The TRANSIT system, also known as NAVSAT (for Navy Navigation Satellite System), was the first satellite navigation system to be used operationally. The system was primarily used by the U.S. Navy to provide accurate location information to its Polaris missile ballistic missile submarines, and it was also used as a navigation system by the Navy's surface ships, as well as for hydrographic and geodetic surveying. Transit provided continuous navigation satellite service from 1964, initially for Polaris submarines and later for civilian use as well.
The TRANSIT satellite system was developed by the Applied Physics Laboratory (APL) of Johns Hopkins University for the U.S. Navy. Just days after the launching of Sputnik I on October 4, 1957, the APL scientists George Weiffenbach and William Guier were able to determine Sputnik's orbit by analyzing the Doppler shift of its radio signals during a single pass . Frank McClure, the chairman of APL's Research Center, suggested that if the satellite's position were known and predictable, the Doppler shift could be used to locate a receiver on Earth.
Development of the TRANSIT system began in 1958, and a prototype satellite, Transit 1A, was launched in September 1959. That satellite failed to reach orbit. A second satellite, Transit 1B, was successfully launched 1960-04-13 by a Thor-Ablestar rocket. The first successful tests of the system were made in 1960, and the system entered Naval service in 1964.
It is noteworthy that surveyors used Transit to locate remote benchmarks by averaging dozens of Transit fixes, producing sub-meter accuracy. In fact, the elevation of Mount Everest was corrected in the late 1980s by using a Transit receiver to re-survey a nearby benchmark.
Literally thousands of warships, freighters and private watercraft used Transit from 1967 until 1991. Even some Soviet warships were known to be equipped with Motorola NavSat receivers.
The TRANSIT system was made obsolete by the Global Positioning System, and ceased navigation service in 1996. Improvements in electronics allowed the GPS system to effectively take several fixes at once, thereby greatly reducing the complexity of deducing a position. In addition the GPS system uses many more satellites than were used with TRANSIT, allowing the system able to be used continually, whereas TRANSIT provided a fix only every hour or more.
After 1996, the satellites were kept in use as spaceborne 'mailboxes' and for the Navy's Ionospheric Monitoring System.
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