COSPAS-S&RSAT (International Satellite System for Search & Rescue Services)
The COSPAS-S&RSAT system is an international, humanitarian satellite-based search and rescue system and service which can detect and locate transmissions from emergency beacons carried by ships, aircraft, or people -- which operates 24 hours a day, 365 days a year. Use of the COSPAS-SARSAT system is free to the beacon operator. Once the rescue signals are detected and verified (located) by the system, search and rescue operations can be initiated.
COSPAS (Space System for the Search of Distressed Vessels) and S&RSAT (Search & Rescue Satellite Aided Tracking System) payloads are part of an international cooperative satellite-based radiolocation system to support search and rescue operations for aviators, mariners, and land travellers in distress. COSPAS is the original system developed by Russia (former Soviet Union) in the mid-1970s; S&RSAT was developed in parallel by France, Canada, and the USA. 1) 2)
Note: Although the original acronym for `Search and Rescue' is `SAR' -- whenever possible, it was changed in this particular documentation to `S&R' to distinguish it from the other widely-used meaning of SAR, namely `Synthetic Aperture Radar,' an active sensor type in the context of EO (Earth Observation) missions. A consequence is the use of `S&RSAT' (instead of SARSAT wherever possible).
The COSPAS-S&RSAT system provides distress alert and location data to RCCs (Rescue Coordination Centers) for 121.5 MHz beacons within the coverage area of COSPAS-S&RSAT ground stations, referred to as LUTs (Local User Terminals), and for 406 MHz beacons activated anywhere in the world. The overall system concept is illustrated in Figure 3. The nominal system configuration comprises two COSPAS and two S&RSAT payloads on polar-orbiting satellites. Russia provides two COSPAS satellites in near-polar orbits at an average altitude of 1000 km (83º inclination). The USA supplies two NOAA POES satellites with on-board S&RSAT payloads provided by Canada and France. The orbital period for each satellites is about 100 minutes, the footprint of the COSPAS-S&RSAT visibility is in the order of 4000 km in diameter. The first COSPAS payload was launched on June 29, 1982, while the first S&RSAT equipment was flown on NOAA-8, launched in March 1983. Note: The Nadezhda (”Hope”) spacecraft series are modified “Tsikada” satellites of Russia that are being used in support of navigation services and/or of COSPAS-S&RSAT services (the launch site is Plesetsk, Russia). 3) 4) 5) 6) 7) 8)
Note: The interested reader is referred to the homepage of COSPAS-SARSAT (reference 1) for detailed documentation on all aspects of the system. This file can only serve for a quick overview of the system.
The early S&R history started in the 1960s when light aircraft and some marine vessels started carrying small, battery-operated radio transmitters, operating at the international distress frequency of 121.5 MHz, that could be activated in an emergency distress situation. Such transmitters, called Emergency Locator Transmitters (ELTs) on aircraft, and Emergency Position Indicating Radio Beacons (EPIRBs) on ships, emitted a low-power signal that could be picked up by a receiver in a nearby air traffic control tower or by an aircraft in the vicinity, thus providing only line-of-sight coverage if one was searching in that location. - By the mid-1970s, more than 250,000 distress beacons were in service in Canada, Europe and the USA. Lives of aviators and mariners were being saved thanks to these transmitters, but there was still room for improvement, particularly as it was now the `space age'. 9)
• The beginnings of S&RSAT date back to 1970 when a plane carrying two U.S. congressmen crashed in a remote region of Alaska. A massive search and rescue effort was mounted, but to this day, no trace of them or their aircraft has ever been found. In reaction to this tragedy, the US congress mandated that all aircraft in the United States carry an Emergency Locator Transmitter (ELT). This device was designed to automatically activate after a crash and transmit a homing signal.
• On November 23, 1979 a Memorandum of Agreement was signed by the agencies of USA, Russia (i.e., the former USSR), Canada, and France on the implementation of the COSPAS-S&RSAT system. Under this Memorandum of Agreement, Russia built and launched LEO satellites with the COSPAS payload [on Tsikada and Nadezhda (Hope) satellite series], while the USA carried the S&R payloads, built by Canada and France, on their NOAA weather satellites (POES series) for the S&RSAT system. Note: the Memorandum of Agreement is also referred to as ICSPA (International COSPAS-S&RSAT Program Agreement).
