Evaluation of HZETRN on the Martian Surface: Sensitivity Tests and Model Results

The Mars Science Laboratory Radiation Assessment Detector (MSLRAD) is providing continuous measurements of dose, dose equivalent, and particle flux on the surface of Mars. These measurements have been highly useful in validating environmental and radiation transport models that will be heavily relied upon for future deep space missions. In this work, the HZETRN code is utilized to estimate radiation quantities of interest on the Martian surface. A description of the modeling approach used with HZETRN is given along with the various input models and parameters used to define the galactic cosmic ray (GCR) environment and Martian geometry. Sensitivity tests are performed to gauge the impact of varying several input factors on quantities being compared to MSLRAD data. Results from these tests provide context for inter-code comparisons presented in a companion paper within this issue. It is found that details of the regolith and atmospheric composition have a minimal impact on surface flux, dose, and dose equivalent. Details of the density variation within the atmosphere and uncertainties associated with specifying the vertical atmospheric thickness are also found to have minimal impact. Two widely used GCR models are used as input into HZETRN and it is found that the associated surface quantities are within several percent of each other

Battery-operated Independent Radiation Detector Data Report from Exploration Flight Test 1

Citation: Bahadori AA, Semones EJ, Gaza R, Kroupa M, Rios RR, Stoffle NN, Campbell-Ricketts T, Pinsky LS, and Turecek D 2015 Battery-operated Independent Radiation Detector Data Report from Exploration Flight Test 1 NASA/TP-2015-218575 NASA Johnson Space Center: Houston, TX http://ston.jsc.nasa.gov/collections/TRS/397.refer.htmlThis report summarizes the data acquired by the Battery-operated Independent Radiation Detector (BIRD) during Exploration Flight Test 1 (EFT-1). The BIRD, consisting of two redundant subsystems isolated electronically from the Orion Multi-Purpose Crew Vehicle (MPCV), was developed to fly on the Orion EFT-1 to acquire radiation data throughout the mission. The BIRD subsystems successfully triggered using on-board accelerometers in response to launch accelerations, acquired and archived data through landing, and completed the shut down routine when battery voltage decreased to a specified value. The data acquired are important for understanding the radiation environment within the Orion MPCV during transit through the trapped radiation belts

Space Radiation Protection Preparations for Commercial Space Station Activities

Nicholas N. Stoffle, Axiom Space, United StatesRoger A. Gard, Axiom Space, United StatesTed Duchesne, Axiom Space, United StatesMichael F. Harrison, Axiom Space, United StatesBen W. McGee, University of Maryland, United StatesICES503: Radiation Issues for Space FlightThe 54th International Conference on Environmental Systems was held in Prague, Czechia, on 13 July 2025 through 17 July 2025.Protection of astronaut crew members from the effects of space radiation is not a novel issue faced by commercial space providers, however, the changing landscape of commercial space regulation presents an increased need to prepare a robust system for radiation environment monitoring and crew exposure tracking. As a wider swath of the population gains access to space travel, the ‘healthy-astronaut’ assumption with respect to risks of living and working in space will become less valid, and impacts to long term health of both professional and customer astronaut crew members require constant re-evaluation. Here, we present a monitoring plan that is expected to provide a comprehensive understanding of the radiation environment inside a commercial space station. The resulting data will be applicable both to crew exposure tracking and to risk modelling. In addition, the plan provides monitoring of the local environments for individual payload needs during missions in low-earth orbit. In conjunction with environment monitoring in-mission, iterative design inputs and preflight evaluations will be critical to ensuring that commercial vehicles and mission plans are within safety margins necessary to meet regulatory guidelines while also meeting the needs of spaceflight customers. A general approach to vehicle shielding evaluation will be discussed with relevant mission design considerations

Full Mission Astronaut Radiation Exposure Assessments for Long Duration Lunar Surface Missions

