GLONASS (Russian: ÃËÎÍÀÑÑ, abbreviation of ÃËÎáàëüíàÿ ÍÀâèãàöèîííàÿ Ñïóòíèêîâàÿ Ñèñòåìà; tr.: GLObal'naya NAvigatsionnaya Sputnikovaya Sistema; "GLObal NAvigation Satellite System" in English) 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 (NAVSTAR GPS), the Chinese Compass navigation system, 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 by September 2010 it is now fully restored (24 of 24 satellites are operational).
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Orbital characteristics
A fully operational GLONASS constellation consists of 24 satellites. 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 (11,868 mi), 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.
Satellites
As with GLONASS's predecessor program, Tsiklon, GLONASS satellites are developed under the leadership of the JSC Information Satellite Systems (formerly called NPO PM), with the assistance of the Institute for Space Device Engineering (ru:ÐÍÈÈ ÊÏ) and the Russian Institute of Radio navigation and Time. Serial production of the satellites is primarily accomplished by the company PC Polyot.
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 (English: hurricane), followed either by a number for operational satellites or by an acronym GVM (Russian: ãàáàðèòíî-âåñîâîé ìàêåò; English: size weight dummy) for test satellites. All Uragan satellites had a 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, they averaged an actual lifetime of 14 months.
First generation
The true first generation of Uragan (also called Glonass) 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 upgraded to 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 spacecraft that made it to orbit worked well, operating for an average of nearly 22 months.
Block IIv was the most prolific of the first 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 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 (7 ft 10 in) in diameter and 3.7 m (12 ft) high, with a solar array span of 7.2 m (24 ft) 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 Glonass-K spacecraft. These satellites are designed with a lifetime of 10 to 12 years and a reduced weight of only 750 kg. As with the previous satellites, these are 3-axis stabilized, nadir pointing with dual solar arrays. They will enter service in 2010.
The third generation satellites will broadcast CDMA navigational signals.
Due to their weight reduction, Glonass-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.
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