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Realistic nuclear reaction cross-section models are an essential ingredient of reliable heavy-ion transport codes. Such codes are used for risk evaluation of manned space exploration missions as well as for ion-beam therapy dose calculations and treatment planning. Therefore, in this study, a collection of total nuclear reaction cross-section data has been generated within a GSI-ESA-NASA collaboration. The database includes the experimentally measured total nucleus-nucleus reaction cross-sections. The Tripathi, Kox, Shen, Kox-Shen, and Hybrid-Kurotama models are systematically compared with the collected data. Details about the implementation of the models are given. Literature gaps are pointed out and considerations are made about which models fit best the existing data for the most relevant systems to radiation protection in space and heavy-ion therapy., 40 pages, 17 figures, 1 table

Real-time estimation of exposure levels has been considered in NASA's operational strategies and structural capability for the protection of astronauts from exposure to large solar particle events (SPEs). The temporal profile of organ dose rates is also important for the analysis of dose-rate-dependent biological responses and the optimization of radiation shielding and future mission planning. A realistic temporal estimation of exposure profiles relies on: (1) the complete energy spectrum of SPE that defines the boundary condition for radiation transport simulation; (2) the radiation transport simulation with detailed shielding and body geometry models that determines particle transmission at each critical body organ; and (3) the assessment of organ dosimetric quantities and biological risks by applying the corresponding response models. This paper introduces a process of rapidly estimating temporal exposures to SPEs by implementing the distributions of the organ doses and the spectral-shape characterization of the major SPEs. Simultaneously, the unconditional probability exceeding the NASA 30-day limit of a blood-forming organ dose is estimated by taking into account the variability of detailed spectra of SPEs for a given predictor fluence. These temporal evaluations of SPEs can be applied to the development of real-time guidance and protection system on improving mitigation of adverse effects during space missions.

The space radiation environment is composed of ionizing particles that may pose health risks to crew members during Low Earth Orbit (LEO) and deep space missions. NASA has established astronaut career radiation limits for cancer of 3% Risk of Exposure Induced Death (REID) at the 95% confidence level. The REID is the increased lifetime risk of death from cancer due to radiation exposure in comparison to an unexposed background population and has been traditionally mitigated by passive shielding design concepts and limiting safe days in space. Additional reduction in radiation exposure risk may be achieved with Medical Countermeasures (MCM). Recent meta-analyses have demonstrated the efficacy of aspirin in the reduction of the background colorectal cancer incidence and mortality rates for specific cohorts. Additional studies of warfarin in patients greater than 50 years of age have indicated statistically significant decreases in stomach, bladder, brain, prostate, and lung cancer incidence as compared to control groups. While ultimate selection of suitable countermeasures will be the responsibility of flight surgeons, this paper presents a general methodology for incorporating MCM into the NASA Space Radiation Cancer Risk model and includes modifications of the background mortality rates (hazard rates) and the radiation risk coefficients to numerically quantify the benefits of MCM. As examples of the method, aspirin and warfarin will be employed as MCM in a sensitivity analysis to compute the REID for astronauts embarking on a one-year deep space mission scenario.

The space radiation environment is a complex mixture of particle types and energies originating from sources inside and outside of the galaxy. These environments may be modified by the heliospheric and geomagnetic conditions as well as planetary bodies and vehicle or habitat mass shielding. In low Earth orbit (LEO), the geomagnetic field deflects a portion of the galactic cosmic rays (GCR) and all but the most intense solar particle events (SPE). There are also dynamic belts of trapped electrons and protons with low to medium energy and intense particle count rates. In deep space, the GCR exposure is more severe than in LEO and varies inversely with solar activity. Unpredictable solar storms also present an acute risk to astronauts if adequate shielding is not provided. Near planetary surfaces such as the Earth, moon or Mars, secondary particles are produced when the ambient deep space radiation environment interacts with these surfaces and/or atmospheres. These secondary particles further complicate the local radiation environment and modify the associated health risks. Characterizing the radiation fields in this vast array of scenarios and environments is a challenging task and is currently accomplished with a combination of computational models and dosimetry. The computational tools include models for the ambient space radiation environment, mass shielding geometry, and atomic and nuclear interaction parameters. These models are then coupled to a radiation transport code to describe the radiation field at the location of interest within a vehicle or habitat. Many new advances in these models have been made in the last decade, and the present review article focuses on the progress and contributions made by workers and collaborators at NASA Langley Research Center in the same time frame. Although great progress has been made, and models continue to improve, significant gaps remain and are discussed in the context of planned future missions. Of particular interest is the juxtaposition of various review committee findings regarding the accuracy and gaps of combined space radiation environment, physics, and transport models with the progress achieved over the past decade. While current models are now fully capable of characterizing radiation environments in the broad range of forecasted mission scenarios, it should be remembered that uncertainties still remain and need to be addressed.

