Engineering Commons^™

Gravitational Lens: Deep Space Probe Design, Berkley R. Davis

Theses and Dissertations

A number of interstellar precursor missions have been designed, but they have all made use of unproven future technologies. This research focuses on designing an interstellar precursor mission to the gravitational lens that can be manufactured solely with today's technology. The design includes an examination of trip time and trajectory, a system trade between subsystems, a launch vehicle analysis and an overall spacecraft performance analysis. The trip time was found to be approximately 108 years using the NEXT thruster and GPHS power source. The GPHS provided approximately 4 kW of power at BOL. The communications subsystem relied on a 12 …

Applications Of Aerodynamic Forces For Spacecraft Orbit Maneuverability In Operationally Responsive Space And Space Reconstitution Needs, Matthew N. Goodson

Theses and Dissertations

Each year multiple satellites are launched to provide end users key pieces of information. This information ranges from remote sensing data for military or civilian purposes (e.g., weather forecasting, troop movements, agricultural production, etc.) to large bandwidth telecommunications sensors. No matter the type of information needed, society is demanding more. Because of this continual rise in information needs, the current model of launching one satellite for one mission is not sustainable. To satisfy the information needs of nations across the globe, a means for satellites to transition from one mission type to another must be developed. One means of transitioning …

Validation Of The Chemistry Module For The Euler Solver In Unified Flow Solver, William C. Humphrey Jr.

Theses and Dissertations

In the world of computational fluid dynamics (CFD), three main types of flow regimes exist: continuum, rarified, and free molecular. Of these regimes, the rarified regime is the most difficult to model because the continuum equations don't apply and using the Boltzmann equation is too computationally expensive to use. The Unified Flow Solver (UFS) is currently being developed to solve this problem by using the kinetic continuum Euler equations where valid, and only using the Boltzmann equation where necessary, thus reducing the computational cost. The use of the kinetic Euler equations helps to aid in the coupling of the Euler …

Electromagnetic Interference Behavior Of Multiwall Carbon Nanotubes And Carbon Nanofibers Composites Under Fatigue, Peter A. Hunt

Theses and Dissertations

The United States military is researching the use of nanocomposite materials for structural applications on space vehicle systems. To reduce vehicle weight and mitigate the electromagnetic interference (EMI) brought on by the harsh space environment, today's space vehicles are made of composites coated with expensive conductive materials. Research on composites made of carbon nanotubes (CNT) and carbon nanofibers (CNF) has shown better EMI shielding performance with these materials compared to the current composites coated with expensive conductive materials. Thus, CNTs and CNFs offer the potential to replace the current composites. This study evaluated the effects of EMI behavior on one …

Cooling Requirements For The Ultra Compact Combuster, Donald D. Johnson

Theses and Dissertations

Over the past several years, AFIT and the Air Force Research Laboratory have collaboratively investigated a novel combustor system that is compact in design and has potential use in an inter-turbine burner system. The ultra-compact combustor (UCC) design wraps the combustion section circumferentially around the axial core flow and exploits the use of high-g combustion. The combustor's volume and weight are reduced by integrating the exit compressor vane and the turbine inlet vane. This creates a new hybrid vane that resides directly below the circumferential combustor. Recently, a computational effort to understand the fundamental aspects of the UCC on a …

Characterization Of Centrifugally-Loaded Flame Migration For Ultra-Compact Combustors, Kenneth D. Lebay

Theses and Dissertations

The Air Force Research Laboratory (AFRL) has designed an Ultra Compact Combustor (UCC) showing viable merit for significantly reducing gas turbine combustor length making it a viable candidate for implementation as an inter-turbine burner and realization of efficiency benefits from the resulting near constant temperature cycle. This concept uses an off-axis combustor cavity and projects approximately 66% length reduction over a conventional combustor. The annular nature of the cavity creates high angular acceleration levels, on the order of 500-3500 g's, resulting in strong centrifugal and buoyant forces. This unique combination works to significantly reduce the required burn time and subsequently …

