Engineering Commons^™

Dynamical Modeling Of Resistojet Style Thrusters For Fault Detection, And Fault Identification, Jonathan Leo Kerivan

Graduate College Dissertations and Theses

The work presented in this thesis investigates and validates the dynamic modeling, fault detection, and fault identification (FDI) for the resistojet thruster system, typically used in low magnitude thrust applications for smaller spacecraft. The resistojet thruster is an improvement upon the widely utilized cold gas thruster, featuring an incorporated heating section aimed at improving propellant efficiency. This additional heating section enhances the performance of the system by increasing the propellant’s thermal energy before its discharge through the nozzle, subsequently leading to a reduction in overall fuel consumption. To implement a model-based FDI technique tailored to the typical resistojet thruster system, …

Surface Temperature Measurement Fidelity In High Enthalpy Plasma Test Facilities, Owen Plante

Graduate College Dissertations and Theses

The classification and study of thermal protection systems (TPS) relies heavily on the accurate measurement of surface temperature. The best way to measure surface temperature in ground test facilities is through optical pyrometery due to the non intrusive nature of this method. Optical pyrometric devices use the emission of a greybody curve to calculate temperatures. These devices are left susceptible to parasitic radiation coming from the plasma generated in ground test facilities. The parasitic radiation comes from the emission lines of the test plasma in the investigation region of the devices. The parasitic radiation from the plasma and short comings …

The Overpressurization And Surface Contamination Of On-Demand Pressure Systems, William Harvey

Graduate College Dissertations and Theses

With advances in space technology, the use of satellites in commercial and academic settings have progressed immensely. The increase in satellite usage has created a need for on-board propulsion systems that provide in-space mobility. Satellites often require maneuvers such as collision avoidance, de-orbiting, and changing orbital positions. These maneuvers help to reduce space clutter but also enable longer and more capable missions. However, chemical propulsion systems present a number of challenges, particularly during launch. Satellites require the use of large rockets to deliver them in space and the addition of a propulsion system means that the rocket will be carrying …

Characterization Of Pressure And Temperature Reactions In An On-Demand Pressurization System For Small Satellite Propulsion, Anna M. Humphreys

Graduate College Dissertations and Theses

With the popularity of small satellites on the rise in the aerospace industry, the need for propulsion systems developed specifically for small satellite applications is ever-present. An emerging subsection of the small satellite field is CubeSats, which are cubic satellites measuring 10cm per side and weighing less than 1.33kg. At launch, CubeSats are fixed to a larger rocket but are deployed once in orbit and must rely on their own propulsion system for orbit control and maneuverability. While propulsion systems exist for rockets and satellites that are orders of magnitude larger, these traditional systems are often too bulky and complex …

Absolute Number Density Measurements Of Atomic Species In Air And Nitrogen Plasmas, Jeffrey C. Schindler

Graduate College Dissertations and Theses

A vehicle reentering Earth's atmosphere at hypersonic velocities violently compresses the air in front of it, creating a shell of plasma at the surface. This plasma imparts energy onto the vehicle's surface via convective, radiative, and chemical heating. Currently, large uncertainties in measurements of surface reaction rates lead to over-designed thermal protection systems. Improvements in the precision of these measurements could substantially decrease the weight of the heat shield, freeing up space for additional fuel or human/scientific payload. This work aims to improve current methods for measurements of atomic number densities in plasmas, so that they may be applied to …

Carbon Monoxide Measurements In A Co2 Plasma Using Two-Photon Laser Induced Fluorescence, Brandon Voll

Graduate College Dissertations and Theses

Uncertainties in surface catalytic reaction rates in a CO2 plasma have led to overdesign of thermal protection systems, which has caused planetary entry vehicles for the Martian atmosphere to be heavier than necessary. This, in turn, has decreased the available payload of various missions. A better understanding of these reaction rates will allow more precise development of thermal protection systems leading to safer and more effective atmospheric entry vehicles. Near wall measurements in a plasma facility using laser spectroscopic techniques with sub-millimeter spatial resolution provide a method to determine surface-catalyzed reaction efficiencies over metallic surfaces. The present work includes laser …

Numerical Simulations Of An Inductively Coupled Plasma Torch, Samuel Whitmore

Graduate College Dissertations and Theses

During entry into a planetary atmosphere, a blunt body (e.g. a spacecraft) traveling at hypersonic velocity creates a bow shock in front of it. In the highly energetic post shock environment, the body experiences heat transfer due to convective, chemical, and radiative processes. To protect the payload against this heating, a thermal protection system (TPS) is employed. Because a given propulsion system has a set amount of mass that it can launch to orbit, reducing the amount of mass used for TPS is desirable as this mass is freed up for mission-oriented payload. At the present, uncertainties in the flow …

