In the 1960s, NRL and the Aerospace Corporation independently developed concepts for systems that could provide precise, all-weather, real-time, 24-hour, worldwide navigation information. The NRL concept was proven in 1967 with the launch of its Timation I satellite. In 1973, NRL's program merged with the Air Force program to form the Navstar GPS program.
NRL's Navigation Technology Satellite II, launched in 1977, was the first satellite in the Navstar GPS. The GPS incorporates NRL's concept of time range, range-rate navigation and a 12-hour orbit. The developmental Block I satellites were an unprecedented success. In more than 700 air, land, and sea tests conducted between 1977 and 1979, they exceeded all performance requirements and affirmed the system's extraordinary precision.
The Navstar GPS satellites transmit a constant signal generated by on-board atomic clocks, which are so precise that they gain or lose only one second every 3 million years. Users equipped with a receiver/processor simply lock onto the signals of four satellites, and then latitude, longitude, altitude, and velocity are automatically computed "within meters" by triangulation.
This remarkable precision proved invaluable during Operation Desert Storm in targeting pinpoint strikes and positioning troops in featureless terrain. GPS was also used in Operation Restore Hope to help aircraft land on makeshift Somalian airfields. Apart from its primary military function, the satellite system serves numerous peacetime functions such as air traffic control, scientific surveying, harbor navigation, and measurement of ocean waves. Today, both development and production satellites are orbiting the Earth, transmitting continuous navigation signals to users around the world. The system hoped for 30 years ago has become the DoD standard and, in the process, has revolutionized the science of navigation.