The Potential of Lunar Lavatubes

© 1996 Copernicus Construction Company

Peter Kokh and Doug Armstrong



Settling into a Lavatube

Brainstorming an Early Lavatube Town

Many of our readers will be familiar with the classical Island II "Stanford Torus" space settlement design [Space Settlements: A Design Study, NASA SP-413, 1977]. Not counting multiple levels, this ring with an overall diameter of 1800 meters and a torus cross section of 130 meters, has a circumference of 5.655 km or 3.5 miles and a usable surface area (lower slopes included) of about 50 acres.

With multiple levels, it was estimated some 10,000 people could occupy 106 acres (Manhattan like sardine packing, i.e. quite dense by modern urban standards of c. 5,000 people per square mile = 640 acres.) That seems overdoing it especially since off Earth settlements wherever they are will first and foremost be farming villages: = lots of plants hosting very few people, not vice versa.

But thanks to the copious artwork that has accompanied the settlement design studies of the seventies, such a torus does give us an assist in conceptualizing a lavatube settlement. Cut it at one point and unroll it, and you have something comparable, if on the small end, to what we might someday see in lavatubes. The average lavatube is likely to be several times wider than the torus of the NASA study.

interior torus view, art by Pat Hill, IBID, p. 90

picture to be scanned in

In practical fact, however, this scene gives us more of a goal to hold before us, than a model for feasible near term reality. Sealing a lavatube so as to pressurize it may be easier said than done. If we succeed, filling the immense volume with the usual buffer gas of nitrogen imported from Earth in a 4:1 ratio with lunar oxygen may be budget-busting. But more on this in an article below.

Near-term, pressurized ceiling clearances will have to be kept to a minimum. We will use lavatubes at first not to escape the vacuum, just to escape the deadly cosmic weather that normally comes with vacuum - on the exposed surface.

The tube ceiling vault functions analogously to the Biblical "firmament" protecting Lunans in their hidden valleys (lavatubes) from cosmic radiation etc. and from the otherwise omnipresent dust. Even if the tube is not sealed and pressurized it may be feasible to spray a high albedo coating on the upper walls and ceilings (CaO lime, or Aluminum Oxide or Titanium Dioxide, all producible cheaply and in quantity, are white. The trick is to make an anhydrous "whitewash". Unfortunately, bluing this inner "sky", e.g. with locally-producible cobaltous aluminate would be expensive.

Sunshine could be brought in down simple shafts or through optical cable bundles, to be turned on this sky-firmament, thus providing comfortable daylight type ambient light. During nightspan, nuke or fuel-cell powered lamps on the surface could use the same light transmission pathways. Possibly any whitewash material on the upper vault of the tube could have a phosphorescent component for a night span treat. Imagineering, it is called.

KEY: (a) sunshine access and defuser system; (b)whitewashed "firmament" for best sunlight reflection; (c) "town deck" on tube-spanning beams; (d) assorted structures; (e) "yurt/ hogan" type home with translucent dome to flood interior with firmament-reflected sunshine; (f) monorail transit system; (g) lavatube floor left natural; (h) nature walks.

Instead of grading or even terracing the lavatube floor, it could be left natural with the town built on a spaceframe deck spanning the lavatube shoulder to shoulder. an overhead crane riding rails along the sides of this deck could be useful in constructing/erecting habitat structures. The use of stilt platforms is a possible alternative to the deck span shoulder to shoulder beams

Elevators to the surface can either be incorporated into "skyscrapers" reaching to the tube ceiling, or be built freestanding to provide great views of the town on the descent from or ascent to the surface.

Access to the settlement from the surface is vital. This can either be by freight and passenger elevator shafts or by a ramp road up the talus slope of a nearby natural entrance. We think the first option will bear the brunt of the traffic.

KEY: (a) sunshine access via suspended "daylux" defuser grid instead of coatings; (b) elevator shaft through "skyscraper"; (c) transit system on stiltway over tube floor.

The tubes are given to us dust-free. Thoughtful engineering of tube access systems will help keep them that way. For example, elevators could have their topside terminals opening not onto the dusty surface directly but onto a suspended platform/launchpad complex.

