Full coverage: China Tiangong-2 Space Lab Launch

The launch and re-entry are often regarded as the two most hazardous phases of a space mission, with even the smallest mistake having potentially catastrophic consequences. But what kind of dangers will astronauts Jing Haipeng and Chen Dong face during their return to Earth?

Firstly--speed. At low Earth orbit, which is between 200 and 2,000 kilometers above the surface of the planet, a spacecraft has to fly at more than 28,000 kilometers per hour to circle the Earth. With the spacecraft travelling at such high speeds, there is little room for error.

Secondly--friction. Due to the high velocity of spacecraft, air friction can cause a tremendous amount of heat. That's why spacecraft re-enter the atmosphere slowly by gradually circling downwards. They are also coated with special materials to shield them from searing temperatures. But accidents still happen. In 2003, the US space shuttle Columbia disintegrated on its return to Earth, because a small part of its wing had been damaged on launch. As a result, all seven crew members on board were killed.

The final test is the actual landing. Objects returning to Earth travel so fast that even a fractional error in timing the descent can mean the craft can land hundreds of kilometers off target. And that's the last thing you would want after a month in space!