Study On Soft-Landing Trajectory Optimization Control Of The Asteroid Probe In The Irregular Weak Gravitational Field

Asteroids exploration have made some great progress in the aerospace sector, with the growing of deep space exploration technology in the domestic and foreign countries.In this paper, trajectory of the asteroid probe was designed in descending to achieve fuel optimal target. Cubic polynomial method is used to fit above optimal trajectory and tracking control, considering the third body gravitation and uncertainties, specific research work can be summarized in the following three areas:At first, consider the asteroid with a small, irregular, weak gravitational field and other characteristics, taking the asteroid as the three-axis ellipsoid, and spherical harmonic coefficients were used to establish asteroid weak gravitational field model; then in view of the probe descending characteristics of the space environment, constructing the dynamic model of small bodies in the solid coordinate, taking the pressure of sunlight, the third body gravitation and other uncertainties into consideration.Secondly, asteroid probe’s trajectory was optimized in order to get fuel optimal target. According to this feature of continuous optimal control problem, we use Gaussian pseudo-spectral method of the direct method of trajectory optimization method to discrete this problems, transforming into a nonlinear programming problem by algebraic constraints, and using sequential quadratic programming algorithm to solve this problem. In this paper, the trajectory optimization is designed considering the solar radiation pressure, using two strategies:leveled thrust control and variable thrust control, to optimize trajectory. Simulation results show that this method can achieve optimal fuel optimization goals, and asteroids can safely descend.Finally, cubic polynomial method is used to design the nominal trajectory for the characteristics in descending, and then tracking nominal trajectory. In the trajectory tracking control phase, the third body gravitation and uncertainties are into account, making it closer to the actual space environment. The sliding mode variable structure control was used for tracking the trajectory based on exponential reaching law, because of variable structure control method has strong robustness. Simulation results show that this method can track descending trajectory safely, to verify the effectiveness of the method.