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Articles 97951 - 97980 of 198044

Full-Text Articles in Engineering

Key Detection Rate Modeling And Analysis For Satellite-Based Quantum Key Distribution, Jonathan C. Denton Mar 2016

Key Detection Rate Modeling And Analysis For Satellite-Based Quantum Key Distribution, Jonathan C. Denton

Theses and Dissertations

A satellite QKD model was developed and validated, that allows a user to determine the optimum wavelength for use in a satellite-based QKD link considering the location of ground sites, selected orbit and hardware performance. This thesis explains how the model was developed, validated and presents results from a simulated year-long study of satellite-based quantum key distribution. It was found that diffractive losses and atmospheric losses define a fundamental trade space that drives both orbit and wavelength selection. The optimal orbit is one which generates the highest detection rates while providing equal pass elevation angles and durations to multiple ground …

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Space Object Self-Tracker On-Board Orbit Determination Analysis, Stacie M. Flamos Mar 2016

Space Object Self-Tracker On-Board Orbit Determination Analysis, Stacie M. Flamos

Theses and Dissertations

Due to the United States' growing dependence on space based assets and the in- creasing number of resident space objects (RSO), improvement of Space Situational Awareness (SSA) capabilities is more necessary than ever. As a way to aid in this need, the Air Force Institute of Technology (AFIT) is developing the Space Object Self-Tracker (SOS) as a proof-of-concept experimental satellite for RSO precision tracking and collision avoidance system in Low Earth Orbit (LEO). Specifically, SOS will use Global Positioning System (GPS) position estimates for on-board orbit de- termination. Currently, SOS will use the Simplified General Perturbations-4 (SGP4) algorithm as its …

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Multi-Cubesat Deployment Strategies: How Different Satellite Deployment Schemes Affect Satellite Separation And Detection For Various Types Of Constellations And Missions, Scott A. Biehl Jr. Mar 2016

Multi-Cubesat Deployment Strategies: How Different Satellite Deployment Schemes Affect Satellite Separation And Detection For Various Types Of Constellations And Missions, Scott A. Biehl Jr.

Theses and Dissertations

As economics drive an increased demand for small satellites and, consequently, an increase in the number of satellites deployed per launch, different deployment schemes and their effects on satellite dynamics must be well understood. While there are advantages to deploying multiple satellites at once, users may have trouble with tracking, identifying, and communicating with their satellites. This investigation examines the deployment of eight 3U CubeSats, and the resulting relative motion within a constellation. Both the distance between any two satellites within a constellation and the volume of a polygon encompassing a constellation are used to analyze the satellite dynamics within …

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Enhanced Flow Migration In Full Annular Ultra Compact Combustor, Nicholas A. Gilbert Mar 2016

Enhanced Flow Migration In Full Annular Ultra Compact Combustor, Nicholas A. Gilbert

Theses and Dissertations

Since combustion efficiency in modern jet engines has stabilized, attention has turned to improving the combustor by improving the thrust-to-weight ratio. The Ultra Compact Combustor (UCC) is a means to reduce the weight of the combustor while ensuring exhaust meets increasingly stringent government emission standards. Combustion occurs within the UCC under a g-load in the circumferential direction, which maintains combustion efficiency while decreasing axial combustor length. Previous analysis optimized the combustion chamber flame characteristics with a common upstream air source. Previously, issues for the UCC were inspired by integration into a traditional axial turbojet. The focus of this investigation was …

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Orbital Resonances In The Vinti Solution, Laura M. Duffy Mar 2016

Orbital Resonances In The Vinti Solution, Laura M. Duffy

Theses and Dissertations

The Vinti Solution offers a more accurate model than the two-body problem as an orbital propagator. Unfortunately, the Vinti solution contains small divisors near orbital resonances in the perturbative terms of the Hamiltonian, which lead to inaccurate orbital predictions. One approach to avoid the small divisors is to apply transformation theory. The methodology of this research is to identify the perturbative terms of the Vinti Solution, perform a coordinate transformation, and derive the new equations of motion for the Vinti system near orbital resonances. The analysis in this research focuses on the 2:1 resonance, which includes the Global Positioning System. …

