This article was revised shortly after publication to reflect an updated forecast from The Aerospace Corporation.
No, you are almost certainly not going to be hit by a 10-story, 23-ton piece of rocket returning to Earth.
That said, the odds are not zero. Part of China’s largest rocket, the Long March 5B, falls out of control in orbit after a section of the country’s new space station launched last week. The rocket is expected to fall to Earth in what is called an “uncontrolled reentry” on Saturday or Sunday.
Whether it’s harmless splashing in the ocean or impacts on the land people live in, why China’s space program allowed this to happen – again – remains unclear. And given the planned launch schedule by China, further uncontrolled rocket re-entries in the years to come are possible.
The country’s space program has made a series of major spaceflight achievements over the past six months, including returning rocks from the moon and putting a spacecraft into orbit around Mars. Yet it continues to create even minimal danger to people all over the planet by not controlling the trajectory of the rockets it launches.
“I think that’s remiss of them,” said Jonathan McDowell, an astrophysicist at the Center for Astrophysics in Cambridge, Massachusetts, who tracks the whereabouts of objects in space. “I think it’s irresponsible.”
The part that will fall out of the sky somewhere is the base booster stage of the Long March 5B, which was designed to lift the large, heavy pieces of the space station. For most rockets, the lower stages usually return to Earth immediately after launch. Upper stages that reach orbit typically trigger the motor again after releasing their payloads, guiding them re-entry into an unoccupied area like the middle of an ocean.
In the past three decades, only China has lifted such large rocket stages into orbit and dropped them somewhere random, Dr McDowell said.
For the Long March 5B recall, this could be anywhere between 41.5 degrees north latitude and 41.5 degrees south latitude. This means Chicago, located a fraction of a degree further north, is safe, but major cities like New York City could be affected by debris.
On Thursday, the Aerospace Society, a largely federally funded nonprofit that conducts research and analysis, predicts that the re-entry will be on Saturday at 11:43 p.m. EST. If this is correct, debris could spread over northeastern Africa, into Sudan.
The uncertainty over time – give or take 16 hours – and location remain important. A the day before, the aerospace prediction set the re-entry more than an hour earlier, over the eastern Indian Ocean.
The moment when the booster burns depends, for example, on the sun. An increase in the intensity of the solar wind – charged particles spewed out by the sun – would inflate Earth’s atmosphere, increasing atmospheric drag on the rocket thruster and hastening its fall. The fall of the rocket stage also complicates the calculations.
The United States Space Command and the Russian Space Agency are both researching the rocket core. Russia’s statement noted that the re-entry would not “affect the territory of the Russian Federation”. Space Command has promised regular updates before a possible re-entry.
Because the booster is traveling at 18,000 miles per hour, a change in minutes moves debris hundreds or thousands of miles. It was only a few hours before the start of the school year that the predictions became clearer.
“It’s an engineering decision based on probabilities,” said Dr. McDowell. He said the Chinese engineers could have designed the trajectory to remain suborbital, falling back to Earth right after launch, or they could have planned an additional shot of the engine to get it out of orbit in a way that does not present any possible danger.
“It’s no small feat to design something for a deliberate reentry, but it is nonetheless something that the world at large moved towards because we needed it,” said Ted J. Muelhaupt , Senior Director of the Center for Orbital and Re. Entrance Debris Studies.
China is planning many more launches in the coming months as it completes construction of the country’s third space station, called Tiangong, or “heavenly palace.” This will require additional mammoth rocket flights and the possibility of more uncontrolled re-entries that people on the ground will nervously monitor, although the risk of a single rocket stage is minimal.
“It is in the common interest of all nations to act responsibly in outer space to ensure the long-term safety, stability, security and sustainability of outer space activities,” Jen Psaki, Attaché, said on Wednesday. White House press release, adding that United Nations states hoped to promote “responsible space behaviors.”
Falling debris has a long, congested space flight.
In March, a rocket stage from a SpaceX Falcon 9 lit up the night sky over Seattle and then dropped debris on a Washington state farm when a scheduled second-stage engine firing for the dropping safely did not happen as expected.
China, on the other hand, has a long history of dropping pieces of its space equipment where they can.
