David Lehman, GRAIL project manager, NASA's Jet Propulsion Laboratory, Pasadena, Calif., speaks at a press conference about the upcoming launch to the moon of the Gravity Recovery and Interior Laboratory (GRAIL) mission, Thursday, Aug. 25, 2011 in Washington. GRAIL's primary science objectives are to determine the structure of the lunar interior, from crust to core, and to advance understanding of the thermal evolution of the moon. The mission will place two spacecraft into the same orbit around the moon which will gather information about the its gravitational field enabling scientists to create a high-resolution map. Photo Credit: (NASA/Carla Cioffi)

On the panel from right: Leesa Hubbard, teacher in residence, Sally Ride Science, San Diego; David Lehman, GRAIL project manager, NASA's Jet Propulsion Laboratory, Pasadena, Calif.; Maria Zuber, GRAIL principal investigator, Massachusetts Institute of Technology, Cambridge and Jim Green, director, Planetary Science Division, NASA Headquarters, Washington are seen at a press briefing to discuss the upcoming launch to the moon of the Gravity Recovery and Interior Laboratory (GRAIL) mission, Thursday, Aug. 25, 2011 in Washington. Photo Credit: (NASA/Carla Cioffi)

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, members of NASA's Gravity Recovery and Interior Laboratory (GRAIL) launch team monitor GRAIL's launch countdown from the Mission Directors Center in Hangar AE. From left are Dana Grieco, launch operations manager, Analex, NASA's Launch Services Program (LSP); Bruce Reid, GRAIL mission manager, LSP; Al Sierra, manager of the Flight Project Office, LSP; Omar Baez, GRAIL assistant launch director, LSP; and Tim Dunn, GRAIL launch director, LSP; David Lehman, spacecraft mission director and GRAIL project manager, NASA's Jet Propulsion Laboratory (JPL); and John Henk, GRAIL program manager, Lockheed Martin Space Systems. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8 from Space Launch Complex 17B on Cape Canaveral Air Force Station. 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. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. -- On Cape Canaveral Air Force Station in Florida, members of NASA's Gravity Recovery and Interior Laboratory (GRAIL) launch team monitor GRAIL's launch countdown from the Mission Directors Center in Hangar AE. From left are David Lehman, spacecraft mission director and GRAIL project manager, NASA's Jet Propulsion Laboratory (JPL); Tom Hoffman, deputy spacecraft mission director, JPL; and John Henk, GRAIL program manager, Lockheed Martin Space Systems. Launch is scheduled for 8:37:06 a.m. EDT Sept. 8 from Space Launch Complex 17B on Cape Canaveral Air Force Station. 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. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – Managers of NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission participate in a post-launch news conference in the Press Site television auditorium at NASA's Kennedy Space Center in Florida. From left are Jim Adams, deputy director, Planetary Science Division, NASA's Science Mission Directorate; Maria Zuber, GRAIL principal investigator, Massachusetts Institute of Technology; and David Lehman, GRAIL project manager, Jet Propulsion Laboratory. Liftoff of the twin GRAIL spacecraft aboard a United Launch Alliance Delta II Heavy rocket was at 9:08:52 EDT Sept. 10 from Space Launch Complex 17B on Cape Canaveral Air Force Station in Florida. The spacecraft are embarking on a three-month journey to reach the moon. 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. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – David Lehman, GRAIL project manager, NASA’s Jet Propulsion Laboratory, participates in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. 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 moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – A Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference is held in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. From left are George Diller, NASA Public Affairs; Ed Weiler, NASA associate administrator, Science Mission Directorate; Tim Dunn, NASA launch director for the agency’s Launch Services Program; Vernon Thorp, program manager, NASA Missions, United Launch Alliance; David Lehman, GRAIL project manager, NASA’s Jet Propulsion Laboratory; John Henk, GRAIL program manager, Lockheed Martin Space Systems, Denver, Colo.; and Joel Tumbiolo, launch weather officer, 45th Weather Squadron, Cape Canaveral Air Force Station, Fla. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. 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 moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett

CAPE CANAVERAL, Fla. – News media participate in the Gravity Recovery and Interior Laboratory (GRAIL) prelaunch news conference held in the NASA Press Site auditorium at NASA's Kennedy Space Center in Florida. On the dais, panelist from left are Ed Weiler, NASA associate administrator, Science Mission Directorate; Tim Dunn, NASA launch director for the agency’s Launch Services Program; Vernon Thorp, program manager, NASA Missions, United Launch Alliance; David Lehman, GRAIL project manager, NASA’s Jet Propulsion Laboratory; John Henk, GRAIL program manager, Lockheed Martin Space Systems, Denver, Colo.; and Joel Tumbiolo, launch weather officer, 45th Weather Squadron, Cape Canaveral Air Force Station, Fla. GRAIL is scheduled to launch Sept. 8 aboard a United Launch Alliance Delta II Heavy rocket from Cape Canaveral Air Force Station in Florida. 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 moon vehicles can safely navigate anywhere on the moon’s surface. For more information, visit http://www.nasa.gov/grail. Photo credit: NASA/Kim Shiflett