The risk of casualties from the uncontrolled re-entry of spacecraft and orbital stages

Pardini C., Anselmo L.

Uncontrolled reentries  Casualty risk  Statistics  Evolution  Geographical distribution  Intact objects  Spacecraft  Orbital stages 

From the beginning of 2010 to the end of 2022, 951 intact objects (spacecraft and orbital stages) with a radar cross-section greater than one square meter re-entered the Earth's atmosphere uncontrolled. The total returned mass was about 1500 metric tons, with a mean of 116 metric tons per year, mostly concentrated (80%) in orbital stages. On average, objects with a mass greater than 500 kg re-entered every 8 days, those exceeding 2000 kg every 2 weeks, and those above 5000 kg around 3 times per year. Only 4% of the re-entries came from orbits with an eccentricity greater than 0.1, while 41% were from nearly circular orbits with eccentricity lower than 0.001. 52% of the re-entries occurred in the northern hemisphere and 48% in the southern one. The areas of the planet most affected where those between 30 deg and 60 deg north. However, excluding the polar regions, the re-entry flux per unit area was relatively uniform, from 60° south to 60° north, implying a ground casualty risk manly driven by the population density. 84% of orbital stages and 19% of spacecraft exceeded a casualty expectancy of 10-4, the ceiling recommended by several guidelines and standards worldwide. The total ground casualty expectancy over the 13 years analyzed was estimated to be 0.194, corresponding to a probability of injuring or killing at least one person of about 18%. After remaining relatively stable from 2010 to 2018, the casualty expectancy and probability have grown systematically from then on, leading in 2022 to a chance of casualty of 2.9%, with orbital stages and spacecraft contributing, respectively, 72% and 28%.

Source: 12th IAASS International Space Safety Conference "Making Space Travel Safer", pp. 13–23, Osaka, Japan, 22-24/05/2023