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Articles 1 - 30 of 48
Full-Text Articles in Engineering
Optimal Attitude Control Of Agile Spacecraft Using Combined Reaction Wheel And Control Moment Gyroscope Arrays, Cole C. Doupe
Optimal Attitude Control Of Agile Spacecraft Using Combined Reaction Wheel And Control Moment Gyroscope Arrays, Cole C. Doupe
Theses and Dissertations
This dissertation explores the benefits of combined control moment gyroscope (CMG) and reaction wheel array (RWA) actuation for agile spacecraft. Agile spacecraft are capable of slewing to multiple targets in minimum time. CMGs provide the largest torque capability of current momentum exchange actuation devices but also introduce singularity events in operation. RWAs produce less torque capability than CMGs but can achieve greater pointing accuracy. In this research, a combined RWA and CMG (RWCMG) system is evaluated using analytical simulations and hardware experiments. A closed-loop control scheme is developed which takes advantage of the strengths of each actuator set.The CMGs perform …
Design And Implementation Of A Unified Command And Control Architecture For Multiple Cooperative Unmanned Vehicles Utilizing Commercial Off The Shelf Components, Jeremy Gray
Theses and Dissertations
Small unmanned systems provide great utility to military applications due to their portable and expendable design. These systems are, however, costly to develop, produce, and maintain, making it desirable to integrate available commercial off the shelf (COTS) components. This research investigates the integration of COTS components through the development of a modular unified command and control (C2) architecture for heterogeneous and homogeneous vehicle teams to accomplish formation flocking and communication relay scenarios. A vehicle agnostic architecture was developed to be applied across different vehicle platforms, different vehicle combination, and different cooperative missions. COTS components consisting primarily of open source hardware …
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 800°C In Air And In Silicic Acid-Saturated Steam, Scott J. Robertson
Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 800°C In Air And In Silicic Acid-Saturated Steam, Scott J. Robertson
Theses and Dissertations
A facility was demonstrated that successfully resolved problems highlighted by previous attempts to study SiC fibers in steam. Monotonic tension and creep tests were conducted to characterize the fibers. The tensile strength of the fibers showed little dependence on applied stress rate, indicating a resistance to environmentally assisted crack growth. Climb-controlled diffusion in air and grain boundary sliding in silicic acid-saturated steam were the dominant damage mechanisms. Silicic acid-saturated steam had a degrading effect on the mechanical performance of the fibers, but much less than unsaturated steam environments. The Monkman-Grant relationship was demonstrated for Hi-NicalonTM S fibers and may be …
Optimal Uas Assignments And Trajectories For Persistent Surveillance And Data Collection From A Wireless Sensor Network, Nidal M. Jodeh
Optimal Uas Assignments And Trajectories For Persistent Surveillance And Data Collection From A Wireless Sensor Network, Nidal M. Jodeh
Theses and Dissertations
This research developed a method for multiple Unmanned Aircraft Systems (UAS) to efficiently collect data from a Wireless Sensor Networks (WSN). WSN are composed of any number of fixed, ground-based sensors that collect and upload local environmental data to over flying UAS. The three-step method first uniquely assigns aircraft to specific sensors on the ground. Second, an efficient flight path is calculated to minimize the aircraft flight time required to verify their assigned sensors. Finally, sensors reporting relatively higher rates of local environmental activity are re-assigned to dedicated aircraft tasked with concentrating on only those sensors. This work was sponsored …
Tension-Compression Fatigue Behavior Of 2d And 3d Polymer Matrix Composites At Elevated Temperature, Saleh A. Alnatifat
Tension-Compression Fatigue Behavior Of 2d And 3d Polymer Matrix Composites At Elevated Temperature, Saleh A. Alnatifat
Theses and Dissertations
In this Research effort, the tension-compression fatigue behavior of the 3D and 2D PMCs with 0/90˚ fiber orientation (newly developed) was investigated. These polymer composites consist of an NRPE (high-temperature polyimide) matrix with carbon fiber reinforcement. Compressive properties were assessed at (1) room temperature and (2) elevated temperature with one side, Tright, at 329˚C and the other side open to the ambient air. Tension-compression fatigue tests were conducted at elevated temperature with a frequency of 1 Hz and a ratio of minimum to maximum stress of -1.
