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  • Other Sources  (871)
  • 2015-2019  (221)
  • 1995-1999  (255)
  • 1985-1989  (379)
  • 1945-1949  (16)
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  • 1
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    The 1994 international transatlantic two-way satellite time and frequency transfer experiment: Preliminary results (1995)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The international transatlantic time and frequency transfer experiment was designed by participating laboratories and has been implemented during 1994 to test the international communications path involving a large number of transmitting stations. This paper will present empirically determined clock and time scale differences, time and frequency domain instabilities, and a representative power spectral density analysis. The experiments by the method of co-location which will allow absolute calibration of the participating laboratories have been performed. Absolute time differences and accuracy levels of this experiment will be assessed in the near future.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Goddard Space Flight Center, The 26th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; p 39-49
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  • 2
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    Results of the Calibration of the Delays of Earth Stations for TWSTFT Using the VSL Satellite Simulator Method (1996)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Two-way satellite time and frequency transfer (TWSTFT) is the most accurate and precise method of comparing two remote clocks or time scales. The accuracy obtained is dependent on the accuracy of the determination of the non-reciprocal delays of the transmit and the receive paths. When the same transponders in the satellite at the same frequencies are used, then the non-reciprocity in the Earth stations is the limiting factor for absolute time transfer.
    Keywords: Physics (General)
    Type: 27th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; 359-372; NASA-CP-3334
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  • 3
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    Preliminary Comparison of Two-Way Satellite Time and Frequency Transfer and GPS Common-View Time Transfer During the INTELSAT Field Trial (1996)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: For a decade and a half Global Positioning System (GPS) common-view time transfer has greatly served the needs of primary timing laboratories for regular intercomparisons of remote atomic clocks. However, GPS as a one-way technique has natural limits and may not meet all challenges of the comparison of the coming new generation of atomic clocks. Two-way satellite time and frequency transfer (TWSTFT) is a promising technique which may successfully complement GPS. For two years, regular TWSTFT's have been performed between eight laboratories situated in both Europe and North America, using INTELSAT satellites. This has enabled an extensive direct comparison to be made between these two high performance time transfer methods. The performance of the TWSTFT and GPS common view methods are compared over a number of time-transfer links. These links use a variety of time-transfer hardware and atomic clocks and have baselines of substantially different lengths. The relative merits of the two time-transfer systems are discussed.
    Keywords: Physics (General)
    Type: 27th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting; 347-358; NASA-CP-3334
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  • 4
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    The X-ray large aray. II - Implementation (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The design of the X-ray Large Array (XLA) which is to be assembled and operated in space is discussed. The XLA is a 100 sq m array of 64 detector modules with a total of 512 detectors, each similar to the ones flown on the HEAO-1 spacecraft, packaged in groups of eight to form a module. The XLA will be able to deal with many extremely fast processes which occur in compact X-ray sources and will be used to study black hole candidates; its fine time resolution will make it possible to resolve the spatial structure of celestial X-ray sources using lunar occulatation, the angular structure of quasars, and active galactic nuclei. Details of the XLA configuration, and the assembly and packaging options are described together with systems requirements. Multiple configuration diagrams are included.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 88-0654
    Format: text
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  • 5
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    Dynamic Calibration of Pressure Transducers (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Sinusoidal calibration signal produced in 4- to 100-Hz range. Portable oscillating-pressure device measures dynamic characteristics of pressure transducers installed in models or aircraft at frequency and oscillating-pressure ranges encountered during unsteady-pressure-measurement tests. Calibration is over range of frequencies and amplitudes not available with commercial acoustic calibration devices.
    Keywords: MECHANICS
    Type: LAR-13094 , NASA Tech Briefs (ISSN 0145-319X); 8; 4; P. 517
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  • 6
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    Testing of the International Space Station and X-38 Crew Return Vehicle GPS Receiver (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper discusses the process and results of the performance testing of the GPS receiver planned for use on the International Space Station (ISS) and the X-38 Crew Return Vehicle (CRV). The receiver is a Force-19 unit manufactured by Trimble Navigation and modified in software by the NASA Goddard Space Flight Center (GSFC) to perform navigation and attitude determination in space. The receiver is the primary source of navigation and attitude information for ISS and CRV. Engineers at GSFC have developed and tested the new receiver with a Global Simulation Systems Ltd (GSS) GPS Signal Generator (GPSSG). This paper documents the unique aspects of ground testing a GPS receiver that is designed for use in space. A discussion of the design of tests using the GPSSG, documentation, data capture, data analysis, and lessons learned will precede an overview of the performance of the new receiver. A description of the challenges that were overcome during this testing exercise will be presented. Results from testing show that the receiver will be within or near the specifications for ISS attitude and navigation performance. The process for verifying other requirements such as Time to First Fix, Time to First Attitude, selection/deselection of a specific GPS satellite vehicles (SV), minimum signal strength while still obtaining attitude and navigation, navigation and attitude output coverage, GPS week rollover, and Y2K requirements are also given in this paper.
