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  • Other Sources  (445)
  • 2005-2009  (216)
  • 2000-2004  (229)
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  • 1
    Publication Date: 2019-07-18
    Description: Higher order numerical algorithms (4th order in time, 3rd order in space) are applied to the Euler equations and are used to examine vorticity transport and wave motion in a non-self gravitating, initially isentropic Keplerian disk. In this talk we will examine the response of the disk to an isolated vortex with a circulation about equal to the rotation rate of Jupiter. The vortex is located on the 4 AU circle and the nebula is simulated from 1 to 24 AU. We show that the vortex emits pressure-supported density and Rossby-type wave packets before it decays within a few orbits. The acoustic density waves evolve into weak (non entropy preserving) shock waves that propagate over the entire disk. The Rossby waves remain in the vicinity of the initial vortex disturbance, but are rapidly damped. Temporal frequencies and spatial wavenumbers are derived from the nonlinear simulation data and correlated with analytical dispersion relations from the linearized Euler and energy equations.
    Keywords: Astrophysics
    Type: AGU Meeting; May 28, 2002 - May 31, 2002; Washington, DC; United States
    Format: text
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  • 2
    Publication Date: 2019-07-13
    Description: A GPS receiver flying on the High Earth Orbit (HEO) AMSAT-OSCAR 40 (AO-40) spacecraft has been returning GPS observations from high above the altitude of the GPS constellation. AO-40, an amateur radio satellite launched November 16, 2000, is currently in a low inclination, 1000 by 59000 lan altitude orbit. This low-cost experiment utilizes a mid 1990's era, 6-channel, CIA code receiver configured with high gain receiving antennas for tracking above the GPS constellation. The receiver has performed well, despite operating significantly outside of its original design environment. It has regularly returned GPS observations from points all around the orbit, with over ten weeks of GPS tracking data collected to date. Signal to noise levels as high as 48 B-Hz have been recorded near apogee, when the spacecraft was at an altitude of close to 60000 km. GPS side lobe signals have been tracked on several occasions, primarily from Block IIR GPS satellites. Although the receiver has not computed a solution in real-time, point solutions have been computed on the ground using simultaneous measurements from four satellites. This experiment has provided important experience dealing with the many challenges inherent to GPS tracking at high altitudes, and the measurements returned are providing valuable information about the characteristics of GPS signals available for future HE0 users.
    Keywords: Space Communications, Spacecraft Communications, Command and Tracking
    Type: ION GPS 2002; Sep 24, 2002 - Sep 27, 2002; Portland, OR; United States
    Format: text
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  • 3
    Publication Date: 2019-07-13
    Description: The GPS flight experiment on the High Earth Orbit (HEO) AMSAT-OSCAR 40 (AO-40) spacecraft was activated for a period of approximately six weeks between 25 September and 2 November, 2001, and the initial results have exciting implications for using GPS as a low-cost orbit determination sensor for future HEO missions. AO-40, an amateur radio satellite launched November 16, 2000, is currently in a low inclination, 1000 by 58,800 km altitude orbit. Although the GPS receiver was not initialized in any way, it regularly returned GPS observations from points all around the orbit. Raw signal to noise levels as high as 9 AMUs (Trimble Amplitude Measurement Units) or approximately 48 dB-Hz have been recorded at apogee, when the spacecraft was close to 60,000 km in altitude. On several occasions when the receiver was below the GPS constellation (below 20,000 krn altitude), observations were reported for GPS satellites tracked through side lobe transmissions. Although the receiver has not returned any point solutions, there has been at least one occasion when four satellites were tracked simultaneously, and this short arc of data was used to compute point solutions after the fact. These results are encouraging, especially considering the spacecraft is currently in a spin-stabilized attitude mode that narrows the effective field of view of the receiving antennas and adversely affects GPS tracking. Already AO-40 has demonstrated the feasibility of recording GPS observations in HEO using an unaided receiver. Furthermore, it is providing important information about the characteristics of GPS signals received by a spacecraft in a HEO, which has long been of interest to many in the GPS community. Based on the data returned so far, the tracking performance is expected to improve when the spacecraft is transitioned to a three axis stabilized, nadir pointing attitude in Summer, 2002.
