Rain-induced attenuation is a factor of utmost importance in designing a satellite link since it can strongly deteriorate the availability and performance of an Earth-space path. Availability and performance are key criteria for the reliable design process. In the present paper the statistics of carrier-to-noise plus interference ratio under rain fade conditions are examined, given that the interference is caused by an adjacent satellite operating at the same frequency, and taking also under consideration double site diversity protection as a countermeasure technique. The method presented herein is based on a model of convective rain cells and the lognormal assumption for the point rainfall statistics. Numerical results have been obtained for heavy rain climatic regions and very large availability times, to examine how effective site diversity can be, not only for lowering fade margins but for compensating severe interference effects. Moreover, the elaboration of the numerical results has revealed how the optimum design of the satellite link can be achieved by selecting proper values for some critical parameters of the system.