The Health Risks of Extraterrestrial Environments
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Welcome to The Health Risks of Extraterrestrial Environments (THREE), an encyclopedic site whose goal is to present a discussion of the space radiation environment and its health risks to humans. The intent is to make this a good starting point for researchers new to either space, radiation, or both; a source of useful information for established investigators; and a teaching tool for students.

There are tabs to five pages, other than the "Home" page you are reading. The "THREE Encyclopedia" tab leads to a set of articles covering all aspects of space radiation concern, as well as an introduction to each topic. The articles have been written by investigators and colleagues of the NASA Space Radiation Program and have been peer reviewed under supervision of an Associate Editor. In addition to articles, the site contains, in Flash format, slides that were presented to students of the NASA Space Radiation Summer School. Articles may be viewed in PDF format. Click on "Recent Articles" below for a list of the most recently posted articles.

Citations to reports and to articles published in the scientific literature, that the Associate Editors consider to be of interest to the space radiation community, are listed monthly, together with a brief description by one of the article authors in most cases. The current month's listing may be accessed by clicking on the "In the News" link below. These citations are collected and archived on the "Bibliography" page, sorted by Encyclopedia topics, as a living bibliographic complement to the encyclopedia articles.

A few important presentations are collected in the "Multimedia" page; future presentations will be added as appropriate. The "Archive" is a store of material previously posted on THREE, and kept for reference. Finally, a glossary of terms related to space radiation research is available on the similarly named page.

The THREE Editorial Board is responsible for oversight of the content and policies for this site. It is hosted by the NASA Johnson Space Center.

Contributions to any part of THREE, especially submissions for articles, are welcome; instructions for authors are posted in the Statement of Policies. Please send your comments and contributions along with your full name, address, institution, and e-mail address to the Page Editor listed in the webpage footer.

Walter Schimmerling
THREE Chief Editor

  • Solar Particle Events and Radiation Exposure in Space (PDF) Shaowen Hu

    Posted March 31, 2017

  • An introduction to space radiation and its effects on the cardiovascular system (PDF) Marjan Boerma, PhD, University of Arkansas for Medical Sciences, Division of Radiation Health

    Posted October 13, 2016

  • Precise Genome Engineering and the CRISPR Revolution (Boldly Going Where No Technology Has Gone Before.) (PDF) Eric A. Hendrickson

    Posted April 6, 2016

  • Introduction to Track Structure and z*22. (PDF) Stanley B. Curtis (ret.) Fred Hutchinson Cancer Research Center, University of Washington, Seattle, WA.

    Posted November 17, 2015

General News Items | Citations


Summer 2018 Radiation Modelling Course in Pavia, Italy

A two-week course on “Modelling radiation effects from initial physical events: Learning modelling approaches and techniques in radiation biophysics and radiobiology research, from basic mechanisms to applications” is being offered by the University of Pavia, Italy from May 28th to June 8th, 2018. The course is also sponsored by CONCERT, a EURATOM-funded Horizon 2020 European Joint Programme set up to promote and integrate European research into the risks of exposure to low doses of ionising radiation. The course is open to: students (e.g. MSc, PhD and specialization students), young investigators, and continuing professional education, in particular with interest in scientific disciplines related to: Radiation Biophysics, Radiobiology and Radiation protection. There is no course fee. A limited number of free lodgings in Pavia colleges will be available. No financial support will be provided. Deadline for applications is April 15th, 2018. Apply by email to the Directors of the course: Andrea Ottolenghi and Giorgio Baiocco, and with copy to

R.J. Michael Fry dies at age 92

We were greatly saddened to learn that R.J. Michael Fry died peacefully Friday evening (November 24, 2017) at age 92 due to the rupture of an abdominal aortic aneurysm. He and his wife Shirley, 3 sons and their families and 8 grandchildren had just celebrated Thanksgiving together the day before. It is indeed sad news: Michael was a source of inspiration for all of us who were fortunate enough to know him, a model of scientific integrity and graciousness, quite apart from his widely recognized qualities as a scientist. He contributed to THREE for many years. and was an Associate Editor for many of them. His death is a loss to the world scientific community, to which he made many signal contributions as a radiobiologist and to NASA in particular, for which he oversaw the generation of guidelines for radiation protection in space over several decades.

22nd Workshop on Radiation Monitoring for the International Space Station

The 22nd Workshop on Radiation Monitoring for the International Space Station (WRMISS) took place on 5-7 September 2017 in Torino, Italy. The pdf files of the presentations are now available on the WRMISS webpage

Special Issue Publication
Mars Science Laboratory Radiation Assessment Detector (MSL/RAD) Modeling

"Blind Challenge" Workshop Special Issue

The Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) Curiosity rover is a sophisticated charged and neutral particle radiation analyzer developed by an international team of scientists and engineers.

During the 6 month cruise to Mars, inside the MSL spacecraft, RAD served as a proxy to validate models of the radiation levels expected inside a spacecraft that future astronauts might experience. Since landing on the surface of Mars in August 2012, RAD has been making detailed measurements of the radiation environment in preparation for human missions in coming decades.

In June 2016, forty scientists, engineers, modelers and instrumentalists from the US and Europe participated in a “blind challenge” workshop where each modeling team had to predict the particle spectra and dose rates for a two month period before the MSL/RAD data had been released to the public, and submit and present their results and predictions at the workshop.

The papers in this volume include contributions from each of the groups on the details of their models and the procedures used in comparing their results with RAD data. This “blind challenge” in predicting the RAD data showed considerable differences in the spectra, but also showed that dose and dose equivalent rates agree very well within a 30% uncertainty. This demonstrates that under- and overestimates in particle fluxes in different energy ranges somehow compensate and clearly indicate that the physics in the models show much room for improvement. Furthermore, the inclusion of the appropriate detector geometry and shielding distributions will certainly contribute to reduce the differences. Based on these first results, further modeling workshops are encouraged, to optimize the capability of the prediction tools.

This Workshop was the first of its kind, and tremendous progress was made by getting the instrument designers and the different modeling teams together to discuss and compare their results in a collegial and open manner. This issue reflects this spirit of cooperation and teamwork and a second workshop is tentatively scheduled for Summer 2018.

International Journal of Radiation Biology:

The Bill Morgan Memorial Special Issue on Biology, Epidemiology, and Implications for Radiation Protection.

The International Journal of Radiation Biology Volume 93, 2017 - Issue 10, containing The Bill Morgan Memorial Special Issue on Biology, Epidemiology, and Implications for Radiation Protection has just come out and is available in open access. Dr William Francis Morgan, known as Bill by many of his friends and colleagues, passed away on 13 November 2015, at the age of 62. This Special Issue is in memory of Bill and consists of 17 articles covering the many areas in which Bill made seminal contributions. . Bill Morgan took a keen interest in radiation issues of importance to NASA and was a member of many advisory panels. He also was Scientific Director of the National Aeronautics and Space Administration (NASA) Space Radiation Summer School (NSRSS) in 2009 and 2010.Those of us who were fortunate enough to know him have lost a friend and a wise colleague.

29th Annual NASA Space Radiation Investigators’ Workshop

The 29th Annual NASA Space Radiation Investigators’ Workshop, in conjunction with the NASA Human Research Program Investigators’ Workshop, will be held January 22-25, 2018, at the Galveston Island Convention Center in Galveston, TX.

The purpose of this workshop is to provide an opportunity for active researchers in the NASA Space Radiation Program to share the results of their work, interact with scientists in other discipline areas within the Human Research Program, and explore new directions for research that may benefit the NASA program. The workshop format will include plenary sessions, short talks, and poster sessions. The NASA HRP Graduate Student/Postdoctoral Fellow Poster Contest will be held to recognize and honor student investigators.

Principal investigators receiving NASA funds are required to attend. Although attendance at the workshop is by invitation only, other scientists with a legitimate interest in space radiation research are also welcome.

The full scheduled agenda for the HRP IWS and the Space Radiation IWS will be available to review in December.

A Mission to Mars: An Encounter with Radiation
This is a science education unit for use in high school biology classes to learn about the effects of cosmic radiation on human biology. The unit integrates biology with chemistry and physics. A focus of the unit is on the ability of radiation to damage DNA, causing mutations that can lead to the development of cancer.

Updated Transport Code “HZETRN2015” Now Available
The HZETRN2015 transport code is now available. This latest update includes the same functionalities as the previous release, HZETRN2010, along with several important new features:

  •  3D transport in user-defined combinatorial geometry or ray-trace geometry.
  • The pion, muon, and electromagnetic cascade components are included in transport procedures.
  • Additional options have been added to the cross section module to enable direct access to certain atomic and nuclear cross sections.
  • The Badhwar-O'Neill 2014 GCR model is fully integrated into the transport module and can be evaluated using mission dates or by specifying a solar modulation parameter.
  • Options for solar particle event boundary conditions have been expanded to enable user-defined parameters for several historical fitting functions.

Users may direct questions, bugs, and related issues to
Instructions on how to access the software are provided in the Computer Tools page of this THREE website.


