Throughout time people have developed a variety of ways to figure out their
position on earth and to navigate from one place to another. Early mariners relied
on angular measurements to celestial bodies like the sun and stars to calculate
their location. The 1920s witnessed the introduction of a more advanced
technique—radionavigation—based at first on radios that allowed navigators to
locate the direction of shore-based transmitters when in range.1 Later, the development
of artificial satellites made possible the transmission of more-precise,
line-of-sight radionavigation signals and sparked a new era in navigation
technology. Satellites were first used in position-finding in a simple but reliable
two-dimensional Navy system called Transit. This laid the groundwork for a
system that would later revolutionize navigation forever—the Global
Positioning System.

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