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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Spacelab-1: An early space station for science and technology

The scientific capabilities of the Spacelab manned pallet are reviewed, together with the implications of an expansion of the research effectiveness with a free-flying platform. The premier Spacelab flight will carry out earth observations with a metric camera and SAR, atmospheric studies will be performed with imaging spectrometers, and space plasma physics will be examined by injecting particle beams or VLF waves into the near-Shuttle environment. Radiance and spectrum data will be gathered of the sun and UV and X ray information will be recorded from the stars. Experimentation will also be carried out for on-board crystal growth, metallurgy, and glassy material production, as well as the response of biological systems to zero-g conditions and hard space radiation. The telemetry, time, crewmember participation, and on-board controls required for Spacelab operations are outlined. Missions for a space platform for studying the atmosphere/space interface are described.

Knott, K.↗
NASA NTRS1988

Identification of new fluorescence processes in the UV spectra of cool stars from new energy levels of Fe II and Cr II

Two fluorescence processes operating in atmospheres of cool stars, symbiotic stars, and the Sun are presented. Two emission lines, at 1347.03 and 1360.17 A, are identified as fluorescence lines of Cr II and Fe II. The lines are due to transitions from highly excited levels, which are populated radiatively by the hydrogen Lyman alpha line due to accidental wavelength coincidences. Three energy levels, one in Cr II and two in Fe II, are reported.

Johansson, Sveneric↗
NASA NTRS1981

Pioneer 10 ultraviolet photometer observations of the interplanetary glow at heliocentric distances from 2 to 14 AU

An analysis is presented of the observed Pioneer 10 interplanetary data from 1972 to 1977, taking into account the interplanetary glow intensity observed by the Pioneer 10 UV photometer at sun-spacecraft distances of 2-14 AU. On the basis of the obtained data, it was determined that the background intensity for the 200-1400 A band pass of the photometer channel is about 40 + or - 10 R, and that the nearby interstellar density is 0.04 + or - 0.91 per ccm for hydrogen and about 0.01 + or - 0.002 per ccm for helium. Accordingly, the He/H number density is about 0.25 at large distances from the sun. The Pioneer 10 spacecraft is leaving the solar system in the downwind direction, while both Pioneer 11 and Voyager will leave in the upwind direction. The combined UV observations of the interplanetary glow will provide accurate results on the physical status of the inflowing interstellar gas and the variability of background radiation as well.

Wu, F. M.↗
NASA NTRS1972

Rocket observations of solar UV radiation during the eclipse of 7 March 1970.

Results of observations of the solar eclipse of Mar. 7, 1970, with photometers sensitive to narrow bands of radiation at Lyman-alpha (1216 A) and at 2600 A included in the payloads of four Nike Apache rockets flown before and during the eclipse. At the center of totality, the flux of Lyman-alpha from the solar corona is 0.15% of the flux from the unobscured sun. The flux at second contact is 0.64%; at third contact, two observations give 0.52 and 0.59%. The brightness of the chromosphere in Lyman-alpha decreases exponentially over the range from 5 to 30 arc-sec from the limb with a scale height of 3835 plus or minus 70 km. In addition to the coronal and chromospheric Lyman-alpha a diffuse source is found. This is restricted to within 20 deg of the earth's horizon and is nearly uniform in azimuth at 170 km, the flux is about 3% of that from the unobscured sun. The flux of Lyman-alpha during the eclipse is considered in relation to the observed variation in electron density. It is concluded that, in totality, the ionosphere near 80 km is not in equilibrium with the ionizing radiation and that the production rate for electrons is not negligible if the loss process is recombination; it is negligible if the loss process is attachment-like.

Smith, L. G.↗
NASA NTRS1982

High-energy observations of stellar flares - Comparison with the sun

This paper reviews recent observations of flaring activity on flare stars of the UV Ceti type, concentrating on X-ray and radio data in comparison with possible solar analogs. Although detailed differences exist, it is concluded that similar mechanisms may work for both cases. Extending the analogy, the hard X-ray and gamma ray fluxes expected from typical stellar flares are estimated. In the solar case, these radiations give information about accelerated particles in the flare region. Hard X-ray observations of stellar flares may be possible, eventually, but the predicted gamma-ray fluxes are prohibitively weak.

