"PASADENA, Calif. - NASA's twin, lunar-orbiting Gravity Recovery and Interior Laboratory (GRAIL) spacecraft began data collection for the start of the mission's extended operations.
At 9:28 a.m. PDT (12:28 p.m. EDT) yesterday, while the two spacecraft were 19 miles (30 kilometers) above the moon's Ocean of Storms, the Lunar Gravity Ranging System -- the mission's sole science instrument aboard both GRAIL twins -- was energized."
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NASA's GRAIL Moon Twins Begin Extended Mission Science - NASA Jet Propulsion Laboratory
Artist concept of GRAIL mission. Grail will fly twin spacecraft in tandem orbits around the moon to measure its gravity field in unprecedented detail. Image credit: NASA/JPL