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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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NASA NTRS1981

Thermal instabilities in radiatively driven winds - Application to emission line clouds of quasars and active galactic nuclei

It is shown that radiatively driven, optically thin winds from active galactic nuclei are thermally unstable, provided that the mass loss rates are not smaller than about 50 solar masses/year. Clouds form at distances of less than about 1 pc, with electron densities greater than 100 million/cu cm, temperatures of more than 10,000 K, and radii between 3 x 10 to the 14th and 10 to the 15th cm. These values agree with the values deduced from observations. Since the clouds are formed in a high velocity wind, this model, as does the model by Eilek and Caroff (1979), avoids problems of disruption inherent in using radiation pressure to accelerate clouds from rest to velocities up to 0.1 c needed to explain the emission line widths. The thermal balance of the gas is discussed, the criteria for thermal instability are given, and a perturbation analysis is made. This analysis is restricted to objects with bolometric luminosities lower than approximately 2 x 10 to the 46th ergs/sec. For more luminous objects, only winds slightly optically thick to electron scattering can be unstable, provided one can extend this analysis to the optically thick case.

Beltrametti, M.↗
NASA NTRS2014

Implementing Badhwar-O'Neill Galactic Cosmic Ray Model for the Analysis of Space Radiation Exposure

For the analysis of radiation risks to astronauts and planning exploratory space missions, accurate energy spectrum of galactic cosmic radiation (GCR) is necessary. Characterization of the ionizing radiation environment is challenging because the interplanetary plasma and radiation fields are modulated by solar disturbances and the radiation doses received by astronauts in interplanetary space are likewise influenced. A model of the Badhwar‐O'Neill 2011 (BO11) GCR environment, which is represented by GCR deceleration potential theta, has been derived by utilizing all of the GCR measurements from balloons, satellites, and the newer NASA Advanced Composition Explorer (ACE). In the BO11 model, the solar modulation level is derived from the mean international sunspot numbers with time‐delay, which has been calibrated with actual flight instrument measurements to produce better GCR flux data fit during solar minima. GCR fluxes provided by the BO11 model were compared with various spacecraft measurements at 1 AU, and further comparisons were made for the tissue equivalent proportional counters measurements at low Earth orbits using the high‐charge and energy transport (HZETRN) code and various GCR models. For the comparison of the absorbed dose and dose equivalent calculations with the measurements by Radiation Assessment Detector (RAD) at Gale crater on Mars, the intensities and energies of GCR entering the heliosphere were calculated by using the BO11 model, which accounts for time‐dependent attenuation of the local interstellar spectrum of each element. The BO11 model, which has emphasized for the last 24 solar minima, showed in relatively good agreement with the RAD data for the first 200 sols, but it was resulted in to be less well during near the solar maximum of solar cycle 24 due to subtleties in the changing heliospheric conditions. By performing the error analysis of the BO11 model and the optimization in reducing overall uncertainty, the resultant BO13 model corrects the fit at solar maxima as well as being accurate at solar minima. The BO13 model is implemented to the NASA Space Cancer Risk model for the assessment of radiation risks. Overall cumulative probability distribution of solar modulation parameters represents the percentile rank of the average interplanetary GCR environment, and the probabilistic radiation risks can be assessed for various levels of GCR environment to support mission design and operational planning for future manned space exploration missions.

Kim, Myung-Hee Y.↗
NASA NTRS1990

Estimates of galactic cosmic ray shielding requirements during solar minimum

Estimates of radiation risk from galactic cosmic rays are presented for manned interplanetary missions. The calculations use the Naval Research Laboratory cosmic ray spectrum model as input into the Langley Research Center galactic cosmic ray transport code. This transport code, which transports both heavy ions and nucleons, can be used with any number of layers of target material, consisting of up to five different arbitrary constituents per layer. Calculated galactic cosmic ray fluxes, dose and dose equivalents behind various thicknesses of aluminum, water and liquid hydrogen shielding are presented for the solar minimum period. Estimates of risk to the skin and the blood-forming organs (BFO) are made using 0-cm and 5-cm depth dose/dose equivalent values, respectively, for water. These results indicate that at least 3.5 g/sq cm (3.5 cm) of water, or 6.5 g/sq cm (2.4 cm) of aluminum, or 1.0 g/sq cm (14 cm) of liquid hydrogen shielding is required to reduce the annual exposure below the currently recommended BFO limit of 0.5 Sv. Because of large uncertainties in fragmentation parameters and the input cosmic ray spectrum, these exposure estimates may be uncertain by as much as a factor of 2 or more. The effects of these potential exposure uncertainties or shield thickness requirements are analyzed.

