LCROSS Impact Characteristics
The life cycle of a lunar impact. The LCROSS instruments are designed to collect data on the evolving impact environment. Credit: NASA
The primary goal of LCROSS is to measure the concentration of water ice (ice to dust ratio) in permanently shadowed lunar regolith or soil. When the approximately 2000 kg Centaur impacts a permanently shadowed crater at 2.5 km/s, there is an initial flash followed by the creation of a debris blanket and plume. If water ice is present on the floor of the crater, it will be thrown skyward. Once above the crater rim, it will be exposed to solar radiation breaking the molecules of water into hydrogen ions (H+) and hydroxyl ions (OH-). The LCROSS spacecraft following four minutes behind will collect and transmit data back to LCROSS mission control about the debris plume using the nine on-board science instruments before impacting the surface. A possible result of the impact is the creation of a temporary thin atmosphere of hydroxyl ions. This resulting atmosphere could be detectable using telescopes on and orbiting the Earth and satellites in lunar orbit.
The resulting Centaur impact crater will be approximately 28m (92 feet) in diameter by 5m (16 feet) deep while the LCROSS spacecraft impact will be approximately 18m (59 feet) in diameter by 3.5m (11.5 feet) deep. Studies using the Ames Vertical Gun Range indicate the LCROSS impacts will create a significantly larger crater than Lunar Prospector (LP). That satellite impacted the moon at 1.7 km/s with a mass of 158 kg at a glancing angle of 6°. Temperatures reached will be insufficient to vaporize most (~90%) of the material, though is expected to create a very brief visible flash that will last < 100ms which will be measured by the S-S/C photometer instrument. Most of the ejecta will be thrown upward at a velocity of >250 m/sec.
Images and information about impact studies conducted at the Ames Vertical Run Range.