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All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

BioSentinel: Mission Development of a Radiation Biosensor to Gauge DNA Damage and Repair Beyond Low Earth Orbit on a 6U Nanosatellite.

We are designing and developing a "6U" (10 x 22 x 34 cm; 14 kg) nanosatellite as a secondary payload to fly aboard NASA's Space Launch System (SLS) Exploration Mission (EM) 1, scheduled for launch in late 2017. For the first time in over forty years, direct experimental data from biological studies beyond low Earth orbit (LEO) will be obtained during BioSentinel's 12- to 18- month mission. BioSentinel will measure the damage and repair of DNA in a biological organism and allow us to compare that to information from onboard physical radiation sensors. In order to understand the relative contributions of the space environment's two dominant biological perturbations, reduced gravity and ionizing radiation, results from deep space will be directly compared to data obtained in LEO (on ISS) and on Earth. These data points will be available for validation of existing biological radiation damage and repair models, and for extrapolation to humans, to assist in mitigating risks during future long-term exploration missions beyond LEO. The BioSentinel Payload occupies 4U of the spacecraft and will utilize the monocellular eukaryotic organism Saccharomyces cerevisiae (yeast) to report DNA double-strand-break (DSB) events that result from ambient space radiation. DSB repair exhibits striking conservation of repair proteins from yeast to humans. Yeast was selected because of 1) its similarity to cells in higher organisms, 2) the well-established history of strains engineered to measure DSB repair, 3) its spaceflight heritage, and 4) the wealth of available ground and flight reference data. The S. cerevisiae flight strain will include engineered genetic defects to prevent growth and division until a radiation-induced DSB activates the yeast's DNA repair mechanisms. The triggered culture growth and metabolic activity directly indicate a DSB and its successful repair. The yeast will be carried in the dry state within the 1-atm P/L container in 18 separate fluidics cards with each card having 16 independent culture microwells, with integral microchannels and filters to supply nutrients and reagents, confine the yeast to the wells, and enable optical measurement. The measurement subsystem will monitor each subgroup of culture wells continuously for several weeks, optically tracking DSBtriggered cell growth and metabolism. BioSentinel will also include physical radiation sensors based on the TimePix sensor, as implemented by JSC's RadWorks group, which record individual radiation events including estimates of their linear-energytransfer (LET) values. Radiation-dose and LET data will be compared directly to the rate of DSB-and-repair events measured by the S. cerevisiae biosentinels. The spacecraft bus will operate in a deep space environment with functions that include command and data handling, communications, power generation (via deployable solar panels) and storage, and attitude determination-and-control system with micropropulsion. Development of the BioSentinel spacecraft will mature and prove multiple nanosatellite advances in order to function well beyond LEO: Communications from distances of ≥ 500,000 km; Autonomous attitude control, momentum management, and safe mode of nanosatellites in deep space; Shielding-, hardening-, design-, and software-derived radiation tolerance for electronics; Reliable functionality for 12 - 18 months of key subsystems for biofluidics, memory, communications, power, etc.; Close integration of living biological radiation event monitors with miniature physical radiation spectrometers; Biological measurement of solar particle events beyond Earth orbit In addition to providing the first biological results from beyond LEO in over 4 decades, BioSentinel will provide an adaptable small-satellite instrument platform to perform a range of human-exploration-relevant measurements that characterize the biological consequences of multiple outer space environments. BioSentinel is being developed under NASA's Advanced Exploration Systems program.

DNA damage↗
NASA NTRS2018

Effects of Mitochondrial-Targeted Human Catalase in Skeletal Tissue of Mice Exposed to Simulated Spaceflight

During prolonged spaceflight, astronauts are exposed to both microgravity and space radiation and are at risk forincreased skeletal fragility due to bone loss, Evidence from rodent experiments has established that bothmicrogravity and ionizing radiation can cause bone loss due to increasd of bone-resorbing osteoclasts and decreasedin bone-forming osteoblasts, although the underlying molecular mechanisms for these changes are not fullyunderstood. We hypothesized that excess reactive oxidative species (ROS) produced by conditions that simulatedspaceflight alters the tight balance between osteoclast and osteoblast activities, leading to accelerated skeletalremodeling and culminating in loss of mineralized tissue. To begin to explore this hypothesis, we used the mCATmouse model [1]; these transgenic mice over-express the human catalase gene targeted to mitochondria, which arethe major organelle responsible for cellular production of free radicals. Catalase is an anti-oxidant that catalyzes theconversion of the reactive species, hydrogen peroxide (H202), into water and oxygen. This animal model wasselected as it displays extended lifespan, reduced cardiovascular disease and reduced central nervous systemradiosensitivity, consistent with elevated anti-oxidant activity conferred by the transgene. We reasoned that miceoverexpressing catalase the mitochondria of osteoblast and osteoclast lineage cells would be protected from the boneloss caused by simulated spaceflight.

