First,unscented Kalman filter parameter estimation method is proposed to solve the optimal low-thrust transfer problem to Geostationary Orbit.Due to operational constraints of attitude control actuators and uncertain perturbations, a robust closed-loop guidance scheme of constant low-thrust is implemented .The essential idea of the guidance law is to decouple the original multiple revolution optimal control problem into a sequence of trajectory tracking problem in one revolution. Analytical equations are deduced under the condition of continuous constant acceleration. Using these equations, taken the node times of the thrust arcs and the attitude of the thrust as variables, the trajectory tracking problem in one revolution is transformed into an optimization problem with the nonlinear constraints of minimum attitude maneuver time and the consistency of attitude. Finally the whole trajectory optimization approach developed in the paper is applied to low thrust GTO-GEO transfer design, the results show that the tracking error and boundary error are very small.
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