A Great Place to Rove: Sinus Iridum and Chang'e 3

China will launch it's third unmanned lunar probe very early in December. Plans for Chang'e 3 include the first soft landing on the Moon since 1976 and the first rover since 1973. The China National Space Agency (CNSA) has long reported the target for this historic mission is Sinus Iridum, "the Bay of Rainbows," on the northwestern frontier of Mare Imbrium.

Meanwhile, following five years of planning, the NASA orbiter LADEE has begun a 100 day examination of the Moon's tenuous exosphere, its formal science mission, in low equatorial orbit. It's all but certain both missions will be underway at the same time, leading some to jump to conclusions in reporting the two missions will interfere with one another. But, as Dr. Paul Spudis of the Lunar and Planetary Institute reports, nothing could be further from truth. Read his assessment, HERE.
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Sinus Iridum - it is likely China will land a rover near Laplace A before the end of 2013. (Arrow shows location of the Soviet Lunokhod 1), LROC Wide Angle Camera mosaic field of view 360 km [NASA/GSFC/Arizona State University].

Mark Robinson
Principal Investigator
Lunar Reconnaissance Orbiter Camera (LROC)
Arizona State University

In the near future China will attempt a robotic landing on the Moon, and will deploy a rover. The launch date and landing dates have not been officially announced. The exact landing spot is also not yet publicly designated, but it seems likely the landing will take place in Sinus Iridum, possibly near the fresh crater Laplace A (8 km diameter).

Why this particular spot on the Moon? Likely there are critical engineering constraints in terms of landing site selection as well as important science goals. And there is the dramatic grandeur of the lunar landscape!

Imagine the first rover-eye view from the crater rim - a sheer drop of 1600 meters at your wheels, and an 8 km view across to the far wall! From LROC NAC images we know rock is exposed in the upper walls and dramatic landslides streamed material down to the crater floor. Speaking of the crater floor - it hosts a now frozen lake of impact melt 2500 meters (1.5 miles) in diameter. Imagine the moments after the crater formed, the floor was a cauldron of molten rock with debris sliding down into the melt, and the crater itself was deforming as the floor uplifted after the initial pressure of the impact was relieved.

Laplace A crater and nearby wrinkle ridge (diagonally across at lower right). The question mark shows a potential landing site from which the rover could traverse northwest across the ridge to the edge of the crater [NASA/GSFC/Arizona State University].

Laplace A is a fascinating scientific target for a rover. It is a great example of a very young crater formed in mare basalt. A rover traversing the crater's ejecta blanket is in essence similar to driving down into the crater (in a geologic sense). We know from studies of terrestrial impact craters (such as Meteor crater) that material ejected from deep in a crater ends up near the rim, and rocks from the pre-impact surface are thrown far from the crater (a crater radius or more). So as a rover drives closer and closer to the rim it can characterize rocks from deeper and deeper below the surface.

Some of the many outstanding questions regarding the nature of the mare basalts include: how thick are individual flows, does the composition of the erupted magma change with time and location, and are pyroclastic (explosive) eruptions intermingled with effusive eruptions? These questions can be directly addressed with the Chang'e 3 rover! No humans or robots have ever visited a fresh crater anywhere near this size on the Moon (or Mars for that matter) so the return from this mission has great potential for advancing our knowledge of the Moon.

LROC NAC view of the interior of Laplace A crater [NASA/GSFC/Arizona State University].

But wait, there's more!

Another key question can be addressed: what is the 3D nature of large contractional ridges on the Moon? The rover is thought to have a ground penetrating radar (GPR) and it just so happens that a large wrinkle ridge (a contractional landform) lies about 10 km east of Laplace A. Although the exact mission plan is not publicly available, one potential scenario is that the lander sets down just east of the wrinkle ridge and deploys the rover. After initial testing of the lander and rover, and geologic characterization of the landing site, the rover could set off to the west towards the crater. As the rover drives up and over the wrinkle ridge the GPR would continuously probe the subsurface, slowly building up a 3D profile down to 100 meters or more (?) beneath the surface. Wrinkle ridges are complex landforms created when mare basalts are compressed, causing them to buckle and break along faults. However, wrinkle ridges have not been fully explored, and the  geometry and number of faults associated with each wrinkle ridge is not known. A subsurface profile of a wrinkle ridge could tell us the number of faults, where the faults are located, and how steeply the faults dip: is it 15°, 30° or 45°?

