The Value of the Moon: How to Explore, Live, and Prosper in Space Using the Moon's Resources (2016)
A Visit to the Future Moon
I believe the central, near-term goal for the American civil space program needs to be a permanent return to the Moon. Once we do this, we create a new and versatile spacefaring infrastructure, one capable of extending human reach beyond low Earth orbit (LEO) into the solar system. If we eventually head in such a direction, what might we expect to see in the future? What benefits will accrue from this direction and how might they develop over time? Here I envision a future for humanity on the Moon and a series of steps and events that are most likely to occur, along with their appropriate implications. On the Moon, we will begin to use and settle space for a variety of beneficial purposes.
In one sense, our lunar return has already begun through the series of robotic spacecraft that have mapped, measured, and surveyed the Moon over the past decade. Most of these missions were orbiters, loaded with a variety of sensors and instruments designed to measure physical properties in almost every part of the electromagnetic spectrum. These data, converted into maps showing shape, size, composition, and physical state, have given us a clearer picture of the makeup and evolution of our nearest neighbor. The Moon is probably the best-mapped object in the solar system, while parts of Earth’s ocean floor are more poorly known than the lunar far side. These survey maps allow us to evaluate the Moon as a planetary object. The regional inventory of its resources determined from orbit show that the Moon possesses what we need to create a new spacefaring capability. The Lunar Reconnaissance Orbiter (LRO) continues to give us the knowledge that fuels research and produces new discoveries.
Impactors and landers have also added critical detailed information for small, selected areas on the Moon. One of the most important pieces of information came from the LCROSS impactor. In this mission, the upper stage of the LRO launch vehicle was crashed into one of the cold, dark regions of the lunar south pole. The collision was observed by a small satellite that had followed the impacting upper stage and by the LRO spacecraft, already in lunar orbit. The ejected material from this impact conclusively demonstrated that water ice is present within this cold trap. The amount is estimated at about 7 weight percent at this location. The ejecta plume also threw up other volatile species, including ammonia (NH4), methane (CH3), carbon monoxide (CO), and some simple organic molecules.1 These data suggest that the volatiles of the Moon’s polar regions are likely of cometary derivation. With this information, we can state with a strong degree of confidence that the materials needed for permanent human habitation on the Moon are present in the Moon’s polar regions.
We have located and quantified the areas near the Moon’s poles that receive the most sunlight over the course of a year (figure 3.1). These lit regions are close to deposits of water ice and other volatiles. Maps produced by LRO and its orbital companions will be crucial in locating likely sites for resource processing on the Moon. In addition to the direct sampling of lunar ice by LCROSS, several different remote measurements support the presence of significant amounts of polar water. The M3 spectral mapper on India’s Chandrayaan-1 spacecraft found evidence for hydroxyl molecules (OH) at high latitudes (figure 9.1), which migrate poleward to possibly serve as a source for polar water.2 A small impactor from Chandrayaan-1 (the Moon Impact Probe) found a tenuous water vapor cloud over the south pole (probably water molecules en route to their ultimate site of deposition in a polar cold trap). Mini-RF radar images show high diffuse backscatter in some polar craters (see figure 5.1). Ultraviolet spectra and laser reflections indicate the existence of water frost on the surface of the floors of some polar craters. Neutron measurements over the poles indicate extensive amounts of hydrogen. These data support our understanding about the presence of significant amounts of ice at both poles, as much as 10 billion tons at each pole.