The NASA Radiation Dosimetry Experiment (RaD-X) stratospheric balloon flight mission, launched on 25 September 2015, provided dosimetric measurements above the Pfotzer maximum. The goal of taking these measurements is to improve aviation radiation models by providing a characterization of cosmic ray primaries, which are the source of radiation exposure at aviation altitudes. The RaD-X science payload consists of four instruments. The main science instrument is a tissue-equivalent proportional counter (TEPC). The other instruments consisted of three solid state silicon dosimeters: Liulin, Teledyne total ionizing dose (TID) and RaySure detectors. The instruments were housed in an aluminum structure protected by a foam cover. The structure partially shielded the detectors from cosmic rays but also created secondary particles, modifying the ambient radiation environment observed by the instruments. Therefore, it is necessary to account for the influence of the payload structure on the measured doses. In this paper, we present the results of modeling the effect of the balloon payload on the radiation detector measurements using a Geant-4 (GEometry ANd Tracking) application. Payload structure correction factors derived for the TEPC, Liulin, and TID instruments are provided as a function of altitude. Overall, the payload corrections are no more than a 7% effect on the radiation environment measurements.

Protecting spacecraft crews from energetic space radiations that pose both chronic and acute health risks is a critical issue for future missions beyond low Earth orbit (LEO). Chronic health risks are possible from both galactic cosmic ray and solar energetic particle event (SPE) exposures. However, SPE exposures also can pose significant short term risks including, if dose levels are high enough, acute radiation syndrome effects that can be mission- or life-threatening. In order to address the reduction of short term risks to spaceflight crews from SPEs, we have developed recommendations to NASA for a design-standard SPE to be used as the basis for evaluating the adequacy of proposed radiation shelters for cislunar missions beyond LEO. Four SPE protection requirements for habitats are proposed: (1) a blood-forming-organ limit of 250 mGy-equivalent for the design SPE; (2) a design reference SPE environment equivalent to the sum of the proton spectra during the October 1989 event series; (3) any necessary assembly of the protection system must be completed within 30 min of event onset; and (4) space protection systems must be designed to ensure that astronaut radiation exposures follow the ALARA (As Low As Reasonably Achievable) principle.

Most accelerator-based space radiation experiments have been performed with single ion beams at fixed energies. However, the space radiation environment consists of a wide variety of ion species with a continuous range of energies. Due to recent developments in beam switching technology implemented at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), it is now possible to rapidly switch ion species and energies, allowing for the possibility to more realistically simulate the actual radiation environment found in space. The present paper discusses a variety of issues related to implementation of galactic cosmic ray (GCR) simulation at NSRL, especially for experiments in radiobiology. Advantages and disadvantages of different approaches to developing a GCR simulator are presented. In addition, issues common to both GCR simulation and single beam experiments are compared to issues unique to GCR simulation studies. A set of conclusions is presented as well as a discussion of the technical implementation of GCR simulation.

Human space flight requires protecting astronauts from the harmful effects of space radiation. The availability of measured nuclear cross-section data needed for these studies is reviewed in the present paper. The energy range of interest for radiation protection is approximately 100 MeV/n–10 GeV/n. The majority of data are for projectile fragmentation partial and total cross-sections, including both charge changing and isotopic cross-sections. The cross-section data are organized into categories which include charge changing, elemental, isotopic for total, single and double differential with respect to momentum, energy and angle. Gaps in the data relevant to space radiation protection are discussed and recommendations for future experiments are made.

The On-Line Tool for the Assessment of Radiation In Space (OLTARIS) is a World Wide Web based tool that assesses the effects of space radiation to humans in items such as spacecraft, habitats, rovers, and spacesuits. This document explains the basis behind the interface and framework used to input the data, perform the assessment, and output the results to the user as well as the physics, engineering, and computer science used to develop OLTARIS. The physics is based on the HZETRN2005 and NUCFRG2 research codes. The OLTARIS website is the successor to the SIREST website from the early 2000 s. Modifications have been made to the code to enable easy maintenance, additions, and configuration management along with a more modern web interface. Over all, the code has been verified, tested, and modified to enable faster and more accurate assessments. The next major areas of modification are more accurate transport algorithms, better uncertainty estimates, and electronic response functions. Improvements in the existing algorithms and data occur continuously and are logged in the change log section of the website.

A Langley research center (LaRC) developed deterministic suite of radiation transport codes describing the propagation of electron, photon, proton and heavy ion in condensed media is used to simulate the exposure from the spectral distribution of the aforementioned particles in the Jovian radiation environment. Based on the measurements by the Galileo probe (1995–2003) heavy ion counter (HIC), the choice of trapped heavy ions is limited to carbon, oxygen and sulfur (COS). The deterministic particle transport suite consists of a coupled electron photon algorithm (CEPTRN) and a coupled light heavy ion algorithm (HZETRN). The primary purpose for the development of the transport suite is to provide a means to the spacecraft design community to rapidly perform numerous repetitive calculations essential for electron, photon, proton and heavy ion exposure assessment in a complex space structure. In this paper, the reference radiation environment of the Galilean satellite Europa is used as a representative boundary condition to show the capabilities of the transport suite. While the transport suite can directly access the output electron and proton spectra of the Jovian environment as generated by the jet propulsion laboratory (JPL) Galileo interim radiation electron (GIRE) model of 2003; for the sake of relevance to the upcoming Europa Jupiter system mission (EJSM), the JPL provided Europa mission fluence spectrum, is used to produce the corresponding depth dose curve in silicon behind a default aluminum shield of 100 mils (∼0.7 g/cm2). The transport suite can also accept a geometry describing ray traced thickness file from a computer aided design (CAD) package and calculate the total ionizing dose (TID) at a specific target point within the interior of the vehicle. In that regard, using a low fidelity CAD model of the Galileo probe generated by the authors, the transport suite was verified versus Monte Carlo (MC) simulation for orbits JOI–J35 of the Galileo probe extended mission. For the upcoming EJSM mission with an expected launch date of 2020, the transport suite is used to compute the depth dose profile for the traditional aluminum silicon as a standard shield target combination, as well as simulating the shielding response of a high charge number (Z) material such as tantalum (Ta). Finally, a shield optimization algorithm is discussed which can guide the instrument designers and fabrication personnel with the choice of graded-Z shield selection and analysis.

