Analysis of Space Crane Articulated-Truss Joints

by K. Chauncey Wu, NASA Langley Research Cent, Hampton, United States,
Thomas R. Sutter, NASA Langley Research Cent, Hampton, United States,

Abstract: Three articulated-truss joint concepts for the space crane 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 still allowing large-angle articulation. A maximum positive articulation angle is computed for each joint concept as the design parameters are varied, along with the actuator length ratio required to reach that angle. Joint geometries which have a maximum articulation angle less than 120 degrees or actuators which require a length ratio greater than two are not considered. The tip rotation and lateral deflections of a truss beam with an articulated-truss joint at the mid-span are used to select a point design (with fixed values of the geometric design parameters) for each joint concept. The computed deflections for one point design are up to 30 percent higher than deflections for the other two designs. The structural dynamic performance (natural frequencies, mode shapes and maximum allowable velocity for an emergency stop scenario) of the three point designs is computed as a function of the joint articulation angle. The two lowest natural frequencies of the three point designs are found to be relatively insensitive to large variations in the joint articulation angle. One point design has a higher maximum allowable tip velocity predicted for the emergency stop scenario than the other two designs.

Subject Headings: Joints | Space structures | Trusses | Structural design | Cranes | Geometrics | Parameters (statistics) | Displacement (mechanics)

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