The spacecraft is expected to make touchdown at about 9 pm local time (1830 IST), the mission's official microblogging page said, 12 days after Chang'e-3 blasted off on a Long March-3B carrier rocket.
    
China is aiming to become the third country to carry out a rover mission, following the United States and former Soviet Union, which also made the last soft landing on the moon 37 years ago.
    
"At about 9pm, Chang'e-3's probe will carry out a soft landing on the Moon," the Chinese Academy of Sciences (CAS) said in an online post written for the official Chang'e-3 page on Sina Weibo, a Chinese version of Twitter.
    
State broadcaster China Central Television (CCTV), who had earlier said on its microblog the landing was scheduled for 9.40 pm, had posted a later message saying it would be at 9 pm.
    
The probe is expected to touch down on an ancient 400-kilometre (250-mile) wide plain known in Latin as Sinus Iridum, or The Bay of Rainbows.
    
The landing -- which is expected to be carried out independently by the spacecraft -- was described as the "most difficult" part of the mission by CAS in an earlier post on Chang'e-3's Weibo page.
    
The landing craft uses sensors and 3D imaging to identify a flat surface. Thrusters are deployed 100 metres (330 feet) from the lunar surface to gently guide the craft into position.
    
The probe, which is also fitted with shock absorbers in the legs to cushion the impact of the landing, will "free-fall" for the crucial final few metres of descent.
    
"Chang'e-3 is completely relying on auto-control for descent, range and velocity measurements, finding the proper landing point, and free-falling," a post on Chang'e-3's Weibo page said.
    
"At this stage, the Earth base is effectively powerless, and there is only about 10 minutes to finish the process." The landing had "practically zero" chance of manual intervention, according to sources cited by a news agency.
    
The sources also warned that "unknown features such as lunar rocks, pits and entrenchments might still influence the outcome of the landing", Xinhua said.
    
Karl Bergquist, international relations administrator at the European Space Agency (ESA), who has worked with Chinese space officials on the Chang'e-3 mission, said the key challenge was to identify a flat location for the landing.

(Agencies)

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