Page 42 - Satellite Communications, Fourth Edition

22 Chapter One

Newer beacons operating at a frequency of 406 MHz are being intro-
duced. The power has been increased to 5 W, which should permit loca-
tional accuracy to 3 to 5 km (Scales and Swanson, 1984). The 406-MHz
carrier is modulated with information such as an identifying code, the
last known position, and the nature of the emergency. The satellite has
the equipment for storing and forwarding the information from a con-
tinuous memory dump, providing complete worldwide coverage with
100 percent availability. The polar orbiters, however, do not provide
continuous coverage. The mean time between a distress alert being sent
and the appropriate search and rescue coordination center being noti-
fied is estimated at 27 min satellite storage time plus 44 min waiting
time for a total delay of 71 min (Cospas-Sarsat, 1994a, b).
The nominal frequency is 406 MHz, and originally, a frequency of
406.025 MHz was used. Because of potential conflict with the GEOSAR
system, new channels at 406.028 MHz and 406.037 MHz have been
opened, and type approval for the 406.025 MHz channel ceased in January
2002. However, beacon types approved before the January 2001 date and
still in production may continue to operate at 406.025 MHz. More details
will be found at http://www.cospas-sarsat.org/Beacons/406Bcns.htm.
The status of the Cospas-Sarsat low earth orbiting search and rescue
(LEOSAR) satellites as of April 19, 2005 is shown in Table 1.9.

TABLE 1.9 Status of LEOSAR Payload Instruments
Search and
Repeater rescue
Satellite instruments, MHz processor Comments
121.5 243 406 Global Local
Sarsat 6 F F F NO NO
Sarsat 7 F L F F F Intermittent loss of
the 243-MHz
service, which
may affect an
entire or partial
satellite pass.
Sarsat 8 L NO F F F Intermittent loss of
the 121.5-MHz
service, which
may affect an
entire or partial
satellite pass.
Sarsat 9 F F F F F
Cospas 4 NO NA NO NO
Cospas 5 F NA NO NO
NOTES: F—fully operational; L—limited operation; NO—not operational; NA—not applicable.
SOURCE: http://www.cospas-sarsat.org/Status/spaceSegmentStatus.htm