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<p>Activity planning for space mission operations has traditionally been a human-in-the-loop effort, conducted by ground operators. Over the past two decades, advances have been made toward automating the mission planning process, in an effort to improve the efficiency of the mission operations system, while increasing the mission return. In keeping with NASA’s goals, some aspects of onboard mission planning are increasingly used for complex missions, particularly for planetary surface missions that are subject to long communication delays.</p> <p>This dissertation research develops an automated mission planning framework and applies it to two spacecraft scenario case studies: a science orbiter and a science rover mission. Mission plans are optimized on the basis of science return, accommodating spacecraft movement</p> <p>to sites of scientific interest according to ground-team preferences, while staying within rover engineering and traverse-related constraints. Automated mission planners offer the capability to schedule engineering and science activities onboard, without ground-in-the-loop interaction. Resource modeling and path planning can be done onboard, reducing the need for modeling and verification by ground operators. Further, automated mission planners</p> <p>may incorporate an optimization executive that maximizes the mission return within the available resource constraints. The proposed planners may be utilized onboard autonomous spacecraft and rovers with limited human support. Also, they may be run on the ground by</p> <p>mission planning teams to provide additional insight during the planning process. Utilizing a variety of optimization approaches, the developed automated mission planners establish the planned sequence of activities, including and engineering activities, while adhering to constraints imposed by orbital geometry or planetary pathing requirements and resource availability. The focus of the work is on remote, robotic missions in which human-in-the loop decision input is delayed or at times unavailable. Two major classes of robotic missions are examined: Orbital science missions in which primary science activities are performed periodically at a specified rate, and a planetary rover mission in which a larger variety of science activities are interspersed with unique terrain navigation activities. The automated mission planning framework is designed to be adapted based upon the application. Optimization methods suitable for different mission planning problems are presented, comparing methods on the basis of computation speed, resources required and solution value.</p> <p>The Aerospace Systems Engineering definitions for “robustness” and “flexibility” are given quantifiable, mathematical definitions and are incorporated into the framework as quality metrics to provide criteria with which to evaluate and compare the produced activity plans.</p> <p>The metrics “reliability” and “latent performance index” provide additional criteria for plan evaluation. A variety of automated mission planning algorithmic approaches are developed and described functionally and mathematically. Planning tools capable of plan verification, Monte Carlo simulation-based verification and plan variation analysis are developed and described in detail. Two detailed, step by step case studies are developed, applying and</p> <p>running all the mission planning and analysis tools to provide planning solutions and analysis of generated plans for the science orbiter and science rover scenarios. The application of the developed planning solutions to the presented missions, including the determination</p> <p>of the quality metrics, are seen as the primary contributions to the advancement of the</p> <p>state of the art in automated mission planning. The Automated Mission Planning and plan analysis techniques and practices are summarized into a User’s Guide to Automated Mission Planning. The guide aids the user in developing their own automated mission planning framework and applying it to their unique mission planning problems. Numerous avenues for future work are proposed to extend this research into other, useful areas. Two areas of road mapping—tasks that must be done to enable a future vision for improved automated planning—are discussed.</p>

A key attribute of resilience, robustness serves as a predictor of infrastructure system performance under disruptions, thus informing proactive infrastructure risk management. A literature review indicated that previous studies did not consider some key factors that can influence the robustness of Air Transportation Infrastructure Networks (ATIN) and thus their (system-level cascade) systemic risk management processes. In this respect, the current study first assesses existing and then develops a new methodology to quantify the robustness of ATIN. Specifically, based on integrating travel time and flight frequency, the study develops alternative best route and link weight approaches to assess key ATIN robustness measures and relevant operating cost losses (OCL). In order to demonstrate the practical use of the developed methodology, the robustness and the associated OCL of the Canadian Domestic Air Traffic Network are evaluated under random failures (i.e., disruptive events that occur randomly) and targeted threats (i.e., disruptive events that occur deliberately). The analysis results show that the network robustness is influenced by the utilized evaluation approach, especially after 20% of the network components become nonoperational. Overall, the methodology developed within this study is expected to provide ATIN policymakers with the means to quantify the network robustness and OCL, and thus enable ATIN resilience-guided proactive risk management in the face of natural or anthropogenic hazard realizations. / Thesis / Master of Applied Science (MASc)

