China Launches Final Space Station Module

China launched its third and final space station module today, completing construction of Tiangong-3. It comes as China gets ready for its first crew rotation later this year, the beginning of China’s permanent human occupancy in Earth orbit. Coincidentally, the launch comes exactly 22 years after the first Russian-American crew launched to the International Space Station, which initiated permanent human occupancy in space for the ISS partners. China’s achievement may be two decades later, but is still a milestone for its growing space program.

The module, Mengtian, launched on a Long March-5B rocket from the Wenchang Satellite Launch Center on Hainan Island at 4:37 am Eastern Daylight Time (07:37 UTC) and docked with the other two modules at 16:27 EDT (20:27 UTC).

The core module, Tianhe, was launched last year. Wentian, a laboratory module like Mengtian, went up in July. Each module has a mass of about 22.5 Metric Tons, making a total of about 68 MT. By comparison, the U.S.-Russian-Japanese-European-Canadian International Space Station is about 420 MT.

Like the International Space Station, Tiangong-3 is resupplied by cargo ships. China’s are called Tianzhou and Tianzhou-4 is currently docked there. Russia, Japan, and the United States all send cargo ships to the ISS — Progress, HTV, and Cygnus and Crew Dragon respectively. Two or three are usually there at any given time.

Crews are ferried back and forth on Shenzhou spacecraft. The three-person Shenzhou-14 crew is there now: Chen Dong, who flew on Shenzhou-11 in 2016 to Tiangong-2; Liu Yang, who became China’s first woman in space when she spent 13 days on China’s first space station, Tiangong-1, in 2012; and Cai Xuzhe on his first flight. They will remain until Shenzhou-15 arrives later this year and for the first time China will have a crew hand-over.

Such crew rotations are routine on the ISS. The first ISS crew, two Russians and one American, launched 22 years ago today and boarded the ISS on November 2, 2000.

At least two people have been aboard the ISS ever since, usually more. A typical crew complement these days is seven and increases to ten or eleven during crew exchanges. Seven are there now — three Russians, three Americans, and a Japanese — who arrived on Russian Soyuz and U.S. Crew Dragon spacecraft.

China’s first two space stations, Tiangong-1 and Tiangong-2, were quite small, 8.5 MT. They were part of China’s slowly-paced human spaceflight program, with the first taikonaut launched in 2003. The program picked up steam recently with the introduction of the new Long March-5 (LM-5) or Chang Zheng-5 (CZ-5) rocket.

The LM-5 family is the largest in China’s fleet, roughly comparable to a U.S. Delta IV Heavy. The Long March-5B is needed to put these modules into low Earth orbit. Unlike its LM-5 cousin, the LM-5B does not have a second stage. Instead, it has a much larger fairing to accommodate big payloads. The LM-5B first stage, or core stage, augmented by four strap-on boosters that drop away soon after launch, does the lifting and reaches orbit along with the payload. After a few days it makes an uncontrolled reentry through the atmosphere to land at a random location between 41.5 degrees North and 41.5 degrees south latitude.

This has happened three times already. A test launch in 2020 rained debris over the Ivory Coast. In 2021, the rocket body for Tianhe’s launch splashed into the Indian Ocean. Earlier this year, debris from the launch of Wentian landed in Borneo and the Philippines.

Once again, the world will be on alert to see where this rocket body comes down. DOD’s Space-Track.org website and the Aerospace Corporation provide data and projections on reentering space objects.

Space objects reenter all the time, but the vast majority are small and burn up in the atmosphere before reaching the ground. Big pieces of the LM-5B rocket body can survive because it is so large: 98 feet (30 meters) long, 16.5 feet (5 meters) wide, with a mass of about 23 tons (21 MT).