Figure 9.1. Schematic showing the five modes of occurrence of lunar water. Water is found within melts formed deep inside the Moon and sampled by volcanic glasses and minerals. Exospheric water occurs as rare molecules that bounce around the Moon in the space just above the surface. Adsorbed water is found as a monolayer of molecules on dust grains; these molecules increase in abundance with increasing latitude (decreasing mean surface temperature). Surface water frost of more substantial quantity is seen within the dark, cold areas near the poles. Larger amounts of water ice may occur near the pole at shallow depths (a few meters or less) in substantial amounts (millions of tons). (Credit 9.1)
Despite the abundant new data, in order to achieve a permanent lunar presence, we must understand and map the variations in polar water content on meter-scales, laterally and vertically. The physical properties of the ice must be determined to plan for excavation and water extraction. We must find areas of the highest water concentration that are closest to the areas of “quasi-permanent” sunlight, so as to make future water processing most efficient. These properties and others can be obtained from additional robotic surface exploration. The ideal way to get the highest quality data is to land a nuclear-powered surface rover, similar to the current Mars Science Laboratory, and conduct an extended traverse across the polar region to find and map out the best areas.3 Identically equipped rovers should be sent to each pole; although we suspect that both north and south poles possess significant volatile deposits, the scouting of both areas by two rovers would help us be certain that we locate the outpost near the highest grade deposits.
Short of this fairly sophisticated level of exploration, a series of smaller missions could gather preliminary information on polar volatiles. One example of an inexpensive mission is to fly a pallet of about a dozen small impactors (hard landers) that would be individually deployed and landed to gather surface compositional and physical data from multiple points. Although less desirable than the detailed, continuous information that a properly equipped rover would provide, this approach may be a good strategy to collect widespread, detailed data in a short period of time for a small amount of money.
When enough prospecting data have been obtained, the next most pressing need is to demonstrate the process of resource extraction and storage on the Moon. Although water extraction is probably the simplest processing of extraterrestrial materials imaginable, in order to be taken seriously by some in the space engineering community, an actual end-to-end system demonstration is needed. Such a demo mission could be quite small; a fixed lander in the sunlight, fed with feedstock from the shadowed area, could heat the soil, collect the water vapor, liquefy it, and store it. Once this demonstration has been accomplished, the production of large amounts of water becomes merely a matter of scale.
Some lingering mysteries about the lunar surface environment also need to be addressed. It has been postulated that the passage of the day/night line (the terminator) across the surface induces an electrical charge, one of possibly dangerous magnitude. This effect could be measured and that possible risk retired through a series of measurements from a fixed lander over the course of a lunar day. Observing the postulated levitation of fine-scale dust by electrical fields should also be studied on the surface, although evidence obtained recently from the orbital LADEE mission suggests that this phenomenon, if it occurs at all, is minor and of local extent.4
Consolidating Our Lunar Presence
As previously described, I believe that the most efficient and least expensive way to return to the Moon will require performing much of the preliminary, early work with robotic assets, followed later by people.5 In the early stages of lunar return, robotic machines operated from Earth can begin the harvesting and processing of lunar water. We should initially plan to build up enough capability to fuel a return trip back to Earth before humans arrive. Such a capability requires the production of about 100 tons of water per year. This isn’t as great a quantity as one might imagine: 100 tons of water is roughly the amount contained in a tank the shape of a cube 15 feet (4.5 m) on a side, or roughly the volume of water in a single backyard swimming pool. Because water is the most enabling resource with the widest possible range of use, it is the first priority for utilization.
Significant mining activity on the Moon will require power and lots of it. Fortunately, there is enough surface area in the polar quasi-permanent sunlit zones (see figure 3.1) to establish networks of multiple solar array power stations. A single station could consist of a tall (~10–20 m), narrow (~2–3 m wide) array of solar cells that can be articulated around its vertical axis (see figure 7.1) to track the Sun as it slowly moves around the horizon over the course of a lunar day. Such an individual station would be low mass (~1 ton). As a modular system, these pieces could be connected together to provide whatever level of power is needed. Initial robotic mining capability would require roughly 150 kilowatts, power that could be provided by eight to ten individual power stations. As outpost capability and size grows over time, additional power stations delivered from Earth can satisfy generating needs. This potential for growth in a surface power system is possible up to about the ten-megawatt level, after which we would probably need to consider the deployment of a nuclear reactor. A thorium molten salt reactor could be sized to provide virtually unlimited power (hundreds of megawatts) for a wide variety of uses and while initially supplied entirely from Earth, could ultimately be operated from locally mined sources of thorium on the Moon.
