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How does a GPS work?

I’ve Always Wanted To Know:
How does a GPS work?

GPS or Global Positioning System, is a group of 24 satellites that are in high earth orbit which are used with a GPS receiver to show your location on the planet. The system was completed in 1994 and today you can find handheld GPS units, car mounted units, cell phone GPS and even cameras with built in GPS functionality. How does it work though?

The answer is surprisingly simple (and complicated at the same time): triangulation. Triangulation uses the distance from multiple points to determine the posistion of an object. Let’s say you had a friend who was lost. If you knew your friend was 50 feet from his house, 200 feet from the shopping mall and 275 feet from the movie theater there is only one location which could be all of those things. Below is an image I made showing circles for each of the distances. There is only one space where all 3 circles overlap and that’s where your friend is!

A GPS receiver works the same way but by using how far you are away from the GPS satellites. But how does a GPS receiver know how far it is from a satellite?

The GPS satellites in orbit transmit a signal with a very accurate telling of the time. The GPS receiver then looks at the time the GPS satellite says it is compared to the time the GPS received the signal and can calculate how far away the satellite must of been because the signal travels at a constant speed. Once the GPS has a few different satellite signals it can do the triangulation by saying “I’m 12,185.00048 miles from this satellite and I’m 11,495.1835 miles from this second satellite and I’m 11,382.8513 miles from this third satellite so I must be here.”

This type of system is powered by amazingly accurate atomic clocks in the GPS satellites and powerful computer chips that can read and do the equations necessary for calculating distance and location hundreds of times per minute. Just how precise are these clocks? The GPS satellite clocks are accurate to 10 nanoseconds or 1 billionth of a second.

Amazing huh? Next time you’re lost think of the amazing technology that goes into finding your way home!

-Tim