YOU probably know how difficult it can be to find your way across an unfamiliar town. So how can a navigator find his way across featureless oceans? Merely having a compass does not help unless a navigator knows what his position is in relation to his destination. Not until the invention of the sextant and the marine chronometer in the 1730’s could navigators determine their exact location and plot their course on a map—with each fix requiring hours of calculation.
Today motorists in many countries navigate using relatively inexpensive devices linked to the Global Positioning System (GPS). You just key in your destination address. The device can show your exact position on its screen. Then it guides you to where you want to go. How does it work?
Satellite navigation devices depend on about 30 satellites that each broadcast signals indicating the satellite’s position and the time to an accuracy of a few billionths of a second. Once your device has established contact with a few satellites, it accurately measures how long a signal takes to travel from the satellite to your receiver. With this information, it can determine your position. Can you imagine the complexity of the mathematics? In a few seconds, it computes the distances to three satellites, all thousands of miles away traveling in different directions at speeds of many miles per second.
Professors Bradford Parkinson and Ivan Getting invented the GPS back in the early 1960’s. Although it was originally developed for military use, it was later made available to the public, becoming fully operational in 1996. A GPS receiver is a marvel of computer technology, but was it the first automatic navigation device?
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Globe: Based on NASA photo