In civil engineering, one of the most important material resources on Earth is “construction aggregate”—the sand, gravel, and cement building materials that make up the infrastructure of modern industrial life. Aggregate is easily one of the most important and valuable economic resources of all mined terrestrial materials, more so than gold, diamonds, or platinum. We depend on aggregate for many different types of objects; they are the fundamental building materials of roads and structures. The use of aggregate in building goes back to ancient civilizations, such as the concrete used for construction in ancient Egypt. The Romans devised a recipe for a concrete so durable that the molded arches, walls, and self-supporting dome of the Pantheon, built more than two thousand years ago, still stand today. Aggregates in terrestrial use typically depend on a lime-based cement that bonds the particulate material together. Both lime (CaO) and abundant water are needed to make concrete on Earth.
By necessity, a permanent presence on the Moon will require an infrastructure that uses as much local material as possible. Aggregate materials probably will become the primary building blocks of industrial society off planet, just as it has on the Earth. The composition and conditions of local materials will require some adjustments as to how we use lunar aggregate. A quick assessment reveals some interesting parallels, as well as differences, with terrestrial use.
On Earth, gravel pits are carefully located to take advantage of the sorting and layering produced by natural fluvial activity. We harvest gravels from alluvial plains and old riverbeds, where running water has concentrated rocks, sand, and silt into deposits that can be easily excavated, loaded, and transported to sites of construction. The highly variable currents, as well as the velocities of flow of our terrestrial streams and rivers, sort the aggregate by size. This natural sorting creates layers of gravel- to cobble-sized stones for the fastest flowing waters. Finer-grained material is likewise concentrated where water speeds are low, and sand and silt settles out from the suspended sediment (the “bed load”).
Unlike the aggregate processing by water on Earth, lunar surface rock has already been disaggregated into a chaotic upper surface layer (regolith) by impact. Regolith is ground-up bedrock; impacting objects of all sizes constantly pummel the surface, breaking, fracturing, and grinding up the Moon’s bedrock, a process of impact that has greatly slowed from the much higher level experienced earlier in lunar history. The regolith is a readily available building material for construction on the lunar surface. It is an aggregate in the same sense as on Earth, but with some significant differences. We could make lime and water from the Moon’s surface materials but that would require too much time and energy. Thus, we should adapt and modify terrestrial practice to take advantage of the unique nature of lunar materials. The fractal grain size in the regolith means that we can obtain any specific size fraction we want through simple mechanical sorting (raking and sieving). Instead of water-set, lime-based cement, we can use the glass in the regolith to cement particulate material together, that is, sinter the aggregate into bricks and blocks, as well as roads and landing pads, using thermal energy (figure 9.2). Both passive solar thermal power (concentrated by focusing mirrors) or electrically generated microwaves can provide the energy to melt grain edges into a hard, durable ceramic.
Figure 9.2. Robotic rover carrying microwave sintering equipment to fuse local regolith into ceramic pavement for use as a landing pad for spacecraft. Power for melting the soil is provided by solar array at center. (Credit 9.2)
The use of aggregate on the Moon will likely be gradual and incremental. Our initial presence on the Moon will be supported almost entirely by materials and supplies brought from Earth. As we gain experience in using lunar resources, we can incorporate local materials into the structures. Simple, unmodified bulk soil is an early useful product. It can be used in building berms to protect an outpost from the rocket blast of arriving or departing spacecraft, and to cover surface assets for thermal and radiation protection. The next phase will be to pave roads and launch/landing pads to limit the amount of randomly thrown dust and to provide good traction for a multitude of wheeled vehicles supporting the outpost. The fabrication of bricks from regolith will allow us to construct large buildings, initially consisting of open, unpressurized workspaces and garages, but ultimately habitats and laboratories. The new technology of three-dimensional (3D) printing will allow nearly autonomous machines to construct the lunar outpost through the use of regolith aggregate assembled into structures by 3-D printers working in conjunction with Earth-controlled construction robots.6 Making glass by melting regolith can produce building materials of extreme strength and durability; anhydrous glass made from lunar soil is stronger than alloy steel, with a fraction of its mass.
