Microwave Journal

Architecture of the Cospas-Sarsat Global Satellite Distress and Safety System for Military Applications

September 13, 2021

This article describes the global international Cospas-Sarsat satellite distress and safety system (SDSS) integrated with low earth orbit (LEO), medium earth orbit (MEO) and geostationary (GEO) satellite constellations that provides services at sea, on land and in the air. The Cospas-Sarsat space segment integrated with the near-polar LEO constellation is known as the LEOSAR subsystem, the space segment integrated with the MEO is known as the MEOSAR subsystem and the space segment integrated with the GEO constellation is known as the GEOSAR subsystem. Similarly, the Cospas-Sarsat ground segment consists of local user terminal (LUT) stations, known as the LEOLUT, MEOLUT and GEOLUT subsystems, and the associated regional Mission Control Centers (MCC) connected with the Rescue Coordination Center (RCC) and local Search and Rescue (SAR) infrastructures. This article also reviews satellite repeaters providing SDSS service via satellite beacons known as emergency position indicating radio beacons (EPIRBs) for maritime, personal locator beacons (PLBs) for land, personal and emergency locator transmitters (ELTs) for aeronautical applications. In addition, types of satellite beacons and testers, LUT receivers with antennas, the Cospas-Sarsat Data Distribution Plan and the Alert Data Distribution and Operating System are described.

Oceangoing ships are sinking or disappearing, airplanes are crashing in disasters without a trace, land vehicles and expeditions are being lost in the wild and other causal emergencies are emerging that threaten many lives and property at sea, in the vast inner landscape and airspace around the world. The constant advancement of technology and the extremely improved use of radio have historically been the goal of those in charge of solving the problem of SAR at sea, on land and in the air. In the early history of mobile radio, only 120 years ago, radio stations were installed on ships to improve the safety of life and property at sea.

Although these improvements started well and helped save many lives and assets, they were not effective enough in the event of a sudden, catastrophic loss of a carrier platform. The most effective improvements occurred at the end of the previous century with the improvement of safety of life at sea using MF/HF and very high frequency (VHF) radio and the recent development of safety systems, such as the integration of a new digital selective call (DSC) radio integrated with Cospas-Sarsat and Inmarsat satellite systems. These new integrations, known as the Global Maritime Distress and Safety System (GMDSS) developed by the International Maritime Organization and the Future Air Navigation System (FANS) of the International Civil Aviation Organization (ICAO), can be used to improve safety and security at sea and in the air.

In 1999, the author of this article invented a better Global Aeronautical Distress and Safety System (GADSS) than the still not fully operational “long way” program of ICAO’s FANS. Since 2005, he has published chapters on GADSS, and in 2020, Springer published his book on GADSS Theory and Applications.


Figure 1

Figure 1 Initial Cospas-Sarsat emblem. Source: Cospas-Sarsat.

Figure 2

Figure 2 Cospas-Sarsat satellite constellation.

The Cospas-Sarsat system is a joint international satellite-assisted SAR system established and signed in 1979 under a memorandum of understanding (MoU) among agencies of Canada, France, U.S. and the former USSR (today Russia).

Following the successful completion of the demonstration and evaluation phase begun in September 1982, a second MoU was signed on October 5, 1984, by the Department of National Defense of Canada, the Centre National d’Etudes Spatiales of France, the National Oceanic and Atmospheric Administration (NOAA) of the U.S. and the Ministry of the Merchant Marine (MORFLOT) of the former USSR (Russia). Shortly after, the Cospas-Sarsat system was then declared operational in 1985. Its first emblem is shown in Figure 1.

On July 1, 1988, the four states providing the space segment signed the International Cospas-Sarsat Program Agreement, which ensures the continuity of the system and its availability to all states on a non-discriminatory basis. In January 1992, the government of Russia assumed responsibility for the obligations of the former USSR. Several other states, non-parties to the agreement, have also associated themselves with the program and participate in the operation and the management of the system.1-3


Initially, Cospas-Sarsat developed the first generation of LEOSAR as a subsegment that employed the two constellations of the polar earth orbit (PEO) and the second generation of the GEOSAR subsegment that deployed the three constellations of GEO satellites. Recently, Cospas-Sarsat and its partners developed the third generation, MEOSAR subsegment, which also uses three constellations.

