Study On Dynamics Control And Trajectory Optimization Of Spacecraft Hovering Orbit

Spacecraft hovering is a relatively static formation configuration,which can provide a stable working environment for space on-orbit service(OOS).Space on-orbit service is mainly for on-orbit maintenance,on orbit assembly and on orbit replenishment of spacecraft.Dynamic control of spacecraft hovering orbit and trajectory optimization of orbit transfer in hovering mission are the key technologies to realize spacecraft hovering.At present,the related research mainly focuses on the control of spacecraft hovering in the case of large distance,but in the actual implementation of space on-orbit mission,due to the limitation of the length of the manipulator or other operational requirements,the spacecraft needs to hover in close range.In order to ensure the successful completion of the spacecraft hovering mission,it is necessary to optimize the hovering orbit transfer trajectory and control it with high precision.In this paper,from the perspective of orbit dynamics modeling,the high-precision hovering control considering J2 perturbation is determined;the hovering sliding mode controller including J2 perturbation is designed;the trajectory of orbit transfer in hovering is optimized by Gauss pseudospectral method;the fuel consumption and the utilization of Lorentz force in hovering are analyzed.The research work is of great significance to the dynamic control and trajectory optimization of spacecraft hovering.The main research works in this thesis are summarized as follows.1)A dynamic model of spacecraft orbit hovering considering J2 perturbation is established.According to the relative static state characteristics of the spacecraft in hovering,the expression of spacecraft hovering control force is determined.In the dynamic model of spacecraft orbit hovering considering J2 perturbation,the orbit elements of the target spacecraft under the influence of J2 perturbation are calculated by numerical method;combined with the J2 perturbation of the mission spacecraft in the geocentric inertial coordinate system,the J2 perturbation in the orbital coordinate system is derived through coordinate transformation.Furthermore,the dynamic model of spacecraft hovering considering J2?J4 perturbation is established,and the expression of control force of spacecraft hovering with J2?J4 perturbation is derived.Two kinds of hovering control are applied to the validated dynamic model,and the numerical integration verification is carried out.The results show that,compared with the hovering control without considering J2 perturbation,the introduction of J2 perturbation can improve the precision of spacecraft hovering state in short-term mission,and the hovering control with considering J2?J4 perturbation has higher precision,which can ensure that the error of hovering state is less than 2%in 100 orbit cycles.With the increase of mission time,the effect of other external perturbations on the hovering will continue to accumulate,and the corresponding error will gradually increase.The hovering error is bound to exceed the error range specified by the mission.Therefore,it is necessary to design a closed-loop controller to ensure the stability of the spacecraft in the long-term hovering mission.2)According to the hovering dynamics model considering J2 perturbation,a sliding mode controller for spacecraft hovering is designed with J2 perturbation as a known term.The range of unknown external perturbation in the sliding mode controller is estimated by the difference method.The boundary layer method is used to weaken the chattering phenomenon in the sliding mode controller,and the thickness of the boundary layer is determined.The research shows that although the sliding mode controller based on switching function has high-frequency chattering,it can ensure that the hovering state of the mission spacecraft is within the allowable error range,which is far less than 1%.After the boundary layer thickness is determined,a sliding mode controller is designed,which satisfies the allowable error and has no high frequency chattering.The relative error of hovering position is within(0.001%?0.01%),and the absolute error of velocity is in the order of 10-8?10-7 m·s-1.The results show that the position and velocity are within the allowable error range and change periodically,which shows that the designed sliding mode controller can ensure the mission spacecraft hovering state is stable in the long-term mission,and there is no high-frequency chattering.3)Gauss pseudospectral method is used to discretize the dynamic model of orbit transfer in spacecraft hovering orbit,and the nonlinear programming problem of orbit transfer is obtained.The interior point method is combined with sequential quadratic programming(SQP)to iteratively calculate the nonlinear programming,and the optimization results of orbit transfer in spacecraft hovering orbit are obtained.The problem that initial value is sensitive and not easy to converge is solved,and the convergence speed is improved.By comparing the numerical results of trajectory optimization and Runge Kutta integral,the accuracy of the combination of interior point method and SQP in solving nonlinear programming problems is verified.The results show that the Gauss pseudospectral method can be applied to the trajectory optimization of orbit transfer in spacecraft hovering.In solving the nonlinear programming problem,the interior point method solves the problem that it is difficult to guess the initial value points.By gradually increasing the discrete points of SQP,the accurate optimization results of orbit transfer in spacecraft hovering orbit are obtained.At the same time,the simulation results also prove the superiority of the combination of interior point method and SQP.The Runge Kutta method is used to integrate the discrete dynamic model.The error between the numerical results and the optimization results increases gradually,but it is very small relative to the state variable itself,about 10-7,which further verifies the accuracy of the combination of interior point method and SQP.4)The influence of eccentricity and semi-major axis of orbit on the hovering control force is calculated and analyzed by using the expression of spacecraft hovering control force considering J2 perturbation.According to the calculation formula of fuel consumption,the fuel consumption in the specified range is calculated in the x-y plane and y-z plane respectively,and the specific fuel distribution nephogram is obtained.Combined with the Lorentz force of spacecraft in space,the thrust assistant effect of Lorentz force on spacecraft hovering with different charge mass ratio is analyzed.The results show that with the increase of eccentricity e,the hovering control force near the perigee increases gradually;when eccentricity e is constant and the semi major axis a increases,the hovering control force decreases in the whole orbit period.When the hovering distance is given,but the hovering position is not strictly required,the larger value should be taken in the y direction,followed by the z direction,and finally the x direction should be considered to ensure the minimum fuel consumption.When the angle between the control forces of Lorentz force hovering is less than the critical angle,the Lorentz force can provide thrust assistance for the mission spacecraft in the whole orbit period.The larger the charge mass ratio of the mission spacecraft,the larger the auxiliary thrust provided by Lorentz force for hovering,but the smaller the hovering area.