Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Navigation, Guidance, Control and Dynamics (234)
- Aerodynamics and Fluid Mechanics (189)
- Space Vehicles (165)
- Physical Sciences and Mathematics (132)
- Structures and Materials (126)
-
- Electrical and Computer Engineering (119)
- Propulsion and Power (118)
- Astrodynamics (94)
- Systems Engineering and Multidisciplinary Design Optimization (84)
- Engineering Science and Materials (77)
- Mechanical Engineering (69)
- Computer Sciences (56)
- Materials Science and Engineering (50)
- Mechanics of Materials (48)
- Physics (45)
- Aeronautical Vehicles (43)
- Other Aerospace Engineering (43)
- Operations Research, Systems Engineering and Industrial Engineering (38)
- Controls and Control Theory (35)
- Heat Transfer, Combustion (34)
- Multi-Vehicle Systems and Air Traffic Control (30)
- Signal Processing (27)
- Ceramic Materials (23)
- Computer Engineering (23)
- Artificial Intelligence and Robotics (18)
- Electrical and Electronics (18)
- Applied Mathematics (17)
- Aviation (17)
- Institution
- Keyword
-
- #antcenter (165)
- #csra (100)
- Flight control (38)
- Global Positioning System (37)
- Drone aircraft (30)
-
- Artificial satellites (29)
- Additive manufacturing (27)
- Finite element method (26)
- Aerodynamics (25)
- Composite materials (23)
- Drone aircraft--Control systems (22)
- Fluid dynamics (20)
- CubeSat (19)
- Kalman filtering (19)
- Optimal control (18)
- Artificial satellites--Orbits (17)
- Computational fluid dynamics (16)
- Aeroelasticity (15)
- Combustion (15)
- Heat--Transmission (15)
- Navigation (Aeronautics) (15)
- Supersonic aerodynamics (15)
- Artificial satellites--Control systems (14)
- Computer vision (14)
- Flexible structures (14)
- Optimization (14)
- Artificial satellites--Tracking (13)
- Electric propulsion (13)
- Inertial navigation systems (13)
- Turbulent boundary layer (13)
- Publication Year
Articles 841 - 870 of 1780
Full-Text Articles in Aerospace Engineering
Optimized Dual Expander Aerospike Rocket, Joshua N. Hall
Optimized Dual Expander Aerospike Rocket, Joshua N. Hall
Theses and Dissertations
Research at the Air Force Institute of Technology (AFIT) focused on designing a cryogenic dual-expander aerospike nozzle (DEAN) upper stage rocket engine to produce 50,000 pounds-force (222.4 kilo-Newtons) vacuum thrust, 464 seconds of vacuum specific impulse and a thrust-to-weight ratio of 106.5. The use of dual expander cycles improves engine reliability, maximizes efficiency, and eliminates some catastrophic failure modes. An upper stage engine with an aerospike nozzle is shorter and lighter than an equivalent performing conventional bell nozzle upper stage engine. Previous research focused on first developing a feasible closed DEAN design model and secondly expanding the model to support …
Follower-Force Experiments With Geometric Non-Linear Coupling For Analytical Validation, Tae H. Kim
Follower-Force Experiments With Geometric Non-Linear Coupling For Analytical Validation, Tae H. Kim
Theses and Dissertations
This study was a follow-up of a previous study where static deflection data of a joined-wing test article was collected from a series of experiments using a laser scanner and a laser tracker while the test articles were subjected to follower-forces. One of the goals of this study was to collect accurate experimental data which could be used to validate analytical methods, such as geometrically exact beam theory, which are used to predict the nonlinear response of joined-wings. The load application system used on the previous study was not able to provide a follower-force on the test articles, and therefore …
Long Term Quadrotor Stabilization, Nicolas S. Hamilton
Long Term Quadrotor Stabilization, Nicolas S. Hamilton
Theses and Dissertations
