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  • Maps  (1)
  • Other Sources  (4,210)
  • 1990-1994  (2,358)
  • 1975-1979  (1,853)
  • 1991  (2,358)
  • 1977  (1,853)
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  • 1990-1994  (2,358)
  • 1975-1979  (1,853)
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  • 1
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    An unusually strong Einstein ring in the radio source PKS1830 - 211 (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: High-resolution radio images of PKS1830 - 211 are obtained to study the possibility that the double structure is a gravitationally lensed object. The VLBI observations, taken from interferometric radiotelescope networks, reveal an elliptical ring that connects two bright spots of similar composition. Because the lens and the lensed object are closely aligned, and because of the structure of the two spots, the source is concluded to be a radio Einstein ring. The source is found to be close to the galactic plane, and the lens and the lensed object are extragalactic. The source is also found to be unusually bright, suggesting that it is aligned with a bright background source or amplified by some mechanism related to a source that is not so bright.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 352; 132-134
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Measurements of the reaction e/+/e/-/ yielding gamma-gamma at center-of-mass energies in the range 6.2-7.4 GeV (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The cross section for the pair-annihilation reaction e(+)e(-) yields gamma-gamma were measured at center-of-mass energies in the range 6.2-7.4 GeV and at production angles close to 90 deg. The experimental apparatus consisted of two identical spectrometers which were set to view the luminous region at SPEAR-II from opposite directions at an azimuthal angle of 45 deg. In each spectrometer there was a NaI(TI) crystal 20 radiation lengths thick and 30 in. in diameter to measure the gamma-ray energies. Annihilation events were detected by an electronic trigger which required only the observation in coincidence of more than 0.2 GeV in each NaI(TI) crystal within + or - 15 nsec of the crossing beams. The observed rates of pair-annihilation events were found to be in agreement with those expected from quantum electrodynamics (QED) at all the center-of-mass energies used.
    Keywords: NUCLEAR AND HIGH-ENERGY PHYSICS
    Type: Physical Review D - Particles and Fields; vol. 15
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Broadband observations of PS conversions from the upper mantle in Eurasia (1991)
    In:  Geophys. J. Int., Houston, Akademie-Verlag, vol. 105, no. 1-2, pp. 801-804, pp. L08310, (ISSN: 1340-4202)
    Details
    Publication Date: 1991
    Keywords: Seismology ; ConvolutionR ; Earth model, also for more shallow analyses ! ; Broad-band ; Body waves ; earth mantle ; Plesinger ; Horalek ; GJI
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Ka-band MMIC array feed development for deep space applications (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Ka-band MMIC transmitter arrays are under development at NASA Jet Propulsion Laboratory for future deep space and ground communication needs. A high efficiency full aperture active antenna array is desired to demonstrate solid state array technology for future NASA missions. This paper reports on a 5 watt Ka-band phased array feed and a full aperture active array for a mobile terminal which are being developed to characterize the design tradeoffs and potential of solid state Ka-band MMIC array communication systems.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Monolithic microwave integrated circuits for sensors, radar, and communications systems; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991 (A93-25776 09-33); p. 243-247.
    Format: text
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  • 5
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    Performance of all-metal demountable cryogenic seals at superfluid helium temperatures (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Two all-metal demountable cryogenic seals with an outside diameter of 36.6 mm, inside diameter of 27.2 mm and thickness of 0.51 mm were leak-tested at room temperature (300 K), liquid nitrogen temperature (21 cycles at 77 K), liquid helium temperature (nine cycles at 4.2K) and superfluid helium temperature (four cycles at 1.6 K). Each seal was mounted and demounted for 13 cycles. Thickness measurements at 90 deg intervals along the circumference showed a maximum seal compression of 0.038 mm. Leak rate measurements at all temperatures showed no detectable leak above the helium background level, typically 0.1 x 10 exp -9 std cu cm/s, during testing.
