GPS is an acronym for Global Positioning System. It is a technology that can help a person reach any destination in the world, accurately. It is a fully functional satellite navigation system, that was developed by the United States Department of Defense, and is currently under the management of the United States Air Force 50th Space Wing. Its actual name is NAVSTAR GPS.
Global Positioning Systems feature three major components, namely, the satellite system, the ground control station, and the hand-held receivers. The satellite system includes 24 satellites, divided into six groups of four satellites each. This system of satellites, orbiting at approximately 20,000 km above the earth's surface in twelve orbits, encompasses the six orbital planes. The ground station consists of a receiver, an antenna, and the communication tools required to transmit the received data to the data center. The data center has an automated system that manages the flow of data. Hand-held user receivers are passive devices that only receive the data from these data centers. A GPS can provide 24-hour efficient and error-free service to numerous users simultaneously. The signal may sometimes get obstructed in dense forest areas or by tall sky scrapers.
The Working of GPS Devices
Satellites continuously send coded radio signals to ground stations, that are received by unidirectional antennas. These signals are sent to ground station receivers and tracking receivers for processing. The radio signals are sent at two different L-band frequencies (range of frequencies between 390 and 1550 MHz). The receiver then isolates the signals to various channels, for a particular satellite, at a particular time. These coded radio waves contain information regarding the time the message was sent and the status of the satellite in the orbit. The receiver decodes the information, and splits them into individual frequencies. It also measures the transmission time of each message and computes the distance to each satellite. Geometric trilateration is used to combine these distances with the location of the satellites to determine the receiver's location and elevation. From the calculated information, the receiver's speed, direction, etc., can be displayed on a live tracker device. Generally, data from three satellites is said to be enough for calculations, if the receiver's elevation is already known (in case of an airplane or a ship); else, data from four satellites is mandatory. The position of the receiver is at the intersection point of the three imaginary spheres that are drawn considering each satellite as the center.
Initially, the accuracy of GPS signals received by the military and civilians were different. In 1983, due to insufficient navigational tools, a Korean Flight 007 was shot down when it flew astray into the USSR's prohibited airspace. After this tragedy, President Ronald Reagan, the then President of US, declared that GPS signals would be available to the world at zero charge. From that day on, the military as well as civilians have received excellent quality GPS service, despite the location or weather. Shortly after the set-up of GPS, the Soviet Union also launched their own global navigation satellite system called GLONASS (GLObal NAvigation Satellite System) which is now controlled by the Russian Space Forces. By 2012/2013, the European navigation system, Galileo is also expected to be available.
Global positioning systems can be termed as one of the greatest inventions of the 20th century. These devices are now within the reach of common people. Currently, it is being extensively used in the constructive task of 'lighting the path' for the lost souls and objects.