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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Suppression of background noise in a transonic wind-tunnel test section

Some exploratory tests were recently performed in the transonic test section of the NASA Marshall Space Flight Center 14-in. wind tunnel to suppress the background noise. In these tests, the perforated walls of the test section were covered with fine wire screens. The screens eliminated the edge tones generated by the holes in the perforated walls and significantly reduced the tunnel background noise. The tunnel noise levels were reduced to such a degree by this simple modification at Mach numbers 0.75, 0.9, 1.1, 1.2, and 1.46 that the fluctuating pressure levels of a turbulent boundary layer could be measured on a 5-deg half-angle cone.

Schutzenhofer, L. A.↗
NASA NTRS1976

The cosmic far-infrared background at high galactic latitudes

Far-infrared background fluxes from various cosmic sources are predicted. These fluxes lie near the high frequency side of the blackbody radiation spectrum. These sources could account for a significant fraction of the background radiation at frequencies above 400 GHz which might be misinterpreted as a comptonization distortion of the blackbody radiation. Particular attention is paid to the possible contributions from external galaxies, rich clusters of galaxies and from galactic dust emission.

Stecker, F. W.↗
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 NTRS1977

Interpretation of observed cosmic microwave background radiation

It is argued that the 'surface of last scattering' of the observed microwave background radiation corresponds to the distribution of dust in galaxies or protogalaxies with a temperature of about 110 K at the epoch corresponding to Z roughly equal to 40. This is in contrast with the plasma temperature of over 3,000 K at an earlier epoch (Z greater than about 1,000), as given by the canonical model of big bang cosmologies. In view of this, the claim that the microwave background radiation lends strong support to hot big bang cosmologies is without foundation.

Alfven, H.↗
NASA NTRS1977

The cosmic far-infrared background at high galactic latitudes

Far-infrared background fluxes from various cosmic sources are predicted. These fluxes lie near the high-frequency side of the blackbody radiation spectrum. The sources could account for a significant fraction of the background radiation at frequencies above 400 GHz, which might be misinterpreted as a 'Comptonization' distortion of the blackbody radiation. Particular attention is paid to the possible contributions from external galaxies, from rich clusters of galaxies, and from galactic dust emission.

Stecker, F. W.↗
NASA NTRS1978

Background of a shielded Ge(Li) spectrometer at balloon altitudes

The background data obtained from an actively shielded Ge(Li) spectrometer flown on a balloon were analyzed and a preliminary model was developed to explain background features including the intensity and time profile of line emission. These features can be explained by a combination of secondary radiation originating in the CsI shield and atmospheric secondary radiation leaking through it.

Mahoney, W. A.↗
NASA NTRS1977

Primeval gas clouds and the low-energy X-ray background

A model for the appearance of the all-sky low-energy X-ray background on a fine angular scale is presented which is based on primeval hot gas clouds associated with the formation of clusters of galaxies according to the Sunyaev-Zel'dovich (1972) model. It is noted that the background could have both granular and diffuse components if it is due to such gas clouds. The observed appearance of the granular component is predicted along with the observable characteristics of collapsing protoclusters. The effects of distant X-ray-emitting QSOs, radio galaxies, and normal galaxies on the observations are considered, and these sources are shown not to interfere with the possibility of observing the protoclusters. It is concluded that if sufficient heating occurred in an intracluster medium within some clusters of galaxies at the protocluster epoch, the ensemble properties of protoclusters could be observed with an X-ray telescope, and the time at which protoclusters formed could perhaps be estimated.

Kellogg, E. M.↗
NASA NTRS1977

A study of the background corona near solar minimum

Equatorial and polar K and F coronal components during the declining phase of the solar cycle are studied through use of the white light coronagraph data obtained by Skylab. At this phase of the solar cycle, streams and holes dominate the equatorial corona (approximately 50 and 30% of the time, respectively) between 2.5 and 5.5 solar radii; however, two episodes are noted when equatorial background density of the corona could be distinguished. The derived background density is less than 15% below values predicted by the models of Newkirk (1967) and Saito (1970). The brightness of the F-corona is also discussed.