Hudson, H. S.↗
NASA NTRS2016

The Habitability of Proxima Centauri b: I. Irradiation, Rotation and Volatile Inventory From Formation to the Present

Proxima b is a planet with a minimum mass of 1.3 M(sub ⨁) orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass, active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet and show that the planet currently receives 30 times more extreme-UV radiation than Earth and 250 times more X-rays. We compute the time evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima b’s obliquity is likely null, and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and level of triaxiality. Next, we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity, we find that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EO(sub H)) before it reached the HZ 100–200 Myr after its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We conclude that Proxima b is a viable candidate habitable planet.

Proxima Cen↗
NASA NTRS2001

Constraints on Variability of Brightness and Surface Magnetism on Time Scales of Decades to Centuries in the Sun and Sun-Like Stars: A Source of Potential Terrestrial Climate Variability

These four points summarize our work to date. (1) Conciliation of solar and stellar photometric variability. Previous research by us and colleagues suggested that the Sun might at present be showing unusually low photometric variability compared to other sun-like stars. Those early results would question the suitability of the technique of using sun-like stars as proxies for solar irradiance change on time scales of decades to centuries. However, our results indicate the contrary: the Sun's observed short-term (seasonal) and longterm (year-to-year) brightness variations closely agree with observed brightness variations in stars of similar mass and age. (2) We have demonstrated an inverse correlation between the global temperature of the terrestrial lower troposphere, inferred from the NASA Microwave Sounding Unit (MSU) radiometers, and the total area of the Sun covered by coronal holes from January 1979 to present (up to May 2000). Variable fluxes of either solar charged particles or cosmic rays, or both, may influence the terrestrial tropospheric temperature. The geographical pattern of the correlation is consistent with our interpretation of an extra-terrestrial charged particle forcing. (3) Possible climate mechanism amplifying the impact of solar ultraviolet irradiance variations. The key points of our proposed climate hypersensitivity mechanism are: (a) The Sun is more variable in the UV (ultraviolet) than in the visible. However, the increased UV irradiance is mainly absorbed in the lower stratosphere/upper troposphere rather than at the surface. (b) Absorption in the stratosphere raises the temperature moderately around the vicinity of the tropopause, and tends to stabilize the atmosphere against vertical convective/diffusive transport, thus decreasing the flux of heat and moisture carried upward from surface. (c) The decrease in the upward convection of heat and moisture tends to raise the surface temperature because a drier upper atmosphere becomes less cloudy, which in turn allows more solar radiation to reach the Earth's surface. (4) Natural variability in an ocean-atmosphere climate model. We use a 14-region, 6-layer, global thermo-hydrodynamic ocean-atmosphere model to study natural climate variability. All the numerical experiments were performed with no change in the prescribed external boundary conditions (except for the seasonal cycle of the Sun's tilt angle). Therefore, the observed inter-annual variability is of an internal kind. The model results are helpful toward the understanding of the role of nonlinearity in climate change. We have demonstrated a range of possible climate behaviors using our newly developed ocean-atmosphere model. These include climate configurations with no interannual variability, with multi-year periodicities, with continuous chaos, or with chaotically occuring transitions between two discrete substrates. These possible modes of climate behavior are all possible for the real climate, as well as the model. We have shown that small temporary climate influences can trigger shifts both in the mean climate, and among these different types of behavior. Such shifts are not only theoretically plausible, as shown here and elsewhere; they are omnipresent in the climate record on time scales from several years to the age of the Earth. This has two apparently opposite implications for the possibility of anthropogenic global warming. First, any warming which might occur as a result of human influence would be only a fraction of the small-to-large unpredictable natural changes and changes which result from other external causes. On the other hand, small temporary influences such as human influence do have the potential of causing large permanent shifts in mean climate and interannual variability.

Baliunas, Sallie L.↗
NASA NTRS1977

Airborne measurements of solar and planetary near ultraviolet radiation during the NASA/ESA CV-900 spacelab simulation

Results from a comparative study of the feasibility of employing experiment operators on the space shuttle to acquire scientifically worthwhile data are presented. The experiments performed during these tests included spectral observations of the Sun and Venus in the near ultraviolet region. The solar measurements were analyzed to determine ozone abundance in the terrestrial atmosphere. Using a detailed spectral matching technique to compare airborne solar UV measurements with synthetic spectral profiles of sunlight, it is deduced that in winter the total atmospheric ozone abundance is about 0.33 atm/cm at midlatitudes in the northern hemisphere.

