The U.S. space agency NASA is preparing to launch a new, nearly half-billion dollar lunar mission that will enable scientists to better understand the moon's gravitational field and the lunar interior, from crust to core. GRAIL, NASA's Gravity Recovery And Interior Laboratory mission, lifts off from Cape Canaveral in Florida on Thursday.
The two solar-powered GRAIL spacecraft will spend more than three months approaching our moon, and they will be flying similar, but separate, trajectories toward their target.
Ed Weiler, of NASA's Science Mission Directorate, explains GRAIL's goal once it reaches its destination.
"GRAIL, simply put, is a journey to the center of the moon," said Weiler. "It will probe the interior of the moon and map its gravity field 100 to 1,000 times better than ever before."
In essence, the washing-machine sized satellites will chase one another around the moon, about 200 kilometers apart, and use radio signals to determine the distance between them.
"As the first satellite goes over a higher mass concentration or higher gravity, it will speed up slightly, and that will increase the distance, and then as the second satellite goes over, that distance will close again," added Weiler.
In this tandem formation, the spacecraft will spend three months mapping the moon's gravitational field. NASA expects GRAIL to yield the most accurate gravity map of the moon to date.
Scientists will then compare gravitational and topographical maps of the lunar surface.
They explain that as the lunar shape varies, gravity varies, and they expect there to be a difference in the gravitational signal over lunar craters and mountains. If that is not the case, it will be a sign that something is going on in the moon's interior.
NASA says the insights gained from the GRAIL mission will help them better understand the way rocky planets, including Earth, formed. The gravitational map will also be an important navigational tool for future lunar spacecraft.
The GRAIL twins are due to arrive at the moon around January 1, 2012.