Backgrounder: China's 'triple jump' progress in lunar probes

BEIJING - The upcoming Chang'e-3 mission will carry the first Chinese spacecraft to soft-land on and explore an extraterrestrial object.

The Chang'e-1 to Chang'e-3 missions have made a "triple jump" between 2007 and 2013.

Chang'e-1: starting from nothing

Blasting off at 6:05 p.m. on October 24, 2007 from southwest China's Xichang Satellite Launch Center, Chang'e-1 entered lunar orbit after 18 days with only one orbital trimming -- the adjustment required to achieve the desired orbit around an object.

On November 12, 2008, a hologram of the whole moon made with data collected by Chang'e-1 was published. It remains the most complete lunar hologram published to date.

At 4:13 p.m. on March 1, 2009, Chang'e-1 hard-landed on the lunar surface.

Chang'e-1 opened up a new age of deep space exploration for China.

Chang'e-2: achieving several world firsts

Chang'e-2, a pilot probe for Stage II of the lunar program, was launched on October 1, 2010 from Xichang, the site from which Chang'e-3 will also be launched in a few days' time.

One of Chang'e-2's tasks was to verify key technology ahead of the soft-landing. Unlike Chang'e-1, Chang'e-2 was sent directly into lunar orbit by a Long March-3C carrier rocket. The transfer from the Earth's orbit to that of the moon was attained in only 112 hours.

On arrival in a circular orbit 100 km over the lunar surface, the spacecraft transitioned to a closer elliptical orbit after finishing in-orbit tests and took a series of 1.5-meter resolution (meaning each pixel captures a 1.5-square-meter area of land) pictures of the moon's Sinus Iridium landmark, the chosen landing site of Chang'e-3.

Wu Zhijian, spokesperson for the State Administration of Science, Technology and Industry for National Defense, said Chang'e-2 achieved several firsts. It was the first time a spacecraft had flown from lunar orbit to the second Lagrange Point (L2) orbit, where the gravity of the sun and Earth balance the orbital motion of the satellite; and the first time a spacecraft encountered the Toutatis asteroid at close range, capturing images with a resolution of 10 meters.

At present, Chang'e-2 is 60 million km from Earth and has become China's first man-made asteroid in the solar system. It continues to fly into deeper space and is expected to go as far as 300 million km from Earth before contact is lost.

Chang'e-3: Soft-landing on an extraterrestrial object

So far, only the United States and the former Soviet Union have soft-landed on the moon. If successful, China will become the third country to do so.

After entering lunar orbit, Chang'e-3 will go through six stages of deceleration to descend from 15 km above to the lunar surface.

The soft-landing processes of the U.S. and former Soviet Union's unmanned spacecraft had no capacity to hover or avoid obstacles. Chang'e-3, on the other hand, can accurately survey landforms at the landing site and identify the safest spots on which to land.

In order to land quickly, the probe is equipped with high-precision, fast-response sensors to analyze its motion and surroundings. The variable thrust engine (completely designed and made by Chinese scientists) can generate up to 7,500 newtons of thrust.

Yutu (Jade Rabbit), the autonomous moon rover which will detach from the lander, will be controlled when necessary by scientists on Earth.