Environmental impact of object breakup in medium-Earth orbit

Large derelict objects are severely affecting the sustainability of the space environment. This has brought attention on the importance of ranking in-orbit objects and future missions, based on the risk they pose to the proliferation of orbital fragments. To this purpose, several sustainability metrics have been formulated to guarantee a scientific support in the definition of remediation measures, as well as for the identification of safe orbital slots for future missions. The index ECOB (Environmental Consequences of Orbital Breakups) was developed with the objective of measuring the space environmental impact of an object in low-Earth orbit based on the risk it represents for satellites operations. The severity of a breakup was computed as the cumulative collision probability induced by the evolving debris cloud on the active satellites population. In this paper, the ECOB metric is extended to the medium-Earth orbital region, leveraging a density-based multi-dimensional fragments cloud propagator and collision risk estimator, capable of working with any arbitrarily complex orbital dynamics and conjunction geometry. The dependency of the effect of a breakup on the fragmentation orbit's shape and orientation is investigated and discussed. The currently in-orbit missions are eventually ranked based on the proposed metric.