Prediction of Solar Particle Events for Exploration Class Missions

Abstract

Manned space missions beyond the Earth’s magnetosphere require forecasts of solar activity to insure that crews are safe enough to perform their duties and live normal lives after they complete their missions. Solar flares and associated activity produce temporary increases in the number of ionized particles in interplanetary space near Earth, Mars, and the Moon. These increases, called Solar Particle Events (SPE), typically last a few hours and are a source of radiation intense enough to degrade people’s ability to perform physical activity, to cause lingering after effects such as cancer and cataracts, and in extreme cases, to endanger lives. Crews on missions beyond the protective shield of Earth’s atmosphere and magnetic field can go into storm shelters or take protective chemicals if they have timely forecasts of SPEs. A forecast and observing system for SPEs and associated solar activity is already in place. In this paper, comparisons of forecasts and observations for the past several years are analyzed to identify strengths and shortcomings of the present program. This data indicates that forecasts made tens of minutes to a few hours in advance are rather reliable in forecasting whether SPEs will occur but are less reliable in forecasting the intensity of SPEs. Longer term forecasts, made one to three days in advance, would be useful for planning exploration trips away from protective shelters. Though such forecasts are moderately reliable for solar flares, they are less reliable in forecasting whether a SPE will follow.

This evaluation provides guidance for planning a forecasting system for future missions. The principal components can be copied in a Martian system. Improvements needed include better observations and research to incorporate the effects of shocks in producing and moderating SPEs and observations and research to improve the prediction of solar activity that will produce SPEs before the source activity occurs.