Efficient optimization method for variable-specific-impulse low-thrust trajectories with shutdown constraint

This paper develops a sequential convex programming (SCP)-based method to solve the minimum-fuel variable-specific-impulse low-thrust transfer problem considering shutdown constraint, with emphasize on improving the computational efficiency. The variable parameter engine is more applicable for many low-thrust scenarios, therefore, both a continuously variable model and a ladder variable model are adopted. First, the original problem is convexified by processing the constraint feasible domain, which is composed of the nonlinear dynamic equations and second-order equality constraint, into convex sets. Then, the approximation is generated to close the optimal solution of the low-thrust problem by iteratively solving the convexified subproblem. Moreover, the switching self-detection and adaptive node refinement methods are presented, which can improve the accuracy of the solution and accelerate the convergence during the approximation process and is especially necessary and effective in the scenarios with shutdown constraint. In numerical simulations, the comparison with the homotopic approach shows that the proposed method only needs 4% computational time as that of the homotopic approach, and two variable-specific-impulse examples further demonstrate the effectiveness and efficiency of the proposed method.