Leroy R. Grumman Cadet Squadron, NER-NY-153

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COSPAS-SARSAT Overview

 

COSPAS is an acronym for the Russian words "Cosmicheskaya Sistema Poiska Avariynyh Sudov", which translates to "Space System for the Search of Vessels in Distress".

 

SARSAT is an acronym for Search And Rescue Satellite-Aided Tracking.

 

The Search and Rescue Satellite (SARSAT) system uses NOAA satellites in low-earth and geostationary orbits to detect and locate aviators, mariners, and land-based users in distress. The satellites relay distress signals from emergency beacons to a network of ground stations and ultimately to the U.S. Mission Control Center (USMCC) in Suitland, Maryland. The USMCC processes the distress signal and alerts the appropriate search and rescue authorities to who is in distress and, more importantly, where they are located.

 

NOAA-SARSAT is a part of the international COSPAS-SARSAT Program to which 38 nations and two independent SAR organizations belong to.  The COSPAS-SARSAT system was made possible by Doppler processing. LUTs detecting non-geostationary satellites interpret the Doppler frequency shift heard by LEOSAR/MEOSAR satellites as they pass over a beacon transmitting at a fixed frequency. The interpretation determines both bearing and range. The range and bearing are measured from the rate of change of the heard frequency, which varies both according to the path of the satellite in space and the rotation of the earth. This triangulates the position of the beacon. A faster change in the doppler indicates that the beacon is closer to the satellite's ground track. If the beacon is moving toward or away from the satellite track due to the earth's rotation, it is on one side or other of the satellite.

 

The COSPAS-SARSAT system space segment consists of SAR signal processors (SARP) aboard:

 

  • 5 geosynchronous satellites called GEOSARs, and

  • 6 low-earth polar orbit satellites LEOSARs.

Technical Description

 

 

Low-Earth Orbiting Search And Rescue (LEOSAR) Satellites

 

The keystone to the Cospas-Sarsat System are the low-earth orbiting (LEO) satellites from which the system takes its name. These satellites provide the ability to detect and locate 406 MHz alerts worldwide and 121.5 MHz alerts for about sixty percent of the world.

 

SARSAT is an instrument package flown aboard the NOAA series of environmental satellites operated by NOAA's National Environmental Satellite, Data and Information Service (NESDIS). These satellites orbit at an altitude of 528 miles and complete an orbit every 100 minutes. Their orbits are inclined 99 degrees from the equator. Typically, each satellite monitors the earth for various weather and climate data.  Yet, each satellite also carries a Search and Rescue Repeater (SARR) that receives and retransmits 121.5 MHz, 243 MHz, and 406 MHz signals anytime the satellite is in view of a ground station. Also carried is a Search and Rescue Processor (SARP) that receives 406 MHz transmissions, provides measurements of the frequency and time, and then retransmits this data in real-time and stores it aboard for later transmission. The satellite also stores each 406 MHz signal it receives and continuously downloads this data for up to 48 hours ensuring ground stations around the world receive it.  That is, if the satellite was not in view of a ground station when it received a beacon signal, the next ground station that sees that satellite views will receive the data. This provides global coverage for 406 MHz distress signals. The SARR is provided by the Canadian Department of National Defence and the SARP is provided by the French Center National D'Etudes Spatiales (CNES).

 

The COSPAS instrument is carried aboard the Russian NADEZHDA navigation satellite orbiting the Earth every 105 minutes at an altitude of 620 miles and an orbital inclination of 83 degrees. The COSPAS instrument was built by the former Soviet Union and continues to be operated by the Russian Federation. The only major difference between COSPAS and SARSAT is that the Russian satellites do not receive 243 MHz distress signals.

 

Geostationary Orbiting Search And Rescue (GEOSAR) Satellites

 

Geostationary satellites are capable of continually viewing large areas of the Earth. These geostationary (GEO) satellites are also able to provide immediate alerting and identification of 406 MHz beacons.  The GEO satellites are not able to use Doppler location processing since they have no relative motion between them and the emergency beacons. Therefore, they are not able to determine a location for a beacon. They can, however, provide immediate alerts. This is a valuable tool for SAR personnel since it allows them to begin their initial verification of the alert.  Often this detective work yields a general location of the vessel or aircraft in distress and SAR assets can be readied or dispatched to that general area. Ideally, a SARSAT or COSPAS (LEO) satellite will fly over the beacon within the next hour and calculate a Doppler location that will be given to the SAR personnel who may already be enroute.

 

There is also one significant advantage with the GEOSAR constellation and that is the ability to use a GPS receiver with a 406 MHz beacon.  Here’s how it works: specially made emergency beacons determine their location using a GPS receiver that is either integrated into the beacon (called a location protocol beacon) or fed by an external GPS receiver. This accurate location information (generally around a football field in size for positional accuracy) is then encoded into the 406 MHz signal that is transmitted by the beacon.  The U.S. Mission Control center (USMCC) then receives that signal with the location and notifies the Rescue Coordination Center (RCC) accordingly.  This information can often be derived in a matter of minutes!  Since every second counts in reaching the scene of a distress this means that there is an increased chance of survival.

 

Two important considerations:

 

1)     A GPS-equipped beacon only works when the receiver has a clear view of the sky in order to permit the receiver to self-locate.  Often times, conditions do not permit this that may either distort the positional accuracy or negate it altogether.  Because of this, the Cospas-Sarsat System relies upon the Doppler locating effect as the primary means for locating a beacon.  This process is able to overcome the limitations of a GPS unit and still generate a fairly accurate location…within a mile for positional accuracy.

 

2)     The GEOSAR component only works if the beacon is registered with NOAA.  Without registration, the RCCs are unable to react as quickly…and ultimately this may delay a SAR response.

Distress Alerting Satellite System (DASS)

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 and 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 406.0–406.1 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.

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