GPS - Global Positioning System is a tool that is widely being used all over the world for location and navigation.





There are a number of functions and applications that depend on GPS, from food delivery to Air force.





The technology came into existence when the USA launched satellites to enhance location and navigation.





Network and control

GPS is a network of 31 satellites as on February 20, 2020. The basic constellation involves 4 satellites in 6 orbits around the earth, totaling 24 satellites. This made sure at any given point in time, at least 4 satellites are in range to a given GPS receiver anywhere in the world.





Later, each orbit was given an additional satellite while one orbit was given 2 more. All together formed a 31 satellite constellation around the earth, where each satellite is revolving the earth 2 times per day.





The satellites are updated, maintained and synchronized by various monitoring stations all over the world headed by the United States Air Force.





Working - The concept of Trilateration

Imagine you are opening the maps application in your smartphone. Your smartphone has a GPS receiver inbuilt.





As of now, consider one satellite ST 1 among the 31 is in connected, the radio waves from the satellite that travel at the speed of light, sends the time (t1) at which the wave started from the satellite and its position as information.





The moment your smartphone receives the wave, it notes down the time of reception (t2). The distance between the phone and the satellite ST 1 is calculated by multiplying the speed of radio waves which is same as the speed of light, ‘c’ and time difference (t2-t1).





Distance, d = c * (t2 - t1)





With this information the phone can be anywhere in the circumference of the circle with radius d from the satellite ST 1.

Any object in the 3 dimensional space should be marked by three coordinates. Similarly, the smartphone is marked by at least 3 different satellites at any given time to mark its exact position on earth. Usually 4 satellites are used to mark position any given time to improve accuracy.





The process continuously happens in order to determine the position of the smartphone that is either stable or moving.





Source: gps.gov





Time Difference Due To Gravity

As mentioned before in the " Is Time Travel Possible? " post, time is relative and it can stretch and squeeze with respect to gravitational force.





Time proceeds at different speeds for satellites and people on earth due to the variation in gravitational pull for a phone or a person in earth and satellites at altitudes of 20000 Km above sea level.





The time is constantly synchronized from various stations located in earth to maintain location accuracy as time plays a main role here in calculating the distance of the satellites.





References:

https://www.gps.gov/





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