Sivjee, G. G.↗
NASA NTRS1981

Study of the response of stratospheric ozone to perturbations in the solar constant and solar UV flux

A one-dimensional radiative-convective photochemical model has been used to examine the response of stratospheric and total ozone to perturbations in the solar flux. The model considers a detailed chemical reaction mechanism; vertical transport is parameterized through eddy diffusion coefficients. The temperature profile is calculated using a radiative transfer model for both time-dependent and steady-state cases. Results are discussed for the following types of perturbations: a 5% increase in the solar UV flux in the wavelength range 175-300 nm, a 5% increase in the solar constant, and an annual 6.6% variation in the solar constant associated with the variation in the earth-sun distance.

Natarajan, M.↗
NASA NTRS1989

Coronagraph observations and analyses of the ultraviolet solar corona

The major activities on the Spartan Ultraviolet Coronal Spectrometer project include both scientific and experimental/technical efforts. In the scientific area, a detailed analysis of the previously reported Doppler dimming of HI Ly-alpha from the July 1982 rocket flight has determined an outflow velocity at 2 solar radii from sun center to be between 153 and 251 km/s at 67 percent confidence. The technical activities include, several improvements made to the instrument that will result in enhanced scientific performance or in regaining a capability that had deteriorated during the delay time in the launch date. These include testing and characterizing the detector for OVI radiation, characterizing a serrated occulter at UV and visible wavelengths, fabricating and testing telescope mirrors with improved edges, testing and evaluating a new array detector system, modifying the slit mask mechanism and installing a mask in the instrument to block the Ly-alpha resonance line when the electron scattered component is being observed.

Kohl, John L.↗
NASA NTRS1993

The solar spectral irradiances from x ray to radio wavelengths

Sources of new measurements of the solar EUV, UV, and visible spectrum are presented together with discussion of formation of the solar spectrum as a problem in stellar atmospheres. Agreement between the data and a modern synthetic spectrum shows that observed radiative variability is a minor perturbation on a photosphere in radiative equilibrium and local thermodynamic equilibrium (LTE). Newly observed solar variability in 1992 defines a magnetic episode on the Sun closely associated with changes in both spectral irradiances and the total irradiance. This episode offers the opportunity to track the relationship between radiation and magnetic flux evolution.

White, O. R.↗
NASA NTRS1981

Active regions from the photosphere to the chromosphere

The structures and physical conditions in that portion of a solar active region extending from the photosphere to the corona are considered. A horizontally averaged model of a solar plage is developed which is in reasonable agreement with observations, and significant discrepancies existing between quiet sun models and UV and IR spectra are noted which cast doubt on the reliability of such models. The nature of the flux tubes comprising the small-scale structure of the active regions is discussed, and the concept of filling factor is described as a basis for a flux tube model explaining changes in spectral properties. The effects of two-dimensional radiative transfer are examined for flux tubes of various cross-sectional size, and it is found that the neglect of explicit horizontal radiative interactions is a good approximation to the two-dimensional treatment. The radiative power loss from active regions is discussed for homogeneous and flux tube models, and a significant difference in total heating requirements is found. Finally, attention is given to the characteristics of the transition zone.

Chapman, G. A.↗
NASA NTRS1981

Theory of stellar coronae - An interpretation of X-ray emission from non-degenerate stellar sources

It is shown that the acoustic wave heating theory of stellar coronae explains neither Einstein Observatory coronae data nor previous UV and X-ray observations of the sun and other stars, on the evidence of data implying that magnetic fields, stellar rotation rates and convection zone parameters figure in the determination of coronal heating. Einstein Observatory results suggest that O-type star coronae are heated by the interaction of turbulent stellar winds with slowly-decaying primordial magnetic fields or by radiative instabilities in the flow. The apparent absence of coronae in Ap stars is due to the stability of atmospheres in which even weak convection is suppressed by the strong field. Dynamo action is implicated in some normal A-type stars and in F- and later-type dwarfs. Coronal characteristics of dMe and dM stars, close binaries, and K- and M-type giants are also considered.

Linsky, J. L.↗
NASA NTRS1992

In orbit degradation of UV optical components for the wavelength range 10-140 microns. AO 138.3 (FRECOPA)

Optical components (thin film filters and multilayered mirrors) for use in the wavelength range 10-140 micro-m were included in the vacuum tight container FRECOPA in preparation for the SOHO mission. They were exposed during 9 months at the beginning of the Long Duration Exposure Facility (LDEF) flight. One batch of components was exposed to the sun, while another one was shielded from solar radiation. The results of the optical transmission measurements of the flight components and of a groundbase reference set, made at the ORSAY Synchotron radiation light source are presented.

