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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Observations of cosmic-ray electrons and positrons using an imaging calorimeter

A ballon-borne magnet spectrometer system was flown for 5.5 hr at an altitude of more than 117,00 feet from Prince Albert, Saskatchewan (Canada), on 1989 September 5, when the Newark neutron monitor rate was 2952. The instrument was a modified version of the one used to observe antiprotons in 1979. The most significant modification was the addition of an imaging calorimeter, 7.33 radiation lengths thick. Inclusion of the calorimeter has significantly improved the ability to distinguish electrons and positrons from the other constituents of the cosmic rays. The absolute electron flux has been determined in the energy interval 1.3-26 GeV. The electron spectrum at the top of the atmosphere was found to be J(sub e-) = 177E(exp -(3.15+/-0.13)) electrons/ sq m/(sr s GeV) in the energy range 4.0-26 GeV. Below 4 GeV, the spectrum showed flattening, which is consistent with the effect of solar modulation. The e(+)/(e(+)+e(-)) ratio was found to be (0.11 +/- 0.03) in the energy range 5.2-13 GeV.

Golden, R. L.↗
NASA NTRS1992

Radiation health for a Mars mission

Uncertainties in risk assessments for exposure of a Mars mission crew to space radiation place limitations on mission design and operation. Large shielding penalties are imposed in order to obtain acceptable safety margins. Galactic cosmic rays (GCR) and solar particle events (SPE) are the major concern. A warning system and 'safe-haven' are needed to protect the crew from large SPE which produce lethal doses. A model developed at NASA Johnson Space Center (JSC) to describe solar modulation of GCR intensities reduces that uncertainty to less than 10 percent. Radiation transport models used to design spacecraft shielding have large uncertainties in nuclear fragmentation cross sections for GCR which interact with spacecraft materials. Planned space measurements of linear energy transfer (LET) spectra behind various shielding thicknesses will reduce uncertainties in dose-versus-shielding thickness relationships to 5-10 percent. The largest remaining uncertainty is in biological effects of space radiation. Data on effects of energetic ions in human are nonexistent. Experimental research on effects in animals and cell is needed to allow extrapolation to the risk of carcinogenesis in humans.

Robbins, Donald E.↗
NASA NTRS1996

Galactic cosmic radiation model and its applications

A model for the differential energy spectra of galactic cosmic radiation as a function of solar activity is described. It is based on the standard diffusion-convection theory of solar modulation. Estimates of the modulation potential based on fitting this theory to observed spectral measurements from 1954 to 1989 are correlated to the Climax neutron counting rates and to the sunspot numbers at earlier times taking into account the polarity of the interplanetary magnetic field at the time of observations. These regression lines then provide a method for predicting the modulation at later times. The results of this model are quantitatively compared to a similar Moscow State University (MSU) model. These model cosmic ray spectra are used to predict the linear energy transfer spectra, differential energy spectra of light (charge less than or = 2) ions, and single event upsets rates in memeory devices. These calculations are compared to observations made aboard the Space Shuttle.

Badhwar, G. D.↗
NASA NTRS1994

Cooperative research in high energy astrophysics

Details of the activities conducted under the joint effort of the University of Maryland and NASA Goddard Space Flight Center Laboratory for High Energy Astrophysics are detailed for the period July 1989 through April 1994. The research covered a variety of topics including: (1) detection of cosmic rays and studies of the solar modulation of galactic cosmic rays; (2) support work for several x-ray satellites; (3) high resolution gamma-ray spectroscopy of celestial sources; (4)theoretical astrophysics; and (5) active galaxies.

Source record↗
NASA NTRS1997

Cooperative Research in High Energy Astrophysics

A joint agreement between NASA/Goddard and The University of Maryland currently supports cooperative research in Satellite Based Studies of Photons and Charged Particles in the following areas: 1) Detection of cosmic rays and studies of the solar modulation of galactic cosmic rays; 2) Research with several past and upcoming X-ray satellites; 3) High resolution gamma-ray spectroscopy of celestial sources; 4) Theoretical astrophysics.

