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Articles 8011 - 8040 of 11196
Full-Text Articles in Aerospace Engineering
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
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 …
Ch-47d Rotating System Fault Sensing For Condition Based Maintenance, Stephen M. Dickerson
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 …
Optimized Dual Expander Aerospike Rocket, Joshua N. Hall
Optimized Dual Expander Aerospike Rocket, Joshua N. Hall
Theses and Dissertations
Research at the Air Force Institute of Technology (AFIT) focused on designing a cryogenic dual-expander aerospike nozzle (DEAN) upper stage rocket engine to produce 50,000 pounds-force (222.4 kilo-Newtons) vacuum thrust, 464 seconds of vacuum specific impulse and a thrust-to-weight ratio of 106.5. The use of dual expander cycles improves engine reliability, maximizes efficiency, and eliminates some catastrophic failure modes. An upper stage engine with an aerospike nozzle is shorter and lighter than an equivalent performing conventional bell nozzle upper stage engine. Previous research focused on first developing a feasible closed DEAN design model and secondly expanding the model to support …
Osculating Relative Orbit Elements Resulting From Chief Eccentricity And J2 Perturbing Forces, Joshuah A. Hess
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 …
Revolutionizing Space Propulsion Through The Characterization Of Iodine As Fuel For Hall-Effect Thrusters, Adam C. Hillier
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 …
Fixed-Wing Aircraft Combat Survivability Analysis For Operation Enduring Freedom And Operation Iraqi Freedom, Christopher L. Jerome
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 …
Follower-Force Experiments With Geometric Non-Linear Coupling For Analytical Validation, Tae H. Kim
Follower-Force Experiments With Geometric Non-Linear Coupling For Analytical Validation, Tae H. Kim
Theses and Dissertations
This study was a follow-up of a previous study where static deflection data of a joined-wing test article was collected from a series of experiments using a laser scanner and a laser tracker while the test articles were subjected to follower-forces. One of the goals of this study was to collect accurate experimental data which could be used to validate analytical methods, such as geometrically exact beam theory, which are used to predict the nonlinear response of joined-wings. The load application system used on the previous study was not able to provide a follower-force on the test articles, and therefore …
Notch Sensitivity Of Fatigue Behavior Of A Hi-Nicalon/Sic Ceramic Composite With An Oxidation Inhibited Matrix At 1200°C In Air And In Steam, Garrett M. Kurtz
Notch Sensitivity Of Fatigue Behavior Of A Hi-Nicalon/Sic Ceramic Composite With An Oxidation Inhibited Matrix At 1200°C In Air And In Steam, Garrett M. Kurtz
Theses and Dissertations
The effects of holes on the fatigue behavior of an advanced Silicon Carbide/Silicon Carbide (SiC/SiC) ceramic matrix composite (CMC) was investigated at 1200°C in laboratory air and in steam environment. The composite consisted of an oxidation inhibited HyprSiC matrix reinforced with laminated Hi-Nicalon fibers woven in an eight-harness-satin weave (8HSW). Fiber preforms were coated with pyrolytic carbon (PyC) fiber coating with boron carbide overlay and were then densified with HyprSiC matrix via chemical vapor infiltration (CVI). Effects if center hole on tensile stress-strain behavior and tensile properties were evaluated at 1200°C. To assess the effect of holes on fatigue performance, …
Flapping Wing Micro Air Vehicle Wing Manufacture And Force Testing, Nathanael J. Sladek
Flapping Wing Micro Air Vehicle Wing Manufacture And Force Testing, Nathanael J. Sladek
Theses and Dissertations
Numerous wing manufacturing techniques have been developed by various universities for research on Flapping Wing Micro Air Vehicles. Minimal attention though is given to repeatability of wing aerodynamics and dynamic response, which is crucial to avoid asymmetric flapping. Thus the focus of this research becomes twofold. First, repeatable wing manufacturing techniques are developed to ensure flapping wings have similar aerodynamic and dynamic characteristics. For this purpose, four wing designs were selected to not only test the aerodynamics of the different designs, but to also validate manufacturing techniques. The various wing designs are assessed using two methods: dynamic and aerodynamic data. …
Using A Gatling-Gun Configured Micro Pulsed Plasma Thruster As A Means To Control Micro Satellites With Extreme Precision, Lee I. Watson
Using A Gatling-Gun Configured Micro Pulsed Plasma Thruster As A Means To Control Micro Satellites With Extreme Precision, Lee I. Watson
Theses and Dissertations
