Operational Space Radiation Environment: Analogs, Pathogenesis, and Translation Into Clinical Outcomes in Humans
Texas A&M University, Department of Physics and Astronomy 
The study of human health risks of spaceflight typically involves analogs that closely
represent the space en- vironment. In most cases, theory, models, and study outcomes
can be validated with available spaceflight data or, at a minimum, observation of
humans subjected to analog terrestrial stresses. In contrast, space radiation research
is limited to the use of analogs or models that for many reasons do not accurately
represent the opera- tional space radiation environment or the complexity of human
physiology. For example, studies on the effects of space radiation generally use mono-energetic
beams and acute, single-ion exposures (including protons, lithium, carbon, oxygen,
silicon, iron, etc.) instead of the complex energy spectra and diverse ionic composi-
tion of the space radiation environment. In addition, a projected, cumulative mission
dose is often delivered in one-time, or rapid and sequential, doses delivered to experimental
animals. In most cases, these dose-rates are several orders of magnitude higher than
actual space environment exposures. Even the use of animal models introduces error,
as studies make use of a variety of animal species with differing responses and sensitivity
to radiation that may not represent human responses to similar exposures. Further,
studies do not challenge multi- ple organ systems to respond concurrently to the numerous
stressors seen in an operational spaceflight scenario. These disparities and numerous
other environmental considerations contribute to the large uncertainties in the outcomes
of space radiobiology studies and the applicability of such studies for extrapolation
and prediction of clinical health outcomes in future spaceflight crews. Here we present
a novel modeling approach of the GCR environment by utilizing large-scale multi-core,
high-performance computing and Monte Carlo methods to simulate 3D nuclear and subnuclear
interactions. We show that the linear energy transfer spectrum of the intravehicular
environment of, e.g., spaceflight vehicles can be accurately generated experimentally
by perturb- ing the intrinsic properties of hydrogen-rich crystalline materials in
order to instigate specific nuclear spallation and fragmentation processes when placed
in an accelerated mono- energetic heavy ion beam. Modifications to the internal geometry
and chemical composition of the materials allow for the shaping of the emerging field
to specific spectra that closely resemble the intravehicular field. Validation of
these results with beam-line mea- surements, both from the peer-reviewed literature
and as performed herein, demonstrate reasonable agreement with model predictions.
Our approach can be generalized to other radiation spectra and is therefore of wide
applicability for biological exposures as well as general radiation studies, such
as the deployment of shielding, electronics, and other materials in a space environment.
This provides the first instance of a true ground-based analog for characterizing
the effects of space radiation.