A novel model based on the bivariate inverse Gaussian (IG) distribution is presented for the prediction of the outage performance of a dual site diversity Earth-space system. In the present paper, the exceeded rain attenuation induced on each Earth-space path is assumed that follows the IG distribution. The joint rain attenuation exceedance probability is calculated using the long-term statistical parameters of rain attenuation on each individual slant path and adopting a spatial correlation coefficient of rain attenuation variables as a function of the separation distance of the two Earth-stations. The Earth-Space path Database of Study Group 3 (DBSG3) of International Telecommunication Union (ITU) is employed in order to compare the performance of the new method with the ITU-R P.618-10 outage model. The numerical results from the comparison tests are very encouraging.