Figure 2 illustrates the Cospas-Sarsat network of LEOSAR, MEOSAR and GEOSAR satellites. Currently, the LEOSAR subsystem contains five American SARSAT, NOAA and PEO satellites, while the Russian first generation of Cospas satellites are not operational. Russia has launched Meteor-M as new generation of this constellation.

The GEOSAR subsystem contains two Russian Elektro-L and two Louch GEO satellites, two American GOES GEO satellites, two Indian GEO satellites and three MSG GEO satellites of the European Space Agency (ESA). The MEOSAR subsystem contains the ESA Galielo, the U.S. GPA and Russian GLONASS satellite constellations. Figure 3 shows the complete space configuration of the Cospas-Sarsat integrated network containing the GEOSAR, MEOSAR and LEOSAR satellite constellations serving all mobile applications. The same figure shows part of the global ship tracking (GST) and global aircraft tracking (GAT) scenarios as important components of the GMDSS and GADSS networks within SAR distress operations, respectively.

Figure 3

Figure 3 Cospas-Sarsat mobile aeronautical GEOSAR, MEOSAR and LEOSAR subsystems.

The GST and GAT satellite network cannot use Cospas-Sarsat satellites, but ships or aircraft can send tracking messages via Inmarsat or Iridium satellites, tracking control stations and RCC for SAR operations. These new solutions can improve the positioning, tracking and detection of ocean ships and aircraft in emergency situations and facilitate their detection if they are missing or hijacked.

As shown in Figure 3, ship earth stations (SES) with EPIRB, persons and vehicle earth stations with PLB and aircraft earth stations (AES) with ELT in distress and emergency situations can be found in the following hypothetical distress situations and SAR operations:

1. Scene I – Ships in distress may manually or automatically activate their EPIRBs and send distress messages via GEOSAR satellite, GEOLUT ground station, MCC and RCC to the ship (SAR) and helicopter (SAR) forces. The EPIRB beacons may also send distress signals via MEOSAR satellites using MEOLUT ground stations and LEOSAR satellites using LEOSAR ground stations for SAR operations.

2. Scene II – All land vehicles (VES), such as trucks, buses and trains, as well as a person in distress, may manually activate PLBs and send distress messages via GEOSAR, MEOSAR and LEOSAR satellites and ground facilities to SAR forces.

3. Scene III – Aircraft (AES) in distress may manually or automatically activate their ELTs and send distress messages via GEOSAR, MEOSAR and LEOSAR satellites and ground facilities to SAR forces.

4. Scene IV – All ships equipped with a SAR transponder (SART) after activation at sea can be detected by radars onboard SAR ships, aircraft and helicopters for enhanced tracking of the position of ships in distress. It is recommended that aircraft also be equipped with a ship’s SART, so that after an emergency landing of an aircraft at sea, they can activate their own SART devices due to their simple identification using SAR radars.

5. Scene V – All ships equipped with an automatic identification system (AIS) SART device after activation at sea can be detected by the AIS receiver onboard SAR ships, aircraft and helicopters for enhanced tracking of the position of ships in distress. In addition, AIS SART or DSC receivers installed onboard SAR units can detect very small special AIS man overboard (MOB) devices mounted on clothing or on lifebelts; which, after activation, enable vessels in the vicinity of a man overboard incident to respond quickly and efficiently to locate and recover a person in the water. It is obvious that these solutions can be used to rescue the crew and passengers after the forced landing of an aircraft on the sea surface.

Figure 4

Figure 4 LEOSAR Cospas-Sarsat system concept. Source: Cospas-Sarsat.

6. Scene VI – The Cospas-Sarsat service via LEOSAR and GEOSAR satellites is only a one-way transmission of distress signals, while the MEOSAR system enables two-way transmission; namely, it transmits distress signals and receives a confirmation of receipt. In fact, the MEOSAR system provides a special service of MEOSAR Acknowledge Message (MAM) sent by a MEOLUT station via a MEOSAR satellite to EPIRB/PLB/ELT terminals (highlighted in red in Figure 4).