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Investigation Into Reynolds Number Effects On A Biomimetic Flapping Wing, Daniel K. Hope Mar 2016

Investigation Into Reynolds Number Effects On A Biomimetic Flapping Wing, Daniel K. Hope

Theses and Dissertations

This research investigated how the nature of the wing changed as a function of Reynolds number by measuring the forces produced by wings with varying characteristic lengths, tested at varying air densities. Increasing the wing span increased the overall weight of the wing, which reduced the 1st natural frequency; and did not result in an increase in vertical force over the baseline 50 mm wing. However; if the decrease in natural frequency was counteracted by increasing the thickness of the joint material in the linkage mechanism, vertical force production did increase over the baseline wing planform. Negligible forces and moments …

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Evaluation Of Unmanned Aircraft Flying Qualities Using Jsbsim, Joshua P. Kim Mar 2016

Evaluation Of Unmanned Aircraft Flying Qualities Using Jsbsim, Joshua P. Kim

Theses and Dissertations

Flying qualities data can be used to predict the future performance of aircraft; however, no flying qualities requirements exist for Unmanned Aerial Vehicles (UAVs). The intent of flying qualities requirements is to guarantee the safety and operational effectiveness of the aircraft. Flying qualities requirements have been extensively researched and specified for fixed-wing and rotary-wing manned aircraft based on a substantial database of assessments. The critical issue today in flying qualities is how to extend them to pilotless aircraft. A simulation study using an open-source flight dynamics model (JSBSim) was conducted to perform various performance maneuvers and evaluate how well the …

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Geolocation Of Rf Emitters Using A Low-Cost Uav-Based Approach, Michael A. Magers Mar 2016

Geolocation Of Rf Emitters Using A Low-Cost Uav-Based Approach, Michael A. Magers

Theses and Dissertations

The proliferation of unmanned aerial vehicles (UAVs) in both military and civilian settings has prompted great interest in finding new and innovative ways to utilize these tools. One such application is to locate ground-based radio emitters from a UAV platform. The goal of this research is to study the feasibility of a low-cost (on the order of $1000) UAV geolocation platform. To accomplish this goal, a series of both real-world flight testing and computer simulated scenarios were conducted. Simulations for different sensor uncertainties and approach path scenarios such as loiter and button hook patterns were investigated. Results showed that a …

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Performance Testing Of Various Nozzle Design For Water Electrolysis Thruster, Yuen Liu Mar 2016

Performance Testing Of Various Nozzle Design For Water Electrolysis Thruster, Yuen Liu

Theses and Dissertations

The purpose of this research is to develop new nozzles for the HYDROSTM thruster, a pulsed chemical thruster, to improve the current flight performance. This research consists of a base line test of the factory nozzle, as well as testing of three 15-degree conical nozzles with different expansion ratios. Experiments were conducted at plenum pressures 30, 40, and 45 psia to ensure the thruster is throttleable. Impulse bit data was collected through measuring the impulse response of each firing using a torsional balance thrust stand. Analysis of the thruster performance included calculations of impulse bit, specific impulse, thrust coefficient, …

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Analysis Of A Modified Equivalent Circuit Model For Lithium-Ion Battery Modules In Cubesats, James J. Liu Mar 2016

Analysis Of A Modified Equivalent Circuit Model For Lithium-Ion Battery Modules In Cubesats, James J. Liu

Theses and Dissertations

Failure of the electrical power system (EPS) to meet mission requirements is a common problem in nano-size satellites commonly referred to as CubeSats. The motivation for this research stems from the desire to prevent EPS failure through a process of testing and space qualification of components. Utilizing models to predict the behavior of an EPS before it is designed, built, and tested for space can provide critical insight in areas of limitation in performance and survivability. Modeling an entire EPS system is challenging because it requires extensive knowledge of all components and their behavior. This research focuses specifically on the …

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Development Of A Modularized Software Architecture To Enhance Ssa With Cots Telescopes, Julian P. Mccafferty Mar 2016

Development Of A Modularized Software Architecture To Enhance Ssa With Cots Telescopes, Julian P. Mccafferty

