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Theses and Dissertations

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Articles 931 - 960 of 1780

Full-Text Articles in Aerospace Engineering

Satellite Reentry Control Via Surface Area Amplification, Salvador Alemán Mar 2009

Satellite Reentry Control Via Surface Area Amplification, Salvador Alemán

Theses and Dissertations

This project endeavors to find whether it is feasible to use an increase in surface area as a way of increasing the drag on an orbiting object, thus decreasing its orbital lifetime. The surface area increase can be achieved by an apparatus that deploys a balloon. The balloon will act as a parachute that will decrease the potential energy of the object through atmospheric drag. This is most effective by objects that reach the Low Earth altitudes of less than 500 kilometers, where an object is encountering a firmer atmospheric density. The project is carried out through propagating three different …

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Near Real-Time Closed-Loop Optimal Control Feedback For Spacecraft Attitude Maneuvers, C. Douglas Mcfarland Mar 2009

Near Real-Time Closed-Loop Optimal Control Feedback For Spacecraft Attitude Maneuvers, C. Douglas Mcfarland

Theses and Dissertations

Optimization of spacecraft attitude maneuvers can significantly reduce attitude control system size and mass, and extend satellite end-of-life. Optimal control theory has been applied to solve a variety of open-loop optimal control problems for terrestrial, air, and space applications. However, general application of real-time optimal controllers on spacecraft for large slew maneuvers has been limited because open-loop control systems are inherently vulnerable to error and the computation necessary to solve for an optimized control solution is resource intensive. This research effort is focused on developing a near real-time optimal control (RTOC) system for spacecraft attitude maneuvers on the Air Force …

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Finite Element Model Optimization Of The Falconsat-5 Structural Engineering Model, Cole C. Doupe Mar 2009

Finite Element Model Optimization Of The Falconsat-5 Structural Engineering Model, Cole C. Doupe

Theses and Dissertations

Space launch vehicles produce tremendously harsh environments for their payloads. One of the worst contributors to this harsh environment is vibration. Launch vehicle contractors require accurate dynamic models in order to perform coupled loads analyses with each payload to mitigate risks. Accurate predictions of the dynamic response of the payload are not achieved easily. The Finite Element (FE) method has proven to be the best approach in creating accurate dynamic models of complex structures. To improve the agreement between an FE model and the structure it represents, a common practice is to `tune' or adjust parameters of the FE model …

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Uas Collision Avoidance Algorithm That Minimizes The Impact On Route Surveillance, Austin L. Smith Mar 2009

Uas Collision Avoidance Algorithm That Minimizes The Impact On Route Surveillance, Austin L. Smith

Theses and Dissertations

A collision avoidance algorithm is developed and implemented that is applicable to different types of unmanned aerial systems ranging from a single platform with the ability to perform all collision avoidance functions independently to multiple vehicles performing functions as a cooperative group with collision avoidance commands computed at a ground station. The collision avoidance system is exercised and tested using operational hardware and platforms and is demonstrated in representative missions similar to those planned for operational systems. The results presented are the first known flight tests of a global, three-dimensional, geometric collision avoidance system on an unmanned aircraft system. Novel …

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Application Of Kam Theorem To Earth Orbiting Satellites, Bryan D. Little Mar 2009

Application Of Kam Theorem To Earth Orbiting Satellites, Bryan D. Little

Theses and Dissertations

An orbit that lies on a Kolmogorov, Arnold, and Moser (KAM) Torus will remain on that torus until and unless it experiences a force that causes it to leave the torus. Earth satellites that are subject only to the Earth's gravity field may lie on such KAM tori. Analyzing on orbit satellite position data should allow for the identification of the fundamental frequencies needed to define the KAM tori for modeling Earth satellite orbits. KAM Tori are created for the Gravity Recovery and Climate Experience (GRACE) and Jason-1 satellites to model their orbital motion. Precise position data for the satellites …

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Failure Detection Of A Pseudolite-Based Reference System Using Residual Monitoring, Michael A. Ciampa Mar 2009

Failure Detection Of A Pseudolite-Based Reference System Using Residual Monitoring, Michael A. Ciampa