High-LET Radiation Increases Tumor Progression in a K-Ras-Driven Model of Lung Adenocarcinoma.
Asselin-Labat ML, Rampersad R, Xu X, Ritchie ME, Michalski J, Huang L, Onaitis MW. Radiation Research. Nov 2017; 188(5):562-570.
A mouse model of lung adenocarcinoma driven by oncogenic K-Ras was used to ascertain the effect of low- and high-LET radiation on tumor formation. We observed increased tumor progression and tumor cell proliferation after single dose or fractionated high-LET doses, which was not observed in mice exposed to low-LET radiation. Location of the tumor nodules was not affected by radiation, indicating that the cell of origin of K-Ras-driven tumors was the same in irradiated or nonirradiated mice. Gene expression analysis revealed an upregulation of genes involved in cell proliferation and DNA damage repair. This study provides evidence that exposure to a single dose or fractionated doses of high-LET radiation induces molecular and cellular changes that accelerate lung tumor growth.
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Whole-Body Exposure to 28Si-Radiation Dose-Dependently Disrupts Dentate Gyrus Neurogenesis and Proliferation in the Short Term and New Neuron Survival and Contextual Fear Conditioning in the Long Term.
Whoolery CW, Walker AK, Richardson DR, Lucero MJ, Reynolds RP, Beddow DH, Clark KL, Shih HY, LeBlanc JA, Cole MG, Amaral WZ, Mukherjee S, Zhang S, Ahn F, Bulin SE, DeCarolis NA, Rivera PD, Chen BPC, Yun S, Eisch SJ. Radiation Research: Nov 2017;188(5):532-551.
To compare the influence of 28Si exposure on indices of neurogenesis and hippocampal function with previous studies on 56Fe exposure, 9-week-old C57BL/6J and Nestin-GFP mice received whole-body 28Si-particle-radiation exposure. In contrast to the clearly observed radiation-induced, dose-dependent reductions in the short-term group across all markers, only a few neurogenesis indices were changed in the long-term irradiated groups. Compared to previously reported studies, present data suggest that 28Si-radiation exposure damages neurogenesis, but to a lesser extent than 56Fe radiation and that low-dose 28Si exposure induces abnormalities in hippocampal function, disrupting fear memory but also inducing anxiety-like behavior. Furthermore, exposure to 28Si radiation decreased new neuron survival in long-term male groups but not females suggests that sex may be an important factor when performing brain health risk assessment for astronauts traveling in space.
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Atmospheric Cosmic-Ray Variation and Ambient Dose Equivalent Assessments Considering Ground Level Enhancement Thanks to Coupled Anisotropic Solar Cosmic Ray and Extensive Air Shower Modeling.
Hubert G and Aubry S. Radiation Research: Nov 2017;188(5):517-531.
This work investigates the impact of Forbush decrease (FD) and ground-level enhancement (GLE) in the atmosphere, based on solar and galactic cosmic-ray models and the extensive air shower simulations. The calculated ambient dose equivalents were compared with flight measurements in quiet solar conditions. Doses induced by extreme GLE events were investigated specifically for London to New York flights.
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Low doses of oxygen ion irradiation cause long-term damage to bone marrow hematopoietic progenitor and stem cells in mice.
Wang Y, Chang J, Li X, Pathak R, Sridharan V, Jones T, Mao XW, Nelson G, Boerma M, Hauer-Jensen M, Zhou D, Shao L. PLoS One: 2017 Dec 12;12(12):e0189466.
While high energy charged particle irradiation as found in space is known to have short-term adverse effects on the hematopoietic system, long-term effects are not well studied. This experiment used a mouse model of oxygen ion exposure to assess stem and progenitor cells isolated from the bone marrow at three months after exposure. The cells of irradiated animals showed increased levels of reactive oxygen species and reduced performance in cell function assays. These results suggest that high energy charged particle irradiation can have long-term adverse effects on the hematopoietic system.
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Low-dose proton radiation effects in a transgenic mouse model of Alzheimer’s disease - Implications for space travel.
Rudobeck E, Bellone JA, Szücs A, Bonnick K, Mehrotra-Carter S, Badaut J, Nelson GA, Hartman RE, Vlkolinsky R. PLoS One. 2017 Nov 29;12(11):e0186168.
Space radiation represents a significant health risk for astronauts and it may accelerate the onset of Alzheimer's disease (AD). Although protons represent the main constituent in the space radiation spectrum, their effects on AD-related pathology have not been tested. We irradiated 3-month-old APP/PSEN1 transgenic (TG) and wild type (WT) mice with protons (150 MeV; 0.1-1.0 Gy; whole body) and evaluated functional and biochemical hallmarks of AD. We performed behavioral tests in the water maze (WM) before irradiation and in the WM and Barnes maze at 3 and 6 months post-irradiation to evaluate spatial learning and memory. We also performed electrophysiological recordings in vitro in hippocampal slices prepared 6 and 9 months post-irradiation to evaluate excitatory synaptic transmission and plasticity. Next, we evaluated amyloid β (Aβ) deposition in the contralateral hippocampus and adjacent cortex using immunohistochemistry. In cortical homogenates, we analyzed the levels of the presynaptic marker synaptophysin by Western blotting and measured pro-inflammatory cytokine levels (TNFα, IL-1β, IL-6, CXCL10 and CCL2) by bead-based multiplex assay. TG mice performed significantly worse than WT mice in the WM. Irradiation of TG mice did not affect their behavioral performance, but reduced the amplitudes of population spikes and inhibited paired-pulse facilitation in CA1 neurons. These electrophysiological alterations in the TG mice were qualitatively different from those observed in WT mice, in which irradiation increased excitability and synaptic efficacy. Irradiation increased Aβ deposition in the cortex of TG mice without affecting cytokine levels and increased synaptophysin expression in WT mice (but not in the TG mice). Although irradiation with protons increased Aβ deposition, the complex functional and biochemical results indicate that irradiation effects are not synergistic to AD pathology.
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Long-Term Deficits in Behavior Performances Caused by Low- and High-Linear Energy Transfer Radiation.
Patel R, Arakawa H, Radivoyevitch T, Gerson SL and Welford SM. Radiation Research. 2017; 188(6):672-680.
Across a range of LET sources, we found that different ion species have different detrimental impacts at extended time points post exposure that can lead sustained declines in behavioral performances. A significant dose effect was observed on recognition memory and activity levels measured 9 months postirradiation, regardless of radiation source. In contrast, we observed that each ion species had a distinct effect on anxiety, motor coordination and spatial memory at extended time points.
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Dose- and ion-dependent effects in the oxidative stress response to space-like radiation exposure in the skeletal system.
Alwood JS, Tran LH, Schreurs AS, Shirazi-Fard Y, Kumar A, Hilton D, Tahimic CGT, Globus RK. Int J Mol Sci. 2017 Oct 10;18(10):E2117.
This article reports on impairment of osteoblastogenesis in 16-weeks old, male, C57BL6/J mice by protons (150 MeV/n) 56Fe ions (600 MeV/n) using either low (5 or 10 cGy) or high (50 or 200 cGy) doses at NASA’s Space Radiation Lab. The authors’ conclusion is that high-LET irradiation at 200 cGy impaired osteoblastogenesis and regulated steady-state gene expression of select redox-related genes during osteoblastogenesis, which may contribute to persistent bone loss.
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Effect of densely ionizing radiation on cardiomyocyte differentiation from human-induced pluripotent stem cells.
Baljinnyam E, Venkatesh S, Gordan R, Mareedu S, Zhang J, Xie LH, Azzam EI, Suzuki CK, Fraidenraich D. Physiol Rep. 2017 Aug;5(15):e13308.
Studies with human hearts are not feasible as cardiac biopsies are extremely rare. Thus, innovative approaches are greatly needed to investigate human cardiac cell biology in a dish. To achieve this, we developed a system whereby human induced pluripotent stem cells (hiPSCs) maintained in culture, were used to evaluate the effects of densely ionizing radiation on cardiac differentiation. hiPSCs were exposed to low fluences of 3.7 MeV a particles (mean linear energy transfer ~109 keV/mm), and then differentiated into beating cardiomyocytes (hiPSC-CMs), permitting us to conduct molecular, morphological, and functional assessments. We report that low mean absorbed doses of a particles (0.5-10 cGy) applied to hiPSCs does not affect their capacity to become beating cardiomyocytes, but has direct consequences on the generation of arrhythmic profiles and on the number of differentiated cells.

