Terminal Powered Descent Guidance for the Smart Lander for Investigating Moon

In January 2024, the Smart Lander for Investigating Moon (SLIM) made the first pinpoint moon landing within 100 m from the target. This paper discusses the powered descent guidance and associated guidance and control effects for the terminal descent phase of the SLIM lander. Minimizing propellant consumption was essential for its guidance and control. Large trajectory correction capability, consideration of a thrust-pointing constraint, and subsurface flight avoidance were also necessary. To do this, we modeled the guidance sequence in three subphases: free fall, followed by horizontal position correction with maximum thrust by the maximum tilt angle under a thrust-pointing constraint, and vertical braking with maximum thrust. The guidance problem was then converted to a parameter-finding problem with only a few unknowns. This modeling ensured SLIM’s robustness against initial state errors, fast runtime, and smooth convergence. The end-to-end results from conceptualization to in-flight validation can bridge theory and practice in guidance and control for lunar and planetary landing missions.