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No / This paper presents the results of a simulation study of 10 fire tests on restrained steel beam–column assemblies using five different types of joints: fin plate, flexible endplate, flush endplate, web cleat and extended endplate. This paper will provide details of the simulation methodology for achieving numerical stability and faithful representation of detailed structural behaviour, and compare the simulation and experimental results, including joint failure modes, measured beam axial forces and beam mid-span deflections. Good agreement between ABAQUS simulations and experimental observations confirms that the finite element models developed through the ABAQUS/Standard solver are suitable for predicting the structural fire behaviour of restrained structural assemblies with realistic steel joints undergoing different phases of behaviour in fire, including restrained thermal expansion and catenary action in the beams. The validated model may be used to conduct numerical parametric studies to generate theoretical data to help develop detailed understanding of steel joint behaviour and their effects on robustness of steel framed structures in fire.

Yes / A full-scale composite floor plate was tested to investigate the flexural behavior and in-plane effects of the floor slab in a grillage of composite beams that reduces the tendency for longitudinal splitting of the concrete slab along the line of the primary beams. This is important in cases where the steel decking is discontinuous when it is orientated parallel to the beams. In this case, it is important to demonstrate that the amount of transverse reinforcement required to transfer local forces from the shear connectors can be reduced relative to the requirements of Eurocode 4. The mechanism under study involved in-plane compression forces being developed in the slab due to the restraining action of the floor plate, which was held in position by the peripheral composite beams; while the secondary beams acted as transverse ties to resist the forces in the floor plate that would otherwise lead to splitting of the slab along the line of the primary beams. The tendency for cracking along the center line of the primary beam and at the peripheral beams was closely monitored. This is the first large floor plate test that has been carried out under laboratory conditions since the Cardington tests in the early 1990s, although those tests were not carried out to failure. This floor plate test was designed so that the longitudinal force transferred by the primary beams was relatively high (i.e., it was designed for full shear connection), but the transverse reinforcement was taken as the minimum of 0.2% of the concrete area. The test confirmed that the primary beams reached their plastic bending resistance despite the discontinuous decking and transverse reinforcement at the minimum percentage given in Eurocode 4. Based on this test, a reduction factor due to shear connectors at edge beams without U-bars is proposed.

Decision-making is an essential topic for multi-robot coordination and collaboration and is also the main topic of this thesis. Examples can be found in autonomous driving, environmental monitoring, intelligent transportation, etc. To study this problem, we first use multiple applications as motivating examples and then construct the general formulation and solution for those applications. Finally, we extend our investigation from the fundamental problem formulation to resilient and decentralized versions. All those problems are studied in the combinatorial optimization domain with the help of submodular and matroid optimization techniques. As a motivating example, we use a multi-robot environmental monitoring problem to extract the general formulation of a multi-robot decision-making problem. Consider the problem of deploying multi-agent teams for environmental monitoring in a precision farming application. We want to answer the question of when and where to deploy our robots. This is a typical task allocation problem in multi-robot systems. Using the above problem as an example, we first focus on this decision-making problem, e.g., intermittent deployment problem, in a centralized scenario. Given a predictable agriculture environment, we want to make decisions for robots for this monitoring task. The problem is formulated as a combinatorial submodular optimization with matroid constraints. By utilizing the properties of submodularity, we aim to develop a solution with performance guarantees. This motivating example demonstrates