The results obtained in the study have broader implications for future investigations. For example, hiPSCs can be generated using fibroblasts or blood lymphocytes, or even urine from astronauts before and after space travel. These astronaut-derived hiPSCs may be invaluable for further characterizations. Another exciting therapeutic possibility is the prospect of using astronaut-derived pre-mission hiPSCs, as these cells can be differentiated into cardiomyocytes, and subsequently transplanted back into the astronaut in a personalized manner to correct for unexpected pathologies resulting from deep space travel.
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Evaluation of HZETRN on the Martian surface: Sensitivity tests and model results.
Slaba TC, Stoffle NN. Life Sci Space Res. 2017 Aug;14:29-35.
The Mars Science Laboratory Radiation Assessment Detector (MSLRAD) provides continuous measurements of dose, dose equivalent, and particle flux on the surface of Mars. Various radiation physics and transport models have been compared to the MSLRAD data, and in June 2016, a workshop was held in Boulder, CO to have a “blind” comparison between models and new MSLRAD measurements. Certain aspects of the environmental conditions on the Martian surface were provided to the modeling teams such as the time period over which the measurements occurred and the atmospheric column density. Other details were intentionally left unspecified. For example, each team was free to choose a model to describe the primary GCR particle spectra, atmosphere and regolith composition, and other related factors. Leveraging the high degree of computational efficiency and accuracy associated with HZETRN, sensitivity tests were performed to determine to what extent some of the unspecified factors influence quantities of interest on the Martian surface. Results of these tests are useful in providing context for the summary comparison paper of Matthia et al. (2017) (contained within the same issue as this paper) so that variation between codes and differences against MSLRAD data can be more clearly interpreted. This paper appears in a special issue of Life Sciences in Space Research along with several other modeling, measurement data analysis, and summary papers.
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Different Sequences of Fractionated Low-Dose Proton and Single Iron-Radiation-Induced Divergent Biological Responses in the Heart.
Sasi SP, Yan X, Zuriaga-Herrero M, Gee H, Lee J, Song J, Onufrak J, Morgan J, Enderling H, Walsh K, Kishore R, Goukassian DA. Radiat Res. August 2017, Vol. 188, No. 2, pp. 191-203.(2017).
We previously reported the effects of a single, whole-body, low-dose 1H (0.5 Gy, 1 GeV) and 56Fe (0.15 Gy, 1 GeV/nucleon) ion irradiation on the CV system during normal aging and under ischemic conditions. These studies signified the long-term (up to 10 months) negative effects of irradiation on systolic and diastolic functions of the heart accompanied by increased hypertrophic signaling contributing to heart failure. In the model of acute myocardial infarct, the cardiac tissue recovery and regeneration after exposure to 0.15 Gy 56Fe radiation demonstrated long-lasting detrimental effects including loss of cardiac function and worsened cardiac remodeling over the period of 10 months. On the other hand, 0.5 Gy 1H irradiation induced positive effects during recovery after a MI event, which may be attributed to a possible ischemic preconditioning-like effect of low-proton irradiation of the heart in case of possible adverse cardiac event, such as acute myocardial infarct (AMI). Because there is essentially no data available on the effects of different sequential, fractionated low-dose charged particle (SPE-like proton and HZE) irradiations to the CV system, we used same murine models to examine the effects of acute, whole-body fractionated low-dose 1H exposure by itself and in combination with a single low dose of 56Fe radiation before or after fractionated 1H to emulate a possible space-like environment. Our1H vs. a single 56Fe-IR. These findings also provide initial mechanistic insight into the development of CV morbidity and mortality induced by mixed charged particle radiation in the heart tissue. Additionally, they emphasize the necessity to determine underlying molecular mechanisms responsible for this significant mix ion fractionation and sequence-dependent divergent responses in the heart during aging and in case of a possible ischemic cardiovascular event.
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Mars science laboratory radiation assessment detector (MSL/RAD) modeling workshop proceedings.
Hassler DM, Norbury JW, Reitz G. Life Sci Space Res. 2017 Aug;14:1-2.
This paper is an introduction to the special issue of Life Sciences in Space Research devoted to comparisons of space radiation transport codes with recent measurements made by the Mars Science Laboratory Radiation Assessment Detector.
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Comparing HZETRN, SHIELD, FLUKA and GEANT transport codes.
J. Norbury, T. Slaba, N. Sobolevsky, B. Reddell Life Sciences in Space Research, vol. 14, pp. 64-73, 2017.
The space radiation transport codes, HZETRN, SHIELD, FLUKA and GEANT are compared to each other for heavy-ion, light-ion (isotopes of Hydrogen and Helium) and pion production after the galactic cosmic ray spectrum is transported through various aluminum shield thicknesses. The paper shows that the biggest differences among the codes occurs for light-ion production.
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The radiation environment on the surface of Mars - Summary of model calculations and comparison to RAD data.
Matthiä D, Hassler DM, de Wet W, Ehresmann B, Firan A, Flores-McLaughlin J, Guo J, Heilbronn LH, Lee K, Ratliff H, Rios RR, Slaba TC, Smith MA, Stoffle NN, Townsend LW, Berger T, Reitz G, Wimmer-Schweingruber RF, Zeitlin C. Life Sci Space Res. 2017 Aug;14:57-63. Epub 2017 Jun 28.
This article summarizes the results of a workshop held in June 2016 in Boulder, CO. The goal of the workshop was validating models and simulations of the radiation environment originating from galactic cosmic rays on the Martian surface with data recorded by the Radiation Assessment Detector (RAD) on the Curiosity rover of the Mars Science Laboratory (MSL). For this purpose, a time period (15 Nov 2015 to 15 Jan 2016) was selected for which the model calculations were performed; measurements taken by RAD during the same time were used for the comparison. The paper presents differential particle fluxes calculated using different galactic cosmic ray spectra in combination with particle transport codes: GEANT4, HETC-HEDS, HZETRN, MCNP6, and PHITS. The results of the numerical models are compared to charged particle spectra stopping in the RAD detector in the energy range between a few tens and a few hundred MeV per nucleon and neutral particle spectra, i.e. photons and neutrons, between 10 MeV and 1 GeV. Dose rates and dose equivalent rates as well as the corresponding quality factors from models and measurement are presented as well.
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A calculation of the radiation environment on the Martian surface.
de Wet WC, Townsend LW. Life Sci Space Res. 2017 Aug;14:51-6.
The radiation environment on the Martian surface, as produced by galactic cosmic radiation incident on the atmosphere, is modeled using the Monte Carlo radiation transport code, High Energy Transport Code—Human Exploration and Development in Space (HETC–HEDS). Calculated fluxes for neutrons, protons, deuterons, tritons, helions, alpha particles, and heavier ions up to Fe are compared with measurements taken by the Radiation Assessment Detector (RAD) instrument aboard the Mars Science Laboratory over a period of 2 months. The degree of agreement between measured and calculated surface flux values over the limited energy range of the measurements is found to vary significantly depending on the particle species or group. However, in many cases the fluxes predicted by HETC–HEDS fall well within the experimental uncertainty. The calculated results for alpha particles and the heavy ion groups Z=3–5, Z=6–8, Z=9–13 and Z>24 are in the best agreement, each with an average relative difference from measured data of less than 40%. Predictions for neutrons, protons, deuterons, tritons, Helium-3, and the heavy ion group Z=14–24 have differences from the measurements, in some cases, greater than 50%. Future updates to the secondary light particle production methods in the nuclear model within HETC–HEDS are expected to improve light ion flux predictions.
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Radiation transport simulation of the Martian GCR surface flux and dose estimation using spherical geometry in PHITS compared to MSL-RAD measurements.
Flores-McLaughlin J. Life Sci Space Res. 2017 Aug;14:36-42.
The Martian surface radiation environment is composed of galactic cosmic radiation, secondary particles produced by their interaction with the Martian atmosphere, albedo particles from the Martian regolith and occasional solar particle events. Despite this complex physical environment with potentially significant locational and geometric dependencies, computational resources often limit radiation environment calculations to a one-dimensional or slab geometry specification. To better account for Martian geometry, spherical volumes with respective Martian material densities are adopted in this model. This physical description is modeled with the PHITS radiation transport code and compared to a portion of measurements from the Radiation Assessment Detector of the Mars Science Laboratory. Particle spectra measured between 15 November 2015 and 15 January 2016 and PHITS model results calculated for this time period are compared. Results indicate good agreement between simulated dose rates, proton, neutron and gamma spectra. This work was originally presented at the 1st Mars Space Radiation Modeling Workshop held in 2016 in Boulder, CO.
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Simulation of the GCR spectrum in the Mars Curiosity Rover’s RAD detector using MCNP6.
Ratliff HN, Smith MBR, Heilbronn L. Life Sci Space Res. 2017 Aug;14:43-50.
The paper presents results from MCNP6 simulations modeling the radiation environment induced by galactic cosmic rays (GCRs) on the surface of Mars as seen by the Radiation Assessment Detector (RAD) onboard NASA’s Curiosity rover. The detector had two separate particle acceptance angles, 4π and 30° off zenith. All ions with Z = 1 through Z = 28 were tracked in both scenarios while some additional secondary particles were only tracked in the 4π cases. This work was part of a collaborative workshop hosted by the Southwest Research Institute comparing RAD measurements with the simulated results of five modeling teams each using a different particle transport code.

