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Full-Text Articles in Engineering

Effects Of A Nitrogen And Hydrogen Build Atmosphere On The Properties Of Additively Manufactured Tungsten, Dana C. Madsen Mar 2022

Effects Of A Nitrogen And Hydrogen Build Atmosphere On The Properties Of Additively Manufactured Tungsten, Dana C. Madsen

Theses and Dissertations

Additively manufactured tungsten was printed in pure nitrogen, nitrogen-2.5% hydrogen, and nitrogen-5% hydrogen atmospheres as part of a 2^3 full factorial designed experiment and subjected to room temperature and high-temperature three-point-bend testing, chemical analysis, hardness testing, and microstructural imaging techniques. The pure nitrogen specimens exhibited the highest strength and ductility at both high temperature and room temperature. Chemical analysis showed a 2-8x reduction in compositional oxygen relative to unprocessed powder. Hardness values for all samples was between 306.8 and 361.5 HV1. It is proposed that adding hydrogen into the build atmosphere reduced the available energy density for tungsten melting by …


Space Domain Awareness Assessment Of Cislunar Periodic Orbits For Lagrange Point Surveillance, Adam P. Wilmer Dec 2021

Space Domain Awareness Assessment Of Cislunar Periodic Orbits For Lagrange Point Surveillance, Adam P. Wilmer

Theses and Dissertations

Cislunar periodic orbits provide an elegant means to fill the observational capability gaps which are present in ground-based and/or near-Earth spaced-base sensors. This research involves theoretical analysis on the effectiveness of cislunar periodic orbits for Space Domain Awareness (SDA) mission architectures. Specifically, cislunar periodic orbits are analyzed, both individually and in constellations with one another, for their effectiveness at monitoring target satellites in Lyapunov and halo orbits about the Earth - Moon L1 and L2 Lagrange points. All orbits are created and modeled in the Circular Restricted Three-Body Problem (CR3BP), then subject to perturbations in both the Elliptical Restricted Three-Body …


Injection Studies On A Small-Scale Rotating Detonation Engine With Improved Flow Control, Jonathan J. Wyatt Dec 2021

Injection Studies On A Small-Scale Rotating Detonation Engine With Improved Flow Control, Jonathan J. Wyatt

Theses and Dissertations

The Rotating Detonation Engine (RDE) has gained increasing attention in recent years for its potential advantages over typical deflagration combustion. A Micro-RDE design with an outer diameter of 28mm operating on Nitrous Oxide and Ethylene was recently developed, which stretched the limits of small-scale detonation engines. The testing on this rig has shown a stable one wave mode detonation with frequencies reaching 16.8 kHz. Key parameters that influence the detonation wave mode are cell size, fill height, and wave speed, which are heavily influence d by injection schemes. Previous testing utilized a partially premixed jets in crossflow (JIC) injection scheme, …


Design And Performance Characterization Of A Water Propellant Resistojet Thruster, Sean M. Weathersby Dec 2021

Design And Performance Characterization Of A Water Propellant Resistojet Thruster, Sean M. Weathersby

Theses and Dissertations

Secondary payloads, such as CubeSats, are being increasingly used by the US Department of Defense in the role of defense capability enhancement, and these increasingly complex defense missions can require extended lifespans that result in the need for a thruster. While many thruster options exist, characteristics such as propellant toxicity, complexity, and low performance limit many viable solutions. However, a potential answer that satisfies these thruster limitations is found in electrothermals, specifically the resistojet. The research presented here represents the first attempt to construct a 1U water-propellant resistojet thruster design and establish an initial characterization through evaluation of various performance …


Investigation Of Mirror Satellite Concept To Augment Natural Lighting Conditions On Orbit, Daniel M. Dombrowski Dec 2021

Investigation Of Mirror Satellite Concept To Augment Natural Lighting Conditions On Orbit, Daniel M. Dombrowski

Theses and Dissertations

A method of augmenting on-orbit lighting conditions for rendezvous and proximity operations through the novel use of solar reflectors is presented. Natural lighting conditions on-orbit pose extreme challenges to these already complex missions. This research summarizes and applies the historical basis of solar reflectors to the proximity operations issues encountered today. Building on this past research, a simulation has been created to test the efficacy of a solar reflector constellation in facilitating less complex servicing/inspection missions. Initial testing has shown promising results for low mass membrane mirrors in augmenting illumination conditions with particular benefit in the geosynchronous orbital regime. Through …