7. Scene VII – All ships and aircraft in emergency or distress situations can communicate via their onboard VHF radios and provide distress on-scene communications (DOC) with SAR units. At the same time, all SAR units can use DOC for their mutual communication.2-5


The Cospas-Sarsat space segment architecture includes three types of satellites to collect and relay emergency messages from the user via the ground segment:

1. Spacecraft in the LEO constellation carry either the Cospas or the Sarsat payload, which is generically referred to as the LEOSAR subsegment. The LEOSAR system is the first designed and it is the longest one in use (see Figure 4). In fact, all radio beacons, such as EPIRB, PLB and ELT, send distress signals via LEOSAR satellites to LEOLUT (LUT) receivers. From there they are sent via MCC and RCC to SAR forces.

2. Spacecraft in GEO constellation carry a SAR payload, generically referred to as the GEOSAR subsegment, which works like the LEOSAR network.

3. Spacecraft in the MEO constellation carry the MEOSAR secondary payload installed on the global navigation satellite system (GNSS), such as the U.S. GPS, Russian GLONASS and European Galileo, which started in 2013 to operate like previous networks.

LEOSAR and GEOSAR Space Segment


Figure 5 Cospas-Sarsat LEO and GEO system block diagram.

In general, the Cospas-Sarsat LEOSAR and GEOSAR space segment configuration and its relation with the ground segment is shown in Figure 5. The distress alerts sent by LEOSAR or GEOSAR beacons on the ultra-high frequency (UHF) of 406 MHz are relayed via the appropriate LEOSAR or GEOSAR satellites to the LEOLUT or GEOLUT ground network subsegment, MCC/RCC, SAR point of contact (SPOC) infrastructures and SAR forces.

Initially, Russia delivered two LEO Cospas satellites placed in near-polar orbits at 1,000 km altitude equipped with SAR instrumentation at 406 MHz. The U.S. delivered two NOAA meteorological satellites of the Sarsat system placed in sun-synchronous polar orbits at about 850 km altitude equipped with SAR instrumentation at 406 MHz, supplied by Canada and France. Each PEO satellite makes a complete orbit of the earth around the poles in about 100 minutes, traveling at a velocity of 7 km/s.

Figure 6

Figure 6 Cospas-Sarsat LEOSAR and GEOSAR operations.

The LEOSAR concept exploits the Doppler shift resulting from relative motion between the distress transmitter and the polar orbiting satellite. A successful alert requires at least one satellite pass over the distress area to detect a signal and locate the position of the emergency transmitter. In some cases, a second pass may be required to resolve ambiguity.

Satellites in the LEOSAR subsegment do not provide continuous coverage. This results in possible delays in the reception of the distress alert. The waiting time for detection by the LEOSAR subsegment is greater in equatorial regions than at higher latitudes. Thus, as shown in Figure 5 and Figure 6, LEOSAR and GEOSAR satellite transponders work in three ways:

1. UHF 406 MHz LEOSAR Local Mode – When the LEOSAR satellite receives 406 MHz distress signals, the onboard SAR processor (SARP) recovers the digital data from the beacon signal, measures the Doppler shift and time-tags the information. The result of this processing is formatted as digital data and transferred to the downlink for transmission to any LEOLUT in view.

2. UHF 406 MHz LEOSAR Global Mode – The 406 MHz SARP system provides near global coverage by storing data derived from the onboard processing of beacon signals in the LEOSAR spacecraft memory unit. The content of the memory is continuously broadcast on the satellite downlink. Each beacon can be located by a LEOLUT terminal, which tracks the satellite and provides global coverage with ground segment processing redundancy. The 406 MHz global mode also offers an additional advantage over the local mode with respect to alerting time when the beacon is in a LUT coverage area. As the beacon message is recorded in the satellite memory at the first satellite pass in the visibility of the beacon, the total processing time can be considerably reduced through the broadcast of the satellite beacon message to the first available LUT.