• The first GEO satellite in the COSPAS-S&RSAT system with a GEOS&R (Geostationary Search and Rescue) payload was flown on the NOAA satellite GOES-7 (launch Feb. 26, 1987).
• In 1988 the four space segment providers signed an agreement which ensures service continuity and availability of the system to all States on a non-discriminatory basis - this is referred to as the “International COSPAS-S&RSAT Program Agreement.” The International COSPAS-S&RSAT Program Agreement established a Council and a Secretariat. The Council oversees the implementation of the Agreement and coordinates the activities of the Parties. The Secretariat, the permanent administrative organ of the Program, takes directions from the Council. The international COSPAS-S&RSAT Secretariat is located in London, UK (at Inmarsat).
• ISRO introduced the COSPAS-S&RSAT service over the Indian Ocean in 1992 with its SAS&R (Satellite Aided Search and Rescue) payload flown on the GEO INSAT-2 series, starting with INSAT-2A (launch July 9, 1992). GEOS&R is also flown on the MSG series of EUMETSAT (launch of MSG-1 Aug. 28, 2002, renamed to Meteosat-8 as of Jan. 29, 2004 when the operational service officially started). 11)
In 2004, the participating countries and organizations of the COSPAS-S&RSAT program included:
- The four parties to the COSPAS-S&RSAT International Program Agreement [Canada (CRC), France (CNES), Russia (ROSHYDROMET), and the USA (NOAA)] that provide and operate the satellites and the ground segment equipment
- 24 ground segment providers that operate ground receiving stations the Local User Terminals (LUTs) and Mission Control Centers (MCCs) for the worldwide distribution of distress alerts (over 40 LUTs for LEOS&R - also referred to as LEOLUTs)
- Nine participants associated with the management of the system.
Note: Several countries participating in COSPAS-S&RSAT service are represented by their S&R agency or a maritime or aviation agency, rather than their space agency.
• In early 2007, ISRO (Indian Space Research Organization) signed a formal Understanding with COSPAS-S&RSAT concerning the long-term provision of INSAT GEOS&R services.
Alert Signal Devices (User Segment)
There are three types of radiobeacon devices (heritage of older rescue services) in use, namely maritime EPIRBs, aviation ELTs, and personal locator beacons (PLBs). 12)
1) EPIRB (Emergency Position Indicating Radio Beacon) for use in maritime applications. A small battery-powered transmitting device which is carried on vessels (several nations require EPIRB devices on all vessels). It can be activated in times of trouble to send out help signals. EPIRB devices operate on a frequency of 121.5/243 MHz (the 243 MHz frequency is used only in some older beacons), they may also include the 406.025 MHz alert signal for global detection. 13)
Introduction of new EPIRB technology in 2009: The 406 MHz EPIRB emits a low power, 25 mW sweeping-tone signal constantly on 121.5 MHz, but emits a 5 W burst about every 52 seconds at 406 MHz. Hence, the 406 MHz emission is 200 times stronger than the 25 mW sweeping-tone signal. If the EPIRB is equipped with an internal or external GPS capability, not only can the 406 MHz DF (Direction Finder) accurately track the course to the 406 MHz signal, but future capabilities will allow the operator to read a GPS position on a monitor inside the search aircraft. Proper registration of a beacon can further assist S&R services by providing immediate access to data critical to mission success.
2) ELT (Emergency Locator Transmitter) for aviation use. The 121.5 MHz band service emergency beacons are required on many aircraft, referred to as ELT 121.5, with a smaller number carried on maritime vessels. The 121.5 MHz frequency band is used by an older type of beacons which do not transmit any encoded information. It is also the frequency used for low-power homing transmitters included in most beacons. The more recent ELT devices on aircraft are provided with dual frequency alert systems, 121.5 and 406.025 MHz.
The development of the new generation of beacons transmitting at 406 MHz commenced at the beginning of the COSPAS-S&RSAT project in the mid-1970s. Although the COSPAS-S&RSAT system was primarily designed to function on the much improved 406 MHz frequency, it still had to make a provision for the thousands of 121.5 MHz beacons already in use. For this reason, the satellites were designed to receive 121.5 MHz as well.
