Research On Robust Control Method For Spacecraft Hovering Over Small Body

Hovering is an important way for small body exploration.Precise control of orbit and attitude of spacecraft is one of the key technologies to achieve hovering.In this thesis,the robust control method of irregular small body hovering is researched,considering the characteristics of dynamic environment nearby small body.The methods of orbit constant low thrust control and precise attitude control are designed.The main contents of this paper are as follows:Firstly,the dynamic model of small body hovering is established and analyzed.Aiming at the characteristics of irregular gravitational field of small body,methods of the spherical harmonic function model,polyhedron model and mascon model are introduced.Then,the orbit and attitude dynamic model of small body hovering is established.Orbital perturbations caused by solar gravity and solar light pressure are analyzed through the gravitational radius of action.In addition,the environmental perturbation torque models of small body are built.Secondly,the method of orbit constant low thrust control is researched in uncertain gravitational field.Aiming to solve the state of constant low thrust engine frequent switch caused by irregular gravitational field,the method of hovering constant low thrust control based on quasi-periodic dynamic switching is proposed.A improved dynamic switching law is designed,for the problem of poor control stability and precision of descent caused of parameter uncertainty of gravitational field.Next,the method of hovering precise attitude control with multi-disturbance torque is studied.The model of gravity gradient torque of small body based on gravitational field model of particle group is built.Then,precise attitude control method utilizing the two-order inversion structure is designed.Moreover,the interference is compensated by the expansion of the state observer,a method of auto disturbance rejection precise attitude control is proposed combining the effect of the environmental perturbation torque.At the last,the simulation of hovering control based on GUI is analyzed.A simulation software system of hovering small body is built based on Matlab/GUI.The dynamic model nearby small body,orbit hovering control and precise attitude control method are simulated.The effect of different parameters for orbit and attitude hovering control precise are analyzed.