Metals are abundant in the Moon and can be extracted from the local materials. The basic process is one of simple chemical reduction, accomplished through a variety of low-tech processes, all of which were known to eighteenth-century industry. Carbothermal reduction of ilmenite, an iron and titanium oxide, has been demonstrated in the laboratory to produce oxygen; it also produces native metal as a by-product. The use of fluorine gas as a reducing agent has also been well studied. Metal production techniques require large amounts of electrical power, as it takes significant energy to break the tight metal-oxygen bonds in common rock-forming mineral structures. For this reason, it is likely that metal production will come late in lunar industrialization; initial surface structures and base infrastructure pieces are likely to be made from lower-energy products, like composites and aggregate.
Although most products made on the Moon will be used locally, eventually we can export lunar products into space. The gravity well of the Moon is a drawback for large mass delivery—its escape velocity is about 2.38 kilometers per second, much smaller than that of Earth (11.2 km/s), but still substantial. In order to use large quantities of lunar materials for space construction, we need to develop an inexpensive means to get material off its surface. Fortunately, the Moon’s small size and lack of atmosphere make this possible by building a system that literally throws material off the Moon into space. A “mass driver” can launch objects off the lunar surface by accelerating them along a rail track using electromagnetic coils that hurl encapsulated material into space at specific velocities and directions.7 We can collect such thrown material at a convenient location, such as one of the libration points. From there, it is a relatively simple matter to send the material to wherever it is needed in cislunar space. A mass driver is not a science-fiction concept; such systems are used to launch planes from the flight decks of aircraft carriers.8
Surface Activities and Exploration
An early goal for lunar return is to become self-sufficient in the shortest amount of time possible. This does not mean that a significant amount of surface exploration and science is not also attainable. By virtue of being on the Moon for extended periods, we will have many opportunities to study lunar processes and history in unprecedented detail. Our scientific tasks include understanding the nature and details of the regolith and its interaction with the space environment (a topic addressable any place on the Moon). Such study has both practical relevance, to better conduct resource processing and to improve product yield, and academic interest, since details of regolith dynamics remain elusive. An example of a simple, easy-to-complete experiment is to dig a trench in the regolith several meters deep.9 In the exposed wall of this trench would be several billion years of solar and impact history available for our inspection, sampling, and detailed study.
The Moon has experienced the processes of impact, differentiation, volcanism, and tectonism. These processes occur on all rocky planets in the solar system. The antiquity of the lunar surface ensures that near-complete examples of these processes are on display for our enlightenment. By using the Moon as a window into early planetary history, we improve our understanding not only of its history and evolution but also the history and evolution of all the planets. As one example, the Earth and Moon have occupied the same volume of space for the last 4.5 billion years, a space where the impact flux affects both objects. As a result of Earth’s highly dynamic surface environment, these ancient events have not been preserved. However, the lunar surface preserves the impact record of the Earth-Moon system dating back to at least 3.8 billion years ago. The study of a multitude of lunar craters can tell us about changes in the impact rates over time, a topic relevant to the extinction and evolution of life in the geologic past.
A common article of faith in many academic and space circles is that robotic spaceflight is the preferred method of scientific exploration. Many famous space scientists, including James Van Allen and Carl Sagan, argued for the superiority of unmanned missions over human ones. Indeed, many phenomena in space, such as plasmas and magnetic fields, cannot be sensed directly by humans, and in some cases, such as detecting the tenuous lunar “atmosphere,” the presence of people interferes with the property being measured. I agree that while some scientific activities cannot or should not be done by people, in other areas, a human presence is not just beneficial—it is critical.
