GLONASS

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GLONASS

GLONASS (Russian ГЛОНАСС; ГЛОбальная НАвигационная Спутниковая Система; Global'naya Navigatsionnaya Sputnikovaya Sistema. GLObal NAvigation Satellite System) is a radio satellite navigation system, the Russian counterpart to the United States' GPS system and the European Union's embryonic Galileo positioning system. It is operated for the Russian government by the Russian Space Forces.

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 signal (precision or P(Y)) was available for Russian military use.

Like GPS, the complete nominal GLONASS constellation consists of 24 satellites, 21 operating and three on-orbit 'spares' placed in three orbital planes. Each plane contains eight satellites identified by "slot" number, which defines the corresponding orbital plane and the location within the plane: 1-8, 9-16, 17-24. The three orbital planes are separated by 120°, and the satellites equally spaced within the same orbital plane, 45° apart. The GLONASS orbits are roughly circular, with an inclination of about 64.8° and a semi-major axis of 25,440 km. The planes themselves have 15° argument of latitude displacement.

GLONASS constellation orbits the Earth at an altitude of 19,100 km (slightly lower than that of the GPS satellites). Each satellite completes an orbit in approximately 11 hours, 15 minutes. The spacing of the satellites in orbits is arranged so that a minimum of 5 satellites are in view at any given time.

GLONASS satellite transmits two types of signal: standard precision (SP) and high precision (HP). SP signal L1 have a frequency division multiple access in L-band: L1= 1602 MHz + n0.5625 MHz, where n is frequency channel number (n=0,1,2...).

All satellites have been launched from Baikonur Cosmodrome. The first three test satellites were placed in orbit in October 1982 with the first operational satellites entering service in December 1983. The system was intended to be operational in 1991, it was announced to be operational on September 24, 1993 but the constellation was not completed until December 1995.

A characteristic of the GLONASS constellation is that the satellite orbits repeat after 8 days. As each orbit plane contains 8 satellites, there is a non-identical repeat (i.e., another satellite will occupy the same place in the sky) after one sidereal day. This differs from the GPS identical repeat period of one sidereal day.

Due to the economic situation in Russia there were only eight satellites in operation in April 2002 rendering it almost useless as a global navigation aid. In June 2006 there were 12 satellites in operation.

The oldest GLONASS satellite still in operation was launched in October 2000, well above the designed lifetime of 3 years.

The GLONASS-M, an advanced GLONASS satellite with an operational lifetime of 7 years, has also been developed. A 2-satellite block of this new version was launched in December 2005. A further improved GLONASS-K satellite, with a reduced weight and an increased operational lifetime of 10-12 years, is due to enter service in 2008. Reducing its weight by 50% will allow to significantly lower launch costs by using the Soyuz-U launch vehicles. All GLONASS satellites to date have been launched by the more powerful Proton launch vehicles.

Following a joint venture deal with the Indian Government, which will launch two GLONASS-M satellites on its GSLV rockets, it is proposed to have the system fully operational again by 2008 with 18 satellites, providing full coverage of Russia territory, and by 2010 with all 24 satellites. During the December 2005 summit between Indian Prime Minister Manmohan Singh and Russian President Vladimir Putin, it was agreed that India would share the development costs of the GLONASS-K series and launch them from India.

For some years, Russia has kept the GLONASS satellite orbits optimized for their operation in Chechnya, giving them significant coverage there at the price of increasingly degrading coverage in the rest of the world.

Current GLONASS availability in Russia, Northern Europe and Canada is 94%. Meaning that at least 4 satelites are visible 94% of time, which is not bad considering that system operates only 12 of 21 required satelites.

Sources from the Russian Federal Space Agency indicate the two remaining GLONASS-M satellites launched in December 2005 may be declared operational in July or August 2006.

Three more are scheduled for launch in December 2006. Six are scheduled for launch in 2007. Five are scheduled for launch in 2008.