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 LCROSS - Lunar CRater Observation and Sensing Spacecraft
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Lunar CRater Observation and Sensing Satellite (LCROSS)

Methods of Water Ice and Water Vapor Detection

LCROSS used several independent methods for the detection of water ice and water vapor, as well as studying the ejecta environment:

  1. Ice: Near-IR spectroscopy of the scattered sunlight absorption (fundamental and overtone) features of water ice in situ
  2. Vapor: Near-IR spectra of H2O vapor (sublimed ice) emission bands (overtone vibration bands at 1.4 and 1.8 um) in situ, and of fundamental bands near 3 um from ground-based 10 m class telescopes
  3. Measurement of an extended OH- atmosphere via spectroscopy at the 308 nm OH- band at UV-visible wavelengths along with nearby scattering continuum
  4. Spectroscopy covering the 619 nm H2O+ band and adjacent scattering continuum
  5. Narrow band imaging at mid-IR wavelengths to follow thermal evolution of plume and newly deposited regolith, which will be affected by water vapor in the ejecta.
Table 1 LCROSS Measurements
Product Measurement Time Scale Spatial Scale Observation “Platform”
Water ice in plume
0.1–10 km
Water vapor in plume
1-100 km
S-S/C, Ground Based, LRO
Water ice in fresh ejecta
1-100 m
S-S/C, LRO, Chandra
Plume properties
0.1-10 km
S-S/C, Ground Based
Regolith properties
1-100 m
S-S/C, LRO, Chandra

Combining multiple independent measurement methods greatly increases the likelihood of obtaining a constrained and definitive understanding of the impact event and the amount of water contained in the regolith. Furthermore, many of these measurements, because of their instrument requirements or the timescale of the physical process, are more effectively made either from a platform very near the event (e.g. the S-S/C) or from ground-based telescopes. Combining measurements from the Shepherding Spacecraft (S-S/C) with ground-based observations and (subsequent) mapping by lunar orbiting assets (e.g., LRO and Chandrayaan-1) enhances the overall robustness and effectiveness of the LCROSS. Table 1 lists the various measurement techniques, the time and spatial scale best suited to each observation, and where the measurement can be made. LRO’s UV, IR and topographic mapping of the impact craters and associated ejecta blankets may provide additional information about water ice and other volatiles in the permanently shadowed regolith together with an evaluation of the mechanical properties of lunar regolith in permanent shadow. Similarly, a possible visit to the craters by follow-on missions will provide detail down to the cm scale for further analysis.

Technical Information
Overview | Mission Rationale | Spacecraft and System Description | Instrumentation | Water Detection | Targeting

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Editor: Brian Day
NASA Official: Daniel Andrews
Last Updated: October 2010