Laboratory erosion data, estimates of the rain environment, and the desired capabilities of the aircraft or missile can be utilized with a rain erosion damage model to provide a fairly reliable estimate of environmental degradation of infrared-transmitting windows and radomes throughout a flight trajectory. If water drop interactions with the flow field around the vehicle are ignored, the suggested approach will provide an upper bound on the extent of the water drop impact damage associated with a particular mission. The design philosophy is that if this level of damage can be tolerated, the actual impact conditions will not be detrimental. A wide range of flight scenarios can be examined on this basis. If the upper bound computation indicates that the resulting level of damage will be well beyond the tolerable limit, then aerodynamic analyses of water drop interactions with the flow field around the vehicle and a more complete statistical analysis of the impact damage will have to be undertaken.