A new model of cumulative solar proton event fluences is presented. It allo
ws the expected total fluence to be calculated for a given confidence level
and for time periods corresponding to space missions. The new model is in
reasonable agreement with the JPL91 model over their common proton energy r
ange of > 1 to > 60 MeV. The current model extends this energy range to > 3
00 MeV. It also incorporates more recent data which tends to make predicted
fluences slightly higher than JPL91.
For the first time, an analytic solution is obtained for this problem of ac
cumulated fluence over a mission. Several techniques are used, including Ma
ximum Entropy, to show the solution is well represented as a lognormal prob
ability distribution of the total fluence. The advantages are that it is re
latively easy to work with and to update as more solar proton event data be
come available.