Finite Element Analysis And Experimentation Of An Icosahedron Frame Under Compression, Mohammed Alghofaily
Finite Element Analysis And Experimentation Of An Icosahedron Frame Under Compression, Mohammed Alghofaily
Theses and Dissertations
A nonlinear analysis of a 3D icosahedron frame was conducted using ABAQUS, under a compressive load in which collapse occurs. The frame was created in SolidWorks using the material properties of the 3D plastic building material VeroBlue. Two considerations were made: the computational features of the frame, and the comparison between the experimental solution to the numerical solution. Two studies were also considered in this research: The first study was a comparison between the seven-inch and the four-inch icosahedron model with identical weight to buoyancy ratios; and the second study was a comparison between the seven-inch icosahedrons frame, with the …
Modular Heat Dissipation Technique For A Cubesat, Melih Eken
Modular Heat Dissipation Technique For A Cubesat, Melih Eken
Theses and Dissertations
In recent years, due to their many advantages, interest in larger scale CubeSats, such as 3U and 6U, has been increased. Correspondingly, dissipating the heat from the heat generating components in the CubeSat has become a challenge for thermal control. In this research, a modular approach was developed to dissipate heat from the overheating components in a CubeSat. To accomplish this, both experimental and computational methodologies were used. A 6U CubeSat was computationally modeled and the model correlated by experimental test results. Subsequently, validated CubeSat thermal model was used to design a modular heat dissipater. Validation and performance experiments of …
Analysis Of Hypersonic Vehicle Wakes, Matthew A. Kania
Analysis Of Hypersonic Vehicle Wakes, Matthew A. Kania
Theses and Dissertations
As advancements are made with ballistic missiles, particularly in the area of hypersonic bodies, there is a growing need to advance the methods of detecting these new ballistic weapons. As a result, the National Air and Space Intelligence Center has asked the Air Force Institute of Technology to examine the wake region behind hypersonic bodies. A thorough understanding of the aerothermal phenomena and the chemical reactions occurring in the wake region will enable an advancement of tracking hypersonic bodies. This research examined the wake region behind a hypersonic body using computational fluid dynamics.
This study used Pointwise® to develop a …
Leveraging External Sensor Data For Enhanced Space Situational Awareness, Charlie T. Bellows
Leveraging External Sensor Data For Enhanced Space Situational Awareness, Charlie T. Bellows
Theses and Dissertations
Reliable Space Situational Awareness (SSA) is a recognized requirement in the current congested, contested, and competitive environment of space operations. A shortage of available sensors and reliable data sources are some current limiting factors for maintaining SSA. Unfortunately, cost constraints prohibit drastically increasing the sensor inventory. Alternative methods are sought to enhance current SSA, including utilizing non-traditional data sources (external sensors) to perform basic SSA catalog maintenance functions. Astronomical data, for example, routinely collects serendipitous satellite streaks in the course of observing deep space; but tactics, techniques, and procedures designed to glean useful information from those collects have yet to …
A Nonequilibrium Finite-Rate Carbon Ablation Model For Radiating Earth Re-Entry Flows, Christopher R. Alba
A Nonequilibrium Finite-Rate Carbon Ablation Model For Radiating Earth Re-Entry Flows, Christopher R. Alba
Theses and Dissertations
Vehicles entering planetary atmospheres at high speed require an ablative heat shield in order to withstand the high thermal energy flux to the body. The interaction between the ablative products and the flow field is not well characterized. Numerical simulations were conducted to investigate the influence of carbon ablation on shock layer radiation. Data collected from experiments performed in the X-2 expansion tunnel at the University of Queensland was used to compare to the simulations. The model was a short half-cylinder made of isomolded graphite and was tested in 8.6 km/s Earth entry flow. The model surface was heated within …
System Architecture Of Small Unmanned Aerial System For Flight Beyond Visual Line-Of-Sight, Kwee Siam Seah
System Architecture Of Small Unmanned Aerial System For Flight Beyond Visual Line-Of-Sight, Kwee Siam Seah