Theses and Dissertations

As the catalog of Earth orbiting objects continues to grow exponentially, so too does the necessity for Space Situational Awareness (SSA). Previous work at AFIT has explored augmenting the Space Surveillance Network (SSN) by demonstrating detection and tracking of orbiting objects using Commercial-Off-The-Shelf (COTS) telescopes and Air Force generated Two-Line Element Sets (TLE). This research explores the process of developing and reengineering code into a modularized, hierarchical component architecture designed for the end user while enabling developers to continue to modify the software for future applications. Three graphical user interfaces (GUI) are compiled into standalone executable programs using MATLAB for …

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Fatigue Behavior Of An Advanced Sic/Sic Composite At 1300° C In Air And Steam, Michael D. Lee Mar 2016

Fatigue Behavior Of An Advanced Sic/Sic Composite At 1300° C In Air And Steam, Michael D. Lee

Theses and Dissertations

The fatigue behavior of an advanced silicon carbide/silicon carbide (SiC/SiC) ceramic matrix composite (CMC) was investigated at 1300 ºC in laboratory air and in steam environments. The composite was manufactured using chemical vapor infiltration (CVI). The composite consisted of an oxidation-inhibited matrix, which was comprised of alternating layers of silicon carbide and boron carbide and was reinforced with laminated Hi-Nicalon™ fibers woven in a plain weave. Fiber preforms had pyrolytic carbon fiber coating with boron carbon overlay applied. Two specimen geometries were evaluated, a dog bone and an hourglass geometry. Tensile stress-strain behavior and tensile properties were evaluated at 1300 …

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Material And Design Considerations For A Portable Ultra-Violet (Uv) Light Emitting Diode (Led) Water Purification Device, Drew D. Gallucci Mar 2016

Material And Design Considerations For A Portable Ultra-Violet (Uv) Light Emitting Diode (Led) Water Purification Device, Drew D. Gallucci

Theses and Dissertations

Department of Defense personnel often deploy to austere environments where clean water is not readily available. Ultraviolet (UV) radiation through the use of light emitting diodes (LEDs) in a portable device offers a potential method for expedient water treatment. This research studied the application of one diode, low power, UV LEDs and nine diode, high power, UV LEDs within a portable steel reactor and Teflon reactors of three different wall thicknesses. Reactor efficiency was determined through measuring and comparing the rate constants for Advanced Oxidation of hydrogen peroxide with yellow tartrazine as a witness dye. Experiments conducted with low power …

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Additive Manufacturing Process Parameter Effects On The Mechanical Properties Of Fused Filament Fabrication Nylon, Eric S. Holm Mar 2016

Additive Manufacturing Process Parameter Effects On The Mechanical Properties Of Fused Filament Fabrication Nylon, Eric S. Holm

Theses and Dissertations

The purpose of this research was to determine how varying Fused Filament Fabrication (FFF) process parameters affect the mechanical properties of PA6 nylon dog-bone specimens produced on the Mark One 3D Printer. A design of experiment (DOE) was conducted using the factors of layer height and raster angle orientation. The mechanical properties measured in the experiment were tensile modulus, yield stress, percent strain at yield, ultimate tensile strength and percent strain at break. An analysis of variance (ANOVA) was performed to identify which factors were statistically significant in influencing mechanical properties. Results of the ANOVA showed that layer height was …

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A Service Oriented Architecture Approach For Global Positioning System Quality Of Service Monitoring, Stuart A. Everson Mar 2016

A Service Oriented Architecture Approach For Global Positioning System Quality Of Service Monitoring, Stuart A. Everson

Theses and Dissertations

This research focuses on the development of a Service Oriented Architecture (SOA) for monitoring the Global Positioning System (GPS) Standard Positioning Service (SPS) in near real time utilizing a Mobile Crowd Sensing (MCS) technique. A unique approach to developing the MCS SOA was developed that utilized both the Depart- ment of Defense Architecture Framework (DoDAF) and the SOA Modeling Language (SoaML) guidance. The combination of these two frameworks resulted in generation of all the architecture products required to evaluate the SOA through the use of Model Based System Engineering (MBSE) techniques. Ultimately this research provides a feasibility analysis for utilization …

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Radiation Response From A Novel Uo2 Crystal, Stephan A. Varga Mar 2016

