that would remain efficient regardless of the angular position of the airplane with respect to the ground-based transmitter. The SHARP program is projected to go through an intermediate stage of development before the final system which will support an airplane flying at 65 000 feet for months at a time, performing useful communication and surveillance functions. The SHARP program today represents the cutting edge of active application of 2.45 GHz technology, and represents a logical step on the learning curve toward a space application. An electronically steered array for a microwave-powered airplane flying at 65 000 feet could also be used experimentally to beam small amounts of power to a low Earth orbit satellite with a rectenna designed for low power density to explore the importance of refraction and attenuation in the Earth's atmosphere under a variety of weather conditions. Space Applications As indicated in the Introduction there are currently three space applications for 2.45 GHz beamed power under review. These are the Solar Power Satellite system where the power is beamed from space to Earth and the Orbiting Industrial Park and the All- Electronic LEO to GEO Transportation System where the power is beamed from Earth to space. The Solar Power Satellite has been discussed earlier in this paper and extensively elsewhere so that it will not be discussed further. The other two applications are relatively new. Both depend upon the thin-film rectenna developed for space use and both depend upon transmitters placed on land sites around the equator. It is therefore logical to think of the space vehicles in both applications and their umbilical
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