Ever since the advent of the Moment-Distribution procedure (1) for analyzing continuous frames, it has been possible to solve many problems conveniently which previously had required laborious solutions. Indeed, the current literature of the engineering profession finds the Cross method being adopted in new fields and being applied to new problems. The classical methods of analysis, while still retaining some measure of their former utility, are being superseded by this and other methods involving less time and labor. Yet, even with this new impetus to the field of structural analysis, the rigid space frame has received far less attention than seems justified. Here is a class of structure devoid of practically any analytical investigation and even less experimental research. The desired characteristic of all current designs has been continuity, and yet there exists this paradoxical neglect of the third dimension, without which all structures would be non-existent. The reasons for this apparent indifference are not difficult to ascertain. Practicing engineers are practical men and as such require reasonably accurate results, obtained with a minimum of effort. Economy has dictated that refinements of analysis be saved for the classroom. A two-plane analysis is generally substituted for the more complex three-dimensional case. The write feels that the interaction of members in different planes of certain structures may be quite important in some cases and that a complete, convenient analysis is justified to determine the extent of such action. / Master of Science

The work that is reported herein deals with system identification methods for large flexible structures. Proposed space missions for the future include the deployment of large flexible structures, e.g., NASA's proposed space station. These structures must be controlled to maneuver the structure to desired locations and to suppress unwanted vibration. Before controlling any structure, it is necessary to have an accurate model which may include accurate estimates of the structure's natural frequencies and mode shapes. System identification is an important process that precludes system control. Precision structures such as those proposed for the Space Based Laser or the Aerospace Plane require high performance control systems which will require robust, computationally efficient system identification algorithms. This work attempts to experimentally verify, develop, and compare existing identification algorithms to determine their properties and improve their efficiency towards potential applicability in a space environment. To this end, we consider the Temporal Correlation Method and the Eigensystem Realization Algorithm. The algorithms are implemented on the Astronautics Laboratory Grid structure, and the results of the algorithms are compared in the presence of damping, noise, and residual modes. In addition, the Temporal Correlation Method is shown to be a constrained version of the Eigensystem Realization Algorithm for cases of light damping. / Master of Science