Theses and Dissertations

The 746th TS uses a flight reference system referred to as the Central Inertial and GPS Test Facility (CIGTF) Reference System (CRS). Currently the CRS is the modern standard flight reference system for navigation testing, but high accuracy is dependent on the availability of GPS. A pseudolite system is currently being developed to augment the CRS and supply the capability to maintain high accuracy navigation under normal and jamming conditions. Pseudolite measurements typically contain cycle slips and other errors (such as multipath, tropospheric error, measurement noise) that can affect reliability. Past work relied on the receiver-reported signal-to-noise (SNR) value to …

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An Investigation Of Shock Wave Physics Via Hybrid Cfd-Bgk Solution Methods For Nonequilibrium Flows, Brook I. Bentley Mar 2009

An Investigation Of Shock Wave Physics Via Hybrid Cfd-Bgk Solution Methods For Nonequilibrium Flows, Brook I. Bentley

Theses and Dissertations

The Unified Flow Solver, a hybrid continuum-rarefied code, is used to investigate the internal structure of a normal shock wave for a Mach range of 1.55 to 9.0 for Argon, and 1.53 to 3.8 for diatomic Nitrogen. Reciprocal shock thickness, density, temperature, heat flux, and the velocity distribution function are calculated for a one-dimensional shock wave and compared with experimental data from Alsmeyer and DSMC results from Bird. Using the Euler, Navier-Stokes, BGK model, and Three-Temperature BGK model schemes, results from UFS compare well with experiment and DSMC. The Euler scheme shows atypical results, possibly resulting from modifications made to …

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Laser Dot Projection Photogrammetry And Force Balance Measurement Techniques For Flapping Wing Micro Air Vehicles, David H. Curtis Mar 2009

Laser Dot Projection Photogrammetry And Force Balance Measurement Techniques For Flapping Wing Micro Air Vehicles, David H. Curtis

Theses and Dissertations

The purpose of this research was to develop testing methods capable of analyzing the performance of a miniature flapping-wing mechanism that can later be adapted to a flapping wing micro air vehicle (MAV). A previously designed and built flapping only mechanism was used for testing, while a previously designed flapping and pitch mechanism was fabricated utilizing an Objet Eden 500V 3-dimensional printer and its operation demonstrated. The flapping mechanism was mounted on a six component force balance. Force and moment data were collected for a variety of wing sets at different flapping frequencies. The testing was conducted using wings composed …

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Development Of Non-Uniform Radiation Solution Methods For Atmospheric Re-Entry Using Detailed Thermal Modeling, Jeffrey R. Komives Mar 2009

Development Of Non-Uniform Radiation Solution Methods For Atmospheric Re-Entry Using Detailed Thermal Modeling, Jeffrey R. Komives

Theses and Dissertations

The line-by-line accurate spectral radiation solver SPRADIAN was integrated with the multi-temperature hypersonic flow-solver NH7Air for the purpose of predicting the radiation incident on the surface of a hypersonic re-entry vehicle. Atomic and molecular radiation mechanisms are considered for chemical species present in an Earth atmosphere re-entry. A new numerical method of radiation propagation is presented that is capable of accurately predicting the radiation propagation through a non-uniform radiation field. This method also introduces a unique treatment of the internal energy of each chemical species, independently tracking the vibrational temperatures of all molecular species. The new radiation propagation method is …

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Least-Squares Finite Element Formulation For Fluid-Structure Interaction, Cody C. Rasmussen Mar 2009

Least-Squares Finite Element Formulation For Fluid-Structure Interaction, Cody C. Rasmussen

Theses and Dissertations

Fluid-structure interaction problems prove difficult due to the coupling between fluid and solid behavior. Typically, different theoretical formulations and numerical methods are used to solve fluid and structural problems separately. The least-squares finite element method is capable of accurately solving both fluid and structural problems. This capability allows for a simultaneously coupled fluid structure interaction formulation using a single variational approach to solve complex and nonlinear aeroelasticity problems. The least-squares finite element method was compared to commonly used methods for both structures and fluids individually. The fluid analysis was compared to finite differencing methods and the structural analysis type compared …