The work of this thesis focuses on the IMU and getting the best performance possible out of the IMU to achieve better long term stability and a better navigation solution. This is done in two ways. First, the IMU accelerometer output is examined to determine if it is possible to use accelerometers to determine attitude. If the quadrotor is stationary or moving at constant velocity, the roll and pitch angles can be determined. Additionally, the accelerometers can be used to determine angular accelerations and angular rates which are integrated to determine heading. The second approach models the quadrotor and uses …
Manufacturing And Evaluation Of A Biologically Inspired Engineered Mav Wing Compared To The Manduca Sexta Wing Under Simulated Flapping Conditions, Nathanial E. Deleon
Manufacturing And Evaluation Of A Biologically Inspired Engineered Mav Wing Compared To The Manduca Sexta Wing Under Simulated Flapping Conditions, Nathanial E. Deleon
Theses and Dissertations
In recent years, researchers have expressed a vested interest in the concepts surrounding flapping wing micro air vehicles (FWMAVs) that are capable of both range and complex maneuvering. Most research in this arena has found itself concentrated on topics such as flapping dynamics and the associated fluid-structure interactions inherent in the motion, however there still remains myriad questions concerning the structural qualities intrinsic to the wings themselves. Using nature as the template for design, FWMAV wings were constructed using carbon fiber and Kapton and tested under simplified flapping conditions by analyzing frozen' digital images of the deformed wing by methods …
Fatigue Behavior Of A Sic/Sic Composite At 1000⁰C In Air And In Steam, Michael W. Knauf
Fatigue Behavior Of A Sic/Sic Composite At 1000⁰C In Air And In Steam, Michael W. Knauf
Theses and Dissertations
Tension-tension fatigue behavior of a prototype Silicon Carbide/Silicon Carbide (SiC/SiC) ceramic matrix composite (CMC) material was investigated at 1000°C in laboratory air and in steam environments. The material consists of a SiC matrix reinforced with CG NICALON™ fibers woven in an eight harness satin weave (8HSW) and coated with a BN/SiC dual-layer interphase. The composite was manufactured by a Polymer Infiltration and Pyrolysis (PIP) process. A seal coat of SiC and elemental boron was applied to the test specimens after machining. The tensile stress-strain behavior was investigated and the tensile properties were measured at 1000°C. Tension-tension fatigue behavior was studied …
Flow Control Application On A Submerged Inlet Characterized By Three-Component Ldv, Tina H. Reynolds
Flow Control Application On A Submerged Inlet Characterized By Three-Component Ldv, Tina H. Reynolds
Theses and Dissertations
A submerged inlet investigation, using flow control in the form of discrete blowing, examined proximity and jet directionality to improve compressor face uniformity. The flow control locations were at the head of the ramp and part way down the ramp, providing four configurations under examination. Laser Doppler velocimetry (LDV)measurements at the throat determined the effect of the flow control based on the statistical velocity measurements. Blowing at closer proximity to the throat and targeting the largest velocity deficit region provided the best results. The airspeed and inlet velocity simulated takeoff and landing conditions; velocities ranged from Mach 0.1-0.3 at the …
Performance Characterization Of A Three-Axis Hall Effect Thruster, Spencer E. Temkin
Performance Characterization Of A Three-Axis Hall Effect Thruster, Spencer E. Temkin
Theses and Dissertations
No abstract provided.
Effects Of Prior Aging At 274⁰C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 288⁰C: Experiment And Modeling, Joseph A. Wahlquist
Effects Of Prior Aging At 274⁰C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 288⁰C: Experiment And Modeling, Joseph A. Wahlquist
Theses and Dissertations
No abstract provided.
