Detection of Lunar Lava Tubes with Orbiting Radar Sounder Systems

Lunar lava tubes are subsurface structures which are potential candidates for future human outposts on the Moon. Recently, remote sensing observations of the Moon based on optical cameras and gravitational field mapping have detected features which can be directly related to the presence of lava tubes. However, the potential for global lava tubes mapping using these types of sensors is very limited. In order to accurately detect lava tubes it is necessary to perform direct subsurface measurements of the shallow lunar subsurface. This can be done by radar sounders which are electromagnetic instruments specifically designed to detect and classify subsurface features from orbit. However, past Moon radar sounder missions were not aiming for for lava tubes exploration, and had thus limited capability to detect them. In this paper, we have studied the optimal type of orbiting radar instrument that would be needed to detect the majority of lunar lava tubes, based on their expected properties. To define this instrument, we conducted both a performance assessment versus different parameters of the radar sounder and an electromagnetic signature analysis to determine the possibility to detect lava tubes having different sizes from orbit.