The 406 MHz units were designed specifically for satellite detection and Doppler location by having:
- High peak power output and a low duty cycle
- Improved radio frequency stability
- A unique identification code in each beacon
- Digital transmissions that could be stored in a satellite's memory
- A spectrum dedicated by the ITU (International Telecommunication Union) solely for distress beacons.
The 406 MHz beacons transmit a 5 W, half-second burst approximately every 50 seconds. The carrier frequency is phase-modulated with a digital message. The low duty cycle provides a multiple-access capability of more than 90 beacons operating simultaneously in view of a polar orbiting LEO satellite, versus only about 10 for 121.5 MHz beacons.
3) PLB (Personal Locator Beacon) used for land-based applications (basically an ELT when carried by a person, but not used in aviation or maritime applications). These are handheld or pocket size dual frequency (121.5 and 406 MHz) or single frequency (either 121.5 or 406.025 MHz) devices which transmit distress signals to search and rescue authorities via the COSPAS-S&RSAT satellite system. On July 1, 2003, FCC (Federal Communication Commission) of the USA authorized the use of PLBs (406 MHz digitally encoded) on a nationwide basis.
At the start of the 21st century, there are more than 30 manufacturers of 406 MHz beacons in 12 countries, and many more distributors around the world, with over 100 different models type-approved by COSPAS-S&RSAT. The number of 406 MHz beacons in use has increased dramatically from zero in 1985 to 20,000 in 1990 and to about 350,000 today.
The international Council of COSPAS-S&RSAT decided in October 2000 \[in response to guidance from the IMO (International Maritime Organization) and the ICAO (International Civil Aviation)\] to cease processing the 121.5 MHz analog signals by satellite on 1 February 2009. From that date on, only the 406 MHz beacons will be detected by satellite. The decision was made to reduce the chronically high false alarm rate from analog distress beacons. Currently 97 percent of analog distress beacon signals are false alarms.
Figure 1: Illustration of typical PLBs (Personal Locator Beacon) systems (image credit: NOAA)
Figure 2: Overall system configuration of COSPAS-S&RSAT (image credit: COSPAS-S&RSAT)
Space segment of COSPAS-S&RSAT:
• Spacecraft in LEO (Low Earth Orbit) carrying either the COSPAS or the S&RSAT payload (generically referred to as LEOS&R). The LEOS&R system is the longest one in use.
• Spacecraft in GEO (Geostationary Earth Orbit) carrying an S&R payload (generically referred to as GEOS&R).
• Spacecraft in MEO (Medium Earth Orbit) carrying the MEOS&R payload. This service refers to plans to install a MEOS&R secondary payload on the navigation satellite constellations (GPS, GLONASS, and Galileo) - starting in about 2010.
Figure 3: System elements of Search & Rescue Satellites
Figure 4: The initial participants in COSPAS-S&RSAT: Nadezhda, POES & GOES of NOAA (clockwise from lower right), image credit: CNES
Figure 5: Schematic of the COSPAS-S&RSAT space segment (image credit: COSPAS-S&RSAT)
Figure 6: Illustration of COSPAS-S&RSAT spacecraft in LEO (image credit: COSPAS-S&RSAT)
Satellite Payloads (LEO Space Segment or LEOS&R)
The nominal LEO satellite constellation consists of four spacecraft payloads, two S&RSAT and two COSPAS providing parallel services for 121.5 MHz and 406 MHz beacons.
This system worked well, and is still in use today (2008). However, the LEOS&R configuration has inherent time delays, ranging from minutes to hours, in detecting and relaying distress signals because the low altitude satellites (< 1000 km) view only a small portion of the Earth at any instant as they circle the globe. In particular, the LEO system could not be made much better for 121.5 MHz beacons, due to technical limitations of the beacons and the radio channel.
The original LEO system also carried payloads that allowed for the implementation of new digital distress beacons operating at 406 MHz, far superior to the original analog 121.5 MHz beacons. Beacons with the 406.025 MHz signal transmit digitally encoded information which may include beacon identification (which allow COSPAS-S&RSAT services to access registration data bases providing additional information on the unit in distress), and beacon location data (determined by satellite navigation devices such as flown on GPS or GLONASS spacecraft). The new beacons at 406.025 MHz permit the distress location to be automatically computed by the satellite system ten times more accurately (to within 2 km) and the beacon user to be identified, whereas the old 1960s technology beacons at 121.5 MHz gave only an approximate location (to within 20 km) and no user identification, since the 'wow, wow, wow' sound of the signal was similar for all these beacons.
