Economical Carbon Use and Process Synergies in Early Lunar Development
Over the last 20 years, many researchers have noted the desirability of using in-situ resources for multiplying the return from each dollar spent on space exploration (reference i). Less explored are the possibilities for combining the results of different in-situ resource extraction processes, much less using them in combination with the biological wastes of base workers. This effort explores some of the possibilities for doing both in the early stages of lunar development.
The traditional suggestion for making the most of every pound of food shipped to the Moon is : Recycle wastes to grow new food! This copying of the carbon cycle we see here on Earth is both natural, and logical. It is also quite expensive to set it up where it has never been before on a stable basis. Research on the subject has shown that large inputs for agriculture on the Moon are most probable, before any payback ever begins, much less breaks even, even on small scales.
These inputs include: Biologically secure acreage in close proximity to the base and its personnel, electrical power capacity to light the crops during the 354 hour lunar night, machinery and material from Earth to illuminate and house and manipulate soil and crops, dedicated base worker man-hours to “keep the farm going”, dedicated man-hours for processing crops into edible foodstuffs, machines and material for processing that process waste and the human waste into acceptable fertilizer for “the farm”. Lastly, we need the lift capacity, and the money to pay, for all this to be shipped to the lunar surface. When we have the example of the ISS in front of us, where most of the man-hours are consumed just keeping the Station running, we do not need to replicate those particular problems on the Moon, at greater cost!
These ideas are illustrated by a particular lunar development concept now in the process of being demonstrated in the virtual world of Second Life, at the NASA CoLab site there. This is a three phase concept for development that starts with an inflatable Outpost Module suspended within the entrance to a lunar lava tubes cave, whose explorers confirm the site as useful for development. Then they begin to help to suspend larger inflatable modules farther inside, with base crews totaling 20 crew installing and running a LOX Plant, a Carbonyl Metals Plant, and a Basalt Fiber Plant for Phase I. It continues with the base crews using these in-situ materials to build most of the mass of the modules for the Phase II Settlement further inside the lava tubes, housing 200 or more people.
People from this settlement can be employed to seal larger lava tubes nearby, creating a Phase III Community as a viable human habitation for thousands of people, who can blossom in a diversified and healthy economy while owning their own real estate in a spacious 1 atmosphere and 1/6th gravity environment. While this development concept includes power sources and other aspects, we will focus on Carbon economy, its possible process synergies, and the question of where do we start to see that the costs of organic recycling can be amortized quickly enough to make it worthwhile.
The functions of the Outpost and Base are both time-limited, and subject to the discipline in crews on a focused and urgent schedule. In this situation, the nutritional constraints of freeze-dried food and vitamins will be an acceptable environment to get their tasks done. Any demand in Phase I for using Carbon only in a full organic recycling system must therefore be justified in reductions of total system costs, including launch. Those total system costs include more uses for Carbon than just human consumption, however.
 Industrial Uses
When all costs are high, make each kilogram do double duty as cheaply as possible.
The industrial processes of the LOX Plant, the Metals Plant, and the Basalt Fiber Plant are good examples of process synergy, extracting more and more from the same gathered material. In the LOX Plant, whether using the direct electrolysis of molten regolith, or the indirect electrolysis of water derived from hydrogen reduction of lunar fines, substantial fine waste material is generated, highly enriched in reduced ferrous metals at minimum. If desirable, this can proceed to reduction of Aluminum oxides as well in the direct process. These reduced ferrous metals are intimately mixed with unreduced oxides of lighter metals and silica.
The ferrous metals can be extracted from the mixture by the Mond Process, using carbon monoxide. The remaining materials, including large amounts of alumina, can be sent to the Basalt Fiber furnace. There, the high alumina and silica content of the Mond Process waste will enrich the basaltic proportions of metal oxides, moving the melt into the composition range of high tensile strength S-glass. If Aluminum has been extracted from the alumina at the LOX Plant, then the mix will be enriched far more by even lighter metal oxides like calcium oxide, producing low melting temperature glass, for use as a matrix between the higher melting point S-glass fibers.
The Mond process, for extracting ferrous metals from in-situ resources at low temperatures, is the basis of the Metals Plant. It requires pressurized carbon monoxide, to form the metal carbonyls that are the intermediate step to vapor deposition of these metals. The carbonyl bonds are broken at lower pressures and higher temperature, depositing metal, and freeing carbon monoxide. While the equipment can and will be designed to recycle carbon monoxide freed from the carbonyl molecules in this vapor deposition process, process losses to the exterior will inevitably occur. Because the vacuum of the lunar environment will cause near instant disassociation of escaped Fe(CO)5 and Ni(CO)4 , that carbon monoxide will be lost. This must be replaced. When we require hundreds of tons of metals to build the Phase II Settlement, and the far greater amounts for the Phase III sealed lava tube community, the replacement of these losses from Earth will become very expensive.
