What is the probability that a free-falling missile somewhere in the world will kill one person? There’s about a 10 percent chance over the next decade if current space industry practices remain the same, according to the authors of a new paper published in the journal natural astronomy†
While that’s not a huge risk, the threat is significantly greater in some parts of the world than in others. In particular, many countries in the Global South is likely dealing with a higher proportion of space debris, even if they aren’t responsible for it, according to the analysis. And it could become a bigger problem as rockets are launched into space more often to carry a growing number of satellites.
“It’s a statistically low risk, but it’s not negligible, and it’s increasing — and it’s completely avoidable,” said Michael Byers, lead author of the analysis and a professor in the Department of Political Science at the University of British Columbia. “So, should we take available measures to eliminate victim risk? I think the answer should be yes,” he says.
As rockets propel themselves into space, they usually drop their own weight — they lose “stairs” or rocket bodies containing empty fuel tanks and engines that are no longer usable for launch. Some rockets drop boosters before reaching orbit and can usually target the ocean with some precision (it helps that oceans cover most of the Earth’s surface).
If a rocket has already entered orbit, it’s possible to safely guide that equipment back to Earth, back into the ocean, using re-ignited engines. SpaceX has also become famous for landing parts from its Falcon 9 rocket so they can be reused, and the company also conducts controlled deorbits of the parts it can’t salvage.
Some rocket stages are still left in orbit after launch — which is the focus of this new article.
To date, there has been no documented death of an uncontrolled rocket entering the atmosphere. But in 2020, a 40-foot (12-meter) pipe and other debris from China’s Long March 5B missile crashed into two villages in Côte d’Ivoire.
Last year, there was another nail-biter when a 30-meter-high Chinese rocket stage weighing about 20 tons plunged back to Earth. It eventually crashed into the Indian Ocean after scaring cities like New York and Madrid under its path. That was the spark for the research Byers led, with help from his son, a student at the University of Victoria, who is also an author on the paper.
Looking back at the last 30 years of rocket launches, Byers and his colleagues found that Jakarta, Indonesia, Mexico City, Mexico and Lagos, Nigeria are at least three times as likely to see an uncontrolled rocket body enter the atmosphere above them as Washington. , DC and New York City in the US.
“The risk on an individual level is very, very small… [but] if you live in a densely populated city at 30 degrees latitude, that should worry you more,” Byers said. That’s because much of the debris from uncontrolled reentry comes from rockets launching payloads into geosynchronous orbit, which roughly follows Earth’s equator and allows a satellite to match Earth’s rotation. There is also a “significantly increased risk” about 30 degrees north of the equator because of the population density at that latitude, Byers said.
If governments impose changes and the space industry is willing to shoulder the extra costs, that risk could disappear. The newly published article points to international agreements that could serve as an example, such as the 1987 Montreal Protocol, which banned much of the ozone-depleting substances previously used as refrigerants in air conditioners and refrigerators. It may mean carrying smaller payloads so that there is enough fuel left to safely guide a discarded rocket stage back to Earth. Fortunately, it seems that the industry is already beginning to adapt.
“Current common practice has yet to go, ‘Oh, well, that’s too bad. We leave the rocket stage in a geotransfer orbit and let it return uncontrollably.’ And that’s starting to change, especially in the US,” said Jonathan McDowell, an astrophysicist at Harvard. The Space Force, for example now requires their launchers to move rocket stages out of orbit. And SpaceX is designing a next-generation rocket called Starship that should be completely reusable.
“The common practice in aviation is to maximize safety. And we believe that the same approach should be taken for space launches,” says Byers. So while it’s still quite unlikely that pieces of a free-falling rocket will land on someone’s head, Byers thinks more can be done to make spaceflight so much easier. safe as possible.