    Keywords: Aircraft Communications and Navigation
    Type: GPS Conference; Sep 14, 1999 - Sep 17, 1999; Nashville, TN; United States
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  • 7
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    Testing of the International Space Station and X-38 Crew Return Vehicle GPS Receiver (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper discusses the process and results of the performance testing of the GPS receiver planned for use on the International Space Station (ISS) and the X-38 Crew Return Vehicle (CRV). The receiver is a Force-19 unit manufactured by Trimble Navigation and Modified in software by the NASA Goddard Space Flight Center (GSFC) to perform navigation and attitude determination in space. The receiver is the primary source of navigation and attitude information for ISS and CRV. Engineers at GSFC have developed and tested the new receiver with a Global Simulation Systems Ltd (GSS) GPS Signal Generator (GPSSG). This paper documents the unique aspects of ground testing a GPS receiver that is designed for use in space. A discussion of the design and tests using the GPSSG, documentation, data capture, data analysis, and lessons learned will precede an overview of the performance of the new receiver. A description of the challenges of that were overcome during this testing exercise will be presented. Results from testing show that the receiver will be within or near the specifications for ISS attitude and navigation performance. The process for verifying other requirements such as Time to First Fix, Time to First Attitude, selection/deselection of a specific GPS satellite vehicles (SV), minimum signal strength while still obtaining attitude and navigation, navigation and attitude output coverage, GPS week rollover, and Y2K requirements are also given in this paper.
    Keywords: Space Transportation
    Type: ION GPS Conference; Sep 14, 1999 - Sep 17, 1999; Nashville, TN; United States
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  • 8
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    Testing of the International Space Station and X-38 Crew Return Vehicle GPS Receiver (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: This paper discusses the process and results of the performance testing of the GPS receiver planned for use on the International Space Station (ISS) and the X- 38CrewReturnVehicle(CRV). The receiver is a Force-19 unit manufactured by Trimble Navigation and modified in software by NASA:s Goddard Space Flight Center (GSFC) to perform navigation and attitude determination in space. The receiver is the primary source of navigation and attitude information for ISS and CRV. Engineers at GSFC have developed and tested the new receiver with a Global Simulation Systems Ltd (GSS) GPS Signal Generator (GPSSG). This paper documents the unique aspects of ground testing a GPS receiver that is designed for use in space. A discussion of the design of tests using the GPSSG, documentation, data capture, data analysis, and lessons learned will precede an overview of the performance of the new receiver. A description of the challenges that were overcome during this testing exercise will be presented. Results from testing show that the receiver will be within or near the specifications for ISS attitude and navigation performance. The process for verifying other requirements such as Time to First Fix, Time to First Attitude, selection/deselection of a specific GPS satellite vehicles (SV), minimum signal strength while still obtaining attitude and navigation, navigation and attitude output coverage, GPS week rollover, and Y2K requirements are also given in this paper.
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking
    Type: Institute of Naviation (ION) GPS; Sep 14, 1999 - Sep 17, 1999; Nashville, TN; United States
    Format: text
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  • 9
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    Oscillation pressure device for dynamic calibration of pressure transducers (1987)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: Method and apparatus for obtaining dynamic calibrations of pressure transducers. A calibration head (15), a flexible tubing (23) and a bellows (20) enclose a volume of air at atmospheric pressure with a transducer (11) to be calibrated subject to the pressure inside the volume. All of the other apparatus in the drawing apply oscillations to bellows (20) causing the volume to change thereby applying oscillating pressures to transducer (11) whereby transducer (11) can be calibrated.
    Keywords: Fluid Mechanics and Thermodynamics
    Format: application/pdf
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  • 10
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    Growth, Spectroscopy and Photorefractive Investigation of Vanadium Doped CdSSe (1997)
    In:  CASI
    Details
    Publication Date: 2019-08-15
    Description: We present two-wave mixing results obtained with a CdS(0.8)Se(0.2):V crystal. The CdS(0.8)Se(0.2):V crystal was grown by physical vapor transport (PVT) along with a concentration of 150 ppm (nominal) vanadium for creating trap centers. The as-grown crystal has a large crystal size, good optical quality, and a medium resistivity of 10(exp 6) - 108 ohms-cm. A large photorefractive gain coefficient of ().24 cm-' was observed at 633 nm with an optical intensity of 60 mW/cm(exp 2) and a grating period of 1.6 microns. To our knowledge, this is the first observation of the photorefractive effect in a vanadium doped CdSSe crystal. Room temperature absorption and low temperature photoluminescence spectroscopy measurements are also discussed. With a significant photorefractive effect, the CdSSe:V crystals are promising for device applications based on photorefractive effect, in the wavelength range of 600-700 nm.
    Keywords: Inorganic, Organic and Physical Chemistry
    Type: URC97033 , NASA University Research Centers Technical Advances in Education, Aeronautics, Space, Autonomy, Earth and Environment; 1; 191-196
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