SEARCH · Engineering Papers

Results for “sun”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34

All sources NASA NTRS DOE OSTI

NASA NTRS1980

On the apparent secular accelerations of the moon and the sun

The discussion of tidal friction in the earth-moon system given in successive editions of 'The Earth' by Jeffreys is shown to contain a serious dynamical error. When the treatment is corrected, it shows that the moment of inertia of the earth must be changing. The apparent secular accelerations of the moon and sun require a diminishing moment of inertia, and the rate is in agreement with the phase-change hypothesis for the nature of the core.

Lyttleton, R. A.↗

NASA NTRS1980

High-resolution Lyman-alpha filtergrams of the sun

The results of an experiment, conducted jointly by the Lockheed Palo Alto Research Laboratory and the Laboratoire de Physique Stellaire et Planetaire du CNRS, which investigated the transition-region plasma and the geometry of coronal active regions, in relation to models of the high-temperature layers, are presented. A Black Brant rocket was used to obtain 1-arc sec resolution L-alpha pictures of the sun, which revealed small scale features not seen previously at this wavelength, that delineate the geometry of the magnetic field in the chromosphere and in the corona. It is concluded that these observations might provide a new way of observing the upper chromosphere and corona, and that they provide direct evidence of the inhomogeneous character of the chromosphere and of the dominant role of the magnetic field

Bonnet, R. M.↗

NASA NTRS1980

Planetary wave coupling between the troposphere and the middle atmosphere as a possible sun-weather mechanism

The possibility of planetary wave coupling between the troposphere and solar-induced alterations in the upper atmosphere providing a viable mechanism for giving rise to sun-weather relationships is investigated. Some of the observational evidence for solar-activity-induced effects on levels of the upper atmosphere ranging from the thermosphere down to the lower stratosphere are reviewed. It is concluded that there is evidence for such effects extending down to the middle stratosphere and below. Evidence is also reviewed that these effects are due to changes in solar ultraviolet emission during disturbed solar conditions. A theoretical planetary wave model is then used to see at what levels in the upper atmosphere moderate changes in the mean zonal wind state would result in tropospheric changes. It is concluded that changes in the mean zonal flow of about 20% at levels in the vicinity of 35 km or below would give rise to changes in the tropospheric planetary wave pattern that are less than but on the same order as the observed interannual variability in the tropospheric wave pattern at middle and high latitudes.

Geller, M. A.↗

NASA NTRS1980

Design and performance of the International Sun-Earth Explorer power systems

The launches of the International Sun-Earth Explorers in October 1977 (ISEE-A) and August 1978 (ISEE-C) marked the first successful implementation of an electrostatically clean spacecraft design on a US-built satellite. The power subsystem design selected was required to operate without induced or coupled electromagnetic interference while meeting the criteria of low cost, low weight (with the resulting removal of almost all redundancy), modular construction techniques, long life (more than 3 years), and maximum utilization of previously qualified/flown designs. To save money, both the ISEE-A and -C power subsystem designs had to be identical even though the two missions are flown in vastly different orbits. Additionally, the requirement for a three year mission utilizing a single silver-cadmium battery had never been imposed before. A power subsystem configuration which met all of the specified requirements was developed. Excellent correlation between preflight and actual flight performance is demonstrated.

Obenschain, A. F.↗

NASA NTRS1980

Structural variability of the Sun

Changes in solar radius and luminosity are discussed as a function of age. Surface and satellite observations showing departures from mean solar irradiance on a time scale of a few days are summarized. The most prominent depressions in these data appear to be correlated with sunspot number, indicating that the activity modulation of solar luminosity may be larger than expected. High activity is correlated with low luminosity, but during the Maunder minimum the mini ice age (presumably low luminosity) was accompanied by a near absence of solar activity. Pulsations driven by sources deep within the Sun are thought to be an unlikely cause of luminosity changes, but causes may be sought in the unstable convective zone. Experiments designed to measure the solar radius are mentioned, along with modelling efforts.

