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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 73 records · Page 4
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NASA NTRS1976

Three-dimensional structure of the extended solar magnetic field and the sunspot cycle variation in cosmic ray intensity

A principal cause for the eleven-year sunspot cycle variation in the primary cosmic ray intensity observed at earth may be a variation in the solid angle of the heliosphere occupied by the extended solar polar magnetic field. Galactic cosmic rays have relatively easy access to the inner solar system through the regular extended solar polar fields, and relatively difficult access through the irregular extended solar sector structure fields.

Svalgaard, L.↗
NASA NTRS1975

A balloon-borne Ge/Li/ spectrometer for gamma-ray astronomy

On June 10, 1974, a new high-resolution gamma ray spectrometer operating in the energy range of 0.05 to 10 MeV was successfully balloon-flight tested. This system uses four 40 cu cm Ge(Li) crystals in a single cryostat as prime sensors. A 6.35 cm thick CsI (Na) shield provides background rejection and collimation, defining a solid angle of 0.095 sr. Cooling is provided by a liquid-nitrogen dewar. The system was highly stable with spectral resolution of better than 2.5 keV at 1 MeV for the flight duration. The background total count rate was about 20 counts/sec. Numerous lines were observed, most of which originated from secondary neutron interactions in the spectrometer. The sensitivity of the system to line emissions originating in cosmic point sources is 0.0001 to 0.001 photons per sq cm s over the energy range.

Jacobson, A. S.↗
NASA NTRS1976

Recent advances in birefringent filters

In the past several years, important developments have been made in the construction and theory of birefringent filters. Tunable filters that operate from 4500 to 7000 A with full widths at half maximum of 0.05 A and maximum transmissions of almost 20 percent have been constructed. Inexpensive large-aperture (at least 15 cm) achromatic waveplates have been fabricated which allow full use of resolution-solid angle products that are 100 times that of Fabry-Perots and 10,000 times that of grating systems.

Title, A. M.↗
NASA NTRS1977

The angular distribution of auroral kilometric radiation

A study based on data from Hawkeye 1, Imp 6 and Imp 8 satellites has shown that the intense kilometric radio emissions generated over the nightside auroral regions are beamed into a cone-shaped region whose axis of symmetry is tilted away from the magnetic axis of the earth, toward evenings, by about 20 deg. The solid angle of this emission cone increases systematically with increasing frequency, varying from about 1.1 sr at 56.2 kHz to about 3.5 sr at 178 kHz.

Green, J. L.↗
NASA NTRS1977

Structure of the iron fluorescence line in X-ray binaries

The paper presents an approximate solution to the iron K alpha line transfer problem in a stellar atmosphere illuminated by an external X-ray source as in a binary X-ray system. The emergent Comptonized line profile can independently yield information on the abundance of heavy elements in the primary atmosphere and on the solid angle subtended by the primary at the X-ray source.

Hatchett, S.↗
NASA NTRS1978

Theory of flux anisotropies in a guiding center plasma

The one particle distribution function f on the scale of the bounce motion of particles in a magnetic field B is considered. The Vlasov equation is expanded through O(epsilon) in the adiabatic parameter which is the ratio of particle gyroradius to scale length of the magnetic field. Because f is directly proportional to particle flux differential in kinetic energy and solid angle, f is in principle measurable in space experiments, and the analysis is tailored to be explicitly applicable to space problems. To O(1), f is gyrotropic; its first velocity moment is (if non-vanishing) parallel to B, and hence macroscopic parallel flow is included in this term. The O(epsilon) contribution is non-gyrotropic and macroscopic flow parallel to B plus additional parallel flow results from these terms. The degree of non-gyrotropy and the amount of cross-field macroscopic flow depend on the perpendicular component of the electric field, on curvature and shear in the magnetic field, and on the spatial gradient, pitch angle derivative, and speed derivative of the lowest order distribution function.

Birmingham, T. J.↗
NASA NTRS1978

Design and performance of a modularized NaI/Tl/ detector /The Crystal Ball prototype/

A prototype NaI(Tl) detector (the Cluster of 54) of spherical geometry subtending a solid angle of 7.5% of 4pi at its center, has recently been assembled and tested. This detector consists of 54 close-packed but optically isolated NaI(Tl) modules and the associated electronic circuitry. The Cluster of 54 is the predecessor of an almost complete spherical detector, the Crystal Ball, which will cover 94% of 4pi. The latter detector is now under construction and is especially designed for the study of gamma-rays produced in electron-positron collisions at colliding beam facilities. This article outlines the mechanical, optical, and electronic assembly of the prototype system.