Appearances aside, a vital part of the settlement will be out on the surface and building material and component manufacturing out of "pre-mined" regolith, "the" asset of the surface. Once a processing, manufacturing, or gas scavenging operation is past the "dust-using" phase, further processing, manufacturing, assembly, or separation can be more safely and more economically done in the lee vacuum environment within the lavatube. Industrial siting decisions will take into account the degree of involvement of solar power and concentrated solar heating, of course. Operations that are electricity driven and not reliant on moondust, will be the first to move into the tube.

For the lunar architect and contractor, however, freedom from the need to be concerned with shielding is a considerable gain. Tube residences and other structures can have simple windows, and lots of them, through which to behold these netherworld landscapes. The shielded windows of in-surface structures which use mirrors and bent optical paths to thwart radiation, will be a cumbersome relic of pioneer beachhead days, still used where Lunans must live in the regolith blanket surface rather than in provident subsurface voids. Tube structure windows may be characteristically convex, curved in to the pressurized interior, so as to put the panes under compression. Glass and concrete are stronger under compression than under tension. Nor will in tube windows need sacrificial panes.

The subsurface Moonscapes within the lavatubes will be quite different from the surface ones, though sharing one all important, all infecting aspect: their barrenness and sterility. So tubers may share with topside moles the practice of placing plants in front of windows as a psychological filter.

Many architectures are possible. One simple tuber home plan would be a squat 2-story vertical cylinder section topped off by a convex-paned geodesic dome to let in the tube's ambient light. The design type might be called the Yurt or Hogan after the Mongolian and Navaho home shapes it resembles.

KEY: (a) 2-story vertical cylinder section, bedrooms on the lower level; (b) lunar translation of the geodesic dome for a high translucent ceiling vault over the family room and other common areas including a central garden atrium; glass panes are neither flat nor concave, but convex; (c) cable stays prevent internal pressure from literally "blowing off the roof"; (d) the residential deck of the townsite, leaving the tube floor ungraded.

NOTE: upscaled, the yurt/hogan design will make a fine church, synagogue, or meditation chapel, with the simple use of stained glass convex panes in the roof dome. A dedicated shaft of directed sunshine on such a dome would surely help set the mood.

The early lavatube settlement will not be an assembly of individually pressurized buildings, but rather, like the in-surface burrowings, a maze of structures conjoined by pressurized walkways, streets, alleys, and parkways. In the netherspaces, thoroughfare cylinders can be generously paned with convex windows to flood their interiors with ambient reflected and diffused sunshine and views.

KEY: (1) cylinder section; (2) convex-glass panes to let in ambient reflected sunshine and views; (3) Yurt/hogan style homes opening onto street via entrance tubes (4); (5) pedestrian "sidewalks"; (6) rail-suspended goods delivery platform; (7) "crosswalks"; (8) landscaped, concrete free garden strips; (9) dust-purged, conditioned regolith geoponic soils.

Along with solar access for reflection off coated upper tube surfaces, there can be some sunshine ports that direct intense pools of light downward, say on the convex-paned lunar geodesic domed park squares. Nothing is so soul-renewing as a visit to a pool of strong over-illumination, the feeling of being outdoors in the undiluted brilliance of the unmediated Sun. Directed sunlight, minus the infrared removed by proper glass filters, will also be needed over agricultural areas.

You can see how construction and architec- ture in lavatube settlements differ from the other types of in-surface settlements we have discussed before. Initially, there will be a strong reliance on inflatable structures and inflatable-rigid hybrids. Here, in lee vacuum, with no need to cover them with shielding, no vulnerability to micrometeorite puncture or ultraviolet and flare and cosmic ray aging, inflatables will have their heyday. All the same, as the costs of new made on lunar building materials and building components come down, and appropriate construction and erection methods are perfected, the bottom line money consideration will move settlement expansion in that direction.

An intermediate phase may involve the use of inflatable structures as slipforms for cold-casting (poured and sprayed lunar concrete) and arch/vault component placement.

As more generous endowments of nitrogen become financially feasible, larger domes over park space commons will make their entrance, affording a more generous "middoors" and the more obvious comfort of luxuriant flora and fauna, plants and urban wildlife.

