Cosmic Ray Fluxes and Permissible Mission Duration Derived from CRaTER Observations

Abstract:

Space weather conditions play a large role in establishing risks for manned space exploration. The biological risks incurred from ionizing radiation exposures can be a limiting factor in determining mission duration. This is especially true for prolonged exploration missions such as a manned mission to Mars, or a deep-space base of operations orbiting the moon. Galactic cosmic radiation (GCR) serves as the primary source of radiation exposure for such long duration missions. The GCR background varies in both magnitude and energy according to solar modulation potential, which is driven by solar activity. Various models and parameterizations of solar modulation potential exist throughout literature and traditionally rely on ground-based surrogate observations, such as neutron monitor data. However, atmospheric and terrestrial influences introduce an additional layer of uncertainty to such measurements. The dose rates observed by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) aboard the Lunar Reconnaissance Orbiter provide a more direct measurement of solar modulation potential. In this work, we provide the methodology for extracting solar modulation potential from CRaTER observations, as well as an analysis of the solar modulation potential observed by CRaTER over the course of the Lunar Reconnaissance Orbiter mission. The observed solar modulation potential timeseries is compared to existing model predictions. Finally, the resulting permissible mission duration, according to the NASA permissible exposure limits, for both male and female astronauts in transit-craft shielding configurations are presented.