Results for “low dose” — Page 27

NASA NTRS2004

Optically stimulated luminescence and thermoluminescence efficiencies for high-energy heavy charged particle irradiation in Al2O3:C

The thermally and optically stimulated luminescence (TL and OSL) response to high energy heavy-charged particles (HCPs) was investigated for two types of Al2O3:C luminescence dosimeters. The OSL signal was measured in both continuous-wave (CW) and pulsed mode. The efficiencies of the HCPs at producing TL or OSL, relative to gamma radiation, were obtained using four different HCPs beams (150 MeV/u 4He, 400 MeV/u 12C, 490 MeV/u 28Si, and 500 MeV/u 56Fe). The efficiencies were determined as a function of the HCP linear energy transfer (LET). It was observed that the efficiency depends on the type of detector, measurement technique, and the choice of signal. Additionally, it is shown that the shape of the CW-OSL decay curve from Al2O3:C depends on the type of radiation, and, in principle, this can be used to extract information concerning the LET of an unknown radiation field. The response of the dosimeters to low-LET radiation was also investigated for doses in the range from about 1-1000 Gy. These data were used to explain the different efficiency values obtained for the different materials and techniques, as well as the LET dependence of the CW-OSL decay curve shape. c2003 Elsevier Ltd. All rights reserved.

Thermoluminescent Dosimetry/instrumentation/method↗

NASA NTRS2012

Antimicrobial Materials for Advanced Microbial Control in Spacecraft Water Systems

Microbial detection, identification, and control are essential for the maintenance and preservation of spacecraft water systems. Requirements set by NASA put limitations on the energy, mass, materials, noise, cost, and crew time that can be devoted to microbial control. Efforts are being made to attain real-time detection and identification of microbial contamination in microgravity environments. Research for evaluating technologies for capability enhancement on-orbit is currently focused on the use of adenosine triphosphate (ATP) analysis for detection purposes and polymerase chain reaction (peR) for microbial identification. Additional research is being conducted on how to control for microbial contamination on a continual basis. Existing microbial control methods in spacecraft utilize iodine or ionic silver biocides, physical disinfection, and point-of-use sterilization filters. Although these methods are effective, they require re-dosing due to loss of efficacy, have low human toxicity thresholds, produce poor taste, and consume valuable mass and crew time. Thus, alternative methods for microbial control are needed. This project also explores ultraviolet light-emitting diodes (UV-LEDs), surface passivation methods for maintaining residual biocide levels, and several antimicrobial materials aimed at improving current microbial control techniques, as well as addressing other materials presently under analysis and future directions to be pursued.

Birmele, Michele↗

NASA NTRSDate not supplied

NAIRAS Model Updates and Improvements to the Prediction of the Ionizing Radiation Environment from the Earth's Surface to Geospace

- NAIRAS Model Description - Nowcast of Aerospace Ionizing RAdiation System (NAIRAS) Model - Running in real-time on LaRC computer cluster since 2011, results hosted on Space Environment Technologies server/website - Running in real-time at CCMC since 2020 - Key Model Features - Global ionizing radiation environment model - Physics-based HZETRN (High Charge (Z) and Energy TRaNsport) code - Real-time inclusion of solar energetic particle (SEP) radiation - Real-time solar-magnetospheric effects on radiation (cutoff model by Kress et al. [2004, 2010]) - New/Current Model Development - Improved SEP dose nowcast and forecast - Extend to low-Earth orbit (LEO) environment - Single-Event Effects (SEE) radiation risk assessment quantities - Run-on-Request (RoR) @ CCMC