Laplace A as plotted using photography and digital terrain model gathered from the CNSA orbiter Chang'e 2 [CNSA/CLEP].

From LROC images we have mapped the location of all the mare wrinkle ridges, and measured their surface topography, but all we have for the subsurface are models! Soon we may have actual measurements providing a good first step towards interpreting these poorly understood features. Wrinkle ridges are also found on Mercury and Mars, so better understanding a lunar example will help scientists unravel the tectonic story across the inner Solar System. Since only a handful of human and robotic missions have ever landed on the Moon, the results from the Chang'e 3 mission will provide important new scientific insights into our Moon.

Full resolution segment of the west wall and rim of Laplace A by Chang'e 2 [CNSA/CLEP].

Once Chang'e 3 has landed, LROC should be able to spot the lander and the rover; LRO will be above Laplace A on 25 December, 22 January, and 18 February.  The LROC team looks forward to posting images of the two vehicles!

Coincidentally, Lunokhod 1 landed only 250 km to the southwest of Laplace A over forty years ago (17 November 1970). This intrepid Soviet rover explored for almost a year and traveled a total distance of 10.5 km. Both the lander vehicle (Luna 17) and the rover can be seen on the surface today.

Perhaps the Chang'e 3 lander and rover will look something like this. Lunokhod 1 rover in its final parking place (38.315°N, 324.992°E) on the surface of Mare Imbrium, 250 km southwest of Laplace A. The Soviet rover, and its French-built laser range reflector array, were lost for four decades until relocated by LRO. The addition of the LLR to astrophysicists on Earth critically improved the accuracy of measurements of the distance to the Moon, bringing the uncertainty to within 3 millimeters. LROC NAC observation M175502049RE, spacecraft orbit 10998, resolution 33 cm per pixel. Original LROC Featured Image, HERE [NASA/GSFC/Arizona State University].

Explore the LROC Featured Mosaic of the Laplace region of interest, HERE.

Related Posts:
Lunar Laser Ranging: The Millimeter Range (November 19, 2013)
'Government landing penalty' removed from Google Lunar Xprize terms (November 7, 2013)
Chang'e 3 and LADEE: The Role of Serendipity, Paul Spudis (October 31, 2013)

LROC: Outcrops in Laplace A

Debris flows and outcrops exposed in the walls of Laplace A crater, offset from Sinus Iridum. Illumination from southwest over a field of view (FOV) approximately 525 meters across, down-slope to the right. LROC Narrow Angle Camera (NAC) M137725771R, orbit 5430, August 29, 2010; incidence angle 52.91° with a resolution 0.52 meters per pixel from 49.72 kilometers. View the original LROC Featured Image HERE [NASA/GSFC/Arizona State University].

James Ashley
LROC News System

As with many mare deposit exposures when viewed at the Narrow Angle Camera imaging scale of 0.5 m/pixel, the bedrock outcrops in the walls of Laplace A appear as layered ledges. The layers are most noticeable in the north-northeast to south-southwest trending rocks visible in the northeast quadrant of the frame. Additional indications of layering can be found in the full NAC image. 

The prominent V-shaped outlines to some of the outcrops are suggestive of constructional deposition. Granular debris flows cascading down the crater walls following excavation appear to have encountered the obstructing ledges and "dammed up" behind them. Resistance to flow in such situations takes on a tapered shape in the direction of flow as the material becomes compacted. Minor occurrences of impact melt may be contributing to the smooth appearance of the flow deposits between the outcrops.