Micro-Pulsed Plasma Thrusters (µPPT) are becoming increasingly attractive for their low power consumption and moderately high specific impulse in the range of 800-1200s. The Gatling Gun micro-Pulsed Plasma Thruster (GG-µPPT) is a new device offering reduced mass and higher thrust than single µPPTs and solid application in precise pointing and orbit maintenance applications. The performance of µPPTs depends on frequency and applied voltage/power levels. Variation of these input parameters and effects on operation and performance of this thruster system were the focus of this research. Contamination aspects were also considered and discussed, since the buildup of carbon results in decreased …
Stochastic Orbit Prediction Using Kam Tori, Max W. Yates
Stochastic Orbit Prediction Using Kam Tori, Max W. Yates
Theses and Dissertations
Kolmogorov-Arnold-Moser (KAM) Theory states that a lightly perturbed, conservative, dynamical system will exhibit lasting quasi-periodic motion on an invariant torus. Its application to purely deterministic orbits has revealed exquisite accuracy limited only by machine precision. The theory is extended with new mathematical techniques for determining and predicting stochastic orbits for Earth satellite systems. The linearized equations of motion are developed and a least squares estimating environment is pioneered to fit observation data from the International Space Station to a phase space trajectory that exhibits drifting toroidal motion over a dense continuum of adjacent tori. The dynamics near the reference torus …
Two Dimensional Positioning And Heading Solution For Flying Vehicles Using A Line-Scanning Laser Radar (Ladar), Brady T. Christel
Two Dimensional Positioning And Heading Solution For Flying Vehicles Using A Line-Scanning Laser Radar (Ladar), Brady T. Christel
Theses and Dissertations
Emerging technology in small autonomous flying vehicles requires the systems to have a precise navigation solution in order to perform tasks. In many critical environments, such as indoors, GPS is unavailable necessitating the development of supplemental aiding sensors to determine precise position. This research investigates the use of a line scanning laser radar (LADAR) as a standalone two dimensional position and heading navigation solution and sets up the device for augmentation into existing navigation systems. A fast histogram correlation method is developed to operate in real-time on board the vehicle providing position and heading updates at a rate of 10 …
High Frequency Direction Finding Using Structurally Integrated Antennas On A Large Airborne Platform, Clair F. Corbin
High Frequency Direction Finding Using Structurally Integrated Antennas On A Large Airborne Platform, Clair F. Corbin
Theses and Dissertations
Estimating the angle of arrival (AOA) of a high frequency (HF) signal, 2-32 MHz, is challenging, especially if the antenna array is installed on a platform with dimensions on the order of one wavelength. Accurate AOA estimates are necessary for search and rescue operations and geolocating RF emitters of interest. This research examines the performance of a direction finding (DF) system using structurally integrated (SI) antennas installed on an airborne platform which allows the aircraft structure to become the receiving element. Two simulated DF systems are analyzed at 4 and 11 MHz. The relationship between the number of SI antennas …
Polarimetric Enhancements To Electro-Optical Aided Navigation Techniques, Jeremiah D. Johnson
Polarimetric Enhancements To Electro-Optical Aided Navigation Techniques, Jeremiah D. Johnson
Theses and Dissertations
Navigation in indoor and urban environments by small unmanned systems is a topic of interest for the Air Force. The Advanced Navigation Technology Center at the Air Force Institute of Technology is continually looking for novel approaches to navigation in GPS deprived environments. Inertial sensors have been coupled with image aided concepts, such as feature tracking, with good results. However, feature density in areas with large, flat, smooth surfaces tends to be low. Polarimetric sensors have been used for surface reconstruction, surface characterization and outdoor navigation. This thesis combines aspects of some of these algorithms along with a realistic, micro-facet …
Long Term Quadrotor Stabilization, Nicolas S. Hamilton
Long Term Quadrotor Stabilization, Nicolas S. Hamilton
Theses and Dissertations
The work of this thesis focuses on the IMU and getting the best performance possible out of the IMU to achieve better long term stability and a better navigation solution. This is done in two ways. First, the IMU accelerometer output is examined to determine if it is possible to use accelerometers to determine attitude. If the quadrotor is stationary or moving at constant velocity, the roll and pitch angles can be determined. Additionally, the accelerometers can be used to determine angular accelerations and angular rates which are integrated to determine heading. The second approach models the quadrotor and uses …
Signals Of Opportunity Navigation Using Wi-Fi Signals, Wilfred E. Noel