Creep Behavior And Deformation Mechanisms Of Spark Plasma Sintered Oxide Ceramics For Aerospace Systems At 1300˚C - 1400˚C, David D. Swanson Dec 2021

Creep Behavior And Deformation Mechanisms Of Spark Plasma Sintered Oxide Ceramics For Aerospace Systems At 1300˚C - 1400˚C, David D. Swanson

Theses and Dissertations

The mechanical behavior of YAG and LuAG was investigated at elevated temperatures. The specific materials investigated in this work include high-purity, polycrystalline YAG, high-purity, polycrystalline LuAG, and two doped variants of YAG: 2at% Yb-doped, polycrystalline YAG and 2at% Er-doped, polycrystalline YAG. Several billets of each material were prepared and processed by means of spark plasma sintering (SPS). Many different sintering parameters were utilized in order to obtain materials with various physical properties and to identify the effects of sintering parameters on the average grain size of the resulting materials. The compressive creep behavior of these materials was investigated at 1300°C …


The Effect Of Shot Dependency On Composite Materials Subject To Ballistic Testing, Clayton C. Hankins Dec 2021

The Effect Of Shot Dependency On Composite Materials Subject To Ballistic Testing, Clayton C. Hankins

Theses and Dissertations

Ballistic analysis was performed on four common composite armor materials: 3k standard modulus plain weave carbon fiber, 8HS satin weave S-glass fiber, plain weave Kevlar® KM2 600 Denier fiber, and Spectra Shield® 4232 ultra-high molecular weight polyethylene to determine shot dependency based upon shot-to-shot impact distance, degree of penetration from the initial impacts, and the delamination effects from the initial impact. The primary measure of ballistic performance was the projectile velocity which represents a 50% probability of penetration, V50. This velocity was determined using a three-phase optimal design test method with an average of twelve shots per test. …


Design, Development, And Testing Of Embedded Computing On Afit's Control & Autonomy Space Proximity Robot (Caspr), Collin A. Gwaltney Dec 2021

Design, Development, And Testing Of Embedded Computing On Afit's Control & Autonomy Space Proximity Robot (Caspr), Collin A. Gwaltney

Theses and Dissertations

This thesis reviews RPO algorithm testbeds and discusses the development of the Control and Autonomy Space proximity Robot (CASpR) kinematic testbed housed at the Air Force Institute of Technology (AFIT). CASpR operates on a rail system to propagate the trajectories of two satellites using the Hill-Clohessy-Wiltshire (HCW) Equations of Motion (EOMs). In this study, the implementation of a Jetson TX2i as an onboard flight computer is discussed and accomplished. Each hardware component used in the process of adding embedded computing as well as the software and paths of communication are all discussed in detail. Tests are conducted to assess the …


A Real-Time Algorithm To Achieve Precise Coordinated Arrival Times In A Time-Variant Environment, Shawn S. Stephens Sep 2021

A Real-Time Algorithm To Achieve Precise Coordinated Arrival Times In A Time-Variant Environment, Shawn S. Stephens

Theses and Dissertations

The coordinated arrival time problem seeks to control a vehicle's trajectory to achieve some pre-defined final state at a desired arrival time. The persistent monitoring problem is a type of coordinated arrival problem where a stationary or moving ground target must be constantly observed by a group of aircraft. This research simplifies the problem to overfly the target at specific time intervals relative to the other aircraft in the group while increasing the difficulty of the problem by considering aircraft traveling at vastly different airspeeds. The result of this research is a real time guidance algorithm which accurately guides a …


Optimal Incorporation Of Non-Traditional Sensors Into The Space Domain Awareness Architecture, Albert R. Vasso Sep 2021

Optimal Incorporation Of Non-Traditional Sensors Into The Space Domain Awareness Architecture, Albert R. Vasso

