Characteristic Analysis And Optimal Design Of Abort Trajectories For Manned Lunar Landing Mission

It is one of the most important constraints that ensures the safety of the astronauts when designs trajectories for manned lunar landing mission. Firstly, the spacecraft is injected to a free return trajectory, which can auto return to the earth without maneuver with assistance of swing-by at the moon; then to access wider lunar surface, if necessary, the spacecraft can turn to a hybrid trajectory by a small maneuver during the translunar coast phase of free return trajectory; however, if an emergency occurs, and mission abort, which results in a fast return to the earth, is necessitated, the spacecraft should be transferred to a direct earth-return trajectory, i.e. the abort trajectory. This thesis mainly investigates the characteristics and optimization design of the trajectories mentioned previously. The primary researches were described as bellow:1) A three-level trajectories design mode, in which translunar trajectory, free return trajectory and hybrid trajectory were designed step by step, was constructed based on characteristics analysis of the trajectories. Firstly, the traditional patched-conic technique was improved with considering noncircular motion of the moon, as well as the patched-conic models of free return trajectory and hybrid trajectory were given. Then characteristics of free return trajectory and hybrid trajectory were analyzed, respectively. According to the characteristics of the trajectories, a coordinate-rotation based optimization method was employed to design the free return trajectory; and the design method of the hybrid trajectory was proposed based on a free return trajectory. Consequently, the three-level trajectory design mode was constructed.2) Aimed at different types of trajectories, the analytical design models of abort trajectories were established and characteristics of the trajectories were analyzed. As different types of the nominal mission trajectories requires different abort trajectories, the analytical mathematical models of near earth abort trajectory and near moon abort trajectory were proposed, respectively. Then the design models of direct abort, multi-impulse abort and abort using free return trajectory were given for near earth abort, and a general trajectory design method was proposed for near moon abort as well. Finally, the characteristics of abort trajectories were analyzed, including the time of flight and the fuel cost, etc.3) Using the patched-conic technique for reference, the methods of launch window determination for manned lunar landing mission were given with the patching occurs at the lunar landing point. Since manned lunar landing mission comprises translunar and transearth flight phases, the launch widow determination algorithms were proposed by means of inducing from the lunar landing point. Then, the design processes of translunar and transearth trajectories were described by considering the constraints of launch widow, where for the transearth mission, the constraints that allow the spacecraft return to recovery sites with different latitude and longitudes were considered, to satisfy water or land landing of the spacecraft.4) For integrated design of the nominal mission trajectories and the abort trajectories for manned lunar landing mission, design methods based on evolution algorithms were proposed. Firstly, an overall mission trajectory optimization model was established, in which the translunar trajectory, lunar parking orbit and transearth trajectory were considered except for the abort capability. Then, considering the abort capability, the integration design models of free return trajectory, hybrid trajectory and abort trajectory were established. The perturbed trajectory design method was proposed by using the results obtained from the unperturbed problem as the initial values. To solve the integration design abovementioned problems, which are multi-variable design problems and more sensitive to the initial value, the evolution algorithms were employed.5) Architecture of an abort planning parallel system was constructed, and algorithms of computational experiments for abort planning were proposed. A frame of abort planning parallel system for manned lunar landing mission was proposed with considering the complexity and uncertainty of the abort problem. Then considering the uncertainty of the initial trajectory errors and the maneuver errors of the abort, algorithms that have the capabilities of online planning were proposed, primarily, based on the characteristics analysis of the errors propagation for the computational experiments.6) The methods used to verify and validate the design results of the nominal mission trajectories and the abort trajectories were established by further development of Satellite Tool Kit (STK). The functions of STK in validation methods for patched-conic technique and lunar point setting and analysis were expanded, by deeply analyzing the principles of STK in trajectory design and simulation validation; then approaches for analysis, design and validation of the lunar exploration mission were established. The approaches were used to validate the nominal trajectory, abort trajectory and characteristic analysis of this thesis.Characteristic analysis and design of the trajectory is an important research subject for manned lunar landing mission during the top-level design phase. The works mentioned above can provide references in pre-research, demonstration and arrangement for our China's coming manned lunar landing mission.