Closest Approach Between a Ground Site and Earth Satellite

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

This submission includes two MATLAB scripts that can be used to determine closest approach conditions between a ground site or observer on an oblate Earth and a satellite in a circular or elliptical Earth orbit. Close approach conditions are computed and displayed whenever the satellite is visible to the ground site or observer. 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 the method described in “Fast Orbit Propagator for Graphical Display”, Journal of Guidance, Control and Dynamics, Vol. 14, No. 2, March-April 1991, by F. Landis Markley and James F. Jeletic. In the second script, site2sat2, the satellite orbit is propagated using an RKF78 numerical integration method which includes the oblateness term in the first-order orbital equations of motion.