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Sunday, July 05, 2009

New Focus On The Moon

NASA's Lunar Reconnaissance Orbiter Camera (LROC) has taken and received its first images of the Moon, kicking off the year-long mapping mission of Earth's nearest celestial neighbor. The LROC imaging system, under the watchful eyes of Arizona State University professor Mark Robison, the principal investigator, consists of two Narrow Angle Cameras (NACs) to provide high-resolution black-and-white images, a Wide Angle Camera (WAC) to provide images in seven color bands over a 60-kilometer (37.28-mile) swath, and a Sequence and Compressor System (SCS) supporting data acquisition for both cameras.

NASA reports that the Lunar Reconnaissance Orbiter, which launched June 18, is performing exceptionally well and spacecraft checkout is proceeding smoothly, so smoothly in fact that LROC was given an early, but short (two orbits) opportunity Tuesday evening to measure temperatures and background values while imaging. Since LRO is in a terminator orbit, much of the area photographed was in shadows, which is actually a good situation for performing engineering checks of camera settings, according to Robinson, with ASU's School of Earth and Space Exploration. Much to the delight of the LROC team, a few of the images captured dramatic views of the surface.

"Our first images were taken along the Moon's terminator – the dividing line between day and night – making us initially unsure of how they would turn out," says Robinson. "Because of the deep shadowing, subtle topography is exaggerated suggesting a craggy and inhospitable surface. In reality, the area is similar to the region where the Apollo 16 astronauts comfortably explored in 1972. Though these images are magnificent in their own right, the main message is that LROC is nearly ready to begin its mission."

LROC NAC: Two details from one of the first images

LRO was 70 kilometers (43.5 miles) above the lunar surface when the summed mode image was taken, resulting in a resolution of approximately 1.4-meters/pixel (34.4°S, 6.0°W). Incredible levels of detail are visible in these two (1000 pixel-by-1000 pixel) cutouts from the full image (2532 pixels-by-53,248 pixels). The NAC data shown has not been calibrated, and the pixel values were stretched to enhance contrast.

Along the terminator, there simply is not much light – the instrument is "photon-starved," resulting in suboptimal signal-to-noise ratios. Without summing, images taken in this circumstance would be underexposed. To compensate for low light levels, the pixels can effectively be made larger by summing adjacent pixels to increase the signal-to-noise ratio, making the image sharper, though with 2x lower resolution. At this resolution, features as small as three meters (9.8 feet) wide can be discerned.

The NAC image shows a starkly beautiful region a few kilometers east of Hell E crater, which is located on the floor of the ancient Imbrian-aged Deslandres impact structure in the lunar highlands south of Mare Nubium. Numerous small, secondary craters can be identified, including several small crater chains. Also identifiable are distinctive lineations made readily apparent by the extreme lighting, representing ejecta from a nearby impact. The quality of these early engineering test images gives the LROC science team confidence it can achieve its primary goals, including obtaining the data needed to support future human lunar exploration and utilization.

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