Cospas-Sarsat is an international satellite-based search and rescue (SAR) distress alert detection and information distribution system, established by Canada, France, the United States, and the former Soviet Union in 1979. It is best known as the system that detects and locates emergency beacons activated by aircraft, ships and backcountry hikers in distress. Over the years many countries have joined the project, either as providers of ground segments or as user states. As of 2011[update], 26 countries (Algeria, Argentina, Australia, Brazil, Chile, China (P.R.of), Greece, India, Indonesia, Italy, Japan, Korea (Rep.of), New Zealand, Nigeria, Norway, Pakistan, Peru, Saudi Arabia, Singapore, South Africa, Spain, Thailand, Turkey, UAE, UK, Vietnam) and two organizations (ITDC of Chinese Taipei and Hong Kong, China) are providers of ground segments, while 11 countries are user states (Cyprus, Denmark, Finland, Germany, Madagascar, Netherlands, Poland, Serbia, Sweden, Switzerland, Tunisia).[1] Cospas-Sarsat is based in Montréal, Québec, Canada, and is headed by Steven Lett of the United States.
The system consists of a ground segment and a space segment:
The space segment of the Cospas-Sarsat system currently consists of SARR instruments aboard 5 geosynchronous satellites called GEOSARs, and SARR and SARP instruments aboard 6 low-earth polar orbit satellites called LEOSARs.[2]
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The first system satellite 'COSPAS-1' (Kosmos 1383) was launched from Plesetsk Cosmodrome on June 29, 1982.[3][4][5] Cospas-Sarsat began tracking the two original types of distress radiobeacons in September, 1982. Specifically, these were:
More recently, a new type of distress radiobeacon became available (in 2003 in the USA) [1]:
The four founding countries led development of the 406 MHz marine EPIRB for detection by the system. The EPIRB was seen as a key advancement in SAR technology in the perilous maritime environment. Prior to the founding of Cospas-Sarsat, the aviation community had already been using the 121.5 MHz frequency for distress. ELTs for general aviation were constructed to transmit on 121.5 MHz, a frequency monitored by airliners and other aircraft. Military aircraft beacons were manufactured to transmit at 243.0 MHz, in the band commonly used by military aviation. Early in its history, the Cospas-Sarsat system was engineered to detect beacon-alerts transmitted at 406 MHz, 121.5 MHz and 243.0 MHz. More recently, the Cospas-Sarsat system has been designed to detect only alerts transmitted at 406 MHz (see below). This allows the system to be optimized for the increasingly sophisticated 406 MHz beacons, and avoids problems (including false alerts) from the less-sophisticated legacy 121.5 MHz and 243.0 MHz beacons. Many ELTs include both a 406 MHz transmitter, for satellite detection, and a 121.5 MHz transmitter that can be received by local search crews using direction-finding equipment.
The design of distress radiobeacons as a whole has evolved significantly since 1982; the newest 406 MHz beacons incorporate GPS receivers; such beacons transmit highly accurate positions of distress almost instantly to SAR agencies via the GEOSAR satellites. The advent of such beacons has created the current motto of SAR agencies --- "Taking the 'Search' out of Search and Rescue." (See MEOSAR below.) [2]
COSPAS (КОСПАС) is an acronym for the Russian words "Cosmicheskaya Sistema Poiska Avariynyh Sudov" (Космическая Система Поиска Аварийных Судов), which translates to "Space System for the Search of Vessels in Distress". SARSAT is an acronym for Search And Rescue Satellite-Aided Tracking.[6]
Cospas-Sarsat is an element of the International Maritime Organization's Global Maritime Distress Safety System (GMDSS). Automatic-activating EPIRBs are now required on vessels subject to requirements of the International Convention for the Safety of Life at Sea (so-called SOLAS-class vessels), commercial fishing vessels, and all passenger ships. Beacons can have vessel identification information pre-programmed into the distress transmission. Or, if the beacon has been properly registered with authorities in advance, Rescue Coordination Centres will be able to retrieve crucial vessel identification and contact information from a beacon registration database.
Starting on 1 February 2009, the Cospas-Sarsat System stopped processing signals from the anachronistic 121.5 MHz and 243 MHz beacons. Now only signals from 406 MHz beacons are processed.[7] The switch to 406 MHz is expected to result in a substantial reduction in wasted use of SAR resources on false alerts while simultaneously increasing the responsiveness of the system for real distress cases.
The ground segment of the system consists of:
The space segment of the system consists of:
The Cospas-Sarsat system space segment consists of SARR/SARP instruments aboard:
A SARR/SARP instrument is a small package, typically attached to a satellite that is being launched primarily for another purpose.[4] These SARR/SARP are considered a secondary payload onboard satellites with a generally unrelated scientific or telecommunications purpose. See the technical information below for lists of SARR/SARP and their associated satellites.
The satellites are monitored by receiving stations equipped with satellite-tracking satellite dishes called local user terminals (LUT). Each nation's LUTs are monitored by an MCC (Mission Control Centre), a data distribution clearinghouse that distributes alert information to the various rescue coordination centres.
