#100 November 1996
Section 126.96.36.199.100.of the Artemis Data Book
Peter Kokh"SUB-TERRAFORMING LAVATUBES:" 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 extra-terrestrial 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
preva-lence of permafrost, a serious challenge to our bios-pheric and
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 dust-bowl 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.
The next step, tried before we risk presur-izing 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. MMM
Contents of this issue of Moon Miners' Manifesto