In addition, the 406 MHz system provides global coverage for beacons activated anywhere on Earth, as the beacon signals are stored onboard the satellite and retransmitted to each ground station as the satellite orbits the Earth.
S&RSAT (Search and Rescue Satellite Payload)
The S&RSAT payload consists of S&RR (S&RSAT Repeater), provided by CRC/Canada \[National Search and Rescue Secretariat (NSS) is funding S&RR while DND (Department of National Defense)\]; S&RP (S&RSAT Processor), provided by CNES/France, and the antenna system provided by the USA. The S&R service problem requires two basic functions for effective S&R operations to take place, namely: 1) alerting and 2) locating. The alerting function only requires a low-capacity one-way communications system. The locating function, however, places far more demands on the system. The overall system uses low-powered battery-operated distress transmitters that are received by polar orbiting satellites with an S&R subsystem on-board. The S&R concept exploits the Doppler shift resulting from relative motion between the distress transmitter and the polar orbiting satellite. A successful alert requires at least one satellite pass over the distress area to detect a signal and locate the position of the emergency transmitter. In some cases a second pass may be required to resolve ambiguity.
Figure 7: S&RSAT instrument package valid up to S&RSAT-10 (NOAA-18, launch May 20, 2005), image credit: NOAA
The S&RSAT payload consist of a 2-band (121.5 MHz and 406.05 MHz) repeater S&RR and a 406.025 MHz processor S&RP. The S&RR downlink is at 1544.5 MHz and, besides the two repeated bands, also includes the 2400 bit/s bit stream S&RP output. The 121.5 and 406 MHz bands are also serviced by two Russian COSPAS satellites which, together with the NOAA satellites, provide timeliness of response. 16) 17) 18)
Table 1: S&RSAT subsystem parameters
Figure 8: Illustration of the S&RR instrument (image credit: NOAA)
Figure 9: Illustration of the S&RP subsystems (image credit: NASA)
Each SARP (S&RP) is composed of a receiver processor, referred to as DRU (Data Recovery Unit), FF (Frame Formatter), and a memory unit. Each SARP is configured redundantly. Throughout the service history of COSPAS-S&RSAT there existed various implementations/configurations of SARP, namely:
• SARP-1 (Search And Rescue Processor-1): The SARP-1 package was installed on all early spacecraft in the COSPAS as well as in the S&RSAT series.
• SARP-2 (Search And Rescue Processor-2): The SARP-2 package has improved performance in system capacity, bandwidth, and protection against interferers. Both long and short messages are supported by this processor. The first SARP-2 configurations were implemented on the NOAA-15 spacecraft (launch May 13, 1998) with the S&RSAT-7 payload, as well as on the Nadezhda-7 spacecraft of Russia (launch Sept. 26, 2002) with the COSPAS-10 payload.
• SARP-3 (Search And Rescue Processor-3): SARP-3 is an improved onboard device which was introduced for the first time on the MetOp-A spacecraft of EUMETSAT (launch October 19, 2006). SARP-3 receives and processes emergency signals from the 406 MHz beacons on aircraft and ships in distress. It determines the name, frequency and time of the signal. These preprocessed data are then fed in real-time to the SARR (Search And Rescue Repeater) instrument for immediate transmission to the S&RSAT (Search and Rescue Satellite) distress terminals in the ground segment (referred to as LUTs). 19) 20)
The objective of SARP-3 is to detect and locate ELTs (Emergency Locator Transmitters), EPIRBs (Emergency Position-Indicating Radio Beacons), and PLBs (Personal Locator Beacons) operating at 406.05 MHz. SARP-3 detects the signal from 406.05 MHz beacons and stores the information for subsequent downlink to a LUT (Local User Terminal). Thus, global detection of 406.05 MHz emergency beacons is provided which is a requirement of the GMDSS (Global Maritime Distress Safety System). After receipt of information from a satellite's SARP, a LUT locates the beacons by Doppler processing. The principle of the Doppler processing is that a transmitter signal will have different frequencies depending on its location in relation to the receiver. The determined beacon frequency by the SARP-3 differs depending on the relative velocity between beacon transmitter and the SARP-3 receiver. The 406.05 MHz beacons are located with an accuracy of ~ 4 km. The LUT forwards the located distress message to a nearby Mission Control Center (MCC), which forwards the information to a Rescue Coordination Center (RCC).