Radiation Response From A Novel Uo2 Crystal, Stephan A. Varga

Theses and Dissertations

The radiation response of a novel, single-crystalline UO2 sample was analyzed using several types of radiation. The crystal was exposed to alpha, gamma, and neutron radiation under various environmental conditions and the electronic response of the crystal was measured using a pulse shape discrimination algorithm. The distributions of pulse amplitude (Vmax) and pulse decay times (τ) were used to compare the output. This research revealed that the crystal radiation response is exceptionally sensitive to surface conditions, specifically humidity, which tends to alter the time dependent currents resulting from the radiation interactions. The pulse τ can be made to …

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Differential (P, P′) And (P, D) Cross Sections Of 89Y And 92Zr, Molly A. Wakeling Mar 2016

Differential (P, P′) And (P, D) Cross Sections Of 89Y And 92Zr, Molly A. Wakeling

Theses and Dissertations

Differential cross sections for the (p, p′) and (p, d) reactions on 89Y and 92Zr were measured using a 28.25-MeV proton beam at the 88-inch cyclotron at Lawrence Berkeley National Laboratory. Angular distributions were obtained for the ground state and several excited states of each isotope using silicon detector telescopes over angles 10° to 140° in the reaction plane. These data were obtained by fitting a Gaussian function to each peak in the energy spectra and integrating the number of counts under each peak. These cross sections will be included in nuclear structure models …

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The Efficacy Of Implementing A Small, Low-Cost, Real Time Kinematic Gps System Into A Small Unmanned Aerial System Architecture, Kevin J. Hendricks Mar 2016

The Efficacy Of Implementing A Small, Low-Cost, Real Time Kinematic Gps System Into A Small Unmanned Aerial System Architecture, Kevin J. Hendricks

Theses and Dissertations

Along with the growing uses for small unmanned aerial systems (UAS) within the Department of Defense (DoD), is the utility of small UAS within the civilian market is also increasing. This has led to significant research and development on small UAS subsystems by the commercial market. The focus of this research is characterizing and investigating the application considerations of a small, low-cost real time kinematic (RTK) GPS receiver system. Work was also accomplished to characterize the accuracy and precision of the commonly used GPS receiver subsystem in small UAS to show the increased utility of the RTK GPS system. The …

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Vibrational Analysis Of A 12u Chassis, Daniel G. Miller Mar 2016

Vibrational Analysis Of A 12u Chassis, Daniel G. Miller

Theses and Dissertations

The objective of this research is to characterize how the natural frequencies of AFIT’s CubeSat design can be controlled to meet launch vehicle requirements while increasing the internal and external volume available for payload and bus components as the chassis increases in size. A reliable Finite Element (FE) model is created and validated using NASA’s General Environmental Verification Standards (GEVS) vibrational test on the 12U chassis. The validated FE model proves that current boundary conditions and geometric properties with minimized chassis wall thicknesses to maximize usable internal and external volume maintain a first frequency of the fully loaded 12U chassis …

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Electro-Mechanical Characterization Of Carbon Nanotube Sheets In Simulated Space Environments: The Dawn Of “Carbon Spacecraft”, Jacob W. Singleton Mar 2016

Electro-Mechanical Characterization Of Carbon Nanotube Sheets In Simulated Space Environments: The Dawn Of “Carbon Spacecraft”, Jacob W. Singleton

Theses and Dissertations

Carbon nanotube (CNT) materials are exciting candidates for spacecraft by virtue of their unprecedented specific mechanical and electrical properties. Analysis in this thesis identifies 14 types of CNT-sheets with distinct variables, and discovers the mechanisms controlling macroscopic properties. Specimen variables include acid treatment, polymer coatings, production method, and combinations. Mechanical testing includes tensile-tests and investigation with scanning electron microscopy and energy-dispersive x-ray spectroscopy. Physical properties testing include electromagnetic interference (EMI) shielding effectiveness (SE) and electrical conductivity. This research also highlights the resilience of CNT-sheets to atomic oxygen and thermal fatigue qualifying them for performance in space. EP CNT-sheets have decreased …