how to use a submodular function and matroids to model and solve decision-making problems in multi-robot systems. Based on this framework, we continue to explore the fundamental decision-making problem in several other directions in multi-robot systems, including the robust decision-making problem. All those problems and solutions are formulated and considered in a centralized scenario. In the second part of this thesis, we switch our focus from centralized to decentralized scenarios. We first investigate a case where the robots in a distributed multi-robot system need to work together to guard the system against worst-case attacks while making decisions. By worst-case attacks, we refer to the case where the system may have up to $K$ sensor failures. To increase resilience, we propose a fully distributed algorithm to guide each robot's action selection when the system is attacked. The proposed algorithm guarantees performance in a worst-case scenario where up to a portion of the robots malfunction due to attacks. Based on this specific task allocation problem in robotics, we then create a unified framework for a more general case in a decentralized scenario, e.g., asynchronous decentralized decision-making problems with matroid and knapsack constraints. Finally, several applications in decentralized scenarios are used to validate the theoretical guaranteed performance in robotics. / Doctor of Philosophy / Robots have been widely used as mobile sensing agents nowadays in various applications. Especially with the help of multi-robot systems and artificial intelligence, our lives have changed dramatically in the last decades. One of the most fundamental questions is how to utilize multi-robot systems to finish tasks successfully. To answer this, we need first to formulate the problem from applications and then find theoretically guaranteed answers to those questions. Meanwhile, the robustness and resilience of the solution also need to be taken care of, as cyber-attacks or system failures can happen everywhere. Motivated by those two main goals, this thesis will first use multiple applications to introduce the thesis's topic. We then provide solutions to those problems in centralized and decentralized scenarios. Meanwhile, to increase the system's ability to handle failures, we need to answer how to improve the robustness and resilience of the proposed solutions. Therefore, the topic of this thesis spread from problem formulation to failure-proof solutions. The result of this thesis can be widely used in multi-robot decision-making applications, including autonomous driving, intelligent transportation, and other cyber-physical systems.

As power conversion technology is being integrated further into high-reliability environments such as aerospace and electric vehicle applications, a full analysis and understanding of the system's robustness under operating conditions inside and outside the safe-operating-area is necessary. The robustness of power semiconductor devices, a primary component of power converters, has been traditionally evaluated through qualification tests that were developed for legacy silicon (Si) technologies. However, new devices have been commercialized using wide bandgap (WBG) semiconductors including silicon carbide (SiC) and gallium nitride (GaN). These new devices promise enhanced capabilities (e.g., higher switching speed, smaller die size, lower junction capacitances, and higher thermal conductance) over legacy Si devices, thus making the traditional qualification experiments ineffective. This work begins by introducing a new methodology for evaluating the switching robustness of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). Recent static acceleration tests have revealed that SiC MOSFETs can safely operate for thousands of hours at a blocking voltage higher than the rated voltage and near the avalanche boundary. This work evaluates the robustness of SiC MOSFETs under continuous, hard-switched, turn-off stresses with a dc-bias higher than the device rated voltage. Under these conditions, SiC MOSFETs show degradation in merely tens of hours at 25si{textdegree}C and tens of minutes at 100si{textdegree}C. Two independent degradation and failure mechanisms are unveiled, one present in the gate-oxide and the other in the bulk-semiconductor regions, detected by the increase in gate leakage current and drain leakage current, respectively. The second degradation mechanism has not been previously reported in the literature; it is found to be related to the electron hopping along the defects in semiconductors generated in the switching tests. The comparison with the static acceleration tests reveals that both degradation mechanisms correlate to the high-bias switching transients rather than the high-bias blocking states. The GaN high-electron-mobility transistor (HEMT) is a newer WBG device that is being increasingly adopted at an unprecedented rate. Different from SiC MOSFETs, GaN HEMTs have no avalanche capability and withstand the surge energy through capacitive charging, which often causes significant voltage overshoot up to their catastrophic limit. As a result, the dynamic breakdown voltage (BV) and transient overvoltage margin of GaN devices must be studied to fully