During collision probability computations, it is typically assumed that the velocity portion of the covariance can be ignored. However, when the relative velocity of the encounter is low, the velocity covariance could be significant in relation to the relative velocity. This study examines through Monte Carlo analysis the effect that such large velocity covariances have on the computation of the collision risk. An assessment of the typical sizes of the velocity uncertainty for on-orbit objects is performed and the likelihood that such low relative velocity / large velocity uncertainty encounters would occur is examined. The study consists of three parts. The first determines the level of velocity uncertainty that would typically be encountered through prediction of SGP4 elsets. The second examines through Monte Carlo analysis at what level of velocity uncertainty will the usual probability computations become unreliable. The third determines whether this issue is of practical concern for operational collision avoidance. It is found that large velocity uncertainty encounters will occur at about 2 conjunctions per satellite per year for LEO conjunctions and 1 conjunction per satellite every 3 weeks for GEO.
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