The core stage of a Chinese Long March 5B rocket is set to tumble uncontrollably back to Earth next week, in a reentry that China is tracking closely and has said poses little risk.
The roughly 25-ton (23 metric tons) rocket stage, which launched on July 24 to deliver the Wentian laboratory cabin module to China's incomplete Tiangong space station, is predicted to reenter Earth's atmosphere on July 30 at 7:24 p.m. ET, give or take 16 hours, according to researchers at The Aerospace Corporation's Center for Orbital and Reentry Debris Studies (opens in new tab).
Exactly where it will land is unknown, but the possible debris field includes the U.S., India, Australia, Africa, Brazil and Southeast Asia, according to The Aerospace Corporation (opens in new tab), a U.S. government-funded nonprofit research center based in California.
The first stage of a rocket, its booster, is typically the bulkiest and most powerful section. Usually, the trajectories of rocket boosters are planned so they avoid orbit and plop harmlessly into the ocean or, if they do make it to orbit, perform a controlled reentry with a few bursts from their engines. But the Long March 5B booster engines cannot restart once they have stopped, dooming the booster to spiral around Earth before landing in an unpredictable location.
This is the third time in two years that China has disposed of its rockets in an uncontrolled manner. In the second instance, in May 2021, the rocket debris landed harmlessly in the Indian Ocean. But the first incident, in May 2020, caused metallic objects to reportedly rain down upon villages in the Ivory Coast, although there were no reported injuries.
Due to their massive size, Long March 5B boosters can be especially risk-prone during uncontrolled reentry, meaning significant portions of their mass don't burn up safely in the atmosphere.
"The general rule of thumb is that 20% to 40% of the mass of a large object will reach the ground, but the exact number depends on the design of the object," Marlon Sorge, a space debris expert at The Aerospace Corporation, said in an online Q&A (opens in new tab). "In this case, we would expect about five to nine metric tons [6 to 10 tons]."
"Generally, for an upper stage, we see small and medium tanks survive more or less intact, and large engine components," Sorge added. "The large tanks and the skin of this core stage are likely to come apart. We will also see lightweight items such as insulation fall out. The melting point of the materials used will make a difference in what remains."
What's the risk?
According to The Aerospace Corporation, as more than 88% of the world's population is located under the rocket's orbital footprint, some surviving debris could land in a populated area. But Muelhaupt said the odds of this debris harming someone range from 1 in 1,000 to 1 in 230 and the risk to a single individual is much lower — around 1 in 6 trillion to 1 in 10 trillion. For comparison, he added, the likelihood of being struck by lightning is roughly 80,000 times greater. The internationally accepted casualty risk threshold for the uncontrolled reentry of rockets is 1 in 10,000, according to a 2019 report issued by the U.S. Government Orbital Debris Mitigation Standard Practices.
Despite the relatively low risk of damage to people or property, China's decision to launch rockets without options for controlled reentry has drawn some stern admonishments from U.S. space experts.
"Spacefaring nations must minimize the risks to people and property on Earth of reentries of space objects and maximize transparency regarding those operations," NASA Administrator Bill Nelson wrote in a statement (opens in new tab) after the 2021 Long March 5B crash landing. "It is clear that China is failing to meet responsible standards regarding their space debris."
"Why are we worried? Well, it did cause property damage the last time [in 2020], and people are having to do preparation as a result," Ted Muelhaupt, a space expert and consultant with The Aerospace Corporation, said during a news conference. "This is not needed. We have the technology to not have this problem."
China has dismissed these concerns as "shameless hype." In 2021, Hua Chunying, then-spokesperson for the Chinese Ministry of Foreign Affairs, accused Western reporting of bias and "textbook-style double standards" in its coverage of China's falling rockets. For instance, in March 2021, debris from a falling SpaceX rocket smashed into a farm in Washington state, an event she claims Western news outlets covered positively and with the use of "romantic words."
According to Article VII of the 1967 Outer Space Treaty, of which all the major spacefaring nations — including China — are parties, any country that sends an object into space is internationally liable for the damage it may cause to another party when it comes crashing back to Earth. If this were to happen, the incident would be processed in a claims commission or handled through diplomatic channels — such as in 1978, when the malfunctioning Soviet satellite Kosmos 954 crashed into western Canada, spraying a roughly 370-mile-long (600 kilometers) path with debris from its broken onboard nuclear reactor.
Christopher Newman, a professor of space law and policy at Northumbria University in London, said all of the major launch nations will have parts of space objects that return to Earth in an uncontrolled manner, but establishing an international consensus on how to deal with them is difficult given current geopolitical tensions.
"This is a problem that needs an international solution, especially as objects such as rocket bodies are three times more likely to impact on cities in the 'Global South,'" Newman told Live Science. "Yet we only have to look at the attitude of countries to space tracking and space situational awareness, as well as the debris problem in Earth orbit, to see that the international community is not yet motivated to try and solve this issue.
"As a lawyer, it is clear to me that momentum for change only comes when there is some form of disaster or tragedy — and by then it is often too late," he said. "The warnings are there for all users of space; the question is whether they will take action now to deal with them."
Originally published on Live Science.