User Manual

Y1-03-0180 Rev. T1

6.2 Satellite Detection

6.2.1 The ThunderBird S.S.A.S. transmits an encoded phase modulated radio signal to the satellite

portion of the COSPAS-SARSAT System. The system was developed and implemented by the

COSPAS-SARSAT Partners (Russian Federation, Canada, France and the United States).

6.2.2 COSPAS-SARSAT is an international system that uses Russian Federation and United States low

altitude, near-polar orbiting satellites that assist in detecting and locating activated 406 MHz

beacon signals. The Russian Federation provides aboard COSMOS navigation spacecraft

COSPAS payloads that are inter-operable with the SARSAT System. In addition to weather and

environmental sensors, SARSAT payloads, provided by Canada and France, are carried aboard

the United States National Oceanic and Atmospheric Administration’s (NOAA’s) Advanced

TIROS environmental satellites. (See Figure 1: Satellite Coverage)

6.2.3 COSPAS and SARSAT satellites receive distress signals from satellite beacons transmitting on

the frequencies of 406.025 and 406.028 MHz. The COSPAS-SARSAT 406 MHz satellite S.S.A.S

signal consists of a transmission of non-modulated carrier followed by a digital message format

that provides identification data. The 406 MHz system uses spacecraft-borne equipment to

measure and store the Doppler-shifted frequency along with the satellite S.S.A.S digital data

message and time of measurement. This information is transmitted in real time to an earth station

called the Local User Terminal (LUT), which may be within the view of the satellite, as well as

being stored for later transmission to other LUTs. In the real-time mode, the signal detection is

limited to a mutual S.S.A.S-satellite-LUT circular visibility area of about 2500 km radius that

moves with the satellite along its track. However, because of the stored-mode capability at 406

MHz, the need for this mutual S.S.A.S-satellite-LUT visibility is not essential, and the system is

fully functional worldwide.

6.2.4 The LUT processes the Doppler-shifted signal and determines the location of the satellite S.S.A.S;

then the LUT relays the position of the distress to a Mission Control Center (MCC) where the

distress alert and location information is immediately forwarded to an appropriate maritime

Rescue Coordination Center (RCC). The RCC dispatches security forces.

6.2.5 The COSPAS-SARSAT System includes 36 LEOSAR LUT stations, 6 GEOSAR LUT stations

and 19 Mission Control Centers that provide real-time as well as global-mode coverage for the

Northern Hemisphere, while the Southern Hemisphere is presently served primarily by the global

mode. Additional LUTs and MCCs are planned for installation in the near future both in the

northern and southern hemispheres.

The addition of the GEOSAR Satellite system greatly improves the reaction time for a security

event. This satellite system has no Doppler capabilities at 406 MHz but will relay the distress

alert to any of the LUT stations. When there is GPS data included in the distress message this

will instantly tell SAR authorities where you are located at. Hence speeding up the reaction time

by not having to wait for one of the LEOSAR satellite's to come around.