resources are more difficult to extract and utilize than others, and this and other nonterrestrial resource issues are the subject of section 9.4. In general, terrestrial knowledge about nonterrestrial resources is quite poor. For space solar power, we need to know what materials are potentially available in order to optimize the final solar power satellite system design, and the earlier we have this information the better. For this reason it is vital to the success of space solar power that the entire Moon be spectroscopically mapped in detail from lunar orbit. Additionally, near Earth asteroid missions such as the US Department of Defense's Clementine, scheduled for launch in 1994, and NASA's proposed NEAR, could also be of great import to space solar power. Lastly, Shuttle External Tanks or Energia Cores represent additional “nonterrestrial” resources that may be utilized by space solar power. It is important to establish orbital control of such structures in order to ascertain the viability of using these tanks for manufacture of solar power satellites. The various nonterrestrial resource studies referred to above tend to equate reduced terrestrial mass content of solar power satellites with economic desirability. However, Woodcock notes that these studies overlooked the problem of manufacturing complicated space hardware from raw nonterrestrial materials [Woodcock, 1989]. Lunar resource manufacturing, as well as space manufacturing in general, is the subject of section 9.5. Before lunar resources can be incorporated into solar power satellite designs, the ability to handle and process these materials in a microgravity environment should be demonstrated. Therefore, we recommend the testing of physical processing methods of lunar simulants on either Space Station Freedom or some other microgravity laboratory. Also, since chemical processing of lunar raw materials might be more efficiently done on the lunar surface than in orbit, it is suggested that in situ chemical processing tests on the lunar surface be performed by penetrators, rovers, and perhaps even automated bases. Base Power The presence of a fully operational lunar base capable of delivering raw materials to Earth orbit could greatly reduce the cost of building solar power satellites. In his 1989 paper, Woodcock attempts to answer what is essentially the fundamental question with regard to the use of lunar resources for solar power satellites: at what level of operation will the energy/cost savings provided by the use of lunar resources outweigh the initial capital investment needed to establish both the cislunar infrastructure and the manufacturing capabilities? Because this manufacturing capability does not yet exist, the latter half of this question is very difficult to quantify. However, by employing a detailed parametric analysis that takes into account the cost of money, Woodcock is able to conclude the following [Woodcock, 1989]: • Generally, the analysis indicates that lunar resources are economically beneficial • Early attempts at “bootstrapping”—another idea popularized by O'Neill—by using lunar oxygen to increase the base's self-sufficiency are likely to pay off • The analysis indicates that lunar resources to be used in the assembly of solar power satellites have a “strong positive economic return,” but this conclusion is uncertain due to the lack of reliable orbital manufacturing costs • The “most critical technology affecting positive economic return” is “lunar surface electrical power supply.” Photovoltaic systems are likely to suffice for early lunar oxygen production, but “support of Solar Power Satellite materials production will require nuclear power or a power beaming system.” Woodcock's analysis provides the justification for the synthesis of two of O'Neill's ideas: “bootstrapping” and lunar-derived solar power satellites. Space solar power systems can benefit from “bootstrapping” by initially providing beamed power to a lunar base, which in turn could provide the system with the materials needed to build more solar power satellites. This power could be implemented in a staged way, as energy might first be provided on the order of kilowatts for a lunar rover (see Appendix B). Then, for an automated base, power can be beamed on the scale of hundreds of kilowatts, and ultimately megawatts can be provided for the manned base. Considering the dearth of near-term and possibly even mid-term Earth-based markets, and the terrestrial problem of atmospheric attenuation which would not be a problem on the atmosphere- free Moon, beaming power to the lunar surface may be the best way to convincingly demonstrate space solar power while simultaneously enhancing its long-term economic viability.
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