Is Chinese space station bigger than ISS?

Tiangong is a space station that the Chinese Manned Space Agency (CMSA) is building in low Earth orbit. In May 2021, China launched Tianhe, the first of the orbiting space station's three modules, and the country aims to finish building the station by the end of 2022. CMSA hopes to  keep Tiangong inhabited continuously by three astronauts for at least a decade. The space station will host many experiments from both China and other countries.

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Tiangong, which means "Heavenly Palace," will consist of Tianhe, the main habitat for astronauts, and two modules dedicated to hosting experiments, Mengtian and Wentian, both of which are due to launch in 2022. Shenzhou spacecraft, launching from Jiuquan in the Gobi Desert, will send crews of three astronauts to the space station, while Tianzhou cargo spacecraft will launch from Wenchang on the Chinese island of Hainan to deliver supplies and fuel to the station.

Tiangong space station specifications

Tiangong will be much smaller than the International Space Station (ISS), with only three modules compared with 16 modules on the ISS. Tiangong will also be lighter than the ISS, which weighs about 400 tons (450 metric tons) following the recent addition of Russia's Nauka module. 

The 54-foot-long (16.6 meter) Tianhe module launched with a docking hub that allows it to receive Shenzhou and Tianzhou spacecraft, as well as welcome the two later experiment modules. A large robotic arm will help position the Mengtian and Wentian modules and assist astronauts during spacewalks.

Tianhe is much larger than the Tiangong 1 and 2 test space labs China launched in the last decade and nearly three times heavier, at 24 tons (22 metric tons). The new Tiangong, visiting spacecraft and cargo spacecraft will expand the usable space for the astronauts; so much that they'll feel as though "they will be living in a villa," compared with how little space was available on previous Chinese space labs, Bai Linhou, deputy chief designer of the space station, told CCTV.

Tianhe features regenerative life support, including a way to recycle urine, to allow astronauts to stay in orbit for long periods. It is the main habitat for the astronauts and also houses the propulsion systems to keep the space station in orbit.  

China has said it will take 11 launches to finish Tiangong: three module launches, four crewed missions and four Tianzhou spacecraft to supply cargo and fuel. The first three launches — Tianhe, Tianzhou 2 and Shenzhou 12 — have gone smoothly.

Once completed, Tiangong will be joined by a huge, Hubble-like space telescope, which will share the space station's orbit and be able to dock for repairs, maintenance and possibly upgrades. Named Xuntian, which translates to "survey the heavens," the telescope will have a 6.6-foot (2 m) diameter mirror like Hubble but will have a field of view 300 times greater. Xuntian will aim to survey 40% of the sky over 10 years using its huge, 2.5-billion-pixel camera.

The space station could potentially be expanded to six modules, if everything goes according to plan. "We can further expand our current three-module space station combination into a four-module, cross-shaped combination in the future," Bai told CCTV. The second Tianhe core module could then allow two more modules to join the orbital outpost.

Tiangong's project history

China embarked on a long journey to reach the point of building its space station. The project was first approved in 1992, after which the country set about developing the Shenzhou crew spacecraft and the Long March 2F rocket to send astronauts into space. Yang Liwei became China's first astronaut in space in October 2003 and made China the third country in the world to independently send humans into orbit. 

China expressed interest in joining the International Space Station partners, but the possibility was ended by a 2011 decree passed by U.S. lawmakers effectively banning NASA from coordinating directly with China or any Chinese-owned company. This means direct collaboration between NASA and Chinese space stations is strictly prohibited, making the prospect of sending U.S. astronauts to Tiangong (or Chinese astronauts to the ISS) impossible. 

To be able to build and operate a crewed space station, China first needed to test out crucial space station systems, including life support and technologies for rendezvous and docking of spacecraft in orbit while traveling 17,448 mph (28,080 km/h). To accomplish this, China launched the 9-ton (8.2 metric tons) Tiangong-1 space lab in 2011, and subsequently sent the uncrewed Shenzhou 8 and the crewed Shenzhou 9 and 10 to join Tiangong-1 in orbit.

The upgraded but similarly sized Tiangong-2 launched in 2016 and hosted the two-astronaut crew of Shenzhou 11 for just over a month, setting a new national record for human spaceflight mission duration. 

As the China Manned Space Agency checked off these initial milestones, the agency was also focused on developing new, larger Long March heavy-lift rockets to make a space station possible. The Long March 5B was designed specifically to launch the huge space station modules into low Earth orbit. The same rocket was the source of one of the largest uncontrolled reentries in recent decades following the launch of Tianhe in late April 2021.

In 2014 China completed its new, coastal spaceport at Wenchang, specifically to launch these larger-diameter rockets, which need to be delivered by sea.

Tiangong's future

The first crewed missions — Shenzhou 12, 13 and 14 — will be for space station construction. A series of operational phase missions lasting six months each will begin in 2023. Crews will carry out experiments in areas such as astronomy, space medicine and life sciences, biotechnology, microgravity combustion and fluid physics and space technologies. Tiangong will also temporarily host six astronauts during crew changeovers, Space.com previously reported.

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Tiangong is also likely to host international astronauts in the future. European Space Agency astronauts Samantha Cristoforetti and Matthias Maurer trained with their Chinese counterparts in 2017 in a small step toward a possible future visit to the Chinese space station, the European Space Agency reported. Astronauts from other countries, particularly those involved in China's Belt and Road initiative, may travel to Tiangong as well; Russia is also considering sending its cosmonauts.

China is looking to develop alternatives for keeping Tiangong supplied, SpaceNews reported. In January 2021, the China Manned Space Agency put out a call for proposals for low-cost, reliable cargo missions to Tiangong. The call was open to commercial companies, echoing NASA's Commercial Resupply Services contracts that provided opportunities to SpaceX.

It will be possible to spot Tiangong from Earth, just as it sometimes is with the ISS. Tiangong will orbit at an altitude of between 211 and 280 miles (340 to 450 kilometers) above Earth and between 43 degrees north and south, and the space station should be a fixture in the sky for at least a decade.

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