Workers move the second stage of a United Launch Alliance Delta II launch vehicle toward the mobile service tower.

At NASA's Space Launch Complex 17B in Florida, workers move the second stage of a United Launch Alliance Delta II launch vehicle toward the mobile service tower. It will then be hoisted atop the first stage. 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. For more information visit: http://science.nasa.gov/missions/grail/. Photo credit: NASA/Jack Pfaller