A no-fault risk compensation approach for radiation risks incurred in space travel.

In this paper we recommend an appropriate compensation approach should be established for fatality and disabilities that may occur due to space radiation exposures of government or industry workers. A brief review of compensation approaches for nuclear energy and nuclear weapons development workers in the United States and other countries is described. We then summarize issues in the application of probability of causation calculation and provide examples of probability of causation (PC) calculations for missions to the International Space Station and Earth's moon or for Mars exploration. The main focus of this paper follows with a recommendation of a no-fault approach to compensation with the creation of appropriate insurance policies funded by employers to cover all disabilities or fatality, without requiring proof of causation or restriction to conditions that imply causation. Importantly we propose that the compensation described should be managed by recourse to private insurers.

Secondary proton buildup in space radiation shielding.

The risk posed by prolonged exposure to space radiation represents a significant obstacle to long-duration human space exploration. Of the ion species present in the galactic cosmic ray spectrum, relativistic protons are the most abundant and as such are a relevant point of interest with regard to the radiation protection of space crews involved in future long-term missions to the Moon, Mars, and beyond. This work compared the shielding effectiveness of a number of standard and composite materials relevant to the design and development of future spacecraft or planetary surface habitats. Absorbed dose was measured using Al2O3:C optically stimulated luminescence dosimeters behind shielding targets of varying composition and depth using the 1 GeV nominal energy proton beam available at the NASA Space Radiation Laboratory at the Brookhaven National Laboratory in New York. Absorbed dose scored from computer simulations performed using the multi-purpose Monte Carlo radiation transport code FLUKA agrees well with measurements obtained via the shielding experiments. All shielding materials tested and modeled in this study were unable to reduce absorbed dose below that measured by the (unshielded) front detector, even after depths as large as 30 g/cm2. These results could be noteworthy given the broad range of proton energies present in the galactic cosmic ray spectrum, and the potential health and safety hazard such space radiation could represent to future human space exploration.

A method to predict space radiation biological effectiveness for non-cancer effects following intense Solar Particle Events.

In addition to the continuous exposure to cosmic rays, astronauts in space are occasionally exposed to Solar Particle Events (SPE), which involve less energetic particles but can deliver much higher doses. The latter can exceed several Gy in a few hours for the most intense SPEs, for which non-stochastic effects are thus a major concern. To identify adequate shielding conditions that would allow respecting the dose limits established by the various space agencies, the absorbed dose in the considered organ/tissue must be multiplied by the corresponding Relative Biological Effectiveness (RBE), which is a complex quantity depending on several factors including particle type and energy, considered biological effect, level of effect (and thus absorbed dose), etc. While in several studies only the particle-type dependence of RBE is taken into account, in this work we developed and applied a new approach where, thanks to an interface between the FLUKA Monte Carlo transport code and the BIANCA biophysical model, the RBE dependence on particle energy and absorbed dose was also considered. Furthermore, we included in the considered SPE spectra primary particles heavier than protons, which in many studies are neglected. This approach was then applied to the October 2003 SPE (the most intense SPE of solar cycle 23, also known as "Halloween event") and the January 2005 event, which was characterized by a lower fluence but a harder spectrum, i.e., with higher-energy particles. The calculation outcomes were then discussed and compared with the current dose limits established for skin and blood forming organs in case of 30-days missions. This work showed that the BIANCA model, if interfaced to a radiation transport code, can be used to calculate the RBE values associated to Solar Particle Events. More generally, this work emphasizes the importance of taking into account the RBE dependence on particle energy and dose when calculating equivalent doses.

Tissue-specific dose equivalents of secondary mesons and leptons during galactic cosmic ray exposures for mars exploration.

