Moon Miners' Manifesto

#23 March 1989

Gas Scavenging

MMM # 23

March 1989

GAS-SCAVENGING

WASTE NOT, WANT NOT: AVAILABLE BYPRODUCTS OF SOIL MOVING

by Peter Kokh based on these sources:

1 Lunar & Planetary Institute, Houston and Research School of Earth Sciences, Australian National Univ., Canberra. pp. 147-169.

2 "WATER" AND CHEESE FROM THE LUNAR DESERT: ABUNDANCES AND ACCESSIBILITY OF H, N, AND C ON THE "MOON" by Larry A. Haskin, Dept. of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington Univ., St. Louis, MO.

The powderlike dust of the lunar surface is a housekeeping scourge. But this same fine grain texture carries with it a fringe benefit that more than makes up for any nuisance factor. It was one of the biggest surprises of the Apollo Moon Rock studies to find that this pulverized soil had been acting like a sponge soaking up the solar wind for four thousand million years. While the lunar rocks and soils themselves are extremely dry and deficient in volatile elements (those which melt and vaporize at relatively low temperatures) there are plenty of these elements both adsorbed to fine grains and trapped in minute cavities and pockets within soil particles.

Particles from the solar wind, from solar flares, and from cosmic rays, each leave characteristic traces and from these it is clear that the solar wind has been the main source of the volatiles we now find. Other sources include volcanic fire-fountains or fumaroles and meteoritic or cometary bombardment¹. By all these means, the upper meters of the lunar surface has become effectively saturated. A lunar form of fossil sunshine if you will.

Foremost of these guest elements is hydrogen - protons comprise 90% of the solar wind - followed by Helium - alpha particles comprising 10% of the solar wind¹. While no hydrogen has yet been found in lunar rocks proper that gives any indication of being native and while no water or water-ice has yet been found [as of 3/'89, eight years before the Lunar Prospector mission], the amount of adsorbed hydrogen is far from negligible. It is now estimated that there is enough hydrogen in one cubic meter of lunar topsoil to yield, combined with lunar oxygen more than a pint and a half of water. Extending this figure to the Moon at large, the total global regolith layer, if it could be harvested 100% for hydrogen, could yield a lake of water 10 km wide x 68 km long by 100 meters deep (roughly 6x40 miles by 330 ft. deep).² While this is hardly an ocean full it is a surprising amount all the same. The real question is whether this endowment can be harvested economically.

Carbon and nitrogen, which are found as traces in the rock (30 and 1 parts per million respectively) are enriched in the regolith soil to 115 and 82 ppm (kg per thousand metric tons).¹ Another way of putting this is that an area mined 6m long x 6m wide and 1m deep contains as much nitrogen as an average human body. Or consider that the amount of carbon locked up in soil organisms on Earth is only 2.7 times the amount of carbon adsorbed to the same amount of moondust. It's just there in a totally different form than we are used to finding and harvesting it. We need new methods, new tools, a new way of living off the land.

In Earthside laboratories, gasses trapped in lunar soil samples have been released by simple heating. Some gasses will need more heating to scavenge, others less. Further pulverizing may be needed to release compressed gasses trapped in glass cavities and vugs (small, irregular-shaped, rough, crystal-walled cavities inside rocks) at pressures commonly as high as five thousand atmospheres! Laboratory methods are one thing. Engineering the equipment to do the job economically on a large scale in routine fashion is another. Here is a hardware R&D job as ultimately important as any.

While it may be true that extracting the H, C, and N in a finite amount of lunar soil could provide for all the needs of an appreciable biosphere², the first milestone might well be the ability to make up for all leakage losses with the gasses extracted from the soil in the everyday 'lith-moving involved in building roads, excavating shelters, covering new habitats with shielding etc. As this would mean that all imported H, C, and N could go towards increasing the size of the biosphere, it would be a major step on the road to self-reliance.

What we are suggesting then is that any piece of 'lith-moving equipment involved in constructing the various parts of the base/settlement-to-be or providing the various processing plants with ores should routinely process all the soil it handles to harvest the gasses trapped in the soil. This capability should be built-in. On page twelve of this issue, there is a sketch by Pat Rawlings (Eagle Engineering) of a mobile soil harvester in the service of the liquid oxygen industry. This sketch appears in Ben Bova's 1988 book Welcome to Moonbase. In our view such a machine should never be built as depicted. Scavenging soil gasses (this does not include oxygen which is chemically combined in soil minerals, up to 45% by weight) must not be an afterthought, an accessory to be added later, a luxury to be built into future models.

Scavenging soil gasses will be an exercise in self-endowment and the settlement that does not practice it 'de rigueur' will not deserve to succeed. Gasses harvested in excess of current need will become a capital investment in the settlement's future. A lunar community that practices such gas scavenging will have a friendlier more at-ease attitude to its adopted world than one which, not doing so, chooses by default to remain a stranger in a strange land.

It's hard to say what a proper gas scavenging soil mover would look like. A lot depends on whether or not it is practical to do at least a first sort of the different gasses into separate tanks on the spot, possibly attached to sequential heating chambers, or whether this task is best done in a fixed plant. If the gasses can be stored compressed, the soil mover can do more work before unloading full tanks and taking on empties. Is anyone working on such a gadgetmobile? We would be surprised.

As to the noble gasses (those which are chemically inert and do not combine with other elements) each cubic meter of 'lith contains an average 20 grams of Helium, 2 each of Neon and Argon, 1 of Krypton, and a milligram of Xenon. The extent to which these gasses can be economically extracted from the soil may well determine which form of lighting bulbs and tubes it will be most feasible to manufacture on the Moon using the highest possible 'lunar content'.

Will neon lighting, presently undergoing a tremendous renaissance in this country, play a major role in illuminating as well as decorating lunar habitats? As soon as a lunar settlement reaches a certain viable size it will pay for it to provide for its lighting needs by self-manufacture so this question is not an idle one.

There are strong implications in all this for lunar city-planning. Contrary to the usual vision of lunar settlements in which personnel are limited to cramped quarters sardine-style, our future lunar sodbusters engaged in routine gas scavenging may find it profitable to construct more square footage of habitat and more footage of pressurized passages and roadways per person. As avoiding cabin fever will be harder than on Earth, this may be the only way to sustain general mental health and morale. Lower density living brings with it lessened vulnerability to impact damage, and a larger biosphere mass per inhabitant i.e. "MM Manifesto"!

Contents of this issue of Moon Miners' Manifesto