Saito, K.↗
NASA NTRS1978

Some problems with the interpretation of recent microwave background observations in the direction of galaxy clusters, or, beware of negative antenna temperatures

Recently reported observations of the 3-K microwave background in the direction of rich clusters of galaxies should be viewed as placing stringent limits on the mass of cooler ionized gas within the clusters, rather than as a verification of thermal bremsstrahlung models for cluster X-ray sources. At the high radio frequencies employed in the observations, there is a positive contribution to the observed source-brightness distributions from free-free emission by any cooler gas. This can overwhelm the anticipated inverse Compton diminution of the background radiation, even when the total mass in cooler gas is significantly less than the mass of hot plasma required to explain the X-ray source. Future experiments of this type should be conducted only when atmospheric stability is sufficient to permit lengthy drift scans across the clusters. Extreme care must be taken to remove the contributions from any discrete sources.

Tarter, j. C.↗
NASA NTRS1978

Radiometer system to map the cosmic background radiation

A 33-GHz airborne radiometer system has been developed to map large angular scale variations in the temperature of the 3 K cosmic background radiation. A ferrite circulator switches a room-temperature mixer between two antennas pointing 60 deg apart in the sky. In 40 min of observing, the radiometer can measure the anisotropy of the microwave background with an accuracy of plus or minus 1 mK rms, or about 1 part in 3000 of 3 K. The apparatus is flown in a U-2 jet to 20 km altitude where 33-GHz thermal microwave emission from the atmosphere is at a low level. A second radiometer, tuned to 54 GHz near oxygen emission lines, monitors spurious signals from residual atmospheric radiation. The antennas, which have an extremely low side-lobe response of less than -65 dB past 60 deg, reject anisotropic radiation from the earth's surface. Periodic interchange of the antenna positions and reversal of the aircraft's flight direction cancel equipment-based imbalances. The system has been operated successfully in U-2 aircraft flown from NASA-Ames at Moffett Field, Calif.

Gorenstein, M. V.↗
NASA NTRS1978

Energetic secondary electrons and the nonthermal galactic radio background - A probe of the magnetic field in interstellar clouds

A previous analysis of the manifestations of charged-pion-decay secondary electrons in interstellar cloud material is extended to include those contributions to the Galactic radio and soft gamma-ray backgrounds that are directly attributable to energetic secondaries. The equilibrium distribution of secondary electrons in dense interstellar clouds is calculated, synchrotron emissivity from isolated interstellar clouds is examined, and it is shown how the value of the magnetic field in these clouds may be determined by observing the radio emission in their directions. The contribution that such clouds make to the integrated radio background is evaluated, and the Galactic distribution of bremsstrahlung gamma rays that arise from interactions of secondary electrons with thermal material in dense clouds is computed. The results indicate that a magnetic field of no more than 80 microgauss is characteristic of dense clouds and that the integrated synchrotron radiation from secondary electrons in interstellar clouds will contribute a significant fraction of the nonthermal brightness along the Galactic equator even if the mean cloud field is as low as 35 microgauss.

Marscher, A. P.↗
NASA NTRS1977

Infrared and millimeter wave techniques for the Cosmic Background Explorer Satellite

The Cosmic Background Explorer Satellite will employ infrared and microwave techniques to gain information about the very early universe. Three instruments will cover the spectral range from 8 microns to 13 mm, determining both the spectrum and angular distribution of the large scale background radiation fields. A cryogenic polarizing Michelson interferometric spectrometer will measure the spectrum of the 3 deg K relic radiation from the big bang with precision. Four differential microwave radiometers will map the sky from 23 to 90 GHz in a search for anisotropy of the universe. A broadband cryogenic IR photometer will map zodiacal dust emission, galactic dust, and an extragalactic residual component.

