摘要：As NASA prepares for longer duration missions beyond the geomagnetic field, the possibility of intensifying galactic cosmic ray (GCR) exposure raises possible concerns for mission planning and crew health and safety. Spaceborne satellite measurements have exhibited increasing GCR intensities and dose-rates over the past few solar minima, consistent with related heliospheric magnetic field data. Surrogate measures of solar activity (e.g., sunspot number records and radionuclide yields from ice cores and/or tree rings) combined with model predictions have also been used to infer that the Sun may be entering into a quiet period similar to the Dalton or Gleissberg minima when GCR fluences reached historically high levels. Using the most up-to-date models for characterizing the ambient GCR environment, physical interactions with shielding, and cancer risk, it is found that projected risks vary by only ±10% over all historical minima since 1750. To provide additional context for this level of variation, two different nuclear interaction models are used within the radiation transport algorithms used to propagate GCR ions and secondary particles through shielding and tissue. It is shown that switching the nuclear interaction model also introduces 10% difference, on average, in projected risks over all historical minima. Furthermore, it is noted that the quantified historical variation is within combined environmental and physics uncertainties already accounted for in the probabilistic cancer risk model used by NASA for crew health and safety considerations.