Risk to astronauts due to ionizing radiation exposure is a primary concern for missions beyond Low Earth Orbit (LEO) and will drive mission architecture requirements, mission timelines, and operational practices. Both galactic cosmic ray (GCR) and solar particle event (SPE) environments pose a risk to astronauts for missions beyond LEO. The GCR environment, which is made up of protons and heavier ions covering a broad energy spectrum, is ever present but varies in intensity with the solar cycle, while SPEs are sporadic events, consisting primarily of protons moving outward through the solar system from the sun. The GCR environment is more penetrating and is more difficult to shield than SPE environments, but lacks the intensity to induce acute effects. Large SPEs are rare, but they could result in a lethal dose, if adequate shielding is not provided. For short missions, radiation risk is dominated by the possibility of a large SPE. Longer missions also require planning for large SPEs; adequate shielding must be provided and operational constraints must allow astronauts to move quickly to shielded locations. The dominant risk for longer missions, however, is GCR exposure, which accumulates over time and can lead to late effects such as cancer. SPE exposure, even low level SPE exposure received in heavily shielded locations, will increase this risk. In addition to GCR and SPE environments, the lunar neutron albedo resulting mainly from the interaction of GCRs with regolith will also contribute to astronaut risk. Full mission exposure assessments were performed for proposed long duration lunar surface mission scenarios. In order to accomplish these assessments, radiation shielding models were developed for a proposed lunar habitat and rover. End-to-End mission exposure assessments were performed by first calculating exposure rates for locations in the habitat, rover, and during extra-vehicular activities (EVA). Subsequently, total mission exposures were evaluated for proposed timelines. A number of computational tools and mathematical models, which have been incorporated into NASA's On-Line Tool for the Assessment of Radiation In Space (OLTARIS), were used for this study. These tools include GCR and SPE environment models, human body models, and the HZETRN space radiation transport code, which is used to calculate the transport of the charged particles and neutrons through shielding materials and human tissue. Mission exposure results, assessed in terms of effective dose, are presented for proposed timelines and recommendations are made for improved astronaut shielding and safer operational practice

Slowing-down and stopped charged particles cause angular dependence for absorbed dose measurements

Citation: Bahadori, Amir A., Rajarshi Pal Chowdhury, Martin Kroupa, et al. (2018) Slowing-down and Stopped Charged Particles Cause Angular Dependence for Absorbed Dose Measurements. Radiation Physics and Chemistry. https://doi.org/10.1016/j.radphyschem.2018.06.012The space radiation environment is dominated by heavy charged particles with atomic numbers ranging from 1 to 93, with broad energy spectra that exceed 10 GeV per nucleon. Despite advances in space radiation modeling and transport, radiation detectors continue to provide critical data for understanding risks of health effects to astronauts in space. In the past, NASA relied on tissue-equivalent proportional counters and passive devices for operational dosimetry; however, in recent years, pixel detectors providing detailed information about the radiation environment through analysis of charged particle tracks have been demonstrated in space. These next-generation detectors, based on Timepix read-out technology, require special analysis considerations that were not necessary or possible for previous dosimetry tools. The impacts of slowing-down and stopped ions on absorbed dose measurements must be explicitly modeled to understand variations with detector orientation. The purpose of the present study is to conclusively demonstrate that while absorbed dose measurements of penetrating charged particles are independent of detector orientation, slowing-down and stopped particles can result in charged particle absorbed dose measurements that are dependent on detector orientation. Monte Carlo simulations of an unshielded detector, irradiated at selected orientations by different kinetic energy domains with fluence spectra representative of two historical solar particle events, are presented to demonstrate the dependence of absorbed dose measurements. Next, results from Monte Carlo simulations of the same energy domains and fluence spectra, isotropically impinging on an anisotropic shield configuration about the detector, are shown, to exhibit the potential for observing varying absorbed doses under realistic environment and shielding conditions. Finally, slowing-down and stopped proton data acquired with Timepix-based detectors at the Tandem Van de Graaff at Brookhaven National Laboratory are used to demonstrate the effect via accelerator-based measurements

The radiation environment on the surface of Mars - Summary of model calculations and comparison to RAD data

The radiation environment at the Martian surface is, apart from occasional solar energetic particle events, dominated by galactic cosmic radiation, secondary particles produced in their interaction with the Martian atmosphere and albedo particles from the Martian regolith. The highly energetic primary cosmic radiation consists mainly of fully ionized nuclei creating a complex radiation field at the Martian surface. This complex field, its formation and its potential health risk posed to astronauts on future manned missions to Mars can only be fully understood using a combination of measurements and model calculations. In this work the outcome of a workshop held in June 2016 in Boulder, CO, USA is presented: experimental results from the Radiation Assessment Detector of the Mars Science Laboratory are compared to model results from GEANT4, HETC-HEDS, HZETRN, MCNP6, and PHITS. Charged and neutral particle spectra and dose rates measured between 15 November 2015 and 15 January 2016 and model results calculated for this time period are investigated