Autonomous Navigation And Guidance Method For Mars Entry

The Mars entry phase is the longest and most complex segment of the whole EDL, which will determine the final landing precision. So, the autonomous navigation and guidance technology was studied on for Mars entry. The main contents include:Firstly, different kinds of dynamic equations were built for Mars inertial coordinate frame, Mars fixed coordinate frame and sphere components for different mission requirements, and their conversion relationship was reseached.Secondly, the error of traditional dead reckoning is large and observation information of navigation is poor in Mars Entry. so Mars entry navigation based on IMU/radio measurements was studied. The method uses acceleration measured and radio ranging information to estimate the states. The impact of the radio measurement interruption and recovery on navigation system was studied. The multiple-model adaptive estimation algorithm was researched for the Mars density error. Each filter corresponds to an atmospheric density model, the method achieves the optimal estimation based on Bayes rule.Thirdly, drag tracking guidance method based on extended high gain observer was proposed. The method can estimate drag acceleration, the change rate of drag acceleration and system disturbances accurately, and can achieve good tracking performance through state feedback control. This method has a certain robustness to the initial state error, atmospheric density error and aerodynamic coefficients error.Finally, an adaptive variable structure neural network trajectory tracking method was studied. The method uses multi-layer neural network with online self-learning ability to compensate nonlinear terms, uncertainties and unmodeled dynamics, which can improve the robustness of guidance system effectively.