3. UHF 406 MHz GEOSAR Global Mode – Three GEO satellites equally spaced in longitude can provide continuous coverage of the globe between approximately 70 degrees north and 70 degrees south, excluding the polar regions. As the GEOSAR satellite remains fixed relative to the earth, there is no Doppler effect, so radio beacons need the GNSS receiver to provide a determination of the distress position. Location of distress is available only if beacon has a GNSS receiver chip and encodes the location in the beacon message. As shown in Figure 6, the detected distress signals are relayed by LEO and GEO satellites on 1544.5 MHz or 4505.7 MHz (INSAT only) to the appropriate GEOLUT station, where the signals are processed to determine the location of the satellite beacons and/or a mobile in distress.3,5,6,7,8

MEOSAR Space Segment

Figure 7

Figure 7 MEOSAR operation.

The U.S., Russia and the European Commission/ESA have designed the Cospas-Sarsat subsegment that includes 406 MHz SAR repeater instruments on their respective MEO satellites together with GNSS networks of current U.S. GPS and Russian GLONASS, including forthcoming European Galileo. In such a way, an implementation plan for integrating MEOSAR components into the Cospas-Sarsat system (document C/S R.012) was developed in 2006 and can be downloaded from the Cospas-Sarsat website.

An innovative MEOLUT system will provide future service, such as: 1) Near global MEOSAR coverage with accurate independent location capability (no reliance on a navigation receiver), 2) Robust distress beacon-to-satellite communication links and a high level of satellite redundancy and availability and 3) Resilience to distress beacon-to-satellite link obstructions, i.e. satellite motion alleviates line-of-sight beacon-to-satellite blockages. Therefore, one of the main goals of the new MEOSAR system is to determine beacon location within 5 km, 95 percent of the time and within 10 minutes via 72 MEOSAR satellites positioned at MEO altitude.

Supporters of the Cospas-Sarsat system are preparing to evaluate a new capability of MEOSAR satellites, consisting of SAR transponders aboard navigation satellites of Europe, Russia and the U.S. (see Figure 7). All distress signals sent from 406 MHz EPIRP, PLB and ELT are detected by the Distress Alerting Satellite System (DASS) GPS, GLONASS or Galileo GNSS transponders and resent to MEOLUT stations. From MEOLUT stations, position data goes to the MCC, RCC and RCC, which give instructions to SAR ships and helicopters. In that MEOSAR network, Galileo ground earth station (GES) can send MAM as a confirmation of receipt only via Galileo satellites. The MEOSAR satellites orbit the earth at altitudes ranging from 19,000 to 24,000 km (see Table 1).3,4,8,9,10

Table 1


The Cospas-Sarsat user segment contains three radio beacons: EPIRB for ships, PLB for personal use or land vehicles (road and rails) and ELT for aeronautics applications. Future users have a list of all manufacturers of emergency satellite beacons presented in the Cospas-Sarsat system data brochure. Soon after purchasing a new or used emergency beacon it is necessary to register it with an authority indicating contact details and physical address.

Figure 8

Figure 8 Cospas-Sarsat EPIRB (a), PLB (b) and ELT (c) satellite beacons. Source: Joton and Orolia Kannad.

1. Jotron Tron 60 S/GPS EPIRB – The Tron 60 S/GPS EPIRB (see Figure 8a) is developed to meet the regulations and rules for use on large vessels and life rafts in the maritime service in SAR operations at sea. The author recommends that the aviation community use this type of EPIRB for installation onboard long-haul aircraft. It is buoyant and has water activated contacts that will start distress transmissions if deployed into water. The 60 S/GPS is currently available with two different brackets, one manual type and one float free version. The purpose of the Tron 60 S/GPS is to give a primary alarm to the SAR authorities. The EPIRB gives an immediate alarm when activated, transmitting the ID of the ship in distress.

2. Orolia Kannad XS-4 PLB/With GPS – This beacon (see Figure 8b) can be used for personal rescue primarily for pilots and aircraft crews, for the needs of various vehicles traveling in remote environments and for personal services. It has a three-stage operation: 1) lift the flip cover, 2) pull the anti-tamper cover to deploy the antenna and 3) push and hold the ON button to activate the PLB. Once activated it works for at least 24 hours. It is perfect to carry in addition to the onboard aircraft and other mobile radios.

