Geosynchronous orbit is 35,400 km above the Earth, while Ll (the location of SSPSs used for lunar power) is 64,400 km above the near side of the Moon. Thus, if lunar SSPSs are identical to terrestrial SSPSs, the microwave beam covers about twice as much area on the surface of the Moon as compared to Earth. Changing the wavelength can reduce beam spread but results in a loss in the (dc-to-dc) efficiency of the system. Terrestrial SSPSs are assumed to transmit at a 10 cm wavelength with 67 percent efficiency. Using information provided by Glaser et.al. (ref. 4), the relationship between microwave efficiency and beamwidth leads to a lunar system with a wavelength of 3 cm, a 30 percent efficiency, and using a rectenna area of 27 km^2
For the lunar system the rectenna is made up of 3,000 dipoles/m^2 and weighs 5 kg/m^2. All is produced on the Moon except gallium arsenide for the diodes and possibly some dielectric materials and glues which need to be brought up from Earth, amounting to about 0.6 kg/m^2.
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