Cospas-Sarsat System Overview

Operational use of Cospas-Sarsat by SAR agencies started with the crash of a light aircraft in Canada, in which three people were rescued (September 10, 1982). Since then, the System has been used for thousands of SAR events and has been instrumental in the rescue of over 24,000 lives worldwide.

The basic Cospas-Sarsat concept is illustrated in the adjacent figure. The System is composed of:

  • distress radiobeacons (ELTs for aviation use, EPIRBs for maritime use, and PLBs for personal use) which transmit signals during distress situations;
  • instruments on board satellites in geostationary and low-altitude Earth orbits which detect the signals transmitted by distress radiobeacons;
  • ground receiving stations, referred to as Local Users Terminals (LUTs), which receive and process the satellite downlink signal to generate distress alerts; and
  • Mission Control Centers (MCCs) which receive alerts produced by LUTs and forward them to Rescue Coordination Centers (RCCs), Search and Rescue Points Of Contacts (SPOCs) or other MCCs.

The Cospas-Sarsat System includes two types of satellites:

  • satellites in low-altitude Earth orbit (LEO) which form the LEOSAR System
  • satellites in geostationary Earth orbit (GEO) which form the GEOSAR System

Cospas-Sarsat has demonstrated that the GEOSAR and LEOSAR system capabilities are complementary. For example the GEOSAR system can provide almost immediate alerting in the footprint of the GEOSAR satellite, whereas the LEOSAR system:

  • provides coverage of the polar regions (which are beyond the coverage of geostationary satellites);
  • can calculate the location of distress events using Doppler processing techniques; and
  • is less susceptible to obstructions which may block a beacon signal in a given direction because the satellite is continuously moving with respect to the beacon.

LEOSAR and GEOSAR Capabilities


  • Beacon identification information and location information provided
  • Global coverage, but not instantaneous


  • Beacon identification provided, and location information available if encoded in beacon message (location protocol beacon)
  • Near instantaneous alerting in the GEOSAR coverage area

For a more detailed description of the Cospas-Sarsat System see document C/S G.003 “Introduction to the Cospas-Sarsat System”.