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  • 1
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    Field evidence that ecosystem service projects support biodiversity and diversify options (2008)
    National Academy of Sciences
    Details
    Publication Date: 2008-06-30
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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    PAPER CURRENT
  • 2
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    Experimental investigation of hypersonic buzz on a high cross-range shuttle configuration (1972)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A wind tunnel investigation has been conducted to determine the nature of an unsteady hypersonic flow phenomenon, often referred to as hypersonic buzz, on a 1:100 scale model representative of a high cross-range shuttle configuration. The tests, conducted in helium at a nominal Mach number of 17.5, were specifically directed at obtaining a better understanding of the character of the hypersonic flow field in the vicinity of a deflected control surface. Power spectral densities and root mean squared values of surface pressure fluctuations are presented along with observations made from high speed motion pictures, schlieren and oil flow photographs. Flap deflections of 0, 20, 30, 35, 40 and 60 deg were tested at various angles of attack from 0 deg to 37 deg. It is quite clear from these tests that, under certain conditions, extremely unstable hypersonic flow patterns are formed.
    Keywords: AERODYNAMICS
    Type: NASA-CR-112053 , RIAS-TR-72-05C
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Examination of the anomalous behavior of three gravity gradient satellites (1971)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The anomalous oscillatory behavior of three satellites was examined. The satellites were all hinged, two-body, gravity gradient configurations passively stabilized about their three principal axes by gravity gradient and damper torques. Two basic behavior patterns were observed. Either the satellites were stable with attitude perturbations less than + or - 5 deg or their behavior tended towards a low frequency rigid body oscillation dominated by large yaw motions and in some cases by yaw inversions. A causal relationship between sun angle and the character of satellite behavior was observed which appears to indicate that thermal distortion is a critical factor in a gravity gradient satellite's dynamic behavior. The behavior appeared to be futher modified by the existence of response frequencies that were higher than anticipated values.
    Keywords: SPACE VEHICLES
    Type: NASA-CR-122294 , TR-71-07C
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Influence of thermal distortion on the anomalous behavior of a gravity gradient satellite (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Consideration of the problem of determining the influence of solar heating on the low-frequency dynamic stability of a gravity-gradient satellite. The scope of the effort includes the development of a computer program that uses a quasi-static approach for describing a satellite's unsteady orbital motion. The essential feature of the quasi-static approach is that the satellite's long, slender booms reach their thermal equilibrium position solely as a result of thermal bending without consideration of the dynamic effects of boom vibration. A nonlinear analytical model and a corresponding computer program have been developed to study the effect of absorptivity, sun angle, and hinge stiffness on the stability of a satellite's motion.
    Keywords: SPACE VEHICLES
    Type: AIAA PAPER 74-922 , Mechanics and Control of Flight Conference; Aug 05, 1974 - Aug 09, 1974; Anaheim, CA
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Instability of a gravity gradient satellite due to thermal distortion (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A nonlinear analytical model and a corresponding computer program were developed to study the influence of solar heating on the anomalous low frequency, orbital instability of the Naval Research Laboratory's gravity gradient satellite 164. The model's formulation was based on a quasi-static approach in which deflections of the satellite's booms were determined in terms of thermally induced bending without consideration of boom vibration. Calculations, which were made for variations in absorptivity, sun angle, thermal lag, and hinge stiffness, demonstrated that, within the confines of a relatively narrow stability criteria, the quasi-static model of NRL 164 not only becomes unstable, but, in a number of cases, responses were computed that closely resembled flight data.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-2516 , TR-74-02C
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Staging loads - Space vehicle design criteria (1969)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Analysis of loads produced on spacecraft by staging operations and practices to insure that staging loads are included in spacecraft design
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-SP-8022
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Flight Flutter Testing of the P6M (1975)
    In:  CASI
    Details
    Publication Date: 2019-08-14
    Description: On the P6M the shake behavior, i.e., the response to random excitation at subcritical speeds of lowly damped airplane modes, is as important as the actual flutter speed. The approach is to first study the problem by means of analyses and wind-tunnel tests. These predictions are compared with flight test data obtained by spectral analysis of tape recordings of the airplane vibration responses to random aerodynamic turbulence. A similar spectrum analysis approach was used in high speed wind-tunnel tests. A resonance excitation technique was developed for low speed wind-tunnel testing, and well defined V-g curves were obtained. The effect of various parameters on both shake and flutter of T-tails with and without dihedral were studied. Preliminary flight tests yielded good correlation; they also yielded interesting information concerning a low frequency transonic snaking mode, and excitation by shed vortices.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA, Washington Flight Flutter Testing Symp.; p 91-96
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Experimental investigation of hypersonic buzz on a high cross-range shuttle configuration. (1973)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An experimental study confirming the existence of hypersonic buzz in the separated region of a space shuttle's downward deflected control surface is described. Wind tunnel tests in helium on a 1:100 scale model of a shuttle type configuration at M = 17.5 clearly demonstrated the occurrence of large scale pressure oscillations throughout a substantial range of angles of attack and control surface deflections. Measurements of surface pressure fluctuations along with high speed schlieren photography served to delineate the boundaries of the phenomenon and to identify the physical parameters necessary for the onset of a buzz condition. Prominent spectral energy peaks were also observed in the surface pressures that could be directly correlated with the instability. These conditions were found to be strongly dependent on the presence of multiple shock interactions and the position of these interactions relative to the location of a reattaching shear layer.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 73-157 , Aerospace Sciences Meeting; Jan 10, 1973 - Jan 12, 1973; Washington, DC
    Format: text
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    NASA TECHNICAL REPORTS
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