Utility of Lava Tubes
on Other Worlds
By Bryce E. Walden, Thomas L. Billings, Cheryl Lynn York,
Stephen L. Gillett, Mark V. Herbert


Location

On Mars, as on Earth, lava tubes are found in the extensive lava fields associated with shield volcanism.1 Lunar lava tube traces are located near mare-highland boundaries,1 giving access to a variety of minerals and other resources: steep slopes,2 prominent heights for local area communications and observation, large surface areas in shade,3 and abundant basalt plains suitable for landing sites, mass-drivers, surface transportation, regolith harvesting, etc.


Detection

Methods for detecting lava tubes include visual observations of collapse trenches and skylights,4 ground-penetrating radar,5 gravimetry, magnetometry, seismography,6 atmospheric effects,7, 8 laser, lidar, infrared, and human or robotic exploration.9


Access

Natural entrances to lava tubes are at the ends of sinuous rille collapse trenches and through roof collapse skylights. Artificial access should be possible by drilling or blasting at any desired location through the roof of the lava tube.10


Composition

Lava tubes are found only in extremely fluid pahoehoe basalt, where they are a major mechanism of lava deposition.11 Lava tubes are therefore an integral part of the basalt bedrock. The bedrock floors and walls may be convenient to provide solid foundations or anchor heavy equipment, particularly on the Moon where bedrock surface exposures appear to be rare.12

On lighter gravity worlds, lava tube caves can be larger than on Earth. On Mars we may find widths of a hundred meters; on the Moon spans of over 300 meters are possible,13 and there is some evidence spans may be much larger, up to 1.3 kilometers, with lengths of several kilometers.4 This amount of sheltered volume can be a significant resource.


Volatiles

Cold air can pool in lava tubes. Water draining into this cold trap freezes. Some terrestrial caves can nearly fill with ice.7 On Mars, some lava tubes may contain reservoirs of ancient water ice, possibly preserving records of the planet's dramatic climate changes as well as serving as a ready resource. Cometary volatiles could have made their way into lunar lava tube shelter and still be preserved. Volcanic volatiles may also be present.4


Dust

Lava tube caverns probably have extensive areas free of the abrasive and problematical dust endemic to the surfaces of the Moon and Mars.


Shelter

Lava tube caverns have roofs tens of meters thick (roughly 40 meters on the Moon, perhaps 20 meters on Mars). This makes the cave environment relatively safe from solar radiation, cosmic rays, micrometeorites, and even small macrometeorites (up to 20-meter crater sustainable on the Moon).14 Transportation between operational and habitation sites within the lavatube is protected by the basalt shield. Stable cave temperatures (Moon est. -20 C)14 are less stressful on equipment than the wide diurnal swings on the surface. The cave interior could act as one pole of an oscillating heat engine, heat transfer occurring inward during the day and outward at night. On Mars the caves are shelter from the winds and dust storms.


Morphology

Lava tube shape can be useful. Lava ponding might provide a stable, level foundation with little preparation. Parallel benches or parallel lava tube walls could support crossbeams. The void below might become a service corridor.

The strong arched roof can support suspended transportation elements and even facilities. Herbert estimates a roof only 3.5 meters thick could support 45,835 kg/m on Earth.10 Assuming similar basalt strengths, this translates to 137,000 kg/m on Mars and 275,000 kg/m on the Moon. Thicker roofs on the Moon or Mars could be expected to carry correspondingly larger loads.

Piles of "breakdown" boulders make surface traverses difficult and dangerous, but they also represent a resource. Their blocky, rectilinear shapes suggest use for simple rock constructions.15 They are also portable weight useful for ballast and counterweights. Transportation over these "breakdown" areas may use a suspended cable car system.

Gentle slopes of the lavatube system can be useful in a variety of ways for utilities and industrial processes.14


Construction

Actually sealing and pressurizing these large caves is a major and expensive undertaking, and probably will not be attempted until later development. Initially construction inside a lava tube could be simple inflatable structures.16 Ongoing construction can be lighter, built faster, and maintained more easily than surface structures.14 Productive base operations can commence sooner than with equivalent surface bases.

