Abstract Crewed missions to Mars will be a milestone of future space exploration programs. However, the absence of Earth's magnetic field leaves astronauts directly exposed to unattenuated energetic particles in deep space, primarily galactic cosmic rays (GCRs), resulting in significantly higher radiation levels and enhanced health risks. Understanding and quantifying these radiation hazards is thus essential for evaluating the feasibility and safety of long‐duration Mars missions. Based on the dose data from the Trace Gas Orbiter mission and the Cosmic Ray Telescope for the Effects of Radiation (CRaTER), we perform correlation analyses between the measured dose rate and solar modulation conditions, parameterized as solar modulation potential, and develop empirical models that can be extrapolated to a broader range of solar activities. Using these models, the GCR‐cumulative dose for mission scenarios following three different transfer trajectories under varying solar modulation conditions during the past ∼60 years are calculated. Our results indicate that missions operated during solar maximum accumulate 30%–55% less GCR effective dose than those during solar minimum, with the specific percentage depending on their execution period and trajectory. Under similar shielding conditions of measurements used here, missions following the minimum energy trajectory and conducted during relatively active solar cycles can generally maintain the cumulative radiation effective dose below 1,000 mSv, but keeping it below the NASA's new limit of 600 mSv requires restricting the mission duration to the solar maximum. Nevertheless, faster transfer orbits can help satisfy this limit during solar minimum years.

Understanding the long-term variation of the galactic cosmic ray (GCR) radiation environment is critical for assessing radiation risks in space exploration missions. In this study, we systematically model the linear energy transfer (LET) spectra of GCRs and the corresponding radiation quality factor, ", in deep space and shielding environments. The Badhwar-O'Neill 2020 (BON20) model is used to represent GCR fluxes under different solar modulation potentials (phi), which characterize the level of solar activity. GCR interactions with spherical shielding of different thicknesses are simulated to obtain the LET spectra, absorbed dose, dose equivalent, and "". We present a comprehensive dataset of these quantities for a range of phi values and shielding thicknesses. The results show that "" depends strongly on the shielding thickness but only weakly on solar activity. Furthermore, model predictions are validated against long-term measurements from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) orbiting the Moon, and the Liulin-MO detector on board the ExoMars Trace Gas Orbiter (TGO) orbiting Mars. In this comparison, we consider factors for anomalous cosmic ray (ACR) contributions and radial gradients of both GCRs and ACRs, applying scaling factors of 6.3"

Human beings are considering going back to the Moon and eventually to Mars within the next decades. However, we are still facing one major hurdle ``space radiation'' which is a significant and unavoidable risk for crews' health, especially for long-term stays at future lunar or martian stations. In particular, sporadic solar energetic particles (SEPs) generated via extreme solar eruptions may enhance the lunar or martian surface radiation levels to potentially hazardous values. Recent lunar and martian surface and orbital radiation detectors have advanced our understanding of the radiation environment of both planetary bodies. We have used the state-of-the-art modeling appoaches to study the radiation environment of the Moon and Mars. In particular, we study and compare the potential radiation effects of historically large SEP events on the surface and subsurface of the Moon and Mars.

Space radiation is a major concern for the safety of robotic and human exploration both in the near-Earth environment and towards deep space and other planetary bodies such as the Moon. It is therefore important to characterize and predict the fluxes of the major sources of energetic particle radiation in the heliosphere including solar energetic particles (SEPs) and Galactic cosmic rays (GCRs). This involves a good understanding of the GCR modulation process and the SEP/GCR transport mechanisms as well as their interaction with the Lunar surface environment. In this talk, we will present our recent porgress in assessing the Lunar radiation environment, both during solar-quiet periods and during solar eruptions. In particular, we developed empirical functions to rapidly assess SEP-induced effective dose on the Moon under different shielding scenarios.

