System Concept

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

Channel Processing

LEOSAR

GEOSAR

406 MHz

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

121.5/243 MHz

Processing of 121.5/243 MHz beacons terminated on 1 February 2009 [read more]