Delabouinere, J. P.↗
NASA NTRSDate not supplied

Use of TEMPO as a Proxy for Hyperspectral Geostationary Ocean Color Measurements from the GeoXO OCX Instrument: Harnessing Machine Learning and Principal Component Techniques for Atmospheric and Glint Correction

Retrievals of ocean color from space are important for better understanding the ocean ecosystem. The launch of atmospheric geostationary hyperspectral sensors such as TEMPO, provides a unique opportunity to examine the diurnal variability in ocean ecology. While TEMPO does not have as high spatial resolution or full spectral coverage as planned coastal ocean sensors such as the Geosynchronous Littoral Imaging and Monitoring Radiometer (GLIMR) or GeoXO Ocean Color instrument (OCX), its hourly measurements provide coverage of regions such as Lake Erie and the Gulf of Mexico at spatial scales of approximately 5 km. These data can be useful for testing new algorithms. We will apply our newly developed machine learning based atmospheric correction approach for ocean color retrievals to TEMPO data. Our approach begins by decomposing measured radiances from hyperspectral sensors into spectral features that describe the scattering and absorption of the atmosphere as well as the underlying surface reflectance. The coefficients of the principal components are then used to train a neural network to predict ocean color properties derived from collocated MODIS/VIIRS physically-based retrievals. This machine learning approach does not rely on radiative transfer modeling, and the use of MODIS/VIIRS data for training accounts for possible calibration b in hyperspectral data. Previously, we applied our approach using blue and UV wavelengths with the Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) to show that it can estimate ocean color properties in less-than-ideal conditions such as lightly to moderately clouded conditions as well as sun glint and thus improve the spatial coverage of ocean color measurements. TEMPO provides an opportunity to improve on this approach since it will provide collocated measurements at green and red wavelengths that were not available from OMI and TROPOMI and are important particularly for coastal waters. Additionally, our technique can be applied early in the mission and has potential to demonstrate the value of near real time ocean color products that are important for monitoring of harmful algae blooms and other oceanic phenomena.

Zachary Fasnacht↗
NASA NTRS1980

Astrophysics in the extreme ultraviolet

The current status of extreme ultraviolet (EUV) astrophysics is reviewed. Seven compact emitters of EUV radiation have been identified in the less than or equal to 5% of the sky surveyed randomly so far and the existence of a diffuse EUV background firmly established. The discussion will focus on the quality of astronomical information that can be gleaned from a combined X-ray, EUV, far UV and optical study of these objects and on the impact EUV observations of the sun and a large number of classes of compact objects will have on understanding the structure and evolution of evolved stars. The diffuse EUV background may be of even greater interest as it probably reveals the distribution of the hot coronal gas responsible for the interstellar OVI absorption and the source of heating and ionization of the interstellar medium.

Paresce, F.↗
NASA NTRS2010

Transparent Large Strain Thermoplastic Polyurethane Magneto-Active Nanocomposites

Smart adaptive materials are an important class of materials which can be used in space deployable structures, morphing wings, and structural air vehicle components where remote actuation can improve fuel efficiency. Adaptive materials can undergo deformation when exposed to external stimuli such as electric fields, thermal gradients, radiation (IR, UV, etc.), chemical and electrochemical actuation, and magnetic field. Large strain, controlled and repetitive actuation are important characteristics of smart adaptive materials. Polymer nanocomposites can be tailored as shape memory polymers and actuators. Magnetic actuation of polymer nanocomposites using a range of iron, iron cobalt, and iron manganese nanoparticles is presented. The iron-based nanoparticles were synthesized using the soft template (1) and Sun's (2) methods. The nanoparticles shape and size were examined using TEM. The crystalline structure and domain size were evaluated using WAXS. Surface modifications of the nanoparticles were performed to improve dispersion, and were characterized with IR and TGA. TPU nanocomposites exhibited actuation for approximately 2wt% nanoparticle loading in an applied magnetic field. Large deformation and fast recovery were observed. These nanocomposites represent a promising potential for new generation of smart materials.

Yoonessi, Mitra↗
NASA NTRS1979

Solar variability and terrestrial weather

The present review article indicates that the past four years have been very active in the field of sun-weather research in the U.S. Some quite specific questions which have arisen from recent research include the time variation of the VAL vs SB effect; the nature of the clear-air electric field; the relationship of the ionospheric potential to thunderstorm formation; and the constancy of the solar 'constant' both in terms of the total luminosity on the climatic time scale and for near UV radiation on the time scale of days to 11 years.

Scherrer, P. H.↗