Autonomous guidance and control with hazard avoidance for a Lunar lander

This work deals with an algorithm based on a linear programming approach to establish the guidance and the control of a Lunar Lander in its final descent phase. The linear programming problem is described and set; in our method the soft-landing manoeuvre depends on the initial state of the lander, the desired landing site and the time of flight needed to complete the manoeuvre. Then, the Pulse Width Modulation is used to make the control sequence obtained exertable by a non-throttleable engine and a strategy is proposed to modify the results of the Pulse Width Modulation in order to achieve a safe landing. A method is shown to take into account the variation of mass of the lander during the descent and a proposal for an algorithm for the estimation of the time of flight is presented. The proposed guidance and control algorithm is tested to evaluate its performances, including cases when a retargeting is needed.