Editing Satellite navigation (section)

== History ==
{{further|GPS#History|GLONASS#History|Galileo (satellite navigation)#History{{!}}GALILEO#History|BeiDou#History}}
[[File:Accuracy of Navigation Systems.svg|thumb]]

Ground-based [[radio navigation]] is decades old.  The [[Decca Navigator System|DECCA]], [[LORAN]], [[Gee (navigation)|GEE]] and [[Omega Navigation System|Omega]] systems used terrestrial [[longwave]] radio [[transmitter]]s which broadcast a radio pulse from a known "master" location, followed by a pulse repeated from a number of "slave" stations.  The delay between the reception of the master signal and the slave signals allowed the receiver to deduce the distance to each of the slaves, providing a [[fix (position)|fix]].

The first satellite navigation system was [[Transit (satellite)|Transit]], a system deployed by the US military in the 1960s. Transit's operation was based on the [[Doppler effect]]: the satellites travelled on well-known paths and broadcast their signals on a well-known [[radio frequency]].  The received frequency will differ slightly from the broadcast frequency because of the movement of the satellite with respect to the receiver. By monitoring this frequency shift over a short time interval, the receiver can determine its location to one side or the other of the satellite, and several such measurements combined with a precise knowledge of the satellite's orbit can fix a particular position. Satellite orbital position errors are caused by radio-wave [[refraction]], gravity field changes (as the Earth's gravitational field is not uniform), and other phenomena. A team, led by Harold L Jury of Pan Am Aerospace Division in Florida from 1970 to 1973, found solutions and/or corrections for many error sources.{{citation needed|date=May 2022}} Using real-time data and recursive estimation, the systematic and residual errors were narrowed down to accuracy sufficient for navigation.<ref>Jury, H, 1973, Application of the Kalman Filter to Real-time Navigation using Synchronous Satellites, Proceedings of the 10th International Symposium on Space Technology and Science, Tokyo, 945-952.</ref>