Earth-space communications links operating above 10 GHz may be adversely affected by the earth's atmosphere and hydrometeors, particularly rain. These propagation phenomena are usually evaluated only for fading and depolarization effects. However, dispersion is an important factor in wide-band digitally modulated satellite links. In this paper we examine the mechanisms responsible for dispersion over bandwidths as great as 500 MHz in the 10-30 GHz range. The amplitude and phase effects of dispersion are quantified for a wide range of propagation conditions. The resulting propagation model is then used to generate estimates of performance degradation in wide-band QPSK systems through the use of computer simulation.