Abstract : Three energetic solar proton events occurred in the August to October 1989 time period. The energetic (1-10 MeV proton fluence from these events was among the highest fluence levels observed during the space age. The solar proton events were of sufficient magnitude to produce easily observable (several percent), irreversible losses in solar array output on geosynchronous and polar low-earth-orbiting satellites. The degradation of solar array output was measured on the GOES-5, GOES-6, and GOES-7 satellites and on two other U.S. Government satellites in geosynchronous orbit. The observed solar array degradation was compared with that computed based on knowledge of the solar cell type, cover glass thickness, the operational mode of the array, the observed proton spectrum, and the length of time on orbit for each satellite. In each case, good agreement was obtained between the observed and the computed results. Solar Flares, Radiation Effects.