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Short Duration Missions To Earth Crossing Asteroids, James B. Millar Iii Mar 2016

Short Duration Missions To Earth Crossing Asteroids, James B. Millar Iii

Theses and Dissertations

My investigation of the Near Earth Object (NEO) catalog has led to identification of numerous short duration, under 40 days, mission opportunities in the future for three different mission types: uncrewed fly-by, uncrewed arrival, and crewed arrival. 2-body propagation techniques were used to model the orbits of various asteroid candidates and the Earth to determine when a close approach would occur. Once the dates were calculated, distance between the bodies was computed to estimate the ∆V to complete the mission. From the mission ∆V values, a possible mission duration was also computed. The values were analyzed to determine the best …

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Minimum-Fuel Trajectory Design In Multiple Dynamical Environments Utilizing Direct Transcription Methods And Particle Swarm Optimization, Alfredo G. Zurita Jr. Mar 2016

Minimum-Fuel Trajectory Design In Multiple Dynamical Environments Utilizing Direct Transcription Methods And Particle Swarm Optimization, Alfredo G. Zurita Jr.

Theses and Dissertations

Particle swarm optimization is used to generate an initial guess for designing fuel-optimal trajectories in multiple dynamical environments. Trajectories designed in the vicinity of Earth use continuous or finite low-thrust burning and transfer from an inclined or equatorial circular low-Earth-orbit to a geostationary orbit. In addition, a trajectory from near-Earth to a periodic orbit about the cislunar Lagrange point with minimized impulsive burn costs is designed within a multi-body dynamical environment. Direct transcription is used in conjunction with a nonlinear optimizer to find locally-optimal trajectories given the initial guess. The near-Earth transfers are propagated at low-level thrust where neither the …

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Military Applications Of High-Altitude Satellite Orbits In A Multi-Body Dynamical Environment Using Numerical Methods And Dynamical Systems Theory, Meredith M. Wilmer Mar 2016

Military Applications Of High-Altitude Satellite Orbits In A Multi-Body Dynamical Environment Using Numerical Methods And Dynamical Systems Theory, Meredith M. Wilmer

Theses and Dissertations

The circular restricted three-body problem (CR3BP) is a simplified dynamical model for a satellite under the gravitational influence of both the Earth and the Moon, maintaining closer fidelity to the gravitational environment experienced by a high-altitude Earth-orbiting spacecraft than modeling in the Earth-satellite two-body problem. Resonant orbit arcs are used to determine an initial guess to input into an algorithm that computes a trajectory solution with specific design requirements and constraints. A test case uses this method to compute a lunar fly-by transfer solution requiring less than two-body transfer methods and offers an unusual pathway that adds an unpredictability element …

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Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 700°C In Air And In Silicic Acid-Saturated Steam, Matthew W. Piper Mar 2016

Creep Of Hi-Nicalon™ S Ceramic Fiber Tows At 700°C In Air And In Silicic Acid-Saturated Steam, Matthew W. Piper

Theses and Dissertations

Aircraft structural and engine components are subjected to elevated temperature and steam environments during operation. Turbine blades experience particularly harsh conditions that are approaching the operating temperature limits of current Nickel-based superalloys even with active cooling. Ceramic matrix composites (CMCs), which demonstrate high specific strength and specific stiffness and maintain these properties at elevated temperatures such that active cooling is not required, are prime candidates to replace superalloys as the materials for turbine blades. Ceramic matrix composites are composite materials that consist of a ceramic matrix with fiber reinforcement. This research investigated a silicon carbide (SiC) fiber, Hi-Nicalon™ S, which …

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Field-Based Phase Retrieval Using Under-Sampled Data, Tatsuki L. Watts Mar 2016

Field-Based Phase Retrieval Using Under-Sampled Data, Tatsuki L. Watts

Theses and Dissertations

A phase retrieval algorithm designed for use with under-sampled astronomical data is developed in this thesis. Blind-deconvolution, Gerchberg Saxton (GS), and a field-based compass search are combined into an algorithm capable of recovering Zernike coefficients 4 through 11 from single frames of noisy, under-sampled data without the need to unwrap the recovered phase. The performance of the algorithm in data under-sampled by a factor of 2 is compared the performance of the algorithm on Nyquist-sampled data. In simulation trials, the magnitudes of all 8 estimated Zernike coefficients converged to within half a wave of the true values for 98% of …

