Full coverage: China Tiangong-2 Space Lab Launch

China's cold atomic clock is the most precise time-keeping device ever built. The clock only weighs a couple kilograms and could fit comfortably in the boot of a car. And because it is powered by atoms, it won't have to be reset for another 30 million years.

Cold atomic clocks are the most accurate clocks in the world. Low-frequency lasers lower their internal temperatures to 273 degrees centigrade below zero, and slow down the movement of atoms inside. Slow-moving atoms decrease the likelihood of counting errors, and result in a more accurate counting of time.

"The frequency of the atom will not change. It is the same wherever it is. Unlike in mechanical clocks and electric clocks, atomic clocks aren't drastically affected by their surrounding environment. We are going to operate the most accurate cold atomic clock in space. It is the first time ever, not only for our country, but also for the world," Liu Liang, chief designer of Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, said.

Rubidium atoms count time inside China's cold atomic clock. Atoms are usually affected by gravity, but the low level of gravity in space will weaken the earth's gravitational pull and increase the accuracy of China's cold atomic clock.

"Atoms usually fall because of gravity, making it difficult to keep track of time for a long time. But up in space, we don't have that problem," Liu said.

The launch of Tiangong-2 marks China's transition from a follower in space research, to a pioneer. China's cold atomic clock project is a good example of that transition.

"The initial plan was brought up in 2006. We have made great efforts over the past ten years. We have been through a lot... and we have been successful" Liu said.

It took years of scientific work to get China's cold atomic clock into space. Researchers are now devising ways how to use the clock to benefit people down on earth.