The Global Positioning System

For thousands of years people have navigated by looking to the sky. Today, using satellites rather than stars, a handheld unit can display its exact position regardless of the time of day or the amount of cloud cover. Such a change has not happened overnight, of course, but over a matter of decades as electronic navigation has matured, culminating today in the Global Positioning System (GPS): a set of satellites and associated control systems that allow a suitable receiver to determine its location anywhere on earth, 24 hours a day. Here the author describes how a system devised to guide the US armed forces may soon be available to every pilot and driver in the developed world