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Space News reports :-

Originally Posted by Space News - Andrew Jones — April 30, 2021

Long March 5B core stage likely to reenter the Earth's atmosphere in the coming days.

HELSINKI — China launched the first module for its space station into orbit late Wednesday, but the mission launcher also reached orbit and is slowly and unpredictably heading back to Earth.

The Long March 5B, a variant of China’s largest rocket, successfully launched the 22.5-metric-ton Tianhe module from Wenchang Thursday local time. Tianhe separated from the core stage of the launcher after 492 seconds of flight, directly entering its planned initial orbit.

Designed specifically to launch space station modules into low Earth orbit, the Long March 5B uniquely uses a core stage and four side boosters to place its payload directly into low Earth orbit.

However this core stage is now also in orbit and is likely to make an uncontrolled reentry over the next days or week as growing interaction with the atmosphere drags it to Earth. If so, it will be one of the largest instances of uncontrolled reentry of a spacecraft and could potentially land on an inhabited area.

Most expendable rocket first stages do not reach orbital velocity and reenter the atmosphere and land in a pre-defined reentry zone. Some other larger, second stages perform deorbit burns to lower altitude to reduce time in orbit and lower chances of collisions with other spacecraft or to immediately reenter the atmosphere.

There had been speculation that the Long March 5B core would perform an active maneuver to deorbit itself, but that appears not to have happened.

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Unpredictable reentry

Where and when the new Long March 5B stage will land is impossible to predict. The decay of its orbit will increase as atmospheric drag brings it down into more denser. The speed of this process depends on the size and density of the object and variables include atmospheric variations and fluctuations, which are themselves influenced by solar activity and other factors.

The high speed of the rocket body means it orbits the Earth roughly every 90 minutes and so a change of just a few minutes in reentry time results in reentry point thousands of kilometers away.

...

Spaceflight observer Jonathan McDowell told SpaceNews that the previous Long March 5B launch saw the most massive uncontrolled reentry in decades and the fourth biggest ever. “The Long March 5B core stage is seven times more massive than the Falcon 9 second stage that caused a lot of press attention a few weeks ago when it reentered above Seattle and dumped a couple of pressure tanks on Washington state.”

McDowell said he hoped China would have enhanced the core stage to perform a controlled deorbit after separating from Tianhe. “I think by current standards it’s unacceptable to let it reenter uncontrolled,” McDowell said.

Full story here :-
https://spacenews.com/huge-rocket-lo...tation-launch/