The current Low-altitude Earth Orbit Search and Rescue (LEOSAR) satellites are being replaced with a new Medium-altitude Earth Orbit Search and Rescue (MEOSAR) satellite system.
The MEOSAR system will detect beacons in almost real-time (i.e within 5 minutes). If the beacon is detected by three or more MEOSAR satellites, then the location of the beacon will be determined as well. When the full constellation of MEOSAR satellites is in operation, this will mean location will be determined within 10 minutes, 95 per cent of the time.
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| ACR personal locator with GPS |
The most modern 406 MHz beacons with GPS (US$ $300+ in 2010) track with a precision of 100 meters in the 70% of the world closest to the equator, and send a serial number so the responsible authority can look up phone numbers to notify the registrator (e.g. next-of-kin) in four minutes.
The GPS system permits stationary, wide-view geosynchronous communications satellites to enhance the doppler position received by low Earth orbit satellites. EPIRB beacons with built-in GPS are usually called GPIRBs, for GPS Position-Indicating Radio Beacon or Global Position-Indicating Radio Beacon.
However, rescue cannot begin until a doppler track is available. The COSPAS-SARSAT specifications say that a beacon location is not considered "resolved" unless at least two doppler tracks match or a doppler track confirms an encoded (GPS) track. One or more GPS tracks are not sufficient.]
The new MEOSAR satellites will be launched by the Russian Federation, the European Union and the USA. An operational constellation is expected to be in place by 2017.
The MEOSAR system consists of MEOSAR satellites that detect emergency distress beacons (EPIRBs, PLBs and ELTs). The satellite sends the beacon message back to earth where it is detected by a MEOLUT (MEOSAR Local User Terminal). With sufficient information, the MEOLUT will generate a location for the distress beacon. The beacon activation information is forwarded to a Mission Control Centre (MCC) and then to the relevant Rescue Coordination Centre (RCC) which responds to the beacon activation.
The three MEOSAR satellite constellations will use transparent repeater instruments to relay 406 MHz beacon signals, without on-board processing, data storage, or demodulation/remodulation. MEOSAR satellite providers will make their satellite downlinks available internationally for processing by MEOLUTs operated by MEOSAR ground segment participants.
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| MEOSAR search and rescue system components |
How does MEOSAR work?
The above diagram shows the major components of the MEOSAR system:
1. A distress beacon is activated and sends a 406MHz message. The message includes the beacon id (also known as the Hex id or UIN). If the beacon has a GPS, the message will include the GPS location.
2. Any MEOSAR satellites that detect the distress beacon relay the message back to earth on 1544.1MHz. The relayed message is detected by a MEOLUT.
3. If a MEOLUT receives sufficient information (typically, relay from three or more MEOSAR satellites) a location for the beacon can be calculated. The MEOLUT sends all information available from the beacon (the beacon id, the GPS location if it exists and the MEOSAR location if it can be calculated) to its associated Mission Control Centre (MCC).
4. The MCC forwards beacon information to the relevant Rescue Coordination Centre (RCC). If the beacon was located in New Zealand, for example, the beacon information would be forwarded to the New Zealand RCC in Wellington. If the beacon as located in Australia, the information would be forwarded to RCC Australia in Canberra.
5. The RCC then coordinates the search and rescue associated with the beacon activation.
RESOURCES
/1/ https://www.amsa.gov.au/media/documents/MEOSARFactSheet.pdf
/2/ http://www.sarsat.noaa.gov/future.html
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