Grumman Aerospace Corporation, and Textron Inc., the concept was accepted for study by NASA. (23, 24) Subsequent studies supported by NASA (25, 26, 27) have not only confirmed its technical feasibility but have established the possibility of it being economically competitive in the future with conventional and other advanced approaches to electrical energy production. One of these studies was devoted to the microwave power transmission system associated with the solar power satellite. (26) The study confirmed the previous finding that to be most economical the power rating of the systems would be large. The typical rectenna would receive over five gigawatts of microwave power, and have an area of 70 square kilometers. The maximum power per rectenna element would be 1. 5 watts while the minimum would be 0. 15 watts, although there is a good reason to believe that in the eventual system these power levels may be increased by a factor of two. The rectenna would have to be fully environmentally protected and have to meet cost goals by a low material cost per unit area and by a low-cost material handling operation which would convert basic materials into completed rectenna subarrays at high speed. 1. 5 Objectives of the Technology Development Reported Upon in this_______ Report The previous sections have been included to serve as a background for understanding the appropriateness of the objectives of the technology development to be reported upon, and for understanding the approaches to achieving those objectives. The broad objective of the effort covered in the subsequent sections of this report is to improve those features of the rectenna which are important to its function in a full scale solar power satellite system. One feature of particular importance is the efficiency associated with the rating of the individual element in the system. Surprisingly the problem is not one of power handling capability since the element has more than enough power handling capability. The problem lies rather in the reduced efficiency that is obtained at the lower power levels which are more representative of the manner in which the rectenna is used in the solar power satellite. Hence, one objective was to do those things to both circuit and diode which would improve efficiencies at lower power levels. Another objective was to develop better instrumentation and procedures to provide better resolution in measurements and to provide a higher confidence level in the efficiency measurements being made. Finally, but of great importance, was the first iteration of an electrical and mechanical design aimed at the high speed, low-cost fabrication of a fully environmentally protected rectenna. The achievement of this latter objective is crucial to the credibility of the economic aspect of the satellite power system.
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