Tube Mission

 For many years now, NASA and other space agencies have agreed that empty lava tubes/caves are scientifically important and would be a very promising habitat option for the Moon and Mars.

We have inferred their existence from the facts that:

•         Other volcanic rocky planets have them (Earth and Mars)
•         We see evidence of collapsed lava tubes (sinuous rilles) on the surface of the Moon
•         Satellites have found holes or skylights that appear to lead to empty lava tubes
•         NASA’s GRAIL mission mapped the gravity of the moon and not only found significant mass cons (mass concentrations of dense rock) but also voids (empty areas) below the lunar surface

In fact, it is believed that the Moon may have the largest lava tubes in the solar system. But to this day, no one has ever located, mapped, explored, or seen the inside of a lunar lava tube. As humankind returns to the Moon, one would think that an exploratory mission would be worthwhile.

Granted this is not the top priority – getting ground truth on the existence, composition, and mining of water ice is rightfully a top priority for lunar exploration. And yes, I, and many others, have noted the desperate need for basic infrastructure in order to support all kinds of lunar exploration – (communications satellites, solar power towers, navigation, positioning, time, etc).  But, at some point, we should have a lunar lava tube scouting mission! 

This mission doesn’t require humans – it can be done by lunar satellite or by rovers on the surface. It is a good candidate for a CLPS mission and wouldn’t impact the Artemis timeline.

A lunar satellite mission to hunt for lava tubes was proposed by a group from Purdue University in 2016 called LAROSS (Lunar Advanced Radar Orbiter for Subsurface Sounding). They concluded:

As a result of the subsurface gravity gradient analysis, several candidate sites have been

recognized with a gravitational signature similar to that of a buried empty lava tube. Some

of these sites are in the vicinity of known sinuous rilles and skylights visible on the lunar

surface. Although the GRAIL mission did result in determining the lunar gravity to an

unprecedented precision, small scale features, such as smaller lava tubes and skylights, are

beyond the resolution of the data. In addition, the near polar orbit of the GRAIL spacecraft

introduced a North-South bias in the measurements. The Lunar Advanced Radar Orbiter

for Subsurface Sounding (LAROSS) spacecraft offers an extension of the findings of the

GRAIL mission by exploring sites with potentially buried empty lava tubes and an expansion

of the process to the whole mare region in search of smaller lava tubes. The low altitude

passes of the radar sounder over the mare region will aid in obtaining better resolution

and penetrating deeper below the lunar surface. This experiment will assist in the search

for buried empty lava tubes that may offer the potential to access and construct habitats,

safe from harsh surface environment and, thus, enabling future human exploration. 

In 2020 a Canadian Group in conjunction with ESA proposed using a gravimeter and ground penetrating radar slung under a lunar surface rover to map empty lava tubes. They have developed the instruments and are designing a rover to carry the instrument packages but this appears to me to be a great candidate for the newly announced Astrobotic Flex rover. It is a large modular rover designed to carry a variety of payloads and could easily handle the mass of a gravimeter, ground penetrating radar, and even a spectrometer.  Astrobotic has announced an agreement with SpaceX to transport the Flex to the Moon as early as mid-2026.

ESA’s work on developing cave-exploring robots and robotic exploration of a tube from a skylight proposal is also very interesting, but it is a decade away and not yet funded.

Lunar lava tube location, mapping, and exploration is not yet in the CLPS pipeline – but it should be.