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  • 1
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    Analysis and testing of a space crane articulating joint testbed (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The topics are presented in viewgraph form and include: space crane concept with mobile base; mechanical versus structural articulating joint; articulating joint test bed and reference truss; static and dynamic characterization completed for space crane reference truss configuration; improved linear actuators reduce articulating joint test bed backlash; 1-DOF space crane slew maneuver; boom 2 tip transient response finite element dynamic model; boom 2 tip transient response shear-corrected component modes torque driver profile; peak root member force vs. slew time torque driver profile; and open loop control of space crane motion.
    Keywords: CYBERNETICS
    Type: Automation and Robotics for Space-Based Systems, 1991; p 123-136
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Analytical comparison of three stiffened panel concepts (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Three stiffened panel concepts are evaluated to find optimized designs for integral stiffeners in the barrels of Reusable Launch Vehicle fuel tanks. The three panel concepts considered are a T-stiffened panel, a panel with one blade stiffener centered between each pair of T-stiffeners, and a panel with two blade stiffeners equally spaced between each pair of T-stiffeners. The panels are optimized using PASCO for a range of compressive loads, and the computed areal weight for each panel is used to compare the concepts and predict tank weights. The areal weight of the T-stiffened panel with one blade is up to seven-percent lower than the other panel concepts. Two tank construction methods are compared for a representative tank design with three barrels. In the first method, 45-degree circumferential sections of a barrel are each designed to carry the same maximum load in the barrel. In the second method, each barrel section is designed for the maximum load in that section. Representative tanks designed with the first method are over 250 lb heavier than tanks designed using the second method. Optimized panel designs and areal weights are also computed for variation of the nominal panel length and skin thickness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-110165 , NAS 1.15:110165 , NIPS-96-08490
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    NASA TECHNICAL REPORTS
  • 3
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    Analytical and Photogrammetric Characterization of a Planar Tetrahedral Truss (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Future space science missions are likely to require near-optical quality reflectors which are supported by a stiff truss structure. This support truss should conform closely with its intended shape to minimize its contribution to the overall surface error of the reflector. The current investigation was conducted to evaluate the planar surface accuracy of a regular tetrahedral truss structure by comparing the results of predicted and measured node locations. The truss is a 2-ring hexagonal structure composed of 102 equal-length truss members. Each truss member is nominally 2 meters in length between node centers and is comprised of a graphite/epoxy tube with aluminum nodes and joints. The axial stiffness and the length variation of the truss components were determined experimentally and incorporated into a static finite element analysis of the truss. From this analysis, the root mean square (RMS) surface error of the truss was predicted to be 0.11 mm (0004 in). Photogrammetry tests were performed on the assembled truss to measure the normal displacements of the upper surface nodes and to determine if the truss would maintain its intended shape when subjected to repeated assembly. Considering the variation in the truss component lengths, the measures rms error of 0.14 mm (0.006 in) in the assembled truss is relatively small. The test results also indicate that a repeatable truss surface is achievable. Several potential sources of error were identified and discussed.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-4231 , L-16758 , NAS 1.15:4231
    Format: application/pdf
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  • 4
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    Structural characterization of a first-generation articulated-truss joint for space crane application (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A first-generation space crane articulated-truss joint was statically and dynamically characterized in a configuration that approximated an operational environment. The articulated-truss joint was integrated into a test-bed for structural characterization. Static characterization was performed by applying known loads and measuring the corresponding deflections to obtain load-deflection curves. Dynamic characterization was performed using modal testing to experimentally determine the first six mode shapes, frequencies, and modal damping values. Static and dynamic characteristics were also determined for a reference truss that served as a characterization baseline. Load-deflection curves and experimental frequency response functions are presented for the reference truss and the articulated-truss joint mounted in the test-bed. The static and dynamic experimental results are compared with analytical predictions obtained from finite element analyses. Load-deflection response is also presented for one of the linear actuators used in the articulated-truss joint. Finally, an assessment is presented for the predictability of the truss hardware used in the reference truss and articulated-truss joint based upon hardware stiffness properties that were previously obtained during the Precision Segmented Reflector (PSR) Technology Development Program.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-4371 , L-17061 , NAS 1.15:4371
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  • 5
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    Natural frequency of uniform and optimized tetrahedral truss platforms (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Qualitative and quantitative estimates for the fundamental frequency of uniform and optimized tetrahedral truss platforms are determined. A semiempirical equation is developed for the frequency of free-free uniform trusses as a function of member material properties, truss dimensions, and parasitic (nonstructural) mass fraction Mp/Mt. Optimized trusses with frequencies approximately two times those of uniform trusses are determined by varying the cross-sectional areas of member groups. Trusses with 3 to 8 rings, no parasitic mass, and member areas up to 25 times the minimum area are optimized. Frequencies computed for ranges of both Mp/Mt and the ratio of maximum area to minimum area are normalized to the frequency of a uniform truss with no parasitic mass. The normalized frequency increases with the number of rings, and both frequency and the ratio of maximum area to minimum area decrease with increasing Mp/Mt. Frequency improvements that are achievable with a limited number of member areas are estimated for a 3-ring truss by using Taguchi methods. Joint stiffness knockdown effects are also considered. Comparison of optimized and baseline uniform truss frequencies indicates that tailoring can significantly increase structural frequency; maximum gains occur for trusses with low values of Mp/Mt. This study examines frequency trends for ranges of structural parameters and may be used as a preliminary design guide.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TP-3461 , L-17307 , NAS 1.60:3461
