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At least 343 records · Page 19

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NASA NTRS1987

Prospective EUV observations of hot DA white dwarfs with the EUV Explorer

The Extreme Ultraviolet Explorer (EUVE) will perform a high sensitivity EUV all-sky survey. A major category of sources which will be detected with the EUVE instruments consists of hot white dwarfs. Detailed preliminary studies of synthetic EUV observations of white dwarfs have been carried out using the predicted EUVE instrumental response functions. Using available information regarding space densities of white dwarfs and the distribution of neutral hydrogen in the interstellar medium, the numbers of DA white dwarfs which will be detectable in the different EUV bandpasses have been estimated.

Finley, David S.↗

NASA NTRS1988

Prospects for exploring the local galaxies through the study of their high-energy gamma-ray emission

In the near future, high-energy (E greater than 20 MeV) gamma-ray astronomy offers the promise of a new means of examining the closest galaxies. Three local galaxies, the SMCs, LMCs, and M31, should be visible to the high-energy gamma-ray telescope on the Gamma Ray Observatory and the first two should be seen by GAMMA-1. It is expected that the intensity and the structure of both of the Magellanic Clouds can be examined in sufficient detail to study the cosmic-ray density and its variation, and, thereby, to determine the relevant scale of coupling for the cosmic rays and diffuse matter. With the assumptions of adequate sources and reasonable magnetic field strengths, both of which should likely be satisfied, very specific predictions of the gamma-ray emission can be made separating the three current cosmic-ray containment concepts, namely that it is on the scale of one to a few kiloparsec mass clustering, the whole galaxy, or some much larger scale. Further, because of the markedly different distributions of molecular and atomic hydrogen in the galaxies and the differences between the galaxies, an independent measure of the normalization of the diffuse molecular hydrogen density is possible.

Ozel, Mehmet E.↗

NASA NTRS1988

Prospects for solar flare X-ray polarimetry

A review of the literature indicates that no experimental evidence has yet been found for solar flare X-ray polarimetry. A satellite instrument is described that has sufficient sensitivity at high energies to detect the predicted solar flare polarization. It is shown that the instrument sensitivity for a moderate event approaches polarization levels of 1 percent in each of seven energy bins spanning the 10-100 keV range for integration times as short as 10 s.

Chanan, Gary↗

NASA NTRS1989

Prospects for a contamination-free ultravacuum facility in low-earth orbit

The old concept of using the wake of a spacecraft to obtain an ultrahigh vacuum is revisited. A wakeshield can be configured so that a surface of interest does not subtend any walls that could become contaminated, thus it should be possible to achieve a contamination-free, ultrahigh vacuum capability with infinite pumping speed even in the presence of high heat loads and moderate gas loads. This papar analyzes the conceptual design for a Space Ultravacuum Research Facility (SURF), both in a shuttle-attached mode and as a free flyer. It is shown that even in the shuttle-attached mode, it should be possible to obtain vacuum levels equivalent to 10 to the -9th to 10 to the -10th Torr with O and N2 as the primary constituents. As a free flyer the SURF will be limited primarily by the gas load from the process being performed. For chemical beam epitaxy it is shown that equivalent vacuum levels of 10 to the -14th Torr should be possible at 300 km.

Naumann, Robert J.↗

NASA NTRS1989

Laminar flow - The past, present, and prospects

Flight research conducted on natural laminar flow (NLF) is discussed. Emphasis is on recent flight testing conducted by the National Aeronautics and Space Administration. To place these flight experiences in perspective, important flight tests from the early days of natural laminar flow research are first reviewed to recall the lessons learned at that time. Then, based on more recent flight experiences and analyses with state-of-the-art boundary layer stability theory, speculation is made on the possibility of extensive NLF on swept wing transport aircraft.

Wagner, R. D.↗

NASA NTRS1988

Summary and future prospects

The 'known' properties of interstellar dust are reviewed. Silicates are present because of the 9.7-micron feature in both circumstellar and interstellar dust. The near-infrared emission bands (3.3-11.4 microns, with continuum extending to longer wavelengths) strongly suggest that aromatic materials of some kind are present. A variety of considerations suggest that large graphite grains are probably absent, but smaller graphite particles are probably the most viable explanation for the 2175 A 'bump'. Considerations mentioned at this meeting regarding several properties of grains are then discussed: the UV continuum, the 2175 A 'bump', and various grain theories.