Christopher J. Mertens↗

NASA NTRS1996

Neutron fluences and dose equivalents measured with passive detectors on LDEF

Neutron fluences were measured on LDEF in the low energy (< 1 MeV) and high energy (> 1 MeV) ranges. The low energy detectors used the 6Li(n,alpha)T reaction with Gd foil absorbers to separate thermal (< 0.2 eV) and resonance (0.2 eV-1 MeV) neutron response. High energy detectors contained sets of fission foils (181Ta, 209Bi, 232Th, 238U) with different neutron energy thresholds. The measured neutron fluences together with predicted spectral shapes were used to estimate neutron dose equivalents. The detectors were located in the A0015 and P0006 experiments at the west and Earth sides of LDEF under shielding varying from 1 to 19 g/cm2. Dose equivalent rates varied from 0.8 to 3.3 microSv/d for the low energy neutrons and from 160 to 390 microSv/d for the high energy neutrons. This compares with TLD measured absorbed dose rates in the range of 1000-3000 microGy/d near these locations and demonstrates that high energy neutrons contribute a significant fraction of the total dose equivalent in LEO. Comparisons between measurements and calculations were made for high energy neutrons based on fission fragment tracks generated by fission foils at different shielding depths. A simple 1-D slab geometry was used in the calculations. Agreement between measurements and calculations depended on both shielding depth and threshold energy of the fission foils. Differences increased as both shielding and threshold energy increased. The modeled proton/neutron spectra appeared deficient at high energies. A 3-D model of the experiments is needed to help resolve the differences.

LDEF Project↗

NASA NTRSDate not supplied

The noise dose range of the X-59 estimated from propagation simulations

NASA’s X-59 aircraft will soon be flown in a series of low-boom community noise surveys across the USA. Community test experimental designs will include noise dose schedules, which require an estimate of the noise dose range that X-59 can produce. To determine the dose range, propagation simulations using NASA’s PCBoom code were completed using CFD-generated X-59 C612A near-field pressure data for an on-design condition (Mach 1.4 at 53,200 feet) and two off-design conditions (Mach 1.4 at 46,000 ft and Mach 1.3 at 43,000 ft). Near-field data at four cardinal aircraft headings were propagated through one year of realistic atmospheric profiles from the Climate Forecast System Version 2 database at several USA locations. Statistics of the mean and range of the Perceived Level (PL) of the booms in the inner 40 km of each carpet as well as the carpet width were computed. Results indicate the typical inner carpet mean PL is approximately 70-87 dB depending on the aircraft condition. The typical PL range across the inner carpet is 6-8 dB (on-design) and 5-13 dB (off-designs). The carpet widths ranged from 32-55 km. Understanding these quantities for various flight and atmospheric conditions is important for planning X-59 community noise surveys.

X-59↗

NASA NTRS2002

A model for interphase chromosomes and evaluation of radiation-induced aberrations

We have developed a theoretical model for evaluating radiation-induced chromosomal exchanges by explicitly taking into account interphase (G(0)/G(1)) chromosome structure, nuclear organization of chromosomes, the production of double-strand breaks (DSBs), and the subsequent rejoinings in a faithful or unfaithful manner. Each of the 46 chromosomes for human lymphocytes (40 chromosomes for mouse lymphocytes) is modeled as a random polymer inside a spherical volume. The chromosome spheres are packed randomly inside a spherical nucleus with an allowed overlap controlled by a parameter Omega. The rejoining of DSBs is determined by a Monte Carlo procedure using a Gaussian proximity function with an interaction range parameter sigma. Values of Omega and sigma have been found which yield calculated results of interchromosomal aberration frequencies that agree with a wide range of experimental data. Our preferred solution is one with an interaction range of 0.5 microm coupled with a relatively small overlap parameter of 0.675 microm, which more or less confirms previous estimates. We have used our model with these parameter values and with resolution or detectability limits to calculate yields of translocations and dicentrics for human lymphocytes exposed to low-LET radiation that agree with experiments in the dose range 0.09 to 4 Gy. Five different experimental data sets have been compared with the theoretical results. Essentially all of the experimental data fall between theoretical curves corresponding to resolution limits of 1 Mbp and 20 Mbp, which may reflect the fact that different investigators use different limits for sensitivity or detectability. Translocation yields for mouse lymphocytes have also been calculated and are in good agreement with experimental data from 1 cGy to 10 cGy. There is also good agreement with recent data on complex aberrations. Our model is expected to be applicable to both low- and high-LET radiation, and we include a sample prediction of the yield of interchromosomal rejoining in the dose range 0.22 Gy to 2 Gy of 1000 MeV/nucleon iron particles. This dose range corresponds to average particle traversals per nucleus ranging from 1.0 to 9.12.

