By considering the global fading process on the link caused by rain attenuation and amplitude scintillations, particularly at Ka band, it is possible to derive a long-term statistical model of the satellite channel capacity. Such a model gives a more realistic account of the channel behavior than has so far been presented using conventional system design approaches, whereby only the dominant fading process is considered. The paper presents the four-parameter distribution, which combines amplitude scintillations and rain fade within an up/down link system. It also presents the degradation (and improvement) of BER in the presence of amplitude scintillations, thus complementing the flat fade effect due to rain only. By implementation of adaptive communication systems, a more efficient channel capacity utilization is then possible. The paper illustrates the concepts and the use of novel analytical expressions, combining a log normal model of rain fade with a Mouls-ley-Vilar distribution for scintillations, are illustrated. These are then applied to a VSAT example of a 29/19 GHz digital communications link through the Olympus satellite using M-ary PSK modulation schemes.