Mather, J. C.↗
NASA NTRS1978

The fluctuating and isotropic components of the cosmic X-ray background

Spatial fluctuations in the surface brightness of the extragalactic hard X-ray sky that are characteristic of distant unresolved discrete sources as well as the possible clumpiness of a hot universal plasma are being studied with the HEAO-1 A-2 experiment. The energy spectrum for this fluctuating component is directly compared to that of the isotropic background. The spectra of identified extragalactic objects recently obtained with experiments aboard both OSO-8 and HEAO-1 are used for examining the contribution of such sources to this fluctuating component of the background.

Boldt, E.↗
NASA NTRS1979

Fluctuations in microwave background radiation due to secondary ionization of the intergalactic gas in the universe

Secondary heating and ionization of the intergalactic gas at redshifts z approximately 10-30 could lead to the large optical depth of the Universe for Thomson scattering and could smooth the primordial fluctuations formed at z approximately 1500. It is shown that the gas motions connected with the large scale density perturbations at z approximately 10-15 must lead to the generation of secondary fluctuations of microwave background. The contribution of the rich clusters of galaxies and young galaxies to the fluctuations of microwave background is also estimated.

Sunyayev, R. A.↗
NASA NTRS1978

Monitoring of particulate contamination and background brightness from IECM based instrumentation

Of particular concern to the astronomical community is the effect of Shuttle Transportation System induced contamination in the form of individual particles and general background on astronomical experiments. In an effort to investigate this problem, two camera/photometers in the Induced Environment Contamination Monitor (IECM) will be used to determine the size and velocity distribution of contaminant particles, their origin, and the extent of sunlit background brightness resulting from spacecraft contamination. The cameras will operate synchronously as a stereo pair to make continuous photographic measurements throughout the missions.

Clifton, K. S.↗
NASA NTRS1978

Low background focal plane array testing in the far infrared

A new long-wavelength infrared test facility is being developed to conduct proof-of-performance tests of focal plane arrays for the Infrared Astronomical Satellite (IRAS) telescope. This facility is believed to be unique in that it will calibrate full-sized arrays designed for the 5-120-micron region of the IR spectrum under simulated spaceflight conditions and at background levels as low as 8 million photons/sq cm-sec. Most of the tests will be performed in a main test chamber which contains a liquid helium shroud, blackbody sources, an arrangement to simulate zodiacal background, and spot scanning optics. A noncontaminating high-vacuum pumping system will be used to evacuate the chamber prior to cool-down to prevent molecular deposition. All housekeeping and focal plane signal outputs are multiplexed, digitized, and transmitted on high-speed data lines to a PDP-11/70 computer. The computer provides real-time displays on a color CRT terminal and stores data for subsequent reduction and hard copy output. An overview of the conceptual design and performance specifications of the test facility are given.

Iufer, E. J.↗
NASA NTRS1979

Tests of low background photo conductors

In support of two infrared astronomy space projects, the IRAS satellite and the IRT on Spacelab 2, low-background tests were carried out on the performance and characterization of Si:Ga, Si:As, Si:Sb and Ge:Ga photoconductive detectors. These test results represent a useful appraisal of this family of detectors when operated at 1.8-4.2 K and at background power levels of 10 to the -14th to 10 to the -13th W. In addition to detector performance data, results are also presented on cryogenically cooled MOSFET amplifiers operated in the source follower and in the balanced-dc-TIA configurations.

Young, E. T.↗
NASA NTRS1979

Detecting a gravitational-radiation background using spacecraft Doppler tracking

The sensitivity of NASA's Deep Space Network spacecraft tracking system to an isotropic cosmological background of gravitational radiation is analyzed. It is found that by using the autocovariance function of the Doppler record in the so-called 'three-way' tracking mode to dig into the noise it is possible to put significant limits on this background with current and future planned deep-space missions.

Hellings, R. W.↗