The Wentian module was loaded onto a Long March 5B rocket and rolled onto a launchpad on Hainan Island.
It's unclear if the rocket will fall to Earth uncontrolled, risking impact, as its two predecessors did.
China seems poised to launch the second module of its new space station on Sunday, and it's not yet clear whether its rocket will go rogue again as it falls back to Earth.
So far, three different astronaut crews have visited the the orbiting live-in laboratory, which is just one large module called Tianhe. Astronauts Chen Dong, Liu Yang, and Cai Xuzhe are currently aboard the Tianhe module waiting to oversee the arrival and attachment of the new module, called Wentian, which is intended for science and biology experiments.
"Wentian is a critical stage in the building of China's space station," Brian Harvey, author of "China in Space: The Great Leap Forward," told SpaceNews. "The Tianhe crew has overseen numerous undockings and redockings, so such maneuvers are well practiced, but nothing can be taken for granted, especially for the first time."
China seems poised to launch Wentian into orbit on Sunday, when there are airspace-clearance notices over its facilities on Hainan Island, SpaceNews reported. The Long March 5B rocket rolled out from its assembly building and onto the launchpad there on Monday, with the Wentian module enclosed in its fairing.
China might let the rocket's body fall back to Earth uncontrolled — for the third time
Last time China launched a Long March 5B, pushing the Tianhe module into orbit in April 2021, it drew international outcry as the rocket's body entered a low orbit around Earth and slowly lost altitude until gravity pulled it into an uncontrolled fall.
Nobody could predict where it would land, but its path covered a vast swath of the planet from Los Angeles to New York to southern Europe to Beijing, as well as down through most of Australia, Africa, and South America.
More than a week after launch, the rocket body fell into the Indian Ocean, likely raining down in pieces. The chances that it would hit humans or property were low, but space-industry experts across the globe called for China to redesign the rocket or its launch plans so that it wouldn't happen again.
It's unclear if the space agency did that for the rocket that is about to launch Wentian.
Normally, rockets are programmed to push themselves into the atmosphere after launch, controlling their fall back to Earth so that they land in remote ocean areas like the South Pacific — a process called "controlled reentry."
"Rockets get launched all the time, and very seldom is there concern about reentry," John Logsdon, the founder of George Washington University's Space Policy Institute, previously told Insider as the world waited for the rocket body to fall in early May 2021. "So yeah, I'm a little confused as to why this is happening."
"Is it just willful disregard of the international guidelines? Or because it's a new vehicle, it wasn't properly designed so it could do a controlled reentry? Whatever," Logsdon added. "It's unfortunate that it puts a lot of people at risk."
China first launched the Long March 5B in May 2020 in a test that put a spaceship prototype into orbit. That rocket's core stage also fell back to Earth uncontrolled. It reentered Earth's atmosphere over the Atlantic Ocean, according to the US Space Force's 18th Space Control Squadron. Some local reports indicated that bits of the rocket fell in Côte d'Ivoire.
"I think, at a minimum, China owes the international community an explanation," Logsdon said in May 2021.
That week, Chinese foreign ministry spokesperson Wang Wenbin said in a press conference that it was "common practice across the world for upper stages of rockets to burn up while reentering the atmosphere," SpaceNews reported.
According to the publication, local clearance notices have outlined drop zones for the rocket's boosters and payload fairing, but not for its body — the part that has returned in an uncontrolled, unpredictable fall in the past.
China is also preparing to launch the third module, called Mengtian, for launch in October, according to Spaceflightnow.
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