–HEDS fall well within the experimental uncertainty. The calculated results for alpha particles and the heavy ion groups Z=3–5, Z=6–8, Z=9–13 and Z>24 are in the best agreement, each with an average relative difference from measured data of less than 40%. Predictions for neutrons, protons, deuterons, tritons, Helium-3, and the heavy ion group Z=14–24 have differences from the measurements, in some cases, greater than 50%. Future updates to the secondary light particle production methods in the nuclear model within HETC–HEDS are expected to improve light ion flux predictions.
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Men, Women, and Space Travel: Gene-Linked Molecular Networks, Human Countermeasures, and Legal and Ethical Considerations
Schmidt MA, Bailey SM, Goodwin TJ, Jones JA, Killian JP, Legato MJ, Limoli C, Moussa S, Ploutz-Snyder L. Gend Genome. 2017 Jun 1;1(2):54-67.
A roundtable discussion to consider the extensive differences between men and women, including both their strengths and vulnerabilities, in preparing professional astronauts for space travel.
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Space-type radiation induces multimodal responses in the mouse gut microbiome and metabolome.
Casero D, Gill K, Sridharan V, Koturbash I, Nelson G, Hauer-Jensen M, Boerma M, Braun J, Cheema AK. Microbiome. 2017 Aug 18;5(1):105.
Pathophysiological manifestations after low dose radiation exposure are strongly influenced by non-cytocidal radiation effects, including changes in the microbiome and host gene expression. Although the importance of the gut microbiome in the maintenance of human health is well established, little is known about the role of radiation in altering the microbiome during deep-space travel. Using a mouse model for exposure to high LET radiation, we observed substantial changes in the composition and functional potential of the gut microbiome. These were accompanied by changes in the abundance of multiple metabolites, which were related to the enzymatic activity of the predicted metagenome by means of metabolic network modeling. The implication of microbiome-mediated pathophysiology after low dose ionizing radiation may be an unappreciated biologic hazard of space travel and deserves experimental validation.
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Microgravity validation of a novel system for RNA isolation and multiplex quantitative real time PCR analysis of gene expression on the International Space Station
Parra M, Jung J, Boone TD, Tran L, Blaber EA, Brown M, et al. (2017) PLoS ONE 12(9): e0183480.
This manuscript describes the WetLab-2 validation flight results. This work, conducted during SPX-8, is the first peer-reviewed publication of the major NASA accomplishment of successfully conducting genomic and molecular biology studies end-to-end, sample-to-data, on ISS. The WetLab-2 system allows ISS experimenters to use biological samples collected on station and in the same day extract RNA, and obtain quantitative gene expression data by PCR analysis, potentially for science, medical diagnostics, and environmental monitoring. The WetLab-2 facility now provides a novel operational on-orbit research capability for molecular biology and demonstrates the feasibility of more complex wet bench experiments in the ISS National Lab environment.
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Bi-directional and shared epigenomic signatures following proton and 56Fe irradiation
Impey, S., Jopson, T, Pelz, C., Tafessu, A, Fareh, F., Zuloaga, D., Marzulla, T., Riparip, L., Stewart, B., Rosi, S, Turker, M.S., Raber, J. Scientific Reports, 7, 10227 (2017)
As the brain’s response to radiation exposure is an important concern for patients undergoing cancer therapy and astronauts on long missions in deep space. We assessed whether this response is specific and prolonged and is linked to epigenetic mechanisms, focusing on the response of the hippocampus at early (2-weeks) and late (20-week) time points following whole body proton irradiation. Significant overlap was observed between DNA methylation changes at the 2 and 20-week time points, demonstrating specificity and retention of changes in response to radiation and a novel class of DNA methylation change was observed following space irradiation characterized by both increased and decreased cytosine hydroxymethylation (5hmC) levels along the entire gene body. These changes mapped to genes encoding neuronal functions including postsynaptic gene ontology categories, indicating that the brain’s response to proton irradiation is both specific and prolonged and involves novel remodeling of non-random regions of the epigenome.
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Low- and high-LET ionizing radiation induces delayed homologous recombination that persists for two weeks before resolving.
Allen CP, Hirakawa H, Nakajima N, Moore S, Nie J, Sharma N, Sugiura M, Hoki Y, Araki R, Abe M, Okayasu R, Fujimori A, Nickoloff JA. Radiation Research July 2017, Volume 188, pages 82-93.
Ionizing radiation has immediate effects on cells and tissues, causing DNA damage, mutations, and cell death that are evident within minutes to days of exposure. Ionizing radiation also causes delayed effects observed weeks to years after exposure, including delayed death and delayed chromosomal instability. The Morgan laboratory pioneered studies of ionizing radiation-induced delayed chromosomal instability, demonstrating that it can persist for years after cells survive low to moderate doses of low LET ionizing radiation. Subsequently, low LET ionizing radiation was shown to induce a mechanistically distinct form of delayed genomic instability, revealed as hyper-homologous recombination. This study extends those findings, revealing that delayed homologous recombination is also induced by high LET carbon ions. Genome instability is a hallmark (and often a driver) of cancer, so genome instability associated with hyper-homologous recombination is concerning, both for environmental and radiotherapy radiation exposures. Importantly, similar levels of hyper-homologous recombination were induced by low and high LET radiation, and in both cases it persists for only two weeks before resolving. These results indicate that this form of genome instability is not as persistent as delayed chromosomal instability, and that the risk of genome instability associated with homologous recombination after high LET carbon ion radiation is no greater than that induced by low LET X-rays.
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Ballooning for Biologists: Mission Essentials for Flying Life Science Experiments to Near Space on NASA Large Scientific Balloons.
Smith DJ and Sowa MB. Gravitational and Space Research, Volume 5(1), July 2017, Pages 52-73
This review paper was written for space biology and radiation research teams, addressing the logistics and benefits of flying life science experiments on large scientific balloons. Earth’s stratosphere has a naturally broad, low, and sustained background radiation spectrum; thus long duration biology experiments flown on balloons can avoid limitations otherwise associated with ground simulation chambers and radiation facilities. The authors provide an overview of balloon operations (Part 1), biology topics that can be uniquely addressed in the stratosphere's radiation environment (Part 2), and a roadmap for developing payloads to fly with NASA (Part 3).
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Measurements of the neutral particle spectra on Mars by MSL/RAD from 2015-11-15 to 2016-01-15.
Guo J, Zeitlin C, Wimmer-Schweingruber R, Hassler DM, Köhler J, Ehresmann B, Böttcher S, Böhm E, Brinza DE. Life Sci Space Res. 2017 Jun 16. [Article in Press]
This paper updates the earlier work by Koehler et al. published in JGR Planets in 2013 (10.1002/2013JE004539). We have studied the time period specified for the RAD Modeling Workshop (see using the same inversion technique as before, but with an improved algorithm for normalizing the neutron and gamma-ray spectra. We find smaller dose and dose equivalent rates than were found previously. The spectral shapes are very similar to what was found previously, and are again well-fit by power laws with spectral indices close to those found in the earlier work.
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Developing Human Radiation Biodosimetry Models: Testing Cross-Species Conversion Approaches Using an Ex VivoModel System.
Jin G. Park, Sunirmal Paul, Natalia Briones, Jia Zeng, Kristin Gillis, Garrick Wallstrom, Joshua LaBaer, and Sally A. Amundson (2017) Radiation Research: June 2017, Vol. 187, No. 6, pp. 708-721.
Because non-human primates (NHP) are the animals most closely related to man, they have generally been accepted to be the most relevant animal model of human biological responses. However, responses in NHP should not be assumed to be identical to those of humans. This study begins to assess the differences in gene expression responses to radiation exposure in NHP and humans in the context of developing radiation biodosimetry. Several approaches are tested for applying dose prediction models developed in NHP to humans. It was found that an NHP biodosimetry model built using interspecies-correlated genes could accurately predict dose to human samples when a multiple regression-based cross-species conversion was applied to the gene expression values.
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Genomic instability induced in distant progeny of bystander cells depends on the connexins expressed in the irradiated cells.
de Toledo SM, Buonanno M, Harris AL, Azzam EI. Int J Radiat Biol. 2017 Jun 1:1-49. [Epub ahead of print]
Using a layered cell culture system, the study examines the time window during which intercellular signaling though gap junctions mediates the propagation of harmful effects from irradiated normal or tumor cells that express specific connexins to contiguous bystander normal human fibroblasts. The irradiated cells were exposed to moderate mean absorbed doses of 3.7 MeV a particle, 1000 MeV/u iron ions, 600 MeV/u silicon ions, or 137Cs γ rays. Increased frequency of chromosomal damage and enhanced oxidative changes were observed in bystander cells exposed to either the sparsely ionizing (137Cs γ rays) or densely ionizing (a particles, energetic iron or silicon ions) radiations. Notably, the distant progeny of isolated bystander cells also exhibited increased levels of spontaneous chromosomal damage, and the effect was dependent on the type of junctional channels that coupled the irradiated donor cells with the bystander cells. Together, the results inform the roles that intercellular communication play under stress conditions, and aid assessment of the health risks of exposure to ionizing radiation.
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Myth-free space advocacy Part I—The myth of innate exploratory and migratory urges.
Schwartz JSJ. Acta Astronaut. 2017 Aug;137:450-60.
Space advocates often argue that we ought to explore space because we are by nature an exploring species, but this is problematic for a number of reasons. Research in biology and genetics has revealed genes associated with exploratory behavior, but `exploratory behavior' is a general term covering a wide range of information- and novelty-seeking activities and does not refer always or exclusively to, e.g., acts of discovery or migration. Though existing work recognizes a link between these genes and prehistoric human migration, the data suggest they did not impel migration but instead were selected for subsequent to migration. Additionally, exploration is not an universal in human history or culture. In cases where societies or nations have engaged in extensive exploration, including the exploration of space, it has seldom been conducted for its own sake but instead as an accessory to other ambitions, e.g., conquest, resource acquisition, prestige. In no sense relevant to space exploration is there good evidence that humans (or human societies) are innately exploratory.
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Non-targeted effects models predict significantly higher Mars mission cancer risk than targeted effects models.
Cucinotta FA, Cacao E. Sci Rep. 2017 May 12;7(1):1832.
Using the mouse Harderian gland tumor experiment, a particle track structure model of tumor prevalence is used to investigate the effects of non-targeted effects (NTE) in predictions of chronic GCR exposure risk. The NTE model led to a predicted risk 2-fold higher compared to a targeted effects model.
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Solid Cancer Incidence among the Life Span Study of Atomic Bomb Survivors: 1958–2009.
Eric J. Grant, Alina Brenner, Hiromi Sugiyama, Ritsu Sakata, Atsuko Sadakane, Mai Utada, Elizabeth K. Cahoon, Caitlin M. Milder, Midori Soda, Harry M. Cullings, Dale L. Preston, Kiyohiko Mabuchi and Kotaro Ozasa. Radiation Research 187(5):513-537. 2017
The Radiation Effects Research Foundation (RERF) and its forerunner, the Atomic Bomb Casualty Commission (ABCC), have been estimating the long-term health effects of radiation among the Life Span Study (LSS) cohort of atomic bomb survivors since that study’s inception in 1950. Cancer incidence has been followed since the establishment of local cancer registries in 1958.

In the accompanying article, 105,444 LSS cohort members were followed from 1958 through 2009. The primary exposure was the radiation dose to the colon, calculated by a weighted sum of gamma and neutron doses. The primary outcome was a first primary solid cancer. Excess relative risk models (ERR) and excess absolute rate models (EAR) were constructed while adjusting for smoking consumption, the first time ABCC/RERF have made such an adjustment in one of their major reports. Radiation risks were allowed to be modified by sex, age at the time of bombing, and attained age.

The most important finding was that the effects of radiation exposure in 1945 continue to be observed more than 60 years since the time of exposure. The most notable finding was a curvilinear dose response among males, while the female response remained linear. Until this paper’s publication (the previous report was made in 2007), the dose responses in both sexes had been linear. The emergence of a curved response in our study was somewhat surprising, and we are now working to ascertain if this is an artifact of the types of cancers occurring among a now elderly population or if it has underlying mechanistic implications for those exposed at young ages.

The paper also reports other findings that may be of interest to the NASA community. First, the lowest dose range for which a sex-averaged linear dose model showed a statistically increased risk in solid cancer was 0–100 mGy. Also, due to the curvilinear response in males, the female-to-male ratio of excess relative risks has increased slightly in comparison with earlier reports.

This manuscript investigated solid cancers in aggregate. We are currently in the process of writing other manuscripts looking at individual organs and organ systems. The first manuscript in that series of reports (on respiratory cancers) was recently published (
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Older In the News items may be found in the Bibliography or in the THREE Archive.

Solar Particle Events and Radiation Exposure in Space (PDF) Shaowen Hu
Radiation exposure from solar particle events (SPEs) presents a significant health concern for astronauts for exploration missions outside the protection of the Earth’s magnetic field, which could impair their performance and result in possible mission failure. Accurate assessment on the impact of SPEs on human exploration missions remains a challenge due to incomplete understanding of many physical processes during the occurring of SPEs. This article summarizes recent observation and theoretical frameworks concerning the origin, acceleration, and transport of energetic particles in SPEs, and reviews knowledge of the sizes, frequencies, energy spectra of SPEs obtained from decades of solar physics research, as well as techniques of radiation exposure modeling relevant to interplanetary space exploration. It is expected that future close collaborations among solar, heliospheric, space weather, and radiation research communities on observational and theoretical studies will enhance the development of reliable and accurate predictive models for SPEs.

Dose rates of the January SPE determined by in situ measurement and model calculation

Donald V. Reames: “Solar Energetic Particles: A Modern Primer on Understanding Sources, Acceleration, and Propagation” (Springer, 2017). (PDF); reviewed by Stephen Kahler.

Proton and HZE Accelerator Sources

Research into the risks of space radiation to human explorers has a fundamental advantage over research into other risks in that all relevant components of space radiation can be delivered as beams by ground-based charged particle accelerators, thus simulating the space radiation environment.

The introductory article on accelerator facilities is taken from the Appendices of a document I authored during my tenure at NASA. It is dated, as can be seen from the reference to the Brookhaven Booster Accelerator Facility (BAF), the name used for the NASA Space Radiation Laboratory during its construction. Updates on this article will be welcome.

The presentations given by NASA Summer School faculty cover the essentials of accelerators used to simulate the proton and HZE components of galactic cosmic rays. Articles on NSRL and microbeams are pending review and should be posted soon.

