Radiation Uncertainties for Constellation Missions

Based on the information below, the non-biological uncertainty for integrated dosimetric quantities (ie dose, dose eq. etc.) is estimated to be approximately 25% for CEV and lunar exploration missions and a factor of two for the Martian surface. Larger uncertainties can be expected for distributions such as LET distributions and differential fluxes. Non-biological uncertainties are mainly due to uncertainties in the external radiation environmental models, transport algorithms, and nuclear and atomic physics models. Note that design limits are currently in terms of integrated dosimetric quantities (CxP 70023 and NASA-STD3001). The probabilistic nature of solar particle events has been accounted for in setting current design limits (CXP 70023) and is not accounted for here.


The NCRP 153 report summarizes the uncertainty associated with current generation of radiation transport codes as follows,

Contributions to uncertainties in radiation risk from these particle sources may be significant. For the GCR spectrum, present uncertainties in the models appear to be ~15%. For SPE spectra, the uncertainties may be much larger. Uncertainties in proton fluences measured by instruments onboard the Geostationary Operational Environment Satellites (GOES) are probably less than a factor of two. 4 Absorbed doses and dose equivalents 5 calculated using the current generation transport codes appear to be uncertain by <25 %, but individual spectral components, especially secondary neutrons, are probably much more uncertain. In addition, the uncertainty increases as the shielding thickness increases. For thick shielding, the uncertainty resulting from radiation physics models is probably still less than a factor of two. None of the existing GCR codes, however, properly treat all of the components produced in the transported radiation fields, especially the three dimensional nature of the secondary neutron and light ion fields produced by the nuclear fragmentation events involving the HZE particle components of the spectrum. Uncertainties in the biological risk due to the transmitted radiation fields present at critical body organs are possibly as large as a factor of four or more

For more detailed information see NCRP 153, Wilson et al. and references therein.

Note that the uncertainty estimates described above were not performed with the same versions of the code included in this radiation analysis tool. However, the majority of the models are similar with mainly minor differences in the present versions. Efforts are currently underway to validate the version in this tool against a wider set of data than has previously been considered.


CxP 70023, Constellation program design specification for natural environments

CxP 70024, Human-Systems Integration Requirements

NASA-STD-3001, NASA Space Flight Human System Standard - Volume 1: Crew Health

NCRP 153, National Council on Radiation Protection and Measurements. "Information Needed to Make Radiation Protection Recommendations for Space Missions Beyond Low-Earth Orbit" (2006)

John W. Wilson et al., "Verification and Validation: High Charge and Energy (HZE) Transport Codes and Future Development" NASA/TP-2005-213784 (2005)