Abstract
Proximity operations around Phobos are critical for the Martian Moons eXploration (MMX) mission, and accurate knowledge of the spacecraft's trajectory is required to perform scientific observations and maximise the chances of understanding the moon's internal structure. Possible solutions to implement autonomous navigation around Phobos while orbiting at lower altitudes are presented in this paper and compared with standard navigation techniques. For this purpose, our analyses will compare the level of knowledge achievable once the connection with the Deep Space Network is cut off, showing what can be achieved without ground support, using only information that can be collected and processed onboard, mainly lidar and optical data. Different strategies to build a map of the moon's surface's landmarks are also discussed, demonstrating how this operation can be performed autonomously by the spacecraft and how landmark-based navigation is paramount in estimating the spacecraft's state. Finally, the capability of this setup to observe the moon's gravity field will be assessed, returning precious information for the future geodetic investigations of the Martian Moons eXploration mission around Phobos.