considered orbital debris and constitutes a hazard, could conceivably be recovered and reused. The amount of effort and expense involved is likely to be unreasonable for this latter scheme, but further study may be warranted. No matter where the non-terrestrial resources come from - the Moon, discarded launch vehicles, or asteroids - there is an interaction of its use with the assembly node for the big satellites to come later in an space solar power program program. If we use non-terrestrial materials, then we probably don't want to transfer the material to LEO and assemble SPS's there since we'll be expending energy to get the material to LEO only to have to raise it to GEO again. This is not true, however, if we are going to use a constellation of satellites in LEO. Our choices for the assembly location are limited to either LEO or some high orbit, since assembly of structures in the Van Allen belts would be harmful to both the crew and the satellite. The cosmic radiation present in very high orbits can be tolerated by humans for a reasonable period, such as several weeks or even months. The safety implications of this are dealt with separately. Also, if we want to traverse the Van Allen belts with a large satellite being slowly accelerated and slowly spiraling out to GEO, we could damage the solar cells and electronics. Preliminary conclusions might be that, if non-terrestrial materials are used and GEO is selected as the orbit for the final product, then we should build it in GEO. If non-terrestrial materials and a constellation of satellites are used, then we should build them in LEO. If non-terrestrial materials are not used, then the assembly point can be decided on its own merits. 9.4.3 Non-terrestrial Resources Development Program Schedule In reducing the above goals to a schedule, we must consider step by step tasks which will address the most important questions presented above. These appear in Figure 9.14. We should then consider how these relate to each other in time. There will also be relations of these tasks to other programs, both within the space solar power program and, more importantly, within other programs which justify their short-term existence. For instance, if lunar oxygen drives the initial study of lunar processing, a schedule focusing on how this will enhance and enable lunar outpost operations would be a driving factor. Such a lunar resource utilization program might entail several steps: • Global orbital mapping of the Moon for resources should begin. This should be followed by robotic landers (such as the proposed Artemis program of NASA) to allow for further in-situ analysis of the chemical and mineralogical content of the regolith as well as, perhaps, some in-situ resource processing tests. • Laboratory process development should continue, with engineering development to begin when appropriate. This should be integrated with die geochemical mapping missions. • Supplying small amounts (500 kg) of oxygen which can re-supply boil-off to a Lunar Excursion Vehicle (LEV) and also be used for life support purposes. Perhaps small amounts of oxygen would obviate the need for closed loop systems on space suits, resulting in lighter weight portable life support systems (PLSS.) • Then supply larger amounts of liquid oxygen. Current baseline designs for direct ascent and return to Earth (NASA's First Lunar Outpost Study) seem to require ~8 to 10 mt of LOX for return to the Earth (Joosten, 1992.) • Eventually, larger amounts of LOX might be justified for round trip propellant use once reusable landers are phased in for trips to/from Low Lunar Orbit. Production of metals from the by-products of oxygen manufacture could begin. • Supply small amounts of water, also for life support. This can be done by reacting the oxygen which is produced (above) with hydrogen in an 8:1 ratio, thus only 1/9 the mass of the product water needs to be brought from Earth. Even better, use the residual hydrogen in an LEV descent stage for this purpose. Eventually, this hydrogen might be supplied from the lunar surface solar wind volatiles, but a large mining capability must be in place for this to be possible. • For solar-wind implanted volatiles extraction, begin a program which produces enough hydrogen to provide small amounts of water (see above.) Other gasses will be released in this process, such as nitrogen (for life support, pressurization, transport gas, etc.), carbon-based gasses (CO, CO2, and CH4), and helium (for pressurization, transport gases, and even preliminary experiments of He-3 extraction). Longer term, if it makes
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