The nucleosynthetic Cr isotope anomalies provides useful information to trace the source and origin of extraterrestrial samples, but it is usually influenced by high-energy cosmic rays, and evaluating such effect of cosmic rays in lunar samples is especially important. Those cosmic radiation particles (primary particles) can react with lunar materials, creating many secondary particles. Both primary and secondary particles can produce cosmogenic nuclides on the Moon. Radiation Environment and Dose at the Moon (REDMoon) is a novel GEANT4 Monte-Carlo model built to simulate the interactions of space particles with the lunar surface and subsurface content. Using this model, we simulate the production of cosmogenic Cr isotopes (50Cr, 52Cr, 53Cr, 54Cr) at different depths of lunar surface, and compare the contribution of different reactions generating these nuclides. The results suggest that spallation reactions are the most important process producing cosmogenic Cr isotopes. We also analyze the relationship between 53Cr/52Cr and 54Cr/52Cr predicted by our model and compare it with different Apollo samples. As previously studied, we also find an approximate linear relationship between e53Cr and e54Cr, where e53Cr (or e54Cr) is the relative deviation from the standard 53Cr/52Cr ratio (or 54Cr/52Cr ratio), normalized to 1/10,000. Furthermore, we reveal a change of this linear relationship in different depths of lunar surface. Besides, we investigate how the slopes can be influenced by exposure age and the Fe/Cr ratio. With these additional factors carefully considered, the comparison between our modeled results and the measurements is better than previous studies. Cosmic rays arriving at the Moon can change the isotopic compositions on the lunar surface including chromium isotopes which can be used to constrain the evolution history of the Moon. Here, we use the particle transport model to simulate the high-energy particles and the chromium isotopes generated in the lunar material by different cosmic ray sources. We compare different processes producing cosmogenic Cr isotopes and suggest that the spallation reactions play the main role. After taking the effect of solar energetic particles and the decay of cosmogenic 53Mn into consideration, we reach a better agreement between our model prediction and the Apollo lunar samples about the relationship between e53Cr and e54Cr. Such an improved analysis of the lunar cosmogenic nuclides contributes to a better understanding of the origin of the Moon. We simulate the production rate of cosmogenic 50Cr, 52Cr, 53Cr, 54Cr in lunar terrain with Radiation Environment and Dose at the Moon model We compare the contributions of different processes producing Cr isotopes We analyze the relationship between 54Cr/52Cr and 53Cr/52Cr constraining lunar evolution models

Abstract On 2022‐02‐15, solar eruptions caused one of the most intensive Solar Particle Events (SPEs) in Solar Cycle 25 observed at various heliospheric locations. This study focuses on the enhancements of energetic proton flux observed by multiple detectors located at the orbit and on the surface of Mars. We carry out the first analysis by the Mars Energetic Particle Analyzer (MEPA) instrument on board the Chinese Tianwen‐1 spacecraft (TW‐1) at Mars orbit which also serves to validate the instrument's capability to measure protons of up to 100 MeV. We reconstruct the event spectrum up to 1 GeV and further model the event doses at Mars's orbit and surface which are then validated against the corresponding dosimetry data. Our study utilizes all available radiation detectors at Mars, advances our understanding of Mars's radiation environment induced by large SPEs, and emphasizes the necessity of continuous and synergistic radiation monitoring at Mars.

Abstract The Moon lacks a global magnetic field and atmosphere, leaving its surface been directly exposed to high‐energy cosmic radiation. Sporadic Solar Particle Events are sources of a significant radiation exposure, potentially posing serious threats to the health of astronauts exploring the Moon. In this paper, we use the Radiation Environment and Dose at the Moon (REDMoon) model based on GEometry And Tracking (GEANT4) Monte‐Carlo method to calculate the body effective dose induced by 262 large historical SEP events on the Moon under different shielding depths which can result from the lunar regolith shielding and/or additional aluminum shielding. We calculate and compare the contributions of different particles from or produced by SEPs to the total body effective dose. Additionally, we develop empirical functions to rapidly assess SEP‐induced effective dose on the Moon under different shielding scenarios.

Abstract On 28 October 2021, solar eruptions caused intense and long‐lasting solar energetic particle (SEP) flux enhancements observed by spacecraft located over a wide longitudinal range in the heliosphere. SEPs arriving at Earth caused the 73rd ground level enhancement (GLE) event recorded by ground‐based neutron monitors. In particular, this is also the first GLE event seen on the surface of three planetary bodies, Earth, Moon, and Mars, by particle and radiation detectors as shown in this study. We derive the event‐integrated proton spectrum from measurements by near‐Earth spacecraft and predict the lunar and martian surface radiation levels using particle transport models. Event doses at the lunar and martian surfaces of previous GLE events are also modeled and compared with the current event. This statistical and comparative study advances our understanding of potential radiation risks induced by extreme SEP events for future human explorations of the Moon and Mars.