A deterministic suite of radiation transport codes, developed at NASA Langley Research Center (LaRC), which describe the transport of electrons, photons, protons, and heavy ions in condensed media is used to simulate exposures from spectral distributions typical of electrons, protons and carbon-oxygen-sulfur (C-O-S) trapped heavy ions in the Jovian radiation environment. The particle transport suite consists of a coupled electron and photon deterministic transport algorithm (CEPTRN) and a coupled light particle and heavy ion deterministic transport algorithm (HZETRN). The primary purpose for the development of the transport suite is to provide a means for the spacecraft design community to rapidly perform numerous repetitive calculations essential for electron, proton and heavy ion radiation exposure assessments in complex space structures. In this paper, the radiation environment of the Galilean satellite Europa is used as a representative boundary condition to show the capabilities of the transport suite. While the transport suite can directly access the output electron spectra of the Jovian environment as generated by the Jet Propulsion Laboratory (JPL) Galileo Interim Radiation Electron (GIRE) model of 2003; for the sake of relevance to the upcoming Europa Jupiter System Mission (EJSM), the 105 days at Europa mission fluence energy spectra provided by JPL is used to produce the corresponding dose-depth curve in silicon behind an aluminum shield of 100 mils ( 0.7 g/cm2). The transport suite can also accept ray-traced thickness files from a computer-aided design (CAD) package and calculate the total ionizing dose (TID) at a specific target point. In that regard, using a low-fidelity CAD model of the Galileo probe, the transport suite was verified by comparing with Monte Carlo (MC) simulations for orbits JOI-J35 of the Galileo extended mission (1996–2001). For the upcoming EJSM mission with a potential launch date of 2020, the transport suite is used to compute the traditional aluminum-silicon dose-depth calculation as a standard shieldtarget combination output, as well as the shielding response of high charge (Z) shields such as tantalum (Ta). Finally, a shield optimization algorithm is used to guide the instrument designer with the choice of graded-Z shield analysis.

The On-Line Tool for the Assessment of Radiation in Space (OLTARIS, https://oltaris.nasa.gov) is a web-based set of tools and models that allows engineers and scientists to assess the effects of space radiation on spacecraft, habitats, rovers, and spacesuits. The site is intended to be a design tool for those studying the effects of space radiation for current and future missions as well as a research tool for those developing advanced material and shielding concepts. The tools and models are built around the HZETRN radiation transport code and are primarily focused on human- and electronic-related responses. The focus of this paper is to highlight new capabilities that have been added to support deep space (outside Low Earth Orbit) missions. Specifically, the electron, proton, and heavy ion design environments for the Europa mission have been incorporated along with an efficient coupled electron-photon transport capability to enable the analysis of complicated geometries and slabs exposed to these environments. In addition, a neutron albedo lunar surface environment was also added, that will be of value for the analysis of surface habitats. These updates will be discussed in terms of their implementation and on how OLTARIS can be used by instrument vendors, mission designers, and researchers to analyze their specific requirements.12

In order to enable long-duration human exploration beyond low-Earth orbit, the risks associated with exposure of astronaut crews to space radiation must be mitigated with practical and affordable solutions. The space radiation environment beyond the magnetosphere is primarily a combination of two types of radiation: galactic cosmic rays (GCR) and solar particle events (SPE). While mitigating GCR exposure remains an open issue, reducing astronaut exposure to SPEs is achievable through material shielding because they are made up primarily of medium-energy protons. In order to ensure astronaut safety for long durations beyond low-Earth orbit, SPE radiation exposure must be mitigated. However, the increasingly demanding spacecraft propulsive performance for these ambitious missions requires minimal mass and volume radiation shielding solutions which leverage available multi-functional habitat structures and logistics as much as possible. This paper describes the efforts of NASA's RadWorks Advanced Exploration Systems (AES) Project to design two minimal mass SPE radiation shelter concepts leveraging available resources: one based upon reconfiguring habitat interiors to create a centralized protection area and one based upon augmenting individual crew quarters with waterwalls and logistics. Discussion items include the design features of the concepts, a radiation analysis of their implementations, an assessment of the parasitic mass of each concept, and the result of a human in the loop evaluation performed to drive out design and operational issues.