Aerospace Engineering Commons^™

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 …

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 …

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 …

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 …

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 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 …

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, …

Autonomous Feature Detection For Capture Path Planning For Rendezvous And Docking With Non-Cooperative Spacecraft, Trupti Mahendrakar

Theses and Dissertations

With the increasing risk of collisions with space debris and the growing interest in on-orbit servicing, the ability to autonomously capture non-cooperative, tumbling target objects remains an unresolved challenge. This thesis provides an autonomous and artificial intelligence solution to either inspect, avoid, or perform on-orbit spacecraft servicing of an uncooperative resident space object (RSO). The solution is built on the fundamentals of Convolutional Neural Networks (CNN), which is used to classify the four most targeted features of a spacecraft essential for docking and collision avoidance during rendezvous, such as solar panels, antennas, spacecraft bodies, and thrusters. The solution was then …

Numerical Validation Of A Cryogenic Thermo-Fluid Mixing Model, Sean William Bowman

Theses and Dissertations

Thermal management of a hot convective gaseous flow can be achieved by the injection of a cold liquid stream. This cooling effect is constrained by the amount of liquid injected, the rate of evaporation of the liquid, and the length of the domain. In this study, such a domain is referred to as a “mixer”. The mixer used to facilitate this process is designed with a venturi geometry, such that the throat of the pipe creates a drop in the static pressure of the gaseous crossflow. Liquid coolant can thereby be passively entrained from a central pipe (plenum) by the …

Helicopter Flight Energy Modeling And Scaling For Urban Air Mobility Applications, Nolan Gene Hopkins

Theses and Dissertations

The costs associated with conducting full-scale helicopter flight tests in terms of both time and money beg to question the validity of using small-scale model helicopters in order to predict full-scale performance. To do this, the energy change for a small time interval is determined throughout a full-scale helicopter’s flight of a given profile, and the overall energy use compared to model results. The profile is then scaled based on a variety of factors, and the accuracy of energy scaling compared for each. Scaling dimensions based off helicopter weight and energy reserve modeling show promising results, but comparison of relative …

Flight Test Evaluation Of Elevator Stick Force Gradients On General Aviation Aircraft, Isaac Lee Faust

Theses and Dissertations

The objective of this research is to establish a suitable method of changing elevator stick force gradients on a Piper Warrior II. After finding a range of stick force gradients, the gradients will later be evaluated to get handling qualities ratings. A stick force gradient is the change in stick force as the airspeed deviates from trim condition. An aircraft’s yoke force gives pilots haptic feedback which improves their situational awareness without the need to assess instrument readings. A high stick force gradient will give the pilots a lot of feedback but will require more physical exertion to fly the …

Experimental Study Of Progressive Crushing Behaviour In Pultruded E-Glass Tubes Using Crown Triggers And A New Perforated Trigger, Chirag Mohan Dodani

Theses and Dissertations

An experimental study is conducted on the progressive crushing behavior and the energy absorption during crushing of pultruded fiberglass tubes, initiated by two types of crush triggers, a previously tested crown trigger, and a new perforated trigger. These crush triggers are introduced at the loading end of a pultruded E-Glass/vinyl-ester, circular tube coupon. Coupons with various trigger diameters and number of holes are crushed under quasi-static compression, to evaluate the trigger effectiveness, crushing response, and energy absorption during sustained crushing. It is observed that all trigger types induced progressive crushing in the splaying mode, characterized by the formation of a …

Crashworthiness Of Metallic Tubes Under Off-Axial Loading, Victor Manuel Bautista Katsalukha

Theses and Dissertations

Energy absorbing structures (EAS) are structures used to make the frame of a vehicle absorb energy during an impact scenario and keep the deceleration forces within survivable limits for the occupant(s). These structures are found in all sorts of vehicles, such as cars, helicopters, airplanes, etc., and come in many types of shapes (circular, square, triangular tubes and flat or curved plates) and materials (metals and composites). In this thesis, 304 Stainless Steel tubes with circular and square cross-sections are investigated when subject to off-axis loading at angles at 0, 5, 15 and 25°. The square tubes had two different …

Exploration Of Simplified Vehicle Operations For Electric Vertical Takeoff And Landing Through A Garmin Autopilot On A Piper Warrior, William Stefan Dietrich

Theses and Dissertations

Urban Air Mobility is an emerging concept that would allow urban transportation of both people and cargo through the air in large metropolitan cities. Because of new propulsion methods like distributed electrical propulsion, the Urban Air Mobility is concentrating on Electric Vertical Takeoff and Landing aircraft to implement its concept. Controlling and maneuvering these aircraft are very different than piloting traditional general aviation even through Electric Vertical Take and Landing aircraft aim to be in the same size category. Because of the more complex controls needed for Electric Takeoff and Landing aircraft, Simplified Vehicle Operation schemes are being developed in …

Feasibility Analysis And Performance Study Of A Pulsed Solid Propellant Integrated Propulsion System For Small Satellites, Tahir Kanchwala

