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At least 613 records · Page 34

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NASA NTRS1975

The background for Skylab experiment T-002, manual navigation sightings

The background of the NASA-DOD manual navigation experiment (T002) on Skylab A is reviewed with emphasis on NASA's development of an error model for sextant measurements in midcourse navigation and on USAF's development of a low earth orbit manual navigation scheme. Instruments briefly described are a space sextant and space stadimeter, both of which are used by USAF in orbit navigation, the sextant by NASA in midcourse sightings. The rationale, data requirements, and data reduction procedures are discussed in terms of the goals of the agencies.

Randle, R. J.↗

NASA NTRS1975

Interdisciplinary study of atmospheric processes and constituents of the mid-Atlantic coastal region. Attachment 5: Data set for background investigation of atmospheric constituents for Richmond, Virginia area

Background data is provided for the photochemical oxident problem in the Richmond area. Particulate data, digitized portrayal of site molecular and meteorological data, and graphical portrayal of molecular data, hourly meteorological data, and streamflow charts and radiosonde data are also given.

Kindle, E. C.↗

NASA NTRS1974

The effect of repeated Compton scatterings on the diffuse X-ray background

Recent Monte Carlo computations, based on a speculative extrapolation of the electron spectrum, suggested that repeated scatterings contribute most of the extragalactic X-ray background around 3 MeV in a Compton model. We have redone this calculation analytically with a similar electron spectrum, but with very different results. The double-scatter contribution near 3 MeV does not exceed 1 percent and cannot improve the fit to data. The effect is largest near 1 keV but will probably not be observable.

Felten, J. E.↗

NASA NTRS1974

Balloon-based measurements of the cosmic background radiation

A balloon-borne liquid-helium-cooled spectrometer was developed and flown to measure the cosmic background radiation in the 3- to 18-per-cm region. It features a cooled horn antenna, a polarizing Michelson interferometer, and a germanium bolometer. These design features and the performance of the instrument are discussed.

Mather, J. C.↗

NASA NTRS1975

Measurement of the spectrum of the submillimeter cosmic background

The spectrum of the night sky has been measured in the wave number range from 3 to 40 per cm using a fully calibrated liquid-helium-cooled balloon-borne spectrophotometer at an elevation of 39 km. A model based on the known molecular parameters was used to subtract the atmospheric emission. In the range from 4 to 17 per cm, the spectrum of the background radiation is that of a blackbody with a temperature of about 2.99 K.

Woody, D. P.↗

NASA NTRS1975

Interpretation of various radiation backgrounds observed in the gamma-ray spectrometer experiments carried on the Apollo missions and implications for diffuse gamma-ray measurements

Since the report of a preliminary analysis of cosmic gamma-ray measurements made during the Apollo 15 mission, an improved calculation of the spallation activation contribution has been made including the effects of short-lived spallation fragments, which can extend the correction to 15 MeV. In addition, a difference between Apollo 15 and 16 data enables an electron bremsstrahlung contribution to be calculated. A high level of activation observed in a crystal returned on Apollo 17 indicates a background contribution from secondary neutrons. These calculations and observations enable an improved extraction of spurious components and suggest important improvements for future detectors.

Dyer, C. S.↗

NASA NTRS1975

Interpretation of the radioactive background observed in the OSO-7 gamma-ray monitor

Application of a spallation activation calculation to the OSO-7 gamma-ray monitor background shows that major line features and about 30% of the continuum can be understood as activation of the central detector crystal by trapped protons. Weaker line features arise from activation of materials unshielded by the anticoincidence cup, while the remaining continuum and annihilation line would seem to come largely from electron-photon cascades originating in the spacecraft.

Dyer, C. S.↗

NASA NTRS1976

Ionising flux of cosmic background radiation

The indirect method of estimating the diffuse metagalactic flux of ionizing radiation proposed by Sunyaev (1969) is reconsidered in the light of further studies of the interaction of this radiation with galactic gas. An upper limit is derived for the intensity of the metagalactic background radiation to which the neutral interstellar medium is exposed. This limit on the ionizing radiation flux severely restricts the emission from a galactic corona containing gas in the temperature range 100,000 to 1,000,000 K. An upper limit of 10 to the 29.2 erg/sec/Hz is obtained for the mean luminosity radiated by a quasar in the energy band 40-170 eV. The 21-cm observations examined indicate that further than about 30 kpc from the center of the galaxy self-shielding by H II is possible only when the critical metagalactic ionizing flux is not exceeded.

Silk, J.↗

NASA NTRS1976

Effects of background gravity stimuli on gravity-controlled behavior

Physiological and developmental effects of altered gravity were researched. The stimulus properties of gravity have been found to possess reinforcing and aversive properties. Experimental approaches taken, used animals placed into fields of artificial gravity, in the form of parabolic or spiral centrifuges. Gravity preferences were noted and it was concluded that the psychophysics of gravity and background factors which support these behaviors should be further explored.

Mccoy, D. F.↗

NASA NTRS1977

Three-band observations of the soft X-ray background and some implications of thermal emission models

The galactic component of the very soft diffuse X-ray background in three bands, covering the energy ranges of approximately 100 to 188 eV, 150 to 284 eV, and 500 to 850 eV, is mapped primarily at middle and low galactic latitudes. Intense regions on the maps are identified, and the dissimilarity of the three maps is shown to indicate spectral as well as intensity variations over the sky. Three emission-mechanism models involving hot gas at a single temperature are examined, a multitemperature model is found to be required, and several such models based on hot gas in a steady state or in equilibrium are considered. The problem of overpressure raised by Shapiro and Field (1976) is briefly discussed.