During a human mission to Mars, astronauts would be continuously exposed to galactic cosmic rays (GCR) consisting of high energy protons and heavier ions coming from outside our solar system. Due to their high energy, GCR ions can penetrate spacecraft and space habitat structures, directly reaching human organs. Additionally, they generate secondary particles when interacting with shielding materials and human tissues. Baryon secondaries have been the focus of many previous studies, while meson and lepton secondaries have been considered to a much lesser extent. In this work, we focus on assessing the tissue-specific dose equivalents and the effective dose for males of secondary mesons and leptons for the interplanetary cruise phase and the surface phase on Mars. We also provide the energy distribution of the secondary pions in each human organ since they are dominant compared to other mesons and leptons. For this calculation, the PHITS3.27 Monte Carlo simulation toolkit is used to compute the energy spectra of particles in organs in a realistic human phantom. Based on the simulation data, the dose equivalent has been estimated with radiation quality factors in ICRP Publication 60 and in the latest NASA Space Cancer Risk model (NSCR-2022). The effective dose is then assessed with the tissue weighting factors in ICRP Publication 103 and in the NSCR model, separately. The results indicate that the contribution of secondary mesons and leptons to the total effective dose is 6.1 %, 9.1 %, and 11.3 % with the NSCR model in interplanetary space behind 5, 20, and 50 g/cm2 aluminum shielding, respectively, with similar values using the ICRP model. The outcomes of this work lead to an improved understanding of the potential health risks induced by secondary particles for exploration missions to Mars and other destinations.

An Augmented Reality Hand-Eye Sensorimotor Impairment Assessment for Spaceflight Operations.

INTRODUCTION: Following a transition from microgravity to a gravity-rich environment (e.g., Earth, Moon, or Mars), astronauts experience sensorimotor impairment, primarily from a reinterpretation of vestibular cues, which can impact their ability to perform mission-critical tasks. To enable future exploration-class missions, the development of lightweight, space-conscious assessments for astronauts transitioning between gravity environments without expert assistance is needed.METHODS: We examined differences in performance during a two-dimensional (2D) hand-eye multidirectional tapping task, implemented in augmented reality in subjects (N = 20) with and without the presence of a vestibular-dominated sensorimotor impairment paradigm: the binaural bipolar application of a pseudorandom galvanic vestibular stimulation (GVS) signal. Metrics associated with both the impairment paradigm and task performance were assessed.RESULTS: Medial-lateral sway during balance on an anterior-posterior sway-referenced platform with eyes closed was most affected by GVS (effect size: 1.2), in addition to anterior-posterior sway (effect size: 0.63) and the vestibular index (effect size: 0.65). During the augmented reality task, an increase in time to completion (effect size: 0.63), number of misses (effect size: 0.52), and head linear accelerations (effect size: 0.30) were found in the presence of the selected GVS waveform.DISCUSSION: Findings indicate that this multidirectional tapping task may detect emergent vestibular-dominated impairment (near landing day performance) in astronauts. Decrements in speed and accuracy indicate this impairment may hinder crews' ability to acquire known target locations while in a static standing posture. The ability to track these decrements can support mission operations decisions.Allred AR, Weiss H, Clark TK, Stirling L. An augmented reality hand-eye sensorimotor impairment assessment for spaceflight operations. Aerosp Med Hum Perform. 2024; 95(2):69-78.

European astronaut radiation related cancer risk assessment using dosimetric calculations of organ dose equivalents.

An illustrative sample mission of a Mars swing-by mission lasting one calendar year was chosen to highlight the application of European risk assessment software to cancer (all solid cancer plus leukaemia) risks from radiation exposures in space quantified with organ dose equivalent rates from model calculations based on the quantity Radiation Attributed Decrease of Survival (RADS). The relevant dose equivalent to the colon for radiation exposures from this Mars swing-by mission were found to vary between 198 and 482 mSv. These doses depend on sex and the two other factors investigated here of: solar activity phase (maximum or minimum); and the choice of space radiation quality factor used in the calculations of dose equivalent. Such doses received at typical astronaut ages around 40 years old will result in: the probability of surviving until retirement age (65 years) being reduced by a range from 0.38% (95%CI: 0.29; 0.49) to 1.29% (95%CI: 1.06; 1.56); and the probability of surviving cancer free until retirement age being reduced by a range from 0.78% (95%CI: 0.59; 0.99) to 2.63% (95%CI: 2.16; 3.18). As expected from the features of the models applied to quantify the general dosimetric and radiation epidemiology parameters, the cancer incidence risks in terms of surviving cancer free, are higher than the cancer mortality risks in terms of surviving, the risks for females are higher than for males, and the risks at solar minimum are higher than at solar maximum.

