GLONASS



GLONASS (ГЛОННСС, abbreviation of ГЛОбальнаѝ ННвигационнаѝ Спутниковаѝ Сиѝтема; 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 (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 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.

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 Tsiklon 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 19100 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 15-channel frequency division multiple access (FDMA) technique spanning either side from 1602.0 MHz, known as the L1 band. The center frequency is 1602 MHz + n × 0.5625 MHz, where n is a satellite's frequency channel number (n=−7,−6,−5,...,7). Signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 to 27 dBW (316 to 500 watts). Note that the 24 satellite constellation is accommodated with only 15 channels by using identical frequency channels to support antipodal (opposite side of planet in orbit) satellite pairs, as these satellites will never be in view of an earth based user at the same time.

The HP signal is broadcast in phase quadrature with the SP signal, effectively sharing the same carrier wave as the SP signal, but with a ten times higher bandwidth than the SP signal.

The L2 signals use the same FDMA as the L1 band signals, but transmit straddling 1246 MHz with the center frequency determined by the equation 1246 MHz + n×0.4375 MHz, where n spans the same range as for L1. Other details of the HP signal have not been disclosed.



At peak efficiency, the SP signal offers horizontal positioning accuracy within 5–10 meters, vertical positioning within 15 meters, a velocity vector measuring within 10 cm/s, and timing within 200 ns, all based on measurements from four satellite signals simultaneously (this reference is outdated, as it's based on URAGAN satellites while the current constellation is 18/19 URAGAN-M satellites. The more accurate HP signal is available for authorized users, such as the Russian Military, yet unlike the US P(Y) code which is modulated by an encrypting W code, the GLONASS P codes are broadcast in the clear using only 'security through obscurity'. Use of this signal bears risk however as the modulation (and therefore the tracking strategy) of the data bits on the L2P code has recently changed from unmodulated to 400bps burst at random intervals.  The GLONASS L1P code is modulated at 50bps without a manchester meander code, and while it carries the same orbital elements as the CA code, it allocates more bits to critical Luni-Solar acceleration parameters and clock correction terms.

Currently, an additional civil reference signal is broadcast in the L2 band with an identical SP code to the L1 band signal. This is available from all satellites in the current constellation, except satellite number 795 which is the last of the inferior original GLONASS design, and one partially inoperable GLONASS-M satellite which is broadcasting only in the L1 band. (see glonass-ianc.rsa.ru for daily updates on constellation status.)

GLONASS uses a coordinate datum named "PZ-90" (Earth Parameters 1990 - 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. As of September 17, 2007 the PZ-90 datum has been updated to differ from WGS 84 by less than 40 cm in any given direction.

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:РНИИ КП) 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, followed either by a number for operational satellites or by an acronym GVM (габаритно-веѝовой макет; ) 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, they 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 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 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 and Trimble Inc produce GNSS receivers making use of GLONASS. NPO Progress describes a receiver called "GALS-A1" which combines GPS and GLONASS reception.

Current status
, the GLONASS system consists of 20 satellites, of which 19 are operational, and one is undergoing maintenance. The system requires 18 satellites for continuous navigation services covering the entire territory of the Russian Federation, and 24 satellites to provide services worldwide.

The GLONASS system now covers 100% of Russian territory.

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 Tsiklon 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 delays
Following the disintegration of the Soviet Union in 1991, continued development of GLONASS was undertaken by the Russian Federation. It was promised to be 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.

Six new GLONASS satellites were added to the network in 2008. The first third generation (GLONASS-K) satellites are set to be launched in 2009, according to RIA Novosti. The head of Russian Space Agency, Anatoly Perminov said in September, 2008, that the number of satellites in the GLONASS network would be increased to 30 by 2011.

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, wherein 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.

Additionally, Mr. Putin acquired a GLONASS-enabled collar for his black Labrador, Koni, as an afterthought of using GLONASS to monitor cattle and animals in the wild.