Next, we need to determine which of these products can reasonably be made at the outpost, considering the constraints both in the near term and in the long range capabilities. Obviously, as in an Earth-based marketplace, some products will have higher value and some will be easier to produce than others. The items described below represent products which we believe are appropriate for near and mid-term programs. As study of the Space Exploration Initiative (SEI) in general and ISMU in particular proceeds, it is likely that the list will grow.
As a result of the six Apollo and two Luna missions, the general surface composition of the Moon is now known. While there are variations between mare and highland regions, the global average provides a basis for our plans to utilize the lunar resources.
Lunar oxygen could also be used in fuel cells to power rovers or to provide some of the power to the outpost. The amount of oxygen required to make up for losses in the life support system is likely to be smaller, but represents yet another market. It would be reassuring to have an operating plant and some storage tanks full of oxygen in case of a failure in the life support system or as a backup if a problem arose in a resupply mission. Large amounts of oxygen might even make it practicable to have less complex life support systems for habitats and extravehicular activities. The cost and maintenance of these systems may therefore be reduced.
Many chemical processes have been identified through NASA studies and workshops which can potentially extract oxygen from lunar rocks and soils. NASA, universities, and industry are all trying to understand these processes more fully to pick the best ones for plant design.
The propellant required to return both humans and scientific samples from the Moon to lunar orbit will be produced eventually from lunar minerals. For every pound of propellant thus off-loaded during descent, an equal amount of more valuable scientific equipment can be brought to the lunar surface.
It is not as if we are trying to develop an entirely new technology:
We have been building plants which extract oxygen from minerals on Earth for hundreds of years. The basic technology is very old.
The major metals present on the Moon are silicon, iron, calcium, aluminum, magnesium and titanium, all combined as compounds in a variety of minerals. As discussed above for iron, when oxygen is released from minerals, one or more metals is necessarily coproduced. Well-designed oxygen plants will take advantage of this fact and produce metals in useful quantities. The specific metal(s) produced would depend on the chemical process used. Silicon has been produced in the lab from simulated lunar soil (natural terrestrial anorthosite, similar to that found in the lunar highlands) at purities acceptable for solar cell production. Aluminum, magnesium, and titanium production could also be practical, as they represent important structural metals in the aerospace industry.
The production of metals, along with the production of oxygen, should be relatively easy. The next step, taking this metal and fabricating a useful product out of it, will require a fair degree of manufacturing capability. Some potential uses for locally produced metals at a lunar outpost or a Mars base might include
The extraction of this hydrogen has considerable importance since, with lunar LOX, we would then have an entirely lunar-derived propellant system. We might choose, instead, to produce methane as a fuel. While methane is not as powerful a propellant as hydrogen, its liquefaction is much easier to accomplish and less regolith would need to be processed, perhaps resulting in a better system overall. Methane is also considered a storable propellant, which means we would lose less from boil-off during the lunar day. This option is especially attractive if we also choose to use the martian atmosphere as a resource to produce methane for operations at a Mars outpost. The choice of propellant is major driver of spacecraft design and needs to be considered from the start.
Other light gases, such as nitrogen and even oxides of carbon, could provide a life support system with critical material. The ability to provide these resources can act as a layer of redundancy, thereby providing a level of safety, in addition to relieving a cargo burden from the transportation system. Helium has many uses, too, including as a pressurant gas, a heat exchange fluid, and perhaps as an important element in terrestrial energy production (see Energy from the Moon).
It is important to realize that a process which aims to produce any particular gas will also release the remaining gases from the regolith. For example, a plant built to produce hydrogen or methane will also isolate helium and nitrogen. However, the amount of mining required to produce these gases is very large. Concentrations of the gases in the regolith vary from a few parts per million (ppm) to a few hundred ppm. Thus, before we can exploit this potential successfully, we must develop our ability to mine and process large amounts of regolith under the harsh lunar conditions. Only if we pursue these technologies in the laboratory and integrate them throughout the system will we know if it makes sense to pursue them on a larger scale.