Cospas-Sarsat

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Cospas-Sarsat is an international satellite-based search and rescue system, established by Canada, France, the United States, and the former Soviet Union in 1979. These four countries jointly helped develop a 406 MHz satellite Emergency Position-Indicating Radio Beacon (EPIRB), an element of the Global Maritime Distress Safety System (GMDSS) designed to operate with the Cospas-Sarsat system. These automatic-activating EPIRBs, now required on International Convention for the Safety of Life at Sea (SOLAS) ships, commercial fishing vessels, and all passenger ships, are designed to transmit to a rescue coordination center a vessel identification and an accurate location of the vessel from anywhere in the world. Newest designs incorporate GPS receivers to transmit highly accurate positions of distress.

Starting on 1 February 2009, the Cospas-Sarsat System will cease processing signals from 121.5 MHz and 243 MHz beacons; from then on only signals from 406 MHz beacons will be processed [1].

COSPAS is an acronym for the Russian words "Cosmicheskaya Sistyema Poiska Avariynich Sudov" which translate to "Space System for the Search of Vessels in Distress". SARSAT is an acronym for Search And Rescue Satellite-Aided Tracking [2].

[edit] Technical Information

The Cospas-Sarsat system consists of 4 geosynchronous satellites called GEOSAR and 7 low-earth polar orbit satellites called LEOSAR. The GEOSAR satellites provide continuous coverage of the entire earth below 70 degrees latitude with a view toward the equatorial sky. Some locations have poor radio reception toward the GEOSAR satellites and polar regions are not well covered. The complementary LEOSAR satellites provide periodic coverage of the entire earth with an emphasis on polar regions. The LEOSAR satellites operate in a store-and-forward mode --- they store distress signals and forward them to the next LEOLUT ground station they overfly. The 4-satellite polar-orbit constellation LEOSAR system provides frequent coverage of the poles with approximately 100 minute orbits. Two of the LEOSAR satellites are the Cospas satellites provided by the former Soviet Union and currently operated by the Russian Federation. These orbit at 1000 km altitude. Five of the LEOSAR satellites are the Sarsat satellites provided by the United States NOAA. These orbit at 850 km altitude. The LEOSARs are monitored by 46 LEOLUTs. The GEOSARs are monitored by 18 GEOLUTs.

Typical rescue beacon radios transmit a 5 watt signal for 0.5 seconds once every 50 seconds. Most of these terminals sold since 1997 include a GPS receiver so they can report precise GPS lat-lgn location. Aircraft rescue radios are automatically activiated by acceleration switches after a crash.

The "406 MHz" channel is 170 kHz wide and centered at 406.05 MHz. The message is either a 112-bit "short" message or a 144-bit "long" message both including 49 bits of identification plus position information.