TYPES OF SATELLITES

Three types of communications satellites are in use by the U.S. Navy today. They are GAPFILLER, Fleet Satellite Communication (FLTSATCOM), and Leased

Figure 2-3.-Equatorial Satellite Antenna Pointing Guide.

Satellite (LEASAT) (figure 2-4). These satellites are in _{geosynchronous orbit over the continental United} States and the Atlantic, Pacific, and Indian oceans. Each satellite is described in the following paragraphs.

_GAPFILLER

^{In 1976, three satellites, called MARISAT, were placed into orbit over the Atlantic, Pacific, and Indian} oceans. Each satellite had three UHF channels for ^{military use, one wideband 500-kHz channel, and two narrowband 25-kHz channels.}

The Navy leased the UHF section of each satellite for communications purposes. To distinguish the special management and control functions for ^{communications on these UHF channels, the Navy gave} the name GAPFILLER to the leased satellite assets. GAPFILLER was intended to fill the need for _{a continuing satellite communications capability in} support of naval tactical operations until the Navy achieved a fully operable Fleet Satellite Communications (FLTSATCOM) system.

The GAPFILLER satellite over the Indian Ocean is the only one still being used by the U.S. Navy. The other two GAPFILLER satellites were replaced by LEASAT.

The active GAPFILLER satellite will also be replaced by LEASAT as it reaches the end of its operational life.

_{Within the 500-kHz band, transponders provide 20} individual 25-kHz low- and high-data-rate communications channels for 75 baud ship-shore

Figure 2-4.-GAPFILLER, FLTSATCOM, and LEASAT satellites.

communications and for the automated information exchange systems. The UHF receiver separates the receive band (302 to 312 MHz) from the transmit band (248 to 258 MHz).

The receiver translates the received carriers to intermediate frequencies (IFs) in the 20-MHz range and separates them into one of three channels. One charnel has a 500-kHz bandwidth, and two have a bandwidth of 25 kHz each. The signals are filtered, hard limited, amplified to an intermediate level, and up-converted to the transmit frequency. Each channel is then amplified by one of three high-power transmitters.

GAPFILLER also supports the FLTSATCOM system secure voice system and the fleet broadcast in the UHF range. The GAPFILLER communications subsystem will eventually be replaced by the FLTSATCOM system.