CATALASE IN SKELETAL TISSUE↗
NASA NTRS2018

Variability in Galactic Cosmic Radiation- Induced DNA Damage Response in Inbred Mice Is Modulated by Genetics

In radiation biology, the ability to predict cancer risk associated with exposure to low doses of high-LET (Linear Energy Transfer) ionizing radiation remains a challenge. Epidemiological methods lack the sensitivity and power to provide detailed risk estimates for cancer and ignore individual sensitivity. We have hypothesized that DNA repair capacity is the primary factor differentiating peoples radiation sensitivity. We previously showed in immortalized human cell lines that characterizing the dose and time dependence of p53-binding protein 1 (53BP1) foci formation in the nucleus following X-rays exposure is sufficient to predict DNA repair response to any other LET in the same cell line. We now tested this hypothesis across a population of mice with different genetic background. Fibroblast cells were extracted and cultivated from 76 individual mice from 15 different strains and exposed to HZE (high (H) atomic number (Z) and energy (E) galactic cosmic ray particles) particles and X-rays. Individual radiation sensitivities were investigated by high throughput measurement of DNA repair kinetics that evaluated 53bp1 foci numbers as a surrogate for DNA double-strand breaks at various times post-irradiation. Instead of just counting foci which can be hard to distinguish for high-LET or high doses, we also took into account the track structure of high-LET particles to compute the remaining number of unrepaired tracks as a function of time post-irradiation. As expected, the percentage of unrepaired track over a 48 hours follow-up period increased with LET. In addition, repair rate was modulated by genetics, with animals from the same strain showing small variance while large rate differences were observed between strains. Radiation strain sensitivity ranking was estimated based on repair rates from exposure to each LET evaluated in this work, and ranking for high-LET correlated better with ranking from high dose of X-ray, not low dose. At the in-vivo level, drops in T-cells and B-cells number measured 24 hours after 0.1 Gy (Gray) X-ray exposure, correlated with slower DNA repair kinetic in fibroblast cells of the same strains of mice. At the genomic level, mouse genome wide association (GWA) analysis identified seven significant genetic loci on chromosomes 2, 3, 7, 10, 11, 13 and 19 with different significance depending on the LET. Interestingly, for the two highest LET, a common locus on Chromosome 10 was identified with high enrichment for DNA repair associated genes.Overall, this work suggests that repair kinetics of primary skin fibroblasts is a good surrogate marker for in-vivo radiation sensitivities in other tissues and that this response is modulated by genetics. Our study also confirms that DNA repair kinetics following high doses of X-ray can be used to predict radiation sensitivity to high-LET.

High-LET Radiation↗
NASA NTRSDate not supplied

Worswick Hot Springs: A Radioactive Hydrothermal Field Site

We report on a systematic characterization of the radiation environment and water temperatures of Worswick Hot Springs, which is in support of companion biochemical and microbial investigations of iron respiration in the ‘extreme’ microbial systems found at the field site. We have discovered localized areas of elevated radioactivity that are approximately four to five times greater than background radiation. Additionally, we have observed that both the radiation environment and the temperature of the spring waters vary over time. Because localized “hot spots” of elevated radiation and biofilms are easily accessible, various biological studies of radiation resistance and biosignature formation are possible, making this field site relevant for analog field studies that consider microbiology, geochemistry, and ionizing radiation. In addition to Worswick being a natural radiation biology laboratory that may also be relevant for space biology applications, we assert that these unusual environmental conditions may inform us about locations on Mars that are also enriched in radioactive elements and their potential for hosting biosignatures.