Note: SARP systems of S&RSAT-11 or higher (Table 2) are using the SARP-3 instrument package.
Figure 10: Functional block diagram of the S&RSAT SARP-3 (image credit: COSPAS-S&RSAT)
COSPAS (Space System for Search of Vessels in Distress)
The USSR (Union of Soviet Socialist Republics) began deploying the space segment with the launch of Cosmos 1383 on June 30, 1982 from Plesetsk into a 989 km x 1028 km, 83º inclination orbit (Tsikada is a first generation navigational satellite series). Designated as COSPAS-1, the 121.5 MHz band remained operational until December 1987, with 406 MHz utilized primarily for interference monitoring. Cosmos 1447 (launched March 24, 1983) and 1574 (June 21, 1984) adopted the roles of COSPAS 2 and 3, with a third vehicle available as replacement. The COSPAS payload normally shares the Nadezda (Hope) satellite platform with a Doppler navigation payload of the Tsikada system.
The COSPAS payload is composed of the following elements: a S&RR (S&RSAT Repeater), a S&RP (S&RSAT Processor), and uplink and downlink antennas. The S&RR provides local mode coverage for the 121.5 MHz band and its parameters. The S&RP provides both local mode and global mode coverage for the 406 MHz band. COSPAS payloads may have one of two possible S&RP configurations installed: S&RP with memory (SARP-1) or an improved S&RP with memory (SARP-2). The SARP-2 instrument has improved performance in system capacity, bandwidth, and protection against interferers. Both long and short messages are supported by this processor. 21)
The COSPAS repeater (Figure 14), S&RR, is redundantly configured and consists of the following units: a) two dual-conversion receivers; b) two 4.0 W phase modulated L-band transmitters; and c) two Power, Telemetry and Command (PTC) units.
Figure 11: Functional block diagram of the COSPAS system (image credit: COSPAS-S&RSAT)
Figure 12: Functional block diagram of the S&RSAT-TIROS (POES) payload and S/C with SARR-1 or SARR-2 and SARP-2 or SARP-3 (image credit: COSPAS-S&RSAT)
Figure 13: Functional block diagram of the S&RSAT-MetOp and S&RSAT-NPOESS payload and S/C with SARR-1 or SARR-2 and SARP-2 or SARP-3 (image credit: COSPAS-S&RSAT)
Figure 14: Functional block diagram of the COSPAS Repeater (image credit: COSPAS-S&RSAT)
Figure 15: Functional block diagram of S&RSAT S&RR-1 repeater (S&RSAT-13 and earlier), image credit: COSPAS-S&RSAT)
Figure 16: Functional block diagram of S&RSAT S&RR-2 repeater (S&RSAT-14 and after), image credit: COSPAS-S&RSAT)
COSPAS-S&RSAT system status:
On February 1, 2009, satellite processing of signals from 121.5 / 243 MHz beacons was terminated. The reason: the 406 MHz beacons have proven superior performance capabilities. They transmit a much stronger signal and are more accurate, verifiable and traceable. 406 MHz distress signals can be accurately detected within a matter of minutes. Each 406 MHz beacon has a unique identifier encoded within its signal. 25)
• 5 LEOS&R satellites in LEO (Low Earth Orbit), from 700 to 1,000 km
• 5 GEOS&R satellites
• 45 LUTs receiving signals transmitted by LEOS&R satellites (LEOLUTs)
• 19 LUTs receiving signals transmitted by GEOS&R satellites (GEOLUTs)
• 29 Mission Control Centers for distributing distress alerts to S&R services
• More than 600,000 406 MHz beacons (Figure 17).
• Since the beginning of its operation in September 1982 through the end of 2006, COSPAS-S&RSAT provided alerts that assisted in the rescue of more than 22,400 persons in about 6,200 S&R events.
