In the 1991 the USA opened to the world the service with name SPS (Standard Positioning System), with detailed lists differentiated that called soldier PPS (Precision Positioning System). In practical it came introduced the so-called Selective Availability (KNOWS) that it introduced intentional errors in marks them satellitari in order to reduce the accuracy of the survey, concurring precisions single in the order of 100-150 m.
The GPS has been created in substitution of the previous system, the Transit, when the USA, rinunciando to the Selective Availability, have rendered the first one taken care of how much the second, supporting it with a net of 24 satellites crafts them.
The degradation of marks them has been disabilitata from the month of May 2000, thanks to a decree of the President of the United States Bill Clinton, putting therefore to disposition the precision puts into effect them of approximately 10-20 m. In the models for civil use a device is present that inhibits the operation to heights and advanced speeds to sure values, in order to prevent of the assembly on unexpected missiles.
The UE has in plan the completion of an own net of satellites, Sistema of Galileo positioning, for civil scopes, between which the GPS. This plan has an obvious strategic valence in how much the net American is property of the single United states and is managed military authorities, than, in particular conditions, they could decide discretionarily and unilaterally to reduce the precision or block the access selective to the system; the sharing of the investment and the property from part of the utilizzatori states guarantees continuity, accessibility and interoperabilità of the service.