Townsend, Lawrence W.↗
NASA NTRS1995

Issues in protection from galactic cosmic rays

Radiation risks to astronauts depend on the microscopic fluctuations of energy absorption events in specific tissues. These fluctuations depend not only on the space environment but also on the modifications of that environment by the shielding provided by structures surrounding the astronauts and the attenuation characteristics of the astronaut's body. The effects of attenuation within the shield and body depends on the tissue biological response to these microscopic fluctuations. In the absence of an accepted method for estimating astronaut risk, we examined the attenuation characteristics using conventional linear energy transfer (LET)-dependent quality factors (as one means of representing relative biological effectiveness, RBE) and a track-structure repair model to fit cell transformation (and inactivation) data in the C3H10 T1/2 mouse cell system obtained for various ion beams. Although the usual aluminum spacecraft shield is effective in reducing dose equivalent with increasing shield thickness, cell transformation rates are increased for thin aluminum shields. Clearly, the exact nature of the biological response to LET and track width is critical to evaluation of biological protection factors provided by a shield design. A significant fraction of biological injury results from the LET region above 100 keV/mu m. Uncertainty in nuclear cross-sections results in a factor of 2-3 in the transmitted LET spectrum beyond depths of 15 g/cm2, but even greater uncertainty is due to the combined effects of uncertainty in biological response and nuclear parameters. Clearly, these uncertainties must be reduced before the shield design can be finalised.

NASA Discipline Number 45-10↗
NASA NTRS2023

NASA’s Galactic Cosmic Ray Simulator – How we study the effects of space radiation on Earth

Earth’s atmosphere and natural magnetic field do a good job protecting us from space radiation. Space radiation is different from radiation on Earth, which mostly comes from isotopes found in rock and soil or from medical procedures like an Xray. Ionizing space radiation comes from particles ejected from the Sun, or solar particle events, and from supernovae outside our solar system making up a background of galactic cosmic radiation. These particles, representing the elements of the periodic table, have been stripped of their electrons as they are accelerated in interstellar space to almost the speed of light. One of NASA’s biggest challenges is protecting astronauts from these high energy particles of galactic cosmic radiation which can cause cancer and other diseases. To understand the biological damage imparted to living systems and to develop protective countermeasures, NASA has built a galactic cosmic ray simulator on Earth.

Space Exploration Missions↗
NASA NTRS2000

Galactic Noise and Passive Microwave Remote Sensing from Space at L-Band

The spectral window at L-band (1.4 GHz) is important for passive remote sensing of parameters such as soil moisture and ocean salinity best measured at long wavelengths. At L-band, radiation from extraterrestrial (galactic) sources is strong enough to warrant inclusion in calibration and retrieval algorithms and unlike the constant cosmic background is spatially variable. Previous estimates of the magnitude and distribution of this background radiation have been rather coarse, However, recent surveys of the radio sky at 1.4 GHz have made it possible to produce maps with sufficient spatial and radiometric accuracy to be relevant to remote sensing applications. This is of particular concern for remote sensing of sea surface salinity because the surface (water) is a good reflector and the salinity signal is relatively small. This paper presents a modem map of the radiometric sky at L-band and a solution to the problem of determining the portion of the sky seen by a radiometer in orbit. The data is derived from recent radio astronomy surveys and is presented as equivalent brightness temperature suitable for remote sensing applications. Examples using orbits and antennas representative of those contemplated for remote sensing of soil moisture and sea surface salinity from space are presented to illustrate the signal levels to be expected. Radiation near the galactic plane can exceed several kelvin.

