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Theses and Dissertations

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Articles 781 - 810 of 1780

Full-Text Articles in Aerospace Engineering

Stochastic Real-Time Optimal Control: A Pseudospectral Approach For Bearing-Only Trajectory Optimization, Steven M. Ross Sep 2011

Stochastic Real-Time Optimal Control: A Pseudospectral Approach For Bearing-Only Trajectory Optimization, Steven M. Ross

Theses and Dissertations

A method is presented to couple and solve the optimal control and the optimal estimation problems simultaneously, allowing systems with bearing-only sensors to maneuver to obtain observability for relative navigation without unnecessarily detracting from a primary mission. A fundamentally new approach to trajectory optimization and the dual control problem is developed, constraining polynomial approximations of the Fisher Information Matrix to provide an information gradient and allow prescription of the level of future estimation certainty required for mission accomplishment. Disturbances, modeling deficiencies, and corrupted measurements are addressed with recursive updating of the target estimate with an Unscented Kalman Filter and the …

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Increasing The Performance Of A Sliding Discharge Actuator Through The Application Of Multiple Potentials, Steven D. Seney Jr. Sep 2011

Increasing The Performance Of A Sliding Discharge Actuator Through The Application Of Multiple Potentials, Steven D. Seney Jr.

Theses and Dissertations

This work encompasses a comparison between a sliding discharge DBD actuator with grounded and AC biased sliding electrode driven at kHz frequency. The induced velocity in the bulk flow was recorded with PIV and compared for multiple potential splits between two test configurations and a baseline sliding discharge actuator over three test phases. In the first test phase, varying potential splits were examined between the primary and secondary electrode with the sliding electrode grounded. The potential splits induced a thicker induced jet than the baseline case with similar peak velocities on the order of 1.25 m/s at the 61 mm …

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Solar Warning Architecture For Manned Missions To Mars, James S. Bohren, John K. Howard Jun 2011

Solar Warning Architecture For Manned Missions To Mars, James S. Bohren, John K. Howard

Theses and Dissertations

Solar radiation storms represent a dire threat to manned interplanetary space travel. Earth's current solar forecasting architecture is Earth-focused and insufficient to provide timely warnings to a manned mission to Mars, therefore a "best value" solar warning architecture must be identified. A total of 14 solar warning architectures were developed by varying 5 solar sensor locations, 2 processing locations, and 2 communications strategies. Using Satellite Tool Kit, performance of the candidate architectures in terms of Warning Time and Solar Coverage was quantified during a Mars mission scenario based on NASA's Design Reference Architecture 5.0. Cost of each candidate architecture was …

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Spacecraft Demand Tasking And Skip Entry Responsive Maneuvers, Robert A. Bettinger Jun 2011

Spacecraft Demand Tasking And Skip Entry Responsive Maneuvers, Robert A. Bettinger

Theses and Dissertations

The purpose of this research was to parametrically investigate the viability of skip entry maneuvers as an alternative to vacuum-only maneuvers, and to identify whether skip entry maneuvers can extend spacecraft mission lifetime by limiting propellant expenditure through the exploitation of the aerodynamic interaction between the upper atmosphere and an example entry vehicle and remote-sensing orbital platform. Employing the X-37B Orbital Test Vehicle (OTV) and a notional satellite design as the example entry vehicles, the entry profile dynamics of a skip entry maneuver were characterized with varying trajectory initial conditions such as entry altitude, entry flight-path angle, and vehicle aerodynamics. …

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Photogrammetric Measurement Of Recession Rates Of Low Temperature Ablators Subjected To High Speed Flow, David W. Callaway Jun 2011

Photogrammetric Measurement Of Recession Rates Of Low Temperature Ablators Subjected To High Speed Flow, David W. Callaway

Theses and Dissertations

This research advances a technique to simulate high temperature/high speed effects in a high speed/low temperature environment and to capture recession of the test article in three-dimensions. A method of fabricating dry ice test articles was developed, and the AFIT Mach 3 pressure-vacuum wind tunnel was used in combination with the dry ice test articles to collect three-dimensional ablation data for models of different shapes at stagnation pressures ranging from approximately 0.4 atm to 3 atm and stagnation temperatures equivalent to room temperature. High speed Schlieren photography was used for visualization, and the three dimensional shape change was quantified with …

