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Emily LakdawallaMay 18, 2011

Chang'E 2 to depart for L2 on June 16

According to a story posted on xinmin.xn and run through Google Translate, there's now been an official announcement from China about Chang'e 2's extended mission: it will depart lunar orbit in mid-June and journey to L2. L2 is one of the five Lagrangian points, semi-stable locations in the gravitational landscape of a two-body system; this particular one is on the far side of the Moon from Earth. The article doesn't state what business Chang'e 2 will conduct from L2. My completely-uninformed-by-fact, speculative guess is that the main purpose of the journey to L2 is to gain experience in deep-space navigation.

Lagrangian points

Wikimedia commons

Lagrangian points
From Wikipedia: given two massive bodies in circular orbits around their common center of mass, there are five positions in space where a third body, of comparatively negligible mass, could be placed which would then maintain its position relative to the two massive bodies. As seen in a rotating reference frame with the same period as the two co-orbiting bodies, the gravitational fields of two massive bodies combined with the centrifugal force are in balance at the Lagrangian points, allowing the third body to be stationary with respect to the first two bodies.

The article goes on to state something about Chang'e 2 producing the "world's clearest map of the Moon" at 7 meters per pixel. I think (but am not sure) that this is the first time I've seen a claim for 7-meter-per-pixel global mapping of the Moon, and of course I may be misinterpreting the machine translation of the article. For context, JAXA's Kaguya Terrain Camera stereo-mapped the Moon at 10 meters per pixel; Lunar Reconnaissance Orbiter is doing global mapping at 100 meters per pixel, with detailed images (lacking global coverage) down to 0.5 meters per pixel. A 7-meter-per-pixel global map from a stereo camera would be a cool thing; but I thought Chang'e 2 was not making a global map. In any case no images at all very few images have ever been released from Chang'e 2 so even their quality is unknown. It's hard to get excited about the "world's clearest maps" when those maps are kept secret!

(It's been pointed out to me in the comments that there are some Chang'E 2 images online, though I haven't yet found my way to any full-resolution data. Thanks to the commenters for the correction.)

Thanks, as ever, to a watchful member of unmannedspaceflight.com for the link.

Read more: mission status, Chang'E program

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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