Whole genome-scale assessment of gene fitness of Novosphingobium aromaticavorans during spaceflight.

In microgravity, bacteria undergo intriguing physiological adaptations. There have been few attempts to assess global bacterial physiological responses to microgravity, with most studies only focusing on a handful of individual systems. This study assessed the fitness of each gene in the genome of the aromatic compound-degrading Alphaproteobacterium Novosphingobium aromaticavorans during growth in spaceflight. This was accomplished using Comparative TnSeq, which involves culturing the same saturating transposon mutagenized library under two different conditions. To assess gene fitness, a novel comparative TnSeq analytical tool was developed, named TnDivA, that is particularly useful in leveraging biological replicates. In this approach, transposon diversity is represented numerically using a modified Shannon diversity index, which was then converted into effective transposon density. This transformation accounts for variability in read distribution between samples, such as cases where reads were dominated by only a few transposon inserts. Effective density values were analyzed using multiple statistical methods, including log2-fold change, least-squares regression analysis, and Welch's t-test. The results obtained across applied statistical methods show a difference in the number of significant genes identified. However, the functional categories of genes important to growth in microgravity showed similar patterns. Lipid metabolism and transport, energy production, transcription, translation, and secondary metabolite biosynthesis and transport were shown to have high fitness during spaceflight. This suggests that core metabolic processes, including lipid and secondary metabolism, play an important role adapting to stress and promoting growth in microgravity.

Results from the Radiation Assessment Detector on the International Space Station, Part 2: The fast neutron detector.

We report the results of the first six years of measurements of so-called fast neutrons on the International Space Station (ISS) with the Radiation Assessment Detector (ISS-RAD), spanning the period from February 2016 to February 2022. ISS-RAD combines two sensor heads, one nearly identical to the single sensor head in the Mars Science Laboratory RAD (MSL-RAD). The latter is described in a companion article to this one. The novel sensor is the FND, or fast neutron detector, designed to measure neutrons with energies in the range from 200 keV to about 8 MeV. ISS-RAD was deployed in February 2016 in the USLAB module, and then served as a survey instrument from March 2017 until May 2020. Data were acquired in Node3, the Japanese Pressurized Module, Columbus, and Node2. At the conclusion of the survey portion of RAD's planned 10-year campaign on ISS, the instrument was stationed in the USLAB; current plans call for it to remain there indefinitely. The radiation environment on the ISS consists of a complex mix of charged and neutral particles that varies on short time scales owing to the Station's orbit. Neutral particles, and neutrons in particular, are of concern from a radiation protection viewpoint, because they are both highly penetrating (since they do not lose energy via direct ionization) and, at some energies, have high biological effectiveness. Neutrons are copiously produced by GCRs and other incident energetic particles when they undergo nuclear interactions in shielding. As different ISS modules have varying amounts of shielding, they also have varying neutron environments. We report results for neutron fluences and dose equivalent rates in various positions in the ISS.

Comprehensive assessment of physiological responses in women during the ESA dry immersion VIVALDI microgravity simulation.