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A Relay-Rover Differential Game, Youngdong Choi Jun 2011

A Relay-Rover Differential Game, Youngdong Choi

Theses and Dissertations

Guidance laws are developed to optimally position a relay Micro-UAV (MAV) to provide an operator at the base with real-time Intelligence, Surveillance, and Reconnaissance (ISR) by relaying communication and video signals when the rover MAV performing the ISR mission is out of radio contact range with the base. The ISR system is comprised of two MAVs, the Relay and the Rover, and a Base. The Relay strives to minimize the radio frequency (RF) power required for maintaining communications, while the Rover performs the ISR mission, which may maximize the required RF power. The optimal control of the Relay MAV entails …

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Study Of Varying Boundary Layer Height On Turret Flow Structures, Renato Jelic Jun 2011

Study Of Varying Boundary Layer Height On Turret Flow Structures, Renato Jelic

Theses and Dissertations

The Air Force Institute of Technology and the Air Force Research Labs are investigating flows over turrets which are commonly encountered in directed energy integrations with air vehicles. In this work, the computational study was performed using the NASA developed time-marching finite volume code OVERFLOW 2.2 to analyze the effect of boundary layer height on symmetrical and non-symmetrical turret geometries. The effects of aerodynamics yield to the aberration of the laser beam through two methods, aero-optical and aero-mechanical jitter. The analysis of the flow features, pressure fluctuations, density fluctuations, and forces and moments on the various geometries was conducted to …

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Simulations For The Test Flight Of An Experimental Hale Aircraft, Brooke E. Kaszynski Jun 2011

Simulations For The Test Flight Of An Experimental Hale Aircraft, Brooke E. Kaszynski

Theses and Dissertations

Recent events, such as the crash of NASA's Helios aircraft during a test flight, show that more must be known about the nonlinear control of HALE aircraft. Shearer, Cesnik and their co-workers have developed a code that is a practical solution to the coupled nonlinear aeroelasticity and flight dynamics of very flexible aircraft called the University of Michigan's Nonlinear Aeroelastic Simulation Toolbox (UM/NAST). They are also in the process of developing a model HALE aircraft called X-HALE which will be used to validate this code experimentally. This research performs flight simulations with UM/NAST so as to make predictions about X-HALE's …

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Design And Characterization Of A Space Based Chromotomographic Hyperspectral Imaging Experiment, Jason D. Niederhauser Jun 2011

Design And Characterization Of A Space Based Chromotomographic Hyperspectral Imaging Experiment, Jason D. Niederhauser

Theses and Dissertations

This research focuses upon the design, analysis and characterization of several systems related to a spacebased chromotomographic experiment (CTEx), a hyperspectral imager, currently in development at the Air Force Institute of Technology. Three interrelated subject-areas were developed. The initial focal point was a generic, system-level mechanical layout and integration analysis of the space-based instrument. The scope of this work was intended to baseline the space-based system design in order to allow for further trade-space refinement and requirements development. Second, development of an iteration upon the ground-based version of CTEx was accomplished in an effort to support higher-fidelity field data-collection. This …

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Operational Characteristics Of A Rotating Detonation Engine Using Hydrogen And Air, Rachel M. Russo Jun 2011

Operational Characteristics Of A Rotating Detonation Engine Using Hydrogen And Air, Rachel M. Russo

Theses and Dissertations

Rotating detonation engines (RDE) are pressure gain combustion engines that have the potential for greater efficiency than traditional, constant pressure, deflagration engines. RDEs are smaller and mechanically simpler than pulsed detonation engines. A small diameter (3 in) engine was successfully run on hydrogen and air. Most of the tests were conducted using air with a slightly lower diluents percentage (77% nitrogen as opposed to 79% nitrogen). These tests provided the foundation for determining the operational space (mass flow rate and equivalence ratio) of the rotating detonation engine. From the tests conducted with the lower diluents air, the appropriate run conditions …

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Optical Flow-Based Odometry For Underground Tunnel Exploration, Terra Kier Jun 2011

