GLONASS

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GLONASS (Russian: ГЛОНАСС - ГЛОбальная НАвигационная Спутниковая Система; tr.: Global'naya Navigatsionnaya Sputnikovaya Sistema; English: GLObal NAvigation Satellite System) is a radio-based satellite navigation system, developed by the former Soviet Union and now operated for the Russian government by the Russian Space Forces. Its United States' counterpart is the Global Positioning System (GPS).

Development on the GLONASS began in 1976, with a goal of global coverage by 1991. Numerous satellite launches progressed the system forward until the constellation was completed 1995. Following completion, the system rapidly fell into disrepair with the collapse of the Russian economy. Beginning in 2001, Russia committed to repairing the system by 2011, and in recent years has diversified to include other governments as partners, including India, and accelerated the program with a goal of 2009.

Contents 1 System description 1.1 Purpose 1.2 Orbital characteristics 1.3 Signals 1.4 Satellites 1.5 Ground control 2 Current status 3 History 3.1 Development by the Soviet Union 3.2 Completion, then decay, under Russia 4 Restoration and modernization 4.1 Cooperation with the Indian government 4.2 Discussions with United States government 5 See also 6 References 7 External links

[edit] System description

[edit] Purpose

GLONASS was developed to provide real-time position and velocity determination, initially for use by the Soviet military in navigating and ballistic missile targeting. It was the third navigation system developed by the Soviets, replacing their Tsikada satellite positioning system which required one to two hours of signal processing to deterine its location. In contrast, once a GLONASS receiver has locked onto the satellite signals, its claimed positional accuracies are 100 m on the surface of the Earth, 150 m in altitude, and 15 cm/s in velocity (all with 95% certainty).

[edit] Orbital characteristics

A fully functional GLONASS constellation consists of 24 satellites, with 21 operating and three on-orbit spares, deployed in three orbital planes. The three orbital planes' ascending nodes are separated by 120° with each plane containing eight equally spaced satellites. The orbits are roughly circular, with an inclination of about 64.8°, and orbit the Earth at an altitude of 19,100 km, which yields an orbital period of approximately 11 hours, 15 minutes. The planes themselves have a latitude displacement of 15°, which results in the satellites crossing the equator one at a time, instead of three at once. The overall arrange is such that, if the constellation is fully populated, a minimum of five satellites are in view from any given point at any given time.

Each satellite is identified by a "slot" number, which defines the corresponding orbital plane and the location within the plane; numbers 1-8 are in plane one, 9-16 are in plane two, and 17-24 are in plane three.

A characteristic of the GLONASS constellation is that any given satellite only passes over the exact same spot on the Earth every eighth sidereal day. However, as each orbit plane contains eight satellites, a satellite will pass the same place every sidereal day. For comparison, each GPS satellite passes over the same spot once every sidereal day.

[edit] Signals

GLONASS satellites transmit two types of signal; a standard precision (SP) signal and an obfuscated high precision (HP) signal. All satellites transmit the same SP signal, however each transmits on a different frequency using a 25-channel frequency division multiple access (FDMA) technique spannign from 1602.5625 MHz to 1615.5 MHz. The HP signals use the same FDMA technique, but transmit in the L2 band between 1240 MHz and 1260 MHz. The equation to calculate the exact center frequency on L1 is 1602 MHz + 0.5625n MHz, where n is a satellite's frequency channel number (n=0,1,2...). Signals are transmited in a 38° cone, as right-hand circularly polarized, at an EIRP between 25 to 27 dBW (316 to 500 watts).

At peak efficiency the system offered a standard (coarse-acquisition or C/A) positioning and timing service giving horizontal positioning accuracy within 57-70 meters, vertical positioning within 70 meters, velocity vector measuring within 15 cm/s, and timing within 1 µs, all based on measurements from four satellite signals simultaneously. A more accurate HP signal is available for authorized users, such as the Russian Military. And in November 2006, Defense Minister Sergei Ivanov announced that the HP signal will become available for civilian use in early 2007.^{[citation needed]}

GLONASS uses a coordinate system named "PZ-90", in which the precise location of the North Pole is given as an average of its position from 1900 to 1905. This is in contrast to GPS which uses a coordinate system named "WGS-84" which uses the location of the North Pole at its location in 1984.

