(Source: China News)
China will be only the third nation to achieve a soft lunar landing, joining the U.S. and Russia, if it succeeds

Forget the mile high club, the Lunar lander club is a truly elite group.  Only two countries -- the U.S. and Russia -- at the height of their Cold War era prowess managed to land a Lunar rover.  Russia required 21 launches, including 11 failed lander launches, before it accomplished a soft landing with Luna 9.  

I. The Launch

China is trying to achieve a soft landing in only 3 launches; and its efforts may be as much as three years ahead of schedule.  We already chronicled the history of China's overachieving space program, which was born in the early 1990s under later Prime Minister Deng Xiaoping administration.

On Dec. 2, the China National Space Administration (CNSA) launched its first attempt at a Lunar soft landing.  The probe -- Chang'e 3 -- took off from the Xichang Satellite Launch Center.

The Chang'e 3 orbitter -- named after the mythical Chinese goddess who in traditional Chinese legends lived on a palace on the Moon -- is being carried onboard a Long March 3B Y-23 rocket. 

First fielded in 1996, the Long March 3B is the world's second most capable launch platform, at present, behind only Russia's Proton rockets.  It has only failed a pair of times in 10 launches (once fully, and once partially, early in testing); a heavier followup 2007 design, the 3B/E, has never failed in 15 launches.
Long March 3B
China's Long March 3B [Original Source: Unknown]

The Long March 3B is boosted initially by four strapped on boosters rockets which contain N2O4 (nitrogen tetroxide) and UDMH (unsymmetrical dimethylhydrazine) (the same chemistry used by Russia in its Proton boosters).  The main rocket has three stages; the first and second stage to detach also use a N2O4/UDMH mix; the third stage uses a mixture of hydrogen (H2) and liquid oxygen (O2) fuel.

The Long March 3B is capable of carrying payloads of up to 5,100 kg (11,000 lb) into Earth orbit.  The launch vehicle -- containing both the orbitter and the lander -- is only 3,800 kg, to allow it to escape Earth orbit.  The lander is 1,200 kg (2,600 lb), while the rover is 120 kg (260 lb), for a total landing weight of 1,320 kg (2,860 lb).

China Chang'e 3 launch
The Moon probe launch was succesful late last week, but debris destroyed at least one unoccupied Chinese home. [Image Source: Getty Images]

The launch was not without incident.  As is often done in these launches, villages in the rocket's trajectory were evacuated as a precaution in case debris fell during the launch -- a lesson that China learned the hard way after the initial failure of the first Long March 3B rocket showered a village with debris, killing several people.
China Chang'e 3 launch plan
China's Chang'e launch will use the three-stage Long March 3B rocket. [Image Source: China News]

The evacuation of villages in the Hunan province proved fortunate as a number of debris showered down on local villages as the first stage of the rocket fell off.  One piece was the size of a desk and destroyed a home, Donnie Darko-style.  Fortunately, no one was home, thanks to the evacuation.

China Chang'e 3 path
China Chang'e 3 launch path and planned orbit [Image Source: China News]

The launch itself, however, was not affected by this ejection.  Below is video of the launch and early engine firing video,

It went off without a hitch, and four days later on Dec. 6 (last Friday) the lander + orbitter entered Lunar orbit. 

China Chang E
Chang'e 3 reached orbit last Friday. [Image Source: Xinhua]

China's space agency has been preparing ever since for the Lunar landing.

II. The Landing

The landing follows the traditional thuster assisted strut-based approach that previous U.S. and Russian missions used.

The lander itself is powered by a radioisotope heater unit (RHU), which both powers the onboard hardware (instruments, communications equipment) and keeps the onboard circuitry from contracting and being damaged by the frigid Lunar night, which even at the warmest region (the Lunar equator) can reach 123 K (-150 ºC) [source].  CNN is reporting that temperature in the crater-plane dips to just 93 K (-180°C; -292°F) at night.

