BEIJING, July 3 -- Jia Yang has two children. One goes to a middle school in Beijing; the other is on the moon.

The trials of parenthood have been far more arduous with the second child for Jia, deputy chief designer of the Chang'e-3 lunar probe, who led a team to develop China's first moon rover, Yutu, or Jade Rabbit.

Chang'e-3, launched on Dec. 2, 2013, landed on the moon after a two-week voyage, becoming China's first soft-landing on an extraterrestrial body.

On Dec. 15, Yutu drove onto the lunar surface. The rover and the lander took pictures of each other for the family album.

After 10 years of dedication to the project, Jia described his feelings as "bittersweet" - a feeling that continues after China declared the mission a "complete success".

In January 2014, Yutu suddenly stopped moving when engineers on earth were controlling it in the small hours one morning.

Jia was torn with anxiety, and joined other experts to solve the problem, sleeping less than two hours each day.

As the moon night - about 14 days on earth - approached and temperatures began falling towards minus 180 degrees centigrade. The rover was supposed to stay in power-off mode, and the solar panels to fold to provide insulation.

But the solar panels couldn't fold because of a "mechanical control abnormality".

Could Yutu survive the severe cold? "We thought the possibility was very low," said Jia.

"It's like that a monster is going to swallow you, while your mind is very clear, but you cannot move. We've done everything we can do. There is nothing else. Maybe it's time to say goodbye," said Jia, smoking and falling into a long silence.

But Jia and the other developers were given a "miracle" when Yutu sent back signals after the moon night on Feb. 12.

After that, they tried various solutions to Yutu's problem. But all failed.

Although Yutu accomplished its scientific and engineering goals, its problem is a source of regret.

"I have tried my best. The enlightenment gained from our trials is more precious than success,"sighs Jia.

"I regard the lunar rover as my child. I would do anything for it. I've never felt I've done enough," Jia says.