Interference effects are of utmost importance to the reliable design of satellite communication systems. In this paper, the differential rain attenuation from an adjacent Earth-space system as well as the rain cross polarization (valid only for frequency reuse systems) are considered as the dominant interference sources. In particular, a method to predict the carrier-to-interference ratio statistics, used for noise dominant systems, is extended to include the general case when the calculation of the carrier-to-noise plus total interference ratio (CNIDR), in the presence of rain fading conditions, is needed. In this way, the total outage time of the interfered system can be calculated. The method is again based on a model of convective rain cells and on the lognormal assumption for point rainfall rate statistics. The numerical results examine the influence of various parameters upon the total availability performance. The deduced conclusions will be very useful toward the optimum design of modern satellite systems where frequency and orbital congestion is expected to be a serious problem.