Optical Flow-Based Odometry For Underground Tunnel Exploration, Terra Kier

Theses and Dissertations

As military operations in degraded or GPS-denied environments continue to increase in frequency and importance, there is an increased necessity to be able to determine precision location within these environments. Furthermore, authorities are finding a record number of tunnels along the U.S.-Mexico border; therefore, underground tunnel characterization is becoming a high priority for U.S. Homeland Security as well. This thesis investigates the performance of a new image registration technique based on a two camera optical- flow configuration using phase correlation techniques. These techniques differ from other image based navigation methods but present a viable alternative increasing autonomy and answering the …

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Process For Refining And Validating A Finite Element Model Of An Experimental High-Altitude, Long-Endurance (Hale) Aircraft, Nicholas A. Sinnokrak Jun 2011

Process For Refining And Validating A Finite Element Model Of An Experimental High-Altitude, Long-Endurance (Hale) Aircraft, Nicholas A. Sinnokrak

Theses and Dissertations

The work presented here focuses on finite element (FE) modeling of X-HALE, a test aircraft designed and built by the University of Michigan, in conjunction with the Air Force Institute of Technology (AFIT) and Air Force Research Laboratory (AFRL). This scaled vehicle is representative of high-altitude, long-endurance (HALE) aircraft and was designed to provide controlled aeroelastic and flight data. FE models of portions of the X-HALE wing structure were created and analysis results were compared against two separate laboratory static bending tests conducted on X-HALE wing sections. The process documented here should improve future efforts to refine FE models of …

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Analysis Of Flow Migration In An Ultra-Compact Combustor, Brian T. Bohan Mar 2011

Analysis Of Flow Migration In An Ultra-Compact Combustor, Brian T. Bohan

Theses and Dissertations

One of the major efforts for turbine engine research is to improve the thrust to weight of the system. One novel concept for accomplishing this is the use of an Ultra-Compact Combustor (UCC). The UCC attempts to shorten the overall combustion length (thereby reducing weight) by performing the combustion in the circumferential direction along the outside diameter of the core flowpath. One of the major benefits of this design is enhanced combustion due to the establishment of a high-g field in the circumferential cavity. AFIT and the Air Force Research Laboratory (AFRL) have been teamed for several years in understanding …

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Architecture Based Workload Analysis Of Uas Multi-Aircraft Control: Implications Of Implementation On Mq-1b Predator, Jason D. Mcgrogan, Michael F. Schneider Mar 2011

Architecture Based Workload Analysis Of Uas Multi-Aircraft Control: Implications Of Implementation On Mq-1b Predator, Jason D. Mcgrogan, Michael F. Schneider

Theses and Dissertations

An increased demand for use of Unmanned Aircraft Systems (UASs) without commensurate increases in pilot manpower has prompted proposals for simultaneous control of multiple aircraft by a single pilot or Multi-Aircraft Control (MAC). To understand the potential effects of MAC, an IMPRINT Pro, Multi-Resource Theory, pilot workload model was developed from pedigreed system architecture. Feedback from active UAS pilots was used to validate the model and establish a workload saturation threshold value of 60, above which pilots may experience performance degradation over extended periods of time. The model predicts that pilots experience low workload when operating one or two UASs …

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Creep Performance Of Oxide Ceramic Fiber Materials At Elevated Temperature In Air And In Steam, Clinton J. Armani Mar 2011

Creep Performance Of Oxide Ceramic Fiber Materials At Elevated Temperature In Air And In Steam, Clinton J. Armani

Theses and Dissertations

The effects of steam on the creep performance for several ceramic materials were investigated at temperatures in the 1100-1300 deg. C range. Experimental programs were designed to explore both tensile and compressive creep behaviors as well as the response in monotonic tension. Subcritical crack growth was determined to be the dominant failure mechanism in ceramic fibers at elevated temperatures in steam. The creep life prediction analysis of ceramic fiber tows was performed using linear elastic fracture mechanics and a power-law crack velocity model. Additionally, the effects of steam at 1300 deg. C on creep performance of high-purity polycrystalline yttrium aluminum …

