History
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 Soviet launch of Sputnik 1, the first man-made earth-orbiting satellite on October 4, 1957. Two physicists at APL, William Guier and George Weiffenbach, found themselves in discussion about the microwave signals that would likely be emanating from the satellite and 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 April 13, 1960, 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.
Thousands of warships, freighters and private watercraft used Transit from 1967 until 1991. Some Soviet warships were 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, greatly reducing the complexity of deducing a position. The GPS system uses many more satellites than were used with TRANSIT, allowing the system to be used continuously, while 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.
Read more about this topic: Transit (satellite)
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