Statistical analysis of conjunctions in Low Earth Orbit

Abstract

In order to describe the risk in space, the European Space Agency releases an Annual Environment Report containing numbers and statistics concerning the debris population and space activities in general. Since 2021, the risk in Low Earth orbit is described also from the perspective of conjunction statistics. For this, a new methodology is proposed that makes use of ESA’s Collision Risk Assessment Software to generate conjunctions for a set of generic targets as well as mapped uncertainty values to further assess the collision probability. The conjunctions are further evaluated by describing the object class and therefore allow a comparison of the involved chasers depending on the altitude and inclination. The analysis reveals that different orbital regions are exposed to different object classes, with significantly high shares of large constellations and fragmentation debris. In lower altitudes, high-risk conjunctions with active and inactive payloads exceed conjunctions with fragments and thus underline the risk induced by emerging mega-constellations or small satellites. This situation is particularly apparent when observing the trend of those conjunctions for the past years. For operators, this could assist the mission planning and risk evaluation for payloads. Finally, the approach is used to describe the conjunctions for a set of real targets that have been labelled as especially important from a risk perspective.