Chan, Y.↗
NASA NTRS1978

Spectral irradiance standard for the ultraviolet - The deuterium lamp

A set of deuterium lamps is calibrated as spectral irradiance standards in the 200-350-nm spectral region utilizing both a high accuracy tungsten spectral irradiance standard and a newly developed argon mini-arc spectral radiance standard. The method which enables a transfer from a spectral radiance to a spectral irradiance standard is described. The following characteristics of the deuterium lamp irradiance standard are determined: sensitivity to alignment; dependence on input power and solid angle; reproducibility; and stability. The absolute spectral radiance is also measured in the 167-330-nm region. Based upon these measurements, values of the spectral irradiance below 200 nm are obtained through extrapolation.

Saunders, R. D.↗
NASA NTRS1978

Quadrispherical LEPEDEAS for ISEE's-1 and -2 plasma measurements

A new generation of spaceflight instrumentation for comprehensive measurements of plasmas within the earth's magnetosphere and its environs is described. These quadrispherical low energy proton and electron differential energy analyzers (LEPEDEAS) for the ISEE's-1 and -2 spacecraft are capable of determining the directional intensities of positive ions and electrons over all but 2 percent of the 4 pi sr solid angle for charged-particle velocity vectors at the spacecraft positions. The energy range of this instrumentation is E/Q of 1 eV to 45 keV with good energy and angular resolutions. An example of inflight observations within the earth's magnetosheath is presented.

Frank, L. A.↗
NASA NTRS1978

Radiative cooling in shock-heated hydrogen-helium plasmas

Axial and off-axis radiative cooling of cylindrical shock-heated hydrogen-helium plasmas is investigated theoretically and experimentally. The coupled fluid dynamic-radiative transfer equations are solved by a combination of approximation techniques aimed at simplifying the computation of the flux divergence term, namely, the quasi-isothermal approximation and the exponential approximation developed for the solid angle integration. The accuracy of the approximation schemes has been assessed and found acceptable for applying the methods to the rapid computation of the radiatively coupled flow problem. Radiative cooling experiments were conducted in a 6-inch annular arc accelerator shock tube (ANAA) for an initial pressure of 1 torr and shock speeds from 35 to 45 Km/sec. The results indicate that the lateral cooling is small compared with the axial cooling, and that better agreement is achieved between the data and the theoretical results by inclusion of the lateral temperature gradient.

Poon, P. T. Y.↗
NASA NTRS1978

A new concept for solar pumped lasers

A new approach is proposed in which an intermediate body heated by sunlight is used as the pumping source for IR systems, i.e., concentration solar radiation is absorbed and reradiated via an intermediate blackbody. This body is heated by focused sunlight to a high temperature and its heat losses are engineered to be small. The cooled laser tube (or tubes) is placed within the cavity and is pumped by it. The advantage is that the radiation spectrum is like a blackbody at the intermediate temperature and the laser medium selectively absorbs this light. Focusing requirements, heat losses, and absorption bandwidths of laser media are examined, along with energy balance and potential efficiency. The results indicate that for lasers pumped through an IR absorption spectrum, the use of an intermediate blackbody offers substantial and important advantages. The loss in radiative intensity for optical pumping by a lower-temperature body is partly compensated by the increased solid angle of exposure to the radiative environment.

Christiansen, W. H.↗
NASA NTRS1978

Directional models for analysis of earth radiation budget measurements

The determination of the radiation heat flux densities at the top of the atmosphere (30 km) for spatial scales ranging from global to regional is necessary for the conversion of satellite irradiance measurements into useful earth radiation budget information. Data reduction algorithms are required which contain assumed directional characteristics of radiation emitted and scattered from the earth-atmosphere system. The directional characteristics are defined by models which express, for a given surface element at the top of the atmosphere, the exiting flux per unit solid angle for each direction out to space as a fraction of the total hemispheric flux exiting the surface element. Both longwave and shortwave directional radiation models are analyzed. It is found that the validity of the Nimbus 2-based limb darkening curves has generally been verified for the longwave data with the exception of the Antarctic snow fields where limb brightening was noticed in the earth radiation budget data.

Suttles, J. T.↗
NASA NTRS1979

Theory of flux anisotropies in a guiding center plasma

Assuming time stationarity of the one-particle distribution function f on the scale of the bounce motion of particles in a magnetic field, the paper expands the Vlasov equation through O(epsilon) in the adiabatic parameter epsilon, which is the ratio of particle gyroradius to scale length of the magnetic field. Since f is directly proportional to particle flux differential in kinetic energy and solid angle, f is in principle measurable in space experiments, and the present analysis is tailored to be explicitly applicable to space problems. It is shown that the usual expression for the electric field which produces plasma corotation in an axisymmetric system such as a dipole also holds for any nonaxisymmetric but rigidly rotating magnetic field pattern, provided the observed magnetic field is used in place of the dipole field. The analysis is applied to the electric field in a rigidly corotating magnetosphere.