Jon C. Rask↗
NASA NTRS2004

Implementation of ALARA radiation protection on the ISS through polyethylene shielding augmentation of the Service Module Crew Quarters

With 5-7 month long duration missions at 51.6 degrees inclination in Low Earth Orbit, the ionizing radiation levels to which International Space Station (ISS) crewmembers are exposed will be the highest planned occupational exposures in the world. Even with the expectation that regulatory dose limits will not be exceeded during a single tour of duty aboard the ISS, the "as low as reasonably achievable" (ALARA) precept requires that radiological risks be minimized when possible through a dose optimization process. Judicious placement of efficient shielding materials in locations where crewmembers sleep, rest, or work is an important means for implementing ALARA for spaceflight. Polyethylene (CnHn) is a relatively inexpensive, stable, and, with a low atomic number, an effective shielding material that has been certified for use aboard the ISS. Several designs for placement of slabs or walls of polyethylene have been evaluated for radiation exposure reduction in the Crew Quarters (CQ) of the Zvezda (Star) Service Module. Optimization of shield designs relies on accurate characterization of the expected primary and secondary particle environment and modeling of the predicted radiobiological responses of critical organs and tissues. Results of the studies shown herein indicate that 20% or more reduction in equivalent dose to the CQ occupant is achievable. These results suggest that shielding design and risk analysis are necessary measures for reducing long-term radiological risks to ISS inhabitants and for meeting legal ALARA requirements. Verification of shield concepts requires results from specific designs to be compared with onboard dosimetry. c2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

NASA Center JSC↗
NASA NTRS1972

Radiation Protection Handbook

A handbook which sets forth the Kennedy Space Center radiation protection policy is presented. The book also covers administrative direction and guidance on organizational and procedural requirements of the program. Only ionizing radiation is covered.

Source record↗
NASA NTRS1996

LDEF Satellite Radiation Analyses

This report covers work performed by Science Applications International Corporation (SAIC) under contract NAS8-39386 from the NASA Marshall Space Flight Center entitled LDEF Satellite Radiation Analyses. The basic objective of the study was to evaluate the accuracy of present models and computational methods for defining the ionizing radiation environment for spacecraft in Low Earth Orbit (LEO) by making comparisons with radiation measurements made on the Long Duration Exposure Facility (LDEF) satellite, which was recovered after almost six years in space. The emphasis of the work here is on predictions and comparisons with LDEF measurements of induced radioactivity and Linear Energy Transfer (LET) measurements. These model/data comparisons have been used to evaluate the accuracy of current models for predicting the flux and directionality of trapped protons for LEO missions.

Armstrong, T. W.↗
NASA NTRS2012

High Energy/LET Radiation EEE Parts Certification Handbook

Certifying electronic components is a very involved process. It includes pre-coordination with the radiation test facility for time, schedule and cost, as well as intimate work with designers to develop test procedures and hardware. It also involves work with radiation engineers to understand the effects of the radiation field on the test article/setup as well as the analysis and production of a test report. The technical content of traditional ionizing radiation testing protocol is in wide use and generally follows established standards (ref. Appendix C). This document is not intended to cover all these areas but to cover the methodology of using Variable Depth Bragg Peak (VDBP) to accomplish the goal of characterizing an electronic component. The Variable Depth Bragg Peak (VDBP) test method is primarily used for deep space applications of electronics. However, it can be used on any part for any radiation environment, especially those parts where the sensitive volume cannot be reached by the radiation beam. An example of this problem would be issues that arise in de-lidding of parts or in parts with flip-chip designs, etc. The VDBP method is ideally suited to test modern avionics designs which increasingly incorporate commercial off-the-shelf (COTS) parts and units. Johnson Space Center (JSC) developed software provides assistance to users in developing the radiation characterization data from the raw test data.

Reddell, Brandon↗
NASA NTRS2014

Role of Oxidative Damage in Radiation-Induced Bone Loss

During prolonged spaceflight, astronauts are exposed to both microgravity and space radiation, and are at risk for increased skeletal fragility due to bone loss. Evidence from rodent experiments demonstrates that both microgravity and ionizing radiation can cause bone loss due to increased bone-resorbing osteoclasts and decreased bone-forming osteoblasts, although the underlying molecular mechanisms for these changes are not fully understood. We hypothesized that excess reactive oxidative species (ROS), produced by conditions that simulate spaceflight, alter the tight balance between osteoclast and osteoblast activities, leading to accelerated skeletal remodeling and culminating in bone loss. To test this, we used the MCAT mouse model; these transgenic mice over-express the human catalase gene targeted to mitochondria, the major organelle contributing free radicals. Catalase is an anti-oxidant that converts reactive species, hydrogen peroxide into water and oxygen. This animal model was selected as it displays extended lifespan, reduced cardiovascular disease and reduced central nervous system radio-sensitivity, consistent with elevated anti-oxidant activity conferred by the transgene. We reasoned that mice overexpressing catalase in mitochondria of osteoblast and osteoclast lineage cells would be protected from the bone loss caused by simulated spaceflight. Over-expression of human catalase localized to mitochondria caused various skeletal phenotypic changes compared to WT mice; this includes greater bone length, decreased cortical bone area and moment of inertia, and indications of altered microarchitecture. These findings indicate mitochondrial ROS are important for normal bone-remodeling and skeletal integrity. Catalase over-expression did not fully protect skeletal tissue from structural decrements caused by simulated spaceflight; however there was significant protection in terms of cellular oxidative damage (MDA levels) to the skeletal tissue. Furthermore, we used an array of countermeasures (Antioxidant diets and injections) to prevent the radiation-induced bone loss, although these did not prevent bone loss, analysis is ongoing to determine if these countermeasure protected radiation-induced damage to other tissues.

