EMERGING SPS CONCEPTS by G.M. Hanley, Rockwell International G.R. Woodcock, The Boeing Company Four new technologies have recently been evaluated to determine their effect on Satellite Power System (SPS) concepts. Two of these technologies, solid-state power amplifiers and magnetrons, are replacements for the klystrons used for de to RF conversion on the satellite. A third technology, laser power transmission, transmits the energy at laser frequencies rather than microwave frequencies. The fourth technology, multibandgap solar cells, has the promise of significantly increased solar to de conversion efficiency as compared to the reference-concept silicon and gallium arsenide solar cells. This paper summarizes the design characteristics of concepts resulting from application of these technologies. One of the solid-state microwave concepts, shown in Figure 1, has a configuration similar to the reference concept, although this concept has two end-mounted antennas rather than one. Solar energy is collected in the same manner as it is on the reference satellite and is conducted to the attached microwave antenna using a modified power distribution system. Because of a lower operating temperature requirement for the solid-state amplifiers (compared to klystrons), larger antennas are needed that produce less power at the utility interface than the reference concept (2.6 GW per antenna compared to 5.0 GW). Although the concept shown in Figure 1 uses a concentrated GaAs solar array, a nonconcentrated silicon solar array also could be employed and would have a similar collector area. The antenna configurations for this concept are quite different from the reference klystron design because of the large number of solid-state power amplifiers needed to provide the RF power compared to klystrons (5-10 watts per amplifier for solid state compared to 50-70 kilowatts for klystrons). The major problem, however, is distribution of power from the solar array to each of the power amplifiers. Feed voltages for the solid-state amplifiers is ten volts compared to voltages for the klystron that vary from 8,000 volts to 40,000 volts. One approach proposed by Rockwell to alleviate this problem employs a combination of series/parallel strings of power amplifiers to achieve higher module voltages along with two-step dc/dc power conversion on the antenna to transform from high voltage from the solar array (40,000 volts) to the string voltage (640 volts). The resulting system requires advanced technology dc/dc converters with masses of 0.27 kg/kW. An alternate approach proposed by Boeing utilizes parallel/series strings up to very high voltages (e.g., 5500 volts) with direct power from the array. A solid-state sandwich concept, shown in Figure 2, overcomes the power distribution problems of the previously described solid-state concept by putting the microwave antenna and power amplifiers directly behind the solar array in a “sandwich" configuration. Since the antenna must constantly be pointed at a receiving site on the ground, the sun must be reflected onto the array with a twb-reflector Figure 1. Solid -State End-Mounted Antenna Satellite Concept
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