Sat Nav Devices - Navigate the Planet

By: Raina Kelsey

Global Navigation Satellite System (GNSS) is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine the location including longitude, latitude and altitude to within a few meters using time signals transmitted by satellite radios. The precise time for the reference of scientific experiment is calculated by the receivers on the ground with a fixed position.

The NAVSTAR Global Positioning System by the U.S. is the only fully operational GNSS. Russia with GLONASS is all set to enter into the field of GNSS. The European Union's Galileo positioning system belongs to the next generation GNSS in the initial deployment phase, which is expected to be operational in 2010. The Beidou navigation system by China is expected to get operational in near future. IRNSS by India is in developmental phase and is expected to be operational by around 2012.

The history of satellite navigation devices traces back to the cold war area. Transit, the first satellite navigation system was deployed by the US defense forces in the 1960s. Transit's operation was mainly based on the Doppler Effect. By monitoring the shift of the frequency over a short time interval, it is possible for the receiver to determine the location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position.

The latest satellite navigation devices are more direct. They are capable of broadcasting a signal that carries the position of the satellite and the precise time of the signal transmitted. The position of the satellite is transmitted in a data message that is superimposed on a code that serves as a timing reference.

The main purpose of satellite navigation devices are military applications. Satellite navigation allows for hitherto impossible precision in the delivery of weapons to targets, greatly increasing their lethality whilst reducing inadvertent casualties from misdirected weapons.

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