Walter Schimmerling
THREE Chief Editor

  • Ground-Based Particle Accelerator Facilities - Walter Schimmerling (PDF)
  • Accelerators Made Simple - Derek Lowenstein (swf) Introduction (PDF)
  • Accelerator-based Space Physics - Cary Zeitlin, Lawrence Heilbronn, John Norbury (swf)
    • Accelerator-based Sources of Albedo Neutrons – Lawrence Heilbronn (PDF)
  • NASA Space Radiation Laboratory – D.I. Lowenstein, P. Guida, A. Rusek – (PDF)
  • A New Low Energy Irradiation Facility at BNL – P. Thieberger (PDF)
  • GCR Simulator Reference Field and a Spectral Approach for Laboratory Simulation - Tony C. Slaba, Steve R. Blattnig, John W. Norbury, Adam Rusek, Chiara La Tessa, and Steven A. Walker. Presentation at 26th Annual Space Radiation Investigators’ Workshop. Galveston, TX., January 15, 2015. NASA Technical Publication NASA/TP-2015-218698 (PDF) NOTE: This presentation is being posted without THREE Editorial Review in order to provide the space radiation research community with timely information about an important development being considered at the NASA Space Radiation Laboratory. A detailed article on this topic will be forthcoming.
  • Microbeams and Other Radiation Sources
    • Ion Microbeams and Their Role in Radiobiology Research in Europe, B.E. Fischer – (PDF)
    • High/Low LET Microbeams, Gerhard Randers-Pehrson – (swf)


Introduction to THREE
Walter Schimmerling

Video presentation of
Research Solutions to Space Radiation Impacts on Human Exploration
Slides in PDF format
Francis A. Cucinotta, Ph.D.
Chief Scientist, Space Radiation Program
NASA Johnson Space Center
Houston, Texas
Aerospace Medicine Grand Rounds
March 23, 2010

Radiation and Human Space Exploration Video
NASA Human Research Program

Radiation tracks and radiation track simulation video
Ianik Plante, Ph.D.
Universities Space Research Association
Division of Space Life Sciences
NASA Johnson Space Center
Houston, Texas

Radiation tracks and radiation track simulation video is excerpted from the article:
Radiation chemistry and oxidative stress (PDF)
Ianik Plante, Ph.D.

Video Presentation of
Space Radiation and Cataracts
Eleanor Blakely
Life Sciences, Lawrence Berkeley National Laboratory
Berkeley, California
July 16, 2003


Glossary derived from:
Human Research Program Integrated Research Plan, Revision A, (January 2009). National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas 77058, pages 232-280.

Exploration Systems Radiation Monitoring Requirements (Sept 2012). Page ii. Ronald Turner.

Report No. 153: Information Needed to Make Radiation Protection Recommendations for Space Missions Beyond Low-Earth Orbit (2006). National Council on Radiation Protection and Measurements, pages 309-318.  Reprinted with permission of the National Council on Radiation Protection and Measurements.

Managing Space Radiation Risk in the New Era of Space Exploration (2008). Committee on the Evaluation of Radiation Shielding for Space Exploration, National Research Council. National Academies Press, pages 111-118.

Contents: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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AAPM: American Association of Physicists in Medicine.

absolute risk: Expression of excess risk due to exposure as the arithmetic difference between the risk among those exposed and that obtaining in the absence of exposure.

absorbed dose (D): Average amount of energy imparted by ionizing particles to a unit mass of irradiated material in a volume sufficiently small to disregard variations in the radiation field but sufficiently large to average over statistical fluctuations in energy deposition, and where energy imparted is the difference between energy entering the volume and energy leaving the volume. The same dose has different consequences depending on the type of radiation delivered. Unit: gray (Gy), equivalent to 1 J/kg.

ACE: Advanced Composition Explorer Mission, launched in 1997 and orbiting the L1 libration point to sample energetic particles arriving from the Sun and interstellar and galactic sources.  It also provides continuous coverage of solar wind parameters and solar energetic particle intensities (space weather).  When reporting space weather, it can provide an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts.

acute effects: short-term biological effects of exposure to radiation, including headaches, dizziness, nausea, and illness that can range from mild to fatal.

acute exposure: Radiation exposure of short duration.

AGS: Alternating Gradient Synchrotron (at Brookhaven National Laboratory).

ALARA (As Low As Reasonably Achievable):  An essential operational safety requirement, as well as a regulatory requirement, that em­phasizes keeping exposure to radiation as low as possible using reasonable methods, and not treating dose limits as “tolerance values”; defined at NASA as limiting radiation exposure to a level that will result in an estimated risk below the limit of the 95 percent confidence level.

albedo: secondary radiation produced by interactions of galactic cosmic rays and high-energy solar protons with matter in the atmosphere or on the surface.

ALL: acute lymphocytic leukemia.

alpha particle: An energetic charged nucleus consisting of two protons and two neutrons. This particle is identical to the 4He nucleus.

ALTEA: Anomalous Long-Term Effects in Astronauts study .

AM: amplitude modulation.

AMA: American Medical Association.

AMAC: American Medical Advisory Committee.

AML: acute myelogenous leukemia.

Amu: atomic mass unit (ALSO: u).

ANLL: acute nonlymphocytic leukemia.

annual risk: The risk in a given year from an earlier exposure. The annual risk (average) from an exposure is the lifetime risk divided by the number of years of expression.

ANP: atrial natriuretic peptide.

ANS: American Nuclear Society.

ANSI: American National Standards Institute.

AU: Astronomical Unit (distance from the Earth to the Sun)

Apoe4: Apoliprotein E isoform 4. Modification of Apo4 is major risk factor in Alzheimer's disease.

apoptosis: A specific mode of cell death (also known as programmed cell death) that can be triggered by exposure to radiation, especially in cells of lymphoid/myeloid or epithelial lineage. Extensive apoptosis contributes to the hematopoietic and gastrointestinal symptoms seen in acute radiation syndrome.

ARC: NASA Ames Research Center.

Ares V/Heavy Lift Launch Vehicle: a NASA vehicle intended to deliver cargo from Earth to low Earth orbit.

ARM: Atmospheric Radiation Measurements.

ascent stage: The pressurized upper stage of the Lunar Lander in which the crew pilots the lander from lunar orbit to the lunar surface and return. The ascent stage takes off from the descent stage, leaving the latter behind on the surface.

AT: ataxia telangiectasia.

ATM: ataxia telangiectasia mutated.

AU: Astronomical Unit (Approx. distance from the Earth to the Sun)

AX-2: NASA Ames Research Center Experimental Suit 2, designed during the Apollo program as a lunar surface hard suit to bend at the waist and rotate in the torso so that the crew member can reach down to the ground with one hand. Fabricated from fiberglass.

AX-5: NASA Ames Research Center Experimental Suit 5, designed during the Space Station Advanced Development program to provide a durable hard suit for extended operations in zero gravity. Fabricated from numerically milled aluminum forgings.

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background radiation: The amount of radiation to which a member of the population is exposed from natural sources, such as terrestrial radiation from naturally-occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally-occurring radionuclides deposited in the human body. The natural background radiation received by an individual depends on geographic location and living habits. In the United States, the background radiation is on the order of 1 mSv y–1, excluding indoor radon which amounts to ~2 mSv/year on average.

BAF: Booster Applications Facility (the name used to designate the NSRL during planning and construction phases).

BaRyoN: Quark bound state with zero strangeness.

BCC: basal cell carcinoma.

BCD: budget change directive.

BEIR: Biological Effects of Ionizing Radiation. One of a series of reports on the health risks from exposure to low levels of ionizing radiation issued by the Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, Board on Radiation Effects, Research Division on Earth and Life Studies, National Research Council of the National Academies of Science of the United States, referred to by a Roman number denoting its position in the sequence of reports. At the time of this writing, the latest report is BEIR VII.

BEVALAC: An accelerator system at Lawrence Berkeley National Laboratory consisting of the Bevatron (an early, high-energy synchrotron accelerator constructed in the 1950s and used to discover the antiproton), accelerating particles delivered by the SuperHILAC (first built as the HILAC - Heavy Ion Linear Accelerator - in 1957; along with a similar one at Yale University, the first machine in the US built specifically to accelerate heavy ions, completely rebuilt into the SuperHILAC in 1971). Closed in 1993.

biological end point: effect or response being assessed, e.g., cancer, cataracts.

bipolar device: a type of semiconductor whose operation is based on both majority and minority carriers.

BNL: Brookhaven National Laboratory in Upton (Long Island), New York.

BRCA1: breast cancer 1 tumor suppressor gene.

BRCA2: breast cancer 2 tumor suppressor gene.

BrdU: bromodeoxyuridine.

BRYNTRN: BaRYoN TRaNsport code, a computer code for simulating baryon transport.

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CAD: computer aided design.

CaLV: Cargo Launch Vehicle.

CAM : computerized anatomical man model.

carbon composite: a composite incorporating carbon and other materials for use in lightweight structures, strong enough to substitute for aluminum and other metals in the construction of many parts of a spacecraft, notably the pressure vessel shell. It may incorporate boron, epoxy, polyethylene, hydrogen, or other materials that enhance radiation shielding properties.

CARD: Constellation Architecture Requirements Document; CxP 7000

cargo habitat: a crew habitat that the Lunar Lander carries for delivery to the Lunar Outpost as a key part of the “Outpost-first” strategy considered by NASA as part of the Space Exploration Initiative program.

CB: Control Board.

CDC: Center for Disease Control and Prevention.

CEDE: committed effective dose equivalent.

CENELEC: European Committee for Electrotechnical Standardization.

CEQATR: Constellation Program Environmental Qualification and Acceptance Testing Requirements; CxP 70036

CERN: European Organization for Nuclear Research.

CEV: Crew Exploration Vehicle.

CFR: Code of Federal Regulations.

CHMO: Chief Health And Medical Officer (NASA).

chronic effects: long-lasting effects of exposure to radiation; includes cancer, cataracts, and nervous system damage.

chronic exposure: Radiation exposure over long times (continuous or fractionated).

CI: confidence interval.

CL: confidence level.

CLV: Crew Launch Vehicle.

CME: coronal mass ejection, an explosion of plasma released from the atmosphere (or corona) of the Sun.

CML: chronic myelogenous leukemia.

CNP: cyclic nucleotide phosphatase.

CNS: central nervous system.

Composites: materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or microscopic scale within the finished structure.

computerized anatomical male/female: a model of human geometry used to evaluate radiation doses at various points inside the body.

Constellation system: the complete ensemble of launch vehicles, flight vehicles, ground support, support services, and lunar and planetary surface systems associated with the Vision for Space Exploration initiated during the Bush administration.

coronal mass ejection (CME): A transient outflow of plasma from or through the solar corona which may be associated with the generation of solar-particle events.

cosmic-ray modulation: The variation of the observed cosmic-ray intensity as a function of the solar cycle. The cosmic-ray intensity within the solar system is observed to vary approximately inversely with the solar activity cycle that controls the interplanetary magnetic field.