Burstein, P.↗

NASA NTRS1977

Spectrum and isotropy of the submillimeter background radiation

Infrared evidence referable to the spectrum and isotropy of the background radiation of the universe is considered, along with theoretical implications. Difficulties in the submillimeter region are indicated. Two types of anisotropy are treated: small-scale granularity (attributable to discrete sources such as galaxies or to condensation in the primordial plasma) and large-scale anisotropies; the anisotropies are discussed as possible indicators of the early history of the universe, and in relation to future possible generalized Michelson-Morley experiments (to detect effects on local physics of the existence of a universal rest frame). A complete blackbody spectrum is seen as the clear signature of the primordial fireball, and slight deviations from a perfect thermal spectrum (or perfect isotropy) are to be sought and scrutinized.

Muehlner, D.↗

NASA NTRS1978

Low-background trace-gas detector

Spectrophone detects very small concentrations of trace gases. With gas in sample cell, laser is tuned to absorption line of interest. Molecular absorption in cell produces pulsed acoustical pressure at chopper frequency. Two optical paths with very different absorption lengths are used to pretune cell to balance out background absorption by cell windows.

Rosengren, L.↗

NASA NTRS1978

Effect of facility background gases on internal erosion of the 30-cm Hg ion thruster

Sputtering erosion of the upstream side of the molybdenum screen grid by discharge chamber ions in mercury bombardment thrusters was considered. Data which revealed that the screen grid erosion was very sensitive to the partial pressure of certain background gases in the space simulation vacuum facility were presented along with results of tests conducted to evaluate this effect. It is shown from estimates of the screen grid erosion in space that adequate lifetime for proposed missions exists.

Rawlin, V. K.↗

NASA NTRS1978

Compton scattering of microwave background radiation by gas in galaxy clusters

Based on data on the X-ray spectrum of the Coma cluster, interpreted as thermal bremsstrahlung, the expected brightness depletion from Compton scattering of the microwave background in the direction of the cluster is computed. The calculated depletion is about one-third that recently observed by Gull and Northover, and the discrepancy is discussed. In comparing the observed microwave depletion in the direction of other clusters which are X-ray sources it is found that there is no correlation with the cluster X-ray luminosity. Consequently, the microwave depletion observations cannot yet be taken as good evidence for a thermal bremsstrahlung origin for the X-ray emission. The perturbation from Compton scattering of photons on the high-frequency (Wien) tail of the blackbody distribution is computed and found to be much larger than predicted in previous calculations. In the Wien tail the effect is a relative increase in the blackbody intensity that is appreciably greater in magnitude than the depletion in the Rayleigh-Jeans domain.

Gould, R. J.↗

NASA NTRS1978

Effect of facility background gases on internal erosion of the 30-cm Hg ion thruster

One life limiting phenomenon of mercury bombardment thrusters is sputtering erosion of the upstream side of the molybdenum screen grid by discharge chamber ions. Data were obtained which revealed that the screen grid erosion was very sensitive to the partial pressure of certain background gases in the space simulation vacuum facility. The results of tests conducted to evaluate this effect are presented. An estimate of the screen grid erosion in space was made which showed that adequate lifetime for proposed missions exists.

Rawlin, V. K.↗

NASA NTRS1978

Effects of the inhomogeneous background on radiation propagating through turbulent planetary atmospheres

Weak scattering, wave optics results are given for the first-order log-amplitude and phase, and for the second-order phase and angle of arrival, of radiation propagating through a turbulent planetary atmosphere. The analytical results include the effects of coupling to the inhomogeneous background upon which the turbulence is superimposed. Such coupling significantly affects signal characteristics in stellar and spacecraft occultation experiments, in contrast to situations involving much shorter paths, as in terrestrial propagation experiments.

Haugstad, B. S.↗

NASA NTRS1977

The correction of Landsat data for the effects of haze, sun angle, and background reflectance

A technique has been developed for simulating the effects of haze, sun angle, and background reflectance in Landsat data and correcting for them. The atmospheric model assumes a two-layer atmosphere: a Rayleigh scattering molecular layer and a Mie scattering haze layer next to the earth's surface. Reflection and transmission matrices describe the reflection and transmission properties of the plane parallel scattering layers. The multispectral scanner response is computed for various values of the parameters under evaluation. This yields expressions for Landsat gray-scale levels used for determining the effect of changes in any parameter. The Atmospheric Correction computer program is used to determine the haze level from the data, to compute the reflectance, and to interpolate in order to find the correction coefficients necessary to make the desired correction.

Potter, J. F.↗

NASA NTRS1978

Assessment study of infrared detector arrays for low-background astronomical research

The current state-of-the-art of infrared detector arrays employing charge coupled devices (CCD) or charge injection devices (CID) readout are assessed. The applicability, limitations and potentials of such arrays under the low-background astronomical observing conditions of interest for SIRFT (Shuttle Infrared Telescope Facility) are determined. The following are reviewed: (1) monolithic extrinsic arrays; (2) monolithic intrinsic arrays; (3) charge injection devices; and (4) hybrid arrays.

Ando, K. J.↗