• The participating countries and organizations in COSPAS-S&RSAT are: Algeria, Argentina, Australia, Brazil, Canada, Chile, China, Cyprus, Denmark, France, Germany,Greece, Hong Kong, India, Indonesia, Italy, ITDC (International Telecommunication Development Corporation), Japan, Korea, Madagascar, Netherlands, New Zealand, Nigeria, Norway, Pakistan, Peru, Poland, Russia, Saudi Arabia, Singapore, South Africa, Spain, Sweden, Switzerland, Thailand, Tunisia, Turkey, UK, USA, Vietnam.
Figure 17: Estimated 406 MHz beacon population at the end of 2007 (image credit: COSPAS SARSAT Secretariat)
COSPAS-S&RSAT Ground Segment:
The emergency signals are detected by the space segment (such as COSPAS-S&RSAT) and relayed to LUTs which process the signals to determine beacon location. Alerts are then relayed, together with location data, via MCC (Mission Control Center) to the appropriate search and rescue point of contact or to RCC (Rescue Coordination Center).
Doppler location is the means used for signal location. The 406 MHz devices include an identification code in the alert message. Most 406 MHz devices also include a 121.5 MHz homing transmitter to support search and rescue operations. 28) 29) 30)
The 406 MHz emergency beacon signals are immediately processed and stored onboard the satellite and are transmitted to the ground from a continuous memory dump, providing complete worldwide coverage. Around the world, ground station LUTs (Local User Terminal) acquire the processed data and unique beacon identification and send these located and identified alerts to MCCs (Mission Control Centers), which forward the alerts to appropriate Rescue Coordination Centers for action. The 406 MHz beacons are designed to work well with the satellite; the system nominally provides better than 4 km accuracy, 90% ambiguity resolution on first pass, and better than 90% location probability on one pass. Note: the US S&RSAT operational ground system facilities consist of S&RSAT, SOCC at Suitland, MD as the MCC, and three LUTs. In addition to the US facilities, many other cooperating nations operate their own LUTs and MCCs.
The 121.5 MHz emergency beacons, whose use predates the satellite system, have not been specified to work with the satellite; consequently the results are variable, depending on the quality of the beacon. Nominally, location accuracy is about 20 km. All the processing is accomplished within the LUT, and because the satellite does not store these data, only beacons with mutual view of the satellite and LUT will be detected. No identification is included with the 125.5 MHz transmissions. Consequently, many nonbeacon sources are also detected as beacons, increasing the difficulty of using these alerts. Even with these problems, the large number of beacons in the field have provided an impressive performance history. COSPAS-S&RSAT reports that by the end of 2002, the COSPAS-S&RSAT system had assisted in the rescue of over 15,700 persons in distress in about 4,500 S&R events. 31)
LUTs (Local User Terminals):
There are various types of LUTs in the COSPAS-S&RSAT ground system: 32)
1) LEOLUTs (Low Earth Orbit Local User Terminals): These operate with the LEOS&R payloads on the various spacecraft in orbit (of the USA, Russia, Europe, etc.)
2) GEOLUTs (Geosynchronous Earth Orbit Local User Terminals): These operate with the GEOS&R payloads flown on various GEO missions
3) MEOLUTs (Medium Earth Orbit Local User Terminals): These are the newest type of LUTs in the definition/prototype phase as of 2008; they will be used to operate the future MEOS&R (Medium Earth Orbit Search and Rescue) payloads on the various navigation satellite constellations.
Figure 18: Locations of COSPAS-S&RSAT LEOLUTs (May 2009), image credit: COSPAS-S&RSAT
Figure 19: Legend to Figure 18 (image credit: COSPAS-S&RSAT)
Satellite Payloads (GEO Space Segment)
The GEOS&R system consists of 406 MHz repeaters carried on board various geostationary satellites, and the associated ground facilities, called GEOLUTs, which process the satellite signal. As of 2008, the GEOS&R system is composed of the following spacecraft: 2 GOES satellites of NOAA, MSG-1 (Meteosat-8) of EUMETSAT, and INSAT-3A of ISRO.
