NASA on Saturday launched a pair of unmanned spacecraft on a journey to study the core of the Moon and reveal how it formed some 4.5 billion years ago. "Liftoff of the Delta II with GRAIL, on a journey to the center of the moon," NASA commentator George Diller said as the twin GRAIL satellites, short for Gravity Recovery And Interior Laboratory, blasted off from Cape Canaveral Air Force Station in Florida.