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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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The establishment of a network of seismic stations on the lunar surface as a result of equipment installed by Apollo 12, 14, and 15 flights is described. Four major discoveries obtained by analyzing seismic data from the network are discussed. The use of the system to detect vibrations of the lunar surface and the use of the data to determine the internal structure, physical state, and tectonic activity of the moon are examined.
Description of a general method for inferring, from the line emission of an optically thin medium, the physical state of a gas along the column in a line of sight. The method is devised for applications to astronomy, especially for studies of the solar corona, the chromosphere-corona transition region, planetary nebulae, and other optically thin sources. A unique specification is found in terms of a bivariate distribution function describing the partitioning of matter in a gas over density and temperature. It is shown that, given sufficient observational data, it is in principle possible to determine both this bivariate distribution function and the chemical composition. The formulation for a situation encountered in the solar corona illustrates the application of the method.
An axisymmetric hydrodynamic model of the sun consisting of a core at radiant equilibrium and a convective envelope is studied with consideration of gravitational forces, rotation, turbulence effects, and electromagnetic forces. The dimensionless parameters that control the equations of plasma motion within the sun and the boundary conditions are investigated; estimates are given for these parameters on the basis of experimental data and the existing theoretical models. Stability conditions are derived for convective equilibrium, developed cellular convection, and developed turbulent convection with consideration of rotation and turbulent Reynolds stresses. These conditions characterize the possible physical state of the matter in the convective envelope. Using estimates of the dimensionless parameters and models of some of them, a method of successive approximations is proposed for solution of the problem as a whole.
The excitation of the interstellar gas is discussed in the light of recent evidence from gamma-ray, molecular, and 21-cm line observations. Previous studies of the excitation of the interstellar gas have not taken into account the substantial density contrast that exists between spiral arms and interarm regions. We examine the role played by the galactic distribution of three sources of excitation (supernovae, OB stars, and ultraviolet stars) in determining the physical state of the interstellar gas in arm and interarm regions.
Sounding-rocket and satellite UV observations of interstellar gas clouds are reviewed with major attention given to Copernicus observations of interstellar absorption lines. Analysis of typical absorption-line data is outlined, and observations are reviewed for atomic hydrogen as well as interstellar H2, HD, and CO molecules. Investigations of atomic abundances in H I regions are summarized, measurements of atomic deuterium abundances in the interstellar gas are examined, and the properties of ionized interstellar gas are described. Theoretical analyses of the physical state of the interstellar gas are summarized with respect to ionization by energetic radiation, cool H I clouds, and the intercloud medium. The data obtained thus far are shown to indicate mean temperatures of about 80 K, particle densities between 10 and 1000 per cu cm, and a depletion of heavy elements that becomes greatly enhanced with increasing condensation temperature for those H I regions with strong H2 lines.
The search for extraterrestrial life in the solar system is reviewed in the light of present knowledge about the physical state of the planets. Arguing that all life in the universe is based on carbon chemistry, the carbon abundance in the solar system is discussed along with the composition of the planets, the presence of organic compounds (particularly amino acids) in meteorites, and the existence of complex organic compounds in interstellar space. Prospects for life in the solar system are evaluated by eliminating most of the bodies as potential biological habitats on the basis of temperature and lack of an atmosphere. Bodies eliminated in this manner include the moon, most of the other satellites, Mercury, Venus, the asteroids, and the giant planets. It is shown that the outlook for life on Titan is uncertain, but that Mars fulfills the minimum conditions for a life-bearing planet. Theories on the Martian surface environment are reviewed, the problem of the lack of water on Mars is examined, and the possibility of climatic changes is considered. The Viking mission is briefly noted.
The possibility of utilizing Mars as a habitat for terrestrial life, including man, is examined. Available data, assumptions, and speculations on the climate, physical state, and chemical inventory of Mars are reviewed and compared with the known requirements and environmental limits of terrestrial life. No fundamental, insuperable limitation of the ability of Mars to support a terrestrial ecology is identified. The lack of an oxygen-containing atmosphere would prevent the unaided habitation of Mars by man. The present strong ultraviolet surface irradiation is an additional major barrier. The creation of an adequate oxygen and ozone-containing atmosphere on Mars may be feasible through the use of photosynthetic organisms. The time needed to generate such an atmosphere, however, might be several millions of years. This period might be drastically reduced by the synthesis of novel, Mars-adapted, oxygen producing photosynthetic strains by techniques of genetic engineering, and modifying the present Martian climate by melting of the Martian polar caps and concomitant advective and greenhouse heating effects.