Featured Image FOV in context of the full 2.5 kilometers wide LROC NAC frame M137735771R [NASA/GSFC/Arizona State University].

The north wall of Laplace A is similarly characterized by the outcrops visible in very high resolution in the LROC NAC frame. The crater and surrounding Sinus Iridum were closely examined as a likely landing site for the Chang'e 3 mission by 2014 by China's lunar orbiter Chang'e 2. Nine kilometer-wide Laplace A (43.64° N, 333.33°E) is a familiar nearside feature because of its place in the largely "featureless" landscape along the frontier of the northwest Mare Imbrium and Sinus Iridum. The crater excavated Imbrium mare over the inundated "missing" southeastern outer ring of the Iridum impact zone. A rewarding 7000 pixel-wide, very detailed version of the image is available from tantaonews.com [CNSA/CLEP].

Nine-kilometer Laplace A is a familiar nearside feature in the mare where Sinus Iridum meets Mare Imbrium. If you have access to a small telescope, it is a challenging target for the eyepiece best viewed two days after First Quarter or a day after Last Quarter. Context information for the LROC NAC Featured Image and the Chang'e 2 study from LROC Wide Angle Camera (WAC) observations gathered during last August's low periapsis period (from an average 33.06 kilometers, at a resolution of 47.6 meters per pixel), orbits 9946 through 9949, August 19, 2011 [NASA/GSFC/Arizona State University].

A 95 km-wide FOV from the WAC monochrome (566 nm) mosaic collected over 4 orbital passes, August 29, 2011 [NASA/GSFC/Arizona State University].

Additional examples of both layering and debris flow in crater wall exposures can be found in the following Featured Image posts: Dawes, Pytheas, and Layering in Messier A.

The apparent isolation of Laplace A (center right) is misleading in this HDTV still of Sinus Iridum, embayed by the vast northwest floor of Mare Imbrium, though there is an authentic paucity of similarly-sized craters in the vicinity, unlike the lunar Highlands. HD video captured by Japan's lunar orbiter SELENE-1 (Kaguya) in 2009. A larger version of this frame can be viewed HERE [JAXA/NHK/SELENE].

On the shore of the Bay of Rainbows

A pair of small craters show different albedos within a spectacular ejecta display along the shore of Sinus Iridum (47.9°N, 31.7°W). LROC Narrow Angle Camera (NAC) observation M104726204L, LRO orbit 591, August 12, 2009; incidence angle 65°, Sun is from the southwest, resolution 1.71 meters per pixel (Field of view < 1 km). View the full size LROC Featured Image HERE [NASA/GSFC/Arizona State University].

James Ashley
LROC News System

In addition to being a spectacular example of a recent impact feature, this pair of small craters was chosen with the small backyard telescope in mind. You won't be able to see this impact feature in your eyepiece, but you should be able to locate the region fairly easily. By the 11th day following a new Moon (during the waxing gibbous phase), Sinus Iridum (the Bay of Rainbows) is ideally illuminated and visible through even a modest-sized instrument, or even a large pair of binoculars! Look for the large, crescent-shaped arc of mountains on the northwest "shore" (44.1°N, 328.5°E) of Mare Imbrium. You will find the partial remains of an ancient crater (236 km diameter), flooded long ago by Mare Imbrium basalts. The range of peaks is known as the Jura Mountains. With a good eye, you might even see the crater Bianchini, nestled within the range along its northwestern edge. You can use Bianchini with the images below to pinpoint the Featured Image location.

This wider view from M104726204L shows foothills high, mountainous rim of Sinus Iridum, immediately to the north, more than 2 km higher in elevation than the wide bay floor to the south. Note how the ejecta rays were forced to curve as the flying debris encountered the topography just northeast of the larger and more recent impact (field of view ~8.3 km across, downsampled to 2.8 meter/per pixel). See the spectacular full size LROC context image HERE [NASA/GSFC/Arizona State University].

