Hatem N. Nounu

Radiation Shielding Evaluation Tools for Risk Reduction on Future Human Space Missions

As the focus of future human space missions shifts to destinations beyond the geomagnetic protection of low Earth orbit such as Near Earth Asteroids (NEA), the moon, or Mars, risks associated with extended stay in hostile space radiation environments need to be well understood and assessed. Since future spacecrafts designs and shapes are evolving continuous assessments of shielding and radiation risks are needed to optimize such designs for radiation protection. In this study, we present a predictive software capability that calculates risks to humans inside a spacecraft prototype and locates weak points in the spacecraft’s radiation shielding. The software uses CAD software, Pro/Engineer, and the Space Radiation Program’s Fishbowl tool kit to quantify radiation shielding provided by the spacecraft geometry by calculating the areal density seen at a certain point, dose point, inside the spacecraft. Shielding results are assessed using the NASA-developed software, HZETRN, BRYNTRN, and QMSFRG to quantify particle spectra at sensitive organs in a human body located in the vehicle exposed to GCR or SPEs. Organ doses are used to quantify risks on astronauts’ health and life using the NASA Space Cancer Risk (NSCR) code. The software locates shielding weak points-hotspots-and visually shows them on the spacecraft’s outer surface by creating a red mark on the surface where the shielding is below a safety threshold set by designers. A color coding capability of the software allows the outer surface to have different colors based on the shielding provided to a single dose point inside the spacecraft. This study presents a future Martian Transport Vehicle prototype design and shows the iterative process of optimizing the mass distribution based on feedback from the predictive software capabilities. The impact of design optimization on point dose and effective dose for August 1972 SPE shows a dose reduction of 7 and 3 folds respectively.

Improvement of Risk Assessment from Space Radiation Exposure for Future Space Exploration Missions

Protecting astronauts from space radiation exposure is an important challenge for mission design and operations for future exploration-class and long-duration missions. Crew members are exposed to sporadic solar particle events (SPEs) as well as to the continuous galactic cosmic radiation (GCR). If sufficient protection is not provided the radiation risk to crew members from SPEs could be significant. To improve exposure risk estimates and radiation protection from SPEs, detailed evaluations of radiation shielding properties are required. A model using a modern CAD tool ProE™, which is the leading engineering design platform at NASA, has been developed for this purpose. For the calculation of radiation exposure at a specific site, the cosine distribution was implemented to replicate the omnidirectional characteristic of the 4π particle flux on a surface. Previously, estimates of doses from SPEs to the blood forming organs (BFO) were made using an average body-shielding distribution for the bone marrow based on the computerized anatomical man (CAM) model. The development of an 82-point body-shielding distribution at BFOs made it possible to estimate the mean and variance of SPE doses in the major active marrow regions. Use of the detailed distribution of bone marrow sites and implementation of the cosine distribution of particle flux is shown to provide improved estimates of acute and cancer risks from SPEs.