Meanwhile, in the lee vacuum but visible out the abundant windows of lavatube structures will be other extensions of the settlement: sculpture gardens and Japanese style rock landscaping. Electronic displays on the tube walls, even something reminiscent of drive-in theaters, or should we say through-the-windshield theaters? Backlit murals on glass can infuse the citizens with the dream of a Green Luna, not altogether out of reach. And I'm sure sooner or later we'll see some gross examples of tagging by artistically inclined youth without direction or access to approved ways of expression.

Nature walks can educate citizens on the fine points of lunar geology and variations in lavatube textures and formation.

The lavatube settlement will not be a solitary community. To provide around the clock manning of industrial and agricultural facilities owned in common, a string of three villages with staggered day/night lighting (the solar access ports can be shuttered after all) will provide a succession of prime work time day shifts. A trio of villages can be separated by some distance along the inside of a lavatube, with intervening light baffle curtains (where convenient bends in the tube route do not offer the same benefit. Mass transit will unit them, and they can share 24 hour around the clock metropolitan facilities and amenities, including schools and parks and other investments that need to earn their peak full-time, or should we say all-time.

Settling the first lavatube should be part of a well-thought out Outpost Conversion Strategy. An initial beachhead outpost is succeeded by a surface Construction Camp once a mature set of feasibility experiments leads to the production of on site building materials. Proper site selection will have taken "graduation" to a nearby lavatube into account as an essential ingredient. Finally, after robot exploration and surveying of the proposed first site, will come the erection of lavatube village one, village two, a metro complex, and village three. Along with warehousing, farms, and industrial park sections - a whole mini urban complex.


Sub-Terraforming Challenges

Challenges of Sealing & Pressurization

While the volumes available in lavatubes are comparable in cross-section to space settlement designs, especially that of "Island Two", they may not be so readily pressurizable. Lavatube walls were not formed as "pressure vessels" and have never been pressurized (except for the possibility of comet puncture and vaporization). Whether they could structurally withstand the expansive stresses of full atmosphere is uncertain. After all, they exist in an ambient vacuum. Deeper lavatubes will have a better chance of maintaining their integrity, more shallow ones a greater chance of "blowing their lid."

Even though lunar lavatubes have come down to us intact through nearly four billion years of time, that does not mean that there are no fractures in their surfaces that could let an atmosphere eke out slowly but inexorably. And those tubes with entrances provided by past section collapse (illustration on page 4), will have to be closed off somehow. Those without open-vacuum entrances can be many miles long. That means they suck up enormous volumes of lunar oxygen and terrestrial nitrogen.

Of the three principal lunar-scarce volatiles, necessary for life, Hydrogen, Nitrogen, and Carbon, it is nitrogen that is most deficient on the Moon in comparison to the quantities we would like to have. But even if the import cost were no problem, or if we find cheaper extraterrestrial sources (the rocks of Phobos for example) there is the question of the sealants needed themselves.

We could use microwaves of laser sweeps to glassify the lavatube inner surfaces, making them impervious to gas transmission. But introduce water and humidity and we have a problem. Water attacks glass over time. Epoxy resin coatings could not be processed from known lunar materials, and in the quantities needed would pose an astronomical cost.

But if water seems to be the problem, it may also be the solution. For if we saturate the lavatube with water vapor, no matter to what level we manage to raise the inner surface temperatures in the tube, at some point in the peripheral rock, water vapor will form a rock-saturated frozen seal against further loss. Water vapor may be self-sealing.

But this brings up another problem which, all the denial in the world notwithstanding, affects space settlement designs as well - the likely prevalence of permafrost, a serious challenge to our biospheric and agricultural visions.

Suppose we solve most of these "engineering challenges". For safety sake, both against possible decompression accidents and biological contamination, we may want to develop a system of sphincters that can pinch shut convenient sections of lavatubes if need ever arises.

Yet the dream of recreating some part of the Earthly paradise is a very strong and persistent and infectious one. In a lot less time than it will take to overcome the challenges of terraforming the Martian surface, we will be able to start terraforming limited lavatube sections. In contrast to the case on Mars, terraforming the Moon's hidden valleys will work to keep the out-vac surface comparatively pristine. For the Moon's dusty surface which has never known water of air, that is important. An attempt to terraform the surface (it is estimated that an Earth-dense atmosphere would hang around for a few thousand years - and that is practical for human purposes), any such attempt is likely to backfire and create a dustbowl condition that will last some centuries.

