ESO-based Attitude Control And Moment Management For Space Station

Space station receives great attention in the world, because it represents the most comprehensive and advanced level in astronautical technology. The attitude control of space station is quite different from ordinary spacecraft, because it’s larger and more complex, it has bigger mass and stronger external disturbance, yet requests longer design life. Due to the stronger disturbance, control moment gyros(CMGs) need to be unloaded frequently. And it will result in consuming the fuel and reducing the space station’s on-orbit life. As the unique problem of the space station, attitude control and momentum management(ACMM) is to maintain its proper flight in orbit for the long term while guaranteeing the CMGs unsaturated. Considering that our space station development project has been formally established, it is highly imperative to address the ACMM problem of space station.At present, the popular controllers to reject the disturbance of the ACMM are based on the Internal Model Principle(IMP). The most classic is the LQR algorithm based on IMP used by International Space Station.Based on the current research, an Extended State Observer(ESO) combined with LQR is designed to estimate and compensate the disturbance of the space station in real time to achieve ACMM. The main contritbutions are stated in the following.(1) ESO is applied to the attitude control and momentum management of the space station for the first time. A third-order Linear Extended State Observer(LESO) and a third-order Nonlinear Extended State Observer(NLESO) are designed to estimate the attitude, the angular velocity and the total disturbance of the space station. Because the attitude and the angular velocity can be measured actually, the LESO and NLESO can be optimized to be more effective. Second-order LESO and NLESO are designed to estimate the angular velocity and the total disturbance of the space station. The stability of the LESO is analyzed.(2) Attitude control and momentum management are coupled by the control, and this makes the space station’s disturbance compensation totally different from ordinary spacecraft. Compensating the disturbance which only acts on the AC passage can introduce the additional disturbance to the MM passage, it needs to be offset on the MM passage. The reasonable compensation of each axis is analyzed to reject the disturbance while avoiding the accumulation of the angular momentum on MM passage. Two compensation strategies based on ESO and LQR are presented to achieve ACMM. The closed-loop stability of each strategy is proved.(3) Lots of simulations are conducted to verify the feasibility of the ACMM scheme based on the ESO and the compensation strategy. Comparisons are made between the different observers and the compensation strategies in dynamic property and stability precision. The result is also compared with the classic LQR algorithm. A third-order LESO based on mixed measurements to promote the performance of the third-order LESO only based on angle error.(4) A control scheme based on the estimated angular velocity afforded by the third-order LESO is presented to achieve the attitude control and moment management of the space station when the rate gyro can not work. And the closed-loop stability of the system is proved in the paper. The simulation results illustrate the effectiveness of the proposed method and the ability to track and reject the disturbance.