A surveillance helicopter passes over Space Launch Complex 17B on Cape Canaveral Air Force Station preparations are being completed.

A surveillance helicopter passes over Space Launch Complex 17B on Cape Canaveral Air Force Station where preparations to launch the United Launch Alliance Delta II Heavy rocket that will carry NASA's Gravity Recovery and Interior Laboratory mission into space are being completed.

GRAIL will fly twin spacecraft in tandem around the moon to precisely measure and map variations in the moon's gravitational field. The mission will provide the most accurate global gravity field to date for any planet, including Earth. This detailed information will reveal differences in the density of the moon's crust and mantle and will help answer fundamental questions about the moon's internal structure, thermal evolution, and history of collisions with asteroids. The aim is to map the moon's gravity field so completely that future lunar vehicles can safely navigate anywhere on the moon’s surface. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA