Cospas-Sarsat
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.
The system consists of both a ground segment and a space segment:
- Distress radiobeacons
- SAR signal processors aboard satellites
- Satellite downlink receiving and signal processing stations called LUTs (Local User Terminalss)
- Mission Control Centres that distribute distress alert data generated by the LUTs
- Rescue Coordination Centres that coordinate SAR response to a distress situation
The space segment of the Cospas-Sarsat system currently consists of SAR processors aboard 4 geosynchronous satellites called GEOSARs and 5 low-earth polar orbit satellites called LEOSARs.

# Background Information
Cospas-Sarsat began tracking the two original types of distress radiobeacons in 1982.  Specifically, these were:
- EPIRBs (Emergency Position-Indicating Radio Beacons), which signal maritime distress; and
- ELTs (Emergency Locator Transmitters), which signal aircraft distress
More recently, a new type of distress radiobeacon became available (in 2003 in the USA) :
- PLBs (Personal Locator Beacons), are for personal use and are intended to indicate a person in distress who is away from normal emergency services (i.e. 9-1-1)
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.  The aviation community had already been using the 121.5 MHz frequency for distress, so ELTs for general aviation were created using 121.5 MHz, a frequency listened to by the airlines.  Military beacons using the 243.0 MHz frequency could also be detected by the system.
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.)  
COSPAS is an acronym for the Russian words "Cosmicheskaya Sistyema Poiska Avariynich Sudov", which translates to "Space System for the Search of Vessels in Distress". SARSAT is an acronym for Search And Rescue Satellite-Aided Tracking.
Cospas-Sarsat is an element of the Global Maritime Distress Safety System (GMDSS).  Automatic-activating EPIRBs are now required on International Convention for the Safety of Life at Sea (SOLAS) ships, commercial fishing vessels, and all passenger ships, are designed to transmit to a Rescue Coordination Centre a vessel identification and an accurate location of the vessel from anywhere in the world.

# Phase-Out of 121.5 & 243.0 MHz Distress Radiobeacons
Starting on 1 February 2009, the Cospas-Sarsat System will cease processing signals from the deprecated 121.5 MHz and 243 MHz beacons; from then on only signals from 406 MHz beacons will be processed. 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.

# System Composition
The ground segment of the system consists of:
- Distress radiobeacons
- Satellite downlink receiving and signal processing stations called LUTs (Local User Terminalss)
- Mission Control Centres that distribute distress alert data generated by the LUTs
- Rescue Coordination Centres that coordinate SAR response to a distress situation
The space segment of the system consists of:
- SAR signal processors aboard satellites

## Space Segment (SAR Processors - SARP)
The Cospas-Sarsat system space segment consists of SAR signal processors (SARP) aboard:
- 4 geosynchronous satellites called GEOSARs, and
- 5 low-earth polar orbit satellites LEOSARs.
A SARP is basically a box stuck on the side of a satellite.  In this way, SARP are considered a secondary payload onboard satellites with more lucrative core purposes.  See the Technical Information below for lists of SARP and their associated satellites.

## Ground Segment
The satellites are monitored by receiving stations equipped with satellite-tracking satellite dishes called LUTs (Local User Terminals).  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 (RCCs).

# Technical Information

## Doppler Processing
The Cospas-Sarsat system was made possible by the advent of Doppler processing.  LUTs detecting non-geostationary satellites profit from the apparent Doppler frequency shift heard by LEOSAR and MEOSAR satellites as they pass over a beacon transmitting at a fixed frequency.  The apparent frequency shift allows processing to triangulate the position of the distress radiobeacon.  See Doppler Processing article at Cospas-Sarsat and Wiki on Doppler radar.

## LEOSAR
LEOSAR predates the GEOSAR system, and it complements it.  LEOSAR satellites are monitored by 44 LEOLUTs (Low Earth Orbit Local User Terminals).  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 4-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, only the American SARSAT satellites are in service.  COSPAS satellites characteristically orbit at 1000 km altitude.
The five operational LEOSAR satellites are the Sarsat satellites provided by the United States NOAA. These orbit at an altitude of 850 km.  They are: 
- Sarsat-7 SARP aboard NOAA-15
- Sarsat-8 SARP aboard NOAA-16
- Sarsat-9 SARP aboard NOAA-17
- Sarsat-10 SARP aboard NOAA-18
- Sarsat-11 SARP aboard METOP-A

## GEOSAR
The GEOSAR satellites are monitored by 16 GEOLUTs (Geostationary Earth Orbit Local User Terminals.)   The GEOSAR satellites provide continuous coverage of the entire earth below 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.
SARP are installed on the following geostationary satellites: 
- The GOES geostationary satellites GOES-East at 75 W and GOES-West at 135 W
- The INSAT-3A geostationary satellite at 93.5 E
- The Meteosat Second Generation (MSG) geostationary satellite MSG-2 fixed over the Prime Meridian

## Beacon Technical Information
Main Article: Distress radiobeacons
Typical rescue beacon radios transmit a 5 watt signal for 0.5 seconds 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 acceleration switches after a crash, while maritime radiobeacons (EPIRBs) are normally activated by contact with sea water.
The "406 MHz" channel is 170 kHz wide and centered at 406.05 MHz. The message is either a 112-bit "short" message or a 144-bit "long" message both including 49 bits of identification plus position information.

# MEOSAR
Supporters of the Cospas-Sarsat system are working to add a new capability called MEOSAR (Medium Earth Orbit Search and Rescue satellites.)  In its current (project) form, it is being called the Distress Alerting Satellite System (DASS) by NASA.  This system will put SAR processors aboard the GPS satellite constellation the Galileo positioning system constellation.  MEOSAR satellites will be able to provide near-instantaneous detection, identification, receipt of encoded position, and determination of Doppler triangulated position of 406 MHz beacons (exclusively.)  MEOSAR assets will report signals from Cospas-Sarsat search and rescue beacons in the 406.0406.1 MHz band.  There is also the possibility that the system will be able to download information back to the distress radiobeacon via the GPS downlink.

# Rescue Statistics
In 2004, the Cospas-Sarsat system provided assistance in rescuing 1,748 people in 466 SAR events.