Characterization Of The University Of Vermont Plasma Torch And Simulation Of Pyrolysis Gas And Plasma Interactions, Precious Jagun

Graduate College Dissertations and Theses

In previous studies done at the University of Vermont’s Inductively coupled Plasma (ICP) touch facility, the plasma conditions were always assumed to be in Local Thermodynamic Equilibrium(LTE) state. To improve the knowledge of the thermodynamic properties of the plasma conditions, in this study, experiments and analysis were conducted to determine whether or not the facility is indeed in LTE. LIF data was collected at 7mm off the exit of the quartz tube and compared with CEA simulations for the same plasma conditions. The facility was also better characterized by using LTE analyses of the absolute emission intensities to determine the …

Experimental And Computational Studies Of Heat Transfer In Flexible Two-Dimensional Woven Fiber Ceramic Materials, Rodrigo Penide Fernandez

Graduate College Dissertations and Theses

Flexible thermal protection materials made from two-dimensional woven ceramics fibers are of significant interest for hypersonic inflatable aerodynamic decelerators being developed by NASA for future missions on Mars and other planets. A key component of the thermal shield is a heat-resistant outer ceramic fabric that must withstand harsh aero-thermal atmospheric entry conditions. However, a predictive understanding of heat conduction processes in complex woven-fiber ceramic materials under deformation is currently lacking. This dissertation presents a combined experimental and computational study of thermal conductivity in alumina-based Nextel-440 and silicon carbide Hi-Nicalon 5-harness-satin woven fabrics, using the hot-disk transient plane source method and …

Optimization Of Mixing Efficiency In Low Reynolds Unlike Doublet Injectors By Incorporating Swirl, Samuel Braggins Ligon

Graduate College Dissertations and Theses

One of the largest issues concerning industrial cube satellite manufacturing is the development of propulsion systems at extremely small scales. Bipropellant cube satellite propulsion systems face challenges associated with the mixing of two fluids which operate in low Reynolds number environments. Low Reynolds, or laminar, fluid flow is unique to cube satellite injection systems because of their unprecedented small scale. This work is intended to both test the validity of a proposed cube satellite injection system, and to test the accuracy of numerical method approaches to solving the problem of laminar flow mixing in such devices. The proposed injector is …

Multi-Objective Optimization Mission Design For Small-Body Coverage Missions, David William Hinckley

Graduate College Dissertations and Theses

Missions concerning small-body celestial objects are of growing interest due to the resources and information they can provide. Such missions require detailed information about the surface of the body for interactions, such as landing on the surface, as well as predicting the gravity field of the object. This work provides a means of optimizing the mission elements of trajectory and imaging target schedules so that the level of knowledge of the surface can be increased. The information required to increase one's knowledge of the surface is described as a set of conditions placed on the collection of images taken of …

Quadrature-Based Gravity Models For The Homogeneous Polyhedron, Jason Pearl

Graduate College Dissertations and Theses

A number of missions to comets and asteroids have been undertaken by major space organizations driving a need to accurately characterize their gravitational fields. This is complicated however by their irregular shapes. To accurately and safely navigate spacecraft in these environments, a simple point-mass gravity model is insufficient and instead higher-fidelity models are required. Several such models exist for this purpose but all posess drawbacks. Moreover, there are some applications for which the currently available models are not particular well suited.

In this dissertation, numerical quadrature and curvilinear meshing techniques are applied to the small body gravity problem. The goal …

Optimization Of Turbulent Prandtl Number In Turbulent, Wall Bounded Flows, Donald Edward Bernard

Graduate College Dissertations and Theses

After nearly 50 years of development, Computational Fluid Dynamics (CFD) has become an indispensable component of research, forecasting, design, prototyping and testing for a very broad spectrum of fields including geophysics, and most engineering fields (mechanical, aerospace, biomedical, chemical and civil engineering). The fastest and most affordable CFD approach, called Reynolds-Average-Navier-Stokes (RANS) can predict the drag around a car in just a few minutes of simulation. This feat is possible thanks to simplifying assumptions, semi-empirical models and empirical models that render the flow governing equations solvable at low computational costs. The fidelity of RANS model is good to excellent for …

Large Eddy Simulation Of Oscillatory Flow Over A Mobile Rippled Bed Using An Euler-Lagrange Approach, Daniel S. Hagan

Graduate College Dissertations and Theses

A volume-filtered Large-Eddy Simulation (LES) of oscillatory flow over a rippled mobile bed is conducted using an Euler-Lagrange approach. As in unsteady marine flows over sedimentary beds, the experimental data, referenced in this work for validation, shows quasi-steady state ripples in the sand bed under oscillatory flow. This work approximately reproduces this configuration with a sinusoidal pressure gradient driven flow and a sinusoidally rippled bed of particles. The LES equations, which are volume-filtered to account for the effect of the particles, are solved on an Eulerian grid, and the particles are tracked in a Lagrangian framework. In the Discrete Particle …