The Cospas-Sarsat system was made possible by Doppler processing. LUTs detecting non-geostationary satellites perform mathematical calculations based on the Doppler-induced frequency shift received by LEOSAR and MEOSAR satellites as they pass over a beacon transmitting at a fixed frequency. From the mathematical calculations, it is possible to determine both bearing and range with respect to the satellite. The range and bearing are measured from the rate of change of the received frequency, which varies both according to the path of the satellite in space and the rotation of the earth. This allows a computer algorithm to triangulate the position of the beacon. A faster change in the received frequency indicates that the beacon is closer to the satellite's ground track. When the beacon is moving toward or away from the satellite track due to the earth's rotation, that Doppler shift also can be used in the calculation.
The more precise the beacon's transmitting frequency is, the more precise will be the results of the mathematical algorithms in determining location, saving search time. Modern 406 MHz beacons are far more precise than the older, retired beacon designs.
LEOSAR predates the GEOSAR system, and it complements it. LEOSAR satellites are monitored by 44 LEOLUTs (low Earth orbit local user terminals).[8] The complementary LEOSAR satellites provide periodic coverage of the entire earth with an emphasis on polar regions. The LEOSAR satellites operate in a store-and-forward mode for 406 MHz signals --- they store distress signals and forward them to the next LEOLUT ground station they overfly. The 6-satellite polar-orbit constellation LEOSAR system provides frequent coverage of the poles with approximately 100 minute orbits.
Up until mid-2007, two of the LEOSAR satellites were Cospas satellites provided by the former Soviet Union and operated by the Russian Federation. However, they were recently taken offline, and now, the American NOAA Polar Operational Environmental Satellites (POES) and the EUMETSAT MetOp-A are the only LEOSAR satellites in service. COSPAS satellites characteristically orbit at 1000 km altitude.
The six operational LEOSAR satellites (with both SARR and SARP instruments) are the Sarsat satellites provided by the United States NOAA and Europe's EUMETSAT. These orbit at an altitude of approximately 850 km. They are:[9]
The GEOSAR satellites are monitored by 16 GEOLUTs (Geostationary Earth Orbit Local User Terminals.)[10] The GEOSAR satellites provide continuous coverage of the entire earth below about 70 degrees latitude with a view toward the equatorial sky. Some locations have poor radio reception toward the GEOSAR satellites and polar regions are not well covered.
Operational SARR are installed on the following five geostationary satellites:[11]
SARR undergoing testing or in a role as an on-orbit spare are installed on the following geostationary satellites:[12]
Typical rescue beacon radios transmit a 5 watt signal for 0.5 second once every 50 seconds. Most of these terminals sold since 1997 include a GPS receiver so they can report precise GPS lat-lon location. Aircraft distress radiobeacons (ELTs) are automatically activated by g-force switches that detect sudden deceleration during a crash, while maritime radiobeacons (EPIRBs) are normally activated by contact with sea water.
The "406 MHz" distress radiobeacon band is 100 kHz wide and centered at 406.05 MHz. Individual beacons transmit in assigned 3 kHz channels. A transmitted distress message is either a 112-bit "short" message or a 144-bit "long" message, both including 49 bits of identification information. If the beacon has a GNSS receiver or position information derived from another local source (such as ship navigation equipment), then that information also is encoded in the transmitted distress message.
Supporters of the Cospas-Sarsat system are preparing to demonstrate and evaluate a new capability called MEOSAR (Medium Earth Orbit Search and Rescue satellites), consisting of SAR transponders aboard navigation satellites of Europe, Russia and the United States. In its current (project) form, the U.S. space-segment component is being called the Distress Alerting Satellite System (DASS) by NASA.[13] MEOSAR will consist of SAR transponders aboard Europe's Galileo constellation, Russian Glonass spacecraft (Glonass-K No. 1 having been launched on 26 February 2011), and the U.S. GPS satellite constellation. MEOSAR assets will report signals from Cospas-Sarsat search and rescue beacons in the 406.0–406.1 MHz band.[14] MEOSAR satellites will be able to provide near-instantaneous detection, identification, and location determination of 406 MHz beacons. The beacon can transmit coordinates of its position encoded in the alert message (if the position information is available from an on-board GNSS receiver or another source such as a ship's navigation sensors). Or the position can be determined independently by the receiving LUT by analyzing the frequency-difference-of-arrival (related to Doppler-induced variations) and/or the time-difference-of-arrival. It is planned that the MEOSAR system will be able to download information back to the distress radiobeacon by encoding "Return Link Service" messages into the Galileo navigation data stream.
In 2010, the Cospas-Sarsat system provided emergency-beacon alert data used in rescuing 2,362 people in 641 SAR events. From September 1982 until December 2010, Cospas-Sarsat alert data has helped to rescue 30,713 people in 8,387 SAR events.[5]
| Category | 2010 SAR Events |
|---|---|
| Aviation | 20% |
| Maritime | 56% |
| Land | 24% |
| Total | 100% |