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Records of solar x-ray emission during the Apollo 8 manned lunar-orbiting mission show only one significant x-ray event. Comparison of this event with other large flares shows that it is completely overshadowed by two huge flares which occurred in July 1968. Events as large as those of July 1968 must be considered possible during the next year or two. (Author)

X-ray and particle emission during solar flares can sufficiently increase the electron density in the lower regions of the ionosphere to cause disruption of high-frequency radio communications. Criteria have been established to predict periods of high solar activity during which solar flares capable of disrupting communications might occur. A study of solar-flare occurrence and solar x-ray flux levels over 14 months has shown that solar flares are three times more likely to occur when the criteria are met than when they are not met. (Author)