The Chinese lander is expected to touch down in the "northern" crater-plane Sinus Iridum (Bay of Rainbows), which features basalt soil.

Sinus IridiumSinus Iridium
Sinus Iridium, the expected northern landing site [Image Source: NASA]

The landing attempt will occur tomorrow at around 3 p.m. GMT (10 a.m. EST).

Post-landing the order of activities (according to's translation of the below image) will be:
  • Deploy solar panels
  • Establish communications
  • Unlock rover
  • Deploy rover mast and panels
  • Create panorama for rover navigation
  • Move to surface (about 350 minutes)
  • Do local exploration (about 30 minutes)
China Chang'e 3 landing
Chang'e 3's landing plan [Image Source: China News]

If the landing is successful (as mentioned Russia and the U.S. failed in initial soft-landing attempts) the lander will deploy the rover, which is named Yutu, which means "Jade Rabbit" (roughly) in Chinese.  The name comes from a white bunny who in Chinese legends was a pet of the Lunar Godess.

Chang'e 3 render
Chang'e 3 and Yutu are shown in a render. [Image Source: CNSA]

The rover is expected to explore a 3 km2 area during the 3-month mission, digging up soil, analyzing soil samples, and transmitting real time video during its daytime travels.  The rover is powered by a solar panel and stands 1.5 m (4.9 ft).
The rover descends
An artist rendering of the rover rolling out of the lander. [Image Source: China News]

Perhaps the most crucial aspect of the rover's onboard equipment will be the ground penetrating radar, which will be able to study the depth and structure of the lunar soil, up to a depth of 30 m (98 ft). 
China Chang E explained
Jade Rabbit is a digger. [Image Source: The Hindu Times]

The radar is also expected to penetrate down several hundred more meters into the lunar crust, giving new insight into the composition of the Moon.  The chemical composition of soil dug up by the rover will be examined using an alpha particle X-ray spectrometer and an infrared spectrometer.
Chian Yutu Rover
An artist rendering shows Yutu roving the Lunar plain. [Image Source: CNSA]

The lander will use extreme UV cameras to study the affects of solar activity on the ion layer surrounding the Earth.

The U.S.National Aeronautics and Space Administration (NASA) is expecting the landing will interfere with its Lunar Atmosphere and Dust Environment Explorer (LADEE) experiment, but may offer some interesting insight into how water from probes compares to observed Lunar water deposits believed to be native.  LADEE and the U.S. Lunar Reconnaissance Orbiter (LRO), which the U.S. launched in 2009, will observe the landing from orbit.

III. What Came Before

It's been just six years since China launched its first Moon mission.  In 2007 China achieved its first major Lunar milestone, successfully launching an orbiter -- Chang'e 1 -- which used a laser altimeter to produce the most accurate 3D map of the Lunar surface to date while it orbitted 100 km above the Lunar surface.  At the end of the mission, China directed it into a controlled crash on the Lunar surface.

Chang'e 1
Chang'e 1 orbited the Moon for over a year before being directed into a controlled crash.
[Image Source: China Daily]

In 2010 a second Lunar orbiter, Chang'e 2 carried out a similar orbital mission, flying in a 100 km orbit.  It cut Chang'e 1's travel time from 12 days to 5 by adding to more boosters to its delivery rocket.  It also added an even more precise laser altimeter, capable of mapping the lunar radius to 5 meters and more points of data thanks to a 5 fps (frames per second) pulse resolution (versus 1 fps for its predecssor).  Its main camera was bumped to a resolution size of 10 meters, versus 120 m in the original.

Chang'e 2's high resolution map can be explored here.  It's in Chinese, but you can use Google Translate to translate terms in the features drop down (planes, landing sites, etc.)

Here's some handy comparison images with the LRO.

