6.80 A . mirror projected ( TT ) (178) 2 - (TT) (25) 2 9.76xl0 4 m 2 This area intercepts sunlight at l.38xlo 3 watts/m 2 , but the selective coatings on the first and second mirrors reflect only the wavelengths between 400 and 700 millimicrons,thus using only 5.6xl0 2 watts/m 2 of the Sun's output (6.9). Twenty percent of this agricultural sunlight is lost due to the parabolic mirror's inefficiency and another 20% due to the second mirror's inefficiency. The remaining power entering the hull's window is: P. inputsunlightmax This value is higher than: (.8) (.8) (5.6xl0 2 ) (9.76xl0 4 ) 3.50xl0 7 watts P = 2.79xl0 7 watts inputsunlight calculated in Section VI.8.2. The higher value includes a 20% allowance in the. parabolic mirror area for degradation of the mirror properties due to meteorites and solar wind over the colony's 30-year lifetime. When the colony operations begin, sections of the second mirror are shadowed, reducing the sunlight power input to the needed 2.79xl0 7 watts. This design allows repair-free operation of the parabolic mirror for 30 years. The largest angle of incidence on the parabolic mirror is 51° at the rim. The second mirror is wrapped around the focal point 71.4 meters from the parabolic mirror's pericenter. The boom supporting the second mirror extends to the plane of the edge of the parabolic mirror to anchor support structure extending out to that edge and to the solar cells. The solar cell array extends outward from the rim of the parabolic mirror in a flat ring. The electrical power generated flows along pathways in the mirror support structure to the hull. Silicon
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