Abstract: A methodology for Sun Synchronous Orbit （SSO） launch trajectory optimization design is proposed, which is based on trajectory decomposition optimization and Genetic Algorithm（GA）.In order to solve the problems caused by coupling of multiple segment trajectories, the all-up trajectory optimization design problem is divided into two segment trajectory optimization design problems based on the decomposition optimization approach. In order to obtain the global solution efficiently and robustly, the basic GA is improved. First, an improved GA including some improvement measures such as multiple mutation operators is proposed.Furthermore, a pipeline hybrid GA combining the global search properties of GA with the local search characteristics of Powell algorithm is developed. The computational results of a two-stage SSO launch vehicle show that the trajectory decomposition optimization approach guarantees the problem to be solved successfully, and that the improved GA and the hybrid GA both locate the global solution reliably. However, it should be pointed out that hybridizing algorithm improves the performance of GA more effectively.

Key words: launch vehicle, optimization of launch trajectory for SSO, decomposition optimization approach, hybrid Genetic Algorithm, global optimization