Global_Positioning_System

The Global Positioning System, usually called GPS, and originally caled NAVSTAR, is a satellite navigation system used for determining one's precise location anywhere on earth. A GPS receiver receives transmissions from multiple satellites, and determines one's position by triangulating this data.

The GPS was designed by and is controlled by the United States Department of Defense. It is used by countless civilians as well, who can use the GPS's Standard Positioning Service free of charge.

In the past, the civilian signal was degraded, and a more accurate Precise Positioning Service was availble only to the United States military and other, mostly government users. However, in May, 2000, Bill Clinton announced that this "Selective Availability" would be turned off, and so now all users enjoy the same level of access.

The GPS normally consists of 24 satellites in 6 orbital planes. Each satellite circles the earth twice every day.

The first GPS satellite was launched in 1978. The final, 24th satellite was launched in 1994.