Theses and Dissertations

The United States Government is the world’s de facto provider of space object cataloging data, but is challenged to maintain pace in an increasingly complex space environment. This work advances a multi-disciplinary approach to better understand and evaluate an underexplored solution recommended by national policy, in which current collection capabilities are augmented with non-traditional sensors. System architecting and literature identify likely needs, performance measures, and contributors to a conceptualized Augmented Network. Multiple hypothetical telescope architectures are modeled and simulated on four separate days throughout the year, then evaluated against performance measures and constraints using optimization. Decision analysis and Pareto optimality …


Stochastic Satellite Air Drag With The Ballistic Coefficient As A Random Variable, Everett B. Palmer Iv Sep 2021

Stochastic Satellite Air Drag With The Ballistic Coefficient As A Random Variable, Everett B. Palmer Iv

Theses and Dissertations

The drag acceleration caused by the Earth's atmosphere is a significant cause of prediction uncertainty for low Earth orbit satellites. Most existing research has focused on improving deterministic atmospheric density predictions or on density as a random variable. This research investigates a new paradigm and focuses on modeling the uncertainty caused by air drag using the ballistic coefficient, a component of air drag that is independent of the model used to predict atmospheric density. Time series of ballistic coefficient values were calculated and analyzed as random processes. These random processes were then used as the foundation of a stochastic satellite …


Visual Navigation And Control For Spacecraft Proximity Operations With Unknown Targets, Wyatt J. Harris Sep 2021

Visual Navigation And Control For Spacecraft Proximity Operations With Unknown Targets, Wyatt J. Harris

Theses and Dissertations

Many current and future spacecraft missions must conduct rendezvous and proximity operations (RPO) with resident space objects (RSOs). An important subset of spacecraft RPO that is yet to be demonstrated on-orbit involves final approach maneuvers with respect to RSOs where no information (such as geometry, inertia, relative velocity, etc.) is known about the target a priori, and no information is actively provided by the target during maneuvering. Such operation with respect to ‘unknown’ targets represents an important possible mission set for Department of Defense spacecraft and is the subject of this research. Two visual servoing frameworks capable of autonomously controlling …


Evaluation Of Additively Manufactured Lattices Under High Strain Rate Impact, Derek G. Spear Sep 2021

Evaluation Of Additively Manufactured Lattices Under High Strain Rate Impact, Derek G. Spear

Theses and Dissertations

Several additively manufactured lattice designs and configurations were evaluated under compression loads under various strain rates from quasi-static to highly dynamic. These experiments examined how the mechanical behavior of the lattice changed based on the lattice design properties and the applied strain rates. The modulus of elasticity, yield strength, plateau stress, and toughness were observed to decrease with an increase in strain rate, revealing that the lattice designs exhibit a negative strain rate sensitivity. A new lattice flow stress model was developed to account for the mechanical response of the lattice and was incorporated into a computational model for simulation. …


Application Of Vortex Tubes To Gas Turbine Film Cooling, Matthew N. Fuqua Sep 2021

Application Of Vortex Tubes To Gas Turbine Film Cooling, Matthew N. Fuqua

Theses and Dissertations

To improve thermal efficiency and reduce fuel consumption, gas turbine engines typically operate at increasingly higher turbine inlet temperatures--well in excess of turbine blade material limits--and film cooling schemes are normally employed to reduce metal temperatures within acceptable limits and prevent structural failure. Cooling requirements vary across a blade surface, but there currently exists no means by which coolant temperatures can be locally adjusted to facilitate optimized usage across a blade. Ranque-Hilsch vortex tubes were investigated as a means of adjusting coolant temperatures solely by fluidic means, induced by the phenomenon of temperature separation. Analytical frameworks were developed to determine …


Improving The Stability And Operability Of A Small-Scale Rotating Detonation Engine, Nathan T. Fiorino Jun 2021

Improving The Stability And Operability Of A Small-Scale Rotating Detonation Engine, Nathan T. Fiorino

Theses and Dissertations

A small scale RDE was designed with a channel diameter of 28 mm and channel gap of 2 mm and operated on nitrous oxide (N2O) and ethylene (C2H4) as the oxidizer and fuel respectively. Changes to the original Jets in Crossflow (JIC) injection scheme and spark plug ignition method were implemented to counteract previously observed wave instabilities. Successful detonation was observed over a range of mass flows (0.035-0.068 kg/s) and equivalence ratios (ɸ = 0.6-1.4) and a stable single wave mode with frequency up to 16.8 kHz was observed for the first time. Injection …