COTS: commercial, off-the-shelf.

CPD: crew passive dosimeter.

CPU: central processor unit.

CRaTER: Cosmic Ray Telescope for the Effects of Radiation.

CRCPD: Conference of Radiation Control Program Directors.

CREME96: Cosmic Ray Effects on Micro-Electronics (1996 revision), a computer code.

cross section (σ): probability per unit particle fluence of a given end point. Unit: cm2.

CT: computed tomography.

CTA: conditioned taste aversion.

CVD: cardiovascular disease.

CW: continuous wave.

CxP: Constellation Program.

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Dr: dose-rate (Gy/hr).

DAAC: Distributed Active Archive Center.

DDREF: dose and dose-rate effectiveness factor (the degree to which both dose and dose rate may influence the biological effects of exposure to a given dose of radiation).

delta rays: Electrons directly ejected from atoms in matter by radiation.

descent stage: The lower stage of the Lunar Lander that includes the descent and landing engines and propellant tanks to serve them. The crew ascending back to lunar orbit in the ascent stage leaves the descent stage behind on the lunar surface.

descent stage habitat: in the descent stage, a pressurized crew habitat in which the crew would live during sortie missions.

deterministic process: process whereby a given event will occur whenever its dose threshold is exceeded.

deterministic effects: early radiation effects usually related to a significant fraction of cell loss, exceeding the threshold for impairment of function in a tissue; so called because the statistical fluctuations in the number of affected cells are very small compared to the number of cells required to reach the threshold (ICRP 1991), above which the severity varies with dose.

detriment: Health detriment is the sum of the probabilities of all the components of health effects. These include in addition to fatal cancer the probability of heritable effects and the probability of morbidity from nonfatal cancer.

DHS: Department of Homeland Security.

DNA: deoxyribonucleic acid.

DOD: Department of Defense.

DOE: Department of Energy.

dose: A general term used when the context is not specific to a particular dose quantity. When the context is specific, the name or symbol for the quantity is used [i.e., absorbed dose (D), mean absorbed dose (DT), dose equivalent (H), effective dose (E), equivalent dose (HT), or organ dose equivalent].

dose equivalent ( H ): Estimate of radiation risk that accounts for differences in the biological effectiveness of different types of charged particles that produce the absorbed dose. H=Q × D, where Q is a quality factor based on the type of radiation (Q = 1 for x-rays). NASA uses Q as specified in ICRP Publication 60 (ICRP, 1991). Unit: sievert (Sv), equivalent to 1 J/kg.

dose limit: A limit on radiation dose that is applied by restricting exposure to individuals or groups of individuals in order to prevent the occurrence of radiation-induced deterministic effects or to limit the probability of radiation related stochastic effects to an acceptable level. For astronauts working in low-Earth orbit, unique dose limits for deterministic and stochastic effects have been recommended by NCRP.

dose rate: Dose delivered per unit time. Can refer to any dose quantity (e.g., absorbed dose, dose equivalent).

dose-response model: A mathematical formulation of the way in which the effect, or response, depends on dose.

dosimeter: A radiation detection device worn or carried by an individual to monitor the individual's radiation exposure. For space activities, a device worn or carried by an astronaut in-flight.

DREF: dose rate effectiveness factor (the degree to which dose rate may influence the biological effects of exposure to a given dose of radiation).

DRM: Design Reference Mission.

DSB: double strand break.

DSNE: Constellation Program Design Specification for Natural Environments; CxP 70023

DTRA: Defense Threat Reduction Agency.

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E: effective dose/ energy.

EAR:excess additive risk (cf. absolute risk).

ED50: dose to cause 50 % of the population to have the effect (e.g., nausea).

EDS: Earth departure stage.

EEG: electroencephalogram.

effective dose ( E ): The sum over specified tissues of the products of the equivalent dose in a tissue (HT) and the tissue weighting factor for that tissue or organ (wT) (i.e., E = wTHT). Effective dose (E) applies only to stochastic effects. Unit: sievert (Sv), equivalent to 1 J/kg.

electron volt (eV): a unit of energy equivalent to 1.602 × 10–19 joules.

ELF: extremely low frequency.

ELR: excess lifetime risk.

EMF: electromagnetic field.

EML: Environmental Measurements Laboratory, New York, NY.

EMS: emergency medical services.

EMU: Extravehicular mobility unit, the space suit developed for space shuttle crews that also serves on the ISS.  The EMU features a hard upper torso and soft lower torso, arms, and legs over the pressure bladder. The entire EMU except the helmets and boots is covered by the thermal micrometeoroid garment.

electron volt (eV): A unit of energy = 1.6 x 10–12 ergs = 1.6 x 10–19 J; 1 eV is equivalent to the energy gained by an electron in passing through a potential difference of 1 V; 1 keV = 1,000 eV; 1 MeV = 1,000,000 eV.

EOS: Earth Observing System.

EPA: Environmental Protection Agency.

equivalent dose ( HT): The product of the mean absorbed dose in an organ or tissue and the radiation weighting factor (wR) of the radiation type of interest. For external exposure wR applies to the radiation type incident on the body.

ERR:excess relative risk.

erythema: A redness of the skin.

ESA: European Space Agency.

ESMD: Exploration Systems Mission Directorate (NASA).

ESP: energetic storm particle.

ESTEC: European Space Research and Technology Centre.

EVCPDS: Extra Vehicle Charged Particle Directional Spectrometer

excess relative risk (ERR): The ratio between the total risk, including the increase due to radiation exposure, and the baseline risk in the absence of radiation exposure; if the excess equals the baseline the relative risk is two.

exposure (technical use): A measure of the ionization produced in air by x or gamma radiation. Exposure is the sum of electric charges on all ions of one sign produced in air when all electrons liberated by photons in a volume of air are completely stopped, divided by the mass of the air in the volume. The unit of exposure in air is the roentgen (R) or in SI units it is expressed in coulombs (C), 1 R = 2.58 x 10–4 C/kg.

exposure (non-technical use): the presentation of an individual or material to radiation likely to deliver a significant dose over a period of time.

EVA: extravehicular activity.

excess risk: the increase in the probability of a certain effect on an individual who has been exposed to a given dose of radiation over the probability of that effect in the absence of radiation exposure.

extravehicular activity: Any activity undertaken by the crew outside a space vehicle or habitat.

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favorable propagation path: A concept suggesting that the Archimedean spiral path from the earth to the sun would connect to a specific solar longitude. It is based on the concept that charged particles travel along the interplanetary magnetic field which is transported out from the sun. For an idealized constant speed solar wind flow, if the interplanetary magnetic field is frozen in the plasma, then the result would form an Archimedean spiral.

FEMA: Federal Emergency Management Agency.

FIRE: First ISCCP Regional Experiment.

first ionization potential: The energy required to remove the least bound electron from an electrically neutral atom. (The ionization potential is usually given in electron volts.)

FISH: fluorescence in situ hybridization.

fluence: (1) ICRU definition : The quotient of dN by da, where dN is the number of particles incident on a sphere of cross-sectional area da (i.e., Φ = dN/da). The unit for fluence is 1/m2, but cm–2 is frequently used; (fluence may be a function of one or more other variables [e.g., Φ (L,t), the distribution of fluence as a function of linear energy transfer (L) and time (t)]. (2) planar fluence (F): The net number of charged particles traversing a given area. Unit: particles/cm2.

fluence rate (dF/dt): Change in fluence over a given small time interval, or the time derivative of the fluence. Unit: 1/m2s.

FLUKA: a general purpose Monte-Carlo computer code for calculations of particle transport and interactions with matter

flux ): Term used historically by the nuclear community for fluence rate and also used for particle flux density, but deprecated by the ICRU convention to eliminate confusion between the terms “particle flux density” and “radiant flux.” See fluence rate.

FM: frequency modulation.

FR: fixed-ratio.

fractionation: The delivery of a given total dose of radiation as several smaller doses, separated by intervals of time.

FSP: fission surface power.

FY: Fiscal Year.

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galactic cosmic rays: the components of galactic cosmic radiation.

galactic cosmic radiation (GCR): The charged-particle radiation outside the Earth magnetosphere comprised of 2 % electrons and positrons, and 98 % nuclei, the latter component consisting (by fluence) of 87 % protons, 12 % helium ions, and 1 % high atomic number, high-energy (HZE) particles.

gamma rays: Short-wavelength electromagnetic radiation of nuclear origin (approximate range of energy: 10 keV to 9 MeV).

GCR: galactic cosmic radiation/ galactic cosmic rays.

GCR: galactic cosmic radiation.

GEANT: A computer application for the simulation of the passage of particles through matter including detector description and simulation.

GEO: Geostationary or Geosynchronous Earth Orbit.

Geostationary Operational Environmental Satellite ( GOES): A satellite in geosynchronous orbit used for monitoring protons. The satellite travel at the same angular speed above the equator as Earth’s rotation and therefore appears stationary when observed from Earth’s surface.

GGTP: gamma-glutamyl transpeptidase.

GI: gastrointestinal.

GLE: ground level event.

GM: geometric mean.

GPM: Global Precipitation Measurement.

gray (Gy): The International System (SI) unit of absorbed dose of radiation, 1 Gy = 1 J kg–1.

gray equivalent (GT or Gy-Eq): The product of DT and Ri, where DT is the mean absorbed dose in an organ or tissue and Ri is a recommended value for relative biological effectiveness for deterministic effects for a given particle type i incident on the body ( GT = Ri × DT). The SI unit is J/kg (NCRP, 2000).

GSD: geometric standard deviation (the standard deviation of the logarithms of a set of random variables, for which the geometric mean is the square root of their product.

GSI(Gesellschaft für Schwerionenforschung): Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany.

GSM: global system for mobile communications.

GT: gray equivalent.

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HACD: Human Adaptation and Countermeasures Division.

HDPE: high-density polyethylene, defined as having a density greater than 0.94 g/cm3.

heavy charged particles: Atomic and subatomic charged particles with masses substantially heavier than that of an electron.

heavy ions: Nuclei of elements heavier than helium such as nitrogen, carbon, boron, neon, argon or iron which are positively charged due to some or all of the atomic electrons having been stripped from them.

HEDS: Human Exploration and Development of Space.