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An Openeaagles Framework Extension For Hardware-In-The-Loop Swarm Simulation, Derek B. Worth Mar 2016

An Openeaagles Framework Extension For Hardware-In-The-Loop Swarm Simulation, Derek B. Worth

Theses and Dissertations

Unmanned Aerial Vehicle (UAV) swarm applications, algorithms, and control strategies have experienced steady growth and development over the past 15 years. Yet, to this day, most swarm development efforts have gone untested and thus unimplemented. Cost of aircraft systems, government imposed airspace restrictions, and the lack of adequate modeling and simulation tools are some of the major inhibitors to successful swarm implementation. This thesis examines how the OpenEaagles simulation framework can be extended to bridge this gap. This research aims to utilize Hardware-in-the-Loop (HIL) simulation to provide developers a functional capability to develop and test the behaviors of scalable and …

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Applications Of Correlated 2d-Acar And Cdbar Using A Low-Energy Positron Beam, Angelo M. Bonavita Mar 2016

Applications Of Correlated 2d-Acar And Cdbar Using A Low-Energy Positron Beam, Angelo M. Bonavita

Theses and Dissertations

The three-dimensional positron annihilation spectroscopy system (3D-PASS) at the Air Force Institute of Technology (AFIT) correlates coincidence Doppler broadening of annihilation radiation with two-dimensional angular correlation of annihilation radiation measurements using two position-sensitive, high-purity germanium (HPGe) detectors. The low photoelectric cross section of germanium, combined with the limited output of the radioisotope-based positron beam, produced sparse data necessitating careful data extraction. Processing techniques employed to increase 3D-PASS spectra quality include an improved algorithm for determining radiation-interaction position on HPGe double-sided strip detectors, a momentum sampling function based correction scheme and spectra folding informed by crystal symmetries. The 3D nature of …

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Pointing Analysis And Design Drivers For Low Earth Orbit Satellite Quantum Key Distribution, Jeremiah A. Specht Mar 2016

Pointing Analysis And Design Drivers For Low Earth Orbit Satellite Quantum Key Distribution, Jeremiah A. Specht

Theses and Dissertations

The world relies on encryption to perform critical and sensitive tasks every day. If quantum computing matures, the capability to decode keys and decrypt messages becomes possible. Quantum key distribution (QKD) is a method of distributing secure cryptographic keys which relies on the laws of quantum mechanics. Current implementations of QKD use fiber-based channels which limit the number of users and the distance between users. Satellite-based QKD using free-space channels is proposed as a feasible secure global communication solution. Since a free-space link does not use a waveguide, pointing a transmitter to receiver is required to ensure signal arrival. In …

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Multi-Trajectory Automatic Ground Collision Avoidance System With Flight Tests (Project Have Escape), John V. Trombetta Mar 2016

Multi-Trajectory Automatic Ground Collision Avoidance System With Flight Tests (Project Have Escape), John V. Trombetta

Theses and Dissertations

Multi-trajectory automatic collision avoidance techniques for heavy-type aircraft are explored to increase aviation safety procedures and decrease losses due to controlled flight into terrain. Additionally, this research includes flight test results from the United States Test Pilot School’s Test Management Project (TMP) titled Have Emergency Safe Calculated Autonomous Preplanned Exit (ESCAPE). Currently, the heavy aircraft community lacks an automatic collision avoidance system that has proven to save lives in fighter-type aircraft. The tested algorithm includes both a 3-path and a 5-path avoidance technique that is compared to an optimal solution which minimizes aircraft control to avoid terrain. The research utilizes …

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Differences In Nutrient And Metal Uptake Among Plant Species In Stormwater Bioretention Systems., M. R. Borecki, Ryan Dupont, Joan E. Mclean Mar 2016

Differences In Nutrient And Metal Uptake Among Plant Species In Stormwater Bioretention Systems., M. R. Borecki, Ryan Dupont, Joan E. Mclean

Civil and Environmental Engineering Faculty Publications

No abstract provided.

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