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.

Childhood Dream
Jia was born in 1970, the year China sent its first satellite, "Dongfanghong I", into orbit, launching the country into the space age.

When he was 8 years old, he read a book about the solar system and became obsessed with astronomy.

He entered the National University of Defense Technology, majoring in solid rocket engines, and got his masters and doctoral degrees in the China Academy of Space Technology (CAST).

He began work for CAST in 1995, when China's market economy was beginning to boom. Many aerospace experts were lured to private or foreign-funded enterprises. A popular jingle at the time - "Making missiles earns less than selling tea eggs" - highlighted low salaries in the sector.

"I was thinking about leaving too," says Jia, "but exploring the universe was my childhood dream."

Over eight years, he helped to develop the Shenzhou-1 to Shenzhou-4 spacecrafts, Beidou navigation satellites, the China-Brazil Earth Resources Satellite, and the Ocean Satellite.

When his daughter was born in 2000, he named her "Sihang", meaning focusing on aerospace.

The Chang'e lunar exploration program began in 2004. In July that year, Jia was asked to develop China's first lunar rover.

He had to simulate the environment of moon's surface. What sort of traction would the rover have on the lunar soil? Would it slip? Would the wheels sink? These questions had to be answered on earth.

How to simulate the lunar soil? After much research, Jia found that ash from a volcanic cluster in northeast China's Jilin Province was similar to the lunar soil samples brought back by the U.S. Apollo missions.

Jia went to the provincial capital Changchun and traveled through snow-covered hills for several hours to Jingyu County. He was taken to a factory in the mountains, where the ash was used to make bricks. He bought several trucks of volcanic ash back to Beijing.

In 2011, the team tested the moon rover in a remote desert in northwest China's Gansu Province, transporting drinking water hundreds of kilometers as they continued their trials.

Challenging Cause
Anxiety over the success of China's moon rover was ever present.

"When we were drawing up the blueprints, we were very confident. But during the development process, all sorts of problems, which we'd never thought of, popped up. Our confidence was battered," Jia says.

"After the problems were solved with efforts, we regained the confidence," he adds.

He discovered an oversight in the design late in the development, when computer analysis revealed that the rover could lose contact with the earth if its antenna was shaded by the lander.

"We were tortured for a whole month before the problems were solved," says Jia.

"It showed a lack of experience. If we had a lot of experience for reference, it would have been gross negligence if we hadn't considered such problems. But for the moon rover, there were too many new problems and these problems were overlooked at first."

Before the lunar probe left factory, Jia's superiors asked if he was confident.

"Yes, I am confident because I've done all I want to do, all I must do and all I am required to do," Jia replied.

On behalf of his team, Jia signed a responsibility certificate, committing to the mission's success, which he framed and put on his desk.

"But even though we spare no effort to achieve success, we cannot be 100 percent sure of success," he admits.

Jia has worked to popularize space science among children and stimulate their interest in the universe.

Once in a high school competition, a student's self-made "moon rover" failed to pick up a cigarette case with its robotic arm. Jia encouraged him: "It's important to find the problems. As long as you find the problems, you have the basis to solve them."

Jia's next goal is Mars: "I hope before my retirement, the Chinese people can begin exploring Mars. I hope we can send a rover, better than Yutu, to Mars."