HEFD: Habitability and Environmental Factors Division.

heliocentric: A measurement system with its origin at the center of the sun.

heliolongitude: Imaginary lines of longitude on the sun measured east (left) or west (right) of the central meridian (imaginary north-south line through the middle of the visible solar disk) as viewed from Earth. The left edge of the solar disk is 90°E and the right edge is 90°W.

heliosphere: The magnetic bubble containing the solar system, solar wind, and entire solar magnetic field. It extends beyond the orbit of Pluto.

HEPAD: High Energy Proton and Alpha Detector.

HIDH: Human Integration Design Handbook; NASA/SP-2010-3407

high atomic number, high-energy ( HZE) particles: Heavy ions having an atomic number greater than that of helium (such as nitrogen, carbon, boron, neon, argon or iron ions that are positively charged) and having high kinetic energy.

high-LET: Radiation having a high-linear energy transfer; for example, protons, alpha particles, heavy ions, and interaction products of fast neutrons.

HIMAC: Heavy Ion Medical Accelerator, Chiba Japan.

HMF: heliospheric magnetic field.

HPC: Hydrological Process and Climate.

HPRT: hypoxanthine-guanine phosphoribosyl transferase.

HQ: Headquarters.

HRP: Human Research Program.

HRP CB: Human Research Program Control Board.

HSIR: Constellation Program Human Systems Integration Requirements; CxP 70024

H T : equivalent dose.

HZE: high atomic number and energy.

HZETRN: a transport code developed specifically for high-charge, high-energy particles that is widely used for space radiation shielding and design calculations.

HZE: high atomic number, high energy/ highly energetic, heavy, charged particles.

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IACUC: Institutional Animal Care and Use Committee.

IAEA: International Atomic Energy Agency.

ICNIRP: International Commission on Non-Ionizing Radiation Protection.

ICRP: International Commission on Radiation Protection.

ICRU: International Commission on Radiation Units and Measurements.

IDIQ: Indefinite delivery/indefinite quantity.

IEEE: Institute of Electrical and Electronics engineers.

IL-2: interleukin-2.

IL-6: interleukin-6.

incidence: The rate of occurrence of a disease, usually expressed in number of cases per million .

IND: improvised (or otherwise acquired) nuclear device.

interplanetary magnetic field: The magnetic field in interplanetary space. The interplanetary magnetic field is transported out from the sun via the solar wind.

interplanetary shocks: An abrupt change in the velocity or density of charged particles moving faster than the wave propagation speed in interplanetary space, so that higher velocity components bunch into lower velocity components before these can get out of the way.

ionizing radiation: Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.

ionization: The process by which a neutral atom or molecule acquires a positive or negative charge through the loss or gain of one or more orbital electrons.

IPT: Integrated Product Team.

IRMA: Integrated Risk Management Application.

ISCCP: International Satellite Cloud Climatology Project.

ISS: International Space Station.

ISSMP: ISS Medical Project.

ITA: Internal Task Agreement.

IVCPDS: Intra Vehicle Charged Particle Directional Spectrometer

IV & V: Independent Validation & Verification.

IWG: Investigator Working Group.

IWS: Investigator Workshop.

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JSC: NASA Johnson Space Center.

JWST: James Webb Space Telescope.

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kerma: (an acronym for “Kinetic energy released in materials;” the sum of the initial kinetic energies for all charged particles released by uncharged ionizing radiation in a small sample of material divided by the mass of the sample. Kerma is the same as dose when charged particle equilibrium exists (i.e., when, on the average, the number of charged particles leaving the sample is compensated by an equal number of charged particles entering the sample).

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LAP: latency associated peptide.

LAR: lifetime attributable risk.

LaRC: NASA Langley Research Center.

LAT: Lunar Architecture Team.

latchup: an anomalous state in a semiconductor in which the device no longer responds to input signals.

latent period: Period or state of seeming inactivity between time of exposure of tissue to an injurious agent and an observed response (also time to response or induction period).

LBNL: Lawrence Berkeley National Laboratory.

LCD: liquid crystal display.

LCVG: liquid cooling and ventilation garment.

LDEF: Long Duration Exposure Facility.

LDL: low-density lipoproteins.

LEND: Low Energy Neutron Detector.

LEO (low Earth orbit): the environment in which most recent space missions have been concentrated, where the magnetic field of Earth provides protection against much of the radiation that would be encountered on more distant exploration missions, approximately 300 to 600 mile orbit radius.

LET (linear energy transfer): Measure of the average local energy deposition per unit length of distance traveled by a charged particle in a material. Unit: keV/μm.

lifetime risk: The lifetime probability of suffering from the consequences of a specific health effect. The total risk in a lifetime resulting from an exposure(s) is equal to the average annual risk times the period of expression.

light ions: Nuclei of hydrogen and helium which are positively charged due to some or all of the planetary electrons having been stripped from them.

lineal energy ( y ): The quotient of ε by , where ε is the energy imparted to the matter in a given volume by a single (energy deposition) event and is the mean chord length of that volume ( i.e., y = ε/ l ). The unit for lineal energy is J /m, but keV/ μm is often used in practice (1 keV/µm ~ 1.6x10-10 J/m).

linear energy transfer ( LET): Average amount of energy lost per unit of particle track length as an ionizing particle travels through material, related to the microscopic density distribution of energy deposited in the material and, therefore, a major characteristic of radiation leading to different effects for the same dose of ionizing radiation of different LET on biological specimens or electronic devices.

linear-quadratic model (also linear-quadratic dose-response relationship): expresses the incidence of (e.g., mutation or cancer) as partly directly proportional to the dose (linear term) and partly proportional to the square of the dose (quadratic term).

LIS: local interstellar energy spectrum.

LIS: local interstellar GCR spectrum.

LIS: Local interplanetary Spectra.

LLD: lower limit of detection.

LLU: Loma Linda University.

LLO: low lunar orbit.

lognormal: If the logarithms of a set of values are distributed according to a normal distribution the values are said to have a lognormal distribution, or be distributed log normally.

low-LET: Radiation having a low-linear energy transfer; for example, electrons, x rays, and gamma rays.

LRV: Lunar Roving Vehicle.

LSAC: Life Sciences Applications Advisory Committee.

LSS: Life Span Study.

LSS: Life-Span Study of the Japanese atomic-bomb survivors.

Lunar Lander: the Constellation system vehicle that will travel between the Orion and the surface of the Moon.

LWS: Living With a Star (a NASA program).

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MARIE: Mars Radiation Environment Experiment.

mass stopping power: (see stopping power ).

MAT: Mars Architecture Team.

MCNPX: Monte Carlo N-Particle eXtended.

MDO: Multi-disciplinary Optimization.

mean absorbed (tissue) dose ( DT): The mean absorbed dose in an organ or tissue, obtained by integrating or averaging absorbed doses at points in the organ or tissue.

mean-free path: The average distance between particle collisions with nuclei, atoms or molecules in a material. Also, the average distance between scattering events in interplanetary particle propagation.

MEEP: Mir Environment Effects Payload.

MEO: Medium Earth Orbit.

MeV: Mega-electron Volts: 106 electron volts

mFISH: Multiplex Fluorescence In Situ Hybridization.

Mir: The Russian (previously Soviet) orbital space station.

MISSE: Materials on International Space Station Experiment.

MML: mouse myelogenous leukemia.

MMOP: Multilateral Medical Operations Panel.

MOA: Memorandum of Agreement.

MODIS: Moderate Resolution Imaging Spectrometer.

MORD: Medical Operations Requirements Documents.

MOU: Memorandum of Understanding.

Mrem: millirem.

MRI: magnetic resonance imaging.

MS: Mission Systems

mSv: millisievert.

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N: nucleon.

NAR: Non-Advocate Review.

NAS: National Academy of Sciences.

NASA: National Aeronautics and Space Administration.

NCI: National Cancer Institute.

NCRP: National Council on Radiation Protection and Measurements.

NEDD: Constellation Program Natural Environment Definition for Design; CxP 70044

neutrons: Particles with a mass similar to that of a proton, but with no electrical charge. Because they are electrically neutral, they cannot be accelerated in an electrical field.

NIEL: Non-ionizing energy loss, also called displacement kerma. The total kerma can be divided into an ionizing component and a displacement, or NIEL, component.

NIH: National Institutes of Health.

NM: neutron monitor.

NOAA: National Oceanic and Atmospheric Administration.

noncancer: Health effects other than cancer (e.g., cataracts, cardiovascular disease) that occur in the exposed individual.

Nowcasting: prediction of total doses and the future temporal evolution of the dose once a solar particle event has begun.

NOVICE: Radiation Transport/Shielding Code.

NPR: NASA Procedural Requirements.

NRA: NASA Research Announcement.

NRC: National Research Council.

NRC: Nuclear Regulatory Commission (US).

NSBRI: National Space Biomedical Research Institute.

NSCOR: NASA Specialized Center of Research.

NSF: National Science Foundation.

NSRL: NASA Space Radiation Laboratory (at BNL).

NTE: Non-Targeted Effects.

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OBPR: Office of Biological and Physical Research.

OCHMO: Office of Chief Health and Medical Officer.

organ dose equivalent ( DET): The mean dose equivalent for an organ or tissue, obtained by integrating or averaging dose equivalents at points in the organ or tissue. It is the practice in the space radiation protection community to obtain point values of absorbed dose (D) and dose equivalent (H) using the accepted quality factor-LET relationship [Q(L)], and then to average the point quantities over the organ or tissue of interest by means of computational models to obtain the organ dose equivalent (DET ). For space radiations, NCRP adopted the organ dose equivalent as an acceptable approximation for equivalent dose (HT) for stochastic effects.

Orion Crew Exploration Vehicle: The Constellation system vehicle that will carry passengers in low Earth orbit, or from low Earth orbit to the Moon or Mars, and then back to Earth. Often referred to as CEV; in this report referred to as the Orion crew module.

OSHA: Occupational Safety and Health Administration.

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PC: Probability of Causation.

PCC: premature chromosome condensation.

PCS: personal communication system.

PDF: probability density function.

PDF: probability distribution function.

PE: Project Executive.

PEL (permissible exposure limit): Maximum amount of radiation to which an astronaut may be exposed. For terrestrial workers, PELs are legal limits, defined by OSHA. NASA PELs are set by the chief health and medical officer.

PET: positron emission tomography.

photosphere: The portion of the sun visible in white light. Also the limit of seeing down through the solar atmosphere in white light.

