Transport & space · 1978

GPS

Atomic-clock satellites let any receiver on Earth find its position to within meters.

The first Navstar GPS satellite launched in February 1978; full operation came in 1995. Receivers time signals from four or more satellites, and relativistic clock corrections of about 38 microseconds per day are essential. Selective availability was switched off in 2000, and GPS now underpins navigation, logistics and timing for power grids and networks.

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