Navigation With Limited Prior Information Using Time Difference Of Arrival Measurements From Signals Of Opportunity, Christopher M. Rondeau
Navigation With Limited Prior Information Using Time Difference Of Arrival Measurements From Signals Of Opportunity, Christopher M. Rondeau
Theses and Dissertations
The Global Positioning System (GPS) provides world-wide availability to high-accuracy navigation and positioning information. However, the threats to GPS are increasing, and many limitations of GPS are being encountered. Simultaneously, systems previously considered as viable backups or supplements to GPS are being shut down. This creates the need for system alternatives. Navigation using signals of opportunity (SoOP) exploits any signal that is available in a given area, regardless of whether or not the original intent of the signal was for navigation. Common techniques to compute a position estimate using SoOP include received signal strength, angle of arrival, time of arrival, …
Orbital Tori Construction Using Trajectory Following Spectral Methods, Ralph E. Bordner Iii
Orbital Tori Construction Using Trajectory Following Spectral Methods, Ralph E. Bordner Iii
Theses and Dissertations
By assuming the motion of a satellite about the earth’s geopotential mimics the known Kolmogorov-Arnold-Moser (KAM) solution of a lightly perturbed integrable Hamiltonian system, this research focused on applying trajectory following spectral methods to estimate orbital tori from sampled orbital data. From an estimated basis frequency set, orbital data was decomposed into multi-periodic Fourier series, essentially compressing ephemerides for long-term use. Real-world Global Positioning System (GPS) orbital tracks were decomposed and reconstructed with error from as low as few kilometers per coordinate axis over a 10-week span to tens of kilometers per coordinate axis over the same time period, depending …
Exploring The Effects Of International Traffic In Arms Regulations Restrictions On Innovation In The U.S. Space Industrial Base, Kalliroi L. Landry
Exploring The Effects Of International Traffic In Arms Regulations Restrictions On Innovation In The U.S. Space Industrial Base, Kalliroi L. Landry
Theses and Dissertations
The International Traffic in Arms Regulations (ITAR) are used to protect United States (U.S.) military technologies. However, changes to ITAR export controls regarding space technologies have had a major impact to the U.S. space industry. The literature mentions a concern for the health of lower-tier firms because they are a major source of innovation, but there is no additional information considering the effects of ITAR on space innovation at those lower tiers. The purpose of this thesis was to explore the implications of continuing the current ITAR restrictions with regard to innovation in the space industry. This research used a …
Satellite Capabilities Mapping - Utilizing Small Satellites, David A. Grigsby
Satellite Capabilities Mapping - Utilizing Small Satellites, David A. Grigsby
Theses and Dissertations
The cost and schedule advantages small satellites have over larger legacy systems have been studied, but there has been very little experimentation performed to determine whether small satellites can actually deliver the capabilities of larger spacecraft. To date, a desired operational capability has not been fully realized by a scalable satellite design. Advances in sensor technology have led to significant reductions in size, weight, and power (SWaP) presenting an opportunity to exploit the evolution of space operations by using small satellites to perform specific missions. This paper describes a methodology that maps a specific set of large space vehicle capabilities …
An Integrity Framework For Image-Based Navigation Systems, Craig D. Larson
An Integrity Framework For Image-Based Navigation Systems, Craig D. Larson
Theses and Dissertations
This work first examines fundamental differences between measurement models established for GPS and those of proposed image-based navigation systems. In contrast to single value per satellite GPS pseudorange measurements, image measurements are inherently angle-based and represent pixel coordinate pairs for each mapped target. Thus, in the image-based case, special consideration must be given to the units of the transformations between the states and measurements, and also to the fact that multiple rows of the observation matrix relate to particular error states. An algorithm is developed to instantiate a framework for image-based integrity analogous to that of GPS RAIM. The algorithm …
A Photogrammetry-Based Hybrid System For Dynamic Tracking And Measurement, Daniel P. Magree
A Photogrammetry-Based Hybrid System For Dynamic Tracking And Measurement, Daniel P. Magree
Theses and Dissertations
Noncontact measurements of lightweight flexible aerospace structures present several challenges. Objects are usually mounted on a test stand because current noncontact measurement techniques require that the net motion of the object be zero. However, it is often desirable to take measurements of the object under operational conditions, and in the case of miniature aerial vehicles (MAVs) and deploying space structures, the test article will undergo significant translational motion. This thesis describes a hybrid noncontact measurement system which will enable measurement of structural kinematics of an object freely moving about a volume. By using a real-time videogrammetry system, a set of …
Velocity Plume Profiles For Hall Thrusters Using Laser Diagnostic, Daniel B. Lee
Velocity Plume Profiles For Hall Thrusters Using Laser Diagnostic, Daniel B. Lee
Theses and Dissertations
