Processing of aluminum at the Factory consists of alloying it with strengthening metals, extruding it into structural shapes and forming beams and other structural members with the basic elements. A solar furnace provides the heat necessary to melt and alloy the aluminum. Extruders process the alloy into strip form and pass it to automated beam builders that "extrude" finished beams. A beam's continuous longitudinal members are held in proper relationship by cross members welded in place at regular intervals and strengthened by diagonal tension braces. The completed, welded beams are low in mass and strong over long lengths. Solar cells are made in the Lunar Orbit Factory from large silicon crystals grown in micro-gravity. Enclosed in glass sandwiches for protection and mounted on large panels interconnected with aluminum power buses, they are produced by manufacturing and assembly robots and stored externally for final assembly into Solar Power Satellites. In the immediate vicinity of the Lunar Orbit Factory, robots construct satellites in basic form from the solar panels and beams. Major onboard structures, such as the SMES (Superconductive Magnetic Energy Storage) and transmission antennas, are also assembled as completely as possible and mounted. When a satellite has been completed to this stage, it is towed by lunar shuttle to its operating position in geosynchronous orbit. Here it is outfitted with the remaining special equipment brought up from Earth, and placed in commission. Solar Power Satellite Assuming a 30 per cent efficiency factor for photovoltaic energy conversion and a conservative 60 per cent transmission efficiency, it would take 116 billion (plus or minus 13 billion) square meters of solar panels to supply all the energy necessary for the world of 2030. One thousand Solar Power Satellites of 116 square kilometers surface area each would furnish this power. It may not be necessary, however, to put such massive solar power systems into space to combat the Greenhouse Effect. The Earth, as it is, is capable of absorbing two fifths of the carbon produced by mankind's present energy load (eliminating 3 billion of the 5 billion metric tons of carbon produced would bring the carbon dioxide production/absorption system into balance). In 1985, fossil fuels provided 90 per cent of the world's energy. Assuming that little has changed since then, the five billion tons of carbon represent about 330 EJ. Two fifths of that, 130 EJ, can still be absorbed by a balanced system. Further, a major effort to remove greenhouse gases from the atmosphere will extend the margin; it is reasonable to think that an additional 2 billion tons of carbon might be removed by a successful program of re-greening, allowing another 130 EJ to be produced by carbon fuels. Finally, the portion of the total energy obtained from non-fossil fuel sources (nuclear, hydroelectric, geothermal and other sources) can be expected to at least expand at a constant rate - remaining 10 per cent of the growing energy supply. Thus, the energy necessary from space can be reduced by 130 + 130 + 90 EJ, or 350 EJ. The result, 550 EJ (a middle estimate of 900 EJ for what will be needed,
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