Notice how one of the featured craters has a low-reflectance interior while the other appears more reflective. The low-reflectance crater is roughly twice the size of the light-floored crater, and therefore excavated to a greater depth. Could this have resulted in the exposure of darker, buried materials that were missed by the less-energetic impact? There are many questions that we could ask about this interesting pair: Which impact happened first? Is there ejecta from one crater on the floor of the other? Why or why not? 

What other clues would you look for in the full NAC frame?

The 39 km-wide crater to the upper left of the Featured Image location (yellow arrow) is Bianchini in this LROC Wide Angle Camera (WAC) mosaic showing a roughly 300 km field of view. See the richer, original LROC WAC context image HERE [NASA/GSFC/Arizona State University].

Related posts include:
Dark-haloed crater in Mare Humorum
Dark-haloed crater near Censorinus A
Sinus Iridum - Next Destination?

LROC: A Strategic Overhang

An outcrop in the south wall of an unnamed rille on the edge of Sinus Iridum, immediately north of the Promontorium Heraclides, may form an overhang. Image field of view 400 meters, LROC Narrow Angle Camera (NAC) Observation M124790534R, LRO orbit 3524; from 38.22 km altitude, April 1, 2010. See the full-size LROC Featured Image release HERE [NASA/GSFC/Arizona State University].

Lillian Ostrach
LROC News System

Sinuous rilles are frequent in the mare-filled basins on the Moon and reflect erosion caused by turbulent, very hot lava extruding from a vent. Oftentimes, sinuous rilles meander in tight twists and turns. However, there are exceptions to the "general rule" of sinuous rilles and today's Featured Image of an unnamed rille near Promontorium Heraclides (41.07°N, 326.49°E) may be one such example. Less than 10 km long, the rille is linear with one gentle twist. The opening image highlights a portion of the southern wall of this rille, where rocks outcrop from the rille walls. The rocks jut out from the wall, forming a jagged shadow with illumination from the lower right, and there is abundant debris on the floor that likely represents eroded wall material. It may be that this outcrop is the ceiling of a slight overhang into the rille. If this is the case, obtaining rock samples from beneath the overhang would be useful in order to ascertain exposure ages of rocks in the outcrop compared to those beneath.

For context, a full-width view of the LROC NAC frame M124790534R shows a center slice of the unnamed rille featuring a possible overhang at a stratigraphic crossroads on the southern edge of Sinus Iridum and Mare Imbrium.

Promontorium Heraclides and the unnamed rille as viewed through a LROC Wide Angle Camera (WAC) monochrome (643 nm) mosaic swept up over orbits 6477-6480, November 19, 2010. Field of view is roughly 30 km-wide [NASA/GSFC/Arizona State University].

In addition, measurements of the ancient solar wind could be made from rock samples as solar wind particles are implanted onto the lunar surface.

Promontorium Heraclides in long shadow and higher relief of LROC WAC monochrome (689 nm) mosaic gathered over the course of orbits 2480-2483, January 9, 2010. The long shadows of the promontory and the southern curve of the semicircle of mountains surrounding Sinus Iridum, bring an early late afternoon sunset to the unnamed rille. Mare Imbrium stretches east-southeastward. A larger view of the image cane be seen HERE [NASA/GSFC/Arizona State University].

However, let's not be too hasty! The interpretation of an overhang created by the outcrop is based largely on the presence of the distinct shadow on the rille floor. This image has an incidence angle of ~40°, so the Sun is just a little more than halfway to noon in the lunar sky. Illumination often plays tricks on scientific interpretation, so just because there is a prominent shadow cast by the outcrop does not mean that an overhang truly exists. The best way to determine whether the overhang is real or an illusion is to observe the location under different illumination conditions. Unfortunately for us, the current LROC coverage contains images with incidence angles of ~40° to ~45°, so we are stuck wondering whether this outcrop overhangs the rille walls for the time being.

Can you find any evidence for other outcrops or potential overhangs in the full LROC NAC image?

