How to Build a Space Communication System Out of Lasers

In October 2013, a moon-orbiting NASA spacecraft aimed a laser beam at Earth, 239,000 miles away. Within seconds, the intended recipient—an observatory in southern California—locked onto the beam of infrared light, invisible to the naked eye. Encoded inside the light was a high-definition video of NASA administrator Charles Bolden delivering a short speech. Bolden had, …

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