Modern Navigational Tools
The next great revolution in navigation occurred in the 20th cent., when radio signals came into wide use. The development of radar, loran, and radio direction finding during World War II caused fundamental changes in navigational practice; a mariner or pilot today can turn on a Loran or Global Positioning System receiver and determine position and course to within a few yards. Inertial guidance systems, most often used to navigate submarines, aircraft, and spacecraft, allow navigation without contact with a ground base. In such systems, a computer navigates the vehicle with the aid of an inertial navigator device, which consists of a gyroscope to indicate direction and an accelerometer to measure changes in speed and direction. Inertial guidance systems and terrain-following radar allow a cruise missile to fly a thousand miles and hit its designated target. The development of navigation satellites beginning in the 1960s led in the 1990s to the U.S.'s Global Positioning System (GPS), which provides location and other information through the reception and interpretation of signals received from satellites; Russia and China have since created similar navigation systems. GPS receivers, which are now incorporated into smartphones and other devices, have made it possible to create navigation systems for vehicles and other forms of transportation.
See also air navigation.
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