The concept for a wideband, embedded/conformal antenna subsystem is presented. A multilayer radome not only protects the antenna from hostile environments, but also is designed to sustain aircraft dynamic loading. The radiating element consists of a planar, dual- flared slot capable of high-performance, multioctave operation. Advanced materials are currently being developed to enhance the low profile and efficient, wideband performance of the radiating element.

The exact field solution of a step index profile fiber was used to determine the excitation efficiency of a distribution of sources in the core of an optical fiber. Previous results of a thin- film cladding source distribution are compared to its core source counterpart. The behavior of Peff with the fiber parameters was examined and found to be similar to the behavior exhibited by cladding sources. It also was found that a core source fiber is two orders of magnitude more efficient than a fiber with a bulk distribution of cladding sources. This result agrees, qualitatively, with previous ones obtained experimentally.

The present paper describes the behavior of embedded optical sensor fibers in a high- temperature PEEK (polyether ether ketone) carbon fiber composite. Sheets of this material, 200 micrometers thick, were layered in alternating directions for the carbon fibers. Typically, 16 sheets were used to form 3' X 6' or 3' X 8' panels by placing the optical fibers in the middle of the `prepreg' sheets, which were then heated to the processing temperature, and subjected to a pressure of 300 psi during the cool-down phase. Since the ordinary polymeric coatings of optical fibers cannot survive the 380 degree(s)C to 400 degree(s)C processing temperature of PEEK impregnated fiber composites, all of the optical sensor fibers tested were polyimide coated. The optical, mechanical, and thermal properties are reported and it is concluded that polyimide coated fibers can withstand PEEK processing conditions.

This paper will report on efforts directed towards the generation and detection of ultrasonic waves using optical fibers. Interferometric optical fiber sensors are embedded within or bonded to the samples. Two different techniques, laser generated ultrasound and piezoelectric ultrasonics, were used in the study of pulse delay measurements in aluminum and in a room temperature cured epoxy. Group velocity in aluminum was determined with both techniques. The application of these two methods to epoxy cure monitoring is discussed.

A procedure to estimate the electromagnetic properties of chiral samples with different volume concentrations is developed based upon the electromagnetic properties of the chiral sample with a specified volume concentration. The electromagnetic properties of the chiral sample is obtained using normal incidence measurements at microwave frequencies. Then the macroscopic susceptibilities and microscopic rotabilities of the chiral sample are computed in the long wavelength (low frequency) limit from the measured electromagnetic properties. As long as the microscopic rotabilities of the chiral sample with a given volume concentration are calculated, then the electromagnetic properties of the chiral samples with different volume concentrations can be computed numerically. Comparison between the extrapolated and measured electromagnetic properties of chiral samples will be reported.

A comparison between two flow visualization studies of an axi-symmetric circular jet issuing into still fluid, using two different experimental techniques, is described. In the first case laser induced fluorescence is used to visualize the flow structure, whilst smoke is utilized in the second. Quantitative information was obtained from these visualized flow regimes using two different digital imaging systems. Results are presented of the rate at which the jet expands in the downstream direction and these compare favorably with the more established data.

A fiber-optic/integrated optic optoelectronic neural computer approach to the design of an 'intelligent' aerospace structure is described, and the methodology of the approach is defined. A source consisting of a strained-layer QW laser emitting 100 micro-W at 978 nm and an Er-doped single-mode polarization preserving fiber laser with a gain of 3.9 dB/mW is assumed. The SNR for the aerospace plane is calculated with 49 sensing arms. A 441-path splitter is required; this is designed using an eight-stage multipath coupler based on a 3X3 polarizer/splitter as the basic repeating element. A surface-mounted implementation is suggested, which includes a 448-path switch, an integrated-optic coupler, a detector, an ADC, and a processor.

A series of structural vibration control experiments and related theory are developed to check the effectiveness of analog and digital control system with piezoelectric material sensors and actuators. Velocity feedback analog control has been tried for the cantilever beam with PZT (lead-zirconate-titanate) wafer sensors and actuators. To improve the control system, steady- state quadratic optimal control algorithm using a digital micro-computer has been used. To apply optimal control algorithms, signals sensed by partially distributed sensors were converted to point concept signals like those from conventional displacement or velocity sensors. Actuating voltage signals were then synthesized from point force output signals. This paper presents excellent results for structural vibration control using both analog and digital systems.

Damage assessment within composite structural components can be undertaken with embedded optical fiber sensors in two very different ways: the optical fibers can be damage sensitized so they fracture when the composite is critically loaded or they can be made into very sensitive strain sensors that can detect acoustic energy released when the composite is subjected to sufficient load to cause internal damage. We shall report on our latest research for these two approaches. This includes the results of impact tests on the first full scale aircraft composite leading edge instrumented with a 'damage assessment system' comprising a multilayered, embedded grid of 250 damage sensitized optical fibers. We shall also report on the extension of this work to glass fiber/epoxy shells, and the first correlation of acoustic emission signals (detected by embedded interferometric fiber optic sensors) to specific cracks and delaminations within Kevlar/epoxy specimens.

