6.17 tolerance). Before such a design could be proposed, however, the issues of sunlight, windows, cutouts, and cargo transfer needed attention. VI.4.3: Sunlight, Windows, and Cutouts: The ES group decided that the energy requirements of the colony would be met by the use of solar energy. The alternative of chemical sources (fuels) was quickly rejected because of transportation costs. Also rejected was the possibility of a nuclear power plant, for safety reasons. It seemed reasonable that a colony in the business of manufacturing Satellite Solar Power Stations should be able to use that technology to power itself. The ES group also anticipated that later colonies would use Earth-type agricultural methods to produce food,relying mostly on photosynthetic plants; current alternatives, such as hydroponics (algae culture) or yeast culture, are neither well verified nor tasty. Thus the prototype should grow plants also. These would require light either from the Sun or from artificial sources. Anticipating inefficiencies in converting sunlight to whatever energy form might operate artifical sources and wishing to duplicate the plants' natural environment, the ES group decided to shine natural sunlight on the agricultural area. Other factors in the decision were personal--we liked sunlight and getting it in was a challenge. Bringing the sunlight into the hull called for one or more windows. However, there were structural arguments against large windows. Materials transparent to the wavelengths used by plants and human eyes usually have poor load-bearing properties. The Structural Design and Analysis (SDA) Group felt that winqows, even reinforced with internal structures (i.e., cables), would be a poor substitute for the surrounding opaque portions of the hull. These issues suggested small windows in low-stress areas. Given uniform hull thickness (desirable to simplify the fabrication process), the lowest stresses in our hull would be at the tips of the endcaps on the spin axis (where there would be no centrifugal loads added to the pressure forces).
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