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Cooperative Unmanned Aerial Surveillance Control System Architecture, Theodore T. Diamond, Adam L. Rutherford, Jonathan B. Taylor Mar 2009

Cooperative Unmanned Aerial Surveillance Control System Architecture, Theodore T. Diamond, Adam L. Rutherford, Jonathan B. Taylor

Theses and Dissertations

Intelligence, surveillance and reconnaissance (ISR) is a high-demand Department of Defense mission performed by unmanned aircraft systems (UASs) at the tactical and theater levels. Coordinating UASs through cooperative control offers the advantages of persistence, distributed and adaptable sensor coverage, and reduced revisit time on points of interest. The purpose of this thesis is to apply systems engineering principles to the problem of developing a flexible, common control system for cooperative UAS surveillance at the tactical level. The AFIT team developed a concept of operations (CONOPS) encompassing various users and surveillance tasks. The team then used the scenarios in the CONOPS …

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Deeply-Integrated Feature Tracking For Embedded Navigation, Jeffery R. Gray Mar 2009

Deeply-Integrated Feature Tracking For Embedded Navigation, Jeffery R. Gray

Theses and Dissertations

The Air Force Institute of Technology (AFIT) is investigating techniques to improve aircraft navigation using low-cost imaging and inertial sensors. Stationary features tracked within the image are used to improve the inertial navigation estimate. These features are tracked using a correspondence search between frames. Previous research investigated aiding these correspondence searches using inertial measurements (i.e., stochastic projection). While this research demonstrated the benefits of further sensor integration, it still relied on robust feature descriptors (e.g., SIFT or SURF) to obtain a reliable correspondence match in the presence of rotation and scale changes. Unfortunately, these robust feature extraction algorithms are computationally …

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Waypoint Generation Based On Sensor Aimpoint, Shannon M. Farrell Mar 2009

Waypoint Generation Based On Sensor Aimpoint, Shannon M. Farrell

Theses and Dissertations

Secretary of Defense Robert M. Gates has emphasized a need for a greater number of intelligence, surveillance, and reconnaissance (ISR) assets to support combatant commanders and military operations globally. Unmanned systems, especially MAVs, used as ISR platforms provide the ability to maintain covertness during missions and help reduce the risk to human life. This research develops waypoint generation algorithms required to keep a point of interest (POI) in the field of view (FOV) of a fixed sensor on a micro air vehicle (MAV) in the presence of a constant wind.
Fixed sensors, while cheaper and less prone to mechanical failure …

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Fusion Of Inertial Sensors And Orthogonal Frequency Division Multiplexed (Ofdm) Signals Of Opportunity For Unassisted Navigation, Jason G. Crosby Mar 2009

Fusion Of Inertial Sensors And Orthogonal Frequency Division Multiplexed (Ofdm) Signals Of Opportunity For Unassisted Navigation, Jason G. Crosby

Theses and Dissertations

The advent of the global positioning system (GPS) has provided worldwide high-accuracy position measurements. However, GPS may be rendered unavailable by jamming, disruption of satellites, or simply by signal shadowing in urban environments. Thus, this thesis considers fusion of Inertial Navigation Systems (INS) and Orthogonal Frequency Division Multiplexed (OFDM) signals of opportunity (SOOP) for navigation. Typical signal of opportunity navigation involves the use of a reference receiver and uses time difference of arrival (TDOA) measurements. However, by exploiting the block structure of OFDM communication signals, the need for the reference receiver is reduced or possibly removed entirely. This research uses …

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Evaluation Of An Opnet Model For Unmanned Aerial Vehicle Networks, Clifton M. Durham Mar 2009

Evaluation Of An Opnet Model For Unmanned Aerial Vehicle Networks, Clifton M. Durham

Theses and Dissertations

The concept of Unmanned Aerial Vehicles (UAVs) was first used as early as the American Civil War, when the North and the South unsuccessfully attempted to launch balloons with explosive devices. Since the American Civil War, the UAV concept has been used in all subsequent military operations. Over the last few years, there has been an explosion in the use of UAVs in military operations, as well as civilian and commercial applications. UAV Mobile Ad Hoc Networks (MANETs) are fast becoming essential to conducting Network-Centric Warfare (NCW). As of October 2006, coalition UAVs, exclusive of hand-launched systems, had flown almost …