Theses and Dissertations
Small Unmanned Aerial Systems (UAS) have increasingly been used in military application. The application in expanding scope of operations has pushed existing small UAS beyond its designed capabilities. This resulted in frequent modifications or new designs. A common requirement in modification or new design of small UAS is to operate beyond visual Line-Of-Sight (LOS) of the ground pilot. Conventional military development for small UAS adopts a design and built approach. Modification of small Remote Control (RC) aircraft, using Commercial-Off-The Shelf (COTS) equipment, offers a more economical alternative with the prospect of shorter development time compared to conventional approach. This research …
Adaptive Automation Design And Implementation, Jason M. Bindewald
Adaptive Automation Design And Implementation, Jason M. Bindewald
Theses and Dissertations
Automations allow us to reduce the need for humans in certain environments, such as auto-pilot features on unmanned aerial vehicles. However, some situations still require human intervention. Adaptive automation is a research field that enables computer systems to adjust the amount of automation by taking over tasks from or giving tasks back to the user. This research develops processes and insights for adaptive automation designers to take theoretical adaptive automation ideas and develop them into real-world adaptive automation system. These allow developers to design better automation systems that recognize the limits of computers systems, enabling better designs for systems in …
Exhaust Composition In A Small Internal Combustion Engine Using Ftir Spectroscopy, Kevin P. Horn
Exhaust Composition In A Small Internal Combustion Engine Using Ftir Spectroscopy, Kevin P. Horn
Theses and Dissertations
The mission-specific needs of small, remotely piloted aircraft demand lighter, more efficient engines with increased performance for their propulsion systems. A wide range of experimental efforts were undertaken to further the ability to obtain performance data on small engines as well as to develop understanding of their operation. Data were collected to quantify friction losses present in the dynamometer drivetrain on the small engine research bench. A correction and calibration model was developed for brake power collected by the dynamometer. Mechanical efficiencies for 28 cm3, 55 cm3 and 85 cm3 engines were 92.4%, 91.3% and 89.7%, respectively. Maximum fuel conversion …
Orbit Estimation Of Non-Cooperative Maneuvering Spacecraft, Gary M. Goff
Orbit Estimation Of Non-Cooperative Maneuvering Spacecraft, Gary M. Goff
Theses and Dissertations
Due to the ever increasing congestion of the space environment, there is an increased demand for real-time situation awareness of all objects in space. An unknown spacecraft maneuver changes the predicted orbit, complicates tracking, and degrades estimate accuracies. Traditional orbit estimation routines are implemented, tested, and compared to a multiple model format that adaptively handles unknown maneuvers. Multiple Model Adaptive Estimation is implemented in an original way to track a non-cooperative satellite by covariance inflation and filtering-through a maneuver. Parameters for successful instantaneous maneuver reconstruction are analyzed. Variable State Dimension estimation of a continuously maneuvering spacecraft is investigated. A requirements …
Creep Of Sylramic-Ibn Fiber Tows At Elevated Temperature In Air And In Silicic Acid-Saturated Steam, Kevin B. Sprinkle
Creep Of Sylramic-Ibn Fiber Tows At Elevated Temperature In Air And In Silicic Acid-Saturated Steam, Kevin B. Sprinkle
Theses and Dissertations
Stressed oxidation experiments on Sylramic-iBN fiber tows were performed to evaluate the novel fiber's mechanical performance, creep behavior, and creep mechanisms. This research effort investigated creep response of Sylramic-iBN fiber tows at elevated temperatures in both air and in silicic acid-saturated steam environments. Creep experiments were conducted at creep stresses ranging from 127 to 762 MPa at 400°C and 500°C in order to examine the mechanical behavior of the Sylramic-iBN fiber tows at temperatures below and above the melting point of boria (450°C). Sylramic-iBN fibers are known to have excellent creep resistance, better than most other non-oxide fibers and significantly …
Effect Of Prior Exposure At Elevated Temperatures On Tensile Properties And Stress-Strain Behavior Of Four Non-Oxide Ceramic Matrix Composites, Sarah M. Wallentine
