Exhaustive evaluation of microgravity landing dynamics for small body exploration

Landing dynamics play a crucial role in the success of planetary missions, particularly in low-gravity environments, and determining optimal landing sites continues to be challenging. This paper reports a method for landing safety evaluation based on spacecraft dynamics for landings on the surface layer of small bodies in the Martian moons exploration project. Unlike conventional short-duration contact explorations, spacecraft designed for the exploration of Martian moons will remain on the surface of Phobos for several hours post landing. Owing to low gravitational forces, small bodies exhibit an inadequate restoring force, which can result in overturning and rebounding of the spacecraft; moreover, the gravitational forces on Martian moons are several tens of times greater than that on other small bodies, such as Ryugu and Itokawa, necessitating a consideration of the impact acceleration during landing. In this study, a distinctive model was constructed based on low-gravity experimental results, with the capacity to replicate the flexibility of the spacecraft structure, tank sloshing, shock absorption, and interaction with the surface layer. Subsequently, we confirmed the unique behaviors of the spacecraft during its landing simulation on authentic terrain, and candidate landing areas were evaluated based on nine safety criteria. This evaluation process entailed the identification of safe landing areas, yielding a 20% reduction in the number of safe landing sites compared with that based exclusively on terrain. • Landing safety under microgravity was evaluated based on spacecraft dynamics. • Landing dynamics were expressed with distinctive models involving landing legs and sloshing. • The simulated spacecraft exhibited intrinsic behaviors resulting from low gravity. • Twenty percent of the landing sites judged based on inclination were deemed unsafe.