This demonstration proved that WPT system could be constructed and that microwave generators and dipole rectifiers could be developed for efficient conversion of microwaves into de. A microwave WPT demonstration was successfully completed in 1975 at the NASA Deep Space Antenna facility at Goldstone, California. In this demonstration, a microwave beam at a frequency of 2.45 GHz transmitted 30 kW over a distance of one mile to a receiving antenna. The microwaves were converted directly into de at an average efficiency of 82%. As part of the Stationary High-Altitude Relay Platform (SHARP) Program, the Canadian Department of Communications in 1987 demonstrated that an aircraft can be maintained at an altitude indefinitely when powered by a controlled microwave beam. Several test projects including WPT to an aircraft in 1992, and from a rocket to a daughter satellite in 1993, were successfully performed in Japan. WPT in the microwave and laser portions of the electromagnetic spectrum was investigated as part of the Space Power System (SPS) Concept Development and Evaluation Program, by NASA and the U.S. Department of Energy. [2] This program evolved a SPS reference system with 5 GW delivered to the terrestrial transmission network, and provided detailed information on the technical and economic feasibility and societal acceptability of WPT. The results of this program were noted by organizations in Europe, Japan, and the former USSR, leading them to investigate power beaming. International organizations such as the Institute of Space and Astronautical Science, Japan, the European Space Agency and Eurospace, and several institutes of the former USSR Academy of Sciences have been and continue to be involved in power beaming studies. Global Power Relay Satellite Network The Power Relay Satellite (PRS) was proposed by Kraft Ehricke [3] as a means to transmit energy to specific locations distant from remote energy resources. A PRS can be located in geosynchronous orbit (GEO) to reflect a microwave beam to a selected receiving site. The energy sources should be located within less than ± 30 degree latitude to reduce system antennae dimensions A global PRS network with each transmitter beaming to a sector of GEO containing one or more PRSs can be envisaged. A global PRS network would provide a high degree of flexibility for supplying energy with attendant socio-economic advantages because renewable energy sources, e.g. hydropower could be used. Renewable Resources A scenario for an assessment of the feasibility of a PRS included hydroelectric power beamed from South America to Spain to supply the European power grid. The
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