International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / During the NASA Ka-band propagation experiment it was discovered that rainwater on the antenna caused significant attenuation. It is necessary to estimate the losses caused by water on the antenna in order to separate these losses from the atmospheric propagation losses. A prediction model is developed for losses caused by rainwater on a satellite dish antenna. The model is based entirely on physical parameters including elevation angle, dish diameter, focal length, properties of present coating layers, feed window properties, frequency, polarization, water temperature and rain rate. The prediction model is implemented using Matlab and has been tested against experimental data.