Navigation Satellite

navigation satellite, artificial satellite designed expressly to aid the navigation of sea and air traffic. Early navigation satellites, from the Transit series launched in 1960 to the U.S. navy's Navigation Satellite System, relied on the Doppler shift. Based on the shift in the satellite's frequency, a ship at sea could accurately determine its longitude and latitude. The Global Positioning System (GPS), which uses a web of 24 Navstar satellites in 12-hour orbits, employs the more accurate triangulation method to determine position. Each satellite broadcasts time and position messages continuously. Precise to within a few yards, the GPS can also be used for nonnavigation purposes, such as surveying, tracking migrating animals, and plotting the crop yields of small sections of farmland. The former Soviet Union established a Navstar-equivalent system known as the Global Orbiting Navigation Satellite System (GLONASS). Russia's GLONASS will use the same number of satellites and orbits similar to those of Navstar when complete.

Bibliography

See T. Logsdon, Understanding the Navstar: GPS, GIS, and IVHS (1995); B. Hofmann-Wellenhoff, Global Positioning System: Theory and Practice (1997).

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Navigation Satellite 

an artificial earth satellite that is designed to facilitate sea and air navigation. The range and velocity of the satellite with respect to a ship or airplane are measured at several points in the orbit by means of electronic navigation equipment. The results of the measurements, combined with the known geocentric coordinates of the navigation satellite as determined for the times of the measurements on the basis of information stored in the memory unit of the navigation satellite and transmitted by radio during communications sessions, make possible determination of the position of the ship from which the measurements were made. A system that consists of several satellites moving in different orbits and a network of ground stations that make systematic measurements of the position of the satellites for more accurate determination of their orbital parameters is used to improve the precision of navigational calculations. The error with which the position of a ship can be determined from results of observations of a single navigation satellite is about 55 m.

REFERENCE

Oakes, J. B. “The Navy Navigation Satellite System and Its Applications.” Journal of the Washington Academy of Sciences, 1969, vol. 59, nos. 1–3, pp. 7–16.

A. M. MIKISHA