LeVine, D. M.↗
NASA NTRS1974

Dust in the galactic center

The strength of the 9.7 microns absorption band in the radiation from the galactic center is used to deduce a range of measures of the visual extinction from 20 to 400 magnitudes. A possible way of arriving at a unique value of the visual extinction consistent with variations in the wavelength dependence of extinction as a function of grain characteristics is indicated. The mass of silicates deduced from the 9.7 microns band appears to imply a gradient of metallicity towards the galactic center.

Greenberg, J. M.↗
NASA NTRS1977

Translational anisotropy in the cosmic microwave background radiation and far-infrared emission by galactic dust clouds

The predicted emission spectrum of galactic dust at about 10 K is compared with the spectrum of 2.8-K universal blackbody radiation and with the spectrum of the anisotropy expected in the 2.8-K radiation due to motion of earth with respect to the coordinate system in which the radiation was last scattered. The extremely anisotropic galactic-dust emission spectrum may contribute a significant background to anisotropy measurements which scan through the galactic plane. The contamination would appear in an 8-mm scan around the celestial equator, for example, as a spurious 200 km/s velocity toward declination 0 deg, right ascension 19 hr, if predictions are correct. The predicted spectrum of dust emission in the galactic plane at longitudes not exceeding about 30 deg falls below the total 2.8-K cosmic background intensity at wavelengths of at least 1 mm.

Forman, M. A.↗
NASA NTRS1998

Comparison of Martian Meteorites and Martian Regolith as Shield Materials for Galactic Cosmic Rays

Theoretical calculations of radiation attenuation due to energetic galactic cosmic rays behind Martian rock and Martian regolith material have been made to compare their utilization as shields for advanced manned missions to Mars because the detailed chemical signature of Mars is distinctly different from Earth. The modified radiation fields behind the Martian rocks and the soil model were generated by solving the Boltzmann equation using a HZETRN system with the 1977 Solar Minimum environmental model. For the comparison of the attenuation characteristics, dose and dose equivalent are calculated for the five different subgroups of Martian rocks and the Martian regolith. The results indicate that changes in composition of subgroups of Martian rocks have negligible effects on the overall shielding properties because of the similarity of their constituents. The differences for dose and dose equivalent of these materials relative to those of Martian regolith are within 0.5 and 1 percent, respectively. Therefore, the analysis of Martian habitat construction options using in situ materials according to the Martian regolith model composition is reasonably accurate. Adding an epoxy to Martian regolith, which changes the major constituents of the material, enhances shielding properties because of the added hydrogenous constituents.

Kim, Myung-Hee Y.↗
NASA NTRS1989

The radiative deceleration of ultrarelativistic jets in active galactic nuclei

A detailed study of the dynamical interaction between a highly relativistic jet and the thermal radiation field from an AGN accretion disk is reported, and the Comptonized spectrum arising from this interaction is self-consistently determined. A simple model that captures the essential radiative and geometrical features of realistic disk configurations is presented, and the disk radiation field is calculated. The results confirm Phinney's (1987) suggestion that the thermal radiation field produced by accretion in an AGN could be very effective in decelerating ultrarelativistic jets that are accreted by electromagnetic or hydromagnetic forces closer to the central black hole. Terminal Lorentz factors are consistent with the values inferred in superluminal radio sources are readily produced in this model for plausible disk and jet parameters without additional acceleration in the interaction zone. A new interpretation of the hard X-ray component detected in BL Lac spectra is proposed.

Melia, Fulvio↗
NASA NTRS1975

Molecular hydrogen in the Galaxy and galactic gamma rays

Recent surveys of 2.6-cm CO emission and 100-MeV gamma-radiation in the galactic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H2 in the inner Galaxy. Both the gamma-ray and CO data suggest a prominent ring or arm consisting of cool clouds of H2 at a galactocentric distance of about 5 kpc with a mean total hydrogen density equivalent to approximately 5 atoms per cu cm. Estimates are made of column densities of H2 at 0 deg galactic longitude and are compared with estimates from infrared and X-ray absorption measurements. These estimates are all consistent, indicating that H2 is far more abundant than H I in the inner Galaxy and is the key to a more satisfactory explanation of the gamma-ray observations than previous suggestions. The importance of H2 in understanding galactic gamma-ray observations is also reflected in the correlation of galactic-latitude distribution of gamma-rays and dense dust clouds. The deduced cosmic-ray distribution inferred from the calculations is similar to that of galactic supernova remnants, suggesting a galactic origin for most cosmic rays.