Gravitational Potential Modeling Of Near-Earth Contact Binaries, Stephanie Wood

Graduate College Dissertations and Theses

A significant component of recent space exploration has been unmanned mission to comets

and asteroids. The increase in interest for these bodies necessitates an increase in demand

for higher fidelity trajectory simulations in order to assure mission success. Most available

methods for simulating trajectories about asymmetric bodies assume they are of uniform

density. This thesis examines a hybrid method that merges a mass concentration ("mascon")

model and a spherical harmonic model using the "Brillouin sphere" as the interface. This

joint model will be used for simulating trajectories about variable density bodies and, in

particular, contact binary asteroids and comets.

The …

Investigation Of Pyrolysis Gas Chemistry In An Inductively Coupled Plasma Facility, Corey Tillson

Graduate College Dissertations and Theses

The pyrolysis mechanics of Phenolic Impregnated Carbon Ablators (PICA) makes it a valued material for use in thermal protection systems for spacecraft atmospheric re-entry. The present study of the interaction of pyrolysis gases and char with plasma gases in the boundary layer over PICA and its substrate, FiberForm, extends previous work on this topic that has been done in the UVM 30 kW Inductively Coupled Plasma (ICP) Torch Facility. Exposure of these material samples separately to argon, nitrogen, oxygen, air, and carbon dioxide plasmas, and combinations of said test gases provides insight into the evolution of the pyrolysis gases as …

Steady State Simulation Of Pyrolysis Gases In An Inductively Coupled Plasma Facility, Nicholas C. Martin

Graduate College Dissertations and Theses

An important step in the more efficient use of PICA (Phenolic Impregnated Carbon Ablator) as a Thermal Protection System (TPS) material for spacecraft is the understanding of its pyrolysis mechanics. The gases released during pyrolysis and their subsequent interaction with the reactive plasma environment is not yet well understood. The surface recession of PICA as it ablates during testing only makes the study and characterization of the chemical reactions more difficult. To this end, a probe has been designed for this study to simulate, in steady state, the pyrolysis gases within the UVM 30kW Inductively Coupled Plasma (ICP) Torch Facility. …

An Alternative Sensor Fusion Method For Object Orientation Using Low-Cost Mems Inertial Sensors, Joshua Lee Bouffard

Graduate College Dissertations and Theses

This thesis develops an alternative sensor fusion approach for object orientation using low-cost MEMS inertial sensors. The alternative approach focuses on the unique challenges of small UAVs. Such challenges include the vibrational induced noise onto the accelerometer and bias offset errors of the rate gyroscope. To overcome these challenges, a sensor fusion algorithm combines the measured data from the accelerometer and rate gyroscope to achieve a single output free from vibrational noise and bias offset errors.

One of the most prevalent sensor fusion algorithms used for orientation estimation is the Extended Kalman filter (EKF). The EKF filter performs the fusion …

Assessment Of Surface-Catalyzedreaction Products From Hightemperature Materials In Plasmas, Luke Daniel Allen

Graduate College Dissertations and Theses

Current simulations of atmospheric entry into both Mars and Earth atmospheres for the design of thermal protections systems (TPS) typically invoke conservative assumptions regarding surface-catalyzed recombination and the amount of energy deposited on the surface. The need to invoke such assumptions derives in part from lack of adequate experimental data on gas-surface interactions at trajectory relevant conditions. Addressing this issue, the University of Vermont's Plasma Test and Diagnostics Laboratory has done extensive work to measure atomic specie consumption by measuring the concentration gradient over various material surfaces. This thesis extends this work by attempting to directly diagnose molecular species production …

Two-Dimensional Numerical Study Of Micronozzle Geometry, Jason M. Pearl

Graduate College Dissertations and Theses

Supersonic micronozzles operate in the unique viscosupersonic flow regime, characterized by large Mach numbers (M>1) and low Reynolds numbers (Re<1000). Past research has primarily focused on the design and analysis of converging-diverging de Laval nozzles; however, plug (i.e. centerbody) designs also have some promising characteristics that might make them amenable to microscale operation. In this study, the effects of plug geometry on plug micronozzle performance are examined for the Reynolds number range Re = 80-640 using 2D Navier-Stokes-based simulations. Nozzle plugs are shortened to reduce viscous losses via three techniques: one - truncation, two - the use of parabolic contours, and three - a geometric process involving scaling. Shortened nozzle are derived from a full length geometry designed for optimal isentropic performance. Expansion ratio (ε = 3.19 and 6.22) and shortened plug length (%L = 10-100%) are varied for the full Reynolds number range. The performance of plug nozzles is then compared to that of linear-walled nozzles for equal pressure ratios, Reynolds numbers, and expansion ratios. Linear-walled nozzle half-angle is optimized to to ensure plug nozzles are compared against the best-case linear-walled design.

