Update: This article was revised shortly after it was published to reflect a revised forecast by Aerospace Corporation.

No, you almost certainly won’t be hit by a 10-story, 23-ton piece of rocket hurtling back to Earth.

That said, the chances are not zero. Part of China’s largest rocket, the Long March 5B, is spiraling out of control in orbit after part of the country’s new space station was launched last week. The missile is expected to fall to Earth sometime on Saturday or Sunday in what is known as “uncontrolled reentry”.

Whether it splashes harmlessly into the ocean or affects land in which people live, why China’s space program allows this again, remains unclear. Given China’s planned launch plan, more such uncontrolled missile re-entries are possible in the coming years.

The country’s space program has had a number of key achievements in space travel over the past six months, including returning stones from the moon and orbiting a spacecraft around Mars. Yet it continues to create even the slightest threat to people around the world by not controlling the paths of the missiles it fires.

“I think it’s negligent on their part,” said Jonathan McDowell, an astrophysicist at the Center for Astrophysics in Cambridge, Massachusetts who tracks the comings and goings of objects in space. “I think it’s irresponsible.”

The piece that will fall from the sky somewhere is the core booster stage of the Long March 5B, which is designed to lift the big, heavy parts of the space station. For most rockets, the lower stages usually fall back to Earth immediately after launch. Upper steps that enter orbit typically re-ignite the engine after releasing their payloads and direct them to re-enter an unoccupied area like the middle of an ocean.

In the past three decades, only China has put rocket stages into orbit that large and accidentally dropped them, said Dr. McDowell.

For the Long March 5B booster, this could be anywhere between latitude 41.5 degrees north and latitude 41.5 degrees south. That means Chicago, which is just a fraction of a degree further north, is safe, but big cities like New York could be hit by rubble.

On Thursday, the Aerospace Corporation, a nonprofit funded largely by the federal government that conducts research and analysis, predicts a re-entry on Saturday at 11:43 p.m. east coast time. If so, debris could pour down over northeast Africa and Sudan.

Uncertainty about the time – give or take 16 hours – and stay great. A day earlier, Aerospace had, according to its prediction, initiated a re-entry over the eastern Indian Ocean more than an hour earlier.

When the booster burns depends, for example, on the sun. An increase in the intensity of the solar wind – charged particles spat out by the sun – would inflate the Earth’s atmosphere, increase the aerodynamic drag of the rocket booster, and accelerate its fall. The falling of the rocket stage also complicates the calculations.

The United States Space Command and the Russian space agency are both tracking the missile core. The Russian statement stated that re-entry would “not affect the territory of the Russian Federation”. The Space Command promised regular updates before a possible re-entry.

Since the booster is traveling at 18,000 mph, changing the minutes will move the debris hundreds or thousands of miles. Only a few hours before re-entry, the predictions become more precise.

“It’s a technical decision based on probabilities,” said Dr. McDowell. He said the Chinese engineers could have designed the trajectory to remain suborbital and fall back to Earth right after takeoff, or they could have planned an additional thruster to get it out of orbit in ways that were not possible Represents danger.

“It’s not a trivial thing to design something for an intentional re-entry, but it’s still something the world as a whole moved to because we had to,” said Ted J. Muelhaupt, chief executive officer of the Aerospace Center for Orbital and Re -Entry debris studies.

China plans many more launches in the coming months as construction of the country’s third space station, Tiangong, or “Heavenly Palace”, is completed. This requires additional flights of the mammoth rocket and the possibility of more uncontrolled re-entries, which people on the ground will be nervously watching, even if the risk of a single rocket stage is low.

“It is in the common interest of all nations to act responsibly in space to ensure the safety, stability and long-term sustainability of space activities,” said Jen Psaki, White House press secretary, on Wednesday, adding that the United States is the United States hoped to promote “responsible space behavior”.

Falling debris has long ruined space travel.

In March, a SpaceX Falcon 9 rocket stage lit the night sky over Seattle and later threw debris over a farm in Washington state when a planned firing shot of the second stage engine to safely lower it did not go as planned.

