In mid-October 2023, a Boeing 737 flying at an altitude of 36,000 feet over Utah suffered a cracked windshield, prompting emergency landing procedures. While the exact cause remains uncertain—speculated to be a remnant of a weather balloon—this incident reignited concerns about the risk of aircraft being struck by space debris. Although the likelihood of such events is small, it is increasing, driven by the growing number of satellites in orbit.
According to the European Space Agency, approximately three pieces of old space equipment, including defunct satellites and used rockets, enter the Earth’s atmosphere each day. As satellite deployment accelerates, projections suggest that the number of active satellites may rise from around 12,900 today to as many as 100,000 within the next decade. To mitigate the risk of collisions, operators typically attempt to direct old satellites to burn up upon reentry. However, the physics of this process is not fully understood, making it difficult to determine how much debris survives the descent.
Richard Ocaya, a professor of physics at the University of Free State in South Africa, notes that “the number of such landfall events is increasing.” He anticipates an exponential growth in these incidents in the near future. So far, no injuries have been reported from space debris strikes, but close encounters are becoming more frequent. In March 2022, a 0.7-kilogram metal fragment struck a house in Florida, identified later as part of a battery pallet discarded from the International Space Station. A resident was resting in an adjacent room during the incident. Similarly, a 1.5-meter piece of SpaceX’s Falcon 9 rocket crashed near Poznan, Poland, earlier this year, while a 2.5-kilogram fragment of a Starlink satellite landed on a farm in Saskatchewan, Canada.
The potential for unnoticed strikes is significant. James Beck, director of Belstead Research, a UK-based space engineering firm, emphasizes that “if you were to find a bunch of burnt electronics in a forest somewhere, your first thought is not that it came from a spaceship.” He warns that the actual risk of space debris may be higher than what satellite operators disclose. For instance, while SpaceX claims its satellites are “designed for demise” and completely burn up upon reentry, Beck’s wind tunnel tests suggest that some components made from durable materials like titanium could survive.
Assessing the risk to aviation is challenging. The International Civil Aviation Organization has acknowledged that the rapid increase in satellite launches creates a new challenge for aviation safety that cannot be precisely quantified. Nonetheless, the Federal Aviation Administration (FAA) has provided preliminary estimates. According to a 2023 analysis, by 2035, the chance that an aircraft will experience a catastrophic encounter with space debris could be around 7 in 10,000 annually.
The risk to people on the ground could be substantially higher. Aaron Boley, an associate professor at the University of British Columbia, indicates that if megaconstellation satellites do not completely burn up upon reentry, the probability of a human injury or fatality from space debris could reach around 10% annually by 2035. This translates to a better than even chance that someone on Earth will be struck by space junk every decade. The FAA’s report posits an even more alarming scenario, estimating that “one person on the planet would be expected to be injured or killed every two years.”
To address these threats, experts are exploring how to integrate space debris considerations into air safety protocols. Okapi Orbits, a German space situational awareness firm, is collaborating with the German Aerospace Center and the European Organization for the Safety of Air Navigation (Eurocontrol) to develop systems that would allow pilots and air traffic controllers to receive timely alerts regarding space debris hazards. However, predicting the trajectory of debris poses its own challenges.
Recent advancements in artificial intelligence have improved the accuracy of predictions for space object paths, yet these systems often fail to account for atmospheric changes during reentry. As Njord Eggen, a data analyst at Okapi Orbits, points out, “even with high-fidelity models, there’s so many variables at play that having a very accurate reentry location is difficult.” Given that debris orbits the planet every hour and a half, even minor timing uncertainties can lead to significant discrepancies in impact locations.
The implications of space debris extend beyond potential strikes. To prevent accidents, authorities may temporarily close airspace in areas at risk, leading to flight delays and significant costs. Boley and his colleagues recently published findings estimating that regions with high air traffic, such as northern Europe and the northeastern United States, already face about a 26% annual chance of disruptions due to reentry of major debris items. As more satellite constellations are launched, the frequency of airspace closures associated with space debris risks could rival those caused by severe weather.
In 2022, when a 21-metric-ton Chinese Long March rocket was predicted to reenter the atmosphere, airspace over southern Europe was closed for 30 minutes, impacting hundreds of flights. Ultimately, the rocket landed in the Pacific Ocean. The effectiveness of current reentry predictions is under scrutiny, as many closures may be unnecessary.
International regulators are increasingly urging satellite operators to manage the end-of-life processes for large satellites and rocket bodies more responsibly. The European Space Agency estimates that only about half of the rocket bodies reentering the atmosphere do so in a controlled manner. Currently, around 2,300 old and uncontrollable rocket bodies remain in orbit, slowly descending towards Earth without safe deorbiting mechanisms.
Boley concludes that while the probability of space debris striking an aircraft is small, the likelihood of debris falling in busy airspace is considerably higher. “That’s actually quite likely,” he states, underscoring the urgent need for improved management and predictive systems to protect both aviation and public safety.