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Rigidizable Inflatable Get-Away-Special Experiment (Rigex) Post Flight Analysis, Ground Testing, Modeling, And Future Applications, Brett J. Cooper Mar 2009

Rigidizable Inflatable Get-Away-Special Experiment (Rigex) Post Flight Analysis, Ground Testing, Modeling, And Future Applications, Brett J. Cooper

Theses and Dissertations

The Rigidizable Inflatable Get-Away-Special EXperiment (RIGEX) Space Shuttle experiment was run successfully onboard STS-123 (Endeavour) in March 2008. The objective of this thesis is to analyze the space flight and post space flight test data, correlate the data to previous ground tests, and update finite element models. In turn, this research will help demonstrate the feasibility of using lightweight and low stowage volume (high packaging ratio) inflatable/rigidizable space structures in remote sensing applications. RIGEX was an Air Force Institute of Technology graduate-student-built Space Shuttle cargo bay experiment intended to heat and inflate three 20-inch long carbon fiber tubes in a …

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Tunable Diode Laser Absorption Spectroscopy Verification Analysis For Use In The Combustion Optimization And Analysis Laser Laboratory, Christina R. Serianne Mar 2009

Tunable Diode Laser Absorption Spectroscopy Verification Analysis For Use In The Combustion Optimization And Analysis Laser Laboratory, Christina R. Serianne

Theses and Dissertations

The AFIT Combustion Optimization and Analysis Laser (COAL) laboratory has state-of-the-art laser diagnostic capability for combustion process. The research for this thesis served to enhance the COAL lab's capability. Currently, there are no known commercially available tunable diode lasers that produce Ultra-Violet radiation required for this analysis. Sum-frequency generation at 313.5 nm was utilized for high speed OH absorption and temperature measurements at a rate of 2kHz. The Tunable Diode Laser Absorption Spectroscopy system was validated by comparison with theoretical and well characterized experimental data by operating the system over a wide range of conditions for an H2 laminar flame …

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A Finite Element Evaluation Of An Experiment Related To Coating Damping Properties, Armando Deleon Mar 2009

A Finite Element Evaluation Of An Experiment Related To Coating Damping Properties, Armando Deleon

Theses and Dissertations

Typically turbine engine blades gain protection from thermal damage by the use of hard coatings, such as magnesium aluminate spinel. Known as Thermal Barrier Coatings (TBC's), they have material properties that include several nonlinearities. These TBC's create damping primarily due to their nonlinear dissipation of energy. In order to effectively represent their damping properties, it is necessary to create a method which combines experimentation and analysis. Previous work has shown the need for a beam bounded and loaded in such a fashion that external support energy dissipation functions i.e. boundary conditions and aerodynamics are eliminated. Thus, a new experimental apparatus …

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Mission Planning For Close-Proximity Satellites, Barry R. Witt Mar 2009

Mission Planning For Close-Proximity Satellites, Barry R. Witt

Theses and Dissertations

Given an initial orbit and a set of other orbits of interest, the lowest change in velocity "path" between them is of high value. Software was developed to visualize the change in velocity required from a user defined window of burn to a user defined window of intercept. The time between burn and intercept is unrestricted. Multiple intercepts require searching an n! solution space, research then is focused on ways to pick optimal choices without fully calculating out the cost of doing all possible combinations. Some code was translated from BASIC and the rest was newly developed in MATLAB. The …

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Ceramic Matrix Composite Characterization Under A Combustion And Loading Environment, Andrew R. Nye Mar 2009

Ceramic Matrix Composite Characterization Under A Combustion And Loading Environment, Andrew R. Nye

Theses and Dissertations

Lightweight materials that can withstand high temperatures and corrosive environments are constantly sought after in the aerospace industry, typically for Gas Turbine Engine (GTE) application. These materials need to retain their strength throughout the long service period they would see in the combustor and turbine components of a GTE. One material that is ideal for these types of applications is an oxide/oxide Ceramic Matrix Composite (CMC). The fatigue behavior of the oxide/oxide CMC NextelTM 720/Alumina (N720/A) was investigated in a unique high temperature environment. N720/A consisted of an 8-harness satin weave of NextelTM aluminum oxide/silicon oxide fibers bound …

