Space capacity-based metric to rank in orbit collision risk

Space capacity is a developing concept, with new models to describe and quantify it emerging in recent years. These models aim to define a sustainable threshold for the space environment, a limit which ensures the continued safety of future launches and satellite operations. They also seek to link this threshold to the impact of both new and existing objects in orbit, effectively assigning each object a share of the total capacity, or the portion it consumes. This definition should be internationally recognised and adopted, serving as the foundation for launch guidelines, debris mitigation strategies, and, more broadly, global Space Traffic Management. Within this work, the concept of space capacity refers to the capacity consumed by a population, examining how this consumption changes over time. The capacity model is applied to assess the level of risk posed by potential orbital fragmentation. The model compares the difference in space capacity consumption between a scenario with fragmentation and one without, in order to determine whether such an event has a significant impact on overall consumption. This approach provides more insights than just counting the number of objects or fragmentation events. (c) 2026 The Author(s). Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).