CAPE CANAVERAL, Fla. -- At NASA's Space Launch Complex 17B in Florida, workers secure the second stage of a United Launch Alliance Delta II launch vehicle to the first stage. The payload fairing then will be raised into the white room of the mobile service tower.The Delta II will carry NASA's Gravity Recovery and Interior Laboratory, or GRAIL, spacecraft into lunar orbit. 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. GRAIL is scheduled to launch Sept. 8.