For Tony Colaprete and the rest of this team at NASA Ames, Thursday culminates two years of intense work, planning and scrutiny.
For them, the most important countdown began with a launch last June and now, their LCROSS Mission, which cost only $79 million, will crash a spent booster rocket and observing satellite into a dark lunar crater, looking for signs of water or even ice.
"We're really on target. We actually called off the last maneuver because we didn't need it," said Colaprete.
For two years, Colaprete and his team have scrutinized craters and changed targets several times, even in recent weeks.
The final one named Cabeus presents a perfect blend of angles, lighting and geography for spectrometers that will look at a 50 mile high cloud of debris from the crash.
"There is a little valley that the sunlight can stream through and illuminate out eject a cloud and voila. That was it," said Colaprete.
NASA predicts impact at exactly 4:31:19 on Friday Morning, Pacific Time. From earth, with a 12-inch telescope, if you look at exactly the right place, you might see what scientists describe as a muted shimmer of light on the South Pole.
The twist is that the darker the flash, the likelihood that they have found a lot of water.
"If we had totally dry dirt, all the energy goes into heating. So the hotter we get, the more light there," said Colaprete.
Put simply, the presence of water becoming vapor would limit the heat. NASA will get most of its crucial data in the first 30 seconds and then will spend three months evaluating.
When finished, they may be able to confirm that our once-assumedly dry moon contains as much water, as all of Lake Erie.