This research built a non-intrusive laser diagnostic tool using Laser Induced Fluorescence (LIF) and absorption techniques to measure the velocity and density plume profiles of low powered Hall thrusters. This tool was then applied to a Busek 200W Hall thruster to validate the performance against previous research on the same thruster. A laser frequency sweep through 834.72 nm produced LIF signals for ionized xenon –collected at 541.9 nm – in the thruster plume and absorption data outside the plume at a neutral transition at 834.68 nm. The absorption data provided a baseline reference to calculate the axial and radially velocity …
Global Navigation Satellite System Software Defined Radio, Jason M. Mcginthy
Global Navigation Satellite System Software Defined Radio, Jason M. Mcginthy
Theses and Dissertations
The GNSS world is quickly growing. The United States’ GPS, the European Union’s Galileo, China’s Compass, and Russia’s GLONASS systems are all developing or modernizing their signals, and there will soon be more navigation satellites in space than ever before. The goal of this research was to develop an initial capability for an AFIT GNSS software receiver. This software receiver is intended to be used for research purposes at the Advanced Navigation Technology (ANT) Center. First a GPS-only software receiver was built. It successfully acquired, tracked, and provided reasonable position estimates. Next, the receiver was successfully modified to acquire and …
Artificial Inhomogeneous Tapered Impedance Sheet Characterization And Applications, Jeffrey P. Massman
Artificial Inhomogeneous Tapered Impedance Sheet Characterization And Applications, Jeffrey P. Massman
Theses and Dissertations
The ability to manipulate a complex impedance sheet about a PEC or general dielectric cylinder of arbitrary diameter to control the overall scattering characteristics at particular angles for shielding or scattering applications is presented. It is shown that with the capability to readily control both the real and imaginary components of a percolated lossy film's effective impedance, specific impedance distributions can be obtained to effectively direct the overall nulls in the bistatic scattering pattern. The exact approach only requires negligible truncation error of the matrix solution and can be applied to cylinders of arbitrary size. This approach relies on general …
Monocular Vision Localization Using A Gimbaled Laser Range Sensor, Don J. Yates
Monocular Vision Localization Using A Gimbaled Laser Range Sensor, Don J. Yates
Theses and Dissertations
There have been great advances in recent years in the area of indoor navigation. Many of these new navigation systems rely on digital images to aid an inertial navigation estimates. The Air Force Institute of Technology (AFIT) has been conducting research in this area for a number of years. The image-aiding techniques are centered around tracking stationary features in order to improve inertial navigation estimates. Previous research has used stereo vision systems or terrain constraints with monocular systems to estimate feature locations. While these methods have shown good results, they do have drawbacks. First, as unmanned exploration vehicles become smaller …
Aiding Gps With Additional Satellite Navigation Services, Yasin A. Mutlu
Aiding Gps With Additional Satellite Navigation Services, Yasin A. Mutlu
Theses and Dissertations
In modern warfare navigation services are very important. GPS is currently providing service for accurate navigation, except in some areas, especially urban areas, where GPS signals cannot always be tracked by users. In these cases some additional navigation support could be provided by other global navigation satellite systems. If GPS is combined with other navigation systems than the navigation gap will be minor. In this thesis, the effect of combining GPS with other satellite navigation systems, specifically GLONASS, Galileo and Compass, is evaluated in terms of availability and position dilution of precision (PDOP) values. First, satellite constellations are simulated in …
Consideration Of Wear Rates At High Velocity, Chad S. Hale
Consideration Of Wear Rates At High Velocity, Chad S. Hale
Theses and Dissertations
The development of the research presented here is one in which high velocity relative sliding motion between two bodies in contact has been considered. The experimental results of a VascoMax 300 maraging steel slipper sliding on an AISI 1080 steel rail during a January 2008 sled test mission were considered for the determination of high velocity wear rates. The numerical model, based on a metallographic study of a test slipper, contained all of the physical features present in order to adequately characterize high velocity wear rates. Two-dimensional, plane strain models have been implemented in the explicit finite element code, ABAQUS. …
Assembly, Integration, And Test Methods For Operationally Responsive Space Satellites, Lisa A. Baghal
Assembly, Integration, And Test Methods For Operationally Responsive Space Satellites, Lisa A. Baghal
Theses and Dissertations
Current government and industry standards in spacecraft testing result in an Assembly, Integration, and Test (AIT) timeline greater than six months. These standards will not support the vision of Operationally Responsive Space (ORS) to deploy a satellite within six days to fill an urgent need. Using the Air Force Research Laboratory’s Plug-and-Play Satellite (PnPSat), multiple Rapid AIT trials were conducted. By exercising the AIT process with various spacecraft configurations and personnel, methods for reducing or modifying traditional testing regimen were investigated.