Sofia, S.↗

NASA NTRS1980

A review of observational evidence for short and long term ultraviolet flux variability of the Sun

Observation of the Sun in the 160 to 400 nm wavelength region reveals no significant broadband variation with solar flares, variability associated with the rotation of active regions, and a possible long term change which may be related to the 11 year sunspot cycle or longer. A continuing ultraviolet solar flux variability below 200 nm was observed from 1969 through the present from satellites, which is modulated at solar rotation rates. Recent observations from Nimbus-7 show the solar flux is varying by significant amounts also in the regions from 200 nm up to the Calcium 2 H-line at 396.8 nm. Typically the flux may vary over a solar rotation from about 10 percent at 160 nm to slightly less than 1 percent at the Ca2 K-line. Results of an evaluation of observations from rockets, satellites, and the ground measurements are discussed.

Heath, D. F.↗

NASA NTRS1980

The collective excitation of g-modes in the sun

Oscillations of the solar interior (linear g-modes) may be strongly driven by the collective influence of all the modes upon the nuclear reactions in the core. This heretofore neglected effect could couple the modes, reduce the effective amplitudes near the center, and spatially concentrate most of the oscillation energy into just a portion of the radiative interior. If operating at sufficient strength, this can reverse the conventional conclusion, drawn from single mode calculations, that almost all solar g-modes are damped. Furthermore, it would put the theory into rough harmony with three otherwise troubling observations: (1) the 'low' neutrino flux measured by Davis (1978), (2) the high correspondence found by Wolff (1976) between recurrence periods in solar activity and the rotational beat periods of g-modes, and (3) the fluctuations in the sun's diameter which imply g-mode activity at high angular harmonics (Hill and Caudell 1979). A nonlinear expression is derived for the local rate of work done on an array of oscillation modes by the nuclear reactions. Three additional tests of the model are suggested.

Wolff, C. L.↗

NASA NTRS1980

Transient phenomena originating at the sun - An interplanetary view

Analyses of several transient phenomena which occurred in 1978 and 1979 are presented using data from the Pioneer Venus, ISEE, and Pioneer 10 and 11 spacecraft. The interplanetary phenomena studied are associated with solar flares and coronal holes. The observations show that phenomena originating at the sun affect the structure of the particle and field regimes throughout the explored solar system, extending out to at least 17-20 AU in the vicinity of the elliptic plane over a range of azimuthal angles greater than 90 deg. High frequency fluctuations in the interplanetary medium appear beyond 1 AU, indicating that transient phenomena are significantly modified by their passage through this medium.

Intriligator, D. S.↗

NASA NTRS1981

The influence of differential rotation on the equatorial component of the sun's magnetic dipole field

This paper examines the effect that solar differential rotation would have on a hypothetical large-scale equatorial dipole field. The evolving large-scale field pattern is expressed as a series of non-axisymmetric moments. As time increases, power is transferred to progressively higher order moments. In the 27d rotating coordinate system, each moment undergoes a small retrograde drift which remains nearly uniform until that mode begins to fade. The synodic rotation periods of the first few moments are comparable to the observed 28.5d period of the sun's large-scale field near sunspot maximum. Differential rotation may be the source of this 28.5d period, but the eruption of new flux is necessary to keep the pattern going.

Sheeley, N. R., Jr.↗

NASA NTRS1981

Ion propulsion for shared Shuttle, sun-synchronous missions

The configuration of an ion propulsion module (IPM) for use in the deployment and retrieval of sun-synchronous satellites on shared Shuttle flights is described. In addition to enabling shared Shuttle payloads requiring large orbital plane changes for achieving desired viewing conditions, the IPM makes over 10 kw available for payload power-sharing on orbit. The IPM also affords a large on-orbit propulsion capability. It has 2.8 x 10 to the 7th N-sec available at full propellant loading, of which less than half was needed for deploying and retrieving the representative spacecraft studied. Its remaining propulsion capability can be used for increasing payload or for additional propulsive functions on orbit.

Zafran, S.↗

NASA NTRS1981

The detection of mesogranulation on the sun

Time averages of velocity measurements at disk center on the quiet sun reveal the presence of a fairly stationary pattern of cellular flow with a spatial scale of 5-10 Mm. Such mesogranulation has a spatial rms vertical velocity amplitude of about 60 m/s superposed on the larger scale supergranular flows. The lifetimes of mesogranules appear to be at least 2 hr.

November, L. J.↗

NASA NTRS1981

The variability of the sun's ultraviolet radiation

Solar UV intensity variations determined by direct irradiance measurements and by measurements of the plage/quiet sun contrast are reviewed. Typical values for the solar UV variability over a solar cycle are: less than 1% at wavelengths longer than 2100 A, 8% at 2080 A (continuum), 20% at 1900 A (continuum), 70% at H Ly alpha, 200% in certain emission lines in the 1200-1800 A range, and more than a factor of 4 in coronal lines at less than 1000 A.

