6.25 (Total sunlight power on agricultural area) (Agricultural area) (400 watts/m 2 ) (6.28xl0 4 ) (400) = 2.5lxl0 7 watts Within the 400-700 millimicron wavelength range, the Sun's rays provide 560 watts/m 2 at L5 (see Section VI.9.3). Neglecting inefficiencies in mirror reflection and transmission through the window, the parabolic mirror should intersect an area perpendicular to the Sun's rays equal to: (Perpendicular area of parabolic mirror) If this area had the shape of a circle, its radius would be: (Radius) = (4 . 49 xl0 4 ) · 5 = 119.5 meters 'IT The actual value of area and therefore that of the radius would be larger due to the inefficiencies mentioned above and to necessary allowances for wear (see Section VI.9.3). If the parabolic mirror were to be attached to the hull and spin at 2 to 3 RPM, the mirror's rim (at 119.5 plus meters from the spin axis) would develop a centrifugal force requiring support structure. The ES group and the SDA group felt that the more desirable alternative was to attach the parabolic mirror to the despun or slowly spinning shield. What the second mirror should be attached to was not immediately decided, pending work on the precession/nutation problem and development of an electrical power system. The ES group anticipated thermal problems if the colony were exposed to direct sunlight; if the shield were hot, it might radiate into the hull and add to the waste heat removal ·requirements. This suggested that the parabolic mirror should be between the colony and the Sun,hiding the colony in its shadow. This could be done by pointing the axis of symmetry of the colony at the Sun, which would also provide the orientation required by the Cassegrain
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