Non-NASA Center↗

NASA NTRS1992

Dose rate, dose-equivalent rate, and quality factor in SLS-1

A tissue-equivalent proportional counter (TEPC) sensitive to the lineal energy range of 0.26-300 keV micrometer-1 was flown on STS-40 (39 degrees x 278 km x 296 km) inside the Spacelab. This instrument was previously flown on STS-31 but was modified to provide a finer resolution at lower lineal energies to better map the South Atlantic Anomaly (SAA) protons. The instrument was turned on 6 June 1991, and operated for 7470 min (124.5 h). The flight duration was characterized by a very large number of X-ray solar flares and enhanced magnetic field fluctuations; however, no significant dose from the solar particles was measured at the location of this instrument. The flight data can be separated into trapped and galactic cosmic radiation parts. The dose rate, dose-equivalent rate and quality factor for trapped radiation were 4.21 +/- 0.03 mrad day-1, 7.72 +/- 0.05 mrem day-1, and 1.83 +/- 0.1, respectively. The dose rate, dose-equivalent rate, and quality factor for galactic cosmic radiation were 5.34 +/- 0.03 mrad day-1, 14.63 +/- 0.06 mrem day-1, and 2.74 +/- 0.1, respectively. The overall quality factor for the flight was 2.38. The dose from the GCR is higher than from SAA protons because of the high inclination and low altitude of this flight. The AP8MAX model of the trapped radiation gives a dose rate of 2.43 mrad day-1 and a quality factor of 1.77. The CREME solar maximum model of galactic cosmic radiation gives a dose rate of 2.54 mrad day-1 and a quality factor of 2.91. Thus the AP8MAX model underestimates the dose by a factor of 1.8 whereas the CREME model leads to an underestimation of the dose by a factor of 2. A comparison of the LET spectra using the AP8MAX model and galactic cosmic radiation transport codes shows only a qualitative agreement.

NASA Discipline Number 00-00↗

NASA NTRS1988

Radiation dose and shielding for the space station

Significant differences in dose prediction for Space Station arise depending on whether or not the magnetic field model is extrapolated into the future. The basis for these calculations is examined in detail, and the importance of the residual atmospheric layer at altitudes below 1000 km, with respect to radiation attenuation, is emphasized. Dosimetry results from Shuttle flights are presented and compared with the computed results. It is recommended that, at this stage, no extrapolation of the magnetic field into the future be included in the calculations. A model adjustment, to replace this arbitrary procedure, is presented. Dose predictions indicate that, at altitudes below 500 km and at low inclination, and with nominal module wall thickness (0.125 in. aluminum), orbit stay times of 90 days in Space Station would result in quarterly radiation doses to the crew, which are well within present limits for both males and females. Countermeasures would be required for stay times of a year or more and the measure of increasing shielding is examined.

Mccormack, Percival D.↗

NASA NTRS2001

Neutron dosimetry in low-earth orbit using passive detectors

This paper summarizes neutron dosimetry measurements made by the USF Physics Research Laboratory aboard US and Russian LEO spacecraft over the past 20 years using two types of passive detector. Thermal/resonance neutron detectors exploiting the 6Li(n,T) alpha reaction were used to measure neutrons of energies <1 MeV. Fission foil neutron detectors were used to measure neutrons of energies above 1 MeV. While originally analysed in terms of dose equivalent using the NCRP-38 definition of quality factor, for the purposes of this paper the measured neutron data have been reanalyzed and are presented in terms of ambient dose equivalent. Dose equivalent rate for neutrons <1 MeV ranged from 0.80 microSv/d on the low altitude, low inclination STS-41B mission to 22.0 microSv/d measured in the Shuttle's cargo bay on the highly inclined STS-51F Spacelab-2 mission. In one particular instance a detector embedded within a large hydrogenous mass on STS-61 (in the ECT experiment) measured 34.6 microSv/d. Dose equivalent rate measurements of neutrons >1 MeV ranged from 4.5 microSv/d on the low altitude STS-3 mission to 172 microSv/d on the ~6 year LDEF mission. Thermal neutrons (<0.3 eV) were observed to make a negligible contribution to neutron dose equivalent in all cases. The major fraction of neutron dose equivalent was found to be from neutrons >1 MeV and, on LDEF, neutrons >1 MeV are responsible for over 98% of the total neutron dose equivalent. Estimates of the neutron contribution to the total dose equivalent are somewhat lower than model estimates, ranging from 5.7% at a location under low shielding on LDEF to 18.4% on the highly inclined (82.3 degrees) Biocosmos-2044 mission. c2001 Elsevier Science Ltd. All rights reserved.

