The Importance of Lro Observations to the Lcross Mission

The LCROSS Mission: LCROSS, the Lunar CRater Observation and Sensing Satellite, will be launched on the same rocket as the Lunar Reconnaissance Orbiter (LRO) later this year (http://lcross.arc.nasa.gov). The LCROSS scientific objectives are: (1) Confirm the presence or absence of water ice in a permanently shadowed region on the Moon. (2) Identify the form/state of hydrogen observed by at the lunar poles. (3) Quantify, if present, the amount of water in the lunar regolith, with respect to hydrogen concentrations. (4) Characterize the lunar regolith within a permanently shadowed crater on the Moon. The presence of water ice is hypothesized based on evidence found by the Lunar Prospector neutron spectrometer for hydrogen in permanently shadowed regions at the poles [1]. The LCROSS spacecraft will set the rocket's Centaur Earth departure upper stage (EDUS) on an impact trajectory with the Moon. Once the trajectory is set, the spacecraft will release the EDUS, which will then impact the Moon in a permanently shadowed region characterized by high concentrations of hydrogen according to the Lunar Prospector neutron spectrometers. Following four minutes behind the EDUS, LCROSS will fly through the impact plume, using its 5 cameras (1 visible, 2 Near IR, 2 Mid IR), three spectrometers (1 visible, 2 NIR), and one photometer to search for water ice. Impact Site Candidates: Four south-pole regions are currently candidates for the LCROSS impact (Fig. 1): Shoe-Several north pole craters are currently under consideration as well (A-F, Fig. 2). Site Criteria and Characterization: Target selection will be key to the success of this mission. The constraints on the impact site selection are: (1) The ejecta plume must be observable by ground-based and orbital observatories. (2) The ejecta must be illuminated by sunlight, since the instruments primarily measure reflected light. (3) The target should have known surface properties (low roughness and slopes, deep regolith cover.) (4) The target should be in a permanently shadowed region with an observed concentration of increased hydrogen, which could indicate the presence of water (Fig. 3) [2]. The first two criteria depend on the angles between the moon and the earth, and the moon and the sun, respectively. These criteria are set by the orbital motion of the bodies, and thus are determined at any given site by the impact date and time. Some impact dates will not provide acceptable viewing and lighting conditions for any impact sites. Other dates will provide acceptable viewing …