Methane Dual Expander Aerospike Nozzle Rocket Engine, Michael D. Moen

Theses and Dissertations

The Air Force Institute of Technology (AFIT), working to meet requirements set by the Air Force Research Laboratory's Next Generation Engine (NGE) initiative, is developing upper stage rocket models. The current path of investigation focuses on combining a dual expander cycle with an aerospike nozzle, or the Dual Expander Aerospike Nozzle (DEAN) using methane fuel. The design process will rely heavily on AFIT's previous work, which focused on the development of tools for and the optimization of a hydrogen/oxygen DEAN engine. The work outlined in this paper expands the existing research by substituting methane for hydrogen. The targets derived from …

Application Of Multi-Input Multi-Output Feedback Control For F-16 Ventral Fin Buffet Alleviation Using Piezoelectric Actuators, Tomoyuki D. Ono

Theses and Dissertations

Control of structural vibrations has been a popular topic. Use of MFC piezoelectric actuators and co-located sensors allows for an active rather than passive control method. The F-16 ventral fin is susceptible to buffet induced vibrations and is a perfect test structure for active vibration control for flight-testing. The research follows the previous ACTIVE FIN project and improves on the design by increasing the number of actuator layers, available actuator power, and using multi-input multi-output (MIMO) control algorithms. The research involved experimental identification of the ventral fin and its principle strain directions, selection of system components, determination of mathematical plant …

Development Of A Star Tracker-Based Reference System For Accurate Attitude Determination Of A Simulated Spacecraft, Jorge G. Padro

Theses and Dissertations

The goal of this research effort is to investigate the analysis, design, integration, testing, and validation of a complete star tracker and star field simulator system concept for AFIT's satellite simulator, SimSat. Previous research has shown that while laboratory-based satellite simulators benefit from star trackers, the approach of designing the star field can contribute significant error if the star field is generated on a flat surface. To facilitate a star pattern that better represents a celestial sky, a partially hemispherical dome surface is suspended above SimSat and populated with a system of light emitting diodes of various intensities and angles …

Desensitizing Flame Structure And Exhaust Emissions To Flow Parameters In An Ultra-Compact Combuster, Adam K. Parks

Theses and Dissertations

A major thrust of turbine engine research is to improve both efficiency and thrust-to-weight ratio of the engine. A promising solution to this challenge is the Ultra-Compact Combustor (UCC). The UCC shortens the axial length of the combustor by performing combustion circumferentially on the outer diameter of the engine. The reduction in axial length yields significant weight savings and increases the thrust-to-weight ratio. The design also increases combustion efficiency by performing the combustion in a centrifugally loaded environment which allows unreacted particles to remain in the combustor sufficiently long enough to become combustion products. The Air Force Institute of Technology …

Creep Behavior In Interlaminar Shear Of A Cvi Sic/Sic Composite At Elevated Temperatures In Air And Steam, Matthew T. Pope

Theses and Dissertations

This research investigated the interlaminar shear performance of a SiC/SiC ceramic matrix composite. The interlaminar shear performance was observed in compression of double notched specimens (DNS) at 1200°C in both laboratory air and in steam. Compression to failure tests determined the as-processed interlaminar shear strength and interlaminar shear creep tests were conducted with stresses ranging from -22 MPa to -16 MPa. Primary and secondary creep regimes were observed in all creep tests. The specimens tested in creep at -16 MPa in air achieved run-out, defined as 100 hours at creep stress. The residual strength decreased slightly after 100 h of …

Ladar Performance Simulations With A High Spectral Resolution Atmospheric Transmittance And Radiance Model- Leedr, Benjamin D. Roth

Theses and Dissertations

In this study of atmospheric effects on Geiger Mode laser ranging and detection (LADAR), the parameter space is explored primarily using the Air Force Institute of Technology Center for Directed Energy's (AFIT/CDE) Laser Environmental Effects Definition and Reference (LEEDR) code. The LADAR system is assessed at operationally representative wavelengths of 1.064, 1.56 and 2.039 μm with several up and down looking engagement geometries at locations worldwide. Results computed with LEEDR are compared to standard atmosphere and Fast Atmospheric Signature Code (FASCODE) assessments. Results show significant climate dependence, but large variances between climatological and standard atmosphere assessments. An overall average absolute …