Flight Experiment↗

NASA NTRS1995

Absorbed dose and LET spectra measurements on LDEF

Total absorbed doses measured with TLD's, linear energy transfer (LET) spectra measured with plastic track detectors, and low energy neutrons measured on LDEF have been compared with model calculations. The total absorbed doses measured in TLD's were higher than predicted in the calculations of Armstrong et al. and differ from the calculations of Atwell et al. LDEF LET spectra are dependent on detector orientation, shielding and experiment location. These factors need to be taken into account when modeling the LDEF LET spectra. LET spectra measured with plastic nuclear track detectors (PNTD's) also deviate significantly from calculations especially for high LET particles (LET(sub infinity) H2O greater than 100keV/micron). Modeling efforts to date do not include the contribution of proton induced secondaries. Analysis of polycarbonate PNTD's from the West-side of LDEF has revealed a very high fluence of tracks (greater than 1 x 10(exp 7) tracks/cm(exp 2) under 2 gm/cm(exp 2) shielding). Fluence drops off rapidly as shielding depth increases. Tracks only form in the region of the detector closest to the surface, not in the bulk of the detector. To date no adequate explanation for this observation has been found. We plan to measure range distribution of very high LET (LET (sub infinity) H2O greater than 500 keV/micron) secondary particles produced in silicon wafer by high energy primary cosmic ray particles. Refinements of experimental techniques and model calculations are being carried out in order to understand existing discrepancies between experimental measurements and calculations.

Benton, E. V.↗

NASA NTRS2007

Radiation Test Results for a MEMS Microshutter Operating at 60 K

The James Webb Space Telescope (JWST), the successor to the Hubble Space Telescope, is due to be launched in 2013 with the goal of searching the very distant Universe for stars that formed shortly after the Big Bang. Because this occurred so far back in time, the available light is strongly red-shifted, requiring the use of detectors sensitive to the infrared portion of the electromagnetic spectrum. HgCdTe infrared focal plane arrays, cooled to below 30 K to minimize noise, will be used to detect the faint signals. One of the instruments on JWST is the Near Infrared Spectrometer (NIRSPEC) designed to measure the infrared spectra of up to 100 separate galaxies simultaneously. A key component in NIRSPEC is a Micro-Electromechanical System (MEMS), a two-dimensional micro-shutter array (MSA) developed by NASA/GSFC. The MSA is inserted in front of the detector to allow only the light from the galaxies of interest to reach the detector and to block the light from all other sources. The MSA will have to operate at 30 K to minimize the amount of thermal radiation emitted by the optical components from reaching the detector array. It will also have to operate in the space radiation environment that is dominated by the MSA will be exposed to a large total ionizing dose of approximately 200 krad(Si). Following exposure to ionizing radiation, a variety of MEMS have exhibited performance degradation. MEMS contain moving parts that are either controlled or sensed by changes in electric fields. Radiation degradation can be expected for those devices where there is an electric field applied across an insulating layer that is part of the sensing or controlling structure. Ionizing radiation will liberate charge (electrons and holes) in the insulating layers, some of which may be trapped within the insulating layer. Trapped charge will partially cancel the externally applied electric field and lead to changes in the operation of the MEMS. This appears to be a general principle for MEMS. Knowledge of the above principle has raised the concern at NASA that the MSA might also exhibit degraded performance because, i) each shutter flap is a multilayer structure consisting of metallic and insulating layers and ii) the movement of the shutter flaps is partially controlled by the application of an electric field between the shutter flap and the substrate (vertical support grid). The whole mission would be compromised if radiation exposure were to prevent the shutters from opening and closing properly. energetic ionizing particles. Because it is located A unique feature of the MSA is that, as outside the spacecraft and has very little shielding, previously mentioned, it will have to operate at temperatures near 30 K. To date, there are no published reports on how very low temperatures (- 30K) affect the response of MEMS devices to total ionizing dose. Experiments on SiO2 structures at low temperatures (80 K) indicate that the electrons generated by the ionizing radiation are mobile and will move rapidly under the application of an external electric field. Holes, on the other hand, that would normally move in the opposite direction through the SiO2 via a "thermal hopping" process, are effectively immobile at low electric fields as they are trapped close to their generation sites. However, for sufficiently large electric fields (greater than 3 MV/cm) holes are able to move through the SiO2. The larger the field, the more rapidly the holes move. The separation of the electrons and holes leads to a reduced electric field within the insulating layer. To overcome this reduction in electric field, a greater external voltage will have to be applied that alters the normal operation of the device. This report presents the results of radiation testing of the MSA at 60 K. The temperature was higher than the targeted temperature because of a faulty electrical interconnect on the test board. Specifically, our goal was to determine whether the MSA would function propey after a TID of 200 krad(Si).

