Research On The Low Energy Moon Return Trajectory Design And Control Strategy

Because of the energy-conserving feature of the low energy moon return orbit, it can be applied to increase the load amount from moon to earth and save the cost of launching. Also it is a good substitution for the traditional return method in emergency circumstances. The research on low energy return robit has significant theoretical and practical significance for the deep space exploration of China. Compared with the traditional patched conic return orbit, the low energy return orbit will significantly save the launching impulse. However, the orbit must reach the gravitational chaotic regions near the libration point of the sun-earth-moon system in which the effects of the moon and sun’s gravity on the probe’s orbit is much more intense and the orbit is more sensitive to the initial flight status. For that reason, the design and control of the low energy orbit will face greater challenges. So in this paper, under the support from the National Natural Science Fund "research on low energy moon to earth transfer orbit", the problems in dynamics modeling, trajectory design, control and implementation of the low energy moon return orbit is researched to provide theoretical and technical support for the lunar exploration and development of our country in the future.Firstly, the dynamics modeling issue of the spacecraft in the low energy moon return mission is researched. Because that the circular restricted three body model cannot reflect the dynamic characteristics in the low energy moon return orbit accurately, the circular restricted three body model is extended to elliptical four body model and the Expression of the orbit energy is given. According to the research, the elliptical four body model can provide an accurate reflection the state of force in the low energy return mission. According to the Invariant manifold theory, the Shape of the tunnel of the invariant manifold of the low energy moon return orbit is analysized to provide the theory foundation to the orbit disigning. Besides, to research the orbit design and control issue in actual engineering application, the accurate four body dynamic model is introduced to simulate the true status of moon and sun with Standard ephemeris.Secondly, the paper analyzed the existence and regularity of the low energy moon return orbit. Because that the previous studies of the low energy return orbit just stay at a stage of example. So, based on these researches, the paper analyzed the energy demand and the orbit shape and demonstrated the general existence of the low energy moon return orbit with the orbit searching result and classification study of the orbit. Forthermore, the paper analyzed the phase relationship of the sun, moon and earth that satisfy the low energy moon return condition based on the invariant manifold theory. As the result, the launching window in2020is computed to provide the data to the orbit designing. Thridly, the methods of low energy moon return orbit designing are researched. To solve the problem that the hard convergence of iteration and the low efficiency of computing in the single-stage iteration method and Intelligent optimization algorithm, it’s proposed a modified patched manifold method to design the low energy moon return orbit that satisfies both initial and terminal conditions. In this method, the return menifold is devided into several sections to provide an initial guess of the low energy return orbit, and then the sections are joined together with a modified multi-stage iteration to give a smooth joining orbit. According to the simulation result, the new method can improve the convergence quality and computing efficiency.Fourthly, the paper researched the Error propagation characteristics and the design method of midcourse correction strategy. In the actual moon return mission, there are orbit errors at the initial point at which the spacecraft injects into the low energy return orbit so the reentry parameters cannot satisfy the task requirement. For that reason, the paper applied the covariance method to analyze the error propagation characteristics and then evaluate the sensitivity of the low energy return orbit to the initial orbit error with the covariance analysis of the reentry error. For the return mission with orbit error, it’s proposed a three maneuver correcting strategy via the analysis of control effect changing with orbit time. According to the simulation result, this strategy can give a good correction effect in the low energy return mission with orbit error, determination error and impletation error.In addition, the paper researched the finite thrust orbit control strategy of the spacecraft. Several methods were compared together in the low energy moon return mission to analyze the control effect and a strategy designing method was proposed that combine the Gauss pseudo spectual method and virtual satellite method. According to the simulation result, this new method can give an accurate orbit control strategy with a high computing efficiency.Finally, with the simulation of the whole moon return mission, the feasibility and effectiveness of the orbit design and control method are verified.