The international Cospas-Sarsat system is based on a network of satellites in low-altitude earth orbit (LEOSAR) and in geostationary orbit (GEOSAR); it also comprises ground receiving stations as well as control and coordination centers. Its mission is to provide accurate and reliable distress alert and homing data. Supplying this information helps search and rescue (SAR) authorities provide fast and efficient assistance to persons in distress. Since its launch in 1985, the Cospas-Sarsat system has helped save more than 26,000 lives.
The maritime, aviation and land operations comprise three steps: alert, homing and rescue. The alert and homing phases used the same 121.5 MHz analog frequency up until 2009, when Cospas-Sarsat decided that it would phase out satellite processing at 121.5 MHz frequency and that alerts would be triggered only on 406 MHz – a digital frequency able to offer enhanced security, to provide more comprehensive information and to reduce the number of false alarms.
The 121.5 MHz signal is nonetheless still received on land, by ships at sea and by airborne aircraft, and remains the most efficient and reliable system for homing in on victims. Distress radio beacons must thus be of the dual frequency type in order to guarantee accurate homing.