LCROSS Lunar Crater Observation and Sensing Satellite
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The Lunar CRater Observation and Sensing Satellite (LCROSS), was purpose built to search for H2O on the Moon. "If LCROSS's booster stage hits a patch of lunar regolith that contains at least 0.5 percent water ice, water should be detectable in the plume of ejecta," per Anthony Colaprete.
Sometime between May and August 2009, depending on launch dates, the booster stage for NASA's LCROSS probe will deliberately crash into a permanently-shadowed lunar crater at 9,000 km/hr, producing an explosion equivalent to about 2,000 pounds of TNT (6.5 billion joules). The blast will jettison material out of the crater where astronomers can search the debris for signs of lunar water.
The other half of the LCROSS mission, a robotic satellite, will observe the impact and then itself crash into the Moon 4 minutes later. Most of the Moon is bone dry, of course. With virtually no atmosphere and 300° temperature swings between night and day, most of the Moon's surface is a hostile place for water. But there are a few cold, dark places where frozen water could stay put. At the lunar poles, the sun is always low on the horizon, so some crater ridges cast shadows that keep parts of the crater floors in perpetual darkness. Temperatures in the inky black shadows hover around 40° above absolute zero (-233° Celsius), cold enough for water ice to survive indefinitely.
The explosion itself will probably be hidden by the walls of the target crater. Instead, what astronomers will look for is the impact plume. An expanding cone of ejecta will rise more than 6 kilometers above the lunar surface and spread outward for about 40 km in every direction. Glistening in the sunlight, the debris is expected to shine like a 6th to 8th magnitude star—invisible to the human eye but an easy target for backyard telescopes.
Sponsor: NASA Ames Research Center
Secondary spacecraft to be ejected from NASA's Lunar Reconnaissance Orbiter
Principal Investigator: Dr. Anthony Colaprete
Prime Contractor: Northrup Space Technologies of Redondo Beach, Calif.