Rapchun, David A.↗

NASA NTRS1999

Impact of Track Structure Effects on Shielding and Dosimetry

Galactic cosmic rays (GCR) consisting of nuclei of all the known elements with kinetic energies extending from tens to millions of MeV pose a significant health hazard to future deep space operations. Even half of the radiation exposures expected in ISS will result from GCR components. The biological actions of these radiations are known to depend on the details of the energy deposition (not just linear energy transfer, LET, but the lateral dispersion of energy deposition about the particle track). Energy deposits in tissues are dominated by the transfer of tens to hundreds of eV to the tissue's atomic electrons. In the case of low LET radiations, the collisions are separated by large dimensions compared to the size of important biomolecular structures. If such events are also separated in time, then the radiation adds little to the background of radicals occurring from ordinary metabolic processes and causes little or no biological injury. Hence, dose rate is a strong determinant of the action of low LET exposures. The GCR exposures are dominated by ions of high charge and energy (HZE) characterized by many collisions with atomic electrons over biomolecular dimensions, resulting in high radical- density events associated with a few isolated ion paths through the cell and minimal dose rate dependence at ordinary exposure levels. The HZE energy deposit declines quickly laterally and merges with the background radical density in the track periphery for which the exact lateral distribution of the energy deposit is the determinant of the biological injury. Although little data exists on human exposures from HZE radiations, limited studies in mice and mammalian cell cultures allow evaluation of the effects of track structure on shield attenuation properties and evaluation of implications for dosimetry. The most complete mammalian cell HZE exposure data sets have been modeled including the C3H10T1/2 survival and transformation data of Yang et al., the V79 survival and mutation data of various groups, and the Harderian gland tumor data of Alpen et al. Model results for the Harderian gland tumor data in comparison with data from Alpen et al. The Harderian target cell initiation cross section compares closely with the transformation cross section found for the C3H10T1/2 cell transformation data of Yang et al. The most notable feature of the cross sections are the multivalued cross sections for a given LET which implies the corresponding relative biological effectiveness (RBE) is dependent not only on the LET but also the ion type. This fact is at variance with the latest ICRP recommended quality factor which is a defined function of only the LET.

Wilson, J. W.↗

NASA NTRS1980

Tailored emitter, low-resistivity, ion-implanted silicon solar cells

Open-circuit voltages as high as 0.645 V (AM0, 25 C) have been obtained by a new process developed for low-resistivity silicon. The process utilizes high-dose phosphorus implantation followed by furnace annealing and simultaneous oxide growth. The effect of the thermally grown oxide is a reduction of surface recombination velocity; the oxide also acts as a moderately efficient antireflection (AR) coating. Boron-doped, float-zone silicon with resistivities from 0.1 to 1.0 (omega)(cm) has been processed according to this sequence; results show that the highest open-circuit voltage is obtained with 0.1(omega)(cm) starting material. The effects of Auger recombination and bandgap narrowing caused by high doping concentrations in the n(+)junction region have been investigated by implanting phosphorus over a wide range of dose levels. The effects of emitter-phosphorus concentrations tailored to optimize electric fields in the emitter have also been investigated.