Trasco, John D.↗
NASA NTRS2003

A New Time-dependent Model for the Martian Radiation Environment

Manned space activities have been until present time limited to the near-Earth environment, most of them to low Earth orbit (LEO) scenarios, with only some of the Apollo missions targeted to the Moon. In current times most human exploration and development of space (HEDS) activities are related to the development of the International Space Station (ISS), and therefore take place in the LEO environment. A natural extension of HEDS activities will be going beyond LEO, and reach asteroids, Mars, Jupiter, Saturn, the Kuiper belt and the outskirts of the Solar System. Such long journeys onboard spacecraft outside the protective umbrella of the geomagnetic field will require higher levels of protection from the radiation environment found in the deep space for both astronauts and equipment. So, it is important to have available a tool for radiation shielding which takes into account the radiation environments found all along the interplanetary space and at the different bodies encountered in the Solar System. Moreover, the radiation protection is one of the two NASA highest concerns and priorities. A tool integrating different radiation environments with shielding computation techniques especially tailored for deep space mission scenario is instrumental in view of this exigency. In view of manned missions targeted to Mars, for which radiation exposure is one of the greatest problems and challenges to be tackled, it is of fundamental importance to have available a tool which allows to know which are the particle flux and spectra at any time at any point of the Martian surface. With this goal in mind, a new model for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (GCR) has been developed. Solar modulated primary particles rescaled for Mars conditions are transported within the Martian atmosphere, with temporal properties modeled with variable timescales, down to the surface, with altitude and backscattering patterns taken into account. The tool allows analysis for manned Mars landing missions, as well as planetary science studies, e.g. subsurface water and volatile inventory studies. This Mars environmental model is available through the SIREST website, a project of NASA Langley Research Center.

G De Angelis↗
NASA NTRS2003

Heavy Ion Flux Comparison of MARIE and ACE/CRIS Instruments

The charged particle spectrum for nuclei from protons to neon, (charge Z=10) has been observed during the cruise phase and in orbit around Mars by the MARIE charge particle spectrometer aboard the Odyssey spacecraft. The cruise data was taken between April 23, 2001 and August 11, 2001. The Mars orbit data was taken from March 5, 2002 through December 2002. Both the cruise data set and the orbital data set are compared with the simultaneous observations made by the CRIS instrument aboard the ACE space-craft, located at L1. Any detectable differences between the two spacecraft data sets could lead to the understanding of the radial dependence of solar modulation.

Lee, K. T.↗
NASA NTRS2010

Probabilistic Assessment of Cancer Risk from Solar Particle Events

For long duration missions outside of the protection of the Earth s magnetic field, space radiation presents significant health risks including cancer mortality. Space radiation consists of solar particle events (SPEs), comprised largely of medium energy protons (less than several hundred MeV); and galactic cosmic ray (GCR), which include high energy protons and heavy ions. While the frequency distribution of SPEs depends strongly upon the phase within the solar activity cycle, the individual SPE occurrences themselves are random in nature. We estimated the probability of SPE occurrence using a non-homogeneous Poisson model to fit the historical database of proton measurements. Distributions of particle fluences of SPEs for a specified mission period were simulated ranging from its 5 th to 95th percentile to assess the cancer risk distribution. Spectral variability of SPEs was also examined, because the detailed energy spectra of protons are important especially at high energy levels for assessing the cancer risk associated with energetic particles for large events. We estimated the overall cumulative probability of GCR environment for a specified mission period using a solar modulation model for the temporal characterization of the GCR environment represented by the deceleration potential (^). Probabilistic assessment of cancer fatal risk was calculated for various periods of lunar and Mars missions. This probabilistic approach to risk assessment from space radiation is in support of mission design and operational planning for future manned space exploration missions. In future work, this probabilistic approach to the space radiation will be combined with a probabilistic approach to the radiobiological factors that contribute to the uncertainties in projecting cancer risks.

Kim, Myung-Hee Y.↗
NASA NTRS2006

Updated Computational Model of Cosmic Rays Near Earth

An updated computational model of the galactic-cosmic-ray (GCR) environment in the vicinity of the Earth, Earth s Moon, and Mars has been developed, and updated software has been developed to implement the updated model. This model accounts for solar modulation of the cosmic-ray contribution for each element from hydrogen through iron by computationally propagating the local interplanetary spectrum of each element through the heliosphere. The propagation is effected by solving the Fokker-Planck diffusion, convection, energy-loss boundary-value problem. The Advanced Composition Explorer NASA satellite has provided new data on GCR energy spectra. These new data were used to update the original model and greatly improve the accuracy of prediction of interplanetary GCR.