oxidative damage↗
NASA NTRSDate not supplied

Worswick Hot Springs: A Radioactive Hydrothermal Field Site.

Introduction: We report on a systematic characterization of the environmental conditions at Worswick Hot Springs, a hydrothermal system in Idaho, USA. Because localized “hot spots” of elevated radiation and biofilms are easily accessible, various biological studies of radiation resistance and biosignature formation are possible, making this fieldsite relevant for analog field studies that consider microbiology, geo-chemistry, and ionizing radiation. In addition to Worswick being a natural radiation biology laboratory that may also be relevant for space biology applications, we assert that these unusual environmental conditions may inform us about locations on Mars that are also enriched in radioactive elements and their poten-tial for hosting biosignatures. Methods: We carried out repeated temperature and radiation measurements at the same hot spring locations to observe the system over time (Figure 2). Radiation: A Bicron Micro Analyst micro-r-meter (Bicron NE, Saint-Gobain Industrial Ceramics, Inc.) capable of sensing x-rays and gamma-rays (0-5000 µR/hr), was used to gather radiation data at twenty-four locations around and above the region of the two main stream channels. Water Temperature: A digital hand-held infrared thermometer (Oakton WD-39642-00 Mini-Temp Tester) was used for all measurements. ICP-MS aqueous geochemistry: Water samples were analyzed at the ISU Center for Archaeology, Materials and Applied Spectroscopy (CAMAS). Results: We have discovered localized areas of elevated radiation that are approximately 4 to 5 times greater than background radiation, and we have ob-served that both radioactivity and temperature of the spring waters vary over time. ICP-MS reveal the presence of thorium and uranium, which are correlated with elevated radioactivity. Several point sources of elevated radioactivity have been identified in both Stream A and Stream B.

Analog↗
NASA NTRSDate not supplied

Creating Benchmark Data for Artificial Intelligence and Machine Learning Space Biology Research

To identify an appropriate AI/ML approach for a specific problem, the best practice is to measure algorithm performance through the benchmarking process. A scientific benchmark consists of an AI-ready dataset and a reference implementation on a specific scientific question. The NASA Science Mission Directorate (SMD) has started the “Benchmark Initiative for AI/ML to create scientific benchmark datasets in three applications: 1) scientific benchmarking, which finds the best algorithm for a specific problem; 2) application benchmarking, which measures algorithm performance against a set of parameters; and 3) system benchmarking, which evaluates performance of hardware and software architecture. Currently, there are no standardized datasets available to benchmark AI/ML algorithms in the domain of space biology. In this work, we constructed two AI/ML-ready biological datasets from experiments in space-flown mice: cellular imaging and RNA-seq. First, radiation-exposed immune cells harbor DNA damage foci that can be fluorescently marked to visualize the amount of damage following exposure to ionizing radiation. However, such large datasets are difficult to analyze visually, due to imaging inconsistencies and human bias, and classical image processing approaches can fail on imaging artifacts. AI/ML are therefore exciting alternative, providing the speed of machines and the accuracy of humans. We have made this dataset available at https://registry.opendata.aws/bps_microscopy/. Second, high-throughput nucleic acid sequencing (DNA-seq, RNA-seq) has become widespread in biomedical research due to the growing availability and affordability of these assays. However, most sequencing datasets suffer from high dimensionality and low sample count. In this work, we used a generative adversarial network to synthesize a standardized, AI-ready, publicly available benchmark dataset for space biology RNA-seq data with sufficient space-flown and ground control mouse liver samples from NASA GeneLab. This dataset is available at https://registry.opendata.aws/bps_rnaseq/. These datasets are now fully open the Space Biology community to test their favorite AI/ML approaches.

