China's Tiangong space station is scheduled to be completed before the end of the year, and will become a massive spacecraft stack with a combined weight of nearly 100 metric tons, according to a program leader.

Zhou Jianping, chief designer of the nation's manned space program, said the assembly phase of the Tiangong program will begin in May and will involve launches of two astronaut crews, two space labs and two cargo craft.

He made the remarks on Friday afternoon at the Great Hall of the People in Beijing before the opening of the fifth session of the 13th National Committee of the Chinese People's Political Consultative Conference. The scientist is a member of the CPPCC National Committee, the nation's top political advisory body.

"We will send six astronauts in the Shenzhou XIV and XV mission crews. The Shenzhou XIV crew will be responsible for monitoring docking between the Tianhe core module and the two space labs and then configuring the two labs," he said. "The Shenzhou XV crew will fly to the station around year's end to meet their Shenzhou XIV peers. That will be an exciting moment that all of us are eager to see."

When Tiangong is complete, it will consist of three major components: a core module linked to two large space labs; two Shenzhou spacecraft; and one cargo ship, weighing around 100 tons. A total of six astronauts will stay inside the station, the largest space-based infrastructure China has ever built, for a certain period of time before the Shenzhou XIV crew returns to Earth, according to Zhou.

He said the Tiangong station will be a platform for scientific experiments and technological demonstrations in a wide range of research fields such as biology, materials science and microgravity hydrodynamics.