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We use the GPS (global positioning system) every day for one or other reason, but have you ever wondered how it works and what technology and calculations were used in order to make it work.

  The GPS allow us to locate where we are in the world an it may one day help run autonomous vehicles, drones and also plane's without the need of there being a pilot. Given below are the calculations, mechanism and the engineering work took to make this network.

  The GPS wasn't always available for the public to use, initially these satellites were launched for the soul purpose of military use ( these satellites were first launched by the USA) , it was created to provide military personnel the pin point accurate location on their air craft, ships and even other military divisions anywhere on the planet. The first global positioning satellite, the "NAVSTAR 1" was launched on 22 February 1978, and in the next 10 years 10 GPS satellites were launched in the orbit. Currently the USA has a set of 24 satellites around the globe which ensures the presences of at-least 4 satellites covering and point on earth, which is necessary to pinpoint your exact location  through "trilateration".

  Also during the early period where GPS was made available to public, all of the satellite's were controlled by USA , which they could block the access to for rest of the world if they wanted and could have crippled  many of  companies and even some governments. To come out of these monopoly of USA some countries have their own network of GPS satellites. CHINA, RUSSIA & EU (European union) have their own set of 24 satellites, japan has 2 GPS satellites and India has 7 of it's own GPS satellites to cover it's land area.



  We know the exact position of a satellite at any time due to their predictable orbits, GPS satellites constantly broadcast radio signal which a GPS receiver in our phones and other devices are always listening for, this tell's our phone the position of the satellite and at what time it was sent, and through this data it can calculate how for away is the satellite.

DISTANCE = VELOCITY * TIME
                                                
  The radio signal always travels a the speed of light ( 299792458 m/s ), each satellite tell's that we were in a X kilometer radius, thus we now know that you are in the circumference of that sphere, getting the information from 4 different satellite's and finding were all the sphere's intersect gives our exact location on the globe.


 
   Knowing the exact time is really essential to make this system accurate, so each satellite contains an atomic clock which is the most accurate time keeping deice available to us right now, but due to their size and cost they cannot be used in phones, so the GPS satellites also constantly update phones time to ensure that it's able to calculate the distance between itself and the satellite accurately, to keep system accurate we also have to keep in mind the effects of special relativity  which is a really vast topic so i'll just be giving a short summary.

  As the receiver on ground is traveling slower as compared to the satellite which travels at about 3889 m/s ( or 14,000 km/h ), due to this difference it's calculated  that the satellite will experience time a little bit slower then the receiver on ground, also the satellite is 20,000 km above the earth surface and the relativity tells that object near heavy mass will fall behind in terms of time as compared to the object which is far away, due to this the time on satellite could differ from one the receiver by about 45 micro seconds a day, this might not sound much by if these calculation are not taken in consideration then the satellites could lose 10 km of accuracy each day.



  But after using all these calculation we can use the GPS on our smart phone with accuracy of about 5 meters, upon this system most of our businesses depend and only because of the GPS system we are able to use navigation tools, use of online maps and many of the apps and games today rely on the GPS technology.

  In the next article we will discuss how GPS was made and why is it free. so stay tuned and do subscribe.

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