There is considerable interest in the development of microwave ceramic phase shifters because of limitations of currently available ferrite and PIN diode phase shifters regarding cost and reliability and complexity. Ceramic phase shifters may provide a cost breakthrough for the phase array antenna designer while maintaining low insertion loss and low drive power and high power handling capacity. This paper describes a ceramic phase shifter which utilizes a ferroelectric material for obtaining phase shifts from changes in dc biasing fields. Also, the dielectric properties were measured as a function of dc biasing fields, frequency, and temperature for a few compositions of barium-strontium titanate material.

The mathematical rationale behind frequency selective surfaces is discussed. Two strategies - one based on exciting standing surface acoustic waves in a piezoelectric film, and the other on arrays of arrays of piezoelectric capacitors - are outlined to obtain tunable frequency selective surfaces.

In this paper a video digital-imaging technique is described that is currently being developed to permit the assessment of surface temperature and shear stress distributions using liquid crystals. The background to liquid crystal research in aerodynamics is given first and this is followed by a description of the experimental apparatus, along with the method of digital analysis of the color components of the liquid crystal traces. Some typical calibrations of the crystals are then presented as well as details of the main aspects that need to be considered when using liquid crystals as a quantitative measurement technique. The use of the technique is then illustrated by taking the simple case of a heated circular jet impinging normally onto a flat plate.

Electrochromic thin film devices are in advanced stage of development for optical application. Films of Tungsten oxide were deposited in the vacuum chamber and were treated at different temperature. Properties of films were studied. The color of the fresh film is closely related with the substrate temperature, changing from colorless to light yellow and even to light blue when the temperature of substrate increased. Infrared spectra results indicate that proton exists in the film as a form of O-H, and that the strength of absorbed peak of active O-H at 3300-3450/cm increases when the substrate temperature rises. The strength of peak of O-H vibration depend on the substrate temperature. No absorbed peak of H-O-H vibration appears. Measurement of visible spectra of the electrochromic film of a-WO3 was done for different conditions of the electrochromic process. The visible light transmittance of bleached film, which stays the same in the electrochromic cycle, was always different from the fresh film.

Sliding control offers a straightforward approach to robust control of nonlinear as well as linear systems. This control technique has been applied to a wide variety of hardware including robotic manipulators, electric motor drives, and automotive transmissions. This paper describes how the sliding control theory developed by Jean-Jacques Slotine can be applied to trajectory control of a single-axis steering mirror. An introduction to sliding control is presented along with an overview of the steps involved in creating the controller. Hardware is described and implementation issues are addressed.

The progress to date and essential features of approaches to optics and controlled structures technology (CST) are reviewed. The CST framework is suggested as a means of gaining new insight on deformable optical surface control. Within the CST approach, control bandwidths may extend into the frequency range of structural vibration modes, enabling possible reduction in area density and improvements in performance.

The necessary parameters required to accurately and completely specify a precision optical pointing system are discussed, and those critical to the design are investigated more fully. Attention is given to the relationship between system and component parameters such as bandwidth and disturbance rejection, pointing jitter and accuracy, and repeating accuracy. It is concluded that the specification process is complex; the requirements interweave with one another, making it difficult to deal with a single issue at a time.

In December 1989, the first optical delay line was delivered to France's Observatorie de la Cote d'Azur (OCA) for the I2T stellar interferometer. In order to meet the very stringent stability requirement imposed on the delay line during its programmed translation, a servocontrolled stage for active vibration filtering has been developed and successfully tested. This paper first describes the requirements specific to this application. The need for active vibration filtering is then demonstrated, considering the state-of-the-art in translation stage technologies. After a brief description of the servocontrolled filtering stage and the overall interferometer's control architecture, the results obtained are presented. In the last section, we discuss the potential future applications of the developed concept.

The paper describes the analysis performed and the hardware designed to simply and inexpensively implement a dither mirror control system. The design philosophy adopted was to achieve the simplest hardware, electronic, and software design possible. For that purpose, simple models of the structure and control system were developed which provided guidelines for the design, and commercially available hardware was used extensively. Testing of the assembled hardware showed that the simple design rules derived from the analyses were sufficient to describe the salient features of the system behavior; however, a small electronic modification was needed to achieve acceptable performance.

For segmented large mirrors to be used effectively for astronomy they must be actively aligned and controlled to extreme levels of precision. We consider the figure control problem for a spaceborne far-IR telescope, the Precision Segmented Reflector Project Focus Moderate Mission Telescope. We propose a two-stage approach. A figure initialization controller is used to achieve initial phasing and alignment of the telescope using an imaging science detector. A figure maintenance controller keeps the telescope aligned during normal operation using a laser metrology optical truss sensor system. We show that performance of any figure control system is subject to limits on the controllability of the wavefront. Maintenance controllers are additionally limited by considerations of the observability of the wavefront from the maintenance sensors. We show preliminary results for the figure initialization controller. We present a 'Wavefront Compensation' method for figure maintenance control that minimizes wavefront errors due to misalignment errors.