Brueckner, G. E.↗

NASA NTRS1981

Structure of the solar chromosphere. III - Models of the EUV brightness components of the quiet-sun

The described investigation is concerned with the solution of the non-LTE optically thick transfer equations for hydrogen, carbon, and other constituents to determine semiempirical models for six components of the quiet solar chromosphere. For a given temperature-height distribution, the solution is obtained of the equations of statistical equilibrium, radiative transfer for lines and continua, and hydrostatic equilibrium to find the ionization and excitation conditions for each atomic constituent. The emergent spectrum is calculated, and a trial and error approach is used to adjust the temperature distribution so that the emergent spectrum is in best agreement with the observed one. The relationship between semiempirical models determined in this way and theoretical models based on radiative equilibrium is discussed by Avrett (1977). Harvard Skylab EUV observations are used to determine models for a number of quiet-sun regions.

Vernazza, J. E.↗

NASA NTRS1980

Solar particle fluxes and the ancient sun

The implications of the statistical data on solar flare particle fluxes, for the present and the ancient sun, considering modern data from the past two solar cycles, C-14 data from the past 7000 years, and Al-26 and Mn-53 data in lunar samples for the last 10-million years are reviewed. All of these records suggest that there is a maximum proton fluence (greater than 10 MeV) from a solar flare on the order of 10 to the 10th p/sq cm, above which the size-frequency distribution steepens sharply. From this it is extremely unlikely that energetic particles from solar flares could have contributed to extinction catastrophes in the fossil record.

Lingenfelter, R. E.↗

NASA NTRS1980

Solar flare and galactic cosmic ray tracks in lunar samples and meteorites - What they tell us about the ancient sun

Evidence regarding the past activity of the sun in the form of nuclear particle tracks in lunar samples and meteorites produced by heavy ions in galactic cosmic rays and solar flares is reviewed. Observations of track-rich grains found in deep lunar cores and meteorite interiors are discussed which demonstrate the presence of solar flare activity for at least the past 4 billion years, and the similarity of track density profiles from various lunar and meteoritic samples with those in a glass filter from Surveyor 3 exposed at the lunar surface for almost three years is presented as evidence of the relative constancy of the solar flare energy spectrum over the same period. Indications of a heavy ion enrichment in solar flares are considered which are confirmed by recent satellite measurements, although difficult to quantify in lunar soil grains. Finally, it is argued that, despite previous claims, there exists as yet no conclusive evidence for either a higher solar activity during the early history of the moon or a change in galactic cosmic ray intensity, average composition or spectrum over the last 50 million years.

Crozaz, G.↗

NASA NTRS1981

The horizontal and vertical semi-diameters of the Sun observed at the Cape of Good Hope (1834 - 1887) and Paris (1837 - 1906): A report on work in progress

Cape and Paris meridian observations of the solar limbs which permit an estimate to be made of the solar semi-diameter were surveyed, sampled, and compared with Greenwich and U.S. Naval Observatory observations. Significant systematic errors were found in the Paris work and have been correlated with changes of instruments and observers. Results from the Cape series indicate that work should continue on the compilation of data from Cape observations of the Sun.

Smith, C.↗

NASA NTRS1981

Observations of large-scale motions of the Sun

Recent observations of large-scale mass motions on the Sun are discussed. The principal large-scale velocity flows are convection, rotation, meridional flow, and torsional and radial oscillations.

Labonte, B.↗

NASA NTRS1982

Documentation for the machine-readable version of the catalogue of stars within 25 parsecs of the Sun

The machine-readable version of the Catalogue of Stars within twenty-five parsecs of the Sun contains essentially all information given in Table Ia of the published catalog, plus positional data and all cross references to other catalog numbers given in Table IIa. Not included from Table Ia are the flags (asterisks appended to catalog numbers) indicating notes in the published catalog, nor are the notes in machine-readable form. Omitted from Table IIa are the finding chart identifiers (Lowell G numbers or notes reference) and miscellaneous cross identifications to other names and catalog identifiers. The machine-readable version of the subject catalog is currently available on magnetic tape from the Astronomical Data Center.

Warren, W. H., Jr.↗