David R. Jacques

An ontological framework for clarifying flexibility-related terminology via literature survey

Despite its ubiquity in the systems engineering literature, flexibility remains an ambiguous concept. There exist a multitude of definitions, which vary not only by domain, but within domains as well. Furthermore, these definitions often conflict with one another, making it difficult to discern the intended meaning in a given study or to form generalizations across studies. Complicating matters, there is a plethora of related terminology that is often used carelessly and/or inter-changeably with flexibility. In this paper, we employ a novel ontological framework for clarifying salient aspects of extant flexibility-related terminology. While it was not possible to distill consensus definitions from the literature, we did identify certain dominant characteristics that enabled us to formulate a set of democratic definitions for flexibility, adaptability, and robustness, as well as recommended definitions for agility and versatility. We believe that the proposed definitions of these key system design principles may provide a baseline for improving analysis and communication among systems engineering practitioners and academics.

Receding Horizon Control Lyapunov Function Approach to Suboptimal Regulation of Nonlinear Systems

established, their nonlinear counterparts are just starting to emerge. Moreover, in most cases these tools lead to partialdifferentialequationsthataredife culttosolve.Inthispaperweproposeasuboptimalregulatorfornonlinear afe nesystemsbaseduponthecombinationofrecedinghorizonandcontrolLyapunovfunctiontechniques.Themain result of the paper shows that this controller is nearly optimal provided that a certain e nite horizon problem can besolved on-line. Additional results include1 )sufe cient conditionsguaranteeing closed-loop stability even in cases wherethere isnot enough computational poweravailable to solvethisoptimization on-lineand 2 )an analysis ofthe suboptimality level of the proposed method. These results are illustrated with two simple examples comparing the performance of thesuboptimal controller against that achieved by some other popularnonlinear control methods.

Autonomous aerial refueling based on the tanker reference frame

An aircraft formation autopilot is designed for flight test to demonstrate autonomous aerial refueling. The controller requirements are stated, and models for the lead and wing aircraft are outlined and stabilized. Control laws are developed for the model, and four frames of reference are investigated for optimal control. Next, a simulation is constructed with modeled disturbances to produce the real-time inputs that will be available to the controller. Results from simulations of the controller are presented and assessed, including an exploration of sensitivity and robustness. Finally, results are presented from a limited flight test investigation conducted with a formation of an Air Force C-12 and a variable stability Learjet LJ-25, flown by the controller. Fully autonomous aerial refueling maneuvers were successfully demonstrated in both level and turning flight. Finally, conclusions and lessons learned from the flight test and the controller development are presented

Search, Classification and Attack Decisions for Cooperative Wide Area Search Munitions

There are currently several wide area search munitions in the research and development phase within the Department of Defense. While the work on the airframes, sensors, target recognition algorithms and navigation schemes is promising, there are insufficient analytical tools for evaluating the effectiveness of these concept munitions. Simulation can be used effectively for this purpose, but analytical results are necessary for validating the simulations and facilitating the design trades early in the development process. Recent research into cooperative behavior for autonomous munitions has further highlighted the importance of fundamental analysis to steer the direction of this new research venture. This paper presents extensions to some classic work in the area of search and detection. The unique aspect of the munition problem is that a search agent is lost whenever an attack is executed. This significantly impacts the overall effectiveness in a multi-target/false target environment. While the analytic development here will concentrate on the single munition case, extensions to the multi-munition will be discussed to include the potential benefit from cooperative classification and engagement.

A MATLAB toolbox for fixed-order, mixed-norm control synthesis

This article introduces a MATLAB toolbox for fixed order, mixed-norm control synthesis. The Mixed-Norm Toolbox contains a complete set of routines for both continuous and discrete-time systems. The problem addressed by the toolbox is that of finding a compensator which minimizes the H/sub 2/ norm of a transfer function, while constraining any combination of H/sub /spl infin// and/or l/sub 1/ (L/sub 1/) norms of possibly dissimilar transfer functions to be below specified levels. Within reason, any number or combination of constraints can be added to the problem, and the method constrains the norms directly without reliance on upper bounds. The primary contribution of the Mixed-Norm Toolbox is a modular collection of norm and gradient algorithms which can be used with almost any nonlinear, constrained optimization solver. While global convergence is not guaranteed for the resulting nonconvex problem, the toolbox has been successfully used to show portions of Pareto optimal curves and surfaces for a wide variety of problems.

