9.4 Non-Terrestrial Resource Utilization Within the near-term time constraints of the design examples prepared for this study, it is difficult to propose a viable role for on-orbit construction, in-space manufacturing, or non-terrestrial materials utilization. There have been several studies which have concluded that large-scale SPS's are not feasible with only Earth-launched material, and have looked at the possibility of using lunar material to provide valuable resources for the construction of Solar Power Satellites [Maryniak, 1991], [Leonard, 1991], [Lewis, 1991], Analysis of the support required for such a scheme [Woodcock, in Glaser, in press] emphasizes the technology development yet to be done and the infrastructure necessary on the Moon as a source of uncertainty in such plans. A program for developing these technologies is necessary so that we have the capability to realize the larger systems which may be proposed for the long term, if they are justified by die prior experiments. The near term goals and products of these programs should make sense in and of themselves, i.e., they should be justified by their benefits vs. the alternatives, regardless of a solar power program. These trades should include not only the economics of mass pay-back, but also ease of operation, mission accomplishments, ease of program evolution, and similar intangibles which are difficult to quantify. In their critique of the NASA/DOE study, the National Research Council cautions that "A decision to proceed with an SPS should not invoke a concurrent decision to develop the capability to use lunar of other non-terrestrial resources. For the next several decades, it would be more practical to use materials from Earth, thus minimizing the new technologies that would have to be developed to construct an SPS" [National Research Council, 1981.] Nevertheless, the mass which must be placed into orbit for any of the commercial, base-load SPS systems proposed to date is just very large. Unless breakthroughs in several technology areas occur, these systems are likely to remain large. Therefore, one can propose that, if commercial SPS's are to be developed in the future, we must consider developing the ability to use resources which already exist in space. These resources could include materials indigenous to the Moon, asteroids, or even refined material such as empty external tanks brought to orbit by the U.S. Space Shuttle. 9.4.1 Lunar Resources The concept of lunar resource utilization gives a new meaning to the phrase "living off the land." Lunar soil may be used to produce the oxygen, water, and radiation shielding astronauts will need to survive on the Moon. Lunar soil may also be used as a source of propellants, metals, and carbon dioxide to support plant growth, resulting in an enormous savings in transportation costs [Mendell, 1985]. The Lunar Energy Enterprise Task Force [NASA, 1990] looked at three options for the use of the Moon to help provide energy to the Earth, including both solar power satellites in Earth orbit and a lunar based solar power system. It concluded that the Moon must play a role in the long term energy supply to Earth. Although one must account for the fact that the study was commissioned by NASA, and might therefore be biased towards large space programs, several good reasons for this conclusion were presented and a timeline was developed. During the Apollo era we learned the detailed mineralogy and chemistry of lunar materials as well as the rock and soil compositions at various locations on the Moon. In addition to abundant oxygen, these materials also contain considerable silicon, iron, calcium, aluminum, magnesium, and titanium which can be extracted as metals, possibly as co-products of the same process which extracts oxygen [Sullivan and McKay, 1991]. The average composition is shown in Figure 9.13. We also learned that lunar soil has trapped particles from the solar wind over the eons, and thus contains helium, hydrogen, nitrogen, and carbon from the sun. These elements can be extracted as gasses (as CH4, CO, and CO2 in the case of carbon) by heating the soil. These gasses are found in most lunar soils, but their concentration is low and varies from place to place. The materials which are likely to be needed in large amounts in a space solar power program, and are likely to available from non-terrestrial sources, include structural materials such as metals and perhaps low tech ceramics such as fiberglass. By quickly quenching a melt of the lunar soil, glass fibers can be produced which might be useful in a variety of ways. Metallic silicon, for solar cell production, has already been produced in the lab from simulated lunar material. It remains to be
RkJQdWJsaXNoZXIy MTU5NjU0Mg==