The Moon is a natural laboratory, a place where important scientific questions can be answered. The conceptual visualization of the four-dimensional—three spatial dimensions plus time—makeup of planetary crusts is achieved through fieldwork. Fieldwork is not merely a matter of picking up rocks or taking pictures. The “field” is the world in its natural state, where the phenomena we study are on display and where we observe facts and clues that permit us to reconstruct past processes and histories.
A good example of the difference in capabilities between humans and robots is illustrated by the experience with the Mars Exploration Rovers (2003–present). Over the course of their first five years on Mars, these machines traversed many kilometers of terrain, examined and analyzed rock and soil samples, and mapped the local surface. These robotic rovers, giving us an unprecedented view of the martian surface and its geology, have returned many gigabytes of data. They are truly marvels of modern engineering. Yet, after all this extended, robotic exploration, we are unable to draw a simple geological cross section through either of the two MER landing sites. We do not know the origin of the bedded sediments, strikingly shown in the surface panoramas; we do not know whether they are of water-lain sedimentary, impact, or igneous origins. We do not know the mineral composition of rocks for which we have chemical analyses. Without this information, the planet’s processes and origins cannot be determined.
Even after more than a decade of Mars surface exploration, we still do not know things about the field site that, given an afternoon’s reconnaissance, a human geologist could have deduced. In contrast, we have an incredibly detailed conceptual model, albeit incomplete, of the geology and structure of each of the human visited Apollo landing sites. The longest stay on the Moon for these missions was three days, most of which was spent inside the Lunar Module.
A robotic rover can be designed to collect samples, but it cannot be designed to collect the correct, relevant samples. Fieldwork involves the posing and answering of conceptual questions in real time, where emerging models and ideas can be tested in the field. It is a complex and iterative process; geologists can spend years at certain field sites on the Earth, asking and answering different and ever more detailed scientific questions. Our objective in the geological exploration of the Moon is knowledge and understanding. A rock is just a rock—a piece of data. It is not knowledge. Robots collect data, not knowledge.
Because people control planetary exploration robots remotely, it has been argued that human intelligence already guides the robot explorer. Having done both types of field exploration on Earth, I contend that remote, teleoperated robotic exploration is no substitute for being there. All robotic systems have critical limitations—important sensory aspects, such as resolution, depth of field, and peripheral vision. Robots have even greater limitations in physical manipulation. Picking a sample, removing some secondary overcoating, and examining a fresh surface is an important aspect of work in the field. The physical limitations of teleoperated robots are acceptable in repetitive, largely mechanical work, such as road construction or mining, but in creative, intellectual exploration they are woefully inadequate. The makers of the MER rovers recognized this need by including an abrasion tool to create fresh surfaces; regrettably, it became worn down and unusable after a short period of operation.
Ultimately, we need both people and machines, each with their own appropriate skill bases and limits, to explore the Moon and other planets. Machines can gather early reconnaissance data, make preliminary measurements, and do repetitive or exhaustive manual work. Only people can think. And thinking, and then taking action and working with those informed results in real time, is what fieldwork is all about.
On the Moon, we will learn more about the universe, and by doing so, we will also learn how to study the universe. Recognizing that people and robots bring unique and only partly overlapping capabilities to the task of exploration, we may find that a combined, specialized approach that builds upon the strengths of both, and that mutually supports the weaknesses in each, is the most efficient and beneficial way to explore.10 It is easy to conduct thought experiments in how telepresent robots could replace people on planetary surfaces, but we have no real experience in using them. By experimenting with these techniques on the Moon, we can learn the optimum approach for specific exploration tasks. Simple reconnaissance may be conducted with minimal human interaction, but detailed field study might require continuous, real-time human presence. Knowledge of the problems appropriate for each technique is something that can be acquired and understood on the Moon. Such understanding is vital to future exploration and for comprehending other planetary objects.
