Preparing the next generation of GPS

Thanks to GPS, your car, your phone, even your watch knows exactly where you are on the planet, by listening to a satellite signal from 12,000 miles over your head. GPS is always on, you don't pay anything to use it, and you never need to know how it works. But don't you kind of wonder? The U.S. Air Force runs the American Global Positioning System. More

(Source: CBS News - Dec 2)