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

Abstract

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 t, with a mean of 116 t 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 were those between 30° and 60° 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 mainly 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 %.