NASA finally launched its GRAIL mission, Gravity Recovery and Interior Laboratory, from Cape Canaveral Air Force Station in Florida on Saturday, its first mission to map the Moon's inner core.

The GRAIL launch was postponed to Saturday after high upper level winds prevented the first attempt on Thursday.

GRAIL-A popped off the upper stage of the rocket one-and-a-half hours after liftoff, followed eight minutes later by GRAIL-B. The near identical probes traveling independently to the moon, with A due to arrive on New Year's Eve and B on New Year's Day. They won't land on the Moon but will conduct their survey from a polar lunar orbit.

It will take close to four months for the spacecraft to reach moon, a long, round about journey in comparison with the direct flight taken by NASA in the ‘60s, which got NASA there in 3 days.

However, the small Delta II rocket used to boost the GRAIL twins will take longer but is more economical. The GRAIL spacecraft will travel more than 2 million miles to get to the moon. The twin probes will travel via the Sun-Earth Lagrange Point 1, a gravitationally stable spot between our planet and the sun. This route is energy-efficient and thus helps keep the $496 million mission's costs down, researchers said.

GRAIL's primary science objectives are to determine the structure of the lunar interior, from crust to core, and to advance understanding of the thermal evolution of the Moon.

Despite having 109 missions to the moon and having men walk on it, Earth's only satellite still has many secrets scientists want to discover. The moon's formation still baffles scientists and its far side is still largely unexplored.

Trying to understand how the moon formed, and how it evolved over its history, is one of the things we're trying to address with the GRAIL mission. But also, (we're) trying to understand how the moon is an example of how terrestrial planets in general have formed, Maria Zuber, principal investigator for GRAIL from the Massachusetts Institute of Technology, said in a statement.

The GRAIL mission will not only reveal information about the moon's thermal history, but how the inner, rocky planets formed as well. Mostly, however, it will be about the moon. As Zuber says, it will explore the moon from crust to core.

Both spacecraft will carry a set of cameras to the moon as part of MoonKam, a project headed by former astronaut Sally Ride. The cameras will offer middle-school students the chance to request photography of lunar targets for classroom study. This will mark the first time a NASA planetary mission has carried instruments expressly for an education and public outreach project.