ONeill, Patrick M.↗
NASA NTRS2011

Use of Apollo 17 Epoch Neutron Spectrum as a Benchmark in Testing LEND Collimated Sensor

The Apollo 17 neutron experiment LPNE provided a unique set of data on production of neutrons in the Lunar soil bombarded by Galactic Cosmic Rays (GCR). It serves as valuable "ground-truth" in the age of orbital remote sensing. We used the neutron data attributed to Apollo 17 epoch as a benchmark for testing the LEND's collimated sensor, as introduced by the geometry of collimator and efficiency of He3 counters. The latter is defined by the size of gas counter and pressure inside it. The intensity and energy spectrum of neutrons escaping the lunar surface are dependent on incident flux of Galactic Cosmic Rays (GCR) whose variability is associated with Solar Cycle and its peculiarities. We obtain first the share of neutrons entering through the field of view of collimator as a fraction of the total neutron flux by using the angular distribution of neutron exiting the Moon described by our Monte Carlo code. We computed next the count rate of the 3He sensor by using the neutron energy spectrum from McKinney et al. [JGR, 2006] and by consider geometry and gas pressure of the LEND sensor. Finally the neutron count rate obtained for the Apollo 17 epoch characterized by intermediate solar activity was adjusted to the LRO epoch characterized by low solar activity. It has been done by taking into account solar modulation potential, which affects the GCR flux, and in turn changes the neutron albedo flux.

Chin, Gordon↗
NASA NTRS2013

Simulation and Comparison of Martian Surface Ionization Radiation

The spectrum of energetic particle radiation and corresponding doses at the surface of Mars is being characterized by the Radiation Assessment Detector (RAD), one of ten science instruments on the Mars Science Laboratory (MSL) Curiosity Rover. The time series of dose rate for the first 300 Sols after landing on Mars on August 6, 2012 is presented here. For the comparison to RAD measurements of dose rate, Martian surface ionization radiation is simulated by utilizing observed space quantities. The GCR primary radiation spectrum is calculated by using the Badhwar-O'Neill 2011 (BO11) galactic cosmic ray (GCR) model, which has been developed by utilizing all balloon and satellite GCR measurements since 1955 and the newer 1997-2012 Advanced Composition Explorer (ACE) measurements. In the BO11 model, solar modulation of the GCR primary radiation spectrum is described in terms of the international smoothed sunspot number and a time delay function. For the transport of the impingent GCR primary radiation through Mars atmosphere, a vertical distribution of atmospheric thickness at each elevation is calculated using the vertical profiles of atmospheric temperature and pressure made by Mars Global Surveyor measurements. At Gale Crater in the southern hemisphere, the seasonal variation of atmospheric thickness is accounted for the daily atmospheric pressure measurements of the MSL Rover Environmental Monitoring Station (REMS) by using low- and high-density models for cool- and warm-season, respectively. The spherically distributed atmospheric distance is traced along the slant path, and the resultant directional shielding by Martian atmosphere is coupled with Curiosity vehicle for dose estimates. We present predictions of dose rate and comparison to the RAD measurements. The simulation agrees to within +/- 20% with the RAD measurements showing clearly the variation of dose rate by heliospheric conditions, and presenting the sensitivity of dose rate by atmospheric pressure, which has been found from the RAD experiments and driven by thermal tides on Martian surface.