Development And Testing Of A Rotating Detonation Engine Run On Hydrogen And Air, Jason C. Shank

Theses and Dissertations

Rotating detonation engines (RDEs) have the potential for greater efficiencies over conventional engines by utilizing pressure gain combustion. A new modular RDE (6 in diameter) was developed and successfully run on hydrogen and standard air. The RDE allows for variation of injection scheme and detonation channel widths. Tests provided the operational space of the new RDE as well as characterized detonation unsteadiness. It was found that a smaller equivalence ratio than previous was required to obtain continuous detonations. Also discovered was VCJ was reached in the RDE, but not sustained.

Creep Of Hi-Nicalon S Ceramic Fiber Tows At Elevated Temperature In Air And In Steam, Benjamin R. Steffens

Theses and Dissertations

Structural aerospace components require materials to have superior long-term mechanical properties that can withstand severe environmental conditions, such as high temperatures, high pressures and moisture, whilst enduring the loads they are designed for. Ceramic-matrix composites (CMCs) are capable of maintaining excellent strength and creep resistance at high temperatures, which make them attractive candidate materials for aerospace applications, particularly in propulsion. Silicon Carbide (SiC) ceramic fibers have been used as constituent materials in CMCs, although oxidation of the SiC to SiO₂ has been a known degredation mechanism. Recently developed near stoichiometric SiC fibers have shown significant improvements in thermochemical stability; …

A Finite Element Analysis Of A Carbon Fiber Composite Micro Air Vehicle Wing, Theodore A. Szelag

Theses and Dissertations

Micro-air vehicles (MAV)s provide a valuable and low observable way to do the jobs that the Air Force deems to be dull, dirty and dangerous. Basing the design of an MAV wing on that of a biological counterpart will provide a proven design that is capable of achieving the mission requirements. This research is designed to analyze the design and manufacturing of a wing based off the Manduca Sexta.

Inaccuracies in the fiber orientation can result in substantial changes in the material properties. Experimental vibration data of composite material samples manufactured using a three-ply [0/90/0] small non-homogenous fiber composite provided …

Empirical Characterization Of Unconstrained Tape Spring Deployment Dynamics, Daniel M. Williams

Theses and Dissertations

Satellite cost and mission capability are very sensitive to mass requirements. Mass or volume savings in one component will either lower total spacecraft mass, or provide greater margin for design error in other components. Solar arrays and antennas in particular are often driven by launch vehicle volume constraints instead of mission needs. Deployable structures provide more on-orbit area for both solar arrays and antennas, while occupying less space during launch. These structures therefore, help address these constraints and have been proven as efficient solutions for many years. Tape springs are one example in this category of structures which offer greater …

Boundary Layer Measurements In The Trisonic Gas-Dynamics Facility Using Particle Image Velocimetry With Co₂ Seeding, Daniel B. Wolfe

Theses and Dissertations

Particle image velocimetry (PIV) is utilized with solid carbon dioxide (CO₂) seeding material to conduct boundary layer measurements in the test section of the Air Force Research Laboratory's Trisonic Gas-dynamics Facility (TGF), which has a 24 inch by 24 inch cross-section. Freestream velocity was set at Mach 0.3, Mach 0.5, or Mach 0.8 while stagnation pressure ranged from 500 to 2400 pounds per square foot (psf). High pressure liquid CO₂ was directed through expansion nozzles into shroud tubes which led to solidified particles in the wind tunnel stagnation chamber. Two different sets of shroud tubes were used …

Trajectory Control And Optimization For Responsive Spacecraft, Costantinos Zagaris

Theses and Dissertations

The concept of responsive space has been gaining interest, and growing to include systems that can be re-tasked to complete multiple missions within their lifetime. The purpose of this study is to develop an algorithm that produces a maneuver trajectory that will cause a spacecraft to arrive at a particular location within its orbit earlier than expected. The time difference, delta t, is used as a metric to quantify the effects of the maneuver. Two separate algorithms are developed. The first algorithm is an optimal control method and is developed through Optimal Control Theory. The second algorithm is a feedback …