Effect Of Prior Exposure At Elevated Temperatures On Tensile Properties And Stress-Strain Behavior Of Four Non-Oxide Ceramic Matrix Composites, Sarah M. Wallentine
Theses and Dissertations
Thermal stability of four non-oxide ceramic matrix composites was studied. The materials studied were commercially available composites: SiC/SiNC; C/SiC; C/SiC-B4C (C/HYPR-SiCTM); and SiC/SiC-B4C (SiC/HYPR-SiCTM). COI Ceramics manufactured the SiC/SiNC and C/SiC composites using polymer infiltration and pyrolysis (PIP). The C/HYPR-SiCTM and SiC/HYPR-SiCTM CMCs were manufactured by Hyper-Therm High-Temperature Composites using chemical vapor infiltration (CVI). All four composites rely on a dense matrix for strength, stiffness, and oxidation protection. Fiber coating provides a fiber-matrix interface that allows fiber-matrix debonding and fiber pullout to occur, imparting fracture toughness to the CMC. The SiC/SiNC, C/SiC, and C/HYPR-SiC …
Modal Characterization Of A Piezoelectric Shaker Table, Randall J. Hodkin
Modal Characterization Of A Piezoelectric Shaker Table, Randall J. Hodkin
Theses and Dissertations
Piezoelectric actuated shaker tables are often used for high frequency fatigue testing. Since natural frequencies can appear in the operating range of these shaker tables, it is necessary to conduct modal characterization of the system before testing. This thesis describes the design and experimental validation of a mechanical model used for modal analysis of a piezoelectric shaker table. A commercially available three-dimensional scanning device was used to produce a point cloud model of the surface geometry, which was converted to a solid model and imported into a Finite Element Analysis (FEA) package for modal analysis. Using a laser vibrometer to …
Simulation Of Metal Particulates In High Energetic Materials, Eduardo Nieto
Simulation Of Metal Particulates In High Energetic Materials, Eduardo Nieto
Theses and Dissertations
This research focused on analyzing the effects of aluminum in high explosives such as PBX9501 using the MPEXS computational simulation code for a wide range of metalized explosive cases. The varying parameters are aluminum particle diameter and mass fraction of aluminum. The addition of metal particulates in explosive mixtures increases the density of the shock wave, causing a higher pressure in the shock. It was concluded that pressure and density steadily increases as the Al particle diameter increases, and pressure and density decreases when Al mass fraction increases. The concentrated pressures will dissipate quickly due to the high density, providing …
Topology Optimization Of An Aircraft Wing, David L. Walker
Topology Optimization Of An Aircraft Wing, David L. Walker
Theses and Dissertations
A Topology Optimization (TO) was conducted on an aircraft wing in order to mathematically determine an ideal structural case for future aircraft. TO generally involves iteratively reducing individual elemental density until the desired mass or volume constraint is met. Two different TO styles where approached: a global three-dimensional concept and a more traditional two-dimensional rib and spar optimization which more closely mimics the baseline model. All optimizations were compared against a baseline wing for von-Mises stress, displacement, and buckling. The objective of this research was to develop a design procedure maintaining the baseline structural integrity of the wing while reducing …
Improving The Performance Of The Space Surveillance Telescope As A Function Of Seeing Parameter, Jae H. Jeon
Improving The Performance Of The Space Surveillance Telescope As A Function Of Seeing Parameter, Jae H. Jeon
Theses and Dissertations
This research paper investigates ways to improve the detection capability and predict the performance of the Space Surveillance Telescope (SST) system when it's relocated to Exmouth, Australia. The dataset collected by the SST observing the Geosynchronous Earth Orbit (GEO) satellite, ANIK-F1, entering the earth's eclipse is used to test the performance of the three existing and one new detection algorithm. The three existing algorithms are the point detection (Binary Hypothesis Test (BHT)), correlation detection (CD-BHT), and Multi-hypothesis Test using ten hypotheses (MHT10), and the new detection algorithm is the Multi-hypothesis Test using six hypotheses (MHT6). To improve the accuracy and …
Theoretical Limits Of Lunar Vision Aided Navigation With Inertial Navigation System, David W. Jones
