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View File - University of Engineering and Technology, Taxila

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FIGURE 2.7constellation.A sketch <strong>of</strong> SBIRS, an example <strong>of</strong> intersatellite links <strong>and</strong> satellitespaceborne, thereby limiting operation to both low transmitter power <strong>and</strong> lowfigure-<strong>of</strong>-merit values. What is the trade<strong>of</strong>f? The answer will become obviousin Sec. 4.2.1 <strong>of</strong> Chap. 4.Typical examples <strong>of</strong> satellite constellation are the U.S Defense satelliteoperational network called FLTSATCOM (Fleet satellite communicationssystem) <strong>and</strong> SBIRS (Space-based infrared system) <strong>and</strong> the Iridium <strong>and</strong>Teledesic networks, which provide global mobile telephone <strong>and</strong> pagingservices.FLTSATCOM provides worldwide communications for the U.S. Navy<strong>and</strong> Air Force units, except for the polar regions. FLTSATCOM comprisesfour satellites. Each satellite is injected into a near-geosynchronous equatorialorbit <strong>and</strong> positioned at longitudes 100 W, 23 W, 71:5 E, <strong>and</strong> 172 E. Eachsatellite overlaps in coverage with the adjacent satellite, thereby avoiding anygap in space-segment continuity. The coverage is between the latitudes <strong>of</strong>70 N <strong>and</strong> 70 S. The fleet constitutes the primary Navy’s broadcast <strong>and</strong> shipinterchange communications system. It also provides vital communications tothe Allied Forces worldwide.SBIRS is proposed to be the next frontier <strong>of</strong> the U.S. missile defensesystem: a sort <strong>of</strong> missile shield [3]. SBIRS would comprise a network <strong>of</strong>satellites: LEO, HEO, <strong>and</strong> GEO (see Fig. 2.7). In theory, the GEO forms thefrontline satellites that provide the first warning <strong>of</strong> missile launches over theequator <strong>and</strong> HEO satellites cover the North Pole. The information received byCopyright © 2002 by Marcel Dekker, Inc. All Rights Reserved.

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