Development Of A Flapping Wing Design Incorporating Shape Memory Alloy Actuation, Jeffrey A. Barrett
Development Of A Flapping Wing Design Incorporating Shape Memory Alloy Actuation, Jeffrey A. Barrett
Theses and Dissertations
This research sought to validate a proof of concept regarding shape memory alloy actuation of a flapping-wing blimp. Specimen wires were subjected to cyclic voltage at increasing frequencies to quantify expected strains. A laser vibrometer captured 2048 sample velocities during single contraction and elongation cycles, and the resulting samples were used to calculate displacements. Displacements were determined ten times for each specimen and frequency to compute averages. Subsequently, a circumventing frame was designed to encase a blimp envelope and provide support for a flapping motion actuation system. Contraction of shape memory wire translated force to the flapping mechanism via bellcranks, …
Verification Of Kam Theory On Earth Orbiting Satellites, Christian L. Bisher
Verification Of Kam Theory On Earth Orbiting Satellites, Christian L. Bisher
Theses and Dissertations
This paper uses KAM torus theory and Simplified General Perturbations 4 (SGP4) orbit prediction techniques compiled by Dr. William Wiesel and compares it to Analytical Graphics ® Incorporated (AGI) Satellite Toolkit ® (STK) orbit data. The goal of this paper is to verify KAM torus theory can be used to describe and propagate an Earth satellite orbit with similar accuracy to existing general perturbation techniques. Using SGP4 code including only truncated geopotential effects, KAM torus generating code, and other utilities were used to describe a particular satellite orbit as a torus and then propagate the satellite using traditional and KAM …
Experiments With Geometric Non-Linear Coupling For Analytical Validation, Jonathan D. Boston
Experiments With Geometric Non-Linear Coupling For Analytical Validation, Jonathan D. Boston
Theses and Dissertations
This study was focused on obtaining accurate experimental data for the validation of the geometrically exact beam theory from a series of experiments in which high quality surface shape and deflection data was collected. Many previous experiments have experienced issues with data collection or test articles which the researchers were unable to overcome. The test program was performed in two stages: qualification and joined-wing. The qualification stage validated the experimental procedures on simple 72 in long aluminum beams with 8 in x 0.5 in cross-sections. The joined-wing stage was the primary experiment focused on obtaining quality data for use in …
Gravity Gradiometry And Map Matching: An Aid To Aircraft Inertial Navigation Systems, Anthony J. Degregoria
Gravity Gradiometry And Map Matching: An Aid To Aircraft Inertial Navigation Systems, Anthony J. Degregoria
Theses and Dissertations
Inertial navigation systems (INS) offer passive, all-weather, and undeniable navigation information, which military customers often view as especially appealing strengths. Unfortunately, Airmen and engineers still struggle with INS’s drifting position errors, and navigation aids generally detract from INS’s strengths. At this year’s Air, Space, and Cyberspace in the 21st Century Conference, the Chief of Staff of the Air Force identified the Global Positioning System (GPS) as a widely-known and exploitable vulnerability, saying that it’s critical the Joint force reduce GPS dependence. Recent advances provide an opportunity for gravity gradient instruments (GGI), which measure spatial derivatives of the gravity vector, to …
Effectsof Prior Aging At 260 °C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 260 °C: Experiment And Modeling, Bradley K. Diedrick
Effectsof Prior Aging At 260 °C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 260 °C: Experiment And Modeling, Bradley K. Diedrick
Theses and Dissertations
