POWER TRANSMISSION AND RECEPTION - AN OVERVIEW AND PERSPECTIVE R. H. Dietz NASA/Johnson Space Center, Houston, Texas 77058 As part of the DOE/NASA Concept Development and Evaluation Program, NASA has been actively involved in conducting the SPS systems definition effort as well as undertaking certain critical technology supporting investigations. Definition and assessment of the Power Transmission and Reception System has been an important part of that activity. Although funding levels have been low, a considerable body of work has been developed which will provide an excellent data base for future activities in this area. Investigations into concepts for power transmission and reception have primarily concentrated on microwaves as a transport means, although preliminary laser concepts have recently begun to be analyzed. (Candidate lasers systems, e.g. electric discharge, indirect optically pumped, and free electron lasers, are currently under evaluation for overall SPS integration feasibility.) The remainder of this paper addresses the Microwave Power Transmission and Reception (PTAR) System activities. System evaluation activities can be categorized into three major areas. First, microwave system studies (includes the portion of the overall SPS system definition studies which concentrated on the microwave system) funded for approximately $825K. Second, independent subsystem studies (e.g. phase control, power amplifiers, etc.) funded for approximately $890K. And third, experimental critical supporting investigations funded for approximately $790K. The completed results of these funded efforts were presented and discussed as part of the peer review process at the SPS Workshop on Microwave Power Transmission and Reception, held at the Johnson Space Center, January 15-18, 1980. Microwave PTAR can be accomplished in a variety of ways. Five options are illustrated in Figure 1. The power amplifiers (RF converters) can either be located on a separate antenna (separate from the photovoltaic array) or can be an integral part of the photovoltaic array. In turn, the separate antenna can be designed to accommodate all three types of power amplifiers; linear beam tubes, crossed-field tubes, or solid state devices. The integrated photovol - taic/power amplifier option can have either an optical reflector or an RF reflector. The RF reflector option has been dropped from the present studies because of the difficult technology development requirements anticipated in the RF waveguide and reflector areas. The separate antenna approach was the basis for development of the present SPS Reference System. The concept for the Microwave PTAR System transmitter is shown in Figure 2. In this concept the linear beam klystron is used to convert from DC to RF energy. The 70 KW klystron, together with a cooling system, slotted waveguide radiators, phase control receiver and conjugation electronics, and other necessary hardware, comprise the transmit antenna's power module. There are 4 to 36 power modules in an antenna subarray depending on where the subarray is located across the overall tapered antenna array. There are 7220 subarrays in the 1 km. diameter array. Basic system sizing was determined from several constraints and assumptions; a maximum thermal limit on the transmit antenna of 21 kW/m2, a maximum power density through the ionosphere of 23 mW/cm2, current projections of microwave system efficiencies, and minimum cost of electricity per kilowatt hour.
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