Minnucci, J. A.↗

NASA NTRS1980

Silicon solar cells with high open-circuit voltage

Open-circuit voltages as high as 0.645 V (AM0-25 C) have been obtained by a new process developed for low-resistivity silicon. The method utilizes high-dose phosphorus implantation, followed by furnace annealing and simultaneous oxide growth to form high-efficiency, shallow junctions. The effect of the thermally grown oxide is a reduction of surface recombination velocity; the oxide also acts as a moderately efficient AR coating. Boron doped silicon with resistivities from 0.1 to 0.3 ohm-cm has been processed according to this sequence; results show highest open-circuit voltage is attained with 0.1-ohm-cm starting material. The effects of bandgap narrowing, caused by high doping concentrations in the junction, were also investigated by implanting phosphorus over a wide range of dose levels.

Minnucci, J. A.↗

NASA NTRS1997

Galactic and Solar Cosmic Ray Shielding in Deep Space

An analysis of the radiation hazards in support of NASA deep space exploration activities is presented. The emphasis is on materials required for radiation protection shielding. Aluminum has been found to be a poor shield material when dose equivalent is used with exposure limits for low Earth orbit (LEO) as a guide for shield requirements. Because the radiation issues are cost related-the parasitic shield mass has high launch costs, the use of aluminum as a basic construction material is clearly not cost-effective and alternate materials need to be developed. In this context, polyethylene is examined as a potentially useful material and demonstrates important advantages as an alternative to aluminum construction. Although polyethylene is useful as a shield material, it may not meet other design criteria (strength, stability, thermal); other polymer materials must be examined.

Wilson, John W.↗

NASA NTRS2005

Managing Space Radiation Risks On Lunar and Mars Missions: Risk Assessment and Mitigation

Radiation-induced health risks are a primary concern for human exploration outside the Earth's magnetosphere, and require improved approaches to risk estimation and tools for mitigation including shielding and biological countermeasures. Solar proton events are the major concern for short-term lunar missions (<60 d), and for long-term missions (>60 d) such as Mars exploration, the exposures to the high energy and charge (HZE) ions that make-up the galactic cosmic rays are the major concern. Health risks from radiation exposure are chronic risks including carcinogenesis and degenerative tissue risks, central nervous system effects, and acute risk such as radiation sickness or early lethality. The current estimate is that a more than four-fold uncertainty exists in the projection of lifetime mortality risk from cosmic rays, which severely limits analysis of possible benefits of shielding or biological countermeasure designs. Uncertainties in risk projections are largely due to insufficient knowledge of HZE ion radiobiology, which has led NASA to develop a unique probabilistic approach to radiation protection. We review NASA's approach to radiation risk assessment including its impact on astronaut dose limits and application of the ALARA (As Low as Reasonably Achievable) principle. The recently opened NASA Space Radiation Laboratory (NSRL) provides the capability to simulate the cosmic rays in controlled ground-based experiments with biological and shielding models. We discuss how research at NSRL will lead to reductions in the uncertainties in risk projection models. In developing mission designs, the reduction of health risks and mission constraints including costs are competing concerns that need to be addressed through optimization procedures. Mitigating the risks from space radiation is a multi-factorial problem involving individual factors (age, gender, genetic makeup, and exposure history), operational factors (planetary destination, mission length, and period in the solar cycle), and shielding characteristics (materials, mass, and topology). We review optimization metrics for radiation protection including scenarios that integrate biophysics models of radiation risks, operational variables, and shielding design tools needed to assess exploration mission designs. We discuss the application of a crosscutting metric, based on probabilistic risk assessment, to lunar and Mars mission trade studies including the assessment of multi-factorial problems and the potential benefits of new radiation health research strategies or mitigation technologies.