Kim, Myung-Hee Y.↗
NASA NTRS2013

Galactic Cosmic-Ray Energy Spectra and Composition during the 2009-2010 Solar Minimum Period

We report new measurements of the elemental energy spectra and composition of galactic cosmic rays during the 2009-2010 solar minimum period using observations from the Cosmic Ray Isotope Spectrometer (CRIS) onboard the Advanced Composition Explorer. This period of time exhibited record-setting cosmic-ray intensities and very low levels of solar activity. Results are given for particles with nuclear charge 5 <= Z <= 28 in the energy range approx. 50-550 MeV / nucleon. Several recent improvements have been made to the earlier CRIS data analysis, and therefore updates of our previous observations for the 1997-1998 solar minimum and 2001-2003 solar maximum are also given here. For most species, the reported intensities changed by less than approx. 7%, and the relative abundances changed by less than approx. 4%. Compared with the 1997-1998 solar minimum relative abundances, the 2009-2010 abundances differ by less than 2sigma, with a trend of fewer secondary species observed in the more recent time period. The new 2009-2010 data are also compared with results of a simple "leaky-box" galactic transport model combined with a spherically symmetric solar modulation model. We demonstrate that this model is able to give reasonable fits to the energy spectra and the secondary-to-primary ratios B/C and (Sc+Ti+V)/Fe. These results are also shown to be comparable to a GALPROP numerical model that includes the effects of diffusive reacceleration in the interstellar medium.

Galactic Cosmic Rays↗
NASA NTRS2015

Comparison of GFED3, QFED2 and FEER1 Biomass Burning Emissions Datasets in a Global Model

Biomass burning contributes about 40% of the global loading of carbonaceous aerosols, significantly affecting air quality and the climate system by modulating solar radiation and cloud properties. However, fire emissions are poorly constrained in models on global and regional levels. In this study, we investigate 3 global biomass burning emission datasets in NASA GEOS5, namely: (1) GFEDv3.1 (Global Fire Emissions Database version 3.1); (2) QFEDv2.4 (Quick Fire Emissions Dataset version 2.4); (3) FEERv1 (Fire Energetics and Emissions Research version 1.0). The simulated aerosol optical depth (AOD), absorption AOD (AAOD), angstrom exponent and surface concentrations of aerosol plumes dominated by fire emissions are evaluated and compared to MODIS, OMI, AERONET, and IMPROVE data over different regions. In general, the spatial patterns of biomass burning emissions from these inventories are similar, although the strength of the emissions can be noticeably different. The emissions estimates from QFED are generally larger than those of FEER, which are in turn larger than those of GFED. AOD simulated with all these 3 databases are lower than the corresponding observations in Southern Africa and South America, two of the major biomass burning regions in the world.

biomass burning↗
NASA NTRS2023

Simulations of 7 Be and 10 Be with the GEOS-Chem global model v14.0.2 using state-of-the-art production rates

The cosmogenic radionuclides 7 Be and 10 Be are useful aerosol tracers for atmospheric transport studies. Combining 7 Be and 10 Be measurements with an atmospheric transport model can not only improve our understanding of the radionuclide transport and deposition processes but also provide an evaluation of the transport process in the model. To simulate these aerosol tracers, it is critical to evaluate the influence of radionuclides production uncertainties on simulations. Here we use the GEOS-Chem chemical transport model driven by the MERRA-2 reanalysis to simulate 7 Be and 10 Be with different production scenarios: the default production rate in GEOS-Chem based on an empirical approach (Lal and Peters, 1967; denoted as LP67), and two production rates from the CRAC:Be (Cosmic Ray Atmospheric Cascade: Beryllium; Poluianov et al., 2016) model considering only geomagnetic cut-off rigidities for a geocentric axial dipole (denoted as P16) or realistic spatial geomagnetic cut-off rigidity variations due to non-dipole moments of the geomagnetic field (denoted as P16spa). The model results are comprehensively evaluated with a large number of measurements including surface air concentrations and deposition fluxes. The model with the P16spa production can reproduce the absolute values and temporal variability of 7 Be and 10 Be surface concentrations and deposition fluxes on annual and sub-annual scales, as well as the vertical profiles of air concentrations. Simulations with the LP67 production tend to overestimate the absolute values of 7 Be and 10 Be concentrations. The P16 simulations suggest less than 10% differences compared to P16spa but tend to produce a significant positive bias (>20%) in the 7 Be deposition fluxes over East Asia. We find that the deposition fluxes are more sensitive to the production in the troposphere and downward transport from the stratosphere. Independent of the production models, surface air concentrations and deposition fluxes from all simulations show similar seasonal variations, suggesting a dominant meteorological influence. The model can also simulate reasonably the stratosphere-troposphere exchange process of 7 Be and 10 Be by producing stratospheric contribution and 10 Be/ 7 Be ratio values that agree with measurements. Finally, we illustrate the importance of including the time-varying solar modulation in the production calculation, which can significantly improve the agreement between model results and measurements, especially at mid- and high- latitudes. Reduced uncertainties in the production rates, as demonstrated in this study, improve the utility of 7 Be and 10 Be as aerosol tracers for evaluating and testing transport and scavenging processes in global models.

