Following insertion, a spacecraft's orbit is essentially fixed, although effects, such as venting and atmospheric drag, can cause orbital perturbations. OMS or RCS thrusting periods can be used to correct or modify the orbit, as required, for mission operations. The direction and magnitude of the thrusting period, as well as the time of application, determine the resulting shape of the orbit.

A posigrade thrusting period increases the speed at the point of application and will raise every point of the orbit except the thrusting point. A retrograde thrusting period decreases the speed at the point of application and will lower every point of the orbit except the thrusting point.

An out-of-plane thrusting period alters the inclination of the spacecraft's orbital plane. It does not change the vehicle's period of orbit or height above the Earth.

A radial thrusting period is one in which the thrust is applied in a direction perpendicular to the spacecraft's velocity vector and in the vehicle's orbital plane. With the vehicle in a circular orbit, a radial thrusting period would be applied along the radius vector either toward or away from the center of the Earth.