BEIJING, June 15 -- China's Tianzhou-1 cargo spacecraft and Tiangong-2 space lab completed their second in-orbit refueling at 6:28 p.m. Thursday.

The second refueling, lasting about two days, further tested the country's refueling technology and cemented technical results from the first refueling.

Tianzhou-1, China's first cargo spacecraft, was launched on April 20 from south China's Hainan Province, and it completed automated docking with the orbiting Tiangong-2 space lab on April 22.

The two spacecraft completed their first in-orbit refueling on April 27, at an orbit of 393 kilometers above the earth.

Since Tianzhou-1 and Tiangong-2 have become a combination, space science experiments and applications have been conducted.

According to the flight plan, Tianzhou-1 will fly around Tiangong-2 and then carry out a second docking.

China is the third country, after Russia and the United States, to master refueling techniques in space, which is crucial in the building of a permanent space station.

As the International Space Station is set to retire in 2024, the Chinese space station will offer a promising alternative, and China will be the only country with a permanent space station.