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  • 1
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    Workshop on Structural Dynamics and Control Interaction of Flexible Structures (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Hubble Space Telescope features the most exacting line of sight jitter requirement thus far imposed on a spacecraft pointing system. Consideration of the fine pointing requirements prompted an attempt to isolate the telescope from the low level vibration disturbances generated by the attitude control system reaction wheels. The primary goal was to provide isolation from axial component of wheel disturbance without compromising the control system bandwidth. A passive isolation system employing metal springs in parallel with viscous fluid dampers was designed, fabricated, and space qualified. Stiffness and damping characteristics are deterministic, controlled independently, and were demonstrated to remain constant over at least five orders of input disturbance magnitude. The damping remained purely viscous even at the data collection threshold of .16 x .000001 in input displacement, a level much lower than the anticipated Hubble Space Telescope disturbance amplitude. Vibration attenuation goals were obtained and ground test of the vehicle has demonstrated the isolators are transparent to the attitude control system.
    Keywords: STRUCTURAL MECHANICS
    Type: Structural Dynamics and Control Interaction of Flexible Structures; p 669-690
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Viscous damped space structure for reduced jitter (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A technique to provide modal vibration damping in high performance space structures was developed which uses less than one once of incompressible fluid. Up to 50 percent damping can be achieved which can reduce the settling times of the lowest structural mode by as much as 50 to 1. This concept allows the designers to reduce the weight of the structure while improving its dynamic performance. Damping by this technique is purely viscous and has been shown by test to be linear over 5 orders of input magnitude. Amplitudes as low as 0.2 microinch were demonstrated. Damping in the system is independent of stiffness and relatively insensitive to temperature.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-Marshall Space Flight Center, The 58th Shock and Vibration Symposium, Volume 1; p 233-243
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Buckling tests of a 10 foot diameter stiffened cylinder with rectangular cutouts (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A 10-foot diameter aluminum cylinder with rectangular cutouts in its ring and stringer stiffened wall was loaded to failure by an end bending moment. A 24x27 inch cutout, centered on the compression side of the shell, was first cut into the cylinder. After testing, the cutout area was enlarged to a 36/36 inch square cutout that removed the material damaged by buckling during the first test. After the second buckling test, the cutout area was patched with an equivalent stiffness plate bolted over the cutout hole. The cylinder was rotated 120 deg. and a 18x18 inch square hole cut into the center of the new compression side of the shell. Test specimen details, test procedures, and test results are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-88996 , NAS 1.15:88996
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Analysis and test of superplastically formed titanium hat-stiffened panels under compression (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Four hat-stiffened titanium panels with two different stiffener configurations were fabricated by superplastic forming/weld brazing and tested under a moderately heavy compressive load. The panels had the same overall dimensions but differed in the shape of the hat-stiffener webs; three panels had stiffeners with flat webs and the other panel had stiffeners with beaded webs. Analysis indicated that the local buckling strain of the flat stiffener web was considerably lower than the general panel buckling strain or cap buckling strain. The analysis also showed that beading the webs of the hat stiffeners removed them as the critical element for local buckling and improved the buckling strain of the panels. The analytical extensional stiffness and failure loads compared very well with experimental results.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-88989 , NAS 1.15:88989
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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