How do you find your location when you are lost while traveling or when you are to a new place? Do you check the stars, the moon, and the sun? No…We check our mobiles and find a way out. How does our mobile know where we are on the earth? How could it be so accurate and lead us to our destination? Because they are integrated with GPS systems. Let’s see what is GPS and how it works.
Global Positioning System is a satellite-based radio navigation system with at least 24 satellites orbiting the earth at 14000 km/hr at an altitude of 20000 km above the surface of the earth that use trilateration principle and Einstein’s theory of relativity to track your location
GPS, originally NAVSTAR GPS was owned by US space force which has a total of 33 satellites that needs at least 24 satellites to cover the earth’s surface among which need at least 4 satellites to track your location. These satellites are equipped with atomic clocks that give the exact time up to billionth of a microsecond. Unlike satellites, our mobiles are equipped with crystal clocks that do not give accurate time compared to atomic clocks. These satellites continuously send the radio signals which are received by our devices. Our mobile receiver records the difference between the time of sent and the time of receiving and multiplies it with the velocity of light to get the distance from each satellite.
Now, the satellites use the trilateration principle by drawing spheres around them with the radius the same as the distance between it and our location. Upon intersection of the spheres, they get a point which is our exact location. But, there is a challenge in this as there comes an offset time due to inaccuracy of time in crystal and atomic clocks because the atomic clocks experience one-quarter of earth’s gravity at such orbits and every day they get 45 microseconds faster than the natural time which gives an offset of 38ms and an error of 10km in accuracy every day. That’s the reason to have at least 4 satellites to remove the offset value and get an accurate location. Thanks to Einstein’s Theory of relativity as it wouldn’t have been possible without his research.
Initially GPS is only used by US forces but later they are made available to all the civilians to avail the benefits of GPS. Other countries also developed their own navigation systems like GLONASS, GALILEO, BeiDou, and IRNSS-by India.