Study On Powered Descent Guidance For Mars Landing

Space activities have greatly expanded the scope of human activities, and Marswill become a new exploration target after space flight, the space station, and the Apollomoon landing. In the Mars landing mission, entry, descent, and landing phase is the lastbut most important stages. Especially at the end of the landing stage, which is usuallycalled powered descent phase, is considered to directly determine the destiny of Marslanding system. Therefore, the primary purpose of the work is to develop guidancealgorithms for Mars lander in powered descent phase.First, consider the physical constraints of thrust engine and various constraintsfrom states, the motion equation of Mars lander is established. In order to achieve theobstacle avoidance performance, some modifications have been made to existedclassical guidance algorithms, typical numerical simulations are implemented to verifytheir performance.Secondly, in order to optimized the usage to fuel, the non-linear and non-convexoptimization problem with up and low limited on thrust magnitude is equivalentlyconverted to a second order cone optimization problem, and typical fuel optimaltrajectories are computed and analyzed. Further, consider the effect of initial conditionerrors, parameter uncertainties and environmental disturbances, the sliding modevariable structure control theory is introduced to design the optimal trajectory trackingguidance law, and it is shown by numerical simulation that the lander is able to track theoptimal trajectory successfully.Since storing the entire fuel trajectory data will take up a considerable storagespace, finally, this work also proposes a new way to achieve near-fuel optimalperformance by feedback guidance algorithm, that is, adding optimized waypoints to thetrajectory. The generalized optimal guidance law is derived using optimal control theory,with its terminal states given and non-constant gravitational acceleration environment;After that, the optimization process of waypoints is summarized, during which anapproximate saturation function is proposed to improve the computational efficiency of the waypoint by specialized optimization software; Finally, and the performance of thewaypoint strategy is illustrated by comparison with open loop fuel-optimal solutions.