Astronauts in microgravity experience multi-system deconditioning, impacting their inflight efficiency and inducing dysfunctions upon return to Earth gravity. To fill the sex gap of knowledge in the health impact of spaceflights, we simulate microgravity with a 5-day dry immersion in 18 healthy women (ClinicalTrials.gov Identifier: NCT05043974). Here we show that dry immersion rapidly induces a sedentarily-like metabolism shift mimicking the beginning of a metabolic syndrome with a drop in glucose tolerance, an increase in the atherogenic index of plasma, and an impaired lipid profile. Bone remodeling markers suggest a decreased bone formation coupled with an increased bone resorption. Fluid shifts and muscular unloading participate to a marked cardiovascular and sensorimotor deconditioning with decreased orthostatic tolerance, aerobic capacity, and postural balance. Collected datasets provide a comprehensive multi-systemic assessment of dry immersion effects in women and pave the way for future sex-based evaluations of countermeasures.

Extended reality quantification of pupil reactivity as a non-invasive assessment for the pathogenesis of spaceflight associated neuro-ocular syndrome: A technology validation study for astronaut health.

The National Aeronautics and Space Administration (NASA) has rigorously documented a group of neuro-ophthalmic findings in astronauts during and after long-duration spaceflight known as spaceflight associated neuro-ocular syndrome (SANS). For astronaut safety and mission effectiveness, understanding SANS and countermeasure development are of utmost importance. Although the pathogenesis of SANS is not well defined, a leading hypothesis is that SANS might relate to a sub-clinical increased intracranial pressure (ICP) from cephalad fluid shifts in microgravity. However, no direct ICP measurements are available during spaceflight. To further understand the role of ICP in SANS, pupillometry can serve as a promising non-invasive biomarker for spaceflight environment as ICP is correlated with the pupil variables under illumination. Extended reality (XR) can help to address certain limitations in current methods for efficient pupil testing during spaceflight. We designed a protocol to quantify parameters of pupil reactivity in XR with an equivalent time duration of illumination on each eye compared to pre-existing, non-XR methods. Throughout the assessment, the pupil diameter data was collected using HTC Vive Pro-VR headset, thanks to its eye-tracking capabilities. Finally, the data was used to compute several pupil variables. We applied our methods to 36 control subjects. Pupil variables such as maximum and minimum pupil size, constriction amplitude, average constriction amplitude, maximum constriction velocity, latency and dilation velocity were computed for each control data. We compared our methods of calculation of pupil variables with the non-XR methods existing in the literature. Distributions of the pupil variables such as latency, constriction amplitude, and velocity of 36 control data displayed near-identical results from the non-XR literature for normal subjects. We propose a new method to evaluate pupil reactivity with XR technology to further understand ICP's role in SANS and provide further insight into SANS countermeasure development for future spaceflight.

Metabolic Cost of a Proposed NMES Spaceflight Countermeasure Compared to Walking in Active Adults.

INTRODUCTION: Astronauts exercise to reduce microgravity-induced bone loss, but the resultant skeletal loading may not be sufficient to reduce fracture risk on an extended Mars mission. Adding additional exercise increases the risk of a negative caloric balance. Neuromuscular electrical stimulation (NMES) induces involuntary muscle contractions, which load the skeleton. The metabolic cost of NMES is not fully understood. On Earth, walking is a common source of skeletal loading. If the metabolic cost of NMES were equal to or less than walking, it could offer a low metabolic cost option for increasing skeletal loading.METHODS:We measured the oxygen consumed and carbon dioxide produced from 10 subjects during 5-min bouts of walking at 2 mph, 3 mph, and 2 mph on a 6° incline, and of NMES to the legs at duty cycles of 1 s on and 5 s, 4 s, or 3 s off. Metabolic cost was calculated using the Brockway equation and the percent increase above resting for each NMES bout was compared to walking.RESULTS: Metabolic cost increased 64.9 ± 52.8% from rest in the most intense NMES duty cycle (1 s/3 s) and 120.4 ± 26.5%, 189.3 ± 59.5%, 281.7 ± 66.8%, for the 2 mph, 3 mph, and incline walking, respectively. The metabolic cost did not differ significantly between the three NMES duty cycles.DISCUSSION: The increase in metabolic cost of the fastest NMES bout was less than that of the slowest walk, indicating that numerous NMES bouts offer a way to increase skeletal loading at a modest metabolic cost. This might allow for more daily skeletal loading cycles, potentially further reducing bone loss.Abitante TJ, Alemi MM, Newman DJ, Duda KR. Metabolic cost of a proposed NMES spaceflight countermeasure compared to walking in active adults. Aerosp Med Hum Perform. 2023; 94(7):523-531.

