China's Space Station and the ISS Compared As Tianhe Module Arrives in Earth's Orbit

China successfully launched the first module of its first permanent space station on Thursday from the southern island province of Hainan.

The planned station, named Tiangong or "Heavenly Palace," is expected to be completed in 2022 once all the components have been launched and assembled.

But how will Tiangong compare to the only other station currently in service—the International Space Station (ISS,) which China is excluded from?

Like the ISS, Tiangong will be a large modular space station assembled from different components that are launched separately. The designs of modular space stations mean that different components can be added or removed from the existing structure, providing greater flexibility.

Tiangong will feature three main components, including the core service module "Tianhe" that was launched on Thursday, as well as two laboratories. Attached to these will be several other components, such as solar arrays and docking ports.

Once fully assembled, the Chinese station will have a mass of around 66 metric tons, according to Chinese state-run media outlet Xinhua, which is roughly one-sixth the mass of the ISS. This means it is closer in size to the Russia's retired Mir station.

According to the China Academy of Space Technology, Tiangong will have a total habitable volume of 3,884 cubic feet and is designed to accommodate three astronauts.

By comparison, the ISS has a total habitable volume of 13,696 cubic feet, according to NASA. The ISS usually hosts six astronauts at a time but at some points there have been more people on board. For example, a record was set in 2009 when a total of 13 people were on board the ISS at once.

Around a dozen missions will be needed to complete the Chinese station. The ISS, meanwhile, required more than 30 missions to assemble, with construction beginning in 1998.

In total, it took more than 10 years to complete the ISS. China hopes to complete its station within two years, building on the knowledge gained from Tiangong's precursors—the space labs Tiangong-1 and Tiangong-2, which were launched in 2011 and 2016 respectively. Both have since de-orbited.

Tiangong will orbit the Earth at an altitude of 211 to 280 miles, which is in the same range as the average altitude of the ISS—250 miles.

The Chinese space station is designed to be used for 10 years, although the mission could be extended. To date, the ISS has been continuously occupied for more than 20 years—the longest continuous presence in low-Earth orbit.

Chinese space station first module launches
A Long March 5B rocket, carrying China's Tianhe core module, lifts off from the Wenchang Space Launch Center in southern China's Hainan province on April 29, 2021. STR/AFP via Getty Images