    Format: application/pdf
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  • 6
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    Structurally adaptive space crane concept for assembling space systems on orbit (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Many future human space exploration missions will probably require large vehicles that must be assembled on orbit. Thus, a device that can move, position, and assemble large and massive spacecraft components on orbit becomes essential for these missions. A concept is described for such a device: a space crane concept that uses erectable truss hardware to achieve high-stiffness and low-mass booms and uses articulating truss joints that can be assembled on orbit. The hardware has been tested and shown to have linear load-deflection response and to be structurally predictable. The hardware also permits the crane to be reconfigured into different geometries to satisfy future assembly requirements. A number of articulating and rotary joint concepts have been sized and analyzed, and the results are discussed. Two strategies were proposed to suppress motion-induced vibration: placing viscous dampers in selected truss struts and preshaping motion commands. Preliminary analyses indicate that these techniques have the potential to greatly enhance structural damping.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TP-3307 , L-17175 , NAS 1.15:3307
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  • 7
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    Characterization of the bending stiffness of large space structure joints (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A technique for estimating the bending stiffness of large space structure joints is developed and demonstrated for an erectable joint concept. Experimental load-deflection data from a three-point bending test was used as input to solve a closed-form expression for the joint bending stiffness which was derived from linear beam theory. Potential error sources in both the experimental and analytical procedures are identified and discussed. The bending stiffness of a mechanically preloaded erectable joint is studied at three applied moments and seven joint orientations. Using this technique, the joint bending stiffness was bounded between 6 and 17 percent of the bending stiffness of the graphite/epoxy strut member.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-101565 , NAS 1.15:101565
    Format: application/pdf
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  • 8
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    Free vibration of hexagonal panels supported at discrete points (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An analytical study to determine the structural dynamic behavior of a hexagonal panel with discrete simple supports is presented. These panels are representative of the facets of a precision reflector surface. The effects of both support point location and panel curvature on the lowest natural frequency of the panel are quantified and discussed.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-102688 , NAS 1.15:102688
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  • 9
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    Structural analysis of three space crane articulated-truss joint concepts (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Three space crane articulated truss joint concepts are studied to evaluate their static structural performance over a range of geometric design parameters. Emphasis is placed on maintaining the four longeron reference truss performance across the joint while allowing large angle articulation. A maximum positive articulation angle and the actuator length ratio required to reach the angle are computed for each concept as the design parameters are varied. Configurations with a maximum articulation angle less than 120 degrees or actuators requiring a length ratio over two are not considered. Tip rotation and lateral deflection of a truss beam with an articulated truss joint at the midspan are used to select a point design for each concept. Deflections for one point design are up to 40 percent higher than for the other two designs. Dynamic performance of the three point design is computed as a function of joint articulation angle. The two lowest frequencies of each point design are relatively insensitive to large variations in joint articulation angle. One point design has a higher maximum tip velocity for the emergency stop than the other designs.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-4373 , L-17047 , NAS 1.15:4373
    Format: application/pdf
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  • 10
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    Preliminary investigation of stability of a fin-stiffened slender strut (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A fin-stiffened strut concept which possesses high bending stiffness and low packaged volume has been identified for use on large space structures. The concept incorporates three curved fins which deploy from a core tube to increase the effective cross-sectional moment of inertia, the buckling load, and the vibration frequency of the strut. A strut design incorporating welded fin connections provides an upper bound of the strut buckling load. A strut design which allows the individual fins and core to move independently in the strut axial direction provides a lower bound of the strut buckling load which is approximately 20 to 25 percent of the upper bound. A practical strut design, incorporating hinge assemblies which constrain the fins to move together but independently of the core tube in the strut axial direction, provides a buckling load which is 75 to 80 percent of the upper bound. Euler's equation can be used to accurately predict buckling loads for the bounding designs. Flat plate finite element models of all designs give results that agree to within 10 percent of the experimental values. Equivalent beam models of the strut give results which are slightly less accurate.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-4034 , L-16411 , NAS 1.15:4034
    Format: application/pdf
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