It will require ingenuity to devise projects that will provide the required data at minimum cost. An example of such ingenuity in project planning is illustrated in Fig. 27. This project is directed towards verification of the ability to electronically form and steer the microwave beam within its required accuracy. The project approach would involve constructing a “slice” of the space transmitting antenna and locating it on the Earth. A pilot beam, which normally would be transmitted from Earth, would be transmitted from geosynchronous orbit to interact with the antenna now located on Earth. The role of the Earth-based rectenna would be played by a beammapping satellite also located in geosynchronous orbit. To complete the simulation, a separate ground-based transmitter would be utilized to heat the ionosphere where the pilot beam passes through so that the beam would be subjected to the same conditions as in the operational case. This “inverted” test concept offers a rather complete simulation while greatly reducing the hardware that must be placed at geosynchronous orbit, thereby greatly reducing project costs. Other projects must be defined to encompass the total requirements of a space technology program for the Solar Power Satellite. A major consideration has to do with a Solar Power Satellite “demonstration.” Since the satellite was first studied, the concept of a “demonstration” has been discussed. The purpose of this “demonstrator,” and consequently its technical definition, varies greatly depending on specific viewpoints. One view would look on the “demonstrator” as a device which would provide significant power, on the order of 500 MW, to the ground to demonstrate for technical and lay persons alike the feasibility of the concept. Variations of this approach include transmission of smaller amounts of power, down to the order of 1 kW or less. In addition to variations in power, there is an option as to whether the demonstration needs to be continuous or whether it could be intermittent. If intermittent power is adequate, then the satellite could be placed in low Earth orbit at much less expense, although certain technical considerations might make such a test difficult to implement. The timing of such a demonstration is critical. If it were done prior to a commitment to full-scale development, it would be important to limit its scope and requirements for new development, such as large-scale transportation system. If the activity were done during the course of the development of the full-scale system, the consideration would be different since the decision for new developments would already have been made. A completely different approach to the “demonstrator” would emphasize demonstration of construction productivity rather than transmission of power to the ground. Given this range of variables, it is apparent that the scope and cost of a “demonstration” project may vary widely. A range of options is being studied in order to provide a quantitative base for further considerations. 6. CONCLUDING REMARKS Over the past years, various studies have defined system approaches for implementing the Solar Power Satellite concept. More important than any specific approach is the identification and quantification of the technological improvements required for the concept to be technologically and economically viable. Environmental studies now underway will soon achieve an equal degree of maturity. There is no question that the technical and economic challenges of the Solar Power Satellite are great; however, before the concept is discarded on this basis,
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