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Tick-Tock Atomic Clock


24 GPS satellites orbit Earth. Modern navigators rely on atomic clocks. Instead of old-style springs or pendulums, the natural resonances of atoms -- usually cesium or rubidium -- provide the steady 'tick' of an atomic clock. The best ones on Earth lose no more than one second in millions of years. Sailers, truck drivers, soldiers, hikers, and pilots ... they all rely on atomic clocks, even if they don't know it. Anyone who uses the Global Positioning System (GPS) benefits from atomic time. Each of the 24 GPS satellites carries 4 atomic clocks on board. By triangulating time signals broadcast from orbit, GPS receivers on the ground can pinpoint their own location.

Tiny instabilities in those orbiting clocks contribute at least a few meters of error to single-receiver GPS measurements. Making the clocks smaller (so that more of them can fit on each satellite) and increasing their stability could reduce such errors to fractions of a meter. Pilots landing on narrow airstrips at night would appreciate the improvement. So would surveyors, prospectors, search and rescue teams ... and farmers. 'Precision farmers' already use GPS-guided tractors to dispense custom-doses of water, fertilizer and pesticides over garden-sized plots. Better GPS data could guide those tractors to individual rows or perhaps even to individual plants for special care.



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Fact Credit:
NASA Marshall Space Flight Center
Science @ NASA

Further Reading
Time's Pendulum: The Quest to Capture Time--From Sundials to Atomic Clocks
by Jo Ellen Barnett


Related Web Links
How Does GSP Work?
by Smithsonian

Cesium Fountain Atomic Clock
by NIST





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