Birmingham, T. J.↗
NASA NTRS1979

Radiative transfer in spherical dust shells using a generalized two-stream Eddington approximation

Application of a generalized two-stream Eddington approximation to the problem of radiative transfer in extended, spherically symmetric dust shells is presented. It is assumed that the radiation field can be characterized by the mean intensity, the flux, and a positionally dependent direction cosine specifying the division into two solid-angle ranges. The direction cosine is not specified a priori and is a function of the geometry, opacity, and emissivity in the dust shell. A multiple-grain-size multiple-temperature-distribution dust shell is postulated in which isotropic and anisotropic scattering as well as absorption and thermal reemission are allowed. A program has been developed that solves for the multiple temperature distributions by applying the constraint of radiative equilibrium to each grain size, and then calculates emergent fluxes. Results of one such calculation are presented for a model dust shell having a maximum optical depth (approximately 41) in the visible, clearly showing large optical extinction and a moderate infrared excess.

Haisch, B. M.↗
NASA NTRS1979

Auroral kilometric radiation - Time-averaged source location

In the present paper, the location of the average generation region of auroral kilometric radiation is determined from an analysis of average electric field strengths as a function of spacecraft position in narrow frequency bands centered at 178, 100, and 56.2 kHz. Intense sources of power radiating at kilometric wavelengths are found near 65 degrees invariant latitude in the Northern and Southern Hemispheres, from 22 to 24 hours MLT, and between 2 and 4 earth radii. These dominant sources of power produce the electromagnetic radiation described by Kurth et al. (1975) as auroral kilometric radiation. Each Northern and Southern Hemisphere auroral kilometric radiation source is well confined and emits radiation into solid angles of about 4.1 sr at 178 kHz, 2.2 sr at 100 kHz, and 1.5 sr at 56.2 kHz.

Gallagher, D. L.↗
NASA NTRS1980

The appearance of dusty H II blisters at radio and infrared wavelengths

Detailed calculations for the observational appearance of nonspherical Stromgren regions at radio and infrared wavelengths are presented. The computations are made feasible by two assumptions, namely (1) no stellar photon leaves the solid angle within which it was emitted, and (2) the radiation spectrum can be represented by three delta functions corresponding to Lyman continuum, Lyman alpha, and softer radiation. These calculations are used to develop models for the H II blisters M17 A and 30 Doradus, and also first order parameters for a sample of other well-studied galactic H II regions. It is concluded that the observations are well explained by an ionizing object in a density gradient, without the need for peculiar dust properties or distribution.

Icke, V.↗
NASA NTRS1979

Optical analysis of Cassegrainian concentrator systems

Cone optics procedures have been developed to treat optical systems employing multiple reflectors. The objective of the procedures is to develop efficient techniques to treat multiple reflections of cones when the secondary reflecting surface is curved - in fact, curved differently in different directions. The particular optical system under consideration is the Cassegrainian Concentrator System - a system consisting of a paraboloidal primary reflector and a confocal hyperboloidal secondary reflector. Multiple reflection cone optics methodology as well as preliminary results for the flux distributions and intercept factors based on it are presented in this paper. It is shown that neglecting local curvature effects of the secondary reflector, i.e. even in the differential solid angle within the sun's cone, may overestimate the peak of the flux distribution at the receiver aperture by a factor of two or more.

Bass, A. H., Jr.↗
NASA NTRS1980

The effect of a nonuniform planetary albedo on the interpretation of earth radiation budget observations

The flux density measured at satellite altitude with a fixed field of view radiometer differs from the true flux density reflected by the earth-atmosphere system within the field of view of the radiometer. This difference is due to angular response characteristics of the radiometer, solid angle effects due to geometry, and angular reflectance effects of the earth-atmosphere system. All of these effects lead to uncertainties in the interpretation of instantaneous earth radiation budget measurements. The differences between the true flux density and the measured flux density are shown to be significant when the field of view of the radiometer is large and when the atmosphere has a nonuniform, or spatially dependent, reflectance (albedo). A simulation experiment is described whereby the scene within the field of view of a nadir looking sensor is divided into a large number of equal area elements, each of which reflects radiation with one of two different reflectance models (corresponding to cloud-free and cloudy areas). The conditional mean values of the measured flux density, given values of the true flux density, are shown to differ significantly from the conditional means of the inverse problem, that of finding the mean value of the true flux density given a value for the measured flux density. The differences between the true flux density and the measured flux density are examined as a function of satellite altitude, field of view of the radiometer and solar zenith angle (including the effects of a terminator within the field of view) for both Lambertian and non-Lambertian reflectance models.

King, M. D.↗