The more modest goal of terraforming lunar lavatubes will be a lot like terraforming O'Neill's Space Settlement structures or Dandridge Cole's hollowed out cigar-shaped asteroids (e.g. Eros).

In H.G. Wells' "First Men on the Moon", we discover a native "Selenite" civilization tucked away in caves within the Moon. The idea is not new, and now it is more timely than ever.

GOALS of an early lavatube terraforming experiment program

We can safely experiment on a small scale, sealing off and pressurizing small sections of tube for transformation into metropolitan centers and village parks. If these special urban facilities failed, it would not interfere with the operation of the rest of the close-pressurized settlement maze.

The next step, tried before we risk pressurizing a whole settlement, might be a lavatube "Natural Park(way)" - Designed as a safety valve and as a bit of Old Earth for those who cannot afford or physiologically risk a trip down the maw-throat of Earth's hexapotent gravity well, our parkway would be visited and toured, but not open to settlement. Here Lunans could appreciate what they might have missed on Earth, and find themselves renewed and inspired to carry forward the great Lunan experiment. Trial biospheres rich in flora and fauna could be developed without risking would-be residents. A place for honeymooners and lovers and students and retirees - for everyone, The Mecca for Lunans.

Next, a more confident, lesson-learned suite of biospheric experiments behind us, we will have the confidence to tackle bigger and better projects. Biospherics could come to Garden Suburbs, whose condo-owners would pay the cost of experimental installations. And why not a tube amusement park?

There is another question here. Creation of a biosphere for our terraformed volume. The go slow experiments above will educate us and give us confidence before we risk citizen lives.


"Down Inside" Civilization & Culture

Part I: Naming Lavatube Settlements

People pick place names for all sorts of reasons: to remember a home town or country, in honor of a fellow pioneer who did not survive the transplantation journey, for a nearby geographic or geologic feature, for a character in a book the leader happened to be reading. The list or rationales is endless. It will be no different on the Moon.

But perhaps there will be a conscious effort among the first pioneers, for whom lavatube life is something new and untried, to make allusion to hidden valley, subterranean, and submarine places and kingdoms of ancient lore. After all, it will be this aspect, something not yet taken for granted, that will be foremost in their consciousness as they embark on this new adventure.

A dictionary or encyclopedia I have of mythological and fictitious places gives lots of leads, but most of them are obscure. Pellucidar (Edgar Rice Burroughs) and all the local place names associated with this fictitious region will be a prime source. Then there are the submarine legends like Atlantis - after all, lavatubes lie beneath the congealed waves of ancient lava seas.

And then there are the hidden valley stories like Shangri-La. Shangri-luna, anyone?

Once the novelty wears off, lavatube and lavatube settlement names are more likely to come from nearby surface features (rilles, craters, etc.).

"Co-names" might include Depths, Nethers, Cloisters, Retreat, Lair, Anchorage, Haven, Warren, Trove, Sanctuary, Sanctum, Burrow, Hollow, Grotto, Lower-, Nether-, -neath, and similar descriptive choices.


"Down Inside" Civilization & Culture

Part II: Lavatube Culture

That we can predict a substantial and marked difference in the maturing cultures of those Lunan settlers who live on the surface, snuggling up under their protective regolith blanket, from that of those who build their townsites within ready-to-occupy lavatubes, should be clear from the length of the list of their respective "transcendental worries".

Coddled by a womb world in which all these basic things are already provided, freeing us to concentrate all our worry-power on lesser if analogous concerns (weather, harvests, economics), it is not hard to see how much more squarely Lunans might feel themselves "behind the 8-ball" than Earth folk. It should also be clear that lavatube dwellers have a substantially reduced worry burden.

Shelter one can count on and take for granted against micrometeorites, against decompression accidents from meteorite debris, against cosmic rays, against the raw naked ultraviolet heat of the Sun, against Solar Flare temper tantrums - this bequest of the lavatube is bound to make its havened citizens a noticeably more carefree lot - even if only in a relative sense. To be sure, the two remaining "transcendental worries" will still provide a strong bond between these two "branches" of Lunan culture.

