Research On Multi-Segment Lunar Free-Return Trajectories And Perturbed Autonomous Rendezvous Guidance Design For Human Lunar Mission

Human lunar exploration mission is the most sophisticated and high-tech Engineering program in history of human being. This behavior demonstrates the nation’s power in science, technology, politics, military and economic areas, and demonstrates the national pursue to unknown world. At the beginning of this century, the lunar exploration programs Constellation, Aurora and Chang’e are proposed by NASA, ESA and CAST, respectively. This behavior completely opens the prelude of human being return to interstellar, and gives new requirements to human lunar mission. In these requirements, more contents should be detected, more accuracy should be given to trajectory design and more safety should be given to human crew. These drive the program more complicated and sophisticated. As a research to time background, the thesis tries to solve the orbital dynamics problems proposed by current lunar mission, and studies the control strategies for autonomous rendezvous and lunar global coverage missions in high-fidelity model. The multi-segment lunar free return trajectories has been proposed, and also with the architecture for high-latitude landing been designed.In the studies of high-latitude reentry, the key factors that affect the reentry orientation and reentry range are analyzed. Based on the patch conic technique, the semi-analytical model of the transearth trajectory has been established, and the trajectory characteristics have been analyzed. The results indicate that the reentry orientation is a function of the lunar latitude and lunar return time; the reentry range is a function of the reentry inclination and landing site latitude.In the studies of multi-segment lunar free return, the characteristics of flexibility trajectory design and safety Earth return under unforeseen circumstance are mainly valued. As the launch window for classical free-return trajectory is narrow, the operation constraints, such as lunar lighting and ground station coverage, will be easily violated. Although the hybrid profile allow more freedom in the choice of the launch window, a safe return will not result without additional maneuvering if the non-free-return trajectory achieved perfectly. In order to eliminate this disadvantage, a multi-segment lunar free-return trajectory is proposed. Differing from hybrid returns, this transfer trajectory consists of free-return sections only, while retaining the advantage of hybrid returns. The patched conic technique has been adopted to establish and analysis the multi-segment free return. To pursue model accurate solution, t he pseudostate model has been introduced. A closed-form analytical trajectory model has been established based on this technique. The results indicat e that the perilune altitude errors for the pseudostate method are less than 10% of their corresponding values for the patched conic technique.In the studies of autonomous rendezvous architecture design for a lunar lander, the attention is focused on the accuracy and convergence behaviors of the autonomous rendezvous control strategy. A three-step iterative procedure is adopted to determine the minimum-impulse control strategies for autonomous rendezvous, involving the progress of the solution from a C-W linear model to a nonlinear, two-body model, and finally, to a high-fidelity model. The two-body model is introduced as an intermediary to enable a smooth transition from the linear to the high-fidelity lunar gravitational model. The optimality of the three-step solutions obtained by the proposed algorithm is verified using the Genetic Algorithm. The results indicate that the three-step solution shows a good agreement with the Genetic Algorithm optimal solutions. An optimal, multi-impulsive rendezvous control strategy based on the simplified Gim-Alfriend state transition matrix(SGA-STM) has been developed for a lunar lander rendezvous problem. This model accounts for the J2 perturbation. The predicted solutions provided by the J2 model are accurate when compared to the numerically-integrated data obtained from a high-fidelity model, and can significantly reduce the calculation time when compared with the three-step iterative procedure. The results indicate that the terminal relative position errors for the SGA-STM model are less than 10% of their corresponding values for the C-W linear model. The impulsive-thrust solutions obtained from the SGA-STM model are reasonably accurate and feasible finite-burn solutions can be obtained with a few iterations of a differential correction procedure.In the studies of architecture design for a lunar global coverage, the interests are focused on the optimal control design and safety Earth return. An algorithm for designing the optimal lunar orbit insertion(LOI) sequence based on the two-segment lunar free-return trajectory is developed. The results indicate that based on the two-segment lunar free returns, any lunar destination orbit orientation can be achieved within a LOI budget of 2.6 km/s and midcourse targeting maneuver budget of 0.4 km/s.