Artist rendering of a lunar base. Credit: Richard Kurbis

Natural caverns occur on the moon in the form of ‘lava tubes’, which are the drained conduits of underground lava rivers. The inside dimensions of these tubes measure tens to hundreds of meters, and their roofs are expected to be thicker than 10 meters. Consequently, lava tube interiors offer an environment that is naturally protected from the hazards of radiation and meteorite impact.

The interiors of lava tubes could protect human explorers from different aspects of the lunar environment, including cosmic rays, meteorite impacts, and the extreme temperature differences between the lunar day and night. Just like caves on the Earth, lunar caves, including lava tubes, have benign temperatures that are constant. These are extremely favorable environmental conditions for human activities and industrial operations. Significant operational, technological, and economical benefits might result if a lunar base were constructed inside a lava tube.

One possible example is the Marius Hills pit, which was discovered in images from the Japanese SELENE/Kaguya Terrain Camera and Multiband Imager, and reported in Geophysical Research Letters. The SELENE/Kaguya Terrain Camera team made a fly-over movie of the hole, which is available here. The hole is nearly circular, 65 m in diameter, and located in a sinuous rille at the Marius Hills region, a volcanic province on the lunar nearside. The hole was estimated to be 80 to 88 m deep. The area around the hole is covered by a thin (20 to 25 m) lava sheet, which may help protect the lava tube from collapse due to meteorite bombardment. Because the Marius Hills pit is in the middle of a sinuous rille, it likely represents a collapse in the roof of a lava tube. The pit itself may have been caused by an impact that punched through the lava tube roof.

Enlarged image of the Marius Hills pit showing a small crater on the northwestern edge and small boulders on the southern lip of the hole. NAC M114328462R [NASA/GSFC/Arizona State University].

It appears such a lava tube could house a lunar base on the Moon. The thickness of the roof would provide safe long-term shelter against radiation and meteorite collisions. Creation of similarly shielded environments would be a significant cost to manufacture for any lunar base on the lunar surface. Lava tubes could be used merely as receptacles for prefabricated, modular habitats, either imported from Earth or fabricated from lunar resources. Penetrative cracks in the roof may exist, which would make it extremely difficult to render the enclosed volume airtight, but the lava tube could act as a receptacle for self-enclosed habitats.

The primary advantage of housing a lunar base in a lava tube is the potential to use extremely lightweight construction materials. None of the components would have to support any shielding mass whatsoever. The habitat shell would not have to support much of its own weight because it could be supported from the walls and ceilings of the lava tube. Habitats could even be inflatable, similar to Bigalow’s Sundancer space hotel, or supported entirely by air pressure.

Also, current designs for lunar equipment must function properly over a wide range of temperatures. While tools are severely limited and degrade rapidly on the lunar surface, the more benign and constant temperatures inside a lava tube would allow the use of existing tools and commonly used materials. Inside a lava tube all equipment would be well shielded from IR and UV radiation, and heavy machinery could be solidly anchored to firm bedrock—a rarity on the lunar surface.

Other advantages, such as dust mitigation, could be realized from a lava tube base. While loose dust may be a nuisance for a large number of operations on the surface, the lava tube could be kept relatively dust-free. Lightweight, highly flexible space suits could be made for crews venturing outside of man-rated habitats but remaining inside the lava tube.

Posted by: Soderman/NLSI Staff
Source: JAXA & Friedrich Horz paper

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