Study calculates chances of space debris entering busy airspace

The chance of space debris hitting an aircraft is very low, but the research from a team at the University of British Columbia (UBC) highlights that the potential for uncontrolled space debris to disrupt flights and create additional costs for airlines and passengers is not. The research is published in Scientific Reports.

In 2022, a re-entering 20-tonne piece of rocket prompted Spanish and French aviation authorities to close parts of their airspace. With rocket launches and flights increasing, UBC researchers said policymakers need to act.

“The recent explosion of a SpaceX Starship shortly after launch demonstrated the challenges of having to suddenly close airspace,” said first author Ewan Wright, an interdisciplinary studies doctoral student at UBC. “The authorities set up a ‘keep out’ zone for aircraft, many of which had to turn around or divert their flight path. And this was a situation where we had good information about where the rocket debris was likely to come down, which is not the case for uncontrolled debris re-entering the atmosphere from orbit.”

When objects such as satellites are launched by rockets into space, large portions of the rockets are often left in orbit. If these leftover rocket stages have a low enough orbit, they can re-enter the atmosphere in an uncontrolled way. Most of the material will burn up in the atmosphere, but many pieces still hurtle towards the ground.

The researchers used the number of aircraft on the busiest day of 2023 and matched it to the probability of rocket pieces re-entering above various levels of air traffic, calculated using a decade of data. Denver, Colorado had the highest density of air traffic on that day, at about one aircraft every 18km2.

Using this as their peak, they calculated the probability of rocket junk re-entering the atmosphere over different air traffic density thresholds. When they looked at regions that have 10 per cent of the peak air traffic density or higher, such as the type of activity seen in the airspace over Vancouver-Seattle, they found a 26 per cent chance per year of rocket junk re-entering in that type of airspace.

“Notably, the airspace over southern Europe that was closed in 2022 is only five per cent of the peak. Around the world, there is a 75 per cent chance of a re-entry in such regions each year,” said Wright.

According to UBC, there were 258 successful rocket launches in 2024, and 120 uncontrolled rocket debris re-entries, with over 2,300 rocket bodies still in orbit. Air passenger numbers are expected to increase by almost seven per cent in 2025, according to the International Air Transport Association.

The researchers also calculated the annual probability of space rocket junk colliding with an aircraft at one in 430,000.

When space rocket junk enters busy air space, aviation authorities either allow flights to continue or act by diverting flights or closing airspace.

“But why should authorities have to make these decisions in the first place? Uncontrolled rocket body re-entries are a design choice, not a necessity,” said co-author Dr. Aaron Boley, associate professor in the department of physics and astronomy. “The space industry is effectively exporting its risk to airlines and passengers.”

To counter this, the industry could use rockets that are designed to re-enter the atmosphere in a controlled way after use, a solution that requires collective international action, said co-author Dr. Michael Byers, a UBC political science professor.

“Countries and companies that launch satellites won’t spend the money to improve their rockets designs unless all of them are required to do so,” he said. “So, we need governments to come together and adopt some new standards here.”