Collision probabilities among the satellites of the second Dnepr launch

The close approaches among the seven bodies (five payloads and two parts of the rocket third stage) injected into orbit during the second Dnepr launch are analysed. Due to the Dnepr vehicle peculiar way of releasing the payloads, they were inserted in very similar orbits, hence an interest has arisen in this near passage events case study. Having defined a 20×8×8 (along-track, radial, out-of-plane) km wide "encounter ellipsoid", the satellites orbits were propagated from the Two-Line Elements, resulting in 22 close encounters occurred from the second orbital month to March the 8th 2001. The features of such close approaches (distance, relative velocity components) are examined; however, as all the payloads are microsatellites, the collision probabilities are extremely small. A forecast of future encounters is also presented, in order to statistically evaluate the global collision probability for each satellite.