Minjie Zheng↗
NASA NTRS1985

Solar activity and modulation of the cosmic ray intensity

Since its discovery by Forbush (1954), the 11-year cycle modulation of the cosmic ray intensity has been studied extensively. Bowe and Hatton (1982) obtained a well-behaved transfer function F between the solar activity S and the cosmic ray intensity modulation Io-I. They suggested that the 11-year variation for sunspot cycle 20 can be attributed to the modulating effect of solar flare-induced shocks propagating through the heliosphere. The cosmic ray intensity in the absence of solar activity is denoted by Io, while I denotes the observed intensity. Bowe and Hatton infer that the boundary of the heliosphere is located at a distance of 70-90 AU. Since their conclusion is of great importance in understanding the mechanism of the 11-year modulation, the present investigation is concerned with a repetition of their study for two cycles, taking into account the use of a slightly modified method. The obtained results confirm the conclusions reached by Bowe and Hatton that there is a well-behaved transfer function for solar flares.

Akasofu, S.-I.↗
DOE OSTI2024

Debris-induced consequences on turbulence and vorticity in solar photovoltaic module-generated array wakes

Particle-laden flows in solar photovoltaic (PV) systems are inevitable, where wind-swept debris in open environments are carried by high winds and turbulence, coating panel surfaces or damaging structures. Particle deposition, or soiling, is a well-known issue for large-scale plants which rely on uninhibited solar rays for optimal production. But understanding the mechanisms leading to soiling requires a physical and fluid dynamics-centered focus, since turbulence dominates PV panel wakes and is also known to alter particle concentration and trajectories. This study presents an experimental campaign toward consequences of particle-laden flow between two model PV panels using time-resolved particle image velocimetry. The model array was subjected to varied particle volume fractions, including a tracer particle case and a water droplet case. Characterization of mean velocity, turbulence statistics, and mean kinetic energy within the single phase and, separately, particle phase flows showed modified features due to particle inertia. Images captured at a frequency of 1 kHz in the near wake of the upstream panel allow for a first experimental look at vorticity and convective velocity of vortex structures for single-phase and particle-phase flows which are crucial to debris transport and soiling in PV environments.

Energy & Fuels↗
NASA NTRS1981

Solar-site test module

Report describes small test set which interrogates solar-energy data acquisition systems. Lightweight, portable set includes microcomputer with keyboard, alphanumeric display, printer, cassette recorder/player for storing programs and data, and cable for connection to Site Data Acquisition System (SDAS). Unit is operated by BASIC program and Assembly language. Report is specific to DOE/NASA application yet contains general information to assist in designing similar units.

Kissel, R. R.↗
DOE OSTI2020

From Defects to Degradation: A Mechanistic Understanding of Degradation in Perovskite Solar Cell Devices and Modules

Metal halide perovskite solar cells (PSCs) have risen in efficiency from just 3.81% in 2009 to over 25.2% today. While metal halide perovskites have excelled in efficiency, advances in stability are significantly more complex and have progressed more slowly. The advance of efficiency, which is readily measured, over stability, which can require literally thousands of hours to demonstrate, is to be expected given the rapid rate of innovation in the field. In the face of changing absorber composition, synthetic approaches, and device stack components it is necessary to understand basic material properties to rationalize how to enable stability in devices. In this article the aim is to present an in-depth review of the current understanding of metal halide perovskite devices and module stability by focusing on what is known retarding intrinsic and extrinsic degradation mechanisms at the material, device, and module level. Once these considerations are presented the discussion then moves to connecting different degradation mechanisms to stresses anticipated in operation and how they can impact efficiency of cells and ultimately modules over time.

36 MATERIALS SCIENCE↗