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Creep And Fatigue Interaction Characteristics Of Pwa1484, Christian J. Pierce Mar 2009

Creep And Fatigue Interaction Characteristics Of Pwa1484, Christian J. Pierce

Theses and Dissertations

One of the main methods for predicting the service life of jet engine turbine blades is through creep analysis. A sample of the turbine blade material will be mechanically tested to characterize its creep performance. This characterization will be used to determine safe operating conditions for the material. While methods for modeling creep behavior are generally well developed, this constant load creep testing does not fully represent the loading conditions present in a jet engine due to cyclic loading caused by the mission profile and throttle movements. As the industry seeks to become more accurate in physics based modeling of …

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Fatigue Evaluation Of Nanocomposites As Lightweight Electronic Enclosures For Satellites' Applications, Javier Rodriguez Mar 2009

Fatigue Evaluation Of Nanocomposites As Lightweight Electronic Enclosures For Satellites' Applications, Javier Rodriguez

Theses and Dissertations

Existing nanocomposite materials used for satellite applications don't offer the required conductivity and electromagnetic shielding protection, requiring metal shields in order to survive in space. The AFRL Materials and Manufacturing Directorate in conjunction with the private sector have developed a material that promises to blend the attributes of nanocomposites and metal materials. The M55J/RS3 material consists of carbon fibers combined with a polyisocyanate matrix, in which Nickel nanostrandsTM are added. The research effort investigated the changes in the EMI and ESD of the material after being subjected to cyclic loads. Four configurations of a symmetric layup with fibers oriented …

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Surveillance Using Multiple Unmanned Aerial Vehicles, Christopher E. Booth Mar 2009

Surveillance Using Multiple Unmanned Aerial Vehicles, Christopher E. Booth

Theses and Dissertations

This study examines the performance and limitations of a heuristic cooperative control (CC) surveillance algorithm for multiple unmanned aerial vehicles (UAVs) under both simulation and demonstration. The algorithm generates Dubin's based paths and provides velocity feedback to accomplish simultaneous arrival onto a surveillance orbit around the target and maintains position while orbiting. The CC algorithm has two modes: one that generates commands to multiple UAVs for simultaneous arrival to a surveillance orbit, and one that maintains equal angular spacing about the orbit. In addition to positional performance metrics, percentage of target in-view time was also measured based on the UAV's …

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Effects Of Prior Aging At 316°C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 316°C: Experiment And Modeling, Ozgur Ozmen Mar 2009

Effects Of Prior Aging At 316°C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 316°C: Experiment And Modeling, Ozgur Ozmen

Theses and Dissertations

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature polymer, was investigated at 316°C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain controlled loading were examined. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading and unloading. Early failures occur in the inelastic regime. The recovery of strain at zero stress and creep response are strongly affected by prior strain …

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Characterizing The Exhaust Plume Of The Three-Electrode Micro Pulsed Plasma Thrusters, Myeongkyo Seo Mar 2009

Characterizing The Exhaust Plume Of The Three-Electrode Micro Pulsed Plasma Thrusters, Myeongkyo Seo

Theses and Dissertations

Three-electrode micro-PPTs are a new version of two electrode micro-PPTs devices. Performance predictions and contamination expectations are essential characteristics needed by satellite designers. In order to focus on thruster specific impulse, thrust and efficiency, measuring the exhaust velocity or impulse bit and propellant consumption rate is essential. While this is not always possible to measure directly, focusing on the ejected mass from the PPT provides significant information allowing determination of these performance statistics. Specifically, focusing on exhaust angle distribution and velocity of the exhaust particles is the emphasis of this work. The results show that the three-electrode micro-PPT is more …

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Effects Of Environment On Creep Behavior Of Nextel720/Alumina-Mullite Ceramic Composite With ±45º Fiber Orientation At 1200ºc, Muzaffer Ozer Mar 2009