Modal domain optical fiber sensors have recently been employed in the implementation of system identification algorithms and the closed-loop control of vibrations in flexible structures. The mathematical model of the modal domain optical fiber sensor used in these applications, however, only accounted for the effects of strain in the direction of the fiber's longitudinal axis. In this paper, we extend this model to include the effects of arbitrary stress. Using this sensor model, we characterize the sensor's sensitivity and dynamic range.

The dynamics relating the transverse motions of a clamped-free graphite/epoxy beam are investigated. A Bernoulli-Euler beam model with viscoelastic damping is used to predict the transfer function relating the displacement of the clamped end (input) to the displacement of the free end (output). Three different damping strategies are considered. One strategy relies simply on the internal damping arising from the presence of the matrix. A second approach uses continuous strips of a 3M viscoelastic damping material included within the layup to enhance the damping characteristics. And a final design considers optimal placement of the damping material within a specimen to achieve the greatest damping enhancement with a minimum impact on strength, stiffness and weight. Each strategy is applied to two different layup geometries, unidirectional and crossply. An experimental apparatus is configured using a shaker to drive the clamped end and a laser velocity/displacement transducer to measure the displacements of the clamped and free ends. Data are collected and analyzed to evaluate the utility of the model structure for capturing the essential system dynamics and the effectiveness of the damping strategies considered.

A complete set of closed form symbolic equations are developed for a 2-D model of a system comprised of a flexible platform with articulated appendages. The system considered has a flexible two link manipulator, with joint compliance, at one end of the flexible platform and an articulated antenna on the other end. The model is formulated using a Lagrangian approach which incorporates homogeneous transformation matrices, similar to those typically seen in the robotics literature, for the kinematic representation. The integrated control/structure design strategy considered emphasizes rapid system response and minimal structural weight. Constraints are included to keep antenna pointing error to a minimum, and at the same time achieve accurate end point positioning of the manipulator with minimal oscillations.

This paper presents a novel method of estimating the optimal steady state Kalman filter gain of a linear discrete time-invariant system from a non-optimal Kalman filter residual sequence. The relation between the optimal residual sequence and a signal derived from the non-optimal residual sequence is described by a moving average (MA) model whose coefficients are expressed in terms of the state space parameters and the optimal steady state Kalman filter gain. In order to identify the MA model, a whitening filter of the derived signal, which corresponds to an autoregressive (AR) model of the signal, is first identified using the least- squares method. Then the inverse filter of the whitening filter, which corresponds to the MA model, is calculated. From the coefficients of the identified MA model, the optimal steady state Kalman filter gain can be obtained. Numerical example is provided to illustrate the feasibility of this approach.

Most methods of system identification of large flexible structures by far are based on the lumped parameter approach. Because of the considerable computational burden due to the large number of unknown parameters, distributed parameter approach, which greatly decreases the number of unknowns, has being investigated. In this paper a distributed parameter model for the estimation of modal characteristics of NASA Mini-Mast truss has been formulated. Both Bernoulli-Euler beam and Timoshenko beam equations are used to characterize the lateral bending vibrations of the truss. The measurement of the lateral displacement at the tip of the truss is provided to the maximum likelihood estimator. Closed-form solutions of the partial differential equations and closed-form expressions of the sensitivity functions are derived so that the estimation algorithm is highly efficient. The resulting estimates from test data by using Timoshenko beam model are found to be comparable to those derived from finite element analysis.

The optical line-of-sight (LOS) stabilization system on a two body platform space platform must be stabilized to sub-microradian levels in the presence of base disturbances to obtain blur free images. In addition, for some applications, the LOS system must assist the platform to rapidly communicate between satellites. An example of a two body spacecraft has a telescope (or beam expander) as the fore body and a sensor suite which can include an active tracking system on the aft body. An isolation system between the two bodies will keep the disturbances generated in each from effecting the other. Such a system could be used for satellite communications, weather tracking systems etc. The need for accurate conirol of angular motion is accomplished with stabilization and isolation platforms and active control of structures and optics. One method includes a concept to blend inertial measuring sensors (IMS) that operate in different frequency ranges to produce an IMS sensor system that can measure base disturbances form DC to over 1000 Hz with minimum distortion. This information is then used to point the LOS at a target with minimumjitter effects. This paper will discuss the second set of experimental results from this method to isolate the LOS from the base motion of a space platform over a wide frequency range. The first set of results can be found in Reference 1. The first set of tests dealt mainly with the aspects of blending sensors that operate in different frequencies together. The second set of results to be reported in this paper will include pointing stability and retargeting results. These experimental results were obtained from implementing this method on a two body spacecraft simulator.