What is GPS?

Credit: Sohail Panjwani for CurrentKids

Late for school? Missed your bus? What do most of us do now? Hop into our cars, open up a map app and figure out the quickest way to get to school so that we are not hauled into the Principal’s office! But how does our map know the fastest route? Or where we are? It’s all thanks to GPS – the Global Positioning System in the sky.

As a race, we have often used the sky to chart our journeys. In years gone by, travellers and mariners used stars, constellations and the position of the sun to map their routes, predict the weather and harvest times. Our GPS is a massive upgrade of this system.

The GPS was first created and used by the US military to find lost soldiers, launch missiles remotely from small handheld devices and other such essential uses. The system became available to the public in the year 2000. The system comprises of over 30 satellites that are constantly zipping around the globe, 16000 miles up in the air. Each one circles the Earth twice in a day in exact orbits.

What these satellites do is ‘talk’ to your mobile phone or other GPS devices to pinpoint where you are. At any given point, at least four satellites are in direct ‘line of sight’ of your device. That means that they can send you a high-frequency radio signal at the speed of light, 180,000 miles per second – whoa! Based on these signals, and using complex mathematical calculations, and how long it takes the satellite signal to reach you, the phone figures out where you are. Therefore each satellite has an atomic clock on it which is accurate to the billionth of a second. If these were out of sync, GPS would not be entirely accurate. Each satellite marks out a small circular area where it thinks you could be located. These are like Venn diagrams in the air. The spot where all four intersect is the place where you are at.  This whole process is called trilateration.

Sometimes, the maps do get it wrong. Have you ever been shown a building on a screen which turns out to be a playground? These map missteps happen when atmospheric disturbances or tall buildings or other obstructions interfere with the GPS signal. However, as GPS usage increases, countries are updating old satellites with new ones. These super satellites will have better signal strength, have clocks which are on point to a fraction of a billionth of a second and will increase pinpointing accuracy from the current 20 ft to less than three feet. There is genuinely going to be no place to hide!

Written by: Pereena Lamba. Pereena is a freelance writer, editor and creative consultant. She is also co-author of Totally Mumbai.

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