No one had heard from Chandrayaan-1 since Aug. 29, 2009. That's when the pioneering moon orbiter — the first lunar probe ever launched by the Indian Space Research Organization — abruptly went silent just 312 days into what was supposed to be a two-year mission. The orbiter has been missing ever since. It's no bigger than a refrigerator and difficult for Earth-based telescopes to discern given the moon's nighttime glow, making the craft hard to track down. Plus, the moon's lopsided topography — riddled with mascons, or areas of dense material with higher-than-average gravitational pull — makes satellites' orbits incredibly unpredictable.
But the silent, stealthy Chandrayaan-1 couldn't evade powerful radio telescopes. Scientists at NASA's Goldstone Deep Space Communications Complex in California's remote Mojave Desert and at the National Science Foundation's Green Bank Telescope in West Virginia worked together to detect the long-lost orbiter by sending out radio waves in its direction and listening for the echoes that bounced back. The search technique, developed by researchers at the Jet Propulsion Laboratory in California, is a new one. Capitalizing on the fact that Chandrayaan-1's orbit takes it over the moon's north pole, they used Goldstone's largest antenna to direct a powerful beam of microwaves toward the spot they expected the probe to be. The antenna is usually used to communicate with spacecraft much farther away — it's still in touch with the Voyager 1 probe way outside the solar system. But it could also be applied much like a police officer's radar gun.
Credits:
https://www.washingtonpost.com/news/speaking-of-science/wp/2017/03/13/nasa-just-found-an-orbiter-thats-been-missing-around-the-moon-for-8-years/?utm_term=.38cf72a5df07
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