128. G. P. S.


Global positioning system or G.P.S is the only functional Global Navigator Satellite System or G.N.S.S. A constellation of 24 or more medium Earth Orbit Satellites (which can transmit precise microwave signals) is utilized to enable the GPS Receiver determine its location, speed, direction and time.

Officially named as NAVSTAR GPS, this was developed by the US Department of Defense. It is managed and maintained by the US Air Force 50th Space Wing, at an enormous cost of 750million US Dollars per annum!

Following a shoot down of a Korean Air Line Flight 007, in 1983, The President of USA, Ronald Reagan issued a directive, making GPS system available for free, for the civilian use, for the common good.

Since then, the GPS has become the most widely used aid in navigation, in the making of maps, land surveying and many other scientific uses. GPS provides a precise time reference used in many scientific applications, in the study of earth quakes, and in the synchronization of telecommunication net works.

A point on a straight line can be defined by just one dimension while we need two for locating a point on a flat surface. For locating a point in space we need three dimensions, X, Y and Z. GPS requires accurate time also as the fourth factor.

Hence a GPS receiver calculates it position using the signals received from 4 or more GPS satellites. These four (or more) values are made available in a user friendly form such as latitude, longitude or location on a map.

Each GPS has an atomic clock. It transmits message containing the time and the parameters to calculate the location of the satellites. These signals travel at the speed of light in the outer space and at slightly reduced speed in atmosphere.

The GPS receiver uses the arrival time of these signals to compute the distance of each of each satellite. Using geometry and trigonometry these values are used to determine the position of the receiver on a map.

GPS receiver can relay position data to a P.C. It can also be integrated into cars, mobile phones and watches. Although mobile handsets with integrated GPS were launched in 1990s, they became available in large number for the consumers only in 2006.

Solar flares can affect the GPS reception over half the earth, facing the Sun. Geomagnetic storms, found near the poles of earth’s magnetic field, can affect the reception of GPS.

Thanks to the GPS and its accurately positioning, you can not get lost even if you wanted to!

Visalakshi Ramani

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