Mathis, J. S.↗

NASA NTRS1990

Studies of compact objects with Einstein - Review and prospects

X-ray images and spectra of a wide range of systems containing compact objects were obtained with the Einstein X-ray Observatory. Accreting white dwarfs, neutron stars and black holes were observed in binary systems in the Galaxy, and new constraints were derived for their formation, nature and evolution. Massive black holes were studied in active galactic nuclei, and X-ray spectra (and evolution) of AGN have led to a new model for the diffuse X-ray background.

Grindlay, Jonathan E.↗

NASA NTRS1990

Uranus photochemistry and prospects for Voyager 2 at Neptune

CH4 is the only photochemically active constituent in the atmospheres of Uranus and Neptune. NH3, H2O and H2S are all removed by condensation at pressures greater than 1.5 bars. Although the bulk mole fraction (about 2 percent) of CH4 is 20-30 times its solar value on both planets, it drops to its saturation limit (about 0.0001) at the Uranus tropopause, but remains high (about 2 percent) at the Neptune tropopause. This results in much greater mixing ratios of the product hydrocarbons in the stratosphere of Neptune. On both planets, the photolysis products of CH4 undergo condensation near the tropopause and the upper stratosphere. Voyager observations of the hydrocarbons at Uranus and those planned at Neptune are discussed, along with their implications for upper-atmospheric physics and thermochemistry.

Atreya, S. K.↗

NASA NTRS1989

Cloud parameterization for climate modeling - Status and prospects

The current status of cloud parameterization research is reviewed. It is emphasized that the upper tropospheric stratiform clouds associated with deep convection are both physically important and poorly parameterized in current models. Emerging parameterizations are described in general terms, with emphasis on prognostic cloud water and fractional cloudiness, and how these relate to the problem just mentioned.

Randall, David A.↗

NASA NTRS1989

Future prospects for space life sciences from a NASA perspective

Plans for future NASA research programs in the life sciences are reviewed. Consideration is given to international cooperation in space life science research, the NASA approach to funding life science research, and research opportunities using the Space Shuttle, the Space Station, and Biological Satellites. Several specific programs are described, including the Centrifuge Project to provide a controlled acceleration environment for microgravity studies, the Rhesus Project to conduct biomedical research using rhesus monkeys, and the LifeSat international biosatellite project. Also, the Space Biology Initiative to design and develop life sciences laboratory facilities for the Space Shuttle and the Space Station and the Extended Duration Crew Operations program to study crew adaptation needs are discussed.

White, Ronald J.↗

NASA NTRS1990

Measuring tropospheric HNO3 - Problems and prospects for Nylon filter and mist chamber techniques

A series of laboratory and field measurements was performed to evaluate the mist chamber technique for determining tropospheric HNO3 concentrations. Both the mist chamber and standard Nylon filter techniques exhibit high collection efficiency and excellent agreement measuring HNO3 vapors from a permeation source. When simultaneously sampling ambient air in eastern Virginia, the Nylon filter measured an average of 70 percent higher HNO3 concentration than the mist chamber technique. The results indicate that O3 causes a low-level positive artifact interference in HNO3 measurements performed with the filter technique. This O3-induced error is small, however, compared to the large difference between atmospheric HNO3 concentrations determined with the two techniques. It is hypothesized that unidentified (organic?) nitrogen species in the atmosphere react for form NO3(-) on the filter and this phenomenon may interfere with Nylon filter measurements of HNO3 vapor. These potential interferences did not appear to affect measurements of HNO3 with the mist chamber method.

Talbot, R. W.↗

NASA NTRS1990

Astronomical observations with normal incidence multilayer optics - Recent results and future prospects

High-resolution X-ray and EUV images of the solar corona have been obtained with two rocket-borne normal incidence Cassegrain multilayer telescopes. The Cassegrain images correspond to material at about 10 to the 6th K and about 80,000 K. Other images, at somewhat lower resolution, were obtained with Herschelian multilayer telescopes and Wolter-Schwarzschild hybrid grazing incidence/multilayer optical systems. The Cassegrain and Herschelian images are discussed emphasizing the analysis of polar plumes observed at the limb of the sun. The application of specific multilayer techniques to astronomical observations is discussed, emphasizing observations of the sun. Current efforts to develop a comprehensive Multi-Spectral Solar Telescope Array rocket instrument for the study of a wide variety of problems related to the solar atmosphere are reported.

