Closest Approach Between a Ground Site and Earth Satellite

Determine the time and closest approach distance between a ground site or observer and an Earth satellite in a circular or elliptical orbit.

This submission includes three MATLAB scripts that can be used to determine closest approach conditions between a ground site or observer and a satellite in a circular or elliptical Earth orbit. These scripts use Brent’s one-dimensional, derivative-free minimization algorithm to calculate geometric close approach conditions.

In the first script (site2sat1), the orbit of the Earth satellite is propagated using Kozai’s method. In the second script (site2sat2) the orbit of the satellite is propagated using an RKF78 numerical integration method which also includes the oblateness term in the first-order orbital equations of motion. The third script (gsite2sat) creates a graphics display of the ground site-to-satellite distance for a user-defined simulation period.