Sun synchronous orbits near critical inclination, including lunisolar and solar pressure perturbations

The paper develops a theory for sun synchronous orbits near the critical inclination 116.6 deg (semimajor axes between 1.54 and 1.70 earth radii). Discussion includes perigee oscillations and double resonances. Stability in the presence of coupling is analyzed in order to find stable orbits which combine the stable perigee features of critically-inclined orbits with the constant ground illumination feature of sun synchronous orbits. The long period Hamiltonian differential equations are derived by repeated application of the method of averaging. Luni-solar perturbations are included, as are all measured zonal harmonic coefficients in the geopotential. Finally, the effects of direct solar radiation pressure upon an unshadowed stable equilibrium orbit are assessed.