Walker, Arthur B. C., Jr.↗

NASA NTRS1990

Prospects for using carbon-carbon composites for EMI shielding

Since pyrolyzed carbon has a higher electrical conductivity than most polymers, carbon-carbon composites would be expected to have higher electromagnetic interference (EMI) shielding ability than polymeric resin composites. A rule of mixtures model of composite conductivity was used to calculate the effect on EMI shielding of substituting a pyrolyzed carbon matrix for a polymeric matrix. It was found that the improvements were small, no more than about 2 percent for the lowest conductivity fibers (ex-rayon) and less than 0.2 percent for the highest conductivity fibers (vapor grown carbon fibers). The structure of the rule of mixtures is such that the matrix conductivity would only be important in those cases where it is much higher than the fiber conductivity, as in metal matrix composites.

Gaier, James R.↗

NASA NTRS1990

The national- and international-wide prospects of future improvements of position location and time synchronization systems and aids

The concept being designed by the Leningrad Scientific Research Radio Technical Institute (LSRRI) of united positioning and timing service on the basis of the utilization of long-range and global radionavigation and common time systems and aids for different users is described. The estimate of its utilization on the national as well as on international scale is given.

Gouzhva, Yuri G.↗

NASA NTRS1991

Technical prospects for utilizing extraterrestrial propellants for space exploration

NASA's LeRC has supported several efforts to understand how lunar and Martian produced propellants can be used to their best advantage for space exploration propulsion. A discussion of these efforts and their results is presented. A Manned Mars Mission Analysis Study identified that a more thorough technology base for propellant production is required before the the net economic benefits of in situ propellants can be determined. Evaluation of the materials available on the moon indicated metal/oxygen combinations are the most promising lunar propellants. A hazard analysis determined that several lunar metal/LOX monopropellants could be safely worked with in small quantities, and a characterization study was initiated to determine the physical and chemical properties of potential lunar monopropellant formulations. A bipropellant metal/oxygen subscale test engine which utilizes pneumatic injection of powdered metal is being pursued as an alternative to the monopropellant systems. The technology for utilizing carbon monoxide/oxygen, a potential Martian propellant, was studied in subscale ignition and rocket performance experiments.

Linne, Diane L.↗

NASA NTRS1990

Cloning crops in a CELSS via tissue culture: Prospects and problems

Micropropagation is currently used to clone fruits, nuts, and vegetables and involves controlling the outgrowth in vitro of basal, axillary, or adventitious buds. Following clonal multiplication, shoots are divided and rooted. This process has greatly reduced space and energy requirements in greenhouses and field nurseries and has increased multiplication rates by greater than 20 fold for some vegetatively propagated crops and breeding lines. Cereal and legume crops can also be cloned by tissue culture through somatic embryogenesis. Somatic embryos can be used to produce 'synthetic seed', which can tolerate desiccation and germinate upon rehydration. Synthetic seed of hybrid wheat, rice, soybean and other crops could be produced in a controlled ecological life support system. Thus, yield advantages of hybreds over inbreds (10 to 20 percent) could be exploited without having to provide additional facilities and energy for parental-line and hybrid seed nurseries.

Carman, John G.↗

NASA NTRS1990

Astrophysical fractals - An overview and prospects

Different astrophysical circumstances under which fractal structures have been identified so far, or are likely to be identified in the future, are reviewed. The observed fractals can be classified into 2 main groups: (1) fractal configurations in space-time, materializing as fractals defined over the time axis at a given position in space, or over the physical configuration space at a fixed instant in time; and (2) fractals in parameter spaces. The theoretical interpretation of the origin of the spatial fractal geometry of the most conspicuous 'irregular' astronomical bodies is still wanting in the context of standard continuum models. In contrast, the less conventional discrete models (cellular automata) naturally produce such spatially fractal structures.

Perdang, J.↗

NASA NTRS1990

Prospects for drag prediction using computational fluid dynamics

An account is given of CFD methods deemed likely to yield aerodynamic drag prediction improvements. Improvements in drag prediction are noted to largely proceed from improvements in viscous-layer resolution. Geometric modeling and grid generation are acknowledged to be major pacing items, and may be more important than turbulence modeling. The use of upwind differencing has led to improved solution accuracy due to the nature of the artificial viscosity in cases involving shocks and nonphysical dissipation across viscous layers. Multiblock algorithms will allow more complex geometries to be treated.

Roberts, Thomas W.↗