https://www.smithsonianmag.com/air-space-magazine/drones-moon-180956187/

"One interesting concept comes from a proposed mission to study lunar lava caves. Mark Robinson, the Principal Investigator for the Lunar Reconnaissance Orbiter Camera, has proposed a mission he calls “Arne” (named after the fictional character Arne Saknussemm, in Jules Verne’s novel Journey to the Center of the Earth, who discovered a passage to the Earth’s interior through Iceland’s Snæfellsjökull volcano crater). Arne consists of a soft landing spacecraft and three small “pit-bots,” spherical flying robots about 30 cm in diameter. The lander would touch down inside one of the newly discovered lava pits found on the Moon; from the bottom of one of the pits, there is a direct line-of-sight to Earth for communications. Once landed, the small flying pit-bots would traverse into the side chambers of this opening into the Moon’s interior, survey the walls and determine if these pits are surface expressions of a cave system created by flowing lava.

The flying pit-bots of Arne could use a lithium hydride and peroxide propulsion system that levitates the vehicle for short, one-to-two-minute hops. Images, magnetic and thermal information, and obstacle avoidance data are taken for the cave walls during flight. Two flying pit-bots can mutually support each other, relaying their data back to the lander at the tube opening, which can then be sent directly back to Earth. By using alternate hops of each pit-bot, they can move into and survey several hundred meters of an existing cave system.

These drone-like vehicles could be a relatively inexpensive way to explore lunar lava tubes. We might also apply this technique to the exploration of above-ground features on the lunar surface. Landforms like sinuous rilles (such as the Rima Hadley—a winding valley briefly investigated during the 1971 Apollo 15 mission) exposes hundreds of kilometers of mare crust in its walls. Flying drones could travel the length of the rille, examining wall outcrops in many wavelengths, looking for compositional variations to decipher the history of the exposed lavas. Flights through and into craters with very steep walls are also possible, so that shock melt deposits (which tend to be found on the floors of craters) can be accessed and studied. Spectacular, 360-degree views from high-flying drones could obtain geologic information at scales in between those obtained from orbit and those made by traversing the ground, allowing us to understand the geology of large areas. Such capability would be particularly valuable in prospecting and mapping the polar regions, where ice deposits are irregularly and heterogeneously distributed deep within permanently shadowed craters."