In 1972, the last Apollo astronauts came home from the moon, and that was that. The consensus was that the rocks they had found were dry as dust -- even more so, in fact.
But the conventional wisdom has changed.
In 1994, a military space probe called Clementine, sent to map the moon as a way of testing sensors for possible Defense Department use, found evidence of ice in the shadowed corners of craters near the moon's south pole.
In 1998 a NASA probe called Lunar Prospector was sent to confirm Clementine's findings, and as it orbited the moon it found evidence of large amounts of ice in the lunar soil.
The working theory is that comets, crashing into the moon over the eons, left tons of ice. In most places, it would have vaporized quickly. But some craters near the moon's south pole are so deep -- and the angle of sunlight is always so shallow -- that ice could have remained frozen.
The earlier probes only took indirect measurements to suggest lunar ice. But could they be right? Engineers on Earth almost salivate at the thought.
That is because NASA's current mandate, laid out by President Bush and so far backed by President Obama, is to use the moon as a base for human exploration of Mars and beyond. As part of Project Constellation, they would set up camp in their Altair landing ships.
If there is frozen water there -- H2O -- it could be used for drinking, or broken down into its components of hydrogen and oxygen for fuel, air to breathe, and myriad other uses.
LCROSS, by NASA standards, is a low-cost mission, with a fixed budget of $79 million -- a good chunk of money, but remember that the movie "Transformers: Revenge of the Fallen" has grossed about $400 million since its release in June.
There has been long debate over the merits of sending astronauts back to the moon, but if LCROSS finds water, it will make the lives of future astronauts much simpler.
"It's a pretty simple mission with profound implications," said Hunt.