Friday, April 20, 2007

The 4 World Global Navigation Satellite Systems

By the end of this decade, the United States’ GPS constellation will not be the only Global Navigation Satellite System (GNSS) in operation. At least two other GNSS systems are in different phases of development, and when coupled with the continued miniaturization of GPS chipsets, they will help drive an entirely new generation of location-aware CE devices.

United States NAVSTAR Global Positioning System (GPS)

GPS is funded by and controlled by the U. S. Department of Defense (DOD). While there are many thousands of civil users of GPS world-wide, the system was designed for and is operated by the U. S. military.
GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time.
Four GPS satellite signals are used to compute positions in three dimensions and the time offset in the receiver clock.


The Global Navigation Satellite System (GLONASS) is based on a constellation of active satellites which continuously transmit coded signals in two frequency bands, which can be received by users anywhere on the Earth's surface to identify their position and velocity in real time based on ranging measurements. The system is a counterpart to the United States Global Positioning System (GPS) and both systems share the same principles in the data transmission and positioning methods. GLONASS is managed for the Russian Federation Government by the Russian Space Forces and the system is operated by the Coordination Scientific Information Center (KNITs) of the Ministry of Defense of the Russian Federation.

European Union's Galileo positioning system

The upcoming European Galileo Positioning System is a publicly funded European satellite navigation system, which is to exist in parallel to America's Global Positioning System (GPS). It is meant to become operational in 2010.

When complete, the Galileo constellation of satellites will consist of 30 spacecraft, orbiting at more than 23,000km of altitude. It promises greater precision than the existing GPS system, as well as better coverage at higher altitudes. Along with its perceived value as an alternative to GPS - which is owned and operated by the American Department of Defense - the Galileo system is intended to have broad commercial applications, and to create more than 1000 jobs in Europe. The free Open Service is meant to offer accuracy of approximately 4m (compared to about 5m for GPS), while the encrypted Commercial Service will offer accuracy down to 1m for a fee. The system will also include an encrypted Public Regulated Service and Safety of Life Service, which are primarily meant to be used by security authorities and emergency services, as well as air traffic control systems.

Many, including The Economist newspaper, have questioned the value of spending approximately three billion Euros on a system that will essentially replicate the functioning of a system that already exists, and it already being upgraded at no cost to European taxpayers.

Beidou Navigation System

Beidou ('Big Dipper') was the satellite component of an independent Chinese satellite navigation and positioning system. This was to be achieved by launching a satellite constellation in stages during 2000-2010 while developing the relevant application systems. The end result would be a Chinese indigenous satellite navigation and positioning industry. Experimental launch of the first two indigenous Beidou navigation satellites was in 2000. Beidou began in 1983 with a proposal by Chen Fangyun to develop a Twinsat regional navigation system using two geostationary satellites. The concept was proven in 1989 in a test using two in-orbit DFH-2/2A communcations satellites. This test showed that the precision of the Twinsat system would be comparable to the American Global Positioning System. In 1993, the Beidou program was officially started. Beidou used the DFH-3 bus and had similar basic performance. The final Beidou constellation was to consist of four geosynchronous satellites, two operational and two backups.

Read more: Building a Multinational Global Satellite System: An Initial Look



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