One Dimensional Study Of Magnetoplasmadynamic Thrusters For A Potential New Class Of Heavy Ion Drivers For Plasma Jet Driven Magnetoinertial Fusion, Patrick M. Brown Jun 2021

One Dimensional Study Of Magnetoplasmadynamic Thrusters For A Potential New Class Of Heavy Ion Drivers For Plasma Jet Driven Magnetoinertial Fusion, Patrick M. Brown

Theses and Dissertations

Plasma Jet Driven Magnetoinertial Fusion (PJMIF) requires high velocity heavy ion drivers in order to compress a magnetized target to fusion conditions. Previous work with heavy ion drivers has revealed sub-par accelerations due to plasma instabilities; thus, it is necessary to investigate new methods of heavy ion plasma acceleration. One such method is Magnetoplasmadynamic (MPD) thrusters. Past studies of these thrusters have been conducted at an initial temperature at or below the energy of full ionization. Here MPD thrusters are investigated using a Godunov type MHD solver with a Harten-Lax van Leer-D (HLLD) flux solving scheme assuming the plasma is …


Autonomous Mission Planning For Spacecraft Rendezvous And Proximity Operations, Julia C. Bell Jun 2021

Autonomous Mission Planning For Spacecraft Rendezvous And Proximity Operations, Julia C. Bell

Theses and Dissertations

The evolving space environment has created a demand for autonomous spacecraft that can maneuver in complex and sometimes contentious environments. Constraint enforcement, such as an avoidance zone to prevent collision with a target, is a key component of autonomous control to ensure safety and performance requirements are met. Finite-horizon Model Predictive Control (MPC) is a popular control method due to its improved computation time while optimizing performance. Two areas of MPC in need of expansion are time-varying constraints and phase transitions in multi-phase applications. In this work, MPC is employed to track the reference trajectory of a multi-phase satellite inspection …


Six Degree-Of-Freedom Mission Planning For Reentry Trajectories, Peter Davis Jun 2021

Six Degree-Of-Freedom Mission Planning For Reentry Trajectories, Peter Davis

Theses and Dissertations

Traditional reentry dynamics and planning has typically explored 3 Degrees-of- Freedom (3 DOF) or pseudo 6-DoF problem formulations. This research expands upon previous work and presents a path-constrained optimal control formulation of a fully 6 Degrees-of-Freedom (3 DOF) dynamic system for an unpowered Reentry Vehicle (RV). In a full 6-DoF dynamic system, the translation, rotation and rotational rates are continually tracked. A system of equations of motion are developed to express the dynamics of the RV in terms of defined states and the RV's physical control detections. A neural-network is used to approximate the aerodynamic database of an exemplary RV. …


Cubesat Development Framework, William D. Sousa Mar 2021

Cubesat Development Framework, William D. Sousa

Theses and Dissertations

AFITs Center for Space Research and Assurance (CSRA) has developed several small satellites without a detailed developmental framework in place but future work will focus on CubeSat development with the intent of managing multiple builds concurrently. With the goal of each satellite being completed in three years, a comprehensive process needs to be established. Research revealed that the Department of Defense (DoD), U.S. Air Force (USAF), and National Aeronautics and Space Administration (NASA) guidance on the acquisition and systems engineering processes require more reviews and deliverables than appropriate for CSRAs projects. The development processes from other universities divulge some aspects …


A Framework For Autonomous Cooperative Optimal Assignment And Control Of Satellite Formations, Devin E. Saunders Mar 2021

A Framework For Autonomous Cooperative Optimal Assignment And Control Of Satellite Formations, Devin E. Saunders

Theses and Dissertations

A decentralized, cooperative multi-agent optimal control framework is presented to offer a solution to the assignment and control problems associated with performing multi-agent tasks in a proximity operations environment. However, the framework developed may be applied to a variety domains such as air, space, and sea. The solution presented takes advantage of a second price auction assignment algorithm to optimally task each satellite, while model predictive control is implemented to control the agents optimally while adhering to safety and mission constraints. The solution is compared to a pseudospectral collocation method, and a study on tuning parameters is included.


