CAPE CANAVERAL, Fla. -- Technicians in the Astrotech payload processing facility in Titusville, Fla., prepare NASA's Gravity Recovery and Interior Laboratory, or GRAIL, twin spacecraft for testing and processing. GRAIL was built at the Lockheed Martin plant in Denver, Colo. The United Launch Alliance Delta II rocket that will carry GRAIL into lunar orbit already is fully stacked at NASA's Space Launch Complex 17B and launch is scheduled for Sept. 8.The GRAIL mission is a part of NASA's Discovery Program. GRAIL will fly twin spacecraft in tandem orbits around the moon for several months to measure its gravity field. The mission also will 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.