Building a Transportation Infrastructure
In contrast to the “build, launch, use, throw away, then repeat” paradigm of the past, we seek to create a permanent spacefaring infrastructure that incorporates reusability for as many assets as possible. Although much of the current focus in space development is on reusable launch vehicles, reusability is actually much easier to achieve for vehicles that are permanently based in space. These spacecraft do not have to undergo the thermal and mechanical stresses of launch and reentry. Cislunar transportation consists of multiple steps, including the marshaling of assets at certain points, such as rendezvous and preparation in LEO and L-points (see figure 9.3) followed by transport to the next marshaling area (involving a rocket burn to increase or decrease orbital energy). Since these activities put little stress on vehicle systems, there is no technical reason not to design as much reusability into them as possible.
Figure 9.3. Deep space staging node located at Earth-Moon L-1, about 60,000 kilometers above the center of the lunar near side. A staging node can serve as the jumping-off point for missions to the Moon and planets; it contains a habitat for temporary layovers and a propellant depot for the refueling of spacecraft. Future Orion spacecraft shown docked to the transport node. (Credit 9.3)
In the lunar architecture described previously, I call for the building of a 30-ton-class reusable lunar lander (see figure 7.1). The purpose of this vehicle is to transport people to and from lunar orbit. By eliminating the need for extended life support, we can make this vehicle smaller than the proposed Altair lander called for by the Constellation architecture. Here, the issue of reusability largely revolves around engine performance and maintenance. A throttleable version of the venerable RL-10 cryogenic engine, used today in the Centaur upper stage, can perform multiple restarts and is a good engine on which to base the creation of a reusable lander. At some point, we will have to change out engines on the reusable vehicles, but they can be made part of a modular system serviceable by suited astronauts and teleoperated machines on the lunar surface. A reusable lander would spend about half of its time on the Moon and the other half in space, at the appropriate staging node, either in low lunar orbit or at one of the L-points. It would be designed to reach its space node with half of its fuel remaining. This permits the lander to make the next descent and landing and then refuel on the Moon with propellant made from lunar water.
Passive, space-based assets require much less work to maintain. Staging nodes, where vehicles can meet and interact to transfer crew, collect cargo, refuel, and the like, will become part of the transportation system. These nodes are actually miniature space stations, complete with their own power, thermal, and attitude control systems. They are much less complex than the ISS, in that they are designed only for a single specialized use and are unoccupied most of the time. However, some maintenance will be needed to keep the nodes functioning correctly. This may include refueling the attitude thrusters and maintaining the electrical and thermal control systems. Transport nodes can be based in several localities, including LEO, an L-point, and in low lunar orbit. The nodes may or may not be associated with a fuel depot.
An orbiting fuel depot is a new technology that can increase the size of payloads placed on the Moon and throughout cislunar space. However, we have much to learn about their construction and operation. The biggest difficulty is learning how to deal with the “boil-off” of extremely low temperature cryogenic liquids. Liquid oxygen boils at —183°C, and liquid hydrogen boils at —253°C. Although we can shield storage tanks from direct exposure to solar illumination with screens, passive thermal radiation from the depot itself will heat these liquids enough to cause evaporation. This problem must be solved to create a permanent space transportation system. Although we do not know how to mitigate this issue at the moment, the solution will probably involve capturing the boil-off gases and recondensing them into liquid.
One way to minimize loss from boil-off is to keep the propellant in a more stable form until it is actually needed. We can transport propellant throughout cislunar space in the form of water, a substance that is easily stored and transferred, and then cracked into the cryogens just before a spacecraft is scheduled to arrive. This would require that the fuel depots of the future also contain a propellant processing system. Such a system would include large solar panels, cryogenic plants, and storage facilities. With this capability, the fuel depot becomes a more complex space station, but it also decentralizes operations throughout the entirety of cislunar space. Note that we will still need these cryogenic processing facilities on the lunar surface in order to refuel arriving spacecraft, along with their obvious importance to the crews who live there.
