Solar Flare Protection for Manned Lunar Missions: Analysis of the October 1989 Proton Flare Event 911351

Several large solar proton events occurred in the latter half of 1989. For a moderately shielded spacecraft in free space, the potential exposure would have been greatest for the flare which occurred between October 19 to 27, 1989. This flare was comparable to the large flare event of August 1972. The temporal variations of the proton energy spectra at approximately 1 AU were monitored by the GOES-7 satellite. These data, recorded and processed at the NOAA-Boulder Space Environment Laboratory, provide the opportunity to analyze dose rates and cumulative doses which might be incurred by astronauts in transit to, or on, the moon. Of particular importance in such an event is the time development of exposure in the early phases of the flare, for which dose rates may range over many orders of magnitude in the first few hours. Consequently, special attention is given to the early time variation of the dose rate. The cumulative dose as a function of time for the entire event is also predicted. In addition to basic shield calculations, dose rate contours are constructed for flare shelters in free-space and on the lunar surface. For longer duration lunar missions, the impact of such a flare exposure is assessed in relation to the predicted steady dose rate of the galactic cosmic rays.