PI: Principal Investigator.

PLR: pressurized lunar rover.

PLSS: personal life support system.

PM: Project Manager.

PP: Project Plan.

PPBE: Planning, Programming, Budgeting and Execution.

PPS: proton prediction system/ pulses per second.

PRD: Passive Radiation Detector; Program Requirements Document.

prevalence: The number of cases of a disease in existence at a given time per unit of population, usually per 100,000 persons.

protons: The nucleus of the hydrogen atom. Protons are positively charged.

protraction: Extending the length of exposure, for example, the continuous delivery of a radiation dose over a longer period of time.

PS: Project Scientist.

PSD: Position-Sensitive Detector; also, Pulse Shape Discrimination.

PVAMU: Prairie View A&M University.

PW: pulsed wave.

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Q: quality factor.

Q(L): quality factor as a function of linear energy transfer.

Qleukemia: quality factor for estimating leukemia risks.

Qsolid: quality factor for estimating solid cancer risks.

QMSFRG: quantum multiple scattering fragmentation model.

quality factor ( Q ): The factor by which absorbed dose (D) at a point is modified to obtain the dose equivalent (H) at the point (i.e., H = Q D), in order to express the effectiveness of an absorbed dose (in inducing stochastic effects) on a common scale of risk for all types of ionizing radiation. There is a specified dependence [Q(L)] of the quality factor (Q) as a function of the unrestricted linear energy transfer (L) in water at the point of interest.

quasithreshold dose: The dose at which the extrapolated straight portion of the dose-response curve intercepts the dose axis at unity survival fraction.

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RAD: Radiation Assessment Detector.

RAM: Radiation Area Monitor.

radiation: 1. The emission and propagation of energy through space or through matter in the form of waves, such as electromagnetic, sound, or elastic waves; 2. The energy propagated through space or through matter as waves; radiation or radiant energy, when unqualified, usually refers to electromagnetic radiation; commonly classified by frequency— Hertzian, infrared, visible, ultraviolet, x and gamma rays; 3. Corpuscular emission, such as alpha and beta particles, or rays of mixed or unknown type, such as cosmic radiation.

radiation quality: A general term referring to the microscopic distribution of of the energy absorbed to yield a given total dose. For example, at resolutions of a few micrometers ionizing events will be more uniformly dispersed for gamma-ray radiation than for the neutron radiation, producing quantitatively different biological effects (see relative biological effectiveness ).

radiation weighting factor ( wR): A factor related to the relative biological effectiveness of different radiations in the calculation of equivalent dose (HT) (see equivalent dose ), independently of the tissue or organ irradiated.

RBE (relative biological effectiveness): Measure of the effectiveness of a specific type of radiation for producing a specific biological outcome, relative to a reference radiation (generally, 250 kVp x-rays). For a defined endpoint, RBE = Dref/Dnew. For HZE particles, RBE generally is greater than 1, meaning that a lower dose of more effective HZE particles will have the same effect as a given dose of the reference radiation.

RCT: Radiation Coordination Team.

RDD: radiological dispersal device.

RDWG: Radiation Discipline Working Group.

regolith: A layer of loose, heterogeneous material covering solid rock on the surface of a moon or planet (including Earth).

REIC: risk of exposure-induced cancer incidence.

REID (risk of exposure induced death): Measure of risk used by NASA as a standard for radiation protection; reflects a calculation of the probability of death due to exposure to radiation in space.

relative biological effectiveness (cf. RBE)

relative risk (cf. excess relative risk)

REM: rapid eye movement.

RF: radiofrequency.

RFI: request for information.

RHIC: Relativistic Heavy Ion Collider (at BNL).

RHO: Radiation Health Officer.

rigidity: The momentum of a charged particle per unit charge. Determines the curvature of the particle’s trajectory in a magnetic field. Two particles with different charge but the same rigidity will travel along a path having the same curvature in a given magnetic field.

risk: The probability of a specified effect or response occurring.

risk coefficient: The increase in the annual incidence or mortality rate per unit dose: (1) absolute risk coefficient is the observed minus the expected number of cases per person year at risk for a unit dose; (2) the relative risk coefficient is the fractional increase in the baseline incidence or mortality rate for a unit dose.

risk cross section: The probability of a particular excess cancer mortality per particle fluence (excluding delta rays).

risk estimate: The number of cases (or deaths) that are projected to occur in a specified exposed population per unit dose for a defined exposure regime and expression period; number of cases per person-gray or, for radon, the number of cases per person cumulative working level month.

roentgen: A unit of radiation exposure. Exposure in SI units is expressed in C kg–1 of air.

ROS: reactive oxygen species.

RRS: radiation Research Society.

RSNA: Radiological Society of North America.

R&T: Research and Technology.

RTG: radioisotope thermoelectric generator.

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SAA: South Atlantic Anomaly.

SACR: Science Advisory Committee on Radiobiology.

SAMPEX: Solar Anomalous and Magnetospheric Particle Explorer.

SAR: specific absorption rate.

SBIR: Small Business Innovation Research.

SCAR: Smoke/Sulfate Clouds and Radiation Experiment.

SCC: squamous cell carcinoma/ small cell cancer.

SCE: sister chromatid exchange.

SCLS: small cell lung carcinoma.

SD: single dose.

SD: standard deviation.

SDO: Solar Dynamic Observatory.

SEC: Space Environment Center. (NOAA).

secondary radiation: radiation that has been generated by the interaction of radiation with the atoms or nuclei of a traversed material.

SEE (single-event effect): a class of effects in which damage results from a single ionizing particle traversing a microelectronic device, rather than the accumulated impact of a large number of particles.

SEE: single event effect/ Space Environment and Effects Program.

SEER: surveillance, epidemiology, and end results.

SET: Space Environment Testbeds.

SEU (single event upset): a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device.

SFHSS: Space Flight Human Systems Standard; NASA-STD-3001

SGZ: subgranular zone.

SI: International System of Units.

sievert ( Sv): The special name for the SI unit of effective dose (E), equivalent dose (HT), dose equivalent (H), and organ dose equivalent (DT ), 1 Sv = 1 J /kg.

SLSD: Space Life Sciences Directorate (NASA).

S&MA: Safety and Mission Assurance (NASA).

SMD: Science Mission Directorate (NASA).

SMO: Science Management Office (NASA).

SOHO: Solar and Heliospheric Observatory.

Solar cycle: The periodic variation in the intensity of solar activity, as measured, for example, by the numbers of sunspots, flares, CMEs, and SPEs. The average length of solar cycles since 1900 is 11.4 y.

solar flare: The name given to the sudden release of energy (often >1032 ergs) in a relatively small volume of the solar atmosphere. Historically, an optical brightening in the chromosphere, now expanded to cover almost all impulsive radiation from the sun.

solar-particle event (SPE): An eruption at the sun that releases a large number of energetic particles (primarily protons) over the course of hours or days. Signatures of solar energetic-particle events may include significant increases in types of electro­magnetic radiation such as radio waves, x-rays, and gamma rays.

solar wind: The plasma flowing into space from the solar corona. The ionized gas carrying magnetic fields can alter the intensity of the interplanetary radiation.

SOMD: Space Operations Mission Directorate (NASA).

spallation: A high-energy nuclear reaction in which a high-atomic-number target nucleus is struck by a high-energy, light particle (typically a proton); this causes the target nucleus to break up into many components, releasing many neutrons, protons, and higher Z particles.

SPE (cf. solar particle event).

Space Radiation Analysis Group (SRAG): the radiation protection group at NASA’s Johnson Space Center, responsible for radiation monitoring, projecting exposures, and ensuring adherence to principles of ALARA for crews on spaceflight missions.

SPENVIS (SPace ENVironment Information System) : a series of computer programs developed by the European Space Agency for the simulation of radiation effects in flight.

SRA: Society for Risk Analysis.

SRAG: Space Radiation Analysis Group

sRBC: Serum deprivation response factor-related gene product that binds to C-kinase.

SRPE: Space Radiation Program Element (NASA).

SSA: Social Security Administration.

STEREO: Solar-Terrestrial Relations Observatory (NASA mission).

stochastic effects: radiation effects attributed to the consequences of changes caused by radiation in one or a few cells; so called because the statistical fluctuations in the number of initial cells are large compared to the number of cells observed when radiation effects, such as cancer, become manifest (ICRP 1991). The probability of occurrence, rather than the severity, is a function of radiation dose.

stochastic process: process whereby the likelihood of the occurrence of a given event can be described by a probability distribution.

stopping power (lineal stopping power): The quotient of the energy lost (dE) by a charged particle in traversing a distance (dx) in a material. Can also be expressed as mass stopping power by dividing the lineal stopping power by the density (ρ) of the material.

STS: Space Transportation System.

STTR: Small Business Technical Transfer Research.

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TEDE: total effective dose equivalent.

TEPC: tissue equivalent proportional counter.

TGF: transforming growth factor.

TIGER: Grid Generation Code.

tissue weighting factor ( wT): A factor representing the ratio of risk of stochastic effects attributable to irradiation of a given organ or tissue to the total risk when the whole body is irradiated uniformly. The factor is independent of the type of radiation or energy of the radiation.

TLD: thermoluminescent dosimeter.

TMG: thermal micrometeoroid garment.

TMI: Three Mile Island.

TOGA/COARE: Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Experiment.  transport (of radiation): the sequence of interactions between radiation traversing one or more materials and their atoms and nuclei; calculations of the relevant characteristics; transport code: computer program to calculate radiation transport.

trapped radiation: Ionized particles held in place by Earth’s magnetic fields. Also known as the Van Allen belt.

TRL: Technology Readiness Level.

TRMM: Tropical Rainfall Measuring Mission.

TVD: tenth-value distance.

TVL: tenth-value layer.

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UNSCEAR: United Nations Scientific Committee on the Effects Of Atomic Radiation.

US: United States.

USAF: United States Air Force.

US NRC: United States Nuclear Regulatory Commission.

USRA: Universities Space Research Association.

UV: ultraviolet.

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vitreous: The semifluid, transparent substance which lies between the retina and the lens of the eye.

VSE: Vision for Space Exploration.

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WBS: Work Breakdown Structure.

WHO: World Health Organization.

Wind: a NASA spacecraft that observes the Sun and solar wind.

WL: working level.

WLM: working level month (170 h).

w R: radiation weighting factor.

w T: tissue weighting factor.

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Z: atomic number, the number of protons in the nucleus of an atom.

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