James Casaletto↗
NASA NTRSDate not supplied

Single-Cell Analysis of Yeast (Saccharomyces cerevisiae) Using Hydrogel Encapsulation

Space radiation poses a major health risk to astronauts. To fulfill NASA’s mission of exploration beyond Earth, the biological effects of Galactic Cosmic Radiation and gamma radiation must be investigated to elucidate cellular damage mechanisms and inform countermeasure protocols to safely bring humans beyond Earth’s magnetosphere. Budding yeast (Saccharomyces cerevisiae) are commonly used in experiments as a model organism for studying the effects of radiation on eukaryotes. Radiobiology of yeast at the single cell level is poorly understood, yet crucial for informing models to aid in the design and interpretation of experiments. We are using a novel method of microencapsulation in hydrogel particles (PicoShells) to enable analysis of the distribution of radiation-induced damage among yeast cells at the single-cell level, in high throughput. Here we describe the development of methods for culturing, visualization, and quantification of encapsulated yeast. The encapsulated yeast are cultured in Yeast extract-Peptone-Dextrose (YPD) medium, fixed in formaldehyde or ethanol, and stained with DAPI or propidium iodide, then visualized using microscopy or enumerated using flow cytometry, with the aim of developing a protocol to enumerate the distribution of viable cells in each PicoShell. This will allow us to quantify how different forms of radiation can generate different distributions of damage across a population of cells, ultimately providing insight into the biological effects of space-relevant ionizing radiation.

yeast↗
NASA NTRS1986

1986 Annual Conference on Nuclear and Space Radiation Effects, 23rd, Providence, RI, July 21-23, 1986, Proceedings

The present conference on the effects of nuclear and space radiation on electronic hardware gives attention to topics in the basic mechanisms of radiation effects, dosimetry and energy-dependent effects, electronic device radiation hardness assurance, SOI/SOS radiation effects, spacecraft charging and space radiation, IC radiation effects and hardening, single-event upset (SEU) phenomena and hardening, and EMP/SGEMP/IEMP phenomena. Specific treatments encompass the generation of interface states by ionizing radiation in very thin MOS oxides, the microdosimetry of meson energy deposited on 1-micron sites in Si, total dose radiation and engineering studies, plasma interactions with biased concentrator solar cells, the transient imprint memory effect in MOS memories, mechanisms leading to SEU, and the vaporization and breakdown of thin columns of water.

Ellis, Thomas D.↗
NASA NTRS2016

Graphene Field Effect Transistor for Radiation Detection

The present invention relates to a graphene field effect transistor-based radiation sensor for use in a variety of radiation detection applications, including manned spaceflight missions. The sensing mechanism of the radiation sensor is based on the high sensitivity of graphene in the local change of electric field that can result from the interaction of ionizing radiation with a gated undoped silicon absorber serving as the supporting substrate in the graphene field effect transistor. The radiation sensor has low power and high sensitivity, a flexible structure, and a wide temperature range, and can be used in a variety of applications, particularly in space missions for human exploration.

Li, Mary J.↗
NASA NTRS2001

Evidence for factors modulating radiation-induced G2-delay: potential application as radioprotectors

Manipulation of checkpoint response to DNA damage can be developed as a means for protecting astronauts from the adverse effects of unexpected, or background exposures to ionizing radiation. To achieve this goal reagents need to be developed that protect cells from radiation injury by prolonging checkpoint response, thus promoting repair. We present evidence for a low molecular weight substance excreted by cells that dramatically increases the duration of the G2-delay. This compound is termed G2-Arrest Modulating Activity (GAMA). A rat cell line (A1-5) generated by transforming rat embryo fibroblasts with a temperature sensitive form of p53 plus H-ras demonstrates a dramatic increase in radiation resistance after exposure to low LET radiation that is not associated with an increase in the efficiency of rejoining of DNA double strand breaks. Radioresistance in this cell line correlates with a dramatic increase in the duration of the G2 arrest that is modulated by a GAMA produced by actively growing cells. The properties of GAMA suggest that it is a low molecular weight heat-stable peptide. Further characterization of this substance and elucidation of its mechanism of action may allow the development of a biological response modifier with potential applications as a radioprotector. GAMA may be useful for protecting astronauts from radiation injury as preliminary evidence suggests that it is able to modulate the response of cells exposed to heavy ion radiation, similar to that encountered in outer space.