On the Moon strong anhydrous glass can be used for structural elements such as beams, walls, and cables. Woven glass threads can create a strong fabric for tents and inflatable structures.17 Steel can be made from in situ resources on the Moon (and probably Mars), and has better structural characteristics than aluminum.18


Psychology

The psychological value of being able to work and relax under the secure shelter of tens of meters of basalt shielding should not be underestimated. Cave-ins are unlikely in lava tube caverns that have survived for thousands, millions, or billions of years. Of course, human activity should be conducted with care where it might provoke collapse, such as blasting or drilling.

Views on the lunar surface are restricted due to the need for radiation shielding. Within the lava tube caverns, large windows can look out on great vistas, increasing the "psychological space" of small pressurized habitats.19 Larger, more spacious habitats can be built without regard for heavy shielding. People will be able to watch the bustling activity of the base.


Economics

Lava tubes can be economically advantageous immediatly and realize continuing economic advantages.16

The amount of excavation necessary to prepare a lava tube entrance should be comparable to that required to shield a surface lunar outpost, and may be used for that purpose. In return, access is provided to a large shielded volume.14

The sheltered construction environment within a lava tube cavern significantly decreases risk from radiation and solar storms. This should reduce insurance costs and other costs of risk. Since construction within the lava tube does not require shielding, each structure can realize a significant cost savings.

The stable interior temperature of the lava tube environment means environmental control can be simpler. It also means less energy need be expended to counter wide diurnal temperature swings. Equipment will require less maintenance due to decreased wear and tear of wide temperature swings.

Lack of dust should reduce maintenance due to that contaminant, as well as reducing the need for dust mitigation in various base and habitat elements.

Lightweight, flexible "thinsuits" might be used in the protected environment, increasing efficiency of workers and reducing fatigue.14


Summary

It would be structurally, economically, and even aesthetically advantageous to utilize lava tube resources which are already in place and available to us on the Moon and Mars.


References

  1. Burke, J.D., "Apollo 15 Lunar Base Site: Steep Slopes as an Energy Resource," Workshop on the Geology and Petrology of the Apollo 15 Landing Site, ed. Spudis, Paul D. and Graham Ryder; (Houston, TX: Lunar and Planetary Institute, 1986) pp. 38-43.

  2. Bergeron, Denis E., "Constant Temperature Vessels for Lunar Base Applications," Papers Presented to the Second Symposium on Lunar Bases and Space Activities of the 21st Century, ed. Mendell, W.W.; Second Symposium on Lunar Bases and Space Activities of the 21st Century, Houston TX 1988 April 5-7 (Houston, TX: Lunar and Planetary Institute LPI Contribution No. 652, 1988) p. 17

  3. Coombs, Cassandra R. and B. Ray Hawke, "A Search for Intact Lava Tubes on the Moon: Possible Lunar Base Habitats," (Honolulu, HI: Planetary Geosciences Division, Hawaii Institute of Geophysics, University of Hawaii, PGD 541, 1988) Ph.D. Thesis, 1988 October, 25 pp. + vii

  4. Billings, Thomas L., "Remote Sensing of Lunar Lavatubes from Earth," JBIS 44, 1991, pp. 255-256.

  5. Billings, Thomas L., Cheryl Lynn York (Singer), and Bryce Walden, "Lavatube Options," Lockheed Large Habitable Volumes Study, ed. (Lockheed Engineering & Sciences Corporation, under NASA Contract, ), 1989 February 03 (Oregon City, OR: Oregon L-5 Society, Inc. (Oregon Moonbase), 1989) 80 pp.

  6. Blacic, James D., "Mechanical Properties of Lunar Materials Under Anhydrous, Hard Vacuum Conditions: Applications of Lunar Glass Structural Components," Lunar Bases and Space Activities of the 21st Century, ed. Mendell, W.W.; Symposium on Lunar Bases and Space Activities of the 21st Century, Washington D.C. 1984 Oct. 29-31 (Houston: Lunar and Planetary Institute ISBN 0-942862-02-3, 1985) pp.487-495

  7. Daga, Andrew W., Meryl A. Daga, and Wendel R. Wendel, "A Preliminary Assessment of the Potential of Lava Tube-situated Lunar Base Architecture," Engineering, Construction, and Operations in Space II: Proceedings of Space 90, ed. Johnson, Stewart W. and John P. Wetzel; Engineering, Construction, and Operations In Space II (Space 90), Albuquerque NM 1990 April 22-26 (New York: American Society of Civil Engineers ISBN 0-87262-752-7, 1990) v1, pp. 568-577

