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APPENDIX A - THE COSPAS-SARSAT SYSTEM
EPIRBs transmit to the satellite portion of the Cospas-Sarsat system.
Cospas-Sarast satellites are an international system that utilizes Russian
Federation and United States’ low altitude, near-polar orbiting satellites
(LEOSAR). These satellites assist in detecting and locating activated 406
MHz satellite beacons.
Cospas-Sarsat satellites receive distress
signals from EPIRBs transmitting on the
frequency of 406 MHz. The Cospas-
Sarsat 406 MHz beacon signal consists of
a transmission of non-modulated carriers
followed by a digital message format that
provides identification data. The 406 MHz
system uses satellite-borne equipment to
measure and store the Doppler-shifted
frequency along with the beacon’s digital
data message and time of measurement.
This information is transmitted in real time to an earth station called the Local
User Terminal (LUT), which may be within the view of the satellite, as well as
being stored for later transmission to other LUTs.
The LUT processes the Doppler-shifted signal from the LEOSAR and
determines the location of the beacon, then the LUT relays the position of the
distress to a Mission Control Center (MCC) where the distress alert and
location information is immediately forwarded to an appropriate Rescue
Coordination Center (RCC). The RCC dispatches Search and Rescue (SAR)
forces.
The addition of the GEOSAR satellite system greatly improves the reaction
time for a SAR event. This satellite system has no Doppler capabilities at 406
MHz, but will relay the distress alert to any of the LUT stations. When there is
GPS data included in the distress message, SAR authorities instantly know
your location to within 110 yards (100 m). This speeds up the reaction time by
not having to wait for one of the LEOSAR satellite to pass overhead. Because
most of the search and rescue forces presently are not equipped to home in
on the 406 MHz Satellite beacons signal, homing must be accomplished at
121.5 MHz.
Once the 406 MHz signal is relayed through the LEOSAR and/or GEOSAR
network, SAR forces determine who is closest, and then proceed to the
beacon using the 121.5 MHz homing frequency.