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  • 1
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    Space structure vibration modes: How many exist? Which ones are important? (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This report attempts to shed some light on the two issues raised in the title, namely, how many vibration modes does a real structure have, and which of these modes are important? The surprise-free answers to these two questions are, respectively, an infinite number and the first several modes. The author argues that the absurd subspace (all but the first billion modes) is not a strength of continuum modeling, but, in fact, a weakness. Partial differential equations are not real structures, only mathematical models. This note also explains (1) that the PDE model and the finite element model are, in fact, the same model, the latter being a numerical method for dealing with the former, (2) that modes may be selected on dynamical grounds other than frequency alone, and (3) that long slender rods are useful as primitive cases but dangerous to extrapolate from.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-173442 , NAS 1.26:173442 , UTIAS-TN-252 , AD-B083791 , (ISSN 0082-5263)
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Order reduction for models of space structures using modal cost analysis (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Modal cost analysis furnishes a promising methodology for developing dynamical models of space structures for use in control systems analysis. Economy and accuracy can be attained by only retaining vibration modes that contribute significantly to an appropriately defined cost function. Expressions for modal costs (especially simple for 'lightly damped' structures) are derived for attitude control, vibration suppression, and shape control. These techniques are illustrated through application to a high-order finite element model of a large platform-type structure.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Flexible space structure model reduction by modal cost analysis (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: It is noted that reduced models and reduced controllers for flexible space structures are obtained by retaining those modes which make the greatest contribution to quadratic control objectives. Attention is given to the relative importance of damping, frequency and mode shapes in the mode truncation decisions for the following control objectives: attitude control, vibration suppression and figure control. It is also shown that using Modal Cost Analysis (MCA) on the closed loop modes of the optimally controlled system allows the construction of reduced control policies which feedback only those closed loop coordinates which are most critical to the quadratic control performance criterion. In this manner, the modes which need to be controlled are deduced from truncations of the optimal controller.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Dynamics and control of large flexible spacecraft; Jun 21, 1979 - Jun 23, 1979; Blacksburg, VA
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Controllability and observability for flexible spacecraft (1979)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Current interest in extended sensing and actuation for the control of flexible spacecraft has led to the use of modern multivariable control theory and the associated concepts of controllability and observability. This paper shows how to evaluate these properties on a mode-by-mode basis for flexible spacecraft control analysis. Relatively simple criteria are derived which indicate the degree of controllability (observability) of each mode in simple literal terms. These criteria provide physical insight and practical guidance on the type, number, and positioning of sensors and actuators. The results are interpreted for force and torque actuators, and for attitude and deformation measurements. To illustrate these ideas, sample controllability and observability 'surfaces' are presented for the Purdue generic flexible spacecraft model.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Dynamics and control of large flexible spacecraft; Jun 21, 1979 - Jun 23, 1979; Blacksburg, VA
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Dynamics of incremental motion devices associated with planetary exploration spacecraft (1975)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Incremental motion devices provide accurate and rapid movement of spacecraft science platforms, antennas and related mechanisms. The paper considers the computerized simulation of a stepper motor/gear train/ science platform system that will be launched on the Mariner Jupiter Saturn 1977. It was determined that a smaller stepper motor could be used as the prime mover for the science platform, and it was concluded that the existing digital controller was unable to achieve the required pointing accuracy, and a new controller design was necessary.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Annual Symposium on Incremental Motion Control Systems and Devices; Apr 01, 1975 - Apr 03, 1975; Urbana, IL
    Format: text
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