Timothy E. Busch

Adaptive jitter rejection technique applicable to airborne laser communication systems

Satellite jitter adversely affects the pointing, acquisition, and tracking (PAT) functions of an intersatellite laser communication system. Reliable aircraft-based testing of PAT systems requires that the detrimental effects of aircraft jitter be controlled and a realistic satellite jitter environment be emulated. A novel jitter rejection technique, the self-tuning feed-forward compensation scheme, is developed to minimize the effects of aircraft vibration on the PAT terminal. The self-tuning results in the implicit characterization of the mechanical jitter propagation path, thus facilitating the injection of prerecorded satellite jitter in the control circuitry of steering mirrors.

Modeling of an acousto-optic laser beam steering system intended for satellite communication

High data rate of laser communication systems should be matched by wide operational bandwidth of beam positioning. This could be achieved by the application of nonmechanical beam steering technologies utilizing acousto-optic phenomena. Major components of acousto-optic beam steering systems, a Bragg cell, and a quadrant detector are subjected to comprehensive laboratory testing and characterization as components of a control system. A mathematical and computer simulation model of the entire steering system addressing system dynamics, cross coupling of azimuth and elevation channels, and nonlinearity, and facilitating synthesis of advanced control laws is developed.

Demonstration of a jitter rejection technique for free-space laser communication

An active jitter compensation scheme intended for free space intersatellite laser communication, utilizing self-tuning feedforward compensation, is developed. It is implemented via computer-controlled analog circuitry. The theory, design, and implementation of the laboratory prototype are discussed. A performance evaluation, comparing the feedforward compensator with the existing closed-loop control, is presented with the feedforward technique demonstrating significant jitter reduction.

Experimental implementation of model-reference-control for fine-tracking mirrors

We proposed the use of model reference control for the improvement in the performance characteristics of fine tracking mirrors. We present both analog and digital implementations of model reference control on a specially designed high bandwidth steering mirror and a commercially available lower bandwidth mirror. Improvement in system response and immunity to environmental jitter are demonstrated.

Modeling Operational Robustness and Resiliency with High-Level Petri Nets

Military operations are highly complex workflow systems that require careful planning and execution. The interactive complexity and tight coupling between people and technological systems has been increasing in military operations, which leads to both improved efficiency and a greater vulnerability to mission accomplishment due to attack or system failure. Although the ability to resist and recover from failure is important to many systems and processes, the robustness and resiliency of workflow management systems has received little attention in literature. The authors propose a novel workflow modeling framework using high-level Petri nets (PNs). The proposed framework is capable of both modeling structure and providing a wide range of qualitative and quantitative analysis. The concepts of self-protecting and self-healing systems are captured by the robustness and resiliency measures proposed in this study. The proposed measures are plotted in a Cartesian coordinate system; a classification scheme with four quadrants (i.e., possession, preservation, restoration, and devastation) is proposed to show the state of the system in terms of robustness and resiliency. The authors introduce an overall sustainability index for the system based on the theory of displaced ideals. The application of the methodology in the evaluation of an air tasking order generation system at the United States Air Force is demonstrated.

Demonstration of jitter rejection technique for free-space laser communication

An active jitter compensation scheme intended for free space intersatellite laser communication, utilizing self-tuning feedforward compensation, is developed. It is implemented via computer-controlled analog circuitry. The theory, design, and implementation of the laboratory prototype are discussed. A performance evaluation, comparing the feedforward compensator with the existing closed-loop control, is presented with the feedforward technique demonstrating significant jitter reduction.

Lyapunov-based decentralized adaptive control for laser beam tracking systems

A successful controller design is crucial for establishing and maintaining an optical link between free-space communication stations engaged in a laser communication session. This task is quite difficult due to nonlinear behavior, cross-coupled dynamics, and time-varying characteristics of all known beam steering technologies. A novel adaptive control technique utilizing Lyapunov function to ensure global asymptotic stability of the system, thus resulting in a highly robust system performance, is developed. The technique applied to a piezo-electric mirror setup results in a highly efficient controller design that does not require prior knowledge of system dynamics, while providing independent access to azimuth and elevation positions of the laser beam. The basic algorithm is presented and the results of its application are demonstrated.

Genetic algorithm optimization for Bragg cell design

Nonmechanical beam steering technologies utilizing acoustooptics enable us to achieve the high-bandwidth laser beam positioning required for optical communications, laser scanners, ladars, etc. The properties of the Bragg cell, which are chiefly responsible for the efficiency and attainable characteristics of the entire positioning system, are ensured by the successful design of this optical component. However, the design of Bragg cells is dominated by the experience and intuition of the designers, and the potential of this technology is not fully utilized. An optimal Bragg cell design problem is formulated on the basis of known equations of the underlying physical phenomena, and a genetic optimization scheme is applied for the solution of the resulting formidable problem. The approach not only yields a design solution, but also enables one to vary the design criterion and emphasize particular properties of the resultant component. The prowess of the proposed approach is demonstrated by design optimization examples.

Model reference control of a laser beam steering system for laser communication applications

High data rates of laser communication systems must be complemented by high tracking bandwidth of acousto-optic beam steering technology utilizing Bragg cells. This research investigates applications of advanced control techniques to enhance characteristics of a laser beam steering system containing a Bragg cell - quadrant detector combination. Laboratory characterization of both devices resulting in detailed mathematical description and simulation models is presented. An adaptive model reference controller is designed and validated by computer simulation.

Modeling of the tracking system components of the laser satellite communication systems

High data rate of laser communication systems should be matched by wide operational bandwidth of beam positioning. This could be achieved by the application of non-mechanical beam steering technologies utilizing acousto-optic phenomena. Major components of acousto-optic beam steering systems, a Bragg cell and a quadrant detector, are subjected to comprehensive laboratory testing and characterization as components of a control system. Mathematical and computer simulation model of the entire steering system, addressing system dynamics, cross-coupling of azimuth and elevation channels, and nonlinearity, and facilitating synthesis of advanced control laws, is developed.