3. Orolia Kannad 406 AS ELT – This survival beacon is intended to be removed from the aircraft and used to assist SAR teams in locating survivors of a crash at sea and on the ground (Figure 8c). Thanks to its small size and light weight, it fits easily inside a life-raft and it is supplied with a floating collar to enable the ELT to float upright if used in water (like the maritime EPIRB units). Its floating collar can be removed if the ELT is attached to a liferaft or any buoyant part. It is a standalone device equipped with an auxiliary antenna and activated manually by survivors or automatically by a “water switch sensor” when in contact with seawater. It is made of molded plastic with excellent mechanical resistance (ASA/PC, light yellow color). The housing is designed to be easily taken in one hand, and a tether is supplied to tie the ELT to a liferaft. 4,10,11,12,13


The Cospas-Sarsat ground segment contains LUT ground stations, such as LEOLUT, GEOLUT and MEOLUT and MCC formations associated with RCC terminals and SAR infrastructures of ships, aircraft and helicopters for SAR missions.

1. Honeywell LEOLUT Receiver and Antenna – The LEOLUT unit single or dual LUT configuration (see Figure 9a) combines LEO/GEO processing capability internalized satellite orbit data. This is a fully automated high performance LEOLUT that receives and processes distress signals from Cospas-Sarsat satellites and distributes location coordinates to the MCC. It maintains satellite orbit data internally, can be configured in a dual configuration and is the only LUT that can perform combined LEO and GEO data processing. Two methods are used to update the orbit: 1) tracking the downlink carrier to provide a Doppler signal using the LUT location as a reference and 2) using local calibration platforms operating at 406 MHz with accurately known locations. The LEOLUT antenna is a phased array that allows the LUT receiver to track satellites (see Figure 9b). It is a lightweight, mast or roof-mounted antenna with digitally controlled motors to provide the entire range of motion required to track the Cospas-Sarsat satellites.

Figure 9

Figure 9 New generation LEOLUT (a) and antenna (b). Source: Honeywell.

Figure 10

Figure 10 New generation GEOLUT (a) and antenna (b). Source: Honeywell..


2. Honeywell GEOLUT 600 GES – This model is a fully configurable ground terminal dedicated to meet SAR needs and exceeds distress data analysis requirements (see Figure 10a). Combined with the LEOLUT 600, it can offer comprehensive SAR integration with unmatched response capabilities provided by the dual processing power of the LEO-GEO system. It provides rapid notification of 406 MHz distress beacon activations to SAR authorities. Using advanced signal processing technology and custom-designed software, the GEOLUT station offers 24-hour automatic monitoring of alerts over a large territory. In conjunction with LEOLUT data, the dual LEO-GEO system provides unrivaled processing capabilities to optimize beacon location accuracy and SAR response time. The LUT hardware comprises an HP processor, GPS clock and Comtech antenna (see Figure 10b). The GEOLUT antenna is a fixed parabolic dish that allows the GEOLUT to receive distress alerts relayed through a single GEOSAR satellite.

Figure 11

Figure 11 MEOLUT (a) with antenna (b). Source: Honeywell.

Figure 12

Figure 12 Cospas-Sarsat MCC terminal. Source: Cospas-Sarsat

3. Honeywell MEOLUT-600 Station – This MEOSAR station (see Figure 11a) process 406 MHz distress alerts sent by the EPIRB, PLB and ELT beacons over next-generation GPS, GLONASS and Galileo MEO satellites and provides rapid notification to SAR authorities worldwide. It is part of an integrated Cospas-Sarsat MEOSAR solution developed by Honeywell Global Tracking, which bridges the existing LEO/LEO infrastructures and can confirm the location of an emergency alert within seconds. Its antenna (see Figure 11b) is a 2.3 m (7.5 ft) mesh dish with radome that allows MEOLUT station to track MEOSAR satellite constellations.3,4,11,14,15


The Cospas-Sarsat mission is to provide MCC and TCC terminals to coordinate between LUT stations and SAR forces.