A complete cislunar transportation system consists of an Earth to LEO transport, multiple staging nodes, fuel depots, transit spacecraft, landers, and the lunar outpost. Such a system permits routine access to the Moon and to all other locations within and throughout cislunar space. For the first time, we will be able to move people and cargo where they are needed, anywhere in cislunar space. Currently, communications satellites at GEO are inaccessible for visits by people. With the new system described here, we can travel to GEO to repair, maintain, or even build new distributed satellite systems of unprecedented power and capability. A communications satellite the size of the ISS could provide uninterrupted communications coverage over a hemisphere, rendering the entire terrestrial cell phone network obsolete in an instant. It could provide enough bandwidth to accommodate thousands of channels of high-definition video, Internet traffic, and personal messaging. Three such complexes would link the entire world with these capabilities; it would generate new wealth and provide endless possibilities for innovation and technology development. In addition, we will be better able to protect sensitive surveillance equipment and other strategic assets. Such capability will make the world safer, in that we would not be rendered blind in the event of aggression and we could better respond to crises, both natural and man-made, that may develop on Earth. The upgrading and enhancement of scientific sensors would also be possible, including such difficult tasks as the servicing of the soon-to-be-launched James Webb Space Telescope, to be located at the Sun-Earth L-2 point and inaccessible to servicing spacecraft with existing systems.
I began this academic journey by explaining how we can use lunar material and energy resources to create a new spacefaring capability—the creation of a permanent transportation infrastructure in space. Such a capability can satisfy all of our requirements to maintain and enhance service satellites, and to open up the Moon (and indeed, the entire solar system) for exploration and development. The rest of the journey—the one that you may envision—is now possible.
Exports from the Moon
Until now, I have mainly focused on the development of lunar resources to obtain a foothold on the Moon, but is there anything on the Moon that has economic value elsewhere, other than at a lunar outpost? What lunar exports might become profitable in the future and how might such markets, be they private or government, be developed? Is there a “killer app” in lunar resources, a product or service that can create new wealth and actually give us a return on our investment in spaceflight and infrastructure? Many people and nations are keenly aware of the possibilities to realize a profit, and are considering ways to exploit an advantage.
The most obvious lunar product of economic value is water. As previously described, water is an extremely useful substance in space: It can support human life, it serves as a medium for energy storage, and it can be used to make rocket propellant. Thus, for spacefaring nations and companies, by having the ability to purchase useable water already in space, it negates the requirement for them to bring water along from Earth. This option makes their space missions more productive, more routine, and more profitable. A space-based market for water will probably emerge first. Special importance will be given to the availability of propellant at the orbital fuel depots. A good policy would be to husband any surplus water at fuel depot-transport nodes for sale or barter with other spacefaring nations. Such fuel sales could be used to support the flights of other countries on their cislunar missions. It will also find use as fuel for attitude control-orbital maintenance thrusters. At the moment, such thrusters use storable propellant, but if a space-based source for cryogens became available, the satellite builders of the world would soon modify their systems to enable its use.
The idea of generating electrical power in space for transmission back to Earth to be sold commercially has been a staple of lunar development schemes for some time. The Solar Power Satellite (SPS) concept has always faced a major stumbling block; the high cost of launch from Earth of the massive solar arrays make it financially infeasible.11 A permanent presence on the Moon changes that picture. Solar arrays can be manufactured from lunar surface materials and launched into cislunar space at lower cost, due to the lower gravity of the Moon.12 In fact, it is likely that if financially viable SPS systems ever become available, they will be made possible only through the use of lunar resources.
