Iterative control method for quasi-Sun-pointing attitude of solar power satellites

Quasi-Sun-pointing (QSP) attitude for ultra-large solar array of solar power satellites solves problems of enormous control fuel consumption and large-amplitude structural vibrations for Sun-pointing attitude and the problem of low solar radiation capturing efficiency for gravity-gradient-stabilized attitude. However, the control of QSP attitude meets great challenges because analytical solution for the QSP attitude has not been obtained, and consequently the objective attitude is unknown. Thus, an iterative control method for QSP attitude is proposed based on dichotomy or secant methods, which is free of objective attitude. Firstly, the attitude dynamic equations of the solar array are established. Then, the continuous process of attitude motion is divided into multiple periods. The initial conditions of the odd periods are adjusted using iterative methods to find the accurate initial conditions of the QSP attitude. In even periods, quintic polynomial trajectory planning and feedforward-feedback controller are employed to obtain the prescribed terminal attitude conditions of even periods, which are also initial conditions of odd periods. Finally, the proposed iterative control method is validated through numerical simulations considering the influences of inertial parameters, structural flexibility, and control frequency. Numerical results reveal that QSP attitude can be obtained if the control frequency is one order smaller than the lowest natural frequency of the structure.