    Keywords: Aircraft Communications and Navigation
    Type: AAS-02-004 , 25th Annual AAS Guidance and Control Conference; Feb 06, 2002 - Feb 10, 2002; Breckenridge, CO; United States
    Format: application/pdf
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  • 4
    Publication Date: 2019-07-13
    Description: Ablatable Thermal Protection System (TPS) coatings are used on the Space Shuttle Vehicle Solid Rocket Boosters in order to protect the aluminum structure from experiencing excessive temperatures. The methodology used to characterize the recession of such materials is outlined. Details of the tests, including the facility, test articles and test article processing are also presented. The recession rates are collapsed into an empirical power-law relation. A design curve is defined using a 95-percentile student-t distribution. based on the nominal results. Actual test results are presented for the current acreage TPS material used.
    Keywords: Nonmetallic Materials
    Type: AIAA Paper 2002-3334 , 8th AIAA/ASME Joint Thermophysics and Heat Transfer Conference; Jun 24, 2002 - Jun 27, 2002; Saint Louis, MO; United States
    Format: application/pdf
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  • 5
    Publication Date: 2019-07-13
    Description: This slide presentation reviews the current status of the launch vehicles associated with the Constellation Program. These are the Ares I and the Ares V. An overview of the Ares launch vehicles is included. The presentation stresses that the major criteria for the Ares I launcher is the safety of the crew, and the presentation reviews the various features that are designed to assure that aim. The Ares I vehicle is being built on a foundation of proven technologies, and the Ares V will give NASA unprecedented performance and payload volume that can enable a range of future missions. The CDs contain videos of scenes from various activities surrounding the design, construction and testing of the vehicles.
    Keywords: Launch Vehicles and Launch Operations
    Type: Human Space Flight Review; Jul 29, 2009; Huntsville, AL; United States
    Format: text
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  • 6
    Publication Date: 2019-07-13
    Description: The methodology used and the results obtained in the pre-flight testing of the Blackjack Global Positioning System (GPS) space receiver for the Vegetation Canopy Lidar Mission (VCL) and the Ice, Cloud, and Land Elevation Satellite (ICESat) spacecraft is described. Both real and simulated signals were used to: (1) assess the accuracy and coverage of the navigation solutions, (2) assess the accuracy and stability of the 1-PPS timing signal, (3) assess the precision of the carrier phase observable, and (4) measure the cold-start time to first fix. In addition, an anechoic chamber was used to measure the antenna phase centers with millimeter-level precision. While the test results have generally been excellent and are discussed in this paper, emphasis is placed on describing the test methodology. It is anticipated that future geodetic satellite missions using GPS for navigation, timing, and precise orbit determination (POD) can employ the same tests for pre-launch performance assessment of their particular receiver.
    Keywords: Composite Materials
    Type: Global Positioning Systems; Jan 01, 2000; Salt Lake City, NV; United States
    Format: application/pdf
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  • 7
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    In:  Bulletin of the Seismological Society of America, Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 92, no. 8, pp. 3134-3151, pp. L08305
    Publication Date: 2002
    Keywords: Site amplification ; High frequency ... ; Strong motions ; BSSA
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  • 8
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    In:  J. Geophys. Res., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 108, no. B2, pp. ESE 22-1 to ESE 22-17, pp. 2122
    Publication Date: 2003
    Keywords: Tomography ; Strong motions ; Site amplification ; Earthquake ; USA ; JGR
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  • 9
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    In:  J. Geophys. Res., Paris, Pergamon, vol. 105, no. B6, pp. 13,253-13,279, pp. 1246
    Publication Date: 2000
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Plate tectonics ; India ; Fault plane solution, focal mechanism ; Waves ; form ; Inversion ; 7215 ; Seismology ; Earthquake ; parameters ; 7230 ; Seismicity ; and ; seismotectonics ; 8102 ; Tectonophysics ; Continental ; contractional ; orogenic ; belts ; 8107 ; Continental ; neotectonics ; JGR
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  • 10
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    In:  J. Geophys. Res., Klagenfurt, Nuclear Technology Publ., vol. 108, no. B4, pp. ETG 7-1 to ETG 7-23, pp. 2199, (ISBN: 0534351875, 2nd edition)
    Publication Date: 2003
    Keywords: Fault zone ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Geol. aspects ; JGR ; 1208 ; Geodesy ; and ; Gravity: ; Crustal ; movements--intraplate ; (8110) ; 1243 ; Space ; geodetic ; surveys ; 7209 ; Seismology: ; Earthquake ; dynamics ; and ; mechanics ; 8107 ; Tectonophysics: ; Continental ; neotectonics ; 8109 ; Continental ; tectonics--extensional ; (0905)
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