Results indicate that the full length plug nozzle delivers poor performance on the microscale, incurring excessive viscous losses. Plug performance is increased by shortening the nozzle plug, with the scaling technique providing the best performance. The benefit derived from reducing plug length depends upon the Reynolds number, with a 1-2% increase for high Reynolds numbers an up to 14% increase at the lowest Reynolds number examined. In comparison to Linear-walled nozzle, plug nozzles deliver superior performance when under-expanded, however, …

Development Of An Additively Manufactured Microthruster For Nanosatellite Applications, Kevin Russell Gagne

Graduate College Dissertations and Theses

Next generation small satellites, also known as nanosatellites, have masses significantly lower than traditional satellites. Including the propellant mass, the total mass of a nanosatellite is often in the range of 1 to 4 $kg$. These satellites are being developed for numerous applications related to research, defense, and industry. Since their popularity began in the early 2000's, limitations on the downscaling of propulsion systems has proven to be problematic. Due to this, the vast majority of nanosatellite missions have limited lifespans of 90-120 days in low Earth orbit before they reenter the Earth's atmosphere. Although satellites on this scale have …

Characterization Of Fillite As A Planetary Soil Simulant In Support Of Rover Mobility Assessment In High-Sinkage/High-Slip Environments, Michael Edwards

Graduate College Dissertations and Theses

This thesis presents the results of a research program characterizing a soil simulant called Fillite, which is composed of alumino-silicate hollow microspheres harvested from the pulverized fuel ash of coal-fired power plants. Fillite is available in large quantities at a reasonable cost and it is chemically inert. Fillite has been selected by the National Aeronautics and Space Administration (NASA) Glenn Research Center to simulate high-sinkage/high-slip environment in a large test bed such as the ones encountered by the Spirit rover on Mars in 2009 when it became entrapped in a pocket of soft, loose regolith on Mars. The terms high-sinkage …

Multi-Satellite Formation Trajectory Design With Topological Constraints Over A Region Of Interest Using Differential Evolution, David William Hinckley

Graduate College Dissertations and Theses

Satellite formation missions allow for scientific measurement opportunities that are only otherwise possible with the use of unrealistically large satellites. This work applies the Evolutionary Algorithm (EA), Differential Evolution (DE), to a 4-satellite mission design that borrows heavily from the mission specifications for Phase 1 of NASA's Magnetospheric Multi-Scale Mission (MMS). This mission specifies goals for formation "quality" and size over the arc when scientific measurements are to be taken known as the Region of Interest (ROI). To apply DE to this problem a novel definition of fitness is developed and tailored to trajectory problems of the parameter scales of …

Numerical Simulations Of Reacting Flow In An Inductively Coupled Plasma Torch, Maximilian Dougherty

Graduate College Dissertations and Theses

In the design of a thermal protection system for atmospheric entry, aerothermal heating presents a major impediment to efficient heat shield design. Recombination of atomic species in the boundary layer results in highly exothermic surface-catalyzed recombination reactions and an increase in the heat flux experienced at the surface. The degree to which these reactions increase the surface heat flux is partly a function of the heat shield material. Characterization of the catalytic behavior of these materials takes place in experimental facilities, however there is a dearth of detailed computational models for the fluid dynamic and chemical behavior of such facilities. …

Aero-Thermal Characterization Of Silicon Carbide Flexible Tps Using A 30kw Icp Torch, Walten Owens

Graduate College Dissertations and Theses

Flexible thermal protection systems are of interest due to their necessity for the success of future atmospheric entry vehicles. Current non-ablative flexible designs incorporate a two-dimensional woven fabric on the leading surface of the vehicle. The focus of this research investigation was to characterize the aerothermal performance of silicon carbide fabric using the 30 kW Inductively Coupled Plasma Torch located at the University of Vermont. Experimental results have shown that SiC fabric test coupons achieving surface temperatures between 1000°C and 1500°C formed an amorphous silicon dioxide layer within seconds after insertion into air plasmas. The transient morphological changes that occurred …

Nonlinear Ball Chain Waveguides For Acoustic Emission And Ultrasound Sensing Of Ablation, Stephen Herbert Pearson

Graduate College Dissertations and Theses

Harsh environment acoustic emission and ultrasonic wave sensing applications often benefit from placing the sensor in a remote and more benign physical location by using waveguides to transmit elastic waves between the structural location under test and the transducer. Waveguides are normally designed to have high fidelity over broad frequency ranges to minimize distortion - often difficult to achieve in practice. This thesis reports on an examination of using nonlinear ball chain waveguides for the transmission of acoustic emission and ultrasonic waves for the monitoring of thermal protection systems undergoing severe heat loading, leading to ablation and similar processes. Experiments …