Rsa Power Analysis Obfuscation: A Dynamic Fpga Architecture, John W. Barron

Theses and Dissertations

The modular exponentiation operation used in popular public key encryption schemes, such as RSA, has been the focus of many side channel analysis (SCA) attacks in recent years. Current SCA attack countermeasures are largely static. Given sufficient signal-to-noise ratio and a number of power traces, static countermeasures can be defeated, as they merely attempt to hide the power consumption of the system under attack. This research develops a dynamic countermeasure which constantly varies the timing and power consumption of each operation, making correlation between traces more difficult than for static countermeasures. By randomizing the radix of encoding for Booth multiplication …

An Fpga Noise Resistant Digital Temperature Sensor With Auto Calibration, Brandon A. Brown

Theses and Dissertations

In recent years, thermal sensing in digital devices has become increasingly important. From a security perspective, new thermal-based attacks have revealed vulnerabilities in digital devices. Traditional temperature sensors using analog-to-digital converters consume significant power and are not conducive to rapid development. As a result, there has been an escalating demand for low cost, low power digital temperature sensors that can be seamlessly integrated onto digital devices. This research seeks to create a modular Field Programmable Gate Array digital temperature sensor with auto one-point calibration to eliminate the excessive costs and time associated with calibrating existing digital temperature sensors. In addition, …

Trade-Offs In A 1 Tbps Mimo Communication System Between An Airship And An Array Of Ground Receive Antennas, Adam R. Brueggen

Theses and Dissertations

As demand for higher data-rate wireless communications increases, so will the interest in multiple-input and multiple-output (MIMO) systems. In a single transmitter, single receiver communication system, there is a fundamental limit to the data-rate capacity of the system proportional to the systems bandwidth. Since increasing the bandwidth is expensive and limited, another option is increasing the system's capacity by adding multiple antennas at the transmitter and receiver to create a MIMO communication system. With a T transmitter, R receiver MIMO communication system, TR channels are created which allow extremely high data-rates. MIMO systems are attractive because they are extremely robust …

Low Cost, Low Complexity Sensor Design For Non-Cooperative Geolocation Via Received Signal Strength, Michael S. Butler

Theses and Dissertations

Obtaining accurate non-cooperative geolocation is vital for persistent surveillance of a hostile emitter. Current research for developing a small, cheap and energy efficient sensor network for non-cooperative geolocation measurements via received signal strength (RSS) is limited. Most existing work focuses on simulating a non-cooperative network (NN) and in doing so, simulated models often ignore localization errors caused from the hardware processing raw RSS data and often model environment-dependent errors as random. By comparing real-time measured non-cooperative geolocation data to a simulated system a more accurate model can be developed. This thesis discusses the development and performance of a small, low …

Field Emission Of Thermally Grown Carbon Nanostructures On Silicon Carbide, Jonathon M. Campbell

Theses and Dissertations

CNTs are known to be excellent field emitter due to their unique physical and electrical properties. Because of their semi-metallic nature, CNT do not suffer the thermal runaway found in metallic emitters, and their near one-dimension shape make them an ideal emission sources. CNTs growth by thermal decomposition of silicon carbide does not utilize a catalyst, therefore relatively defect free. One drawback to this method, however is that the CNT grow in a very dense carpet. This very dense CNT carpet comes under the affect of field emission screening effects which dampen the field emission. In this thesis, silicon carbide …

Dismount Threat Recognition Through Automatic Pose Identification, Andrew M. Freeman

Theses and Dissertations

The U.S. military has an increased need to rapidly identify nonconventional adversaries. Dismount detection systems are being developed to provide more information on and identify any potential threats. Current work in this area utilizes multispectral imagery to exploit the spectral properties of exposed skin and clothing. These methods are useful in the location and tracking of dismounts, but they do not directly discern a dismount's level of threat. Analyzing the actions that precede hostile events yields information about how the event occurred and uncovers warning signs that are useful in the prediction and prevention of future events. A dismount's posturing, …

Development Of A Radar-Frequency Metamaterial Measurement And Characterization Apparatus, Stephen I. Faris

