Optimization of Variable-Specific-Impulse Gravity-Assist Trajectories

This paper presents a series of optimization methods for finding fuel-optimal gravity-assist trajectories that use the practical solar electric propulsion with variable specific impulse. The fuel-optimal low-thrust gravity-assist trajectories are first solved using specific impulse as a control variable. An optimization method combining the particle swarm optimization and the indirect method is proposed to optimize the variable-specific-impulse gravity-assist low-thrust trajectories. Additionally, the modified logarithmic homotopy function is applied to serve as a gateway in variable-specific-impulse case. The algorithm for optimizing multiple-gravity-assist trajectories is also presented in this paper. Moreover, the experimental data of NASA's Evolutionary Xenon Thruster (NEXT) are employed in numerical simulations. Main-belt asteroids missions are given to substantiate the feasibility and efficiency of the proposed methods.