|Rich detail and context is seen in this "medium resolution" image of a familiar part of the complex Aristarchus Plateau from the Lunar Reconnaissance Orbiter (LRO). Prior to a recent mission-conserving transfer to higher orbit, capturing the entire width of the 165 kilometer-long Vallis Schroteri in a single Narrow Angle Camera (NAC) frame was not possible. The maneuver should add some years to the record-smashing mission following three years in an energy-taxing low lunar orbit, and welcome perspectives like this one in a 'middle range' between the best of the orbiter's narrow and wide angle camera catalogs. LROC NAC frame M183861408R, LRO orbit 12190, February 14, 2012; angle of incidence 41.03° at 1.39 meters resolution from 140 kilometers [NASA/GSFC/Arizona State University].|
Other nations can rightly boast of recent accomplishments in low Earth and lunar orbit, and its easy to lament the embarrassing length of time since America sent six manned expeditions to the lunar surface. It might seem a small thing in comparison, and easy to forget, but the United States presently has five vehicles in lunar orbit. Queen among them is the under-rated Lunar Reconnaissance Orbiter.
The LRO will soon celebrate three years in lunar orbit, far longer than any spacecraft in history, and by all accounts the vehicle is healthy and still shy of middle age. It's no small accomplishment maintaining close-lunar orbit precisely for the very reason the twin GRAIL gravity probes, "Ebb" and "Flo," were designed and subsequently dispatched to spy out. The Moon is "lumpy," with mass concentrations putting uneven drag on objects in orbit, and it also dances through a realm of space overwhelmed by the influences of Earth and Sun. To remain in lunar orbit requires skill and fuel, even over robust design.
After more than two years surveying the lunar surface from within 40 kilometers, close enough to photograph the forty year-old footprints of the Apollo astronauts and allowing more than half the Moon to be imaged at high resolution, in 2011 flight directors included two periods when LRO was swept through the 20 kilometer range. It was a last slow dance before the spacecraft was brought up above 100 kilometers.
Eventually, planning requires LRO to be wound down tightly for more unprecedented close-ups before what is hoped will be a controlled impact, good to the last thruster fire. In the meantime, since late last year scientists have been enjoying a "medium range" perspective using the LROC Narrow Angle Camera from a higher altitude.
|It difficult to disparage the quality of this LROC NAC frame of Rima Galilaei and the exposed layering of the surrounding floor of Oceanus Procellarum. This image is a full-resolution crop from LROC NAC M181552312R, orbit 11867, January 18, 2012; angle of incidence 62.51° at 1.25 meters resolution, from 125.4 kilometers altitude. For comparison, from 24.16 kilometers in orbit 9978 the previous August 21, two insets from LROC NAC frame M168584181R show half-meters resolution fields of view of the same region [NASA/GSFC/Arizona State University].|
Soon after LRO arrived in lunar orbit and the first of Arizona State University's LROC Narrow Angle Camera images began arriving back on Earth, Charles Wood, who is the steadfast lunar observer and architect of the Lunar Picture of the Day (LPOD) website, was quick to point out the level of detail and small fields of view seen in those images seemed almost overwhelming. He looked forward to the time, still several months off, when LROC's Wide Angle Camera (WAC) catalog premiered on the Planetary Data System (PDS). He wasn't disappointed. That wider context showed familiar landmarks Wood had long witnessed under every available illumination and focus in ways that were truly new.
These are still high-resolution images, even at less than half their previous detail. A new range of medium resolution photography from the LROC NAC offers a welcome opportunity to continue the long process of digesting the incredible volume of data that's been returned to Earth from what may already be the most cost-effective deep space mission in history.