An extreme variant of this idea proposes to make the solar arrays in place on the Moon. A small rover rolls along the ground, fabricating amorphous solar cells that are connected and wired together as the rover slowly moves across the lunar surface, manufacturing a solar array that can be tens to hundreds of square kilometers in extent. In the equatorial zones of the Moon, gigantic solar panels farms, with enormous gigawatt-level power output, can transmit to space or directly to Earth via lasers or microwaves. Receivers in either location can collect this power and offer it at commercially competitive rates. To receive constant solar illumination, this system would require the construction of two solar array farms on the equator on opposite sides of the Moon. Seemingly something from science fiction, if undertaken at the appropriate scale, such energy production on the Moon (which has been analyzed economically) is workable.13
The possibility of extracting helium-3 from the lunar soil to power fusion reactors on Earth for commercial power generation may be possible within the next few decades, once a determination is made whether such a plan is technically viable or not.14 If so, helium-3 mining could be a competitor to large-scale solar power generation on the Moon. It would require a significant amount of surface infrastructure to produce commercially useful quantities of the fuel. One wild card in the helium-3 story is that we do not know how much of it might be contained in the polar cold trap volatiles. If these volatile substances are of cometary origin—and analysis of the LCROSS data suggests that they are—helium-3 might be present at roughly solar abundance.15 Thus, it could be easier and less costly to extract large amounts of helium-3 from polar ice, than from equatorial mare regolith. This is a missing piece of information that will be answered once we are able to send a properly instrumented rover into the polar dark areas on the Moon.
Other lunar products may eventually become economically attractive. We are not imaginative enough to envision them all. The earliest product to have monetary value from export comes from the first product that we make on the Moon—water, in all of its forms. To move through space requires the expenditure of energy in the form of rocket firings. Thus, the freedom of space is energy change. Energy change is a rocket firing. Rocket firings require propellant. To make propellant, we need water. And water is available in large quantity from the polar cold traps of the Moon. Thus, water is the currency of spaceflight. By establishing a resource processing facility on the Moon, we position ourselves to participate in the world markets of the future.
Learning to Live and Work on Another World
Several skills must be mastered and many different technologies must be developed if humanity is to become a multiplanetary species. One recommendation of the 2009 Augustine Committee was to table the notion of selecting destinations in space such as the Moon or Mars and instead work on developing the technology to go anywhere.16 Then, when we have the technology necessary, we ramp up and go to the planets. This approach, called the “Flexible Path,” was quickly embraced by the administration that chartered the committee. Adoption of the Flexible Path was an attempt to distract national attention from the fact that our civil space program was going nowhere.
The largest and most comprehensive expansion of space technology in history was the product of the Apollo program, the antithesis of a “no-destination” effort. The truth is, we get more technology development as a result of the need to solve specific problems, problems that arise when we try to do something or go to someplace in space. Confronted with specific issues and needs, technical solutions must be developed or we go nowhere, learn little, solve nothing, and become vulnerable. Historically, a pressing need for answers drives innovation much more quickly and efficiently, than does tinkering around in a hobby shop.
We go to the Moon to learn how to use what it has to offer. One of those offerings is its virtue as a world on which to live and work. Humans have almost no experience with this. The Apollo missions fifty years ago allowed a few people to experience the Moon for a few tens of hours each. From that experience came a dream that has never faded: that a great adventure and future awaits the first people who attempt to make life in space an extended experience. The Moon is our first step. The struggles humans will face learning to survive in a hostile, foreign environment are difficulties we need to face and solve before we venture further into the solar system. Learning how to live and work on the Moon involves both humans and machines, together, coping with an environment of low gravity, vacuum, thermal extremes, and hard radiation. We can design equipment to use and to protect us for short durations, but we need to understand how well these instruments and machines work on timescales of months and years. Using the Moon as a natural laboratory will teach us how to arrive, survive, and thrive on other worlds.
Besides survival, we also need to learn how to explore and study alien worlds. We have a vague idea that such an exploration template somehow involves both humans and robots, but how do they interact and work together and apart to yield the maximum benefit? As space destinations and objectives become more complex and dangerous, it makes good sense to use the Moon to learn how to properly conduct the serious business of exploration. Humans yearn to explore. By doing so, they acquire strategic knowledge that increases our odds for survival. Making new discoveries broadens the imagination and allows us to envision solutions to problems that might otherwise not have occurred to us. Practical experience on the Moon will serve us well as we begin humanity’s movement into the universe.