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Theses and Dissertations

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Articles 1321 - 1350 of 1780

Full-Text Articles in Aerospace Engineering

Design Study Of Triggered Isomer Heat Exchanger-Combustion Hybrid Jet Engine For High Altitude Flight, Christopher E. Hamilton Mar 2002

Design Study Of Triggered Isomer Heat Exchanger-Combustion Hybrid Jet Engine For High Altitude Flight, Christopher E. Hamilton

Theses and Dissertations

This study investigated the possibility of utilizing a Triggered Isomer Heat Exchanger (TIHE) within a conventional jet engine in order to increase the endurance of a High Altitude Long Endurance (HALE) Intelligence, Surveillance, and Reconnaissance (ISR) aircraft. Optimizations of the conventional and TIHE engines along with selection of a switchover flight condition, where the aircraft switches from combustion to TIHE operations, were made utilizing engine design and mission analysis software. Radiation shield weights were determined utilizing point source gamma ray shielding methods. The jet engine best suited for the hybrid use, where both combustion and TIHE components located in a …

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A Study Of Satellite Navigation, Dilution Of Precision, And Positioning Techniques For Use On And Around The Moon, John H. Macnicol Mar 2002

A Study Of Satellite Navigation, Dilution Of Precision, And Positioning Techniques For Use On And Around The Moon, John H. Macnicol

Theses and Dissertations

The National Aeronautics and Space Agency is examining several approaches to meet navigational requirements for spacecraft in lunar orbit, in transit to or from the moon, and for personnel on the lunar surface requiring an accurate, real-time, on-board navigation capability. This work addresses one possible solution to the navigation problem in the vicinity of the moon using a lunar satellite navigation system. Dilution of precision is the figure of merit used to determine if a candidate lunar satellite navigation system can meet accuracy specifications based on a given satellite constellation and the measurement types used. Ten satellite constellations, using two …

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Using The Gps To Collect Trajectory Data For Ejection Seat Design, Validation, And Testing, Brian R. Tredway Mar 2002

Using The Gps To Collect Trajectory Data For Ejection Seat Design, Validation, And Testing, Brian R. Tredway

Theses and Dissertations

The dynamic characteristics of an aircraft ejection seat are a crucial concern when evaluating aircraft ejection systems and their ability to separate aircrew members safely from disabled aircraft. Every ejection seat model undergoes real-time dynamic tests to determine potential injury to aircrew members during ejection. Ejection seat tests are conducted at high-speed test tracks. The test track facilities provide the required telemetry and high-speed photography to monitor and validate the aircraft escape system performance. Ejection seat test and evaluation requires very accurate position and velocity determination during each test run to determine the relative positions between the aircraft, ejection seat, …

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Flight Control Failure Detection And Control Redistribution Using Multiple Model Adaptive Estimation With Filter Spawning, Michael L. Torres Jr. Mar 2002

Flight Control Failure Detection And Control Redistribution Using Multiple Model Adaptive Estimation With Filter Spawning, Michael L. Torres Jr.

Theses and Dissertations

In the current research, the MMAE with Filter Spawning and Control Redistribution (MMAE/FS/CR) are used together to identify failures and apply appropriate corrections. This effort explores the performance of the MMAE/FS/CR in different regions of the flight envelope using model and gain scheduling. The MMAE/FS/CR is able to detect complete and partial actuator/surface failures, as well as complete sensor failures. Once the actuator/surface failure is identified and the effectiveness is determined in the case of partial failures, proper control is applied in order to accomplish the desired pilot command. Improvements in the algorithm are required in order to enhance the …

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Microdot - A Four-Bit Microcontroller Designed For Distributed Low-End Computing In Satellites, Anthony R. Woodcock Mar 2002

Microdot - A Four-Bit Microcontroller Designed For Distributed Low-End Computing In Satellites, Anthony R. Woodcock

Theses and Dissertations

Many satellites are an integrated collection of sensors and actuators that require dedicated real-time control. For single processor systems, additional sensors require an increase in computing power and speed to provide the multi-tasking capability needed to service each sensor. Faster processors cost more and consume more power, which taxes a satellite's power resources and may lead to shorter satellite lifetimes. An alternative design approach is a distributed network of small and low power microcontrollers designed for space that handle the computing requirements of each individual sensor and actuator. The design of microdot, a four-bit microcontroller for distributed low-end computing, is …

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Ins Aiding By Tracking An Unknown Ground Object, Mursy Polat Mar 2002