Neurocognitive assessment in microgravity: review of tools and benefits of increasing their clinical validity for long duration missions.

INTRODUCTION: Clinical complications are not expected in current space missions; however, for future long-duration missions to the Moon and Mars, a new perspective may be needed - a more clinical approach. Different risks, both environmental, such as radiation, accidents, and biopsychological, including neurological problems, represent potential sources of subsequent neurocognitive deficits. AIMS: This study aims to review research studies published to this date in microgravity conditions using existing spaceflight neurocognitive assessment batteries. This study also discusses the different risks of neuropsychological impairment in spaceflight and the potential benefits of increasing the clinical validity of these tools with neurological clinical samples on Earth for future long-duration missions. METHOD: A PRISMA guidelines-based review of specialized literature on neurocognitive assessment batteries and human spaceflight was performed. Different factors including type of tool or battery used, sample size, mission duration, etc. were included in this review. After the scrutiny of 192 articles, a total of 27 studies were detailed in the review outcome. RESULTS: Results showed that neuropsychological function research target has changed over the years, with working memory and perception studies being predominant in the 80s and 90s while reaction time being more frequent in recent research. We also found a lack of language-related research in microgravity and the predominance of two neurocognitive assessment batteries in microgravity research. CONCLUSIONS: With this study, we want to emphasize the importance of increasing the clinical validity of neurocognitive or neuropsychological assessment tools to be used in space, especially in long-duration missions because in this type of mission the risk of suffering a brain injury or neurological condition increases due to multiple factors. Testing these tools with neurological clinical samples and using machine learning, predictive systems may help crews in early detection of potential clinical, neurological, or neurocognitive problems during these long-duration missions to Mars and beyond.

Of Men and Mice: Using Terrestrial Radiation Epidemiology Methods to Inform Analysis of Animal Models for Space Radiation Risk Assessment.

Prediction of cancer risk from space radiation exposure is critical to ensure spaceflight crewmembers are adequately informed of the risks they face when accepting assignments to ambitious long-duration exploratory missions. Although epidemiological studies have assessed the effects of exposure to terrestrial radiation, no robust epidemiological studies of humans exposed to space radiation exist to support estimates of the risk from space radiation exposure. Mouse data derived from recent irradiation experiments provides valuable information to successfully develop mouse-based excess risks models for assessing relative biological effectiveness for heavy ions that can provide information to scale unique space radiation exposures so that excess risks estimated for terrestrial radiation can be adjusted for space radiation risk assessment. Bayesian analyses were used to simulate linear slopes for excess risk models with several different effect modifiers for attained age and sex. Relative biological effectiveness values for all-solid cancer mortality were calculated from the ratio of the heavy-ion linear slope to the gamma linear slope using the full posterior distribution and resulted in values that were substantially lower than what is currently applied in risk assessment. These analyses provide an opportunity to improve characterization of parameters used in the current NASA Space Cancer Risk (NSCR) model and generate new hypotheses for future animal experiments using out-bred mouse populations.

Head-Mounted Dynamic Visual Acuity for G-Transition Effects During Interplanetary Spaceflight: Technology Development and Results from an Early Validation Study.

