A major perturbation (disturbance and trouble) of the close artificial satellite orbits: An atmospheric drag is caused by the resistance of the atmosphere. The secular effects are decreasing eccentricity, semidiameter (apparent radius of a celestial body when viewed as a disk from the earth), and period.

An atmospheric drag can be a critical perturbation of the orbits of closely adjacent low-orbit artificial satellites due to atmospheric resistance. The effects, extending over ages of time, are semidiameter, period, and decreasing eccentricity.