Global Positioning System (GPS), Controlled by U.S.

(GPSS background)

Who controls the Global System Positioning Satellites?

The GPS system was designed by and is controlled by the United States Department of Defense and can be used by anyone, free of charge.

The GPS system is divided into three segments: space, control, and user. The space segment comprises the GPS satellite constellation.

The control segment comprises ground stations around the world that are responsible for monitoring the flight paths of the GPS satellites, synchronizing the satellites' onboard atomic clocks, and uploading data for transmission by the satellites.

The user segment consists of GPS receivers used for both military and civilian applications. A GPS receiver decodes time signal transmissions from multiple satellites and calculates its position by trilateration.

The cost of maintaining the system is approximately US$400 million per year, including the replacement of ageing satellites.

The first of 24 satellites that form the current GPS constellation (Block II) was placed into orbit on February 14, 1989. The 52nd GPS satellite since the beginning in 1978 was launched November 6, 2004, aboard a Delta II rocket.

Selective Availability

In the past, the civilian signal was degraded, and a more accurate Precise Positioning Service was available only to the United States military, its allies and other, mostly government users; however, on May 1, 2000, then US President Bill Clinton announced that this "Selective Availability" would be turned off, and so now all users enjoy nearly the same level of access, allowing a precision of position determination of less than 20 meters.