In addition, the needs of humans for Oxygen do not require biological recycling. The LOX Plant will be sized to deliver propellant for vehicles leaving the site for elsewhere on the Moon, or other bodies. This will mean that a small fraction of the Plant output can support the human crews. It will extract Oxygen through electrolyzing either directly melted regolith, or the water derived from Hydrogen reduction of regolith fines. The other volatiles bound to the Carbon in wastes can also be reused using the heat of solar mirrors to pyrolyze the wastes, and then the cold of LOX to selectively freeze out each volatile. Liquified volatiles can then be electrolyzed for their respective Nitrogen, Hydrogen, Oxygen and carbon monoxide separately. The Hydrogen and Oxygen can be turned into pure water, and the Nitrogen can be used for replacing atmospheric losses through airlocks. Alternatively, it can be stored for making AlON (reference ii) window panels for the Phase II Settlement Modules.
In addition, there will be some uses for the fibers from the Basalt Fiber Plant which do not lend themselves to either ferrous metal-coated fibers, or to ferrous metals as the matrix of the composites, or to low temp. glass matrix materials. These requirements will have to be fulfilled by using plastics as coatings and matrix materials, in which Carbon, Hydrogen and Silicon will have a strong part. The Carbon , Nitrogen and Hydrogen will either be derived from the wastes of humans, or be shipped up in the form of ready plastics, at great cost.
Obviously, at some point these needs for Carbon and other volatiles in the industrial processes supporting human activities will become greater than the volatiles available from human wastes at the site. At this point, importation of Carbon and other volatiles for industrial uses becomes essential. If these must be got from Earth, then costs will be so high as to limit further lunar development.
Their importation from asteroid resources has been suggested, and seems a high probability, once a market for volatiles large enough to support such measures already exists. The energy costs for delivery to the lunar surface from a near-earth asteroid are as much as 20 times lower than Earth-launched material. It simply requires large capitalization to get started. That is where the previous use of these “waste” materials in industrial processes may be essential to provide the low-investment availability of Carbon and other volatiles, before the asteroids are tapped. Using these materials already present on site, because of human biology, the market for larger amounts of volatiles can be built up to levels that will justify the investments needed to establish processing at and shipping from the asteroids.
 The Uses of Food
In the preceding section it is obvious that we are using food to ship up Carbon and other volatiles, only pausing to process them through humans before their industrial applications begin. As the focused and urgent schedule of a Phase I Base site gives way to the Phase II Settlement's longer-term viewpoint, the balance for human psychology will change, however, and food has always been part of that. The attitudes and emotions of humans are their lowest mass attributes, but they are huge contributors to their productivity.
Even as the population of the Phase II Settlement's 200 or more people are less schedule driven, they now have a settlement, with families to support, both physically and psychologically. Fresh food, as a treat and a reward for family members, can become a regular part of settlement life, now that all material inputs for the “farms” needn't be lifted from Earth. With this decrease in capital costs, growing small volume high value foods can become economically viable.
While agronomists can plan on Earth what foods can be grown most easily in some larger Phase II modules, the crucial test will be what the settlers will want enough to buy at a high price, as a treat or reward. Here entrepreneurial farmers will come into their own, providing in small volumes the tastes that settlers actually prefer, rather than a pre-planned menu with volume and nutrition as the main selection criteria. The farm module's costs will still be high, as even shipping the farmer to the Moon will be costly. Any planning of these investments that overly limits the cropping flexibility of these farms will put their success at high risk. The use of human wastes, tapped out of the flow to industrial processes will be a natural option. The point in the flow they are tapped from must be planned, beginning the tapping even as more dried foods are shipped from Earth.
This change in human waste flows, from industrial to agricultural processes, must eventually be managed in concert with the introduction of carbonaceous volatiles from near earth asteroids. These will need processing before they can sustain plants, and the human wastes will be preferred for agriculture, while the asteroidal material takes up the vast majority of industrial inputs of volatiles.
Eventually, the growing agricultural sector of the settlement's economy will displace most shipments of dried food from Earth with fresh tasty fare. This will speed up as the open space of the Phase III Community allows starting farms without individual modules. While this will result in plant-produced Oxygen becoming a larger share of the atmosphere in the later stages of development, this will be economically incidental by that time.
The presence of the LOX Plant will undo any arguments that plants are needed to recycle volatiles into atmospheric Oxygen. The use of LOX in heat exchangers to cool volatiles for selective freezing out will simplify the separation processes for all volatiles from human wastes. The need for metals, and for safer metal refining through the Mond Process, will require that carbon monoxide be available to replace process losses.
Thus, the initiation of agriculture to support human lunar activity will depend on the very highest return strategies, involving the morale and rewards of the growing population. These will, after all, be more crucial to the success of lunar communities than anything else that fresh foods could help with. Once farms are established, and fertilizer flows are switched totally to growing plants instead of metals, the incremental growth towards more organic nutritional sustenance can flow quickly.
 Related Articles
- Lunar Carbon Production
- Bootstrapping Industry
- Fluorine Reaction
- Ilmenite Reduction
- Magma Electrolysis
 External Links
- i. John S. Lewis and Ruth A. Lewis, “Space Resources:Breaking the Bonds of Earth”, 1987, Columbia University Press, ISBN 0-231-06498-5