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Time Resolved Filtered Rayleigh Scattering Measurement Of A Centrifugally Loaded Buoyant Jet, Firas Benhassen Mar 2011

Time Resolved Filtered Rayleigh Scattering Measurement Of A Centrifugally Loaded Buoyant Jet, Firas Benhassen

Theses and Dissertations

The combustion process within the Ultra-Compact Combustor (UCC) occurs in the circumferential direction. The presence of variable flow density within the circumferential cavity introduces significant buoyancy issues. On the other hand, G-loading caused by the presence of centrifugal forces, ensures the circulation of the flow in the circumferential cavity and enhances the completion of the combustion process before allowing the exit of the hot gases to the main flow. The coupling between buoyancy and high G-loading is what predominately influences the behavior of the flow within the UCC. In order to better understand the combustion process within the UCC, three …

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Airborne Wind Energy: Implementation And Design For The U.S. Air Force, Troy L. Cahoon Mar 2011

Airborne Wind Energy: Implementation And Design For The U.S. Air Force, Troy L. Cahoon

Theses and Dissertations

Excitement among researchers about Airborne Wind Energy (AWE) technology matches DoD aims to advance and employ renewable energy. AWE seeks to cost-effectively tap the vast supply of wind energy available at altitudes high above the reach of conventional, ground-based wind turbines (e.g. 500-12,000m). This paper explores viability and implementation of AWE technology for fulfilling USAF energy needs. Characteristics, potential, and developmental status of the AWE resource are presented. A design tool for a rotor-based AWE system is developed, facilitating the analysis of blade performance to simplify design and provide the best efficiencies for a range of conditions. USAF bases are …

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An Investigation Of Cavity Resonance And Its Relationship To Store Force And Moment Loading, Christopher J. Coley Mar 2011

An Investigation Of Cavity Resonance And Its Relationship To Store Force And Moment Loading, Christopher J. Coley

Theses and Dissertations

A store which is released from an internal bay is subjected to a highly unsteady flowfield which influences the release characteristics for the store. Pressure transducer information is often used to estimate store loading, although no direct correlation between the observed frequencies from the pressure transducers and the store loading has been developed. The relationship between the acoustic modes present in the cavity and the force and moment loading on a store released from a bay are investigated through a CFD study using the OVERFLOW 2.1 solver. The acoustic modes of the cavity are calculated from the pressure fluctuation histories …

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Repeatable Manufacture Of Wings For Flapping Wing Micro Air Vehicles Using Microelectromechanical System (Mems) Fabrication Techniques, David S. Dawson Mar 2011

Repeatable Manufacture Of Wings For Flapping Wing Micro Air Vehicles Using Microelectromechanical System (Mems) Fabrication Techniques, David S. Dawson

Theses and Dissertations

While there have been great advances in the area of Flapping Wing Micro Air Vehicles (FWMAV), prototype parts have been constructed with the objective of scientific discovery and basic research. There has been little effort to make parts that could be consistently and repeatedly manufactured. Until recently, there has been little, if any, focus on methods that could be used and verified by subsequent researchers. It is herein proposed that Microelectromechanical System fabrication methods will provide a fast, cheap, and highly repeatable manufacturing method for the FWMAV wings. The wings manufactured to demonstrate this process, bio-inspired by the Manduca Sexta, …

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Performance Characterization Of A Novel Plasma Thruster To Provide A Revolutionary Operationally Responsive Space Capability With Micro- And Nano-Satellites, John-David C. De La Harpe Mar 2011

Performance Characterization Of A Novel Plasma Thruster To Provide A Revolutionary Operationally Responsive Space Capability With Micro- And Nano-Satellites, John-David C. De La Harpe

Theses and Dissertations

Few options currently exist to provide propulsion for extremely small satellites due to design constraints on power, volume, and weight. However, future operation will require a capability to conduct orbital maneuvers, momentum dumping, and precision pointing for these low cost satellites. The research presented here represents the first effort to operate and quantify the performance of a new micro plasma thruster design which provides a novel solution to these disparate competing constraints. The thruster in this study represents a deviation from traditional circular Hall thruster design practices, because it eschews a central magnetic circuit, which results in nearly parallel electric …