Stecker, F. W.↗
NASA NTRS1979

Observations of diffuse galactic gamma rays

The observations of galactic diffuse gamma radiation are reviewed. The connections of the gamma ray observations with galactic structure and cosmic rays are discussed. The high latitude galactic component and the low latitude emission from the galactic plane are examined. The observations in other regions of the gamma ray spectrum are discussed.

Simpson, G. A.↗
NASA NTRS1982

A coded aperture gamma ray telescope

A gamma ray telescope is being developed to operate in the energy range 100 keV to 5 MeV, utilizing coded aperture imaging. The design incorporates a mask pattern based on a Uniformly Redundant Array (URA), which has been shown to have ideal imaging characteristics. A mask-anti-mask procedure is used to eliminate the effects of any possible systematic variations in detector background rates. The detector array is composed of 35 elements of the high-Z material Bismuth Germanate (BGO). Results of laboratory testing of the imaging properties will be presented. A southern hemisphere balloon flight is planned for 1982 with the goal of observing the 0.511 MeV radiation from the Galactic Center. Computer calculations show that a point source of this radiation can be located to within + or - 1 deg.

Mcconnell, M. L.↗
NASA NTRSDate not supplied

The Environmental Data Application for Analysis of Space Telemetry Data

Sensors on the International Space Station (ISS) and multiple spacecraft elsewhere in Earth orbit and in deep space continuously monitor and collect environmental data, transmitting this information back to Earth. These data include ionizing radiation and, on the ISS and spacecrafts, CO2, relative humidity levels, and temperature, and are of great importance to space biology research. Looking ahead to future long duration crewed missions beyond low Earth orbit, the ability to study how factors including CO2 levels, light cycle, temperature modulate the response to ionizing radiation and microgravity is essential. To date, access to these data has been fragmented across space agencies, spacecraft, and databases. To address this issue, NASA’s Open Science Data Repository (OSDR) has developed a user interface for interrogation of telemetry data: the Environmental Data Application (EDA). The EDA provides the capability to visualize telemetry and radiation data collected on the International Space Station and corresponding ground platforms during the Rodent Research missions. Telemetry data includes temperature, relative humidity, and CO2 levels. Radiation data includes galactic cosmic rays, the contribution of the South Atlantic Anomaly, total radiation dose rate, and accumulated radiation dose. The application allows users to view single missions, compare multiple missions, and view and download summary or full data tables. In summary, the EDA provides GUIs for data visualization and exploration, as well as means for data export, making these data FAIR (Findable, Accessible, Interoperable, and Reusable), complementing the biological data contained in OSDR, and providing the space science community with a valuable resource for scientific analyses.

telemetry↗
NASA NTRS1989

The nature of the annihilation radiation and gamma-ray continuum from the Galactic center region

Analysis of the observations of the time-dependent, electron-positron annihilation line radiation and gamma-ray continuum emission from the region of the Galactic center shows that ther are two components to the emission: (1) a variable, compact source of 511 keV annihilation line and higher energy continuum emission active from about 1977 through 1979 at or near the Galactic center; and (2) a steady, diffuse interstellar source of 511 keV annihilation line and orthopositronium continuum emission, having a galactic longitudinal distribution consistent with that of the more than 70 MeV gamma rays or the molecular (CO) gas. It is found that the continuum spectrum of the compact source shows no evidence for orthopositronium annihilation. It is suggested that all of the three-photon orthopositronium continuum observed so far originates from the diffuse interstellar component. The continuum spectrum of the compact source is very similar to that of the black-hole candidate Cygnus X-1, supporting our earlier arguments that this object, at or near the Galactic center, is a black hole of stellar mass.

Lingenfelter, Richard E.↗