John A. Garba

Adaptive Structures for Precision Controlled Large Space Systems

Future space missions, such as Optical Interferometers and Space Telescopes place very stringent functional requirements upon the structural sub-system. Current approaches to structural design, analysis, and testing cannot assure project man agers that such systems will meet the dimensional stability requirements of nanometers over tens of meters or more. The concept of adaptive structures, structures that can vary their geometric configurations as well as their physical characteristics, is most promising for meeting the requirements of future missions. Adaptive structures are intended to relax ground test requirements, to enable static shape adjustment, to provide a mechanism for linearizing the structure by preloading nonlinear joints, to provide the required excitation forces for performing on-orbit system identification, and to attenuate dynamic response by substantially increasing passive and active structural damping.

Structural Damage Assessment Using a System Identification Technique

Abstract The need for monitoring the dynamic characteristics of large structural systems for purposes of assessing the potential degradation of structural properties has been established. This paper develops a theory for assessing the occurance, location, and extend of potential damage utilizing on-orbit response measurements. Feasibility of the method is demonstrated using a simple structural system as an example.

Vibration Suppression For Precision Segmented Reflector Backup Structure

This paper describes an ongoing effort at the Jet Propulsion Laboratory on the vibration suppression for the Precision Segmented Reflector backup structure. The effort is centered on the vibration damping augmentation through a system consisting of active and passive damping members. An active member is a structural member with built-in piezoelectric actuator and sensors. A bridge feedback technique developed in the communication engineering is applied locally to the active member for active damping augmentation. An efficient method was developed for optimal placement of active and passive damping members in the truss-type backup structure. A simple synergistic model between the active and passive damping was proposed based on a weighted energy dissipation criterion. A baseline passive member design with constrained viscoelastic material treatment was used as the source of passive damping.

US perspective on technology demonstration experiments for adaptive structures

Evaluation of design concepts for adaptive structures is being performed in support of several focused research programs. These include programs such as Precision Segmented Reflector (PSR), Control Structure Interaction (CSI), and the Advanced Space Structures Technology Research Experiment (ASTREX). Although not specifically designed for adaptive structure technology validation, relevant experiments can be performed using the Passive and Active Control of Space Structures (PACOSS) testbed, the Space Integrated Controls Experiment (SPICE), the CSI Evolutionary Model (CEM), and the Dynamic Scale Model Test (DSMT) Hybrid Scale. In addition to the ground test experiments, several space flight experiments have been planned, including a reduced gravity experiment aboard the KC-135 aircraft, shuttle middeck experiments, and the Inexpensive Flight Experiment (INFLEX).<<ETX>>

On the Transition Matrix for First Order Systems

In structure — control interaction problems, it is often desirable to convert the second order real symmetric system in n-variables

Launch Vehicle Payload Interface Response

\mathop M\limits_ \sim \mathop {\ddot \xi }\limits_ \sim + C\mathop {\dot \xi }\limits_ \sim + \mathop K\limits_ \sim \mathop \xi \limits_ \sim = \mathop P\limits_ \sim \quad ;\quad t > o;\;\mathop \xi \limits_ \sim (o) = \mathop \xi \limits_{ \sim o} ,\;\mathop {\dot \xi }\limits_ \sim (o) = \mathop {\dot \xi }\limits_{ \sim o}

Ground test validation for precision structures

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Active vibration isolation using fuzzy CMAC neural networks (Cerebellar Model Arithmetic Computer)

Abstract In an alternate formulation to the Hamilton-Jacobi approach for finding the optimal control of linear systems with Quadratic cost functionals, one must solve a Volterra integral equation of the second kind. Using explicit expressions derived from the Volterra formulation, the paper describes an ilerative algorithm for the numerical computation of the optimal control at equally spaced & number of time stations in the control interval 0 ≤ t ≤ 1. It is assumed that the structural system with large number of degrees-of-freedom n is identified with fewer vibration modes 1 ≤ r ≤ n. the computational complexity of the algorithm is shown to be of order [4r (qmax + r) ms +n2)], where m is the number of control variables, and qmax is the required maximum number of iterations of Jacobi-type