Modeling And Control Of Lunar Soft Landing

Guidance, Navigation and control (GNC) plays a key role in lunar soft-landing, which is in turn the basic demand of lunar exploration. In this dissertation, the attitude-orbit coupling dynamics model is built. On the basis of summarizing current work and employ the optimal control,we design a explicit guidance law.First, the specific process of soft-landing, autonomous navigation method and the navigation sensor which is needed during the process are studied. Then we analyze the request of guidance law, guidance method, nonlinear control method, orbit constraints and the choice for land spot about the lunar landing. The program of lunar landing system is built considering the actual space technology conditions in China and the foreign experience in lunar exploration. The whole work in the dissertation is based on this.The attitude-orbit coupling dynamics model is built considering the rotation of moon. Because that while attitude system track the attitude of lunar lander, error is inevitable. In order to reduce it we must built a dynamics model which the attitude is coupling with orbit.Optimal control theory is used to generate a guidance law for lunar landing, which can be regarded as an open loop one. Generally, a two-point boundary value problem is to be solved in order to obtain the numerical solution for optimal trajectory. Similar to the guidance of launch vehicles, a uniform gravity field on lunar surface is assumed. Under the assumption and take consideration of the real-time request, an explicit guidance method is studied to minimize the fuel consumption. Result shows that a near minimum fuel landing can be implemented by this method. Moreover system errors can barely affect the result.