China's ailing moon rover Yutu has entered its 11th dormancy as the lunar night falls, with its functions degrading gracefully, its designer said Friday. The rover is currently in good condition and works normally, but its control problem persists, said Yu Dengyun, deputy chief designer of China's lunar probe mission.

"Yutu has gone through freezing lunar nights under abnormal status, and its functions are gradually degrading," Yu told Xinhua at an exclusive interview.

He said that the moon rover and the lander of the Chang'e-3 lunar mission have completed their tasks very well. The rover's designed lifetime is just three months, but it has survived for over nine.

Chang'e-3 mission was the second phase of China's lunar exploration program, which includes orbiting, landing and returning to the Earth. The program is scheduled to end around 2020.

The Chang'e-3 probe was launched on Dec. 2 last year and landed on the moon on Dec. 14..

The rover, Yutu, named after the pet rabbit of the lunar goddess Chang'e in Chinese mythology, separated from the lander and touched down on the moon's surface on Dec. 15.

Yutu's radar started working on Dec. 15 when the lander and rover took photos of each other and beamed them back to Earth.

The rover, as its name implies, was intended to roam the lunar surface, surveying the geological structure and substrate while looking for natural resources, but control problems emerged before the second lunar night fell on Jan. 25.

The lunar program authorities said the problem was probably caused by the "complicated lunar surface," including stones and dust, but this has not been confirmed.

"We hoped the moon rover would go farther, and we really want to find the true reason why it didn't," Yu said, adding that they can only try to deduce the cause via ground-based simulation.

Yu said the Chang'e-4 mission is under further analysis.

As the backup probe of Chang'e-3, Chang'e-4 will verify technology for Chang'e-5. The more sophisticated Chang'e-5/6 missions are aimed for tasks including unmanned sampling and returning to Earth.

China plans to launch an experimental recoverable moon orbiter before the end of this year to test technology vital for the success of Chang'e-5.