The intentional crash on Friday morning is the first and bigger of two planned collisions that are expected to kick up miles of lunar dust.
The space probe is called LCROSS (L-cross), short for Lunar Crater Observation and Sensing Satellite. It has five cameras and four other scientific instruments aboard, and follows the empty hull by a few minutes.
NASA is broadcasting the crashes live on the Internet. Telescopes across the world are trained to the moon for the event. NASA expects to know whether there was ice below the lunar surface in about an hour.