Substantive mass loss resulting in appreciable circumstellar dust envelopes is common in late-type stars. The evolutionary history and physical state of a cool star determine the chemistry within the outer stellar atmosphere mirrored by the molecular and particulate material present in the envelope. The observational consequences of this debris determined by moderate spectral resolution infrared spectrophotometry are reviewed. Significant information is provided by observations of the emergent energy flux of both the cool stellar photosphere and of the circumstellar dust envelope. The observation suggests that mass-loss occurs to some degree throughout late stellar evolutionary phases and that occasional periods of high mass loss are not uncommon.
An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.
A broad survey is presented of our current knowledge of the Galilean satellites. Attention is given to the physical properties (size, masses, densities, and rotation) and to the surface properties (albedo, surface markings, composition, and physical state) of the satellites. In particular, Io's atmosphere is considered with emphasis on the sodium, hydrogen and sulfur clouds and the ionosphere. The atmospheres of the other satellites are examined briefly and consideration is given to models of planetary origin, evolution and interior structure.
Organic contamination of ultraviolet optical systems is discussed. Degradation of signal by reflection, scattering, interference, and absorption is shown. The first three processes depend on the physical state of the contaminant while absorption depends on its chemical structure. The latter phenomenon is isolated from the others by dissolving contaminants in cyclohexane and determining absorption spectra from 2100A to 3600A. A variety of materials representing the types of contaminants responsible for most spaceflight hardware problems is scanned and the spectra is presented. The effect of thickness is demonstrated for the most common contaminant, di(2 ethyl hexyl)phthalate, by scanning successive dilutions.
The Beta Cephei stars are a group of variables of spectral type B, whose light and radial velocity periods lie between about three and seven hours. An up-to-date summary of the observational data for individual stars considered to be members of the Beta Cephei group is provided. The general properties of Beta Cephei stars as determined from a comparison between theory and observation are considered, taking into account location in the HR diagram and evolutionary state, physical properties, statistics and galactic distribution, and period-luminosity relation and pulsation mode. Recent trends concerning the observation of Beta Cephei stars are examined, giving attention to a search for new variables, ultraviolet observations from spacecraft, and high-resolution studies of profile variations.
The present paper deals with some of the principal data on extraterrestrial atmospheres obtained during the period 1975-1978. The atmospheres of Venus, Mars, Jupiter, and the Jovian satellites are examined, showing that many first-order questions concerning composition, physical state, and kinematics of these atmospheres have been answered.
It is noted that the explanation of the origin of a magnetic field of Uranus is difficult because the structure of the planet's interior is not well known and the strong thermal flux, which is associated with the operation of hydromagnetic dynamos in Jupiter and Saturn, seems to be absent or very low. It is shown that the composition, physical state and electrical conductivity of the planet's core permits the generation of a magnetic field within the very low observational limits of its heat emission. Further, it is suggested that the higher density and higher pressures in the core of Neptune could explain the suspected absence of a measurable field on that planet even though it is a relatively strong source of heat.
The ullage compression ignition sensitivity of NOS-365 monopropellant under the pressure condition expected to be found in a medium caliber regenerative liquid propellant gun is evaluated. The results from the rapidly loaded propellant tests performed to date are presented. For this case, the physical state of the propellant is characterized by the presence of turbulence and a finely distributed ullage field. A description of the test fixtures, procedures and results is given. It is argued that the results to date indicate that with relatively simple precautionary measures NOS-365 can be rendered sufficiently immune to the ullage compression ignition mechanism to permit it to be safely used in a regenerative liquid propellant gun.
Eighteen high-dispersion IUE spectra of six stars in the Large Magellanic Cloud, three stars in the Small Magellanic Cloud, and two foreground stars were analyzed. Fourteen spectra cover the wavelengths 1150-2000 A, and four cover 1900-3200 A; the velocity resolution is about 25 km/s. All the Magellanic Cloud spectra exhibit very strong interstellar absorption lines due to a wide range of ionization stages at galactic velocities and at velocities associated with the IMC or SMC. The observational results are related to current theoretical ideas about the origin and physical state of gaseous galactic halos; the analysis is restricted to the Milky Way absorption features.
The detection of the optical emission /O I/ 6300 A (8 + or - 4 R) and /S III/ 6312 A (48 + or - 5 R) is reported. It is noted that these emissions are indicators of the ion source morphology and the plasma physical state and that the S III emitters have a kinetic temperature of approximately 10 to the 6th K. When combined with observations of UV lines from the same species, the optical measurements separately imply effective electron temperatures for radiative processes that are mutually consistent (approximately 50,000 K).
When observations of B stars made from space are added to observations made from the ground and the total body of observational information is confronted with theoretical expectations about B stars, it is clear that nonthermal phenomena occur in the atmospheres of B stars. The nature of these phenomena and what they imply about the physical state of a B star and how a B star evolves are examined using knowledge of the spectrum of a B star as a key to obtaining an understanding of what a B star is like. Three approaches to modeling stellar structure (atmospheres) are considered, the characteristic properties of a mantle, and B stars and evolution are discussed.