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  • 1
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    Active and passive vibration suppression for space structures (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The relative benefits of passive and active vibration suppression for large space structures (LSS) are discussed. The intent is to sketch the true ranges of applicability of these approaches using previously published technical results. It was found that the distinction between active and passive vibration suppression approaches is not as sharp as might be thought at first. The relative simplicity, reliability, and cost effectiveness touted for passive measures are vitiated by 'hidden costs' bound up with detailed engineering implementation issues and inherent performance limitations. At the same time, reliability and robustness issues are often cited against active control. It is argued that a continuum of vibration suppression measures offering mutually supporting capabilities is needed. The challenge is to properly orchestrate a spectrum of methods to reap the synergistic benefits of combined advanced materials, passive damping, and active control.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, Part 2; p 743-779
    Format: application/pdf
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  • 2
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    Double lead spiral platen parallel jaw end effector (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The double lead spiral platen parallel jaw end effector is an extremely powerful, compact, and highly controllable end effector that represents a significant improvement in gripping force and efficiency over the LaRC Puma (LP) end effector. The spiral end effector is very simple in its design and has relatively few parts. The jaw openings are highly predictable and linear, making it an ideal candidate for remote control. The finger speed is within acceptable working limits and can be modified to meet the user needs; for instance, greater finger speed could be obtained by increasing the pitch of the spiral. The force relaxation is comparable to the other tested units. Optimization of the end effector design would involve a compromise of force and speed for a given application.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA, Marshall Space Flight Center, The 23rd Aerospace Mechanisms Symposium; p 195-206
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  • 3
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    Design and implementation of robust decentralized control laws for the ACES structure at Marshall Space Flight Center (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An experiment was conducted to design controllers that would provide substantial reduction of line-of-sight control errors. The satisfaction of this objective required the controllers to attenuate the beam vibration significantly. Particular emphasis was placed on controller simplicity (i.e., reduced-order and decentralized controller architectures). Complexity reduction in control law implementation is of paramount interest due to stringent limitations on throughput of even state-of-the-art space qualified processors. The results of this experiment successfully demonstrate active vibrator control for a flexible structure. The testbed is the ACES structure at the NASA Marshall Space Flight Center. The ACES structure is dynamically traceable to future space systems and especially allows the study of line-of-sight control issues.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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  • 4
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    Enhancement of the no-vent fill process (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper presents an analytical and experimental evaluation of an enhanced techniques for no-vent fill. The method entails injecting liquid through the top of the receiver vessel, thereby increasing surface area and agitation of the ullage/liquid interface. Both of these factors promote condensation induced ullage collapse, and reduce compressive impedance to the incoming liquid. The enhanced process was analyzed by modifying the surface area algorithm of an existing tank thermodynamic code to model a downward-pointing, conical jet impringing on a steadily rising liquid surface. Transient pressure and temperature measurements from several tests with Freon-114 were input into the revised model to calculate condensation rate as a function of fill level. By expressing these rates in dimensionless form (i.e., in terms of Stanton number and Prandtl number), an empirical correlation similar to the submerged jet model of Brown and Sonin (1989) was derived. This provided a basis for developing an expression which relates top fill to bottom fill performance.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-1842
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  • 5
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    Status of high power electric propulsion technology (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The growing emphasis on very challenging missions and the anticipated availability of high power levels in space have led to renewed interest in high power electric propulsion. The status of high power electric propulsion technology and its applicability to various missions are reviewed. The major thruster and system technology issues are identified which must be addressed in a focussed program in order to assure technology readiness for these missions.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: New Mexico Univ., Transactions of the Fifth Symposium on Space Nuclear Power Systems; p 337-340
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  • 6
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    A comparison of refined models for flexible subassemblies (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Interactions between structure response and control of large flexible space systems have challenged current modeling techniques and have prompted development of new techniques for model improvement. Due to the geometric complexity of envisioned large flexible space structures, finite element models (FEM's) will be used to predict the dynamic characteristics of structural components. It is widely accepted that these models must be experimentally 'validated' before their acceptance as the basis for final design analysis. However, predictions of modal properties (natural frequencies, mode shapes, and damping ratios) are often in error when compared to those obtained from Experimental Modal Analysis (EMA). Recent research efforts have resulted in the development of algorithmic approaches for model improvement, also referred to as system or structure identification.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, The Fifth NASA(DOD Controls-Structures Interaction Technology Conference, Part 1; p 215-230
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  • 7
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    Space Station integrated truss structure and assembly techniques (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The current design and on-orbit assembly techniques are examined for several principal elements and distributed systems attached to the Work Package 2 Space Station Freedom integrated truss structure. The truss structure is examined, including its configuration, the materials used in its construction, and the erectable joints used in its assembly in space. The unpressurized elements and distributed systems attached to and integrated into the truss structure are discussed and the assembly techniques relevant to them are described.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: IAF PAPER 90-066
    Format: text
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  • 8
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    The NASA Lewis Research Center electric propulsion program (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Lewis Research Center conducts an electric propulsion program aimed at a broad class of space missions. The program is structured in an evolutionary fashion in order to both maximize expectations for the acceptance of developed concepts and accommodate anticipated developments of critical system technologies. Recent efforts have assisted in the acceptance of low power electric rockets. Primary electric propulsion concepts are also being developed for both Solar Electric Propulsion Systems and Nuclear Electric Propulsion Systems class space missions, and the paper briefly describes the concepts under evaluation for potential Space Exploration Initiative missions.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-3443
    Format: text
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  • 9
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    Static and dynamic deflection studies of the SRM aft case-nozzle joint (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The redesign of the joints on the solid rocket motor (SRM) has prompted the need for analyzing the behavior of the joints using several different types of analyses. The types of analyses performed include modal analysis, static analysis, transient response analysis, and base driving response analysis. The forces used in these analyses to drive the mathematical model include SRM internal chamber pressure, nozzle blowout and side forces, shuttle vehicle lift-off dynamics, SRM pressure transient rise curve, gimbal forces and moments, actuator gimbal loads, and vertical and radial bolt preloads. The math model represented the SRM from the aft base tangent point (1,823.95 in) all the way back to the nozzle, where a simplified, tuned nozzle model was attached. The new design used the radial bolts as an additional feature to reduce the gap opening at the aft dome/nozzle fixed housing interface.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA-TM-100373 , NAS 1.15:100373
    Format: application/pdf
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  • 10
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    High performance, accelerometer-based control of the Mini-MAST structure at Langley Research Center (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line of sight pointing accuracy and constraints on rms surface roughness. In order for these concepts to become operational, it is imperative that the benefits of active vibration control be shown to be practical in ground based experiments. The results of an experiment shows the successful application of the Maximum Entropy/Optimal Projection control design methodology to active vibration control for a flexible structure. The testbed is the Mini-Mast structure at NASA-Langley and has features dynamically traceable to future space systems. To maximize traceability to real flight systems, the controllers were designed and implemented using sensors (four accelerometers and one rate gyro) that are actually mounted to the structure. Ground mounted displacement sensors that could greatly ease the control design task were available but were used only for performance evaluation. The use of the accelerometers increased the potential of destabilizing the system due to spillover effects and motivated the use of precompensation strategy to achieve sufficient compensator roll-off.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-4377 , NAS 1.26:4377
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