A Modeling Framework for Studying Quantum Key Distribution System Implementation Nonidealities

Quantum key distribution (QKD) is an innovative technology that exploits the laws of quantum mechanics to generate and distribute unconditionally secure shared key for use in cryptographic applications. However, QKD is a relatively nascent technology where real-world system implementations differ significantly from their ideal theoretical representations. In this paper, we introduce a modeling framework built upon the OMNeT++ discrete event simulation framework to study the impact of implementation nonidealities on QKD system performance and security. Specifically, we demonstrate the capability to study the device imperfections and practical engineering limitations through the modeling and simulation of a polarization-based, prepare and measure BB84 QKD reference architecture. The reference architecture allows users to model and study complex interactions between physical phenomenon and system-level behaviors representative of real-world design and implementation tradeoffs. Our results demonstrate the flexibility of the framework to simulate and evaluate current, future, and notional QKD protocols and components.

Air vehicle optimal trajectories between two radars

The problem of formulating and analyzing the single vehicle path planning problem for radar exposure minimization is addressed. A single vehicle with given initial and final positions is exposed to two radars and the optimal path between the radars is sought. The objective cost of the optimal paths are compared with the direct path (a straight line) as well as trajectories generated using the graphical Voronoi path planning approach. Finally, each radar is given a different weight, simulating differing transmission powers, and optimal paths are sought for the same radar configurations. The objective costs of these trajectories are again compared to the direct path and the weighted Voronoi path. The nonlinear differential equations governing the optimal trajectory against multiple radars constitute a difficult, numerically sensitive two-point boundary value problem. Results indicate that approaching the Voronoi-generated curves in an optimal way from the end points may provide for feasible online and real-time utilization.

A General Method of Measuring Interoperability and Describing Its Impact on Operational Effectiveness

A general method of measuring the interoperability of a heterogeneous set of systems, experiencing any type and number of interoperations, in the context of an operational process is given. Furthermore, for confrontational operations (friendly versus adversary), the method gives sufficient conditions for relating the interoperability measurement to operational effectiveness. Owing to the difficulty in creating a general method of interoperability measurement, developers of extant interoperability assessment methods have relied upon problem decomposition to produce methods of assessing the interoperability of specific types of systems experiencing distinct modes of interoperation. Unfortunately, this approach fractured the problem, effectively driving them further from the solution.Therefore, in this research, a holistic, fundamental, and flexible means of describing a general method of interoperability measurement was undertaken which models systems according to their interoperability-related features in the context of an operational process.An application of the method highlights the new concept of confrontational interoperability, demonstrates the relationship between interoperability and operational effectiveness in the context of a suppression of enemy air defenses (SEAD) scenario, and illustrates how an interoperability measurement can motivate system upgrades.

Optimal Control of Sensor Threshold for Autonomous Wide Area Search Munitions

The optimal employment of autonomous wide area search munitions is addressed. The scenario considered involves an airborne munition searching a battle space for stationary targets in the presence of false targets. Targets are modelled with uniform, Poisson, and normal distributions. False targets are modelled with Poisson distributions. All relevant parameters can be extracted from intelligence information on the enemy’s order of battle and the sensor performance specification. Analytic weapon effectiveness measures are derived using applied probability theory. The effectiveness measures derived in this paper handle time-varying parameters which characterize the battle space environment and the performance of the munition’s sensor. This allows the formulation and solution of optimization problems that maximize the probability of a target attack while at the same time constraining the probability of a false target attack. Optimal schedules for controlling the sensor threshold during the flight are derived and compared to the optimal constant-threshold results. An increase in weapon effectiveness is demonstrated when the sensor threshold is dynamically controlled during the flight.

A receding horizon state dependent Riccati equation approach to suboptimal regulation of nonlinear systems

The problem of rendering the origin an asymptotically stable equilibrium point of a nonlinear system while, at the same time, optimising some measure of performance has been the object of much attention in the past few years. In contrast to the case of linear systems where several optimal synthesis techniques (such as /spl Hscr//sub /spl infin//, /spl Hscr//sub 2/ and /spl Lscr//sup 1/) are well established, their nonlinear counterparts are just starting to emerge. Moreover, in most cases these tools lead to partial differential equations that are difficult to solve. We propose a suboptimal regulator for nonlinear affine systems based upon the combination of receding horizon and state dependent Riccati equation techniques. The main result of the paper shows that this controller is nearly optimal provided that a certain finite horizon problem can be solved online. Additional results include sufficient conditions guaranteeing closed loop stability even in cases where there is not enough computational power available to solve this optimization online, and an analysis of the suboptimality level of the proposed method.