NASA Discipline Radiation Health↗
NASA NTRS2009

Validity of the Aluminum Equivalent Approximation in Space Radiation Shielding

The origin of the aluminum equivalent shield approximation in space radiation analysis can be traced back to its roots in the early years of the NASA space programs (Mercury, Gemini and Apollo) wherein the primary radiobiological concern was the intense sources of ionizing radiation causing short term effects which was thought to jeopardize the safety of the crew and hence the mission. Herein, it is shown that the aluminum equivalent shield approximation, although reasonably well suited for that time period and to the application for which it was developed, is of questionable usefulness to the radiobiological concerns of routine space operations of the 21 st century which will include long stays onboard the International Space Station (ISS) and perhaps the moon. This is especially true for a risk based protection system, as appears imminent for deep space exploration where the long-term effects of Galactic Cosmic Ray (GCR) exposure is of primary concern. The present analysis demonstrates that sufficiently large errors in the interior particle environment of a spacecraft result from the use of the aluminum equivalent approximation, and such approximations should be avoided in future astronaut risk estimates. In this study, the aluminum equivalent approximation is evaluated as a means for estimating the particle environment within a spacecraft structure induced by the GCR radiation field. For comparison, the two extremes of the GCR environment, the 1977 solar minimum and the 2001 solar maximum, are considered. These environments are coupled to the Langley Research Center (LaRC) deterministic ionized particle transport code High charge (Z) and Energy TRaNsport (HZETRN), which propagates the GCR spectra for elements with charges (Z) in the range I <= Z <= 28 (H -- Ni) and secondary neutrons through selected target materials. The coupling of the GCR extremes to HZETRN allows for the examination of the induced environment within the interior' of an idealized spacecraft as approximated by a spherical shell shield, and the effects of the aluminum equivalent approximation for a good polymeric shield material such as genetic polyethylene (PE). The shield thickness is represented by a 25 g/cm spherical shell. Although one could imagine the progression to greater thickness, the current range will be sufficient to evaluate the qualitative usefulness of the aluminum equivalent approximation. Upon establishing the inaccuracies of the aluminum equivalent approximation through numerical simulations of the GCR radiation field attenuation for PE and aluminum equivalent PE spherical shells, we Anther present results for a limited set of commercially available, hydrogen rich, multifunctional polymeric constituents to assess the effect of the aluminum equivalent approximation on their radiation attenuation response as compared to the generic PE.

Badavi, Francis F.↗
NASA NTRS1995

Synthetic properties of starburst galaxies

We present the results of an extensive grid of evolutionary synthesis models for populations of massive stars. The parameter space has been chosen to correspond to conditions typically found in objects like giant H II regions, H II galaxies, blue compact dwarf galaxies, nuclear starbursts, and infrared luminous starburst galaxies. The models are based on the most up-to-date input physics for the theory of stellar atmospheres, stellar winds, and stellar evolution. A population of massive stars is not only important in terms of its output of radiation but also via its deposition of mechanical energy. The output of radiative and mechanical luminosity is compared at various starburst epochs. In a supernova dominated instantaneous starburst, the mechanical luminosity can be as large as almost 10% of the total radiative luminosity. This occurs when most massive O stars have disappeared, and the synthetic spectrum in the optical and near-ultraviolet is dominated by B and A stars. During this epoch, the output of ionizing radiation below 912 A becomes very small, as indicated by a very large Lyman discontinuity and a very small ratio of ionizing over mechanical luminosity. We discuss the relevance of these results for the interpretation of starburst galaxies, active galactic nuclei, and the energetics of the interstellar medium.

Leitherer, Claus↗
NASA NTRS1993

Radiation model predictions and validation using LDEF satellite data

Predictions and comparisons with the radiation dose measurements on Long Duration Exposure Facility (LDEF) by thermoluminescent dosimeters were made to evaluate the accuracy of models currently used in defining the ionizing radiation environment for low Earth orbit missions. The calculations include a detailed simulation of the radiation exposure (altitude and solar cycle variations, directional dependence) and shielding effects (three-dimensional LDEF geometry model) so that differences in the predicted and observed doses can be attributed to environment model uncertainties. The LDEF dose data are utilized to assess the accuracy of models describing the trapped proton flux, the trapped proton directionality, and the trapped electron flux.

Armstrong, T. W.↗