Lockheed Martin Space Systems delivered NASA’s twin GRAIL lunar orbiters to Kennedy Space Center, Fla., May 20 where they will undergo four months of final testing and preparation before they are launched from Cape Canaveral Air Force Station in early September aboard a United Launch Alliance Delta 2 Heavy rocket.

The 200-kilogram orbiters are designed to fly 50 kilometers above the surface of the Moon in precision formation to determine the structure of the lunar interior and advance understanding of the Moon’s thermal evolution.

GRAIL, which is short for Gravity Recovery and Interior Laboratory, was selected in December 2007 for development under NASA’s Discovery program of scientist-led, cost-capped planetary missions. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., is managing the mission.