China's first space cargo ship, the Tianzhou-1, is about to refuel the Tiangong-2 space lab for the first time, using "in-flight refueling" techniques.

The spacecraft blasted off from the Wenchang Launch Center on April 20 and successfully docked with the space lab two days later. During its two-month orbit, the cargo ship is expected to refuel the space lab three times. The refueling procedure takes 29 steps and lasts for several days each time. If the Tianzhou-1 completes its objective, China will become the third country, after Russia and the United States, to master the technique of refueling in space. Chinese engineers consider it a major breakthrough for future space station operations.