Theses and Dissertations

Solid propellant has come a long way since the 13th century when gunpowder was widely used as the go-to means in rocket propulsion. Of course, back then, rockets were not intended to carry humanity out of the atmosphere. Untill the introduction of liquid propellants in the mid-20th century, solid propellants were the foundation. Still, liquid propellants aimed to add more stability and controllability to rocketry and thus were preferred over their solid counterparts. This thesis seeks to analyze a novel type of propulsive device that aims to eliminate challenges faced by both types of fuels and instead utilize the advantages …

Integration Of Process Planning Into The Automated Fiber Placement Design For Manufacturing Cycle, Alex Brasington

Theses and Dissertations

Automated Fiber Placement (AFP) is a composite manufacturing technique utilizing a robotic or gantry-based system and an attached fiber placement head to lay a prescribed number of strips of composite material, additively forming large composite structures. This technique has enabled increased throughput with increased accuracy and reliability when compared with prior composite manufacturing methods. However, even with the current state-of-the-art AFP process which employs advanced computer simulations and complex robotic operations, the data from various levels of the manufacturing lifecycle is isolated. This results in an incoherent system between the initial design phase and final part completion with limited ability …

Development Of A Converging-Channel Drop Tower For Sphere Symmetric Isolated Single Droplet Combustion, Nicholas Alexander Demaio

Theses and Dissertations

The dawn of a new Space Age is upon us; Microgravity combustion of hydrocarbon fuels is a popular method of research and characterization. This allows for a one-dimensional analysis by suppressing the buoyancy forces produced by gravity and the large temperature differential between the flame boundary and the surrounding air. The current testing methods are expensive and require extensive preparation on the researchers behalf. There is a need to investigate an alternative method that is inexpensive, repeatable, and comparable to the other approaches that coincides with the literature.

A low-cost converging-channel drop tower was designed and fabricated for sphero-symmetric single …

Nonlinear Intelligent Model Predictive Control Of Mobile Robots, Benjamin Albia

Theses and Dissertations

This thesis presents a framework for an artificial neural network (ANN) model-based nonlinear model predictive control of mobile ground robots. A computer vision analysis module was first developed to extract quantitative position information from onboard camera feed with respect to a prescribed path. Various strategies were developed to construct nonlinear physical plant models for model predictive control (MPC), including the physics-based model (PBM), the ANN trained on PBM-generated data, the ANN trained on test-captured data, and the ANN initially trained on PBM-generated data and then retrained with captured data. All the models predict physical states and positions of the robot …

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 …

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 …

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

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 …

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. …

Pseudospectral Methods Of Robust Optimal Motion Planning For Multi-Aperture Space Systems With Motion And Vibration Compensation, Brian W. Bishop

Theses and Dissertations

For multi-body, flexible systems, the ability to achieve rapid reorientation maneuvers can be impacted by nonlinear dynamics and uncertainty in the model parameters impacting the ability to achieve an optimal trajectory computed using nominal parameter values. Trajectory sensitivity to parameter variations increases final pointing error and residual vibrational energy in the system. This manuscript explores using pseudospectral methods to generate robust optimal control trajectories minimizing trajectory sensitivity to parameter variations and derives maneuvers minimizing residual energy and pointing error. The robustness of open-loop optimal control is compared to a standard maneuver derived using traditional methods demonstrating the ability to simultaneously …

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 …

Reduced Sample Minimum Strength Estimates For Novel Material Systems: Effects On Confidence And Structural Risk, Andrew Carl Ollikainen

Theses and Dissertations

There are ongoing efforts to standardize the materials, methods and process controls used in additive manufacturing. To support the broader use of additive manufacturing (AM) in the aerospace industry, the statistics working group of the Composite Materials Handbook (CMH-17) is evaluating whether its current methods of calculating minimum strength values are suitable for these new materials. The work presented in this dissertation investigates methods for determining minimum strength estimates in a way that will benefit application of AM materials in engineering practice. The greatest challenge in conducting such an assessment is accounting for the many variables in material, processing, and …

Scaling Flight Test Data Between A Scaled Aircraft And A Cessna 172 For Use In Trajectory Energy Model Validation, Cody William Nettleton

Theses and Dissertations

Currently in the general aviation sector, a new type of aircraft is rising to prominence. It is known as Urban Air Mobility (UAM) and takes many shapes and sizes. The goal of UAM is to produce aircraft that can be used to travel into and out of the city in an efficient manner through the sky. This may cut down on many people’s commutes and lower the amount of ground traffic in cities. One core component of UAM research is to determine the fuel consumption during phases of flight such as conventional takeoff and landing, as well as cruise travel …

Fluid-Structure Interaction Of Nrel 5-Mw Wind Turbine, Mohamed Sayed Elkady Abd-Elhay

Theses and Dissertations

Wind energy is considered one of the major sources of renewable energy. Nowadays, wind turbine blades could exceed 100 m to maximize the generated power and minimize produced energy cost. Due to the enormous size of the wind turbines, the blades are subjected to failure by aerodynamics loads or instability issues. Also, the gravitational and centrifugal loads affect the wind turbine design because of the huge mass of the blades. Accordingly, wind turbine simulation became efficient in blade design to reduce the cost of its manufacturing. The fluid-structure interaction (FSI) is considered an effective way to study the turbine's behavior …

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 …

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. …