On the decision making criteria for cis-lunar reference mission scenarios

Space agencies are currently developing reference mission scenarios to determine if occupational dose limits, already adopted for low-Earth orbit (LEO) missions to the International Space Station (ISS), are also applicable for deep space cis-lunar missions. These cis-lunar missions can potentially last upwards of a year, during which astronauts will experience a daily low-dose from galactic cosmic radiation (GCR) and a potentially high-dose from single, or multiple, solar particle events (SPEs). Unlike GCR exposure, SPEs are difficult to predict and model due to their sporadic nature. Consequently, mission planners have decided to rely on historical SPE spectra to prepare for the 'worst case' scenario. Assuming a spherical aluminum shell as a reference spacecraft, this paper demonstrates how the choice of SPE parametric model, shield thickness, dose metric, and radiation transport code can impact the decision-making criteria for the worst case SPE, the estimated GCR dose, and consequently whether current LEO dose limits are applicable.