GEOS&R (Geostationary Search & Rescue)
With the launch of GOES-H (GOES-7) on Feb. 26 1987, NOAA has started to introduce the S&RSAT payload also on its geostationary satellites (406 MHz beacon). The use of geostationary satellites means that the alert signals can be received almost instantly. However, in order to automatically determine the coordinates of the emergency signal, it is necessary to wait for the system's LEO satellite (position determination can only be provided from a system that moves relative to the Earth). Note: A satellite in GEO remains fixed with respect to an observer on Earth; hence, there is no relative motion between the satellite and the distress beacon in the GEOS&R system - with the consequence of no Doppler shift to automatically locate the beacon.
The GEOS&R system concept thus works in two stages. In the first stage only the emergency signal is received via the geostationary satellite (it is planned to equip GMS and GOMS satellites for this service as well). The received alert signal is transmitted to the search and rescue service to prepare for the operation. In the second stage, the site of the signal origin is determined by the S&R payload on the nearest LEO satellite.
In addition, the capability exists for 406 MHz beacons to encode location information derived from a satellite navigation receiver, such as GPS, Glonass or the future Galileo system, and to transmit this location data along with the beacon identification code.
SAS&R (Satellite Aided Search and Rescue)
ISRO (Indian Space Research Organization), Bangalore, India, has introduced the “COSPAS-S&RSAT” prototype service in 1992 with its SAS&R (Satellite Aided Search and Rescue) demonstration payload flown on the GEO INSAT-2 series, starting with INSAT-2A (launch July 9, 1992). Alert messages of the 406 MHz beacon in the ground segment are being received and relayed by the SAS&R system.
Based on the performance demonstrations of INSAT, the SAS&R system has now been adopted (2004) as an integral part of the international COSPAS-S&RSAT system for satellite-aided search and rescue operations complementing the LEOS&R system.
The INSAT-GEOS&R Local User Terminal (GEOLUT), located at Bangalore, is integrated with INMCC (INSAT Mission Control Center). The distress alert messages originating from the Indian service area are detected at INMCC which are passed on to Indian Coast Guard and Rescue Coordination Centers (RCCs) at Mumbai, Kolkata, Delhi and Chennai. Coast Guard, Navy and Air Force carry out the search and rescue activities. The INMCC is linked to the RCCs and other international MCCs through automatic telex and Aeronautical Fixed Telecommunication Network (AFTN). The Indian LUTs and MCC provide service round the clock and maintain the data base of all 406 MHz registered beacons equipped on Indian ships and aircraft.
Satellite payloads in the MEO (Medium Earth Orbit) Space Segment
The future of COSPAS-S&RSAT will be realized through the third phase of development, based on a Medium Earth Orbit Search and Rescue (MEOS&R) system. These new MEOS&R services are being planned by the three navigation system constellations: GPS (USA), GLONASS (Russia), and Galileo (Europe). The three potential MEOS&R providers have confirmed that their systems would be fully compatible with existing COSPAS-S&RSAT beacons of 406 MHz (this includes also new beacon designs with improved capabilities). The density of all the satellites in the three constellations offer the potential of practically immediate (real-time and continuous) alert recognition. It is also planned to use the future beacons with “return link” capability. 33) 34) 35) 36)
All GNSS (Global Navigation Satellite System) satellites feature orbits of about 20,000-23,000 km altitude in various orbital planes with periods of about 12 hours (half a day). Hence, MEO orbits provide considerably longer contact times with the user on Earth's surface, as well as larger footprints than spacecraft in LEO. For the planned MEOS&R payloads on GNSS, it implies that the Doppler shift of 406 MHz beacons will be considerably smaller (than the one experienced on LEOS&R systems), resulting in a reduced location identification capability. On the other hand, the dense future GNSS network (starting from about 2010 onwards) implies, that alert signals from anywhere on Earth will be received simultaneously by several GNSS satellites, thus permitting precise location identification by triangulation algorithms.
The USA program is called the DASS (Distress Alerting Satellite System), Russia's program is called S&R/GLONASS, and the EC program is named S&R/Galileo. In July 2006, the Canadian Government offered to NASA to provide DASS (Distress Alerting Satellite System) transponders for GPS-III series satellites as a continuation of their national contribution to the COSPAS-S&RSAT Program.
The ground system of each MEOS&R system implementation will feature MEOLUTs (MEO Local User Terminals) which will be connected to the existing MCCs (Mission Control Centers) of the respective systems (DASS, S&R/GLONASS, S&R/Galileo). 37) 38) 39)
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.