Definitions

GLONASS

GLONASS

GLONASS (ГЛОНАСС - ГЛОбальная НАвигационная Спутниковая Система; tr.: GLObal'naya NAvigatsionnaya Sputnikovaya Sistema; 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. It is an alternative and complementary to the United States' Global Positioning System (GPS) and the planned Galileo positioning system of the European Union (EU).

Development on the GLONASS began in 1976, with a goal of global coverage by 1991. Beginning on 12 October 1982, numerous rocket launches added satellites to the system until the constellation was completed in 1995. Following completion, the system rapidly fell into disrepair with the collapse of the Russian economy. Beginning in 2001, Russia committed to restoring the system, and in recent years has diversified, introducing the Indian government as a partner, and accelerated the program with a goal of restoring global coverage by 2009.

System description

Purpose

GLONASS was developed to provide real-time position and velocity determination, initially for use by the Soviet military for navigation and ballistic missile targeting. It was the Soviet Union's second generation satellite navigation system, improving on the Tsikada system which required one to two hours of signal processing to calculate a location with high accuracy. By contrast, once a GLONASS receiver is tracking the satellite signals, a position fix is available instantly. It is stated that at peak efficiency the system's standard positioning and timing service provide horizontal positioning accuracy within 57-70 meters, vertical positioning within 70 meters, velocity vector measuring within 15 cm/s, and time transfer within 1 µs (all within 99.7% probability).

Orbital characteristics

A fully operational GLONASS constellation consists of 24 satellites, with 21 used for transmitting signals and three for 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 arrangement 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.

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 code as their SP signal, however each transmits on a different frequency using a 25-channel frequency division multiple access (FDMA) technique spanning from 1602.5625 MHz to 1615.5 MHz, known as the L1 band. The equation to calculate the exact center frequency is 1602 MHz + n × 0.5625 MHz, where n is a satellite's frequency channel number (n=0,1,2,...24). Signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 to 27 dBW (316 to 500 watts).

The HP signals use the same FDMA technique, but transmit between 1240 MHz and 1260 MHz, known as the L2 band, with the center frequency determined by the equation 1246 MHz + n × 0.4375 MHz. Other details of the HP signal have not been disclosed.

At peak efficiency, the SP signal offers 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. The more accurate HP signal is available for authorized users, such as the Russian Military.

In the future, an additional civil reference signal in the L2 frequency band is planned to be added with the next generation of satellites to substantially increase the accuracy of navigation relaying on civil signals.

GLONASS uses a coordinate datum named "PZ 90" (Parametry Zemli 1990), 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 the GPS's coordinate datum, WGS 84, which uses the location of the North Pole in 1984.

Satellites

As with GLONASS's predecessor program, Tsikada, GLONASS satellites were developed under the leadership of the Applied Mechanics NPO (НПО ПМ), with the assistance of the Institute for Space Device Engineering (РНИИ КП) 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, separated here as generations. The name of each satellite was Uragan (hurricane), followed either by a number for operational satellites or by an acronym GVM (габаритно-весовой макет; size weight dummy) for test satellites. All Uragan satellites had a 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, referred to as Block I vehicles, were prototypes and GVM dummy vehicles. Three dummies and 18 prototypes were launched between 1982 and 1985. Designed 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 they 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, of which 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 prolific 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 lasting 68 months.

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, an Etalon geodetic reflector satellite was substituted for a GLONASS satellite.Second generation The second 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. On-board cesium clocks provide the local clock source.

A total of fourteen second generation satellites were launched through the end of 2007. As with the previous generation, the second generation spacecraft were launched in triplets using Proton-K Blok-DM-2 or Proton-K Briz-M boosters.Third generation The third generation satellites are known as Uragan-K (GLONASS-K) spacecraft. 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 the previous satellites, these are 3-axis stabilized, nadir pointing with dual solar arrays. They will enter service in 2009.

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 boosters or in six-at-once from the Baikonur Cosmodrome using Proton-K Briz-M launch vehicles.

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 Saint Petersburg, Ternopol, Eniseisk, Komsomolsk-na-Amure.

Receivers

Septentrio, Topcon, JAVAD, Magellan Navigation, Novatel, Leica-Geosystems Leica Geosystems and Trimble Inc produce GNSS receivers making use of GLONASS.

Current status

As of March 2008, the system is not fully available, however it is maintained and remains partially operational with 16 operational satellites.

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. In January 2008, with 13 operational satellites, GLONASS availability (the amount of the day when a position can be calculated) in Russia was 66.2% and average availability for the whole Earth was at 56.0%.

History

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 for many navigation purposes and for the 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.

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. By April 2002, this resulted in only eight satellites remaining in operation, which rendered the system almost useless as a global navigation aid.

Restoration and modernization

With GLONASS falling rapidly into disrepair, a special-purpose federal program named "Global Navigation System" 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. 24 satellites in orbit and continuous global coverage) by 2011.

The New York Times reported in April 2007 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. Microcom Systems reported on its website that two launches, in September and December 2007, would lift the final six second-generation satellites, and that April 2008 will see the first launch of two third-generation satellites.

The 2007 launches occurred on 26 October and 25 December. Both launches were successful, orbiting six satellites altogether. Following the launches, Russia's First Deputy Prime Minister Sergei Ivanov predicted that the launches would bring the GLONASS satellite fleet to up 18 satellites, the number necessary to provide navigation services over the entire Russian territory, and repeated that the system would have the required 24 satellites for worldwide coverage by 2010. Once all of these satellites are fully commissioned and set to healthy, GLONASS signals will be available across 90 percent of Russia and 80 percent of the globe, according to RISDE.

For 2008, six satellites are scheduled for launch. The first third generation (Glonass-K) satellites are set to be launched in 2009, according to RIA Novosti.

Cooperation with the Indian government

In January 2004 the Russian Space Agency (RSA) announced a joint venture deal with India's space agency, the Indian Space Research Organization, where-in the two government agencies 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 Centre in Andhra Pradesh state, using the Indian Geosynchronous Satellite Launch Vehicle (GSLV) rockets. As of April 2007, India has yet to launch any satellites as part of this project.

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 the new satellites from India, in return for access to the HP signal.

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 a signal pattern that is 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 simply-designed receiver to use both satellite systems simultaneously.

GPSWorld reported that the group had met twice prior to then and that the working group would likely make an announcement when they meet again in April 2007, during the International Satellite Forum 2007 in Moscow. However no announcement was made.

Discussions with Cuba and Venezuela

Russia could include Cuba and Venezuela in a satellite navigation system originally designed for missile targeting by the Soviet military, the head of Russia's space agency said."We discussed the theme of joint use of the Glonass satellite navigation system," Roskosmos chief Anatoly Perminov was quoted by RIA Novosti news agency as saying, referring to talks with officials in Venezuela.

Civilian signals made officially available

On May 18, 2007, Russian president Vladimir Putin signed a decree officially providing open access to the civilian navigation signals of the GLONASS system, to Russian and foreign consumers, free of charge and without limitations. The Russian president also directed the Federal Space Agency to coordinating work to maintain, develop and enable the system for civilian and commercial needs.

See also

Notes and references

Bibliography

External links

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