Theses and Dissertations

The overall purpose of this research was to design, build, and test an apparatus for the measurement and characterization of radar-frequency metamaterial performance in the S-band through Ku-band (2-18 GHz). Measurement and characterization is vital to metamaterial taxonomy and ultimately vital to metamaterial definitions. Thus, the current lack of clarity in metamaterial definitions has served as the primary motivation for pursuing a method for taxonomy and thus, this apparatus. The technical goal of this thesis was to aid in the understanding of a metamaterial's radar-frequency response by developing an apparatus that would take simple, yet significant measurements of a metamaterial's …

Ofdm-Based Signal Exploitation Using Quadrature Mirror Filter Bank (Qmfb) Processing, Felipe E. Garrido

Theses and Dissertations

By performing QMFB processing with a given signal it is possible to obtain Frequency-Time (F-T) outputs that represent signal features such as bandwidth (W), center frequency (fc), signal duration (Ts), modulation type (AM, FM, BPSK, QAM, etc), frequency content and time allocation. Because of its unique structure, two widely used signals based on Orthogonal Frequency Division Multiplexing (OFDM) were chosen as signals of interest for demonstration. The general implementation of the QMFB process is described along with the basic structure of OFDM signals related to the physical layer perspective of 802.11a Wi-Fi and 802.16e WiMAX frame structures are described. The …

Air-To-Air Missile Enhanced Scoring With Kalman Smoothing, Jonathon S. Gipson

Theses and Dissertations

A correct estimate of a missile's flight path is essential to USAF test and evaluation efforts. The USAF air-to-air Weapons System Evaluation Program (WSEP) targets unmanned aerial drones in hundreds of live-fire missile tests each year. The current QF-4 drone inventory is expected to be depleted by 2015. The QF-16 Full Scale Aerial Target (FSAT) contract has been awarded to convert usable early model F-16s into remote-controlled drones. The QF-16 will provide a highly-maneuverable, realistic testing environment for 5th generation fighters. To accomplish their mission, WSEP requires a scoring system capable of estimating the trajectory of a missile relative to …

Enhanced Image-Aided Navigation Algorithm With Automatic Calibration And Affine Distortion Prediction, Juan D. Jurado

Theses and Dissertations

This research aims at improving two key steps within the image aided navigation process: camera calibration and landmark tracking. The camera calibration step is improved by automating the point correspondence calculation within the standard camera calibration algorithm, thereby reducing the required time for calibration while maintaining the output model accuracy. The feature landmark tracking step is improved by digitally simulating affine distortions on input images in order to calculate more accurate feature descriptors for improved feature matching in high relative viewpoint change. These techniques are experimentally demonstrated in an outdoor environment with a consumer-grade inertial sensor and three imaging sensors, …

The Effects Of Cognitive Jamming On Wireless Sensor Networks Used For Geolocation, Michael A. Huffman

Theses and Dissertations

The increased use of Wireless Sensor Networks (WSN) for geolocation has led to an increased reliance on this technology. Jamming, protecting jamming, and detecting jamming in a WSN are areas of study that have greatly increased in interest. This research uses simulations and data collected from hardware experiments to test the effects of jamming on a WSN. Hardware jamming was tested using a Universal Software Radio Peripheral (USRP) Version 2 to assess the effects of jamming on a cooperative network of Java Sun SPOTs. The research combines simulations and data collected from the hardware experiments to see the effects of …

Binary Classification Of An Unknown Object Through Atmospheric Turbulence Using A Polarimetric Blind-Deconvolution Algorithm Augmented With Adaptive Degree Of Linear Polarization Priors, Mu J. Kim

Theses and Dissertations

This research develops an enhanced material-classification algorithm to discriminate between metals and dielectrics using passive polarimetric imagery degraded by atmospheric turbulence. To improve the performance of the existing technique for near-normal collection geometries, the proposed algorithm adaptively updates the degree of linear polarization (DoLP) priors as more information becomes available about the scene. Three adaptive approaches are presented. The higher-order super-Gaussian method fits the distribution of DoLP estimates with a sum of two super-Gaussian functions to update the priors. The Gaussian method computes the classification threshold value, from which the priors are updated, by fitting the distribution of DoLP estimates …