On the motion of nearly synchronous satellites

The longitudinal forces due to the very slight asymmetry of the Earth about its axis can have considerable effects on nearly synchronous satellites. For orbits of general inclination and eccentricity the disturbing function for the combination of all tesseral harmonics is developed in terms of the usual elliptic elements and the resonant terms retained. Provided the eccentricity is small and the satellite nearly synchronous, the motion in mean longitude relative to the Earth is approximately equivalent to a particle moving in a one-dimensional potential. The analysis is carried to the stage where it could be used to determine the even tesseral harmonic coefficients from observations on existing synchronous satellites, giving due consideration to lunisolar effects and other correction terms.