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:
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:
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.
|Number of active satellites||17/24||2/24||6/24||0/24|
|Number of orbital planes||6||3||3||6|
|Orbital altitude||20.180 km||19.140 km||23.222 km||20.180 km|
|Period of revolution||11h 58m||11h 15m||14h 22m||11h 58m|
|Downlink Frequency / Pol.||2226 MHz RHCP||1544.9 MHz LHCP||1544.1 MHz LHCP||1544.9 MHz RHCP|
|In Test||Operational||In Development|
|First Launch date||January 2001||February 2011||October 2012||Planned 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).
As of 1 June 2015, the status of MEOSAR payloads is:
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.