The mountainous 411 kilometer-wide semi-circumference and interior of Sinus Iridum, on the northeast edge of Mare Imbrium. At lower left is Promontorium Heraclides, marking the border with the Imbrium impact zone. The rest of the original Sinus Iridum crater was presumably destroyed and carried under by the weight of the basalt-flooded Imbrium basin over repeated inundations. An early LROC WAC mosaic released late in 2010 [NASA/GSFC/Arizona State University].

Related Posts:
Discontinuous rilles
Rima Calippus
Sublunarean void!

Chang'e-2 completes lunar mission and departs

Detail from the Digital Elevation Model (DEM) of Sinus Iridum, an area of high interest to the Chinese Lunar Exploration Program surveyed by the PRC's second lunar orbiter Chang'e 2, which has now left the Moon's vicinity and departed for "Outer Space" [CNSA/CLEP].

Deng Shasha
xinhua

Beijing -- China's second moon orbiter Chang'e-2 on Thursday set off from its moon orbit for outer space about 1.5 million km away from the earth, Chinese scientists said Thursday.

The orbiter left its moon orbit at 5:10 p.m. and it will take about 85 days for the orbiter to reach outer space, according to the State Administration of Science,Technology and Industry for National Defence (SASTIND).

The orbiter had finished all its tasks within its designed life span of six months by April 1.

Scientists decided to let it carry out additional exploratory tasks as the orbiter still had fuel in reserve.

Traveling into outer space from the moon's orbit is the most important task among five additional ones, according to the SASTIND.

"It's the first time in the world for a satellite to be set off from the moon in remote outer space," said Zhou Jianliang, deputy chief engineer of the Chang'e-2 measure and control system of the Beijing Aerospace Control Center (BACC).

Moon exploration means about 400,000 km away from the earth, but outer space exploration means 1.5 million km, posing great challenges to the country's technology in measure and control, telecommunications, data transaction and orbit design, scientists said.

Before flying away, the orbiter had finished two additional tasks as of May 23.

One was to take photos of the northern and southern poles of the moon. The other was to descend again to the perilune orbit, about 15 km away from the surface, to catch high-resolution images of the Sinus Iridum, or Bay of Rainbows, the proposed landing ground for future moon missions.

Scientists hope the satellite can continue operations until the end of next year.

Nine kilometer-wide Laplace A (43.64° N, 333.33°E) is a familiar nearside feature because of its place in the largely "featureless" landscape along the frontier of the northwest Mare Imbrium and Sinus Iridum. The crater, also extensively surveyed by NASA's LRO - see links below - has "pre-excavated" Imbrium seabed over the inundated "missing" southeastern outer ring of the Iridum impact. A rewarding 7000 pixel-wide, very detailed version of the image is available from tantaonews.com [CNSA/CLEP].

"We are developing outer space measure and control stations in outer space and they will be capable to carry out tasks by the end of the second half next year," said an SASTIND scientist, who declined to be named.

At that time, the satellite can be used to test the two stations' functions, the scientist said.

Challenges exist as Chang'e-2 was not designed for the additional task and it is now in extended service without extra capacities to deal with abnormal risks, Zhou said.

Meanwhile, long-distance brings many problems like weakening signals and difficulties in measure and control, Zhou said.

The Chang'e probes are named after a legendary Chinese moon goddess who flew to the moon.

Besides the current operations, China's ambitious three-stage moon mission will include a moon landing and launch of a moon rover around 2012 in the second phase. In the third phase, another rover will land on the moon and return to earth with lunar soil and stone samples for scientific research around 2017.

The country has no plan or timetable for a manned moon landing for now.

China launched its first lunar probe, Chang'e-1, in October 2007.

It became the third country after Russia and the United States to send a person into space in 2003. Two more manned space missions followed with the more recent in 2008 involving the country's first human space walk.