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Ch-47d Rotating System Fault Sensing For Condition Based Maintenance, Stephen M. Dickerson Mar 2011

Ch-47d Rotating System Fault Sensing For Condition Based Maintenance, Stephen M. Dickerson

Theses and Dissertations

The Department of Defense (DoD) has mandated the use of maintenance practices based on component condition rather than component time in service or age. This new practice is known as Condition Based Maintenance, and it relies on accurate detection and identification of material deficiencies in system components. Rotor system components in rotary-wing aircraft can be difficult to monitor due to the rotational environment experienced by the sensors and the difficulty of signal transmission. Current methods are able to detect the existence of a fault in the rotor system but cannot link the vibrations experienced in the airframe to a specific …

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Vibration Interaction In A Multiple Flywheel System, Jordan A. Firth Mar 2011

Vibration Interaction In A Multiple Flywheel System, Jordan A. Firth

Theses and Dissertations

This study uses a linear model of an Integrated Power and Attitude Control System (IPACS) to investigate the vibration interaction between multiple flywheels. An easily extendable Matlab® script is created for the analysis of flywheel vibrations. This script is used to build a vibration model consisting of two active magnetic bearing flywheels mounted on a support structure. The flywheels are rotated at varying speeds, with an imbalance-induced centripetal force in one or both wheels causing vibrations in both wheels. Flywheel and system responses are examined for low frequency vibrations which would cause undesirable excitation to a satellite using IPACS, with …

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An Experimental Characterization Of Damping Properties Of Thermal Barrier Coatings At Elevated Temperatures, Oliver T. Easterday Mar 2011

An Experimental Characterization Of Damping Properties Of Thermal Barrier Coatings At Elevated Temperatures, Oliver T. Easterday

Theses and Dissertations

This research program developed the apparatus and associated techniques to mechanically characterize the complex modulus of hard coatings across a temperature range from about 70 deg F to 900 deg F. Major effort in designing, analyzing, and experimentally validating the chamber were performed to establish that it isothermally heated a beam specimen, accomplished modal detuning, and achieved a near free-free boundary condition, and that the chamber was characterized for its forcing excitation. Novel aspects of the chamber include non-contact for the excitation, nearly non-contacted boundary conditions, and measurement of the field variables within the specimen using a hybrid experimental-numerical approach. …

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Kam Torus Frequency Generation From Two-Line Element Sets, Gregory R. Frey Mar 2011

Kam Torus Frequency Generation From Two-Line Element Sets, Gregory R. Frey

Theses and Dissertations

The Kolmogorov Arnold and Moser (KAM) theorem states that a lightly perturbed Hamiltonian system will have solutions which lie on a torus. Earlier work by the second author has shown that most Earth satellite orbits perturbed by the geopotential lie on KAM tori. The problem then arises as to how to convert the current satellite tracking orbits to KAM tori. A KAM torus is characterized by three frequencies and three phase angles. The frequencies are essentially the rates of change of the mean anomaly, the longitude of the ascending node, and the argument of perigee. In this paper we explore …

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Implementation Of A Rule-Based Open-Loop Control Strategy For A Hybrid-Electric Propulsions System On A Small Rpa, Collin Greiser Mar 2011

Implementation Of A Rule-Based Open-Loop Control Strategy For A Hybrid-Electric Propulsions System On A Small Rpa, Collin Greiser

Theses and Dissertations

Currently fielded electric-powered small remotely-piloted aircraft (RPA) lack endurance desired by warfighters, and internal combustion engine (ICE) RPAs generate undesirable acoustic and thermal signatures. Hybrid-electric (HE) propulsion systems would combine both electric power for endurance and ICE power for cruise and climb modes. Use of HE systems would eliminate undesirable signatures in addition to providing considerable fuel savings over time. Five components were used in this HE system: the ICE, electric motor (EM), electromagnetic clutch, battery pack, and a propeller. Control of such a system in a small RPA has never been attempted before. A rulebased controller was developed to …

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Effects Of Air Drag And Lunar Third-Body Perturbations On Motion Near A Reference Kam Torus, Luke J. Hagen Mar 2011