In contrast, China has a long history of lowering parts of its space equipment where it likes.

Missiles from one of China’s major launch sites, the Xichang Satellite Launch Center in Sichuan Province, routinely fell on rural areas and occasionally caused damage. China has since moved many of its launches, including last week’s launches, to a new location in Wenchang, a city on Hainan, an island off the southeast coast. From there, rocket stages can fall harmlessly into the sea.

In this case, the rocket core that carried the module for China’s new space station also entered orbit and has since been slowly withdrawn towards the earth’s atmosphere.

Last year, when a Long March 5B rocket was first launched, a prototype of the Chinese space capsule and crew was lifted. The booster on this missile also made an uncontrolled re-entry, with some debris raining on an Ivory Coast village.

This led to a reprimand from then NASA administrator Jim Bridenstine.

“It could have been extremely dangerous,” he said. “We’re really happy in the sense that it doesn’t seem to have hurt anyone.”

China’s first space station, called Tiangong-1, launched in 2011, fell back to earth in an uncontrolled descent in 2018 before finally crashing harmlessly in the South Pacific. The following year, China’s space administration successfully steered the second station out of orbit into the Pacific. This time the booster stage is more than twice as massive as the first two Tiangong space stations.

The United States also had problems returning its first space station to Earth. Skylab, which operated in 1973 and 1974, disbanded when NASA scientists tried to control its descent in 1979. The 77-ton station largely disintegrated over the Indian Ocean, but debris scattered over Western Australia. President Carter apologized.

In 2011, the Upper Atmosphere Research Satellite (UARS), a defunct NASA satellite the size of a school bus, also fell back to Earth. NASA calculated a 1 in 3,200 probability that UARS, slightly smaller than Tiangong-1 or Tiangong-2, would injure someone on the ground.

Dr. McDowell said he thinks the Long March 5B booster debris threat is likely comparable – unlikely, but high enough to be cause for concern. Since the Chinese did not provide construction details for the missile, it is difficult to predict how much material will reach the surface.

Mr Muelhaupt said it could be 10 tons spread over hundreds of kilometers. “Think of the rubble from three pickups,” he said.

The largest cascade of space debris on the surface occurred when the space shuttle Columbia disintegrated over Texas in 2003 when it reentered the atmosphere on its way to a landing in Florida. The seven astronauts on board died, but no one on the ground was injured when 85,000 pounds of debris fell on sparsely populated areas. However, if the disaster had occurred a few minutes earlier, heavy parts of the spacecraft such as the thrusters could have hit the ground near Dallas at hundreds of miles per hour.

China’s new space station is intended as an alternative to the international space station. The current orbiting outpost, jointly built by NASA, Russia, and other partners, has kept humans continuously in space for more than two decades. However, Chinese astronauts have been banned by a US law prohibiting cooperation with China in space.

After the broadcaster’s main residential area launched on April 29, China’s leader Xi Jinping called it “an important pilot in building a powerful nation in both technology and space,” according to the state television network. CCTV.

Chinese space officials have not publicly addressed the uncontrolled reentry since then, despite worldwide attention and concern.

The Global Times, a Chinese Communist Party-controlled newspaper, quoted scientists and experts on Wednesday that there was little danger and that the space administration had “carefully examined” the prospect of falling debris.

Often reflecting the views of more Hawkish officials, the newspaper said the concerns and criticism reflected Western efforts to discredit China’s space program.

More launches of Long March 5B are pending, and unless the way China works, the chances of someone being injured by a falling booster will increase.

“The chances of you winning the lottery today are slim – and I bet my paycheck you won’t – but the odds that no one wins the lottery is a whole different bet,” Muelhaupt said. “And that’s the thing. The risk to a person is tiny. However, the risk to all people is not. “

Last week’s start was the first of eleven planned over the next year and a half to build the Tiangong. In June, three astronauts could fly to the station aboard a spacecraft from Shenzhou. This would be China’s first crewed mission since 2016. If everything goes as planned, the space station will be fully operational by the end of 2022.

Qiqing Lin and Claire Fu did research.