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Article Information
Category: General General
Content source: SKYbrary About SKYbrary



COSPAS-SARSAT is a system that detects and locates emergency beacons and sends them to search-and-rescue (SAR) authorities.

COSPAS is an acronym for the Russian words "Cosmicheskaya Sistema Poiska Avariynyh Sudov", which translates to "Space System for the Search of Vessels in Distress". SARSAT is an acronym for Search And Rescue Satellite-Aided Tracking.

The system consists of:

  • Beacons that send the distress signals;
  • Satellites that detect the distress signals;
  • Ground receiving stations that receive and process the satellite signals to generate distress alerts;
  • Mission Control Centers (MCCs) that receive the alerts and forward them to SAR bodies.

The beacons supported operate at 406 MHz (processing of 121.5/243 MHz signals by COSPAS-SARSAT ceased on 1 February 2009). They can be used by:

  • aircraft - these are called Emergency Locator Transmitters (ELTs);
  • ships - these are called Emergency Position-Indicating Radiobeacon Stations (EPIRBs) or Ship Security Alert System (SSAS). The latter are designed and used in an effort to strengthen maritime security.
  • people - these are called Personal Locator Beacons (PLBs).

Two satellite systems are used:

  • GEOSAR, that consists of geostationary earth orbit (GEO) satellites. Geostationary satellites orbit the Earth at an altitude of 36,000 km, with an orbit period of 24 hours, thus appearing fixed relative to the Earth over the equator. A single geostationary satellite provides coverage of about one third of the globe, except for polar regions. Therefore, three geostationary satellites equally spaced in longitude can provide continuous coverage between approximately 70 degrees North and 70 degrees South latitude. The main advantage of the GEOSAR system is that it can provide almost immediate alerting due to its broad footprint.
  • LEOSAR, that consists of low earth orbit (LEO) satellites that use polar orbits. This system complements the GEOSAR as it:
    • provides excellent 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.

The development of the Medium-altitude Earth Orbiting Satellite System for Search and Rescue (MEOSAR system) started in 2004, with SAR repeaters placed on the satellites of the Global Navigation Satellite Systems (GNSS) of Europe (Galileo), Russia (Glonass) and the USA (GPS). Once fully operational, the MEOSAR system is expected to offer the advantages of both the LEOSAR and GEOSAR systems without their limitations by providing transmission of the distress message and independent location of the beacon, with near-real-time worldwide coverage. Other enhancements are also planned, such as a return-link-service (RLS) transmission to a distress beacons that would provide, for example, a confirmation that the distress message has been received.

There are two types ground stations (Local User Terminals or LUTs) that receive the satellite signals: those that are designed to operate with the LEOSAR satellite constellation are referred to as LEOLUTs, and those that operate with the GEOSAR satellite constellation are referred to as GEOLUTs. LEOLUT and GEOLUT operators are expected to provide the SAR community with reliable alert and location data, without restriction on use and distribution.

The MCCs are set up in most countries operating at least one LUT. Their main functions are to:

  • collect, store and sort the data from LUTs and other MCCs;
  • provide data exchange within the COSPAS-SARSAT System;
  • distribute alert and location data to associated Rescue Coordination Centres (RCCs) or SAR Points of Contact (SPOCs).

A total of 34 MCCs are operational in 2018 with 3 more under development. A list and map of MCCs is avaliable here (external link).

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Further Reading