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The space radiation environment is a complex combination of fast-moving ions derived from all atomic species found in the periodic table. The energy spectrum of each ion species varies widely but is prominently in the range of 400 - 600 MeV/n. The large dynamic range in ion energy is difficult to simulate in ground-based radiobiology experiments. Most ground-based irradiations with mono-energetic beams of a single one ion species are delivered at comparatively high dose rates. In some cases, sequences of such beams are delivered with various ion species and energies to crudely approximate the complex space radiation environment. This approximation may cause profound experimental bias in processes such as biologic repair of radiation damage, which are known to have strong temporal dependancies. It is possible that this experimental bias leads to an overprediction of risks of radiation effects that have not been observed in the astronaut cohort. None of the primary health risks presumely attributed to space radiation exposure, such as radiation carciogenesis, cardiovascular disease, cognitive deficits, etc., have been observed in astronaut or cosmonaut crews. This fundamentally and profoundly limits our understanding of the effects of GCR on humans and limits the development of effective radiation countermeasures., Comment: 9 pagers, 4 figures, manuscript accepted to Journal of Environmental Science and Health, Part C

As human spaceflight seeks to expand beyond low-Earth orbit, NASA and its international partners face numerous challenges related to ensuring the safety of their astronauts, including the need to provide a safe and effective pharmacy for long-duration spaceflight. Historical missions have relied upon frequent resupply of onboard pharmaceuticals; as a result, there has been little study into the effects of long-term exposure of pharmaceuticals to the space environment. Of particular concern are the long-term effects of space radiation on drug stability, especially as missions venture away from the protective proximity of the Earth. Here we highlight the risk of space radiation to pharmaceuticals during exploration spaceflight, identifying the limitations of current understanding. We further seek to identify ways in which these limitations could be addressed through dedicated research efforts aimed towards the rapid development of an effective pharmacy for future spaceflight endeavors., Comment: in press, Nature Microgravity

Space radiation research has progressed rapidly in recent years, but there remain large uncertainties in predicting and extrapolating biological responses to humans. Exposure to cosmic radiation and Solar Particle Events may pose a critical health risk to future spaceflight crews and can have a serious impact to all biomedical aspects of space exploration. The relatively minimal shielding of the cancelled 1960's Manned Orbiting Laboratory program's space vehicle and the high inclination polar orbits would have left the crew susceptible to high exposures of cosmic radiation and high dose-rate SPEs that are mostly unpredictable in frequency and intensity. In this study, we have modeled the nominal and off-nominal radiation environment that a MOL-like spacecraft vehicle would be exposed to during a 30-day mission using high performance, multi-core computers. Projected doses from a historically large SPE (e.g. the August 1972 solar event) have been analyzed in the context of the MOL orbit profile, providing an opportunity to study its impact to crew health and subsequent contingencies.It is reasonable to presume that future commercial, government, and military spaceflight missions in low-Earth orbit will have vehicles with similar shielding and orbital profiles. Studying the impact of cosmic radiation to the mission's operational integrity and the health of MOL crewmembers provides an excellent surrogate and case-study for future commercial and military spaceflight missions., Comment: 6 pages, 4 figures, 2 tables

Despite years of research, understanding of the space radiation environment and the risk it poses to long-duration astronauts remains limited. There is a disparity between research results and observed empirical effects seen in human astronaut crews, likely due to the numerous factors that limit terrestrial simulation of the complex space environment and extrapolation of human clinical consequences from varied animal models. Given the intended future of human spaceflight, with efforts now to rapidly expand capabilities for human missions to the moon and Mars, there is a pressing need to improve upon the understanding of the space radiation risk, predict likely clinical outcomes of interplanetary radiation exposure, and develop appropriate and effective mitigation strategies for future missions. To achieve this goal, the space radiation and aerospace community must recognize the historical limitations of radiation research and how such limitations could be addressed in future research endeavors. We have sought to highlight the numerous factors that limit understanding of the risk of space radiation for human crews and to identify ways in which these limitations could be addressed for improved understanding and appropriate risk posture regarding future human spaceflight., Comment: Accepted for publication by Nature Microgravity (2018)

Current radiobiology studies on the effects of galactic cosmic ray radiation utilize mono-energetic beams, where the projected dose for an exploration mission is given using highly-acute exposures. This methodology does not replicate the multi-ion species and energies found in the space radiation environment, nor does it reflect the low dose-rate found in interplanetary space. In radiation biology studies as well as in the assessment of health risk to astronaut crews, the differences in the biological effectiveness of different ions is primarily attributed to differences in the linear energy transfer (LET) of the radiation spectrum. Here we show that the LET spectrum of the intravehicular environment of spaceflight vehicles can be simulated with a single particle, mono-energetic ion beam accelerated at target blocks constructed of one or more materials. The LET spectrum of the emerging field can then be moderated by the amount of mass or length of material the primary and secondary nuclei travels, thus preferentially producing specific nuclear spallation and fragmentation processes and allowing for a continuous generation of ionizing radiation that mimics the space radiation environment. This approach could allow more accurate simulation of not only intravehicular spaceflight conditions, but also could be used to simulate the external galactic cosmic ray field, planetary surface spectrum (e.g., Mars or Moon), and the local radiation environment of orbiting satellites, providing a much-needed ground-based space radiation analog for future experimentation., Comment: 10 pages, 8 figures

Historical solar particle events (SPEs) provide context for some understanding of acute radiation exposure risk to astronauts traveling outside of low Earth orbit. Modeling of potential doses delivered to exploration crewmembers anticipates limited radiation-induced health impacts, including prodromal symptoms of nausea, emesis, and fatigue, but suggests that more severe clinical manifestations are unlikely. Recent large animal-model research in space-analogs closely mimicking SPEs has identified coagulopathic events independent of the hematopoietic sequelae of higher radiation doses, similar in manifestation to disseminated intravascular coagulation (DIC). We explored the challenges of clinical management of radiation-related clinical manifestations, using currently accepted modeling techniques and anticipated physiological sequelae, to identify medical capabilities needed to successfully manage SPE-induced radiation illnesses during exploration spaceflight.