| GPS, or Global Positioning System, is the latest thing in | | | | distance to each and from that information determine |
| keeping from getting lost when trekking out to visit | | | | where on the planet the receiver itself is located. It |
| your Aunt Louise. Years ago you had to rely on | | | | then transmits this location back to the person who |
| landmarks, your handy compass or the guy at the | | | | happens to be in possession of the receiver. The |
| corner gas station, assuming he knew where | | | | operation is based on a simple mathematical principal |
| everything was. Today for about a hundred bucks you | | | | called trilateration. To simply explain how this works, |
| can get a little gadget that will tell you exactly where | | | | let's say someone tells you that you are 10 miles from |
| you are, any place on Earth. By using some basic | | | | Newark, NJ, another person tells you that you are 15 |
| mathematical calculations and a rather complex | | | | miles from Maplewood, NJ and a third person tells you |
| system, you can be in the middle of the desert, lost as | | | | that you are 20 miles from Woodbridge, NJ. By taking |
| can be, push a button and have your GPS tell you | | | | those three facts you can figure out exactly where |
| exactly where you are so that you can hopefully find | | | | you are because each radius of each distance when |
| your way back home.So what exactly is GPS and | | | | linked together will intersect at only one point. That |
| how does it work?GPS is actually a very complex and | | | | point is where you are located.In order to actually do |
| expensive system but the fundamental concepts of | | | | the calculation from space the GPS receiver needs to |
| the system are very simple.The GPS system is a | | | | know 2 things. The location of at least 3 satellites |
| group of 27 Earth orbiting satellites. Twenty-four of | | | | above you and the distance between you and each |
| them are in operation and 3 are backups in case one | | | | of those satellites. The reason that only 3 satellites or |
| fails. The system was originally created for the US | | | | spheres are needed is because the Earth itself can |
| military but was eventually opened up to everyone | | | | act as a fourth sphere. The GPS receiver itself works |
| else.Each one of these satellites, weighing in at about | | | | by radio waves which are a kind of electromagnetic |
| 4,000 pounds, circles the Earth at about 12,000 miles | | | | energy and travel at the speed of light The receiver |
| per hour and makes 2 complete rotations everyday. | | | | can actually figure out how far the signal has travelled |
| The orbits are arranged so that at any one point in the | | | | by timing how long it took for the signal to arrive from |
| day 4 of these satellites are visible from any place on | | | | each of the satellites.In the next article on GPS we'll go |
| Earth.The complimenting receiver that was created to | | | | over exactly how this system works to measure |
| receive signals from these satellites has the job of | | | | distance. |
| locating 4 or more of these satellites, figure out the | | | | |