Investigation of Secondary Neutron Production in Large Space Vehicles for Deep Space

Future human spaceflight programs will focus on deep space, asteroids, lunar, and Mars surface operations with larger, more massive spacecraft structures necessary for transportation of crew and cargo. In addition to the challenges of manufacturing and launching these larger, more massive structures, there are added challenges from the space radiation environment and its impacts on the crew, electronics, and vehicle materials. Primary radiation from the sun (solar particle events) and from outside the solar system (galactic cosmic rays) interact with materials of the vehicle and the elements inside the vehicle. These interactions lead to the primary radiation being absorbed with production of secondary radiation (primarily pions, nuclear fragments, and neutrons). With all vehicles, the highenergy primary radiation is of most concern. However, with larger, more massive vehicles, there are more opportunities for secondary radiation production in the larger spacecraft effective shielding thickness, which can be significant enough to cause concern. In a previous paper, we embarked upon our first steps toward studying neutron production in more massive vehicles by validating our radiation transport codes for neutron environments against flight data from the Space Shuttle, Mir, and the International Space Station. The following paper will extend the previous work to focus on the deep space environment and the resulting secondary neutron flux internal to vehicles that are more massive.