Preparation for the 2017 launch of China's lunar probe Chang'e-5 is going as planned, the country's leading space scientist Ye Peijian told Xinhua on Saturday.

Chang'e-5, as part of China's third-phase lunar program, is expected to bring back moon rock samples to Earth, a move hailed by Ye as "a historic moment" for the country.

China's lunar program covers three stages. It completed the second phase after the Chang'e-3 probe soft-landed on the Moon on Dec. 14, with the country's first moon rover Yutu (Jade Rabbit) aboard.

But Yutu has experienced a mechanical problem that scientists are still trying to repair.

Ye said the Chang'e-3 mission has helped China to better understand the lunar environment and has paved the way for further explorations.

As the backup probe of Chang'e-3, Chang'e-4 should not repeat the mission, but do something more "innovative and meaningful", said Ye, without elaborating.

The more sophisticated Chang'e-5 mission, including unmanned sampling and returning, requires technology breakthroughs in moon surface takeoff, sampling encapsulation, rendezvous and docking in lunar orbit, as well as high-speed Earth reentry.

To make sure the returning mission is a success, a Chang'e-5 test probe will be launched this year to rehearse the route, Ye disclosed.

Chang'e-1 and Chang'e-2 missions were in 2007 and 2010.

Launched on Oct. 1, 2010, China's first man-made asteroid Chang'e-2 is now about 70 million km from Earth and continues heading to deep space.

Ye said the asteroid could travel as far as 300 million km from Earth.

Despite a latecomer in space development, China has made steady progress in recent years. It is the third nation, after the United States and Russia, to acquire the skills necessary for extravehicular activities and space docking.