Rockets from one of China’s main launch sites, the Xichang Satellite Launch Center in Sichuan Province, regularly hit rural areas downstream, sometimes causing damage. China has since moved many of its launches, including last week’s one, to a new site in Wenchang, a city in Hainan, an island off the southeast coast. From there, the rocket stages can safely fall into the sea.
In this case, however, the core of the rocket that carried the module for the new Chinese space station was also put into orbit and has since been slowly returned to Earth’s atmosphere.
Last year, the first launch of a Long March 5B rocket raised a prototype of the Chinese manned space capsule. The propellant of this rocket also made an uncontrolled reentry, with debris raining on a village in Côte d’Ivoire.
This drew a rebuke from then-NASA administrator Jim Bridenstine.
“It could have been extremely dangerous,” he said. “We’re really lucky in the sense that it doesn’t seem to have hurt anyone.”
China’s first space station, called Tiangong-1 and launched in 2011, also fell back to Earth in an uncontrolled descent in 2018 before harmlessly crashing into the South Pacific. The following year, the Chinese space administration succeeded in bringing the second station out of orbit and heading towards the Pacific. The booster stage is this time more than twice as massive as the first two space stations in Tiangong.
The United States also struggled with the return of its first space station to Earth. Skylab, which operated in 1973 and 1974, erupted when NASA scientists attempted to guide its descent in 1979. The 77-ton station mostly separated from the Indian Ocean, but debris dispersed throughout Western Australia. President Carter apologized.
In 2011, the Upper Atmosphere Research Satellite, or UARS, a former NASA satellite the size of a school bus, also fell back to Earth. NASA has calculated a one in 3200 chance that UARS, a little smaller than Tiangong-1 or Tiangong-2, will injure anyone in the field.
Dr McDowell said he believed the threat posed by the Long March 5B booster debris was likely comparable – unlikely but high enough to be of concern. Because the Chinese did not provide rocket design details, it is difficult to predict how much material will reach the surface.
Mr Muelhaupt said it could be 10 tonnes spread over hundreds of kilometers. “Think about the wreckage value of three pickup trucks,” he said.
The largest cascade of space debris on the surface occurred when the Space Shuttle Columbia disintegrated over Texas in 2003 as it re-entered the atmosphere en route to a landing in Florida. All seven astronauts on board died, but no one on the ground was injured as 85,000 pounds of debris fell on sparsely populated areas. But if the disaster had occurred a few minutes earlier, heavy parts of the spacecraft like the engines could have struck the ground near Dallas at hundreds of kilometers per hour.
The new Chinese space station is designed as an alternative to the International Space Station. The current orbiting outpost, jointly built by NASA, Russia and other partners, has kept humans permanently in space for more than two decades now. But Chinese astronauts have been excluded by a US law banning cooperation with China in space.
After the launch of what will be the station’s main living area on April 29, Chinese leader Xi Jinping called it “an important pilot project in building a nation that is both powerful in technology.” and in space, ”according to state broadcaster CCTV.
Chinese space officials have not publicly spoken about the unchecked re-entry since then, despite worldwide attention and concerns.
The Global Times, a newspaper controlled by the Communist Party of China, quoted scientists and experts on Wednesday as saying there was little danger and that the space administration had “carefully considered” the prospect of the falling debris.
The newspaper, which often reflects the views of more hawkish officials, said the concern and criticism reflected Western efforts to discredit China’s space program.
More launches of the Long March 5B are on the way, and unless there is a change in the way China is handling it, the chances of someone being injured by a piece of a booster in decline will increase.
“The odds of you winning the lottery today are minimal – and I’m betting my paycheck you won’t – but the odds that no one wins the lottery is a whole different bet,” Mr. Muelhaupt. “And that’s the problem. The risk to an individual is minimal. But the risk for all individuals is not. “
Last week’s launch was the first of 11 planned over the next year and a half to erect the Tiangong. In June, three astronauts could fly to the station aboard a Shenzhou spacecraft, which would be China’s first manned mission since 2016. If all goes according to plan, the space station will be fully operational by end of 2022.
Qiqing Lin and Claire Fu contributed to the research.