Page 43 - Satellite Communications, Fourth Edition

Overview of Satellite Systems 23

The nominal space segment of LEOSAR consists of four satellites,
although as shown in Table 1.9 more satellites may be in service at any
one time. The status of the 121.5-MHz LEOSAR system as of November
2004 consisted of repeaters on five polar orbiters, 43 ground receiving
stations (referred to as LEOSAR local user terminals, or LEOLUTs), 26
mission control centers (MCCs), and about 680,000 beacons operating
at 121.5 MHz, carried mostly on aircraft and small vessels. The MCC
alerts the rescue coordination center (RCC) nearest the location where
the distress signal originated, and the RCC takes the appropriate action
to effect a rescue. In 2006, Cospas-11 will be launched aboard a new LEO
satellite called “Sterkh.” This is a small, 190 kg satellite designed specif-
ically for Cospas-Sarsat operations.
The status of the GEOSAR segment of the Cospas-Sarsat system is
shown in Table 1.10.
Since the geostationary satellites are by definition stationary with
respect to the earth, there is no Doppler shift of the received beacon
carrier. The 406-MHz beacons for the GEOSAR component carry
positional information obtained from the global navigational satel-
lite systems such as the American GPS (see Sec. 17.5) system, the
Russian global navigation satellite system (GLONASS) and Galileo
(European). These navigational systems employ medium earth orbit-
ing (MEO) satellites, and the space agencies responsible for these
navigational systems have plans to include 406-MHz repeaters on the
MEO satellites.
Although the GEOSAR system provides wide area coverage it does not
cover the polar regions, the antenna “footprint” being limited to latitudes
of about 75° N and S. The coverage areas are shown in Fig. 1.10.

TABLE 1.10 Status of GEOSAR Payload Instruments
Satellite Status Gain control Comments
GOES-9 (155°E) F Fixed
GOES-East (75°W) F AGC
GOES-West (135°W) F Fixed
INSAT 3A (93.5°E) L TBD INSAT 3A is currently under test;
however, alerts from the system
are distributed operationally.
INSAT system does not process
second protected field of long
format messages.
MSG-1 (3.4°W) F Fixed
NOTES: F—fully operational; L—limited operation; NO—not operational; NA—not
applicable; TBD—to be determined; GOES—Geostationary Operational Environmental
Satellite (USA); INSAT—Indian Satellite; MSG—Meteosat Second Generation (European).
SOURCE: http: //www.cospas-sarsat.org/Status/spaceSegmentStatus.htm