At 9:28 p.m. (EST) on January 6, 1998, Lunar Prospector (LP) blasted off to the Moon aboard a Lockheed Martin solid-fuel, three-stage rocket called Athena II. It was successfully on its way to the Moon for a one-year, polar orbit, primary mission dedicated to globally mapping lunar resources, gravity, and magnetic fields, and even outgassing events. About 13 minutes after launch, the Athena II placed the Lunar Prospector payload into a "parking orbit" 115 miles above the Earth. Following a 42-minute coast in the parking orbit, Prospectorís Trans Lunar Injection (TLI) stage successfully completed a 64-second burn, releasing the spacecraft from Earth orbit and setting it on course to the Moon, a 105-hour coast. The official mission timeline began when the spacecraft switched on 56 minutes, 30 seconds after liftoff. Shortly after turning the vehicle on, mission controllers deployed the spacecraftís three extendible masts, or booms. Finally, the spacecraftís five instruments -- the gamma-ray spectrometer, alpha particle spectrometer, neutron spectrometer, magnetometer and electron reflectometer -- were turned on. On Sunday, January 11, at 7:20 a.m. (EST), Lunar Prospector was successfully captured into lunar orbit, and a few days later began its mission to globally map the Moon.
Lunar Prospector is a small,1.3m in diameter X 1.4m tall bus with three 2.5 meter science masts carrying its five science instruments and isolating them from the spacecraft's electronics, spin-stabilized spacecraft in a polar orbit with a period of 118 minutes at a nominal altitude of 100 km (63 miles). Since the Moon rotates a full turn beneath the spacecraft every lunar cycle (~27.3 days) as it zips around the Moon every 2 hours, Prospector visits a polar region every hour and completely covers the lunar surface twice a month. Prospector's one-year-long primary mission with an optional extended mission of a further 6 months at an even lower altitude enables large amounts of data to collect over time. For some science instruments, a significant amount of time is required to obtain high quality usable data. Thus, Prospector's polar orbit and long-mission time render it ideal from the standpoint of globally mapping the Moon.
Evidence for Water Ice Near the Lunar Poles
Improved versions of Lunar Prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the Moon. Improved spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade. In the north, these regions consist of a heavilycratered terrain containing many small (less than about 10 km diameter), isolated craters. These border circular areas of hydrogen abundance ([H]) that is only modestly enhanced above the average equatorial value, but that fall within large, flat-bottomed, and sunlit polar craters. Near the south pole [H] is enhanced within several 30 km-scale craters that are in permanent shade, but is only modestly enhanced within their sunlit neighbors. We show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently-shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences. We conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules.
Feldman el al. 2001
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