The choice for NASA's next lunar mission, to be announced on Monday, will be the "Lunar Impactor" proposed by the Jet Propulsion Laboratory. The probe will crash at several thousand km/hour into the lunar surface and hopefully into one of the permanently shadowed craters located near the south pole. The resulting impact debris thrown up will provide additional information on the amount of ice that is thought to be mixed into the lunar soil there. The resulting cloud of water vapor from the vaporized ice would be detected by Lunar Reconnaissance Orbiter's LAMP (Lyman-Alpha Mapping Project") instrument. LAMP will look for the ultraviolet glow produced by water vapor struck by solar ultraviolet light as it rises out of the shadowed part of the crater. Many of LRO's other instruments could then quickly inspect the fresh crater interior for any sign of exposed water ice. The craft's "Mini-RF" imaging radar -- designed to map shadowed regions for traces of surface ice -- could have a high enough resolution (several dozen meters) to detect a concentration of ice in the small impact crater's bottom, while the LRO's onboard infrared laser altimeter may be able to detect a frost-brightened crater bottom. A similar American imaging radar on India's "Chandrayan-1" lunar orbiter, already scheduled to orbit the Moon at the same time as LRO, could provide additional confirmation -- especially since the two radars are even more sensitive when working together, with one transmitting while the other receives. And a high-resolution American imaging near-infrared spectrometer also riding on Chandrayaan -- the Moon Mineralogy Mapper -- may also be able to detect exposed crater ice using small amounts of scattered light. LRO's onboard neutron spectrometer and the LAMP instrument might also have a chance of detecting any uncovered local concentrations of below-surface water ice in the crater. In short, while the Lunar Impactor is probably the simplest of the four final proposals for the LRO's piggyback spacecraft, it offers potentially the biggest scientific rewards. This is especially true if the percentage of ice actually on the exposed normal surface of the Moon in such shadowed craters turns out to be rather low, and there are much more concentrated layers a short distance below the surface, as some scientists think possible. The main Lunar Reconnaissance Orbiter (LRO) will initiate a new phase of unmanned exploration of the Moon that forms the first phase of the Bush Administration's "Vision for Space Exploration" that aims to return humans to on the Moon by 2020 in a much more intensive, permanent and science-oriented way than the Apollo program of the 1960s and early 70s. The primary goal of LRO will be to map the entire lunar surface in unprecedented detail, studying the dangers of the lunar radiation environment, and very intensively studying the permanently shadowed craters near the north and south poles to confirm initial indications that there may be significant amounts of water ice mixed with the lunar soil there, which is not only scientifically important but could be an extremely important resource for any long-term human colonization of the moon. LRO was to be launched by a Delta 2 booster. But in December 2005 -- due to the fact that Delta 2 uses a spin-stabilized third stage the decision was made to launch it instead on an Atlas 5 or Delta 4 booster. These, however, are so much more powerful than Delta 2 that this move left an additional 1000 kg of spare mass that the booster could also launch to the Moon. And so, in late January, NASA asked its 10 regional field centers to submit proposals for a piggyback spacecraft-- costing no more than $80 million -- that could be launched at the same time. Nineteen proposals were submitted, and in late February four were selected as finalists. The final selection - which SpaceDaily understands to be JPL's lunar impactor will be official announced at a press conference from NASA Headquarters at 2 PM EDT on Monday.