The purpose of this research was to investigate the inelastic deformation behavior of PMR-15 neat resin, a high-temperature polymer, at 260 °C. The experimental program was designed to explore the influence of strain rate on loading and unloading behaviors. In addition, the effect of prior strain rate on creep, relaxation, and recovery responses was evaluated. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading. Early failures occur before fully establishing inelastic flow. The creep, relaxation, and recovery responses are significantly influenced by prior strain rate. The experimental results suggest the behavior of PMR-15 at 260 °C can be …
Fatigue Behavior Of An Advanced Sic/Sic Composite With An Oxidation Inhibited Matrix At 1200°C In Air And In Steam, Jacob Delapasse
Fatigue Behavior Of An Advanced Sic/Sic Composite With An Oxidation Inhibited Matrix At 1200°C In Air And In Steam, Jacob Delapasse
Theses and Dissertations
The fatigue behavior of an advanced Silicon Carbide/Silicon Carbide (SiC/SiC) ceramic matrix composite (CMC) with oxidation inhibited matrix was investigated at 1200˚C in laboratory air and in steam environments. The composite consisted of an oxidation inhibited SiC matrix reinforced with Hi-Nicalon fibers coated with pyrolytic carbon (PyC) with a boron carbide overlay woven into eight-harness-satin (8HS) weave plies. Tensile stress-strain behavior and tensile properties were evaluated at 1200˚C. Tension-tension fatigue tests were conducted in both laboratory air and in steam at 1200˚C at frequencies of 0.1 Hz, 1.0 Hz, and 10 Hz. The tension-tension fatigue tests had a ratio of …
Numerical Investigation Of Pre-Detonator Geometries For Pde Applications, Robert T. Fievisohn
Numerical Investigation Of Pre-Detonator Geometries For Pde Applications, Robert T. Fievisohn
Theses and Dissertations
A parametric study was performed to determine optimal geometries to allow the successful transition of a detonation from a pre-detonator into the thrust tube of a pulse detonation engine. The study was performed using a two-dimensional Euler solver with progress variables to model the chemistry. The geometrical configurations for the simulations look at the effect of shock reflections, flow obstructions, and detonation diffraction to determine successful geometries. It was observed that there are success and failure rates associated with pre-detonators. These success rates appear to be determined by the transverse wave structure of a stably propagating detonation wave and must …
Validation Of A Novel Approach To Solving Multibody Systems Using Hamilton's Weak Principle, Ashton D. Hainge
Validation Of A Novel Approach To Solving Multibody Systems Using Hamilton's Weak Principle, Ashton D. Hainge
Theses and Dissertations
A novel approach for formulating and solving for the dynamic response of multibody systems has been developed using Hamilton’s Law of Varying Action as its unifying principle. In order to assure that the associated computer program is sufficiently robust when applied across a wide range of dynamic systems, the program must be verified and validated. The purpose of the research was to perform the verification and validation of the program. Results from the program were compared with closed-form and numerical solutions of simple systems, such as a simple pendulum and a rotating pendulum. The accuracy of the program for complex …
Analysis Of Hybrid-Electric Propulsion System Designs For Small Unmanned Aircraft Systems, Ryan M. Hiserote
Analysis Of Hybrid-Electric Propulsion System Designs For Small Unmanned Aircraft Systems, Ryan M. Hiserote
Theses and Dissertations
Currently fielded electric-powered small unmanned aircraft systems (UAS) lack the endurance desired by warfighters, while their internal combustion engine (ICE) driven counterparts generate mission compromising acoustic and thermal signatures. Parallel hybrid-electric propulsion systems would meet the military’s needs by combining the advantages of hydrocarbon and electric power systems. Three distinct parallel hybrid-electric system designs, each with three unique battery discharging profiles, were analyzed and compared using a constrained static optimization formulation based upon traditional aircraft design equations. Each system combined an ICE sized for cruise speed with an electric motor sized for endurance speed. The nine hybrid variations were compared …