ical problems to construct and operate the SPS, which produces clean and pollutionless energy. However, the SPS is such a huge system that many issues need further invesitga- tions. These are: 1. Development of mass transportation technology into Space. 2. Development of technology for large scale construction in Space. 3. Development of highly efficient and inexpensive solar cells. 4. Development of technology of microwave energy transmission. 5. Study of possible interactions of microwave energy beam with the ionosphere and neutral atmosphere. 6. Study of possible microwave impact on biological bodies. The SPS will transmit the 2.45 GHz and 5 GW microwave beam through the ionosphere to the rectenna on the ground. Even though the ionosphere is transparent to the miceowave beam, the microwave beam may interact nonlinearly with the ionospheric plasma because of its high electric field. The microwave-ionosphere interaction has been theoretically studied (1-4). Ohmic heating, self-focusing and parametric instabilities are expected as possible effects, which may interfere with the telecommunications. The examination of these effects is very important, along with item 6, in order to determine the maximum power density of the SPS microwave. Maximum transmission power is limited to no impacts on biological bodies and no interference with telecommunications. The METT project is planned in order to resolve items 4 and 5 by using the Space Station. We have already conducted the MINIX (Microwave Ionosphere Nonlinear Interaction experiment) project using a space chamber (5) and sounding rockets with the same objectives as the METT. The MINIX rocket experiment was carried out with a S-520-6 sounding rocket on August 29, 1983 (6-8). Strong excitations of the plasma waves were observed at the frequency of three halves f3/?) of the gyrofrequency. Ohmic heating was not detected because the rocket flew so fast, 2 km/sec, through the D layer of the ionosphere that the microwave beam transmitted from the rocket at a power of 780 W could not radiate to the surrounding plasma enough to heat it up. A heating experiment was carried out with the high power transmitter on the ground in Platteville (9). Many effects (Spread F, Wideband attenuation and airglow) were observed. However, a frequency of 10 MHz, three orders of magnitude lower than the SPS microwave (2.45 GHz), was radiated into the ionosphere in this experiment. The METT aims to examine underdense heating on a large scale. THE OBJECTIVES AND SYSTEMS OF THE METT The concrete objectives of the METT are itemized as follows: 1. Development of microwave transmitter system for space use. 2. An empirical study of the efficiency of wireless energy transmission by microwaves through the ionosphere and neutral atmosphere. 3. A study of underdense heating of the ionospheric plasma by high power microwaves. 4. A study of nonlinear plasma wave excitations through Raman and Brillouin scattering of the SPS microwave beam.
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