Cospas-Sarsat MCC terminals have been set up in most countries that operate at least one LUT (see Figure 12). Their main MCC functions are to: 1) Collect, store and sort the data from all LUT stations and other MCCs and 2) Provide data exchange within the entire Cospas-Sarsat system and distribute alert and location data to the associated RCC or SPOC. Each MCC is responsible for distributing all alert data for distresses located in its service area (SA). An MCC SA includes aeronautical and maritime SAR regions in which the national authorities facilitate or provide SAR services and includes regions of other countries that have appropriate agreements for the provision of Cospas-Sarsat alert data.


The SARMaster solution provides comprehensive management of Cospas-Sarsat alerts. Alerts messages are displayed on the Geographic Information System while associated attribute information, such as frequency, time and search region of responsibility, is shown in a textual view. The TSi RCC workstation is internet enabled, putting the vast resources of the internet at the fingertips of the SAR mission planner. Several features of the RCC workstation, including weather, satellite imagery and SAR information, are automatically updated from the internet. Data and information flowing into and out of the workstation are shown in Figure 13. The Precision SAR Manager is a full-featured SAR management system that provides crucial, time-critical information to SAR personnel, resulting in safe and successful rescues. It ideally functions as an RCC workstation, communicating with MCC units or other national or international sites to receive distress calls and conduct a rescue. It also contains cutting-edge software for general SAR mission planning and analysis, resulting in a powerful SAR management system even without the benefit of Cospas-Sarsat.3, 4,11,16


Figure 13

Figure 13 Cospas-Sarsat RCC workstation block diagram. Source: Cospas-Sarsat.

The global SAR mission is a complex ecosystem of products, technologies and personnel with one universal goal—to save lives. The existing Cospas-Sarsat LEOSAR, MEOSAR and GEOSAR satellite network has saved five lives a day for the last 30 years. As the awareness and understanding of this ecosystem increases, from the moment of sending a distress alert to satellite connectivity, rescue coordination and solutions are increasing, so it will be possible to see new emerging applications, innovations and procedures that will save even more time and cost, all devoted to the mission of saving more lives.


  1. Utilisation des Satellites pour les Recherches et le Sauvetage, Cepadues, SNES, 1984.
  2. COSPAS-SARSAT System Documentation, Cospas-Sarsat, 2001.
  3. Cospas-Sarsat, Web. http://www.cospas-sarsat.int/en/.
  4. D. S. Ilcev, Global Mobile Satellite Communications for Maritime, Land and Aeronautical Applications, Vol. 1 & 2, 2016/2017.
  5. J. King, Description of the Cospas-Sarsat Space Segment, 2006.
  6. Introduction to the COSPAS-SARSAT System, 2015.
  7. Cospas-Sarsat LEOSAR and GEOSAR Systems, 2010.
  8. L. Tetley and D. Calcutt, Understanding GMDSS, 1994.
  9. Cospas-Sarsat MEOSAR Implementation Plan, Cospas-Sarsat, 2012.
  10. COSPAS-SARSAT System Monitoring and Reporting, 2015.
  11. D. S. Ilcev, Mobile Distress and Safety System, Manual, DUT, Durban University of Technology, 2011.
  12. Jotron, Web, https://jotron.com.
  13. Orolia, Web, https://www.orolia.com.
  14. Cospas-Sarsat LEOLUT, GEOLUT and MEOSAR Systems, 2018.
  15. Honeywell, Web. https://www.honeywell.com.
  16. Mission and Rescue Control Centres, Cospas-Sarsat, 2019.

Professor Dimov Stojce Ilcev is a research leader and founder of the Space Science Centre for research and postgraduate studies at Durban University of Technology. He has three B.S. degrees in Radio, Nautical Science and Maritime Electronics and Communications. He received his M.S. and Ph.D. degrees in Mobile Satellite Communications and Navigation as well. Prof. Ilcev also holds the certificates for Radio operator 1st class (Morse), for GMDSS 1st class Radio Electronic Operator and Maintainer and for Master Mariner without Limitations. He is the author of several books on mobile radio and satellite CNS, DVB-RCS, satellite asset tracking and stratospheric platform systems for maritime, land (road and railways) and aeronautical applications.