BEIJING — Three Chinese astronauts docked early Wednesday with their country’s space station, where they will overlap for several days with the three-member crew already onboard and expand the facility to its maximum size.

Docking with the Tiangong station came at 5:42 a.m. Wednesday, about 6 1/2 hours after the Shenzhou-15 spaceship blasted off atop a Long March-2F carrier rocket from the Jiuquan Satellite Launch Center.

The six-month mission, commanded by Fei Junlong and crewed by Deng Qingming and Zhang Lu, will be the last in the station’s construction phase, according to the China Manned Space Agency. The station’s third and final module docked earlier this month, one of the last steps in China’s effort to maintain a constant crewed presence in orbit.

The crew of the Shenzhou-15 will spend several days working with the existing three-member crew of the Tiangong station, who will return to Earth after their six-month mission.

Fei, 57, is a veteran of the 2005 four-day Shenzhou-6 mission, the second time China sent a human into space. Deng and Zhang are making their first space flights.

The station has now expanded to its maximum size, with three modules and three spacecraft attached for a total mass of nearly 100 tons.

Tiangong can accommodate six astronauts at a time and the handover will take about a week. That marks the station’s first in-orbit crew rotation.

China has not yet said what further work is needed to complete the station. Next year, it plans to launch the Xuntian space telescope, which, while not part of Tiangong, will orbit in sequence with the station and can dock occasionally with it for maintenance.

Without the attached spacecraft, the Chinese station weighs about 66 tons — a fraction of the International Space Station, which launched its first module in 1998 and weighs around 465 tons.

With a lifespan of 10 to 15 years, Tiangong could one day be the only space station still up and running if the International Space Station retires in the coming years as planned.

While China’s crewed space program is officially three decades old this year, it truly got underway in 2003, when China became only the third country after the U.S. and Russia to put a human into space using its own resources.

The program is run by the ruling Communist Party’s military wing, the People’s Liberation Army, and has proceeded almost entirely without outside support. The U.S. excluded China from the International Space Station because of its program’s military ties, although China has engaged in limited cooperation with other nations’ space agencies.

China has also chalked up uncrewed mission successes: Its Yutu 2 rover was the first to explore the little-known far side of the moon.

China’s Chang’e 5 probe also returned lunar rocks to Earth in December 2020 for the first time since the 1970s, and another Chinese rover is searching for evidence of life on Mars.

Officials are reporting considering an eventual crewed mission to the moon, although no timeline has been offered, even as NASA presses ahead with its Artemis lunar exploration program that aims to send four astronauts around the moon in 2024 and land humans there as early as 2025.

While proceeding smoothly for the most part, China’s space program has also drawn controversy. Beijing brushed off complaints that it has allowed rocket stages to fall to Earth uncontrolled after NASA accused it of “failing to meet responsible standards regarding their space debris.” In that case, parts of a Chinese rocket landed in the Indian Ocean.

China is also reportedly developing a highly secret space plane and its increasing space capabilities feature in the latest Pentagon defense strategy, which said the program was a component of China’s “holistic approach to joint warfare.”