Short-term space safety analysis of LEO constellations and clusters

The large satellite constellations currently planned and deployed in Low Earth Orbit (LEO) bear some similarities with the clusters of derelict objects abandoned in different altitude bands in LEO. Given these similarities, an analysis of the collision risk associated with these orbital systems is performed with different analytical and numerical techniques. Different tools developed at IFAC-CNR for short to long-term constellation impact analysis are applied to ascertain the immediate (i.e., 1-20 years) effects related to the constellation deployment and execution and to evaluate the risk associated to the accumulation of massive derelict objects in a restricted region of space (i.e., clusters). The intra-group collision probability caused by the repeated orbital crossing between the members of two selected constellations and of some of the clusters of objects in LEO are computed, cumulated over the time span of the analysis (20 years) and compared. While the collision probability obtained in the case of the constellation could be efficiently mitigated by proper management and operations (i.e., debris mitigation practices and collision avoidance), the high level of risk associated with the clusters of derelict uncontrolled objects cannot be avoided, unless pro-active actions are undertaken to remove the large targets from the space. From all the analysis performed, the cluster located around 975 km of altitude stands up as particularly dangerous population in the already critical LEO region.