The LCROSS mission was designed to search for water on the moon by sending a rocket crashing into the moon, causing a big impact, and creating a crater throwing tons of debris and potentially water ice and vapor above the lunar surface. This impact released materials from the lunar surface that were analyzed for the presence of hydrated minerals to tell researchers if water is there or not. The two main components of the LCROSS mission were the Shepherding Spacecraft (S-S/C) and the Centaur upper stage rocket. The Shepherding Spacecraft guided the rocket to a site selected on the moon with a high probability of containing water. Because they had only one chance with this mission in finding water, the researchers had to be very precise where they programmed the Shepherding Spacecraft to guide the rocket.
The Shepherding Spacecraft and Centaur rocket were launched together with another spacecraft called the Lunar Reconnaissance Orbiter (LRO). All three were connected to each other for launch, but then the LRO separates one hour after launch. The Shepherding Spacecraft guided the Centaur rocket through multiple Earth orbits, each taking about 38 days. The rocket then separated from the Shepherding Spacecraft and impacted the Moon at more than twice the speed of a bullet, causing an impact that resulted in a big plume or cloud of lunar debris. While this was happening the Shepherding Spacecraft, which had scientific instruments on-board including cameras, took pictures of the rocket’s descent and impact into the moon. Four minutes later, the Shepherding Spacecraft followed almost the exact same path as the rocket, descending down through the plume and analyzing it with special instruments. The analysis specifically looked for water (ice and vapor), hydrocarbons and hydrated materials.