Generally one mass(satellite) orbits about another mass(earth). Consider them each as a mass concentrated at a single point each. Typically the smaller mass object orbits in an elliptical path with the larger mass at one of the focii. Now the focus about which the smaller mass travels is at the center of the earth. Consider a special case orbit that is circular so that the focii are at the same point. The attraction of these two masses, gravity, must be offset by the centrifugal force that results from their circular motion to keep the smaller mass in its circular orbit about the larger mass. This orbit must have its center at the earth's center so it follows a "great circle" route around the earth's center of mass.