Hopefully more in friendly jest than in contempt, those of either persuasion may take jabs at those of the other. Surface dwellers may call their cousins "tube toads", "cozies", "womb-retentives". In counterplay, lavatubers may call their surface relatives "mound moles", "dust eaters", and the like. One side or the other may retranslate the long litany of ethnic jokes, translated oft before (the very same jokes some tell of Poles, Poles tell of Russians, etc.). We can hope. such jibes will be more a symptom of friendly rivalry than a hint of unjust contempt.

On the other hand, in describing themselves, surface folk might call themselves "blanketeers" or "the star-sighted" or some other name which heralds the compensating glories of a life on or just under the surface. By the same token, tube folk might call themselves "down insiders" or "the sanctuaried" or by some other term that highlights the advantages they enjoy and appreciate.

Being a "Tuber"

Settlers who live much of their lives within the lavatube environments may exhibit as a group, relatively speaking, a more "laid back" personality, They must still be much more alert to individual and communal danger and potential catastrophe than most terrestrials. (Granted many of us Earthlubbers relish in the nature-daring risks of living on active faults or on the slopes of active volcanoes or in the path of hurricanes etc.)

In addition to this somewhat more relaxed mien, tubers will employ different set of architectural solutions in building their homes and settlements [see last issue, pages 7-9 "Settling into a Lavatube"]. They will look out their windows on radically different underworld "moonscapes". They will tend to establish and preferentially use their own distinct "networks" with other outposts, settlements, industrial parks, farms, resorts, etc. "up" or "down" the line in the same tube, or in intersecting neighboring tubes (in comparison to the mainly overland connections between in-surface outposts).

Tubers, doing all the ordinary things to earn their individual and communal living as settlements elsewhere, will be further boosted in their sense of fulfillment by the very unique to their situation communal "vocation" of "archiving" [see below]. And finally they may feel a certain affinity with settlers in the geologically analogous lavatubes we expect to find on Mars, and elsewhere. All of these strongly distinguishing characteristics should work to give tubers a sense of special identity and fellowship.

Will they in fact identify themselves as "tubers", refer to their communities as "tubetowns", and to their collective realm as "Tubedom"? Or will they call themselves lunar netherworlders, or underworlders, or selenospeles, or find some other set of words? That's up to them.

Surely they will publish their own magazines (<Lunar Tubes & Trails , Lunar Tubeways , Hidden Lavascapes>, or whatever.) These publications will share information about new tube-appropriate architectural and construction methods, about new lavatube developments and recreations, about the developing culture and arts and crafts of nether-worlders, and promote continued lavatube exploration in adjoining areas, lower levels, and new areas.

Ever "Remapping" the Moon

It will be the tubers who keep publishing ever new editions of lunar maps. The surface having been well mapped for a long time, new selenographical discoveries will be predominantly those coming from discovery, surveying, and exploration of new lavatubes, of lavatube extensions and connections, of lover level tubes etc.

Nor will this be information relevant only to scholars> The expansion of the <Terra Habitabilis Cognita> (known habitable [= pre-shielded] land) on the Moon, the identification of natural <metropolitan complexes>, the growing square mile count of known usable tubes reserves; this will all have considerable economic significance.

Special legend maps will be color-coded to indicate the relative density or paucity of the subsurface maze. The latest maps, with their "upwards revisions" of the real expanse of "Terra Habitabilis Cognita", will be on hand in quantity at space frontier development trade shows on Earth or elsewhere, to acquaint would be developers, investors, and settlers, with the ever expanding opportunities.

Lure of the Covered and Hidden

In the last issue [page 11 "Naming Lavatube Settlements"], we mentioned some of the especially romantic names available from Earth's literature and mythology that would seem specially appropriate. While choosing such names might have a welcome initial moral-boosting effect on the settlers (after a time, a name becomes just a name), the naming of a new or proposed settlement or of its host lavatube, will be a very conscious and deliberate part of "packaging" aimed at prospective new settlers, developers, and investors - in a mostly friendly but ever serious rivalry for the most and the best. After all, any community is a virtual "team", and some teams are quite frankly better and more successful economically than others.

