China's first cargo spacecraft, the Tianzhou 1, has docked with the country's Tiangong II space laboratory and will stay in space about five months to conduct tests and experiments.

The docking took place on the afternoon of April 22 about 380 kilometers above Earth, according to the China Manned Space Agency.

Tianzhou 1, the country's largest and heaviest spacecraft, was launched atop a Long March 7 rocket on April 20 at the Wenchang Space Launch Center in Hainan province. The Tiangong II has been in space since mid-September and carried two Chinese astronauts from mid-October to mid-November. It is now unmanned.

The two spacecraft will stay in combined orbit for about two months, during which the Tianzhou 1 will resupply fuel to Tiangong II and conduct scientific experiments, the agency said.

After the two months, the cargo spacecraft will undock and redock with the space lab. It will then undock again and start a three month independent flight before a third docking.

The cargo craft will inject fuel into Tiangong II during the second and third dockings. After the third docking, Tianzhou 1 will depart from Tiangong II and will be directed by ground control to fall back to Earth.

If the mission is successful, China will become the third nation to use its own technology to conduct in-orbit refueling, joining Russia and the United States. It is part of China's plan to have a manned space station in orbit by about 2022.

The reason for repeating the docking and undocking process is that scientists want to test the technology developed to enable a spacecraft to dock with a space station from different directions.

According to designers, after the first undocking from Tiangong II, the cargo vessel will fly to the opposite side of Tiangong II and dock with a different section.

Xu Xiaoping, deputy chief designer of the Tianzhou 1 at the China Academy of Space Technology, says China's space station will have multiple adapters to dock with spacecraft from various directions, so Tianzhou 1's dockings will help scientists collect experience and data.

Zhang Qiang, another deputy chief designer of the cargo ship, says Tianzhou 1 will make sophisticated, automated maneuvers circling Tiangong II before the second docking. He says that in the third docking, Tianzhou 1 will use fast-docking technology, which will take six hours for the entire process. By comparison, a typical docking will take two days.

In future, the Tianzhou series will be tasked with bringing supplies of fuel and other necessities to China's manned space station, for which construction will start around 2018.

The station will consist of three parts - a core module attached to two space labs, each weighing about 20 tons - and will operate for at least 10 years, according to the manned space agency.

zhaolei@chinadaily.com.cn