Comparison of the Exclusion Volume and Probability Threshold Methods of Debris Avoidance for the STS Orbiter

摘要

Both the 'exclusion volume' and 'maneuver threshold' methods have been carefully investigated by performing detailed calculations of debris risk over time and debris avoidance maneuver rate for the Space Transportation System Orbiter and the International Space Station. The underlying mathematics of the two methods is identical. Also, conjunction screening is based upon an exclusion volume the efficiency of the screening exclusion volume is the limiting efficiency of the debris avoidance process, whether the threshold method or the exclusion box method is employed in the final decision process. This analysis shows the threshold method to have the advantages of somewhat better risk reduction and far fewer maneuvers. All computations are based on empirically determined covariance distributions for STS and the orbital debris population. The covariance of the ISS is assumed to be that of an orbital debris object, subject to the same atmospheric drag as the ISS. State vector covariances for STS were determined from recent tracking data for 2, 4, 8, and 12-hour propagation times for low, moderate, and high vehicle activity. These covariances were combined with the debris covariances, to determine the maneuver rate and fractional residual risk associated with different screening box shapes and sizes and different collision probability maneuver thresholds.