The number of individual power circuits required across the rotating joint also influences the design. For simplicity of design, it would be beneficial to minimize the number of circuits across the joint; however, this complicates the power distribution network and switch gear necessary to handle extremely large blocks of power. 7. 3. 11 REQUIRED TECHNOLOGY ADVANCEMENTS The SPS could be produced with today's technology but would be grossly inefficient and prohibitively expensive. Many advancements in technology are required to produce an SPS with the projected efficiencies and acceptable economics. The following paragraphs will summarize the more important advancements needed on the microwave power system. The transmitting antenna structure will require advancement in space manufacturing of large beams, thermal coatings that maintain their stability over 30 years, assembly and service techniques for the overall structure, and improved ground analytical techniques and methods for simulating static and dynamic properties of large structures in space. Although the actual power tube has not been selected, both prime candidates require some technology advancements. The amplitron projected in this study and in the Raytheon report does not exist; therefore, the development of a low noise and highly efficient tube is a necessity. The open cathode construction and high power will require safeguards against arcing. Materials will have to be developed that withstand the heat generated and to maintain the retentivity of the magnet. The klystron, although more widely used, would require technology advancement to operate at the projected level of efficiency. Advancements are required in active cooling, safeguarding against arcing because of open cathodes and high current, and cathode material for hot cathodes that will last 30 years. The subarray subsystem will require technology advancement for space manufacturing of waveguides that meet the tolerances and low loss requirements of the system. New materials will have to be developed that are insensitive to thermal distortion and yet easily conduct microwaves. Current phase shifting devices operate in discrete steps of several degrees. New devices will be needed that are continuously variable with resolutions in the order of fractions of degrees. Completely new methods of phase control need to be developed.
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