NASA finds India's missing lunar orbiter with Earth-bound radar
From The Register
In 2009, a lunar orbiter launched by India went quiet and never heard from again. Fast-forward eight years and NASA say it's spotted it using an Earth-based radar.https://www.theregister.co.uk/2017/03/14/nasa_finds_indias_missing_lunar_orbiter_with_earthbound_radar/The Indian Space Research Organisation's Chandrayaan-1 orbiter was supposed to spend two years on its mission, but after 312 days its communications systems conked out.
As NASA explains, it couldn't simply extrapolate the little orbiter's last-known orbit because the moon is “riddled with mascons (regions with higher-than-average gravitational pull) that can dramatically affect a spacecraft's orbit over time”.
The agency's orbital calculations suggested, however, that the refrigerator-sized spacecraft was most likely around 200 km from the surface, and because it was in a polar orbit, the scientists knew it would always pass the poles.
NASA scientists therefore beamed microwaves from the 70m dish at the Goldstone Deep Space Communication complex in California, aimed at a point about 160 km above the moon's north pole. The 100m dish at the Green Bank Telescope in West Virginia was used as the receiver.
“Chandrayaan-1 was predicted to complete one orbit around the moon every two hours and eight minutes. Something that had a radar signature of a small spacecraft did cross the beam twice during four hours of observations, and the timings between detections matched the time it would take Chandrayaan-1 to complete one orbit and return to the same position above the moon's pole.”
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