1 Introduction.- 2 The Earth's Gravitational Field and Basic Methodology.- 3 The Effect of Earth's Equatorial Ellipticity.- 4 Sun and Moon Effect.- 5 Combined Effects of the Sun, Moon, and Solar Radiation Pressure.- 6 Station-Keeping.- 7 Verification of the Theory by the Early Bird Synchronous Satellite.- Appendix A. The Fourth-Order Earth Gravitational Potential Model.- Appendix B. Constants in (4.97), (4.98), (4.103), and (4.104).- Appendix D. Expressions of Constants in (4.127), (4.128), and (5.39).- Appendix E. Satellite under the Influence of a Low Thrust Having a Fixed Angle with Its Orbital Radius Vector.- Appendix F. Fourth-Order Earth Gravitational Potential Model Constants Used in Numerical Integration Computer Program.