Assessment of Acute Radiation Outside Low Earth Orbit: Likelihood and Integration for Mission Risks

For human spaceflight missions outside low Earth orbit, there is an increased risk to astronaut health due to space radiation. Solar particle events are one of the components of space radiation that constitute this risk due to their probabilistic nature in occurrence and severity. From 30 years of solar particle data, an analysis of solar particle events was conducted to derive model components for a probabilistic risk model. After generating fluence spectra from the data analysis, dose from each event was calculated through the use of one of NASA’s online space radiation assessment tools, OLTARIS. To form the final model, a combination of the fluence and dose distributions with a literature occurrence rate model were integrated. Finally, an orbital scaling factor was applied to reduce event fluence further from the Sun and increase event fluence closer to the Sun. After verification and validation, the solar particle probabilistic risk model was used to generate the number of expected solar particle event numbers for a spacecraft with 5 g/cm^2 of aluminum shielding for different Mars transits. The transit with the highest risk was a Mars to Earth Venus swing-by transfer, which had approximately triple the number of expected solar particle events and four times the total expected transit dose compared to the other Mars transits. This result was expected since the Mars-Venus-Earth has the longest transit, and brings the spacecraft closest to the Sun, increasing exposure time and intensity. The average expected doses, even for the highest risk transit, are not likely to cause major astronaut health or mission impacts, but may need to be accounted for during mission planning and design. Future work on this model may include development of different shielding levels, application of more complex orbital scaling factors, and organ specific dose studies