China LRO v. Chang'e 2

LRO v. Chang'e 2

LRO v. Chang'e 2
(Top images are Chang'e 2, with the low-res parts coming from the camera, prior to laser-scanning; lower images are from LRO.) [Image Source: via NASA/CNSA]

After effectively serving as a scout for potential landing sites of Chang'e 3, Chang'e 2 successfully boosted out of Lunar orbit.

Chang E 1 and 2
Chang'e 2 was bigger, better, faster, [and] stronger than Chang'e 1. [Image Source: China Daily]

It completed a fly-by of the asteroid 4179 Toutatis, an asteroid that frequent crosses near the Earth's orbit and is expected to come very close to the Earth in 2069.  The asteroid has an estimated mass of 5e13 kg -- roughly the mass of a 3 km high mountain.

The fly-by occured at the Earth-Sun L2 point, and the Chang'e 2 probe passed within 3.2 km of the asteroid.  The asteroid is about 4.5 km at its widest point.

Asteroid 4179
3D models of 4179 Toutatis [Image Source: Wikimedia Commons]

Should it ever collide it will likely split into two roughly 2 km chunks of porous sedimentary rock, each of which would produce a roughly 200,000 megaton explosion, producing two roughly 20 kilometer impact craters, according to calculations made via the Imperial College of London and Purdue University online impact calculator.

That's not likely enough to cause the extinction of man (by contrast the dinosaur-killing asteroid that made the Chixulub crater in the Yucatan had an estimated impact energy of 100 million megatons -- or roughly 500 times more energy.

China became only the fourth space agency to do a fly-by on an asteroid.  NASA, the Japanese Aerospace Exploration Agency's (JAXA), and the European Space Agency (ESA) have all performed similar fly-bys.  China's fly-by was the closest for a non-landing mission.

Chang'e is currently travelling in deep space away from Earth, approaching 1e8 km (~0.67 AU) away next year.  It is expected to reach about 3e8 km away from Earth (2 AU) -- putting it close to the asteroid belt and midway between the Earth and Jupiter.  This deep space mission is serving as a test for China's deep space communications technology, which could be used for future missions to Mars, the Asteroid belt, or Jupiter's moons.

The Chang'e probes are built by the state-owned contractor China Aerospace Science & Technology Corp. (yes, the Chinese gov't contracts itself). Chang'e 1 was estimated cost CN¥1.4B ($230M USD); Chang'e 2 cost CN¥900M ($148.2M USD).  The cost of the Chang'e mission has not yet been revealed, according to China's Xinhua news agency.

(A point of comparison: the LRO cost U.S. taxpayers roughly $580M USD, more than twice the cost of either probe.)

IV. What Comes Next

A backup to Chang'e 3 (Chang'e 4) is schedule for a 2015-2016 launch.  After the soft landing, the next major step in Chinese Lunar exploration will be the Chang'e 5 mission, which will try to return Moon rock samples to Earth.

China Yutu
A mockup of Yutu is displayed to the press. [Image Source: Facebook/HuffPost]

While the U.S. achieved manned Lunar sample collection, only Russia achieved robotic Lunar sampling, with its Luna 16, 20, and 24 missions.  Luna 24 (1976) collected the most rock of the three missions -- but only about 170 g.  While the Chinese lander won't collect as much as American manned missions did (up to 111 kg), it will substantially surpass the Russians, collecting (at least) 2 kg.

A Chang'e 5 mockup
A Chang'e 5 mockup [Image Source: China Daily]

That mission, which will use the heavier Chang Zheng 5 next-generation rocket will also operate slightly differently from its manned/unmanned foreign predecessors in terms of Earth return.  The Russian sample rockets launched directly to Earth. 

The Chinese lander module will deorbit similar to the Apollo landers, redock with an orbiter and returning to Earth.  However, unlike the U.S. missions, which required manned manual docking, the planned lander will automatically robotically dock with the orbitter, a first in Lunar exploration.

Sources: Xinhua, CNN, CCTV on YouTube, [NASA impact]

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