Human visits to the Moon will be the next milestone for human space exploration. During deep space crewed missions, radiation risk is an important and unavoidable risk for astronauts' health, especially for their long-term stays at future lunar stations. In this work, we present the first protocol of a lunar mission schedule given space radiation constraints. We use the recently developed and validated "Radiation Environment and Dose at the Moon (REDMoon)" model [1] to calculate radiation dose rates due to omnipresent Galactic Cosmic Rays (GCR) and sporadic Solar Energetic Particles (SEP) as well as the secondary particles induced by them at the surface and subsurface of the Moon. We evaluate the biologically-weighted body effective dose rate, its variation with solar activity, and its dependence on the shielding thickness, including both the lunar soil shielding and the module aluminum shielding. For surface bases assuming a historical solar activity period (e.g., that between year 2000 and 2020), we obtain the background GCR exposure rate to be 20-40 cSv . year - 1 considering different solar modulation conditions and various Al-shielding thicknesses of the module. In comparison, the average radiation exposure for an astronaut in International Space Station at low-Earth orbit is ≈20 cSv . year -1 in the middle of solar cycle in 2006 [2]. Large SEP events throughout this period are also accounted for and some single-event effective dose may exceed the annual GCR level if shielding is insufficient. We thus consider potential bases utilizing in-situ lunar regolith for shielding protection. We investigate different combinations of depth and Al-shielding for lunar base scenarios to derive mission schedules which allow the persistent presence of crew operation on the Moon. With our schedule throughout the aforementioned period, the radiation exposure is kept under certain recommended levels. As a first protocol, our work provide valuable radiation mitigation considerations for future human lunar bases and mission cost estimates.

A comprehensive understanding of the lunar radiation environment is essential in preparing for future human exploration of the Moon. The radiation environment on the Moon includes primary space radiation and secondary radiation, which is induced in the lunar soil. Both primary and secondary radiation may pose severe health issues to future crews on the Moon. In this work, we build a detailed radiation environment model "Radiation Environment and Dose at the Moon (REDMoon)" for the lunar surface and subsurface. We use the GEANT4 (GEometry ANd Tracking) Monte-Carlo code and "response function" approach to calculate type-, energy-, angular-, depth-, and time-dependent particle spectra induced by galactic cosmic rays at the surface and subsurface of the Moon. Calculated radiation particle fluxes on and beneath the surface are in good agreement with previous experimental and numerical results while offering more details on the lunar radiation fields, such as angular and depth information. The depth profile of secondary particle spectra in the lunar soil has a maximum between 0.5 and 1 m below the surface, depending on particle type and energy. The angular distribution of secondary particles (in particular neutron, gamma-rays, electrons) with energy less than or similar to 1 MeV is mostly isotropic, while higher energy particles preferentially propagate downward. Our model provides full coverage of the spatial, directional, and energy information of the radiation field at the surface and subsurface of the Moon, which can serve for designing future human bases on the Moon.

Abstract Space radiation is one of the main concerns in planning long‐term human space missions. There are two main types of hazardous radiation: solar energetic particles (SEP) and galactic cosmic rays (GCR). The intensity and evolution of both depends on solar activity. GCR activity is most enhanced during solar minimum and lowest during solar maximum. The reduction of GCRs is alagging behind solar activity only by 6–12 month. SEP probability and intensity are maximized during solar maximum and are minimized during solar minimum. In this study, we combine models of the particle environment arising due to SEP and GCR with Monte Carlo simulations of radiation propagation inside a spacecraft and phantom. We include 28 fully ionized GCR elements from hydrogen to nickel and consider protons and nine ion species to model the SEP irradiation. Our calculations demonstrate that the optimal time for a flight to Mars would be launching the mission at solar maximum, and that the flight duration should not exceed approximately 4 years.