Together, rival lavatube settlements can chose language, phrases, conjure up images etc. that will predispose would-be-settlers to choose one of them over a surface settlement. The safety angle of given all-but-invulnerable shielding ("Realm of the [Inner] Firmament [Down Under]") will be played up. Brochures will invite: "Come to the Moon's Inner Sanctum", "Visit the Inner Worlds of Luna", "Experience the Mystique of the Moon's "Hidden Valleys."

To reinforce the general impression, some developers will specialize, not in settlements per se, but in "Utopia for a Moment" resorts: Lunar Hidden Valley recreations of mythological utopias: Camelot, Shangri-Lá, Walden, Briggadoon, and so on. Tongue-in-cheek, a legend of lavatube formation, not as relic dry subterranean lava wadis or arroyos, but as "lavaworm holes" will catch the attention of the over imaginative fantasy-loving.

And something too for the all important market segment: the risk-it-all for adventure types. Ads will hype the possibility of finding more than just empty wall-fused vacutoria - of finding special treasure troves of inestimable market value. If we find just one lavatube in which a penetrating-but-not-collapsing comet has vaporized to freeze out as a minable coating of ice on the tube's walls, a new "49er" or "Klondike" rush will be on. And there may be unsupportable and unconscionable talk of lavatubes full of gems, or of easy-to-imagine alien-left troves of high technology craft and equipment, etc.

That Extra, Communal Vocation - "Archiving"

The primary asset offered by the lavatube environment is "protection - protection with a multibillion year warranty". Any intact lavatube on the Moon has already survived nearly four billion years and will loooong outlast any feature, surface or subsurface on the geologically active Earth.

These are sanctuaries from bombardment - the vast bulk of tube-collapsing impacts occurring in the 500 million year epoch early in Solar System history, when there was still a lot of planet-forming debris to sweep up. Team that up with the "ideal" designer combination of radiation-free, ultraviolet-free, solar flare-free, fixed temperature ultra-dry "lee" (shielded) vacuum. What we have, in great abundance, is a place in which to achieve, store, and preserve humanity's treasures , not just for the current age, not just for millennia, not just for millions of years, but for billions of years to come, for as long as humanity will be able to inhabit the Inner Solar System.

And Beyond. Long after we have vanished from the stage, what we have preserved in lunar lavatube archives will remain a well-preserved, degradation free reliquary for the examination of any other intelligent folk who come our way. Eons-stable lavatubes are the very first place, indeed the only place, any visitors would think to look for preserved ancient relics of a native but now-extinct or just-vanished space-faring species. Such visitors might indeed be <our own distant progeny>, making a pilgrimage to legendary Earth Space in search of their roots.

The establishment of some Grand Archives of All Humanity in a lunar lavatube site is potentially the greatest gift (after an environmentally rescued and preserved home planet, of course) we can bequeath successor human generations to come. So what might we store and preserve therein.

Only a small number of lavatube settlers may be involved in this special industry tailor-made for tube towns. Yet that the Lunan lavatube community as a whole serves this special unique added function of inestimable economic impact long term and a vocation of unfathomable cultural, psychological, and spiritual impact, is likely to insert itself in the general communal consciousness at large. It will be a point both of pride, and duly prideful self-identity. In archiving, Lunan lavatube dwellers will serve a need no other pocket of humanity, not even (especially not) any of the bulk of humanity still on Earth!

This Service will quickly become a tradition. It may in time even take on trappings that are quite "sacerdotal" (priestly) in nature. Special technologies will be developed precisely to better preserve, index and catalog, access, and display all of these priceless, timeless treasures. There are sure to be college courses and degree programs (in the various Lunan universities at least) in "Lavatube Archival Science". <MMM>

Comments on the above Lava Tube Articles by Bryce Walden

Lava tube formation & characteristics by Peter Kokh

Lava Tube Dimensions by Richard Marsden

Lunar Volcanism by Richard Marsden

Visiting Oregon Moonbase by Bryce Walden

Searching Mars for Lavatubes by Peter Kokh


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