An additional civil reference signal on L2 frequency is to be added with the next generation of satellites to substantially increase the accuracy of navigation relaying on civil signals.

[edit] Satellites

As with GLONASS's predecessor program, Tsikada, GLONASS satellites were developed under the leadership of the Applied Mechanics NPO, with the assistance of the Institute for Space Device Engineering and the Russian Institute of Radio navigation and Time. Also following the Tsikada precedent, serial production for GLONASS satellites was accomplished primarily by the Polet PO.

Over the three decades of development, the satellites themselves have gone through numerous revisions, seperated here as generations. The name of each satellite was Uragan (English: hurricane),^[1] followed either by a number for operational satellites or by an acronym GVM (Russian: габаритно-весовой макет; English: size weight dummy) for test satellites. All Uragan satellites had GRAU designation 11F654, and each of them also had the usual ordinal "Cosmos-NNNN" designation.

Prototypes (Generation zero)

The first GLONASS vehicles to be launched, refered to as Block I vehicles, were prototypes and GVM dummy vehicles. Three dummys and 18 prototypes were launched between 1982 and 1985. Design to last only one year, many averaged an actual lifetime of 14 months.

First generation

The true first generation of Uragan satellites were all 3-axis stabilized vehicles, generally weighing 1,250-kg and were equipped with a modest propulsion system to permit relocation within the constellation. Over time there were divided into Block IIa, IIb, and IIv vehicles, with each block containing evolutionary improvements

Six Block IIa satellites were launched in 1985-1986 with improved time and frequency standards over the prototypes, and increased frequency stability. These spacecraft also demonstrated a 16-month average operational lifetime. Block IIb spacecraft with a 2-year design lifetimes appeared in 1987, and a total of 12 were launched, but half were lost in launch vehicle accidents. The six vehicles which made it to orbit worked well, each operating for an average of nearly 22 months.

Block IIv was the most prodigious of the second generation. Used exclusively from 1988 to 2000, and continued to be included in launches through 2005, a total of 25 satellites were launched. The design life was three years, however numerous spacecraft exceeded this, with one late model lasted 68 months.^[2]

Block II satellites were typically launched three at a time from the Baikonur Cosmodrome using Proton-K Blok-DM-2 or Proton-K Briz-M boosters. The only exception was when, on two launches, a Etalon geodetic reflector satellites was substitued for a GLONASS satellite.

Second generation

The second, and current, generation of satellites, known as Uragan-M (also called GLONASS-M), were developed beginning in 1990 and first launched in 2001.

These satellites possess a substantially increased lifetime of seven years and weigh slightly more at 1,480 kg. They are approximately 2.4 m in diameter and 3.7 m high, with a solar array span of 7.2 m for an electrical power generation capability of 1600 Watts at launch. The aft payload structure houses 12 primary antennas for L-band transmissions. Laser corner-cube reflectors are also carried to aid in precise orbit determination and geodetic research. The on-board cesium clocks provide absolute time accuracy of 1000 nanoseconds.

Eight satellites had been launched as of April 2007, with 14 planned in total. As with the previous generation, the second generation spacecraft can be launched in triplets using Proton-K Blok-DM-2 or Proton-K Briz-M boosters. At least one single launch using an Indian GSLV is also planned.

Third generation

The latest designed generation of Uragan-K (GLONASS-K) spacecraft are the third generation of satellites. These satellites are designed with a lifetime of 10 to 12 years, a reduced weight of only 750 kg, and offer an additional L-Band navigational signal. As with previous satellites, these are 3-axis stabilized, nadir pointing with dual solar arrays. They will enter service following the Uragan-M inventory depletion, expected in 2008.

Due to their weight reduction, Uragan-K spacecraft can be launched in pairs from the Plesetsk Cosmodrome launch site using the substantially lower cost Soyuz-2 1a boosters or in six-at-once from the Baikonur Cosmodrome using Proton-K Briz-M launch vehicles.

[edit] Ground control

The ground control segment of GLONASS is entirely located within former Soviet Union territory. The Ground Control Center and Time Standards is located in Moscow and the telemetry and tracking stations are in St. Petersburg, Ternopol, Eniseisk, Komsomolsk-na-Amure.^[3]

[edit] Current status

As of January 2007, the system is not fully available, however it is maintained and remains partially operational. There were 16 satellites in the GLONASS system, of which 11 were in operation and five "temporarily switched off".^[4] In recent years, Russia has kept the satellite orbits optimized for navigating in Chechnya, increasing signal coverage there at the cost of degrading coverage in the rest of the world. Current GLONASS availability in Russia was 50.8% and global availability was 39.8%.^[5] Meaning that at least 4 satellites are visible 39.8% of time everywhere on the Earth.

