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NASA’s climate-monitoring space laser is the last to ride to space on a Delta II rocket

This weekend, NASA is launching a new high-tech satellite to monitor the planet’s glacier and sea ice levels — with space lasers, naturally. ICESat-2 will be a huge boon for climatologists, and it’s also a bittersweet occasion: it will be the final launch aboard the trusty Delta II rocket, which has been putting birds in the air for nearly 30 years. Takeoff is set for 5:46 AM Pacific Time Saturday morning, so you’ll have to get up early if you want to catch it. You can watch the launch live here , with NASA coverage starting about half an hour before. Keeping track of the Earth’s ice levels is more important than ever; with climate change causing widespread havoc, precise monitoring of major features like the Antarctic ice sheet could help climatologists predict and understand global weather patterns. Like Aeolus, which launched in July, ICESat-2 is a spacecraft with a single major instrument, not a “Christmas tree” of sensors and antennas. And like Aeolus, ICESat-2 carries a giant laser . But while the first was launched to watch the movement of the air in-between it and the ground, the second must monitor the ground through that moving air. It does so by using an industrial-size, hyper-precise altimeter: a single, powerful green laser split into six beams — three pairs of two, really, arranged to pass over the landscape in a predictable way. But the real magic is how those lasers are detected. Next to the laser is a special telescope that watches for the beams’ reflections. Incredibly, it only collects “about a dozen” photons from each laser pulse, and times their arrival down to a billionth of a second. And it does this 10,000 times per second, which at its speed means a pulse is bouncing off the Earth every 2.3 feet or so

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