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  • 1
    Publication Date: 2013-08-31
    Description: We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 7-8
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  • 2
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: Results of a 2-yr (1988-90) investigation of cometary activity in 2060 Chiron based on CCD photometry and spectroscopy are reported. The photometry observations include a new rotational light curve of Chiron, a newly refined rotation period, recent developments of its long-term photometric behavior and surface brightness profiles, a deep image of the coma of Chiron, and narrowband images at wavelengths ranging from 3200 to 6840 A. The spectroscopic data include moderate resolution CCD spectra (10-20 A FWHM). Major results include the detection of impulsive brightening on a time scale of hours, evidence for a secular change in the blue portion of the reflectivity spectrum of the nucleus, no evidence for Rayleigh scattering in the near ultraviolet, and an upper limit of the column density of CO(+) ions in the coma.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 100; 913-932
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  • 3
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    Publication Date: 2011-08-19
    Description: The redshifts and colors of nearly 10,000 galaxies at galactic latitudes SA57 and SA68 were determined by photometric scans which included UV and near-IR bands, covering 0.5 sq deg of sky. Slopes were calculated for UV, IR, red and blue counts of galaxies with respect to the brightness detected. It was found that galaxies of magnitudes over 20 show increasingly greater UV excess, which may be indicative of star formation regions. Future applications of the data generated for examining galaxy clustering patterns and evolutionary scenarios are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 311; 651-679
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  • 4
    Publication Date: 2019-06-28
    Description: This paper presents an analytical and experimental evaluation of an enhanced techniques for no-vent fill. The method entails injecting liquid through the top of the receiver vessel, thereby increasing surface area and agitation of the ullage/liquid interface. Both of these factors promote condensation induced ullage collapse, and reduce compressive impedance to the incoming liquid. The enhanced process was analyzed by modifying the surface area algorithm of an existing tank thermodynamic code to model a downward-pointing, conical jet impringing on a steadily rising liquid surface. Transient pressure and temperature measurements from several tests with Freon-114 were input into the revised model to calculate condensation rate as a function of fill level. By expressing these rates in dimensionless form (i.e., in terms of Stanton number and Prandtl number), an empirical correlation similar to the submerged jet model of Brown and Sonin (1989) was derived. This provided a basis for developing an expression which relates top fill to bottom fill performance.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-1842
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  • 5
    Publication Date: 2019-06-28
    Description: Numerical simulation of the structure and evolution of interstellar clouds was conducted. Steps were taken toward an integrated treatment of the dynamical, thermal, and chemical processes entering model calculations, and a detailed study was made of radiative transfer in molecular lines to allow model predictions to be tested against empirical data. It is shown that the shapes of molecular lines are sensitive to details of the cloud structure and evolutionary state and are thus useful in inferring the cloud density, temperature, chemical composition, age, and initial conditions. The calculations have successfully reproduced and explained several observed cloud properties, including abundances of complex molecular species and the apparent depletion of CO in dense cores.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-180933 , NAS 1.26:180933
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  • 6
    Publication Date: 2017-10-02
    Description: The growing emphasis on very challenging missions and the anticipated availability of high power levels in space have led to renewed interest in high power electric propulsion. The status of high power electric propulsion technology and its applicability to various missions are reviewed. The major thruster and system technology issues are identified which must be addressed in a focussed program in order to assure technology readiness for these missions.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: New Mexico Univ., Transactions of the Fifth Symposium on Space Nuclear Power Systems; p 337-340
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  • 7
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    Publication Date: 2019-06-28
    Description: The Lewis Research Center conducts an electric propulsion program aimed at a broad class of space missions. The program is structured in an evolutionary fashion in order to both maximize expectations for the acceptance of developed concepts and accommodate anticipated developments of critical system technologies. Recent efforts have assisted in the acceptance of low power electric rockets. Primary electric propulsion concepts are also being developed for both Solar Electric Propulsion Systems and Nuclear Electric Propulsion Systems class space missions, and the paper briefly describes the concepts under evaluation for potential Space Exploration Initiative missions.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-3443
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  • 8
    Publication Date: 2019-06-28
    Description: The redesign of the joints on the solid rocket motor (SRM) has prompted the need for analyzing the behavior of the joints using several different types of analyses. The types of analyses performed include modal analysis, static analysis, transient response analysis, and base driving response analysis. The forces used in these analyses to drive the mathematical model include SRM internal chamber pressure, nozzle blowout and side forces, shuttle vehicle lift-off dynamics, SRM pressure transient rise curve, gimbal forces and moments, actuator gimbal loads, and vertical and radial bolt preloads. The math model represented the SRM from the aft base tangent point (1,823.95 in) all the way back to the nozzle, where a simplified, tuned nozzle model was attached. The new design used the radial bolts as an additional feature to reduce the gap opening at the aft dome/nozzle fixed housing interface.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA-TM-100373 , NAS 1.15:100373
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  • 9
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    Publication Date: 2019-06-28
    Description: The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.
    Keywords: ASTROPHYSICS
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  • 10
    Publication Date: 2019-07-13
    Description: In 1984, the market for commercial geosynchronous communications satellites (comsats) was expanding and there was strong competition between spacecraft builders for market share. The propellant required for the north-south stationkeeping (NSSK) function was a major mission limiter, and the small chemical and resistojet systems then in use were at or near their physical limits. Thus, conditions were right for the development of a high performance NSSK system, and after an extensive survey of both propulsion technologies and the aerospace community, the NASA program chose hydrazine arcjets for development. A joint government/industry development program ensued which culminated in the acceptance of arcjet technology. NASA efforts included fundamental feasibility assessments, hardware development and verification, and multiple efforts aimed at the demonstration of critical operational characteristics of arcjet systems. Throughout the program, constant contact with the user community was maintained to determine system requirements. Both contracted and cooperative programs with industry were supported. First generation, kW-class arcjets are now operational for NSSK on the Telstar 401 satellite launched in December of 1993 and are baselined for use on multiple future satellite series (Intelsat 8, AsiaSat, Echostar). Arcjet development efforts are now focusing on the development of both high performance (600 s), 2 kW thrusters for application on next generation comsats and low power (Pe approximately 0.5 kW) for a variety of applications on power limited satellites. This paper presents a review of the NASA's role in the development of hydrazine arcjets with a focus on approaches, lessons learned, and the future.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA-TM-106695 , E-9053 , NAS 1.15:106695 , AIAA PAPER 94-2463 , Plasmadynamics and Lasers Conference; Jun 20, 1994 - Jun 23, 1994; Colorado Springs, CO; United States
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