Heads Up: Barbara A. Cohen, Marshall Space Flight Center

Related Posts:
Mounds in a Melt Pond
February 24, 2011
Sinus Iridum - Next Destination?
October 16, 2010
Chang'e-2 arrives in mission orbit
October 9, 2010

A different look at 'Target Rainbow'

HDTV still from Japan's lunar orbiter Kaguya (SELENE-1) shows the full semi-circle of Sinus Iridum, the "Bay of Rainbows," and the contact between basalt melt that flooded the ancient crater and Imbrium basin. Yet another look at one of the high-priority areas of interest targeted by China's Lunar Exploration Program (CLEP) as a possible landing site in 2013. China's second lunar orbiter Chang'E-2 arrived in lunar orbit October 6, 2010. Click HERE for full 1920x1080 view [JAXA/NHK/SELENE].

Recent Related Posts:
Sinus Iridum - Next Destination?
Mark Robinson, Saturday, October 16, 2010

Chang'E-2 arrives in lunar orbit
Joel Raupe, Saturday, October 9, 2010

Chang'E-2 arrives alive in mission orbit

Following a third orbital trim, Chang'E-2 has been successfully inserted into it's targeted mission orbit.

Dr. Yong-Chun Zheng of the Chinese Academy of Sciences reported early Saturday (UT) that the third braking of Chang'E-2 was successfully completed at 03:17, October 9 (UT).

"The braking action lasted for about 15 minutes," Zheng said "Chang'E-2 has entered its initial target orbit of 100 x 100km with a period of about 117 minutes."

There was no word yet on when perilune for China's second lunar orbiter will be brought down to as low as 15 km to enable very high resolution surveys of potential landing sites for Chang'E-3 and 4.

'Target Rainbow,' Sinus Iridum, the "Bay of Rainbows," high resolution survey target for Chang'E-2, the second lunar orbiter that entered orbit October 6 after a nominal direct transit after only 112 hours from launch. (As impressive as such navigation still is, contrary to press account, this was not the "fastest" such transit in history.) 411 km-wide Iridum is an announced landing target for the Chang'E-3 stationary lander and rover under development for 2013. From LROC WAC mosaic of 40 observations (see below) during LRO orbits 2469 through 2491, January 9-10, 2010 [NASA/GSFC/Arizona State University].

"In the target orbit, Chang'E-2 will work and explore the lunar surface for about half a year. The topography and material composition of the lunar surface will be measured in the future. During that time, the space environment and microwave thermal emission of the moon will be measured by Chang'E-2."

Instruments on board Chang'E-2 began checking in beginning soon after launch, October 1. Following a 17 second orbital trim Friday, October 8 Chang'E-2 was brought down to an 3.5 hour elliptical orbit.

"The two ground stations in Beijing and Yunnan have recieved the first data sets, amounting to 1.6 Gb," Zheng said. "There are seven scientific instruments on board Chang'E-2," Zheng said. An improved stereo CCD camera, laser altimeter, gamma ray spectrometer (GRS), X ray spectrometer (XRS), Microwave radiometer (MRM), solar wind ion dector (SWID) and high-energy particle dector (HPD).

"The GRS, SWID, HDP were powered up and began work duirng the 112 hour trans-lunar coast. The CCD and MRM will be powered up after Chang'E-2 enters its mission orbit and will begin mapping the topography of the lunar surface.

"Topography data and technology testing," Zheng said, "will be helpful for the soft landing of Chang'E-3.

Chang'E-3, a stationary lander and lunar rover, are under development for launch in 2013. Further along, planning is also under way for Chang'E-4, an unmanned sample return mission in 2017.

Promonitorium Laplace (46.0°N, 314°E), 24.8 x 49.6 km (east at top) full resolution detail from LROC Wide Angle Camera mosaic, January 9-10, 2010. At it's highest point, the cliffs rise 2600 meters over the basin's interior rim [NASA/GSFC/Arizona State University].

