Lunar Lander Braking Deceleration Control

In the second stage of Chinese lunar exploration project, soft landing of the lunar explorer on the lunar surface is to be realized. The control of lander in the powered descending phase is very important for the successful soft landing on the lunar surface. The dissertation makes systematically research in the motion of powered descending phase of lander. The deep study on the navigation and control for the lander in this course is made. The main contents of the dissertation are as follows:Firstly, the power analysis for the lunar lander in the powered descending phase is deep studied, and the math reference frame is chosen reasonably. The engine model of rocket with installation error is built by analyzing the actual lunar characters detailedly. The math model with complete six degree of freedom is built considering the influence of lunar rotation.Secondly, the math model is logically predigested according to the motion of the powered descending phase and environment character. Considering fuel optimality and according to the practical analysis, the attitude angles are replaced reasonably, and the expectative calculation formula are solved without iterative loop. The explicit guidance method in relevance with the state variables and terminal restrict are deduced, and the simulation is made to validate the results.Thirdly, the attitude model of the lunar lander is presented according to the requirement of attitude control for the flying. The switch equation for linear sliding surface is deduced by the result of the deflection between the real attitude angles and the anticipant angles based on variable structure control with sliding mode. The formula of anticipant control moment is deduced by adopting the method of exponent reaching law and twitter reducing of boundary layer. The dissertation also introduces the configuration character and ignition logic of the attitude control engine, and the method of calculating the actual control moment by anticipant moment is given.At last, the simulation model of relatively integrate lunar lander is built by using MATLAB. The simulation results of large loop show that math model of the lander has high integrality and exactly. The fuel sub-optimality navigation is an achievable explicit guidance. The attitude control system based on variable structure control with sliding mode has good dynamic and stable property.