Signals Of Opportunity Navigation Using Wi-Fi Signals, Wilfred E. Noel
Theses and Dissertations
Since GPS is generally limited to areas with clear sky view, additional methods of navigation are currently being explored. This thesis explores navigation using Signals of Opportunity(SoOP). The signals chosen for evaluation in this thesis are the common Internet IEEE 802.11a/g signals, or Wi-Fi. This thesis presents SoOP navigation based on cross-correlations of received data from multiple Wi-Fi stations. It shows the effectiveness of the methods using collected Wi-Fi signals in a real-world environment. By using simple statistical representations of collected data in large groups, or windows, cross-correlation calculations can produce timing offsets between simulated stations. The timing offsets, or …
Coupling Vanishing Point Tracking With Inertial Navigation To Estimate Attitude In A Structured Environment, Dayvid Prahl
Coupling Vanishing Point Tracking With Inertial Navigation To Estimate Attitude In A Structured Environment, Dayvid Prahl
Theses and Dissertations
This research aims to obtain accurate and stable estimates of a vehicle's attitude by coupling consumer-grade inertial and optical sensors. This goal is pursued by first modeling both inertial and optical sensors and then developing a technique for identifying vanishing points in perspective images of a structured environment. The inertial and optical processes are then coupled to enable each one to aid the other. The vanishing point measurements are combined with the inertial data in an extended Kalman filter to produce overall attitude estimates. This technique is experimentally demonstrated in an indoor corridor setting using a motion profile designed to …
Effects Of Cyclic Prefix Jamming Versus Noise Jamming In Ofdm Signals, Amber L. Scott
Effects Of Cyclic Prefix Jamming Versus Noise Jamming In Ofdm Signals, Amber L. Scott
Theses and Dissertations
Signal jamming of an orthogonal frequency-division multiplexing (OFDM) signal is simulated in MATLAB. Two different means of jamming are used to see, which is a more efficient way to disrupt a signal using the same signal power. The first way is a basic additive white Gaussian noise (AWGN) jammer that equally jams the entire signal. The second way is an AWGN jammer that targets only the cyclic prefix (CP) of the signal. These two methods of jamming are simulated using different channel models and unknowns to get varying results. The three channel models used in the simulations are the no …
Architecture Based Workload Analysis Of Uas Multi-Aircraft Control: Implications Of Implementation On Mq-1b Predator, Jason D. Mcgrogan, Michael F. Schneider
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 …
Creep Performance Of Oxide Ceramic Fiber Materials At Elevated Temperature In Air And In Steam, Clinton J. Armani
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 …
Vibration Interaction In A Multiple Flywheel System, Jordan A. Firth
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 …
Kam Torus Frequency Generation From Two-Line Element Sets, Gregory R. Frey
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 …
X-Hale: The Development Of A Research Platform For The Validation Of Nonlinear Aeroelastic Codes, Alexander A. Kaszynski
X-Hale: The Development Of A Research Platform For The Validation Of Nonlinear Aeroelastic Codes, Alexander A. Kaszynski
Theses and Dissertations
In conjunction with the Air Force Institute of Technology (AFIT) and the Air Force Research Laboratory (AFRL), the University of Michigan has designed and is currently building a remotely piloted aircraft (RPA) experimental high altitude long endurance (X-HALE) aircraft to collect non-linear aeroelastic data to validate HALE aircraft design codes developed by academia, industry, and the federal government. While X-HALE is representative of HALE aircraft, the manufacturing and evaluation techniques are applicable to larger full size HALE aircraft such as the concepts being developed under Defense Advanced Research Projects Agency's (DARPA's) Vulture program. This paper documents the development of the …
Tension-Compression Fatigue Of Hi-Nicalon/Sic Ceramic Matrix Composite At 1200°C In Air And Steam, Tyler P. Jones
Tension-Compression Fatigue Of Hi-Nicalon/Sic Ceramic Matrix Composite At 1200°C In Air And Steam, Tyler P. Jones
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 …
Small Internal Combustion Engine Testing For A Hybrid-Electric Remotely-Piloted Aircraft, Isseyas H. Mengistu
Small Internal Combustion Engine Testing For A Hybrid-Electric Remotely-Piloted Aircraft, Isseyas H. Mengistu
Theses and Dissertations
Efficient operation of a hybrid-electric propulsion system (HEPS) powering a small remotely-piloted aircraft (RPA) requires that a controller have accurate and detailed engine and electric motor performance data. Many small internal combustion engines (ICEs) currently used on various small RPA were designed for use by the recreational hobbyist radio-control (R/C) aircraft market. Often, the manufacturers of these engines do not make accurate and reliable detailed engine performance data available for their engines. A dynamometer testing stand was assembled to test various small ICEs. These engines were tested with automotive unleaded gasoline (the manufacturer's recommended fuel) using the dynamometer setup. Torque, …
