Home' RTCA Documents for Review : DO-204B, MOPS Aircraft ELT 406MHZ Contents © EUROCAE, 2018
The system consists of a ground segment and a space segment that include:
distress radio-beacons to be activated in a life-threatening emergency;
SAR signal repeaters (SARR) and SAR signal processors (SARP) aboard
several satellite downlink receiving and signal processing ground stations called
local user terminals (LUTs); and
mission control centres (MCCs) that exchange, route and distribute the distress
alert data (particularly beacon location data) provided by the LUTs.
The Cospas-Sarsat system space segment consists of SARR and SARP instruments
satellites in polar low-altitude Earth orbit called LEOSARs;
satellites in geostationary Earth orbit called GEOSARs; and
satellites in medium-altitude Earth orbit called MEOSARs.
The distress-alert instruments are attached as secondary payloads to satellites that
are being launched primarily for meteorological or navigation purposes.
Cospas-Sarsat provides a robust data distribution system for distress alerts and
a network of more than 30 MCCs, operated by governments, and distributed
communication links to global SAR authorities.
The Cospas-Sarsat system has the capability to both relay distress location data that
is provided by the navigation or GNSS receiver data embedded in the beacon
message, and to mathematically analyze the relayed beacon signal to calculate the
distress location “independently” from location data in the distress message. Cospas-
Sarsat is the only satellite distress-alerting system that is capable of this dual
redundant means of locating an activated distress beacon. The independent
calculation of the location is made from measurements of the Doppler-effect-induced
frequency differences and/or distance-dependent time-of-arrival seen in the distress
signal at the LUT receiver when relayed by LEOSAR and MEOSAR satellites.
Over time there will be more than 70 MEOSAR satellites, and the MEOSAR system
will become the dominant space-segment capability of Cospas-Sarsat. MEOSAR
consists of receivers aboard the following navigation-satellite constellations: the
European Union’s Galileo, the Russian Federation’s Glonass, and the United States’
Global Positioning System (GPS). Operational distribution of MEOSAR alert data
began in December 2016 in an early operational capability (EOC). The MEOSAR
system will be able to provide near-instantaneous detection, identification, and
location-determination of 406-MHz beacons.
For the 406-MHz distress signal received by the Cospas-Sarsat satellites there are
two radio signal schemes: the original (referred to as “first generation”) narrowband (3
kHz) modulated signal compliant with document C/S T.001, with diversity of channels
used within the satellite bandwidth (compliant with document C/S T.012); and a recent
(“second generation”) wideband (“spread spectrum”) modulated signal compliant with
document C/S T.018 that uses a single channel which utilizes most of the 100 KHz
satellite bandwidth. Along with the difference in signal structure, “second generation”
beacons also have additional features and can convey more information.
Some beacon models also can receive “return link messages” sent to them over the
navigation channels of the Galileo satellite system to, for example, provide an
indication to the beacon user that the distress signal has successfully been received.
Many beacon models also include transmitters operating on other frequencies defined
by national administrations for localized homing and on-scene locating purposes.
Further information on Cospas-Sarsat, the system and beacons can be found at
Links Archive Navigation Previous Page Next Page