There is a lot more water on the moon than previously believed, according to an analysis of NASA data being published Friday, a finding that may bolster the case for a manned base on the lunar surface.

The discovery grew out of an audacious experiment last year, when the National Aeronautics and Space Administration slammed a spent-fuel rocket into a lunar crater at 5,600 miles an hour, and then used a pair of orbiting satellites to analyze the debris thrown off by the impact. They discovered that...