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Imaging Radars for Exploring the Lunar Poles

The existence of ice in the polar cold traps of the Moon has long been an intriguing possibility. The Clementine spacecraft conducted a radar bistatic experiment in 1994, which supported the idea of an ice deposit within Shackleton crater, near the south pole. However this result generated controversy and there is still disagreement whether observed polarization anomalies are due to ice, particularly from the Earth based radar community. However there is no argument related to the discovery by Lunar Prospector of enhanced hydrogen levels in the polar regions. The question is whether this hydrogen is in the form of water ice. Ice deposits would represent a significant potential resource for the manned human base that is to be set up at one of the Moon's poles late in the next decade.

The Mini-RF (MiniSAR), designed and built in collaboration with USRA's Lunar and Planetary Institute, the U.S. Navy, and the Applied Physics Laboratory at Johns Hopkins University, is a miniature orbiting Single Aperture Radar imaging instrument capable of measuring signals at two different wavelengths. By mapping the dark areas near the poles and determining the backscattering properties of these surface materials, the instrument will place firm constraints on the nature and occurrence of water ice deposits on the Moon.

The instrument is flying on India's Chandrayaan-1 that was launched October 2008. A second instrument was included on NASA's Lunar Reconnaissance Orbiter (LRO) mission that launched to the Moon in June 2009. Each Mini-RF instrument consists of electronic boxes, and an antenna. The combined mass of these items for Mini-SAR on Chandrayaan-1 is about 7 kilograms while the Mini-RF instrument on LRO weighs approximately 13 kilograms.

Mini-SAR on Chandrayaan-1 collects strips of data over the lunar poles. Each strip is 8 kilometers wide and either 300 or 150 kilometers long. Polar mosaics covering from 80° latitude to each pole by combining hundreds of these individual strips. Mini-RF on LRO will make targeted observations of exciting areas discovered by the Chandrayaan-1 instrument, using its advanced capabilities to investigate ice deposits.

Data will be analyzed to search for ice deposits in the floors of the permanently shadowed craters, as well as to learn more about the impact cratering process on the Moon.