For these small eccentricities, the actual satellite position oscillates sinusoidally about its nominal position on the circular orbit. To first order, it can be shown that where 6f is the variation of the true anomaly and M is the mean anomaly of the orbit. For the worst eccentricity, this corresponds to a maximum deviation from the nominal geostationary position of ±5°. Hence, the main affect of solar pressure is to cause the satellites to cyclicly deviate from their nominal positions by small angles. These effects can be controlled by the stationkeeping system to reduce the amplitude of the deviations. The most direct method of control is to continuously thrust in the opposite direction from the solar pressure. The AV per orbit provided by the stationkeeping system is For the reference configuration, the annual AV requirement is 311 m/sec. For approximately 45 days every six months, the satellites are eclipsed by earth for part of their orbit. All of the orbital elements are affected by the eclipsing. However, changes to the semimajor axis are the most important since they cause changes in the orbital period. The change in semimajor axis per orbit is given by
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