DETERMINING SATELLITE CLOSE APPROACHES .2.

Improvements to the original Alfano/Negron Close Approach Software (AN CAS) tool are presented that increase accuracy and/or step size. Minim um spacing between two satellites is determined by creating a time-dep endent third-order relative-velocity waveform produced from adjoining pairs of distances, velocities, and accelerations. Times of closest ap proach are obtained by extracting the real roots of the localized poly nomial with the associated distances reconstructed from a set of fifth -order polynominals. Close approach entrance and exit times for an ell ipsoidal quadric surface are found using a similar process. Both metho ds require a simplified computation of acceleration terms of the objec ts of interest. For this study a close approach truth table is constru cted using a 0.1 second sequential step along the orbits and differenc ing the two position vectors. The simulation results show this algorit hm produces close approach times almost identical to those of the trut h model for larger time steps (up to 10 minutes), with a corresponding reduction in computer runtime. The results are created from real orbi tal data and include solution sets for three operational uses of close -approach logic. Satellite orbital motion is modeled by, but not limit ed to, first-order secular perturbations caused by mass anomalies.