Effects Of Air Drag And Lunar Third-Body Perturbations On Motion Near A Reference Kam Torus, Luke J. Hagen

Theses and Dissertations

The KAM Theory was developed in the 1960s but only in the last decade has it been applied to Earth orbiting satellites. Physical state variables of position and velocity are transformed into KAM Torus variables. The KAM Torus is a geometrical structure similar to that of a multi-dimensional donut. The Earth satellite's motion can be described as traversing the surface of this donut. There are two primary advantages of this transformation: (1) The new generalized coordinates which are analogous with mean anomaly, right ascension of the ascending node, and argument of perigee, increment linearly with time, and (2) Perturbations due …

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Characterization Of Horizontally-Issuing Reacting Buoyant Jets, Joshua J. Heffernen Mar 2011

Characterization Of Horizontally-Issuing Reacting Buoyant Jets, Joshua J. Heffernen

Theses and Dissertations

This research studied the mixing and combustion behavior of low Reynolds number, horizontally-issuing gaseous fuel jets with ambient air. The study focused on the mixing characteristics of propane and ethylene. These fuels are, respectively, heavy and neutral with respect to air, and were tested at various Froude numbers and laminar tube Reynolds numbers. Using low Froude and Reynolds number flows allowed for isolation of the buoyant jet effects. The process was characterized through the use of a non-invasive, OH Planar Laser-Induced Fluorescence (PLIF) technique, and supplemented with filtered (CH*) and unfiltered high speed imaging. The resulting cross sectional PLIF images …

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Osculating Relative Orbit Elements Resulting From Chief Eccentricity And J2 Perturbing Forces, Joshuah A. Hess Mar 2011

Osculating Relative Orbit Elements Resulting From Chief Eccentricity And J2 Perturbing Forces, Joshuah A. Hess

Theses and Dissertations

Relative orbit elements (ROEs) based on a circular chief satellite orbit are erroneous when applied to a perturbed,non-circular reference orbit. In those situations, the ROEs will encounter geometric instability and drift. To counter this, a set of time-variant ROEs have been derived to describe the relative orbit for both the unperturbed, elliptical chief, and the perturbed, circular chief. A highly coupled relationship is found that describes the relative trajectory to higher accuracy when compared to numerical integration. To show the applicability of the ROEs to formation design, methods to initialize a stationary relative orbit are detailed and an algorithm for …

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Revolutionizing Space Propulsion Through The Characterization Of Iodine As Fuel For Hall-Effect Thrusters, Adam C. Hillier Mar 2011

Revolutionizing Space Propulsion Through The Characterization Of Iodine As Fuel For Hall-Effect Thrusters, Adam C. Hillier

Theses and Dissertations

The demand for increased performance in space propulsion systems is higher than ever as missions are becoming more advanced. As the global supply of xenon depletes, missions demanding high thrust will require alternatives. The research presented here examines iodine as an alternate propellant. The propellant was successfully operated through a BHT-200 thruster in the T6 vacuum facility at Busek Co. Inc. A feed system for the iodine was developed for controlled thruster operation at varying conditions. An inverted pendulum was used to take thrust measurements. Thrust to power ratio, anode efficiency, and specific impulse were calculated. Iodine performance is compared …

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Fixed-Wing Aircraft Combat Survivability Analysis For Operation Enduring Freedom And Operation Iraqi Freedom, Christopher L. Jerome Mar 2011

Fixed-Wing Aircraft Combat Survivability Analysis For Operation Enduring Freedom And Operation Iraqi Freedom, Christopher L. Jerome

Theses and Dissertations

The primary tenet of the aircraft survivability discipline is threat definition. In order to deliver relevant capabilities and protection to the warfighter it is imperative; therefore, to provide timely, accurate, and actionable threat data to the survivability community. In an attempt to identify the evolution of aircraft threats in today's combat environment, an analysis of fixed-wing aircraft battle damage was conducted. This analysis reports battle damage incidents from OPERATIONS ENDURING FREEDOM (OEF) and IRAQI FREEDOM(OIF). Additionally, reported damage incidents were then validated by crosschecking aircraft maintenance records from this period to eliminate non-hostile fire data points. This revolutionary approach uncovered …

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