Galileo’s contribution to the MEOSAR system

Galileo’s contribution to the MEOSAR system

In 2000, the USA, the European Commission and Russia began consultations with COSPAS-SARSAT on the feasibility of installing SAR repeater payloads on their Medium-Altitude Earth Orbit Navigation Satellite Systems (MEOSAR), and incorporating a 406 MHz MEOSAR capability into COSPAS-SARSAT. The USA MEOSAR programme is called SAR-GPS, the European programme is called SAR/Galileo, and the Russian programme is referred to as SAR/Glonass.

The initial investigations identified many possible SAR alerting benefits that might be realised from a MEOSAR system. These include:

  • near instantaneous global coverage with accurate independent location capability;
  • robust beacon to satellite communication links, high levels of satellite redundancy and availability;
  • resilience against beacon to satellite obstructions;
  • the possible provision of additional (enhanced) SAR services.

Once fully operational, the MEOSAR system will offer the advantages of both the Low Earth Orbit Search and Rescue (LEOSAR) and the Geostationary Earth Orbit Search and Rescue (GEOSAR) systems without their current limitations. It will provide for the transmission of the distress message and the independent location of the beacon with near real-time worldwide coverage.

The large number of MEOSAR satellites that will be in orbit when the system is fully operational will allow each distress message to be relayed at the same time by several satellites to several ground antennas. This will improve the likelihood of detection and the accuracy of location determination.

The COSPAS-SARSAT MEOSAR System is currently under preparation. The following operational phases are planned:

  • Early Operational Capability (EOC) in 2016-2017
  • Initial Operational Capability (IOC) in 2017-2018
  • Full Operational Capability (FOC) in 2019.

Diagram showing the COSPAS-SARSAT MEOSAR System

MEOSAR satellites

MEOSAR satellites orbit the Earth at altitudes ranging from 19 000 to 24 000 km. The primary missions for the satellites used in the three MEOSAR constellations are their respective Global Navigation Satellite Systems (GPS, Galileo and Glonass).

The following table shows the characteristics of all the constellations available on 1 June 2015.

*Note: GPS/DASS satellites are S-Band satellites. They are viewed as experimental payloads and cannot therefore be considered for long-term MEOSAR operations. Their operational use on a temporary basis for the MEOSAR EOC and IOC is authorised however.

MEOSAR ConstellationGPS-DASS
(S band)
(L band)
Number of active satellites17/242/246/240/24
Number of orbital planes6336
Orbital Inclination55°64°56°55°
Orbital altitude20.180 km19.140 km23.222 km20.180 km
Period of revolution11h 58m11h 15m14h 22m11h 58m
Downlink Frequency / Pol.2226 MHz RHCP1544.9 MHz LHCP1544.1 MHz LHCP1544.9 MHz RHCP
StatusExperimental payloads
(S band)*
In TestOperationalIn Development
First Launch dateJanuary 2001February 2011October 2012Planned 2020

All MEOSAR satellite constellations use transparent repeater instruments to relay 406 MHz beacon signals, without on board processing, data storage, or demodulation. The SAR/Galileo and SAR/Glonass payloads operate with downlinks in the 1544 – 1545 MHz band (L band) and the GPS-DASS uses the S band at 2226 MHz (experimental).

MEOSAR communication

As of 1 June 2015, the status of MEOSAR payloads is:

  • GPS/DASS – 17
  • SAR/Galileo – 6
  • SAR-Glonass – 2

MEOLUT ground stations

To provide beacon identification and location information, the satellite downlinks are processed by ground receiving stations called MEO Local User Terminals (MEOLUT). The distress alert information computed by MEOLUTs is forwarded to COSPAS-SARSAT Mission Control Centres (MCCs) for distribution to SAR services. The MEOSAR payloads are designed according to interoperability requirements which allow the MEOLUTs to compute the location of distress beacons based on any combination of signals received from the MEOSAR satellites.