    Keywords: MECHANICAL ENGINEERING
    Type: Cryogenics (ISSN 0011-2275); 31; 993-995
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Autonomous docking ground demonstration (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Autonomous Docking Ground Demonstration is an evaluation of the laser sensor system to support the docking phase (12 ft to contact) when operated in conjunction with the guidance, navigation, and control (GN&C) software. The docking mechanism being used was developed for the Apollo/Soyuz Test Program. This demonstration will be conducted using the 6-DOF Dynamic Test System (DTS). The DTS simulates the Space Station Freedom as the stationary or target vehicle and the Orbiter as the active or chase vehicle. For this demonstration, the laser sensor will be mounted on the target vehicle and the retroflectors will be on the chase vehicle. This arrangement was chosen to prevent potential damage to the laser. The laser sensor system, GN&C, and 6-DOF DTS will be operated closed-loop. Initial conditions to simulate vehicle misalignments, translational and rotational, will be introduced within the constraints of the systems involved.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA, Washington, NASA Automated Rendezvous and Capture Review. Executive Summary; p 21-22
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Autonomous docking ground demonstration (category 3) (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The NASA Johnson Space Center (JSC) is involved in the development of an autonomous docking ground demonstration. The demonstration combines the technologies, expertise and facilities of the JSC Tracking and Communications Division (EE), Structures and Mechanics Division (ES), and the Navigation, Guidance and Control Division (EG) and their supporting contractors. The autonomous docking ground demonstration is an evaluation of the capabilities of the laser sensor system to support the docking phase (12ft to contact) when operated in conjunction with the Guidance, Navigation and Control Software. The docking mechanism being used was developed for the Apollo Soyuz Test Program. This demonstration will be conducted using the Six-Degrees of Freedom (6-DOF) Dynamic Test System (DTS). The DTS environment simulates the Space Station Freedom as the stationary or target vehicle and the Orbiter as the active or chase vehicle. For this demonstration the laser sensor will be mounted on the target vehicle and the retroreflectors on the chase vehicle. This arrangement was used to prevent potential damage to the laser. The sensor system. GN&C and 6-DOF DTS will be operated closed-loop. Initial condition to simulate vehicle misalignments, translational and rotational, will be introduced within the constraints of the systems involved. Detailed description of each of the demonstration components (e.g., Sensor System, GN&C, 6-DOF DTS and supporting computer configuration) including their capabilities and limitations will be discussed. A demonstration architecture drawing and photographs of the test configuration will be presented.
    Keywords: ASTRODYNAMICS
    Type: NASA, Washington, NASA Automated Rendezvous and Capture Review. A Compilation of the Abstracts; 2 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Space Shuttle Program: Automatic rendezvous, proximity operations, and capture (category 3) (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The NASA Johnson Space Center is actively pursuing the development and demonstration of capabilities for automatic rendezvous, proximity operations, and capture (AR&C) using the Space Shuttle as the active vehicle. This activity combines the technologies, expertise, tools, and facilities of the JSC Tracking and Communications Division (EE), Navigation, Control and Aeronautics Division (EG), Automation and Robotics Division (ER), and Structures and Mechanics Division (ES) of the Engineering Directorate and the Flight Design and Dynamics Division (DM) of the Mission Operations Directorate. Potential benefits of AR&C include more efficient and repeatable rendezvous, proximity operations, and capture operations; reduced impacts on the target vehicles (e.g., Orbiter RCS plume loads); reduced flight crew work loads; reduced ground support requirements; and reduced operational constraints. This paper documents the current JSC capabilities/tools/facilities for AR&C and describes a proposed plan for a progression of ground demonstrations and flight tests and demonstrations of AR&C capabilities. This plan involves the maturing of existing technologies in tracking and communications; guidance, navigation and control; mechanisms; manipulators; and systems management and integrating them into several evolutionary demonstration stages.
    Keywords: ASTRODYNAMICS
    Type: NASA, Washington, NASA Automated Rendezvous and Capture Review. A Compilation of the Abstracts; 3 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Aircraft measurements of the microwave scattering signature of the ocean (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Microwave scattering signatures of the ocean have been measured over a range of surface wind speeds from 3 m/s to 23.6 m/s using the AAFE RADSCAT scatterometer in an aircraft. Normalized scattering coefficients are presented for vertical and horizontal polarizations as a function of incidence angle (nadir to 55 deg) and radar azimuth angle (0 to 360 deg) relative to surface wind direction. For a given radar polarization, incidence angle, and azimuth angle relative to the wind direction, these scattering data exhibit a power law dependence on surface wind speed. The relation of the scattering coefficient to azimuth angle obtained during aircraft circles (antenna conical scans) is anisotropic and suggests that microwave scatterometers can be used to infer both wind speed and direction. These results have been used for the design of the Seasat-A Satellite Scatterometer (SASS) to be flown in 1978 on this first NASA oceanographic satellite.
    Keywords: OCEANOGRAPHY
    Type: IEEE Transactions on Antennas and Propagation; AP-25; Jan. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Advanced Solid-State Array Spectrometer (ASAS) data sets from the 1990 field season: A unique look at two forested ecosystems (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Advanced Solid-state Array Spectrometer (ASAS) is a pointable imaging spectrometer which uses a solid-state array to acquire imagery of terrestrial targets in 29 spectral bands from .4 to .8 microns. Performance and calibration of the instrument are described. The ASAS data sets obtained in 1990 provide a unique look at forest canopies from two different forest regions of the North America continent under varying temporal, spectral, and bidirectional conditions. These data sets will be used to study such parameters as the albedo of forest canopies, the dynamics of scene radiation due to factors such as canopy architecture, moisture stress, leaf chemistry, topography, and understory composition.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA, Washington, 4th Airborne Geoscience Workshop; p 287-288
    Format: application/pdf
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