orbit servicing in the close-range stage is studied.From the most basic motion law,relative motion of spacecraft is determined by the differential forces applied on two spacecraft.Based on the analysis of magnitude of differential spherical earth gravity and space environment perturbation,a scientific concept of the close-proximity flying is proposed: when two spacecraft keeps in close range,the differential spherical earth gravity is weak and can be overcome by a small control input,which enables the free flying of relative motion in the three-dimensional space.At the same time,when the differential space environment perturbation has similar magnitude with the differential spherical earth gravity,analysis of the relative motion needs to consider the influence of space environment perturbation.It is also possible to use space environment perturbation to assist relative motion control.Therein,the close-proximity relative dynamics model is established,and the selection criteria of the relative dynamics for on-orbit servicing is systematically analyzed.Secondly,according to the mission requirements of close-proximity for on-orbit servicing,the trajectory planning research on fast fly-around flying and relative state transition is carried out.By introducing the concept of artificial gravitational constant,an analytical guidance law for fast fly-around flying is designed.Based on the guidance law,the two spacecraft in any initial relative state can form a elliptical flying configuration.The influence of the artificial gravitational constant and the initial relative state on the cycle and shape of the fly-around trajectory is analyzed.Furthermore,the fuel consumption of the circular configuration under the circular reference orbit is derived.Aiming at the relative state trajectory transfer problem,the artificial potential function guidance law is designed.Two new types of attractive potential function and repulsive potential function are proposed,which can effectively ensure the collision avoidance between the servicing spacecraft and the target during the transfer process.The sliding mode variable structure control law for trajectory tracking is designed to complete the high-precision tracking and maintenance of the planning trajectory under the influence of the space environment.Then,the relative motion of close-proximity flying under the influence of solar radiation pressure is discussed.When the magnitude of differential solar radiation pressure is similar to the differential spherical earth gravity,the solar radiation pressure has a significant influence on the relative motion of close-proximity flying.A dynamics model considering the solar radiation pressure is established.When the normal direction of the spacecraft solar sails is directed to the sun,the analytical solution of the relative motion under the circular reference orbit is solved and compared with the analytical solution of the C-W equation.At the same time,the motion control strategy using the solar radiation pressure assisted propulsion system is established,and the advantages of using solar radiation pressure are analyzed through detailed comparison for hovering control,which provides a new technical approach for saving spacecraft fuel consumption.The control strategy with solar radiation pressure can be expaneded to other control missions for close-proximity flying.Finally,the observation mission and the arrest mission for uncontrolled tumbling target are studied.Based on the measurements according to the stereovision system,the six-degree-of-freedom relative states and the moment-of-inertia ratios of the non-cooperative spacecraft are jointly identified by the designed adaptive filter.The experiment system is constructed to verify the tracking of features on the surface of non-cooperative,and the estimation of relative states based on filter.The obtained results can provide information support for on-orbit operatiom missions.At the same time,referring to failed spacecraft with two types of complex configurations and tumbling motion,the approaching maneuvering stategy is designed.The approaching pracess is divided into long-disatance flying and close-proximity flying,and the correspongding controllers are designed.Considering the collision avoidance with the target in close-proximity flying,the mathematical model of collision avoidance constraint in approaching process is established.The sequence convex optimization algorithm is adopted to obtain the model predictive control input in real time,and the servicing spacecraft can remain relatively stable with the terget,which lays a foundation for the next-step capture and manipulator with robot arm.