Timing a space laser with a NASA-style stopwatch

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To time how long it takes a pulse of laser light to travel from space to Earth and back, you need a really good stopwatch -- one that can measure within a fraction of a billionth of a second. That kind of timer is exactly what engineers have built at NASA's Goddard Space Flight Center in Greenbelt, Maryland, for the Ice, Cloud and land Elevation Satellite-2.
via Science Daily
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