Twin probes to circle moon to study gravity field

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LOS ANGELES (AP) ? After a roundabout journey, two unmanned probes the size of washing machines are heading for the moon and are poised to enter orbit over the New Year’s weekend.

While previous spacecraft and astronauts have visited the moon, this is the first mission dedicated to measuring the uneven lunar gravity field. The near-identical probes named Grail-A and Grail-B blasted off from Florida in September and have been cruising independently to the moon.

If all goes well, Grail-A will fire its engine and slip into orbit on New Year’s Eve followed by Grail-B on New Year’s Day.

Data collection won’t begin until March.

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Online:

Mission details: http://www.nasa.gov/mission_pages/grail/news/index.html

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