Lava Tubes

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Lavatubes are good candidates for habitats on the Moon because they are ready made structures with dozens of meters of solid basalt shielding. In addition to radiation shielding, these environments are also thermally stable (estimated temperature -20° Celsius / -4° Fahrenheit). Lightweight, compact inflatables can be used at first to provide habitable space. Eventually, It should be possible to seal cracks in the lavatube walls to provide an airtight, shirt-sleeve environment. Some lunar lavatubes may be large enough to contain small cities. Living in a lavatube provides many advantages.

Benefits

  • There is substantual shielding due to having several meters of solid basalt between you and the outside. This is good against micrometerorites and radiation.
  • There is heat insulation because you are underground.

Size

A 1969 paper by Oberbeck, Quaide, and Greeley, taking into account only the Moon's lighter gravity, and not the stronger nature of lunar anhydrous glass, calculated lunar lavatubes could reach 340 meters in span (lengths could go to kilometers). There are some indications in Coombs and Hawke's work (see "Locations" below) that some lavatubes may be much larger.

References:

Size of lavatubes: Oberbeck, V.R., W.L. Quaide and R.G. Greeley, "On the Origin of Lunar Sinuous Rilles", _Modern Geology, v. 1, p. 75, 1969.

Strength of anhydrous lunar glass (significant component of basalt): Blacic, J.D., "Mechanical Properties of Lunar Materials Under Anhydrous, Hard Vacuum Conditions: Applications of Lunar Glass Structural Components", in _Lunar Bases and Space Activities of the 21st Century_, W.W. Mendell, Ed., Houston, Lunar and Planetary Institute, p. 487, 1985.

Locations

For her doctoral thesis under advisor B. Ray Hawke at the University of Hawaii, Cassandra Coombs scoured Lunar Orbiter photographs to identify a number of likely sites for lunar lavatubes. Due to the limiting resolution of the images, only the largest candidates could be identified. It is likely there are many smaller lavatubes in the identified areas and elsewhere. Smaller, but still large by human scale.

Reference:

Coombs, C.R., and B.R. Hawke, "A Search for Intact Lava Tubes on the Moon: Possible Lunar Base Habitats", in _The Second Conference on Lunar Bases and Space Activities of the 21st Century_, W.W. Mendell, Ed., NASA CP-3166, v. 1, p. 219, 1992

Shielding

An analysis of lavatube shielding from Solar Proton Events, Galactic Cosmic Rays, etc., has been done by De Angelis et al. When it comes to shielding, a little may be worse than nothing, because primary particles can interact with shielding material to produce a spray of secondary particles. Additional shielding is necessary to protect against these daughter particles. Findings by De Angelis et al. are that one meter of shielding is sufficient against Solar Proton Events, but powerful Galactic Cosmic Rays need roughly six meters for effective shielding. The analysis took into account the upper five meters is regolith. The findings were, "The radiation safety of lunar lava tubes environments has been demonstrated."

Reference:

Giovanni De Angelis, J.W. Wilson, M.S. Clowdsley, J.E. Nealy, D. Humes, and J. M. Clem: “Lunar Lava Tube Radiation Safety Analysis”. Journal of Radiation Research, Vol. 43, S41-S45 (2002), online at: http://www.jstage.jst.go.jp/article/jrr/43/S/43_S41/_article/-char/en

Habitat

As early as 1957, the prescient Robert A. Heinlein described people living and working in giant volcanic voids in the Moon (although they were large bubbles rather than lavatubes). In the 1976 second edition of _Depths of the Earth_, speleologist William R. Halliday suggests large lavatube caves may exist on the Moon and Mars, and "mankind may look to these. . .caves for ultimate survival." NASA "experimental planetologist" Friedrich Hörz finally put it all together in his 1985 paper, "Lava Tubes: Potential Shelters for Habitats". Oregon L5 Society expanded on this work, holding analog exercises in lavatube caves with Young Astronauts and filling-in research topics such as "Lavatube Entrance Amelioration on the Moon and Mars" and "Moon Lighting: Illumination for Lunar Base Construction and Operations". Their multi-year effort to publicize and bring the lavatube option to the attention of NASA and space development enthusiasts in general has been effective.

References:

Heinlein, Robert A., "The Menace from Earth", in collection _The Menace From Earth_, Signet, pp. 92-115, 1962 (orig. story copyright 1957).

Halliday, William R., M.D., _Depths of the Earth_, Revised and Enlarged Edition, Harper & Row, pp. 377-397, 1976.

Oregon L5 Society papers can be found at http://www.OregonL5.org/