A pair of spacecraft rocketed toward the moon Saturday on the first mission dedicated to measuring lunar gravity and determining what's inside Earth's orbiting companion – all the way down to the core.

"I could hardly be happier," said the lead scientist, Maria Zuber. After two days of delays and almost another, "I was trying to be as calm as I could be."

NASA launched the near identical probes – named Grail-A and Grail-B – aboard a relatively small Delta II rocket to save money. It will take close to four months for the spacecraft to reach the moon, a long, roundabout journey compared with the zippy three-day trip of the Apollo astronauts four decades ago.

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