Cucinotta, F. A.↗

NASA NTRS2005

Managing Space Radiation Risks on Lunar and Mars Missions: Risk Assessment and Mitigation

Radiation-induced health risks are a primary concern for human exploration outside the Earth's magnetosphere, and require improved approaches to risk estimation and tools for mitigation including shielding and biological countermeasures. Solar proton events are the major concern for short-term lunar missions (<60 d), and for long-term missions (>60 d) such as Mars exploration, the exposures to the high energy and charge (HZE) ions that make-up the galactic cosmic rays are the major concern. Health risks from radiation exposure are chronic risks including carcinogenesis and degenerative tissue risks, central nervous system effects, and acute risk such as radiation sickness or early lethality. The current estimate is that a more than four-fold uncertainty exists in the projection of lifetime mortality risk from cosmic rays, which severely limits analysis of possible benefits of shielding or biological countermeasure designs. Uncertainties in risk projections are largely due to insufficient knowledge of HZE ion radiobiology, which has led NASA to develop a unique probabilistic approach to radiation protection. We review NASA's approach to radiation risk assessment including its impact on astronaut dose limits and application of the ALARA (As Low as Reasonably Achievable) principle. The recently opened NASA Space Radiation Laboratory (NSRL) provides the capability to simulate the cosmic rays in controlled ground-based experiments with biological and shielding models. We discuss how research at NSRL will lead to reductions in the uncertainties in risk projection models. In developing mission designs, the reduction of health risks and mission constraints including costs are competing concerns that need to be addressed through optimization procedures. Mitigating the risks from space radiation is a multi-factorial problem involving individual factors (age, gender, genetic makeup, and exposure history), operational factors (planetary destination, mission length, and period in the solar cycle), and shielding characteristics (materials, mass, and topology). We review optimization metrics for radiation protection including scenarios that integrate biophysics models of radiation risks, operational variables, and shielding design tools needed to assess exploration mission designs. We discuss the application of a crosscutting metric, based on probabilistic risk assessment, to lunar and Mars mission trade studies including the assessment of multi-factorial problems and the potential benefits of new radiation health research strategies or mitigation technologies.

Cucinotta, F. A.↗

NASA NTRS2006

Managing Space Radiation Risks on Lunar and Mars Missions: Risk Assessment and Mitigation

Radiation-induced health risks are a primary concern for human exploration outside the Earth's magnetosphere, and require improved approaches to risk estimation and tools for mitigation including shielding and biological countermeasures. Solar proton events are the major concern for short-term lunar missions (<60 d), and for long-term missions (>60 d) such as Mars exploration, the exposures to the high energy and charge (HZE) ions that make-up the galactic cosmic rays are the major concern. Health risks from radiation exposure are chronic risks including carcinogenesis and degenerative tissue risks, central nervous system effects, and acute risk such as radiation sickness or early lethality. The current estimate is that a more than four-fold uncertainty exists in the projection of lifetime mortality risk from cosmic rays, which severely limits analysis of possible benefits of shielding or biological countermeasure designs. Uncertainties in risk projections are largely due to insufficient knowledge of HZE ion radiobiology, which has led NASA to develop a unique probabilistic approach to radiation protection. We review NASA's approach to radiation risk assessment including its impact on astronaut dose limits and application of the ALARA (As Low as Reasonably Achievable) principle. The recently opened NASA Space Radiation Laboratory (NSRL) provides the capability to simulate the cosmic rays in controlled ground-based experiments with biological and shielding models. We discuss how research at NSRL will lead to reductions in the uncertainties in risk projection models. In developing mission designs, the reduction of health risks and mission constraints including costs are competing concerns that need to be addressed through optimization procedures. Mitigating the risks from space radiation is a multi-factorial problem involving individual factors (age, gender, genetic makeup, and exposure history), operational factors (planetary destination, mission length, and period in the solar cycle), and shielding characteristics (materials, mass, and topology). We review optimization metrics for radiation protection including scenarios that integrate biophysics models of radiation risks, operational variables, and shielding design tools needed to assess exploration mission designs. We discuss the application of a crosscutting metric, based on probabilistic risk assessment, to lunar and Mars mission trade studies including the assessment of multi-factorial problems and the potential benefits of new radiation health research strategies or mitigation technologies.

Cucinotta, F. A.↗