The risk on the ground and in the airspace posed by uncontrolled re-entries: should the growth observed in recent years be considered worrying?

Between 2010 and 2024, the risk posed by uncontrolled orbital re-entries of spacecraft, upper stages, and large debris to people on the ground and commercial aviation was assessed using realistic models for the number and casualty area of surviving fragments, as well as for the latitudinal distribution of population and air traffic. Each re-entered object was analyzed individually, taking into account its dry mass and actual orbital inclination. Furthermore, the effects of complete atmospheric demise were evaluated for objects with a re-entry dry mass of less than 300 kg. The nominal estimates obtained with the various approaches are expected to be affected by uncertainties of a factor of 2 or 3. Throughout the decade from 2010 to 2019, the risk levels remained relatively stable. However, from 2020 onward, there was a significant increase in risk, primarily due to the intensification of space activities. In 2024, the estimated collective casualty probability for people on the ground ranged between the nominal values of 5 % and 10 %, depending on the assumptions and models adopted. In the same year, the likelihood of a commercial aircraft being struck by re-entry debris capable of causing catastrophic failure was assessed to be between the nominal values of 3.7 × 10−5 and 1.5 × 10−4. This equates to an average of one aircraft impact every 27,000–6700 years, respectively. For passengers aboard commercial aircraft, the nominal collective casualty probability ranged from 0.44 % to 1.82 %. Although the overall re-entry risk remains relatively low, a notable upward trend was observed between 2019 and 2024. Specifically, the number of uncontrolled re-entries increased by a factor of 7, the cumulative re-entered mass increased by a factor of 3, the ground casualty probability rose by a factor of 3–4, and the casualty probability for commercial aircraft passengers increased by a factor of 3–6. This marked escalation highlights the urgent need for timely and effective mitigation strategies to prevent risks from exceeding thresholds deemed unacceptable from both operational and societal perspectives.