Abstract: A high precision approach for the skip entry trajectory optimization of lunar return vehicles based on an adaptive sparse collocation method is presented. Firstly, the whole skip entry trajectory is optimized by using an adaptive sparse collocation method; then, the numerical integration of the state dynamic equations is carried out according to the obtained optimal control; when the integration reaches the highest point of the skip trajectory, the re-optimization of the secondary entry trajectory is carried out with the state values that are obtained by the integration as new initial conditions. The numerical simulation results show that: 1) the optimization accuracy is significantly improved when the secondary optimization is used and otherwise the accuracy is poor and the terminal errors are large; 2) the secondary optimization that is performed at the highest point of the skip trajectory is a quasi real time optimization which has potential applications in the field of skip reentry trajectory guidance.

Key words: Skip entry, Trajectory optimization, Secondary optimization, Collocation method