Collision Risk Posed to the Global Positioning Systemby Disposed Upper Stages

Abstract

Block IIF satellites in the Global Positioning System will be directly inserted into the constellation by the Evolved Expendable Launch Vehicle. However, the upper stages will not be able to relocate to recommended disposal orbits above the constellation and will remain at least partially in the constellation. The purpose of this study is to determine the collision risk posed to the operational constellation by the disposed upper stages. The analysis includes the effect of the long-term eccentricity growth of the upper-stage disposal orbits. Because eccentricity growth is very sensitive to the initial conditions of the disposal orbit, it is necessary to account for the statistical spread in the initial conditions. This spread is caused by dispersions in launch vehicle and upper-stage maneuvers and by inability to predict the sequence of orbit planes in which disposal will occur. A Monte Carlo procedure was used to quantify this statistical variation. Only one version of the launch vehicle was considered here. Study results include 5-, 50-, and 95-percentile profiles over 200 years of cumulative collision probability and cumulative number of collision avoidance maneuvers that may have to be performed by operational constellation satellites.