NASA's twin GRAIL Satellites finally launched on their mission to the moon on Saturday, after two previous failed attempts caused by severe weather conditions.

Two, almost identical, probes called the Gravity Recovery and Interior Laboratory (GRAIL) lifted off in a United Launch Aliance (ULA) Delta II from the Space Launch Complex 17Bin the Cape Canaveral Air Force Station in Florida on Saturday Morning.

The mission is set to land on the moon in about three to four months and will be used to map the gravitational field of the moon to determine the lunar interior to help scientists understand the moon's evolution.

A recent study of a lunar rock found that the Earth's moon may be 200 million years younger than previously believed.

GRAIL-A is scheduled to reach the moon on New Year's Eve 2011, while GRAIL-B will arrive New Year's Day 2012. The two solar-powered spacecraft will fly in tandem orbits around the moon to measure its gravity field.

This is NASA's third successful mission launched by United Launch Alliance (ULA) this year and the U.S. space agency is planning to launch two more in October and November.

Our GRAIL twins have Earth in their rearview mirrors and the moon in their sights, said David Lehman, GRAIL project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. The mission team is ready to test, analyze and fine-tune our spacecraft over the next three-and-a-half months on our journey to lunar orbit.

The straight-line distance from Earth to the moon is approximately 250,000 miles (402,336 kilometers). NASA's Apollo moon crews needed approximately three days to cover that distance. However, each spacecraft will take approximately 3.5 months and cover more than 2.5 million miles (4 million kilometers) to arrive

Both spacecraft are carrying a set of cameras which will, for the first time, give middle-school children a chance to view images from their classrooms.

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