Research On Displaced Orbit Keeping And Flexible Attitude Control For Solar Sail Spacecraft

As a new type of spacecraft propelled by light pressure,solar sail spacecraft has a wide application prospect in the future deep space exploration mission.The heliocentric displaced orbit is an important kind of non-Keplerian orbits,which can provide ideal conditions for the study of solar physics,the continuous observation of the earth’s polar region and the early warning of extreme disasters.In order to keep the solar sail spacecraft in the desired orbit,the sail attitude needs to be adjusted to change the size and direction of solar radiation pressure.Therefore,the research on the displaced orbit keeping and flexible attitude control of solar sail spacecraft is carried out in this paper.Firstly,a second-order sliding mode control strategy is proposed to solve the nonaffine problem of the solar sail spacecraft in the heliocentric displaced orbit.First,all the nonlinear terms about the control variables are transformed into the linear terms about their derivatives.Then,for the new control input,the non-singular terminal sliding surface based on the PD variable is adopted.Afterwards,the stability of the whole system is analyzed by three steps,which proves that the orbit radius error and the displaced height error both can converge asymptotically.The simulation results further show that the control strategy can keep the solar sail spacecraft in the desired displaced orbit.Secondly,a high-performance sliding mode control strategy is proposed for the solar sail spacecraft using hybrid propulsion in geosynchronous heliocentric displaced orbit,considering the internal unmodeled dynamics and external unknown disturbances.First,the uncertain part of the model is estimated and compensated by the adaptive radial basis function neural network,and the sliding mode controller is designed combing the improved conditional integral sliding mode surface with the double power approach law.Then,based on Lyapunov theory,the stability of the system is analyzed,which proves that the orbit radius error,the displaced height error and the angular velocity error all can converge asymptotically.Afterwards,under the principle of propellant optimization,the virtual control variable is allocated to the actual solar sail attitude angles and solar electric propulsion force.Numerical simulation results further show that the control strategy effectively enhances the robustness of the system,significantly reduces the orbit position overshoot,and the hybrid propulsion has higher control efficiency than the single solar radiation propulsion.Finally,an adaptive backstepping control strategy based on extended state observer(ESO)and command filter is proposed for the attitude-vibration coupling dynamic equation of the flexible solar sail spacecraft,which does not depend on the parameters related to the flexible mode and considers the actuator and angular velocity constraints at the same time.First,an ESO is used to estimate the total uncertainty,and the command filter is adopted to limit the angular velocity amplitude,and the compensation signal for filtering error is further designed.Then,owing to the strict feedback form of the system,a backstepping controller is designed,combing with the adaptive law to estimate the unknown parameter introduced when dealing with actuator constraints.Afterwards,based on Lyapunov theory,the stability of the system is analyzed,and it is proved that the attitude quaternion error and angular velocity error can achieve bounded stability.The simulation results show that the above control strategy can accomplish the attitude maneuver without exciting the flexible vibration mode,and only the measured attitude angles and angular velocity information are needed in the designed controller,which has practical application value.