Optimization of Earth-Mars transfer trajectories with launch constraints

This report describes a study involving the design and optimization of Earth-Mars transfer trajectories with launch constraints by taking the Chinese Mars mission Tianwen-1 as a typical case. The trajectory characteristics of the mission are investigated, and the results indicate that the launch and transfer trajectories do not match at the injection point owing to the constraints on the launch site in China, the allowed range of the launch azimuth, and the launch vehicle’s limited capability. Two strategies are presented to overcome these challenges. One involves performing a single deep space maneuver during the cruise, which was the option implemented in the Tianwen-1 mission. An alternative strategy involves skillfully utilizing a lunar gravity assist to efficiently change the velocity of the probe. Herein, the orbital elements, the velocity increments of the maneuvers, and the launch windows are analyzed for each strategy. The simulations were optimized by applying the particle swarm optimization algorithm under the patched conic model and by a local optimization algorithm under a high-fidelity model; the results indicate that both strategies are efficient for the investigated mission, and the velocity increment differences arising from the two models are small. The advantages and disadvantages of the two strategies are summarized. In general, the first strategy is more robust in design, but the second approach reduces the velocity increment. The method comprising the two strategies proposed in this paper has certain relevance for other similar space missions, especially in terms of dealing with launch constraints.