Research On Guidance Law Of Main Descent Phase Of Small Lunar Lander

Small robotic lunar lander(SRLL) is a kind of scheme that is applied widely in the world, which is a soft-landing platform that carries light experimental devices such as HD camera, and magnetic field probe, so that it is able to accomplish various experiments on lunar surface. At present, there is still no such research about the small robotic lunar lander in China. Therefore, the international projects about SRLL are investigated. The GNC scheme for SRLL equipped with Solid Rocket Motor(SRM) is designed and simulated.Firstly, the features of SRLL equipped with SRM are considered and the model of GNC system is conducted. The model consists of the working mode of GNC system, dynamic model of the mass center and dynamic model of the rotation motion. For the purpose of reduce the deviation with the real circumstance, the error generated from deviation of motor is considered. In addition, the discrete working mode of GNC system is also considered.The guidance law for the main descent phase is researched considering the bounds of final horizontal velocity. Using the relationship between the Kepler Orbit Elements and the final states, the target orbit can be designed, and the problem of path planning is converted to the problem of finite-thrust maneuver. Least-Squares correction method is used to solve the guidance parameter. The method is likely to converge. Because the initial states of iteration are all meaningful parameters, it is not difficult to get the guess.Then the guidance law is researched considering the bounds of final height. The dynamic model is evaluated in the polar frame, so that the bounds can be regarded as states. The problem of path planning is raised. Pseudospectral method is used to solve the problem. According to this method, the accessible range of the main descent phase is evaluated. In addition, the features of trajectory are researched as well.Finally, the attitude control law is designed based on quaternion elements. The deviation quaternion elements are introduced to eliminate the divergence of the target attitude. The control law and the guidance law evaluated above are substitute in the GNC system model. The 6Do F simulation is conducted and the performance of GNC system is evaluated.