INTRODUCTION: Dynamic visual acuity (DVA) refers to the ability of the eye to discern detail in a moving object and plays an important role whenever rapid physical responses to environmental changes are required, such as while performing tasks onboard a space shuttle. A significant decrease in DVA has previously been noted after astronauts returned from long-duration spaceflight (0.75 eye chart lines, 24 h after returning from space). As part of a NASA-funded, head-mounted multimodal visual assessment system for monitoring vision changes in spaceflight, we elaborate upon the technical development and engineering of dynamic visual acuity assessments with virtual reality (VR) technology as the first step in assessing astronaut performance when undergoing G-transitional effects. We also report results from an early validation study comparing VR DVA assessment with traditional computer based DVA assessment.METHODS: Various VR/AR headsets have been utilized to implement DVA tests. These headsets include HTC Vive Pro Eye system. Epic's game engine UnrealEngine 4 Version 4.24 was used to build the framework and SteamVR was used to experience virtual reality content. Eye tracking technology was used to maintain fixation of the participant. An early validation study with five participants was conducted comparing this technology versus traditional DVA with a laptop.RESULTS: The head-mounted technology developed for assessing DVA changes during G-transitions is fully functional. The results from the early validation study demonstrated that the two DVA tests (laptop-based and VR) indicated a strong association between both methods (Pearson correlation coefficient of 0.91). A Bland-Altman plot was employed to assess levels of agreement, with all data points falling within the limits of agreement.DISCUSSION: The results from this early validation study indicate that head-mounted DVA assessment performs similarly to traditional laptop-based methods and is a promising method for assessing DVA during spaceflight, particularly in G-transitions. Future studies are required for further assessment of validation and reliability of this technology. With its ease of use, accessibility, and portable design, VR DVA has the potential in the near-future to replace conventional methods of assessing DVA. The technology will likely be an important aspect to help monitor functionality and safety during interplanetary missions where astronauts are exposed to G-transitions.Waisberg E, Ong J, Zaman N, Kamran Sa, Lee AG, Tavakkoli A. Head-mounted dynamic visual acuity for G-transition effects during interplanetary spaceflight: technology development and results from an early validation study. Aerosp Med Hum Perform. 2022; 93(11):800-805.

Dose Attenuation in Innovative Shielding Materials for Radiation Protection in Space: Measurements and Simulations.

Galactic cosmic rays (GCR) are among the main deterrents to manned space exploration. Currently, the most realistic way to reduce the dangers caused by GCR to acceptable levels is passive shielding. Light materials guarantee the strongest dose attenuation per unit mass. High-density polyethylene is considered the gold standard for radiation protection in space. Nevertheless, accelerator-based experimental campaigns already showed the advantages of more hydrogen-rich innovative shielding materials such as lithium hydride. The experimental campaigns of this work focused on the absorbed dose attenuation properties of lithium-based hydrides chemically stabilized with a paraffin matrix. Such materials were compared to pure lithium-based hydrides, polyethylene, structural materials such as spacecraft aluminum alloys and lithium batteries, and in situ shielding materials such as Moon regolith and its main components silicon and silicon dioxide. The experimental results were compared to simulations performed with PHITS, FLUKA, and Geant4, which are among the most used Monte Carlo codes for radiation protection in space. The simulations showed systematic differences and highlighted the pressing need for reliable nuclear cross-section models.

Considerations for practical dose equivalent assessment of space radiation and exposure risk reduction in deep space.

Shielding from space radiation, especially galactic cosmic rays (GCRs), is a significant safety challenge for future human activities in deep space. In this study, the shielding performances of potential materials [aluminum (Al), polyethylene (PE), and carbon fiber reinforced plastic (CFRP)] were investigated using Geant4 Monte Carlo simulation considering two types of biological scale parameters, the International Commission on Radiological Protection (ICRP) quality factor (QFICRP) and the plausible biological effectiveness (RBEγacute), for GCRs. The effective dose equivalent was reduced by 50% for QFICRP and 38% for RBEγacute when shielding using 20 g/cm2 of CFRP. A spacecraft made from CFRP will have a better radiation shielding performance than conventional Al-based spacecraft. The contribution of heavy ions for QFICRP based effective dose equivalent was larger by a factor of ~ 3 compared to that for RBEγacute based effective dose equivalent. The shielding materials efficiently reduced the effective dose equivalent due to ions with QFICRP > 3.36 and RBEγacute > 2.26. QFICRP and RBEγacute have advantages and disadvantages in quantifying the dose equivalent of space radiation, and the establishment of a standard parameter specified for a mixed radiation environment occupied by protons and heavy ions is necessary for practical dose assessment in deep space.