Very small thumbnail of the 9184 x 6312 pixel LROC mosaic study of Pre-Imbrium Sinus Iridum from which these smaller-scale higher resolution images were sampled. Iridum is centered near 45.0°N, 32.0°W and has an outer ring and full interior submerged by the northwestern Mare Imbrium basin melt. 39 km Bianchini crater straddles the Jura mountains on Iridum's rim, and Promonitorium Laplace stand out sharply in the long shadows three days following a Full Moon. A small part of Mare Frigoris stretches through the northwest. The landing site of Luna 17 (Lunokhod 1) is well outside the field of view. The entire scene exceeds 1000 km west to east, at an average 62 meters per pixel in full resolution (see below) [NASA/GSFC/Arizona State University].

Dispatch from Chang'E-2: Sinus Iridum

Clementine (1994) Near-Infrared Multi-Spectral Mosaic (USGS Map-A-Planet] view of Sinus Iridum (44.4°N, 330.0°E), the 414 km-wide "Bay of Rainbows" on the northwestern tier of Mare Imbrium (with the lofty Jura Mountains on its west). Xinhua news agency reports the relatively high-latitude feature is the intended target of a low a planned low-perigee, high-resolution survey by Chang'E-2 as the intended target for a planned landing by Chang'E-3 in 2013.

Dr. Yong-Chun Zheng, associate professor at the National Astronomical Observatories, Chinese Academy of Sciences (NAOC) reports from Beijing, "the high energy particle detector (HPD) on board Chang'E-2 was switched a day after Trans-Lunar Injection, "suggesting the scientific instrument has begun working"

"Data transmitted from Chang'E-2, such as the temperature, voltage and power of the HDP, are all within range, indicating the instrument works well."

Chang'E-2 carries seven scientific instruments. "The HPD is responsible for surveying the space environment in the journey from the earth to the moon and space environment near the moon," Zheng said. HPD is one of two instrument stages of the Chang'E'2 Space Environment Monitor System, designed to measure heavy ions, proton spectra and the composition and spatial distribution of low-energy solar wind.

Second of Three Course Corrections Unnecessary

Beijing Aerospace Command and Control Center completed an initial adjustment of Chang'E-2's course at 12:25, October 2 (Beijing time). Further adjustments are expected, but Xinhua has reported that the second of three planned TLC maneuvers had been deemed "unnecessary."

Chang'E-2 was launched at 18:59:57 pm, October 1 (Beijing time) and was directly inserted into an earth-moon transfer orbit. Direct Earth-Moon transfers generally require an initial critical course correction.

"Chang'E-2 needed to slightly change its orbit at the appropriate time," Zheng reports. "If the orbit correction is not on time, the satellite could depart from its correct orbit to the moon and might not be captured by the moon's gravity," which is overwhelmed first by Earth and then, about half the distance to the Moon, by the Sun. "So, for Chang'E-2," Zheng said, "the orbit correction was very important."

Telemetry indicates the Long March 3C booster successfully sent Chang'E-2 into its target course and, "everything is going well," Zheng said. "We give the mission perfect evaluation marks."

"Chang'E-2 needed to slightly change its orbit at the appropriate time," Zheng said. "If the orbit correction is not on time, the satellite could depart from its correct orbit to the moon and might not be captured by the moon's gravity," which is overwhelmed first by Earth and then, about half the distance to the Moon, by the Sun.

China's state news agency Xinhua reported Monday Chang'E-2 is expected to travel a total of 112 hours before lunar orbit insertion.

Xinhua also disclosed the relatively high-latitude Sinus Iridum, the familiar 411 km "half-moon" embayment "Bay of Rainbows," on the northwestern edge of Mare Imbrium is one intended target of the Chang'E-2 survey. "To acquire more detailed moon data, Chang'E-2 will enter a lower lunar orbit about 100 km above the surface (compared with the 200-km altitude of Chang'E-1) according to the control center.

"The satellite will eventually be maneuvered into an orbit just 15 kilometers above the moon. At that point, Chang'E-2 will take pictures of moon's Bay of Rainbows area, the proposed landing site for Chang'E-3, with a resolution of 1.5 meters. The spatial resolution of Chang'E-1's CCD stereo camera was 120 meters, said Wu Weiren, chief designer of China's lunar orbiter project.