The Universat-SOCRAT project is developed in the Moscow State University aiming to forecast space-related risks for aviation, suborbital, and orbital flights and provide new knowledge on the magnetosphere and atmosphere of the Earth. An essential part of the system is a multi-satellite constellation, which would operate in the low-Earth orbit. Among other things, it would monitor the radiation and magnetic-wave environment in the vicinity of the Earth: in space and atmosphere. An Earth observation system, which operates in gamma and visible spectral range, should allow attribute detected changes in the environment to the atmospheric phenomena. We have already designed the instruments to detect increases in the flux of energetic charged particles (solar energetic particles, galactic cosmic rays, and electrons precipitating from radiation belts), geomagnetic disturbances, and electromagnetic transients in the atmosphere. The first stage of the program started on July 5, 2019, with a successful launch of three 3U CubeSats from the Vostochny cosmodrome. These satellites carry instruments for monitoring space radiation and prototype of the device for observing the Earth’s atmosphere in the ultraviolet range. The collected data has confirmed the advantages of multi-satellite observations for the goals of the project. During this year, we plan to launch two more 6U CubeSats with charged particle and gamma-ray detectors, magnetometers, and instrument for detecting of atmospheric electromagnetic transients. We suppose that these satellites will lay the foundation of the space threat monitoring system.

We use the GEANT4 Monte Carlo code to calculate the radiation dose equivalent due to Galactic Cosmic Rays (GCRs) during an out-of-magnetosphere space flight. We provide a detailed analysis of the radiation dose composition, distinguishing between the contribution of primary GCR particles and different species of secondary particles. We show that for realistic shielding thicknesses, the radiation dose equivalent is mostly due to GCR protons and alpha particles. The Blood-Forming Organs (BFO) dose equivalent is the same in the shielding spheres with the radius of 50 and 100 cm, although the dose composition differs. We show that indirectly scattered secondary particles make up to 60% to the net radiation dose. Up to 90% of the secondary neutron dose equivalent is associated with indirectly scattered particles.

Space radiation is one of the main concerns for human space flights. The prediction of the radiation dose for the actual spacecraft geometry is very important for the planning of long-duration missions. We present a numerical method for the fast calculation of the radiation dose rate during a space flight. We demonstrate its application for dose calculations during the first and the second sessions of the MATROSHKA-R space experiment with a spherical tissue-equivalent phantom. The main advantage of the method is the short simulation time, so it can be applied for urgent radiation dose calculations for low-Earth orbit space missions. The method uses depth-dose curve and shield-and-composition distribution functions to calculate a radiation dose at the point of interest. The spacecraft geometry is processed into a shield-and-composition distribution function using a ray-tracing method. Depth-dose curves are calculated using the GEANT4 Monte-Carlo code (version 10.00.P02) for a double-layer aluminum-water shielding. Aluminum-water shielding is a good approximation of the real geometry, as water is a good equivalent for biological tissues, and aluminum is the major material of spacecraft bodies. The method is applied to model the dose distribution on the surface of the spherical phantom in the MATROSHKA-R space experiment. The experiment has been carried out onboard the ISS from 2004 to the present. The absorbed dose was determined in 32 points on the phantom's surface. We find a good agreement between the data obtained in the experiment and our calculation results. The simulation method is thus applicable for future radiation dose predictions for low-Earth orbit missions and experiments.

1. Max Planck Institute for Solar System Research, Göttingen, Germany, 2. Ludwig Maximilians University, Munich, Germany, 3. Helmholtz Centre Potsdam GFZ German Research Centre For Geosciences and University of Potsdam, Potsdam, Germany, 4. The Aerospace Corporation, El Segundo, California USA, 5. Skolkovo Institute of Science and Technology, Skolkovo, Russia, 6. Center for Space Physics, Boston University, Boston, MA, USA, 7. Belgian Institute for Space Aeronomy (BISA), Brussels, Belgium, 8. Max Planck Institute for extraterrestrial Physics, Garching, Germany, 9. Space Science and Applications, Los Alamos National Laboratory, Los Alamos, New Mexico USA, 10. Department of Earth Planetary and Space Sciences, University of California, Los Angeles, CA, USA