Jing Haipeng and Chen Dong enter Tiangong-2.
Controlled from Earth, Tianzhou-1 began to approach Tiangong-2 at 5:24 p.m. Tuesday and it took six and a half hours to complete the fast-docking with the space lab.
It was the third docking between the two spacecraft using fast-docking technology. Previously, it took about two days to dock.
The experiment tested the cargo spacecraft's capability of fast-docking, laying a foundation for future space station building.
Tianzhou-1 was launched on April 20 from south China's Hainan Province, and it completed the first and second docking with the orbiting Tiangong-2 space lab on April 22 and June 19, respectively.
The cargo spacecraft will conduct the third refueling of the space lab before returning to Earth.
The two spacecraft completed their first in-orbit refueling on April 27 and their second in-orbit refueling on June 15.
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.
Tiangong-2, which was sent into space on Sept. 15, 2016, is China's first space lab "in the strict sense" and a key step in building a permanent space station.
Cargo ships play a crucial role maintaining a space station and carrying supplies and fuel into orbit.
China's first space freighter, Tianzhou-1, successfully docked with the Tiangong-2 space lab for the third time late on Tuesday, as part of tests for a large future space station.
China's Tianzhou-1 and Tiangong-2 completed their docking at 23:58 Beijing time (15:58 UTC). The craft had been separated for three months.
Commands for the rendezvous and docking were issued at 17:24 Beijing time, according to the China Manned Space Agency, with the new 'fast' process taking 6.5 hours to complete.
Previously the rendezvous and docking process took around two days, or 30 orbits. The breakthrough will be used to allow crewed Shenzhou craft to reach the future Chinese Space Station (CSS) much sooner after launch.
Tianzhou-1 will soon perform a third and final refuelling test with Tiangong-2, before the cargo spacecraft is carefully deorbited over the South Pacific
Tiangong-2 will continue to orbit and perform a range of science experiments.
Tiangong-2 was launched in September 2016 and hosted the Shenzhou-11crewed mission - by far China's longest - which marked another step towards to the CSS.
Jing Haipeng and Chen Dong enter Tiangong-2.
This followed two docking and refuelling tests, and a period of 60 days coupled in orbit.
Tianzhou-1 was launched on April 20 via a Long March 7 rocket from Wenchang, and, with length of 10.6 metres, a maximum diameter of 3.35m and a mass of 13 tonnes, the cargo ship is also China's largest spacecraft so far.
A view of the inside Tianzhou-1 and its cargo while in orbit.
In future missions to the CSS, Tianzhou craft will also be used to carry waste away from the space station, much like the cargo craft used by Russia, Japan and the United States, with the exception of SpaceX's partly reusable Dragon 2.
BEIJING, China's Tianzhou-1 cargo spacecraft and Tiangong-2 space lab completed their third and last in-orbit refueling at 8:17 p.m. Saturday.
The third refueling, lasting about three days, confirmed the technical results from the second 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 and second on June 15.
In the past five months, Tianzhou-1 has operated smoothly and completed various tasks.
BEIJING, China's first cargo spacecraft, Tianzhou-1, separated from Tiangong-2 space lab at 4:15 p.m. on Sunday.
At 3:29 p.m. on Sunday, the cargo ship started to separate from the space lab under orders from the ground. After separation, it operated at an orbit of about 400 kilometers above the earth.
Tianzhou-1 will continue to carry out experiments before it leaves orbit, and will gain experience for building and operating a space station.
Tianzhou-1 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 the first in-orbit refueling on April 27, a second refueling on June 15 and a final one on Saturday. In the past five months, Tianzhou-1 has operated smoothly and completed various tasks.