Chinese rocket updates: What to know about the uncontrolled return to Earth

The rocket debris reentered over the Indian Ocean on Saturday.

A massive section of a rocket made its uncontrolled return to Earth on Saturday.

Aerospace experts had been tracking the debris for days, as it was initially unclear exactly when -- and where -- it will land.

The section is part of a rocket called Long March 5B, which China launched into orbit on July 24 to deliver a lab module to China's Tiangong Space Station.

Typically, rocket debris is meant to come back down in a controlled way, usually into the ocean to avoid populated areas. But during launch, the 23-metric-ton rocket booster reached orbit and is now being dragged toward Earth for an uncontrolled reentry, according to the Aerospace Corporation, a nonprofit that provides technical guidance on space missions to military, civil and commercial customers.

The exact point where the rocket booster would reenter the Earth's atmosphere couldn't be determined until within hours of reentry, experts said.

"The snag is that the density of the upper atmosphere varies with time -- there's actually weather up there -- and so that makes it impossible to predict exactly at what point the satellite will have plowed through enough atmosphere to melt and break up and finally reenter," astronomer Jonathan McDowell said in a Twitter conversation on the uncontrolled reentry of the rocket hosted by the Aerospace Corporation this week.

"If you're an hour off in predicting when that's going to happen, because it's going at 17,000 miles an hour, you're 17,000 miles off in where it's going to come down. And that's the big challenge with all this," he said.

The two previous launches of the Long March 5B rocket both had uncontrolled reentries, with rocket debris landing near the west coast of Africa in 2020 and in the Indian Ocean in 2021.

Next Long March 5B rocket to launch in October

A second Long March 5B rocket is scheduled to be launched later this year, with experts preparing for another uncontrolled entry.

"Well, that's a wrap on the Chang Zheng 5B Y3 reentry," astronomer Jonathan McDowell said on Twitter Saturday. "We'll go through this again in October with Chang Zheng 5B Y4, which is scheduled to launch the next Chinese space station module."

The rocket will deliver the third and final lab module, Mengtian, to China's Tiangong Space Station.

Latest projection places reentry near Malaysian coastal town's latest projection estimated the reentry to be at 12:51 p.m., give or take a minute, at an approximate latitude and longitude that would place it near Bintulu, a coastal town on the island of Borneo in the Malaysian state Sarawak.

NASA comments on uncontrolled reentry

NASA administrator Bill Nelson commented on the uncontrolled return of the rocket debris on Saturday, saying that China "did not share specific trajectory information as their Long March 5B rocket fell back to Earth."

"All spacefaring nations should follow established best practices, and do their part to share this type of information in advance to allow reliable predictions of potential debris impact risk, especially for heavy-lift vehicles, like the Long March 5B, which carry a significant risk of loss of life and property," he said in a statement. "Doing so is critical to the responsible use of space and to ensure the safety of people here on Earth."

Rocket makes reentry over Indian Ocean

The U.S. Space Command has confirmed that the rocket booster reentered the atmosphere over the Indian Ocean at approximately 12:45 p.m.