Theoretical Limits Of Lunar Vision Aided Navigation With Inertial Navigation System, David W. Jones
Theses and Dissertations
The precision navigation capabilities of the Global Positioning System (GPS) are used extensively within US military operations. However, GPS is highly vulnerable to intentional and unintentional external interference. Therefore, a need exists to develop a non-GPS precision navigation method to operate in GPS degraded environments. This research effort presents the theoretical limits of a precision navigation method based on an inertial navigation system (INS) aided by angle measurements with respect to lunar surface features observed by a fixed camera. To accomplish this task, an extended Kalman filter (EKF) was implemented to estimate INS drift errors and bring in simulated lunar …
Expected Position Error For An Onboard Satellite Gps Receiver, Anthony S. Williams
Expected Position Error For An Onboard Satellite Gps Receiver, Anthony S. Williams
Theses and Dissertations
The Global Positioning System (GPS) constellation provides ranging information that delivers inexpensive, high precision positioning for terrestrial users. Satellites in Low Earth Orbit (LEO) can use an onboard GPS receiver resulting in meter-level navigation solution accuracy. There are limitations to using GPS for positioning for satellites above LEO. The number of GPS satellites who's signal can be received decreases as the receivers altitude approaches that of the GPS constellation. Above the GPS constellation, the available GPS signals for ranging will originate from satellites on the opposite side of Earth. This research calculates the available GPS signals to the receiver and …
Effect Of Prior Exposure At Elevated Temperatures On Tensile Properties And Stress-Strain Behavior Of Three Oxide/Oxide Ceramic Matrix Composites, Christopher J. Hull
Effect Of Prior Exposure At Elevated Temperatures On Tensile Properties And Stress-Strain Behavior Of Three Oxide/Oxide Ceramic Matrix Composites, Christopher J. Hull
Theses and Dissertations
Thermal stability of three oxide-oxide ceramic matrix composites was studied. The materials studied were NextelTM610/aluminosilicate (N610/AS), NextelTM720/aluminosilicate (N720/AS), and NextelTM720/Alumina (N720/A), commercially available oxide-oxide ceramic composites (COI Ceramics, San Diego, CA). The N610/AS composite consists of a porous aluminosilicate matrix reinforced with laminated woven alumina N610 fibers. The N720/AS and N720/A composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (NextelTM720) fibers. The matrix materials are aluminosilicate in N720/AS and alumina in N720/A. All three composites have no interface between the fibers and matrix, and rely on the porous …
Non-Destructive Techniques For Classifying Aircraft Coating Degradation, Kody A. Wilson
Non-Destructive Techniques For Classifying Aircraft Coating Degradation, Kody A. Wilson
Theses and Dissertations
In this research non-destructive techniques were examined as possible methods of determining aircraft coating degradation. Single Value Decomposition(SVD)-Linear Discriminant Analysis(LDA) algorithms were applied to measured spectra. When applied to infrared emittance spectra only 52% classification accuracy was achieved. When applied to Raman spectroscopy a higher classification accuracy of 70.4% is attained when using the same SVD-LDA algorithm. However the best performing measurement was using infrared reflectance classification accuracies were 100%, 99.83% and 94.4% when using the Bomem FTS, DRIFTS and Telops respectively for one of the sample sets. For DRIFTS data a more accurate fingerprint region was identified 865.6 - …
Dynamic Response Analysis Of An Icosahedron Shaped Lighter Than Air Vehicle, Lucas W. Just
Dynamic Response Analysis Of An Icosahedron Shaped Lighter Than Air Vehicle, Lucas W. Just
Theses and Dissertations
The creation of a lighter than air vehicle using an inner vacuum instead of a lifting gas is considered. Specifically, the icosahedron shape is investigated as a design that will enable the structure to achieve positive buoyancy while resisting collapse from the atmospheric pressure applied. This research analyzes the dynamic response characteristics of the design, and examines the accuracy of the finite element model used in previous research by conducting experimental testing. The techniques incorporated in the finite element model are confirmed based on the experimental results using a modal analysis. The experimental setup designed will allow future research on …
