Under the Cospas-Sarsat 1979 agreement,
France provided the Search and Rescue Processor, developed by the Center for National D'Etudes Spatiales (CNES).
Canada's Department of National Defence developed the Search and Rescue Repeater.
The United States provided the Search and Rescue Receive Antenna – designed and built by the
East Windsor team, which also performed the integration, test and fielding of the system that also needed to work in conjunction with the
Soviet Union's Cospas satellites. In the U.S. the SARSAT system was developed by NASA. Once it became fully functional, its operation was turned over to NOAA where it remains today.
The Cospas-Sarsat system swings into action when a distress beacon is activated in a life-threatening emergency. The beacon is picked up by the satellites equipped with the SARSAT hardware. Satellites downlink the distress data to ground stations and mission control centers that distribute it to rescue coordination centers that dispatch personnel to effect a rescue. Typical rescue beacon radios transmit a strong 5-watt signal once every 50 seconds. Most beacons also include a GPS receiver so they can report a precise latitude/longitude location. Aircraft Emergency Locator Transmitters (ELTs) are automatically activated by g-force switches that detect sudden deceleration during a crash, while maritime Emergency Position Indicating Radio Beacons (EPIRBs) are normally activated by contact with seawater. Personal Locator Beacons (PLBs) are activated manually.
Initially, SARSAT hardware was installed only on low earth orbit polar-orbiting satellites, like the Advanced TIROS-N series. These orbit at about 500 miles in altitude, making a single revolution each 100 minutes, with sensors viewing a different swath of the planet on each pass as the Earth turns beneath them. When a distress beacon is detected, its location can be computed based on the Doppler shift of the beacon signal as the satellite passes overhead. Satellites in polar orbit provide emergency beacon users with global coverage (including the polar regions).