power transmission and reception. Microwave power transmission is certainly a critical element in the feasibility of the satellite power system concept and warrants this level of attention. I would now like to say a few things which will relate to results of some of these activities during the Concept Development and Evaluation Program. First, I would like to discuss the use of solid state microwave converters which was mentioned earlier. We conducted research on the application of solid state converters and studies of concepts which might use these devices in place of klystrons or other tube type converters because of the potential for high reliability in solid state devices. One version would be to make a simple replacement of the klystron tubes with an array of many millions of small DC-RF converter transistors. And this has been studied under the Systems Definition portion of the program. Another radical approach to using solid state converters is to create what we call a sandwich of solar cells, circuitry and solid state DC-RF converters which would be mounted on satellites as illustrated in this viewgraph (Figure 9). Here we show two versions where the microwave transmitting antenna is actually the sandwich structure. One face contains the waveguides and the DC-RF converter transistors and the other side contains the gallium aluminum arsenide solar cells, which are illuminated by a system of reflectors. A great deal of importance in the SPS studies have been placed on the matter of construction. In fact, considerations of construction operations has played a large role in the selection of the reference system concepts. Studies have also been made of the ground operations required to support the building of the rectenna and the industrial demands of SPS. In addition to the activities I've described, a number of significant items of work have been accomplished in the systems studies activities. Among them are the studies of variations in launch trajectories for the Heavy Lift Launch Vehicles required to deliver payloads to low Earth orbit to reduce the impact of the effluents from the rocket engines on the ionosphere. Studies are also under way to explore alternative designs for the launch vehicles in order to determine what is the most favorable concept for delivery of payload into orbit. Studies of alternative power levels and transmitting frequencies for satellite power system have been conducted. At the reference frequency of 2.45 gigahertz, larger antenna systems with smaller rectennas and lower power outputs are economically feasible under certain conditions as shown by these studies. It was also shown that satellites operating at 5.8 gigahertz transmitting frequency instead of 2.45 gigahertz were feasible and could provide power within an economic range or costs. Studies also showed that multiple antennas on the satellite power system were feasible and perhaps desired in order to make best use of the orbital spacings available at geosynchronous altitudes. In order to obtain expert assessment of the results of the Systems Definition studies and technology investigations that NASA has conducted during the SPS Concept Development and Evaluation Program, the NASA Centers involved sponsored five workshops addressing the major SPS technology areas. These workshops are listed on the next viewgraph (Figure 10). The results and findings of these
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