The LCROSS mission is a search for water on the moon. The LCROSS mission is going to do this by directly impacting one of the permanently-shadowed regions near the moon's pole and creating a crater, throwing tons of debris and potentially water ice and vapor above the lunar surface. This impact will release materials from the lunar surface that will be analyzed for the presence of hydrated minerals which would tell researchers if water is there or not. The two main components of the LCROSS mission are the Shepherding Spacecraft (S-S/C) and the Centaur upper stage rocket. The Shepherding Spacecraft guides the rocket to a site selected on the moon that is suspected of containing water ice. Because suspected deposits of water ice are concentrated in specific permanently-shadowed craters, the researchers have to be very precise where they program the Shepherding Spacecraft to guide the rocket.

The Shepherding Spacecraft and Centaur rocket are launched together with another spacecraft called the Lunar Reconnaissance Orbiter (LRO). All three are connected to each other for launch, but then the LRO separates about two hours after launch. The Shepherding Spacecraft guides the Centaur rocket through multiple Earth orbits, each taking about 38 days. The rocket then separates from the Shepherding Spacecraft and impacts the Moon at more than twice the speed of a bullet, causing an impact that results in a big plume or cloud of lunar debris, and possibly water. While this is happening the Shepherding Spacecraft, which has scientific instruments on-board including cameras, is taking pictures of the rocket’s descent and impact into the moon. Four minutes later, the Shepherding Spacecraft follows almost the exact same path as the rocket, descending down through the big plume and analyzing it with special instruments. The analysis is specifically looking for water (ice and vapor), hydrocarbons and hydrated materials. The Shepherding Spacecraft is collecting data continuously and transmitting it back to Earth before its own demise. This impact will be so big that we on Earth may be able to view the resulting plume of material it ejects with a good amateur telescope.