When Is China’s Rocket Supposed to Fall?: Here’s What to Know

A piece of China’s largest rocket is tumbling back to Earth this weekend. No one really knows when or where it will land.

On April 29, a Long March 5B launched a big piece of China’s next space station, Tiangong. Usually the large booster stages of rockets immediately drop back to Earth after they are jettisoned, but the 23-ton core stage of Long March 5B accompanied the space station segment all the way to orbit. Because of friction caused by the rocket rubbing against air at the top of the atmosphere, it has been losing altitude since and will soon make what is called “uncontrolled re-entry” back to Earth.

The chances that any debris from the Long March 5B rocket will strike anything or hurt anyone are slight but not zero.

Here’s what you need to know about the Long March 5B’s journey.

The Long March 5B booster could re-enter Earths’s atmosphere anywhere between 41.5 degrees north latitude and 41.5 degrees south latitude. That means Chicago, located a fraction of a degree farther north, is safe, but major cities like New York could be hit by debris.

As of Saturday, the Aerospace Corporation, a nonprofit largely financed by the federal government that performs research and analysis, predicted re-entry would occur on Saturday at 11:26 p.m. Eastern time. If accurate, that would bring it down somewhere in the North Atlantic Ocean, with little risk to people on land.

The full rocket contained multiple pieces. Several smaller side boosters dropped off shortly after the launch, crashing harmlessly in the Pacific Ocean. (Disposing of used, unwanted rocket pieces in the ocean is a common practice.) But the core booster stage — a 10-story cylinder weighing 23 tons empty — carried the Tianhe module into orbit.

In recent decades, rocket stages that reach orbit typically fire the engine again after releasing their payloads so that they drop out of orbit, aimed at an unoccupied area like the middle of an ocean.

China did not elect to do that for this launch, and so that large booster is now headed back uncontrollably to the surface.

China has a long history of letting pieces of its space equipment come down where they may.

Rockets from one of its principal launch sites, the Xichang Satellite Launch Center in Sichuan Province, routinely fell on rural areas downrange, occasionally causing damage. China has since moved many of its launches, including the Long March 5B’s, to a new site in Wenchang, a city on Hainan, an island off the southeastern coast.

Last year, the first launch of a Long March 5B rocket lifted a prototype of China’s crewed space capsule. The booster from that rocket also made an uncontrolled re-entry, with some debris raining down on a village in Ivory Coast.

With more large pieces of China’s space station scheduled to go to orbit, more launches of the Long March 5B are expected through 2022. Unless there is a change to how China operates it, the odds that someone will be hurt by a piece of a falling booster will grow.

In March, an out-of-control SpaceX rocket stage re-entered Earth’s atmosphere near Seattle, surprising residents there as it lit up night skies. Pieces of the rocket landed on a farmer’s property in Washington State. In that case, a firing of the engine of the second stage to bring it down safely did not occur as planned.

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