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navigation satellite,artificial satellitesatellite, artificial,
object constructed by humans and placed in orbit around the earth or other celestial body (see also space probe). The satellite is lifted from the earth's surface by a rocket and, once placed in orbit, maintains its motion without further rocket propulsion.
..... Click the link for more information. 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), whose satellites replaced the Transit series, uses a web of 24 satellites in 12-hour orbits; additional satellites orbit in reserve. First satellite in the development series was launched in 1978. The first satellite in the second generation, for a worldwide GPS system, was launched in 1989, and the system began full operation in the 1990s. The third generation of satellites had its first launch in 2018. The satellites broadcast time and position messages continuously, and GPS receivers employ the more accurate triangulation method to determine position; the signals picked up by a GPS receiver can calculate position to within a few yards.
GPS receivers and navigation software may be incorporated into aviation and marine navigation equipment, built-in vehicle dashboard devices, smartphones, computer tablets, and other equipment. Standalone GPS devices are manufactured for use in vehicles and by hikers, but the increasing prevalence of GPS receivers and navigation software on smartphones offers a reasonable alternative to such units. The GPS system can also be used for nonnavigation purposes, such as surveying, tracking migrating animals, plotting the crop yields of small sections of farmland, and determining an individual's or vehicle's location or movements.
The Soviet Union (now Russia) established a Navstar-equivalent system known as the Global Orbiting Navigation Satellite System (GLONASS). Russia's GLONASS uses a similar number of satellites and orbits similar to those of the Navstar satellites. China's Beidou navigation satellite system began operations in 2011 with 10 satellites and now has its full complement of 35 satellites (plus some additional satellites), and the European Union and European Space Agency's Galileo system began operations in 2016 with 18 satellites and will eventually have 30 satellites.
The widespread use of GPS for navigation and location has led to the development of defense systems that interfere with GPS signals, disrupting the proper functioning of GPS equipment. The jamming tactic, which is known as GPS spoofing, uses strong, locally generated false GPS radio signals to overwhelm the ability of GPS equipment to find the satellite signals, resulting in unreliable GPS navigation.
See T. Logsdon, Understanding the Navstar: GPS, GIS, and IVHS (1995); B. Hofmann-Wellenhoff, Global Positioning System: Theory and Practice (1997).
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.
REFERENCEOakes, 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