Heat Transfer Experiments On A Pulse Detonation Driven Combustor, Nicholas C. Longo
Heat Transfer Experiments On A Pulse Detonation Driven Combustor, Nicholas C. Longo
Theses and Dissertations
Heat transfer experiments were conducted using a heat exchanger behind a pulse detonation combustor and a Garrett automotive turbocharger at the Air Force Research Lab (AFRL). The equivalence ratio and purge fraction were held at 1.0 and 0.9, respectively, while the frequency of operation was varied from 10 to 12 Hz in 1 Hz movements, and the fill fraction was varied from 0.5 to 0.8 in 0.1 increments. Temperature measurements were calculated using an energy balance allowing for the calculation of heat exchanger inlet enthalpy. The heat exchanger inlet enthalpy was estimated to be the exit enthalpy of the turbocharger …
Detonation Propagation Through Ducts In A Pulsed Detonation Engine, Jeffrey M. Nielsen
Detonation Propagation Through Ducts In A Pulsed Detonation Engine, Jeffrey M. Nielsen
Theses and Dissertations
Development of a continuously operating pulsed detonation engine (PDE) without a high energy ignition system or a deflagration-to- detonation transition (DDT) device will increase engine efficiency, reduce cost, improve performance, and reduce weight. This report is a study of configurations that allow a consistent and predictable transition of a detonation from one detonation tube to second tube. The intent was, via visualization of detonation propagation through a cross-over tube, to develop a cross-over passage leading to minimization of energy losses and effective and repeatable tube-to-tube initiation. Detonation tube cross-over width, cross-over geometry and fuels were varied to determine their effect …
Conceptual Design Tool To Analyze Electrochemically-Powered Micro Air Vehicles, Douglas J. Pederson
Conceptual Design Tool To Analyze Electrochemically-Powered Micro Air Vehicles, Douglas J. Pederson
Theses and Dissertations
A multi-fidelity conceptual design tool was developed to assess electrochemically-powered micro air vehicles(MAVs). The tool utilizes four areas of contributing analyses (CAs): aerodynamics, propulsion, power management, and power sources to determine the endurance duration of a given mission. The low-fidelity aerodynamic CA consisted of drag polar calculations and the high-level CA used a vortex theory code called Athena Vortex Lattice (AVL). The propulsion CA employed QPROP and a MATLAB code that used experimental propeller data and motor constants to predict propeller-motor combination performance for the low- and high-fidelity tracks, respectively. The power management CA determined the percentage of required power …
Effect Of Atmospheric Pressure And Temperature On A Small Spark Ignition Internal Combustion Engine's Performance, Peter J. Schmick
Effect Of Atmospheric Pressure And Temperature On A Small Spark Ignition Internal Combustion Engine's Performance, Peter J. Schmick
Theses and Dissertations
The ever increasing use of man portable unmanned aerial vehicles, UAV, by the US military in a wide array of environmental conditions calls for the investigation of engine performance under these conditions. Previous research has focused on individual changes in pressure or temperature conditions of the air stream entering the engine. The need was seen for a facility capable of providing an environment representative of various simulated altitude conditions. A mobile test facility was developed to test small internal combustion engines with peak powers less than 10 hp. A representative engine was tested over a range of speeds from 2000 …
Vision-Aided Autonomous Precision Weapon Terminal Guidance Using A Tightly-Coupled Ins And Predictive Rendering Techniques, Jonathan W. Beich
Vision-Aided Autonomous Precision Weapon Terminal Guidance Using A Tightly-Coupled Ins And Predictive Rendering Techniques, Jonathan W. Beich
Theses and Dissertations
This thesis documents the development of the Vision-Aided Navigation using Statistical Predictive Rendering (VANSPR) algorithm which seeks to enhance the endgame navigation solution possible by inertial measurements alone. The eventual goal is a precision weapon that does not rely on GPS, functions autonomously, thrives in complex 3-D environments, and is impervious to jamming. The predictive rendering is performed by viewpoint manipulation of computer-generated of target objects. A navigation solution is determined by an Unscented Kalman Filter (UKF) which corrects positional errors by comparing camera images with a collection of statistically significant virtual images. Results indicate that the test algorithm is …