II. THE REFERENCE SYSTEM The reference system was based on a number of guidelines and assumptions. Some of these guidelines were derived from the results of earlier studies, and others were more judgmental. They were considered necessary to delimit the effort to a manageable size. The guidelines were as follow: Source of Satellite Material — Earth Satellite Location — Geosynchronous Transmission Frequency — 2.45 GHz Microwave Power Density — <23 mW/cm2 in Ionosphere Output from Rectenna — 5 GW Design Lifetime — 30 years Technology Availability — 1990 Initial Commercial — 2000 Satellite Implementation Rate — 10 GW/year The reference system includes elements to be located on Earth and in space. The most significant or “visible” elements of the systems are illustrated in Fig. 1 and include the following: • The SPS located in geosynchronous orbit, • The rectifying antenna, or rectenna, located on Earth, • A construction base in geosynchronous orbit, • An orbital transfer vehicle to transport cargo from low Earth orbit to geosynchronous orbit, • A staging depot located in low Earth orbit, • A space freighter to carry cargo from Earth to low Earth orbit. The configuration of the satellite is presented in Fig. 2. It consists of a planar structure built from a composite graphite material. The planar structure solar array is covered with solar cells. The size of the array is 10 x 5 km. The satellite is designed to deliver 5 GW of d.c. power to the utility system. Therefore, its size is determined by the efficiency levels of the various elements in the system. If the overall efficiency of the system is 7%, it is necessary to size the solar arrays to intercept approximately 70 GW of solar energy. The energy is transmitted to Earth utilizing the end-mounted microwave antenna which is 1 km in diameter. The antenna is made up of subarrays consisting of klystrons and wave guides. The klystrons convert the d.c. power from the solar cells to radio frequency waves. The microwave power beam was designed not to exceed 23 mW/cm2 at the center of the rectenna. The rectenna, or rectifying antenna, is elliptical in shape and has subarray panels consisting of half-wave dipole antennas to collect the energy radiated from the satellite. Early SPS studies indicated that construction of the satellite in space was desirable because the absence of severe loading conditions at 0-g would allow a very lightweight structure. As concepts for space construction have been developed, the constructability of a design is a major parameter in selecting a configuration. A variety of equipments will be necessary to construct a satellite in space. Be-
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