6. Supporting Terrestrial Systems The supporting terrestrial systems for any SPS concept would fall into one of three categories, viz, (1) The ground receiving/rectifying antenna (rectenna), and its associated systems, including the interface with the power utility network. (2) The launch facilities required for handling earth to orbit transport for construction, maintenance and re-supply, and also for providing the necessary communications and control functions. (3) The industrial facilities required for producing the materials and components that would ultimately be assembled into an operational SPS. In addition, the Power Relay Satellite would require a ground-based, de to rf conversion and transmission facility. Of the above three categories, the third, i.e., industrial facilities, has not been addressed at this point. The second, launch facilities, has not yet been addressed beyond studies of transportation systems. These studies have primarily considered the numbers and types of vehicles that will be needed, but some attention has been given to flight schedules and launching considerations. These studies are summarized in Section IV. The first category, i.e., the rectenna, has been considered in some detail. It would consist of dipole elements, each connected to a solid state (Schottky barrier) diode to convert the microwave power back to de power. Low pass filters could be incorporated into these elements to prevent radiation of harmonics. A typical system would contain on the order of 10^^elements, and they would be assembled into an array about 6 miles (10 km) in diameter, with panels tilted at right angles to the incoming wave front. Except for a few differences in detail, the rectenna concepts under consideration by all contractors are essentially the same. The accuracy of the rectenna construction would not be critical since the individual elements have broad dipole gain patterns. For the same reason, the phase front can be distorted by the atmosphere or ionosphere without appreciably affecting efficiency. The ground plane would be open metal construction for low cost and low wind resistance. The rectenna
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