Optimizing Soft Landing Trajectory Design for Lunar Missions: Fuel Efficiency and Control Strategies

Lunar landing technology has undergone extensive research over the years, yet fully autonomous landing systems are still in development. The most critical phase of planetary landing missions occurs between powered descent and touchdown, necessitating a reliable Guidance, Navigation, and Control (GNC) system. For manned lunar missions, an optimal GNC system enables precise vertical landing on the Moon’s surface. This is achieved through a multiphase guidance scheme. The multiphase landing is performed in three phases; powered descent phase, approach phase, and vertical landing phase. The powered descent phase initiates from a 100x18 km elliptical orbit, chosen as the mission’s perilune, and continues until 7 km altitude. Fuel optimization is accomplished by minimizing net acceleration, utilizing Model Predictive Static Programming (MPSP) to design the guidance law. The subsequent approach phase, which spans 7 km to 100 m, involves vertical orientation of the lander. The objective is to guide the lander to the desired landing region and altitude, adhering to the terminal velocity constraints. By augmenting the circular law with a quadratic acceleration term, the guidance solution is obtained, ensuring a precise landing while reducing the velocity for a soft touchdown.