Navigation Constellation Design Using A Multi-Objective Genetic Algorithm, Heather C. Diniz
Navigation Constellation Design Using A Multi-Objective Genetic Algorithm, Heather C. Diniz
Theses and Dissertations
In satellite constellation design, performance and cost of the system drive the design process. The Global Positioning System (GPS) constellation is currently used to provide positioning and timing worldwide. As satellite technology has improved over the years, the cost to develop and maintain the satellites has increased. Using a constellation design tool, it is possible to analyze the tradeoffs of new navigation constellation designs (Pareto fronts) that illustrate the tradeoffs between position dilution of precision (PDOP) and system cost. This thesis utilized Satellite Tool Kit (STK) to calculate PDOP values of navigation constellations, and the Unmanned Spacecraft Cost Model (USCM) …
Optimized Flight Path For Localization Using Line Of Bearing, Namkyu Kim
Optimized Flight Path For Localization Using Line Of Bearing, Namkyu Kim
Theses and Dissertations
This research develops optimized flight paths for localization of a target using LOB measurements. The target area is expressed as an error ellipse using the measurement errors of the LOBs. The optimization approach is focused on minimizing the size of the error ellipse. The algorithm for the optimized path is generated and compared with typical flight paths. The optimization routine is based on the results revised from previous similar research in the literature. A geometrical method to estimate the error ellipse is combined with optimal control in this research. Each LOB gives a possible target area and this target area …
A Cubesat Mission For Mapping Spot Beams Of Geostationary Communications Satellites, Jacob A. Lasarge
A Cubesat Mission For Mapping Spot Beams Of Geostationary Communications Satellites, Jacob A. Lasarge
Theses and Dissertations
As space-rated technologies become more compact and more readily available over time, the concept of accomplishing space missions with smaller nanosatellite-class spacecraft becomes increasingly feasible. This research focuses specifically on a CubeSat mission to assist with radio frequency (RF) domain verification; that of characterizing and mapping K-band spot beams from communications satellites in geostationary orbit. By flying a constellation of CubeSats through the edges of spot beams originating from geostationary communication satellites, the spot beam's coverage area will be characterized. This research conducts a mission feasibility assessment, identifies the principle mission requirements to complete a spot beam mapping CubeSat mission, …
Overall Effectiveness Measurement At Engine Temperatures With Reactive Film Cooling And Surface Curvature, Andrew J. Lynch
Overall Effectiveness Measurement At Engine Temperatures With Reactive Film Cooling And Surface Curvature, Andrew J. Lynch
Theses and Dissertations
The thesis presented here details the design, construction and initial testing of rig for use with high temperature film cooling testing. The film cooling rig was supplied with hot mainstream gas from a well-stirred reactor operating on a propane/air mixture capable of multiple equivalence ratios. The Hastelloy test plates contained an internal cooling channel to allow for overall effectiveness measurements. Thermocouples on both the freestream and internal surfaces of the test plate provided temperature differences for heat flux calculations. The test plates had a quarter circle leading edge with a tapered trailing edge to provide surface curvature for the film …
Design And Test Of An Attitude Determination And Control System For A 6u Cubesat Using Afit's Cubesat Testbed, Michael L. Tibbs
Design And Test Of An Attitude Determination And Control System For A 6u Cubesat Using Afit's Cubesat Testbed, Michael L. Tibbs
Theses and Dissertations
The design and test of a 6U CubeSat Attitude Determination and Control System (ADCS) are explored to establish single-axis control using AFIT's CubeSat testbed consisting of a Helmholtz cage and hemi-spherical air bearing. The Helmholtz cage produces a near-uniform magnetic field inside the cage while the air bearing provides a near-frictionless surface for ADCS testing. The ADCS testbed includes a four wheel pyramid reaction wheel array (RWA) for actuation and an inertial measurement unit (IMU) for attitude determination. Along with the ADCS hardware, the ADCS testbed also includes an Electrical Power System (EPS) and Command and Data Handling (CDH) for …