Design And Analysis Of Air-Stiffened Vacuum Lighter-Than-Air Structures, Ruben Adorno-Rodriguez Mar 2021

Design And Analysis Of Air-Stiffened Vacuum Lighter-Than-Air Structures, Ruben Adorno-Rodriguez

Theses and Dissertations

Lighter-than-air (LTA) systems have been developed for numerous applications and have taken several forms. Airships, aerostats, blimps, and balloons are all part of this family of systems, which uses Archimedes principle to achieve neutral and positive buoyancy in air by replacing an air volume with LTA gases. These lifting gases stiffen the otherwise compliant envelope structures, allowing them to sustain the pressure difference brought by the displaced air. The compliance of these structures is a byproduct of the weight requirement, materials and geometrical arrangement of which these structures are built from, typically resulting in dimensionalities that exhibit low or virtually …


Optimizing Design Parameters For Active Flow Control Boundary-Layer Fence Performance Enhancement On A Delta Wing, Nathan L. Tedder Mar 2021

Optimizing Design Parameters For Active Flow Control Boundary-Layer Fence Performance Enhancement On A Delta Wing, Nathan L. Tedder

Theses and Dissertations

Utilizing computational fluid dynamic (CFD) simulations, the presented study is able to further the investigation of replicating and improving upon the performance of a NACA 0012 cropped half-span delta-wing at high angles-of-attack with an active flow control fluidic fence via wall-normal, steady blowing from an optimized single chordwise slot located at z/b = 70%,. The data is generated using CREATE-AV Kestrel v10.1rc5 CFD software on the Department of Defense High Performance Computing systems. The flight regime is held constant at a Mach number of 0.18 and a Reynolds number (Re) of 5.0 x 105, based on the root …


Delayed Authentication System For Civilian Satellite, Sean M. Feschak Mar 2021

Delayed Authentication System For Civilian Satellite, Sean M. Feschak

Theses and Dissertations

This thesis presents the feasibility of a Delayed Authentication System (DAS) for civilian satellite navigation (satnav) receivers. In satnav systems, encrypted signal components are transmitted synchronously with civilian components. Hence, the civilian signals can be authenticated by detecting the presence of encrypted signal components within the received signal. To authenticate, a reference station transmits estimated encrypted signal spreading code symbols processed using a high gain antenna. In this thesis, it is shown that a 1-meter diameter dish antenna is adequate to provide a high probability of successful authentication, thereby reducing overall system complexity and cost.


Low-Cost Terrestrial Demonstration Of Autonomous Satellite Proximity Operations, Zackary R. Hewitt Mar 2021

Low-Cost Terrestrial Demonstration Of Autonomous Satellite Proximity Operations, Zackary R. Hewitt

Theses and Dissertations

The lack of satellite servicing capabilities significantly impacts the development and operation of current orbital assets. With autonomous solutions under consideration for servicing, the purpose of this research is to build and validate a low-cost hardware platform to expedite the development of autonomous satellite proximity operations. This research aims to bridge the gap between simulation and existing higher fidelity hardware testing with an affordable alternative. An omnidirectional variant of the commercially available TurtleBot3 mobile robot is presented as a 3-DOF testbed that demonstrates a satellite servicing inspection scenario. Reference trajectories for the scenario are generated via optimal control using the …


A Reference Architecture For Rapid Cubesat Development, Sean R. Kelly Mar 2021

A Reference Architecture For Rapid Cubesat Development, Sean R. Kelly

Theses and Dissertations

The CubeSat class of nanosatellites has lowered the barrier of entry to space and has rapidly gained popularity in recent years. To successfully design a CubeSat system in a rapid cycle conducive to academic timelines, a Reference Architecture geared towards University CubeSat development would be helpful. A Reference Architecture would speed up the development process by providing a template, capturing previous work and lessons learned from subject matter experts, providing a framework to focus on the CubeSats design rather than the fine details of modeling software. A Reference Architecture can also add functionality that student teams could use and improve …


Scaling Gas Turbine Film Cooling Adiabatic Effectiveness Through Simultaneous Matching Of Momentum Flux Ratio And Advective Capacity Ratio, Evan C. Glowiak Mar 2021

