assumed [20], The corresponding nominal, design-rule [20], optical primary diameter (for MACROLASER-downlink, beam output) would be l/60th x 22 miles = 1936 ft. If the given MACROLASER system should illuminate a "solar cell sea such as to produce an irradiance of 5 times normal sunlight, then if GaAs cells are used in the "Quadrispectral Converter" mode, the best efficiency = 43% [30]. Under these circumstances, a 1-mile-diameter receiver expanse is required. The 1936-ft.-diameter-primary output beam must of course slightly diverge to illuminate a 1-mile-diameter ("sea of solar cells") receiver 22,240 miles below. Such divergence could be handled easily by the primary mirror's "variable-focus" apparatus as described above (Figure 28). Of course for interplanetary/interstellar propulsion applications of the same MACROLASER beam, focusing as well as diverging geometry of the primary mirror (probably) will be required. 80000 feet high balloon carrying "solar cell sea" Meanwhile ideal balloon support for the 1-mile-diameter "solar cell sea" is a single, flat, circular-platform, shallow, wafer-shaped helium balloon which carries the solar cells on its upper surface; one that is one mile in diameter (Figure 32). Assuming the balloon is l/10th of a mile thick, the volume is 1.156 x 10^ ft3. Conservatively [31, 32] this balloon will support net 3.354 x 10$ lb. Let's say this capacity (of 3-1/3rd million lb. net) is used for supporting the weight of all solar cells and power conditioning equipment used to achieve a platform-output voltage of 500,000 Vdc. "Beanstalk" umbilical to 80000 feet The weight of the pair of continuous 16-mile-long, approximately 1-1/2-inch- diameter (arbitrary), copper umbilical rods could be carried inside a continuous series of 160 individually pivotable, 500-ft.-long, enveloping vertical wing-shaped aerodynamic- shroud/helium-balloon units (Figure 32). Rod weight (total) will be: 160 x 6407 lb. = 1025120 lb., where through each 500-ft.-long section passes a pair of 1-1/2-inch-diameter copper rod weighing (inside that section) 6407 lb. Let’s consider only the enveloping (low-drag, "weathervaning"), helium-balloon section #1, supporting the first 500 ft. of umbilical (at ground level), and section #160, supporting the last 500 ft. of umbilical (at 80000 ft.). Shroud Unit #1 will of course have length 500 ft. and chord 73 ft. and thickness 9 ft., for a thickness ratio about 12%. The horizontal cross-section area is 500 ft.3. The net sea-level buoyancy under these circumstances will be some 17400 lb. [31, 32], Beanstalk umbilical self-supported by aerodynamic shroud helium balloons By the ratios inferred from [31], 17400 lb. of gross vertical balloon-lift should be adequate to lift 170% more than the gross weight of copper rod in the section. It is believed
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