COSPAR Sample Safety Assessment Framework (SSAF).

The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presence of martian life in the samples, (2) carrying out an analogue test program, and (3) acquiring relevant contamination knowledge from all Mars Sample Return (MSR) flight and ground elements. Although the SSAF was developed specifically for assessing samples from Mars in the context of the currently planned NASA-ESA MSR Campaign, this framework and the basic safety approach are applicable to any other Mars sample return mission concept, with minor adjustments in the execution part related to the specific nature of the samples to be returned. The SSAF is also considered a sound basis for other COSPAR Planetary Protection Category V, restricted Earth return missions beyond Mars. It is anticipated that the SSAF will be subject to future review by the various MSR stakeholders.

Assessment of Sex-Dependent Medical Outcomes During Spaceflight.

Background: In this study sex-differences in medical outcomes during spaceflight are reviewed and probabilistic risk assessment (PRA) is used to assess the impact on spaceflight missions of varying lengths. Materials and Methods: We use PRA to simulate missions of 42 days, 6 months, and 2.5 years. We model medical outcomes using three crews: two men and two women, four women, or four men. Total medical events (TME), crew health index (CHI), probability (0-1) of medical evacuation (pEVAC), probability of loss of crew life (pLOCL), and influential medical conditions were determined. Results: No differences were seen in any metric for the 42-day mission. There were no differences seen for any mission length, in any crew, for TME, CHI, pLOCL, or environmental causes of pEVAC. Sex-dependent differences are seen for rates of nonemergent pEVAC during the 6 month and 2.5-year missions, where women have a higher pEVAC in the 182-day (0.0388 vs. 0.0354) and 2.5-year missions (0.350 vs. 0.228). These differences were driven by higher incidence of partially treated urinary tract infection (UTI). In the 2.5 year mission, with resupply of medical resources, the influence of UTI in women on pEVAC decreases (0.35-0.11). Conclusion: Although resupply is unlikely for deep space missions, modeled results suggest that sex-specific medical needs can be readily managed through preventive measures and inclusion of appropriate medical capabilities. Within its many limitations, PRA is a useful tool to estimate medical risks in unique environments where only expert opinion was previously available.

Thick shielding against galactic cosmic radiation: A Monte Carlo study with focus on the role of secondary neutrons.

The exposure to galactic cosmic radiation (GCR) is a major health concern for astronauts. Crewed missions with durations of several years are foreseen in future space exploration projects such as permanent habitats on the Moon and flights to Mars. This aim requires elaborate space radiation shielding concepts and a proper understanding of the underlying radiation physics and radiobiology as well as their interplay. In the present work, Monte Carlo simulations to assess the performance of different materials (polyethylene, aluminum, Moon regolith) as thick shields (up to 400 g/cm2) against GCR were conducted using the FLUKA code. Absorbed dose, dose equivalent and the mean quality factor at 1 cm depth in the ICRU sphere as a function of shielding thickness were calculated in a spherical shell configuration for both solar minimum and solar maximum GCR conditions. Large differences were observed in the performance of the studied materials as thick GCR shields. Special attention was paid to the build-up and moderation of secondary neutrons. A method to reduce the neutron contributions to ambient dose equivalent by means of a two-layer shielding combination is proposed. The present study can be useful for considerations on thick shielding of Moon or Mars habitats built from local regolith.