Effects Of Environment On Creep Behavior Of Nextel720/Alumina-Mullite Ceramic Composite With ±45º Fiber Orientation At 1200ºc, Muzaffer Ozer

Theses and Dissertations

The present effort will investigate the off-axis creep behavior of the Nexte720/Alumina-Mullite CMC, a material system which relies on a porous alumina/mullite matrix for damage tolerance as compared to the pure alumina matrix in earlier studies. This research evaluated the creep behavior of N720/AM with a ± 45° fiber orientation at 1200°C in: laboratory air, steam, and argon environments. Creep-rupture tests at the creep stress levels of: 32, 30, 26, and 20 MPa were conducted in each environment. Additionally 35 MPa stress level examined in air and 13 MPa stress level examined both in air and steam. The N720/AM with …

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Hyperspectral Imaging Of A Turbine Engine Exhaust Plume To Determine Radiance, Temperature, And Concentration Spatial Distributions, Spencer J. Bowen Mar 2009

Hyperspectral Imaging Of A Turbine Engine Exhaust Plume To Determine Radiance, Temperature, And Concentration Spatial Distributions, Spencer J. Bowen

Theses and Dissertations

The usefulness of imaging Fourier transform spectroscopy (IFTS) when looking at a rapidly varying turbine engine exhaust scene was explored by characterizing the scene change artifacts (SCAs) present in the plume and the effect they have on the calibrated spectra using the Telops, Inc.-manufactured Field-portable Imaging Radiometric Spectrometer Technology, Midwave Extended (FIRST-MWE). It was determined that IFTS technology can be applied to the problem of a rapidly varying turbine engine exhaust plume due to the zero mean, stochastic nature of the SCAs, through the use of temporal averaging. The FIRST-MWE produced radiometrically calibrated hyperspectral datacubes, with calibration uncertainty of 35% …

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Predicting Solar Protons: A Statistical Approach, Jonathan C. Spaulding Mar 2009

Predicting Solar Protons: A Statistical Approach, Jonathan C. Spaulding

Theses and Dissertations

A small fraction of solar flares are accompanied by high energy (>10 MeV) protons. These events can cause degradation or failure of satellite systems and can be harmful to humans in space or in high altitude flight. For risk management purposes, the Air Force is interested in predicting these events. Several algorithms exist to do this operationally, but none predict when these events will occur with much accuracy. Here, we analyzed 3610 M1 and greater flares including 106 with proton events from the GOES sensors from 1 Jan 1986 to 31 Dec 2004 to produce new results, including a …

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Non-Destructive Evaluation Of Aerospace Composites, Jeremy D. Johnson Mar 2009

Non-Destructive Evaluation Of Aerospace Composites, Jeremy D. Johnson

Theses and Dissertations

Five methods of non-destructive material evaluation (NDE) were used to inspect various forms of damage commonly found in aerospace fiberglass composites: voids, edge and sub-surface delaminations, surface burning, and cracking. The images produced by X-ray, X-ray Computed Tomography, terahertz (THz) imaging, ultrasound, and flash IR thermography were analyzed for the detection of defects. Test results and analysis of each NDE method's capabilities provide a comparison study of conventional techniques versus the emerging technology of THz imaging for the non-destructive evaluation of aerospace composite materials. A comparison guide to the five methods' damage detection effectiveness for fiberglass composites is provided by …

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Electrostatic Discharge Properties Of Irradiated Nanocomposites, Joshua D. Mcgary Mar 2009

Electrostatic Discharge Properties Of Irradiated Nanocomposites, Joshua D. Mcgary

Theses and Dissertations

Modernization in space systems requires employment of new light-weight, high performance composite materials that reduce bulk weight and increase structural integrity. This thesis explored the behavior of one such material prior to and following a 35-year simulated space radiation life-cycle. Select electrical properties of nickel nanostrandTM-carbon composites in seven configurations were characterized prior to electron irradiation via surface and bulk resistivity measurements and contact electrostatic discharge (ESD) measurements. Following irradiation at a fluence of 1016 e-/cm2 at an average energy of 500 keV, measurements were repeated and compared against pre-irradiation data. Configuration D is …

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