Journal of Aerospace Engineering

As NASA progresses toward the construction and assembly of the international space station, the dynamic influence of massive, highly flexible payloads becomes more and more of an important consideration. In particular, attention must be focused on the robotic manipulation of these payloads and their effect on the space shuttle's remote manipulator system, which will place and assemble them in orbit. While the payloads of the past were considered as rigid for analysis purposes, the dynamic influence of a new generation of payloads will begin to play a more important role in predicting the overall system's dynamic response. This paper presents the results of a study performed to show the effects of these new payloads on the shuttle's remote manipulator system. The supporting data is presented along with recommendations as to the dynamic influence they can have on response predictions.

An algorithm to aid designers and planners of large integrated space systems requiring on-orbit assembly has been prototyped. This methodology is being implemented in an advanced knowledge-based expert system intended for conceptual design studies. Intended to work interactively with a commercial three-dimensional computer-aided design solid modeler, it studies the feasibility of packing multiple space system hardware elements into a given launch vehicle shroud. Previous study results have indicated that to minimize assembly complexity, while avoiding potentially unreliable deployments, the designers would have to either design systems that can be launched in a single large vehicle, or use multiple smaller vehicles and risk manifesting relatively inefficient launches (e.g. a low mass density truss with fluid and electrical systems installed). This algorithm is one of a suite of tools being developed to aid the conceptual design engineer in identifying and quantifying space vehicle design alternatives, and the corresponding launch vehicles and shrouds that minimize overall cost and mission risk from a launch and flight assembly operations perspective.

A numerical solution to investigate the free vibrational characteristics of doubly curved laminated angle-ply shallow shells on quadrangular planforms is presented. The first-order composite shell theory is used in the formulation and the rotary inertia and shear deformation terms are included. The shell equation is solved by the Ritz method, in which the admissible displacement fields are defined in terms of the parametric Bezier surface patches. Owing to the special characteristics of Bezier functions, treatment of the geometric boundary conditions at a particular edge becomes very simple and straightforward by manipulating the coefficients that control the shape of the Bezier surface patch. Rapid convergence of the solution algorithm is found with only the fifth-order function. The natural frequencies are calculated for the four-layer angle-ply cantilevered cylindrical shells on square, rhombic, and trapezoidal boundaries. The numerical comparison indicates that the present solution method yields more accurate results than the ones obtained by the finite-element method using the eight-noded isoparametric shallow-shell element.

In this paper, a set of simple formulations is derived to predict the instability critical loads of orthotropic composite tubes under pure bending. The formulations are based on the assumption that the instability of an orthotropic composite tube under pure bending is due to the ovalization of its cross section. For the static instability case, the ovalization increases steadily as the curvature increases, which results in a reduction in the bending rigidity of the tube. The interaction of longitudinal bending and cross-section ovalization causes the tube to have a limit load instability. For the dynamic instability case, the instability of the tube is due to the interaction of two vibrations, one is the longitudinal bending of the tube as a beam, the other is the circumferential bending of the tube as a thin-walled shell.