LOS ANGELES - NASA's Gravity Recovery And Interior Laboratory spacecraft (Grail) will begin final preparations for a launch on a Moon mission in late summer, the Jet Propulsion Laboratory (JPL) said on Monday.

The moon appears near the earth's horizon in this photograph of an orbital moonset taken from aboard the International Space Station May 17, 2011. [Photo/Agencies]

The dynamic duo will orbit the moon to determine the structure of the lunar interior from crust to core and to advance understanding of the thermal evolution of the moon, according to JPL in Pasadena, Los Angeles.

After arriving at the Astrotech payload processing facility in Titusville, Florida last week, the Grail twins, known as Grail-A and Grail-B, were removed from their shipping containers Monday. Later this week, they will begin functional testing to verify their state of health, said JPL.

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The twins were shipped from Lockheed Martin Space Systems, Denver.

Over the next four months at the Astrotech facility, the spacecraft will undergo final testing, fueling and packaging in the shroud that will protect them as the Delta II launch vehicle lifts them into space. The spacecraft will then be transported to the Cape Canaveral Air Force Station for installation atop the rocket that will carry them toward the moon, JPL said.

"We're only a few full moons away from a mission that will reveal clues not only into the history of the moon and Earth, but will provide important data for future lunar exploration," said Maria Zuber, Grail's principal investigator, based at the Massachusetts Institute of Technology.

Grail will be carried into space aboard a United Launch Alliance Delta II Heavy rocket lifting off from Launch Complex-19 at the Cape Canaveral Air Force Station in Florida. The launch period opens September 8, 2011, and extends through October 19. For a September 8 liftoff, the launch window opens at 5:37 am PDT (8:37 am EDT) and remains open through 6:16 am PDT (9:16 am EDT).

Grail-A and Grail-B will fly in tandem orbits around the moon for several months to measure its gravity field in unprecedented detail.

The mission will also answer longstanding questions about Earth' s moon, and provide scientists a better understanding of how Earth and other rocky planets in the solar system formed, according to JPL, which manages the Grail mission.