Interplanetary Trajectory Optimization for Venus-Mercury Exploration

The large number of variables for Venus-Mercury exploration trajectory design results in the difficulty to find the global optimum. Therefore, a segmented optimization method was proposed. Firstly, the Venus-Mercury transfer window was searched to reduce the cost for Venus capture and Mercury capture. Then, the Earth-Venus transfer trajectory with Venus gravity assists was optimized, and the launch window was obtained. Finally, the Venus/Mercury capture trajectory with successive Venus/Mercury gravity assists was optimized. Based on V∞-leveraging maneuver principle, an optimization index of leveraging maneuver efficiency was proposed. The trajectory after each gravity assist was optimized separately so that the velocity increment for Venus/Mercury capture was reduced steadily. The simulation results reveal that the velocity increment for the Earth-Venus transfer segment and the Venus-Mercury transfer segment could be zero when 2 Venus gravity assists were executed. The velocity increment for Venus capture could be reduced by 1.4 km/s when 2 or 3 Venus gravity assists and V∞-leveraging maneuvers were executed. The velocity increment for Mercury capture could be reduced by 2.3 km/s when 4 Mercury gravity assists and V∞-leveraging maneuvers were executed. Compared with trajectory optimization for Mercury exploration, the proposed method can reduce the overall velocity increment for Venus-Mercury exploration by constraining the V∞ for departing from Venus and arriving at Mercury.