GPS - Global Positioning System-
Now a days when technology is going higher and higher every day, we all are using many technologies which are now integral part of our day to day life. So this post is an introduction to such a technology which is very useful in our day to day life.In this modern era people can go almost everywhere on the earth and its surroundings with the help of GPS. When a person leave his home for office or airport or market or weekend parties, he can easily track his destination using his mobile device or another device which is equipped with GPS receiver chip.GPS has made our daily life very easy in many ways. So let's go through this interesting technology in this post.
History:
During the world war 2nd US has developed a system which is known as the First GPS System named as LORAN (Long Range Navigation System). This system used to work on low range frequencies and it was used to track up to 1,500 miles (2,400 km) with accuracy of tens of miles
.This system was mostly used by the US Military and Large Commercial Users.This system was used to send one signal in every 60 minutes to the receiver.The drawback of this system was its cost and size so it was succeeded by LORAN -C (LOARN -B was not successful). Below is the picture of LORAN System.
Modern GPS System:
The Modern GPS System was launched by US Military in 1970s. Initially its usage was limited for military purposes,but in 1980s US government allows its usage for Civilian purposes.
This modern GPS system is a global navigation satellite system (GNSS) made up of a network of a minimum 24 satellites.This system also consist 6 more satellites for backup purposes.So GNSS contains total of 30 satellites.These 24 satellites are situated in 6 orbits i.e. 4 satellites per orbit.Also these satellites are not Geo synchronous.The satellite orbits are arranged on six planes. The inclination of the
angles of the planes towards the equator is 55° and these planes are
rotated by 60° against each other. This gives complete coverage of the
globe. This means that the orbits range from 55° north to 55° degrees
south.
The GPS satellites orbit the earth in a Medium Earth Orbit (MEO). The mean distance from the center of the Earth is 26560 km (the mean radius of the Earth is 6360 km) and this means that the orbit altitude of the satellites is around 20 200 km.
The GPS satellites travel with a speed of about 3.9 km /s relative to the Earth as a whole, as opposed to relative to a fixed point on its surface. They have an orbit time of 12 hours (sidereal time) which equates to about 11 hours 58 minutes "Earth" time. This means that each satellite reaches a given position four minutes earlier each day (as it orbits the earth twice a day).
Within each orbit, there are at least four satellites. The system was designed for four satellites in each slot, but additional satellites are in orbit to act as "hot" spares in case of failure. In this way, when a satellite fails, and other one can be quickly put into its position to fill the gap.
This arrangement provides the earth user with a view of between five and eight satellites at any time from any point on the Earth. When four satellites are visible, sufficient information is available to be able to calculate the position on Earth.
