CAPE CANAVERAL, FL - A United Launch Alliance Delta 2 launch vehicle successfuly sent NASA's twin Gravity Recovery and Interior Laboratory (GRAIL) spacecraft into space this morning. After a two days delay for weather and techical concerns, the Delta rocket blasted off into partly cloudy skies above Cape Canaveral at 9:08:52 a.m. EDT to begin a three and a half month journey to the Moon and a mission to explore the interior of Earth's only natural satellite.

The two spacecraft will measure how slight variations in gravity affect them individually. Scientists will use the data to create a full map of the Moon's gravitational field and, by extension, of the structure of the interior of the Moon.

As one satellite passes over a feature, it will be either sped up or slowed down slightly by changes in the gravitational force. This will result in a change in its separation distance and relative orientation with respect to the other spacecraft. When the second spacecraft passes over the area, its orbit will be modified in the same manner.

The changes can be very slight, as small as the width of a blood cell, but GRAIL is precise enough to detect that. With such sensitivity, scientists will be able to create a map of the lunar gravitational field that is at least an order of magnitude more accurate and detailed than previous studies.

Using the data collected, GRAIL will also be the most sophisticated mission to explore the inner structure of the Moon.