evaluate the switching ruggedness of devices. This work characterizes the transient overvoltage capability and failure mechanisms of GaN HEMTs under hard-switched turn-off conditions at increasing temperatures, by using a clamped inductive switching circuit with a variable parasitic inductance. This test method allows flexible control over both the magnitude and the dV/dt of the transient overvoltage. The overvoltage robustness of two commercial enhancement-mode (E-mode) p-gate HEMTs was extensively studied: a hybrid drain gate injection transistor (HD-GIT) with an Ohmic-type gate and a Schottky p-Gate HEMT (SP-HEMT). The overvoltage failure of the two devices was found to be determined by the overvoltage magnitude rather than the dV/dt. The HD-GIT and the SP-HEMT were found to fail at a voltage overshoot magnitude that is higher than the breakdown voltage in the static current-voltage measurement. These single event failure tests were repeated at increasing temperatures (100si{textdegree}C and 150si{textdegree}C), and the failures of both devices were consistent with room temperature results. The two types of devices show different failure behaviors, and the underlying mechanisms (electron trapping) have been revealed by physics-based device simulations. Once this single-event overvoltage failure was established, the device's robustness under repetitive overvoltage and surge-energy events remained unclear; therefore, the switching robustness was evaluated for both the HD-GIT and SP-HEMT in a clamped, inductive switching circuit with a 400 V dc bias. A parasitic inductance was used to generate the overvoltage stress events with different overvoltage magnitude up to 95% of the device's destructive limit, different switching periods from 10 ms to 0.33 ms, different temperatures up to 150si{textdegree}C, and different negative gate biases. The electrical parameters of these devices were measured before and after 1 million stress cycles under varying conditions. The HD-GITs showed no failure or permanent degradation after 1-million overvoltage events at different switching periods, or elevated temperatures. The SP-HEMTs showed more pronounced parametric shifts after the 1 million cycles in the threshold voltage, on-resistance, and saturation drain current. Different shifts were also observed from stresses under different overvoltage magnitudes and are attributable to the trapping of the holes produced in impact ionization. All shifts were found to be recoverable after a relaxation period. Overall, the results from these switching-oriented robustness tests have shown that SiC MOSFETs show a tremendous lifetime under static dc-bias experiments, but when excited by hard-switching turn-off events, the failure mechanisms are accelerated. These results suggest the insufficient robustness of SiC MOSFETs under high bias, hard switching conditions, and the significance of using switching-based tests to evaluate the device robustness. These inspired the GaN-based hard-switching turn-off robustness experiments, which further demonstrated the dynamic breakdown voltage phenomena. Ultimately these results suggest that the breakdown voltage and overvoltage margin of GaN HEMTs in practical power switching can be significantly underestimated using the static breakdown voltage. Both sets of experiments provide further evidence for the need for switching-oriented robustness experiments to be implemented by both device vendors and users, to fully qualify and evaluate new power semiconductor transistors. / Doctor of Philosophy / Power conversion technology is being integrated into industrial and commercial applications with the increased use of laptops, server centers, electric vehicles, and solar and wind energy generation. Each of these converters requires the power semiconductor devices to convert energy reliably and safely. textcolor{black}{Silicon has been the primary material for these devices; however,} new devices have been commercialized from both silicon carbide (SiC) and gallium nitride (GaN) materials. Although these devices are required to undergo qualification testing, the standards were developed for silicon technology. The performance of these new devices offers many additional benefits such as physically smaller dimensions, greater power conversion efficiency, and higher thermal operating capabilities. To facilitate the increased integration of these devices into industrial applications, greater robustness and reliability analyses are required to supplement the traditional tests. The work presented here provides two new experimental methodologies to test the robustness of both SiC and GaN power transistors. These methodologies are oriented around hard-switching environments where both high voltage biases and high conduction current exist and stress the intrinsic semiconductor properties. Experimental evaluations were conducted of both material technologies where the electrical properties were monitored over time to identify any degradation effects. Additional analyses were conducted to determine the physics-oriented failure mechanisms. This work provides insight into the limitations of these semiconductor devices for both device designers and manufacturers as well as power electronic system designers.