  8. Gillett, Stephen L., "Preliminary Geologic Characterization of Young’s Cave Lava Tube System, Bend, Oregon, and Implications for Lunar Base Lava Tube Siting," Site Characterization and Phase One Development Plan for the Oregon Moonbase, ed. York (Singer), Cheryl Lynn, Bryce Walden, and Thomas L. Billings; (Oregon City, OR: The Oregon L-5 Society, Inc. (Oregon Moonbase) under NASA NASW-4460, 1990) 14 pp. + 8 Figures.

  9. Greeley, Ronald, Geology of Selected Lava Tubes in the Bend Area, Oregon, (Portland, OR: State of Oregon, Department of Geology and Mineral Industries, 1971) 47 pp.

  10. Greeley, Ronald, Planetary Landscapes, Second Edition, (New York: Chapman & Hall, 1994) 286 pp. + xiii

  11. Herbert, Mark V., "Preliminary Engineering Analysis, Proposed Oregon Moonbase Research Project, Deschutes County, Oregon," Site Characterization and Phase One Development Plan for the Oregon Moonbase, ed. York (Singer), Cheryl Lynn, Bryce Walden, and Thomas L. Billings; (Oregon City OR: The Oregon L-5 Society, Inc. (Oregon Moonbase) under NASA NASW-4460, 1990) 31 pp. + 5 figures & Appendix (2 pp.).

  12. Horz, Friedrich, "Lava Tubes: Potential Shelters for Habitats," Lunar Bases and Space Activities of the 21st Century, ed. Mendell, W.W.; Symposium on Lunar Bases and Space Activities of the 21st Century, Washington D.C. 1984 Oct. 29-31 (Houston, TX: Lunar and Planetary Institute ISBN 0-942862-02-3, 1985) pp. 405-412

  13. Kelso, Hugh, et al., "Comparing Structural Metals for Large Lunar Bases," Engineering, Construction, and Operations in Space II: Proceedings of Space 90, ed. Johnson, Stewart W. and John P. Wetzel; Engineering, Construction, and Operations in Space II (Space 90), Albuquerque NM 1990 April 22-26 (New York: American Society of Civil Engineers ISBN 0-87262-752-7, 1990) v1, pp. 429-438

  14. Khalili, E. Nader, "Regolith and Local Resources to Generate Lunar Structures and Shielding," Papers Presented to the Second Symposium on Lunar Bases and Space Activities of the 21st Century, ed. Mendell, W.W.; Second Symposium on Lunar Bases and Space Activities of the 21st Century (Lunar Bases II), Houston TX 1988 April 5-7 (Houston, TX: Lunar and Planetary Institute LBS-88-027, 1988) 14 pp.

  15. Larson, Charlie & Jo, Central Oregon Caves, (Vancouver, WA: ABC Printing, 1987) 44 pp

  16. Larson, Charlie & Jo, Lava Beds Caves, (Vancouver, WA: ABC Publishing, 1990) 56 pp.

  17. Lewis, William, "Lunar Machining," Lunar Bases and Space Activities of the 21st Century, ed. Mendell, W.W.; Symposium on Lunar Bases and Space Activities of the 21st Century, Washington D.C. 1984 October 29-31 (Houston TX: Lunar and Planetary Institute ISBN 0-942862-02-3, 1985) pp. 519-527

  18. Oberbeck, Verne R., William L. Quaide, and Ronald Greeley, "On the Origin of Lunar Sinuous Rilles," Mod Geol 1, 1969, pp. 75-80.

  19. York, Cheryl Lynn, Bryce Walden, Thomas L. Billings, and P. Douglas Reeder, "Lunar Lava Tube Sensing," Poster Presentation at Joint Workshop on New Technologies for Lunar Resource Assessment, Santa Fe, New Mexico 1992 April 6-7 (Oregon City, OR: The Oregon L5 Society, Inc. (Oregon Moonbase) 1992)
Portions of this work were supported under NASA contract NASW-4460.


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