The METT needs the transmitter system onboard the bus platform near the Space Station, the sub-satellite with a rectenna and a balloon system, and the ground station in order to examine the above mentioned items. Items 1 and 2 are examined by the transmission test between the transmitter onboard the bus platform and the rectenna onboard the sub-satellite or on the ground. A simulated ionosphere is necessary to investigate items 3 and 4 near the bus platform because the microwave power of 20 kW transmitted from the bus platform is not high enough to heat the natural ionosphere. The various conditions of the ionosphere are produced in a large balloon. FUNCTION OF THE METT SUB-SATELLITE The METT Sub-Satellite has two mission programs. One is an orbital test program (OTP) for the microwave energy transmission. This OTP is used to check the transmission system which is installed on the bus platform. The other is an environmental study program (ESP) to investigate effects of the high power microwave on the ionospheric environment. Orbital Test Program (OTP) A critical technology of the microwave transmission system in the SPS is the control of the microwave beam. In the OTP two approaches for the control, adaptive and command methods, are proposed. The transmission system onboard the bus platform should, therefore, have two phase control systems for the microwave beam: a computer controlled system and a system controlled by a retrodirective antenna. Before an energy transmission test to the ground is conducted, the transmission system should be analyzed for safety with the present transmission test between the bus platform and the sub-satellite. The sub-satellite has a pilot signal transmitter for a retrodirective antenna control. The reference beam is transmitted from the subsatellite to the retrodirective antenna on the bus platform, and a correction of the direction of the main lobe of the transmission antenna is made by changing the phase of the transmitted microwave beam fed to each element in the subarray. This guarantees the microwave beam is directed toward the sub-satellite. The sub-satellite has also a microwave sensor matrix to determine the center and actual shape of the received microwave power beam. The information on this collected by the sub-satellite is telemetered to the bus platform. This information assisted by a central processor on the bus platform is used to control the subarray of the transmitting antenna. The antenna pattern including side lobe patterns as well as the overall efficiency of the transmission system can be measured with the sensor matrix. The OTP for the microwave energy transmission between the bus platform and the sub-satellite could give a good measure for the estimation of the function of the transmission system. During this program the key factors to be monitored are the DC RF converter, phase control, driving mechanism of the antenna, safety (high power microwave and high voltage), and thermal analysis of the overall transmitter system onboard the bus platform. Environmental Study Program (ESP) The effects of the high power microwave used by the SPS are now believed to be significant in terms of the increase of the electron temperature, modification of the
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