Satellite Orbital Decay Calculations

Abstract

The decay of a satellite from low earth orbit is of interest to many people. The drag force that such a satellite experiences is due to its interaction with the few air molecules that are present at these altitudes. The density of the atmosphere at LEO heights is controlled by solar X-ray flux and particle precipitation from the magnetosphere and so varies with the current space weather conditions. This article presents a simple model for atmospheric density as a function of space environmental parameters, and shows how this may be applied to calculate decay rates and orbital lifetimes of satellites in essentially circular orbits below 500 km altitude. A computer program in QBASIC is presented showing how the model may be implemented. Practical use and limitations of the program are discussed, and references are given to guide those interested in further study.