[edit] History

[edit] Development by the Soviet Union

In the late 1960s and early 1970s, the Soviet Union identified the need and benefits of developing a new satellite-based radio navigation system. Their existing Tsikada satellite navigation system, while highly accurate for stationary or slow-moving ships, required several hours of observation by the receiving station to fix a position, making it unusable many navigation purposes and in guidance of the new generation of ballistic missiles.

From 1968 to 1969, the research institutes of the Ministry of Defence, Academy of Sciences, and Soviet Navy cooperated to develop a single system for navigation of their air, land, sea, and space forces. This collaboration resulted in a 1970 document that established the requirements for such a system. Six years later, in December, 1976, a plan for developing GLONASS was accepted in a Decision of the Central Committee of the CPSU and of the Council of Ministers of the USSR entitled "On Deployment of the Unified Space Navigation System GLONASS."

From 1982 through April 1991, the Soviet Union successfully launched a total of 43 GLONASS-related satellites plus five test satellites. In 1991, twelve functional GLONASS satellites in two planes were available; enough to allow limited usage of the system.

[edit] Completion, then decay, under Russia

Following the disintegration of the Soviet Union in 1991, continued development of GLONASS was undertaken by the Russian Federation. It was declared operational on September 24, 1993 by then-president Boris Yeltsin, however the constellation was not completed until December 1995.

In the six years following completion, Russia was unable to maintain the system. This resulted in only eight satellites remaining operation in April 2002, which rendered the system almost useless as a global navigation aid.

[edit] Restoration and modernization

With GLONASS falling rapidly into disrepair, a Federal Target program named "Global Navigation System"^[6] was undertaken by the Russian government on August 20, 2001. According to it, the GLONASS system was to be restored to fully deployed status (i.e. with 24 satellites in orbit and the global continuous coverage) by 2011.

As of April 2007, there were 12 operational satellites in the GLONASS system and one new satellite in its commissioning phase.^[4] The New York Times reported that Russia had committed to accelerated launches, with eight satellites scheduled to be orbited in 2007 and a goal of reaching global coverage in 2009.^[7]

[edit] Cooperation with the Indian government

In January 2004 the Russian Space Agency announced a joint venture deal with India's spacy agency, the Indian Space Research Organization, where-in the two government agencyies would collaborate to restore the system to constant coverage of Russian and Indian territory by 2008 with 18 satellites, and be fully operational with all 24 satellites by 2010.

Details announced in mid 2005 reported that Russia would build the satellites and that between 2006 and 2008 two satellites would be launched from India’s Satish Dhawan Space Center at Sriharikota in Andhra Pradesh state, using the Indian Geosynchronous Satellite Launch Vehicle (GSLV) rockets.

During a December 2005 summit between Indian Prime Minister Manmohan Singh and Russian President Vladimir Putin, it was agreed that India would share some of the development costs of the GLONASS-K series and launch two of them from India, in return for military-grade signal access.

[edit] Discussions with United States government

Following the December 2006 meeting in Moscow of the GPS-GLONASS Interoperability and Compatibility Working Group (WG-1), an announcement appeared on both US and Russian government websites stating both sides had made significant progress in understanding the benefit to the user community of changing GLONASS to signal pattern in common with GPS and Galileo. A change in the GLONASS system from its current FDMA technique to the GPS and Galileo's CDMA format would enable a simple-designed receiver to use both satellite systems simultaneously.

GPSWorld reports the group had meet twice prior and that the working group will likely make an announcement when they meet again in April 2007, during the International Satellite Forum 2007 in Moscow.

[edit] See also

• Transit
• Global Navigation Satellite System - the generic term for a global satellite positioning system
• Multilateration - the mathematical technique used for positioning

[edit] References

[edit] External links

• Russian Spacy Agency's English language GLONASS site

Satellite navigation systems
Historical	Operational	Developmental
Transit	GPS | / GLONASS| Beidou	Galileo | IRNSS
Related topics
EGNOS | GPS·C | LAAS | MSAS | WAAS