Scaling Gas Turbine Film Cooling Adiabatic Effectiveness Through Simultaneous Matching Of Momentum Flux Ratio And Advective Capacity Ratio, Evan C. Glowiak

Theses and Dissertations

The study of gas turbine engine performance improvement requires extracting usable work from the hot section turbine. To prevent heat damage to turbine blades, film cooling is employed. Low temperature tests are conducted at ambient pressure on scale models to analyze the effects of gas flow parameters on scaling adiabatic effectiveness at easily repeatable conditions. This research aims to determine how matching coolant flow rate parameters Momentum Flux Ratio (I) and Advective Capacity Ratio (ACR) can scale adiabatic effectiveness on flat plate and leading edge geometries between air and carbon dioxide gas. Results indicate improvement in scaling adiabatic effectiveness when …


A Reduced Order Model Of The Celestial Icosahedron As The Substructure For A Lighter Than Air Vehicle, Torin C. Quick Mar 2021

A Reduced Order Model Of The Celestial Icosahedron As The Substructure For A Lighter Than Air Vehicle, Torin C. Quick

Theses and Dissertations

A finite element approach was used to investigate a novel reduced order model to determine the minimum structure dimensionality to support vacuum for a VLTAV. This modeling technique represented the individual segments of the substructure as curved beams with clamped radially-resisted boundary conditions. The full structure was then modeled as a bare structure and structure with skin to validate the results of the reduced order model. The beam geometry for the material Ultem 9085 was determined through this process leading to the 3-D printing of the structure. It was then experimentally tested under uniaxial compression complimented with a FEA model.


Fatigue Of Two Oxide/Oxide Ceramic Matrix Composites At 1200°C In Air And In Steam. Effect Of Diamond Drilled Effusion Holes, Anthony R. Cabri Mar 2021

Fatigue Of Two Oxide/Oxide Ceramic Matrix Composites At 1200°C In Air And In Steam. Effect Of Diamond Drilled Effusion Holes, Anthony R. Cabri

Theses and Dissertations

The tension-tension fatigue behavior of two oxide-oxide ceramic matrix composites (CMCs) was investigated at 1200°C in laboratory air and steam. Both composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (NextelTM720) fibers. The first composite had an alumina matrix, while the second had an alumina-mullite matrix. First, we assessed the effects of incorporating mullite into the matrix material on fatigue performance by studying the tension-tension fatigue behavior of alumina-mullite matrix CMC. Second, we evaluated the effects of effusion holes on the alumina matrix CMC's fatigue performance. Specimens containing an array of 17 effusion holes of 0.5-mm diameter …


Improving Manufacturability And Reducing Cracking In Additively Manufactured Tungsten Alloys, Christopher P. Fassio Mar 2021

Improving Manufacturability And Reducing Cracking In Additively Manufactured Tungsten Alloys, Christopher P. Fassio

Theses and Dissertations

Additively Manufactured tungsten suffers from low () densities due to high concentrations of microcracks as the printed layers cool past tungsten's high ductile to brittle transition temperature. In this study, tungsten-rhenium and tungsten rhenium hafnium carbide compositions were evaluated on density and tensile strength. In addition to varying the compositions of each alloy, printing parameters and post-processing methods were also compared. Print parameters varied for all compositions on an MLab 200R C using included the laser scan strategy, hatch spacing, scan speed, laser power, and print bed material. Post processing techniques of the WRe compositions included hot isostatic pressing and …


Modeling Situation Awareness In A Uav Scenario Using Sysml, Tommy R. Hernandez Mar 2021

Modeling Situation Awareness In A Uav Scenario Using Sysml, Tommy R. Hernandez

Theses and Dissertations

The U.S. Department of Defense (DoD) is rapidly moving towards using increasingly automated systems. Unmanned Aerial Systems (UAS) will be used in contested environments where direct human control may be impossible for long stretches of time. This increase in automation brings with it challenges in maintaining resilient Situation Awareness (SA) for operators, who still need to set goals for the UAS to accomplish their missions. Simultaneously, the DoD is increasing the adoption of Model-Based Systems Engineering (MBSE) in the development of weapon systems. This thesis explores the use of SysML to model of an SA repair system for a UAS …