Ins Aiding By Tracking An Unknown Ground Object, Mursy Polat

Theses and Dissertations

The reduction of the navigation error in an inertial navigation system by optically tracking a ground object is investigated. Multiple observations of the ground object are used. The location of the ground object is assumed unknown. A careful analysis of the measurement situation at hand reveals that by optically tracking an unknown ground object using passive, bearings-only measurements, the aircraft's angle of attack and sideslip angle can be measured. Thus, two new independent measurement equations featuring the aircraft's angular navigation variables are obtained. Hence, by optically tracking over time an unknown ground object, inertial navigation system aiding is in fact …

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Evaluation And Mission-Specific Optimization Of Satellite Packet Telemetry Protocol For Use On Dod Flight Test Ranges, Beth A. Trapp Mar 2002

Evaluation And Mission-Specific Optimization Of Satellite Packet Telemetry Protocol For Use On Dod Flight Test Ranges, Beth A. Trapp

Theses and Dissertations

The DoD test range community has come to the realization that its telemetry abilities are obsolete. Efforts are therefore underway to improve telemetry systems at DoD test ranges. The overall objective of this project was to evaluate the practical use of the CCSDS packet telemetry protocol in DoD test ranges and determine the configuration that would maximize performance based on mission requirements. A secondary objective was to compare the CCSDS and ATM protocols in order to substantiate further exploration of using ATM in future DoD telemetry systems. Modeling and simulation of the CCSDS protocol showed a correlation between three CCSDS …

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Performance Tradeoff Study Of A Gps-Aided Ins For A Rocket Trajectory, Muhittin Istanbulluoglu Mar 2002

Performance Tradeoff Study Of A Gps-Aided Ins For A Rocket Trajectory, Muhittin Istanbulluoglu

Theses and Dissertations

The Turkish Air Force (TuAF) has started a project to launch a satellite using only Turkish resources. Primary motivation behind this research is to assist TuAF's project by keeping up with these innovations in the navigational arena. The basic challenge in navigation system design is to decide which navigation system (or systems) and implementation techniques will be used, depending on accuracy requirements. The two primary navigation systems that will be integrated in this research are the Inertial Navigation System (INS), and the Global Positioning System (GPS). The Kalman filter algorithm is used to integrate INS and GPS. The rocket (Atlas …

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An Examination Of Latency And Degradation Issues In Unmanned Combat Aerial Vehicle Environments, Shane A. Dougherty Mar 2002

An Examination Of Latency And Degradation Issues In Unmanned Combat Aerial Vehicle Environments, Shane A. Dougherty

Theses and Dissertations

Since the multidimensional knapsack problems are NP-hard problems, the exact solutions of knapsack problems often need excessive computing time and storage space. Thus, heuristic approaches are more practical for multidimensional knapsack problems as problems get large. This thesis presents the results of an empirical study of the performance of heuristic solution procedures based on the coefficients correlation structures and constraint slackness settings. In this thesis, the three representative greedy heuristics, Toyoda, Senju and Toyoda, and Loulou and Michaelides methods, are studied. The purpose of this thesis is to explore which heuristic of the three representative greedy heuristics perform best under …

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Broadcast Vs Precise Gps Ephemerides: A Historical Perspective, David L. M. Warren Mar 2002

Broadcast Vs Precise Gps Ephemerides: A Historical Perspective, David L. M. Warren

Theses and Dissertations

In most recent years, both high-resolution imagery systems and images were only available to military and national security organizations. Distinctive changes within the commercial image industry allowed space-borne pioneers to provide high-resolution images. Space-borne Image Company's Ikonos satellite provides a 1-meter resolution for the past 3 years. Current development of .5-meter resolution will be offered in the near future. Access of these images is available in ground stations located worldwide in different regions. Studies have shown that these high quality images are eye-catching and may serve a purpose through its design; on contrary high cost and accessibility does not met …

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Experimental Vibration Analysis Of Inflatable Beams For An Afit Space Shuttle Experiment, Thomas G. Single Mar 2002

Experimental Vibration Analysis Of Inflatable Beams For An Afit Space Shuttle Experiment, Thomas G. Single

Theses and Dissertations

This study investigated the use of MEMS based devices to control the boundary layer separation from a circular cylinder in cross flow. Velocity profiles were measured experimentally in a low speed wind tunnel. Momentum thickness was measured as the primary way to determine a change in the flow field. The goal was to determine the angular location and frequency of operation that would provide an effect on the boundary layer of the cylinder. A 25% reduction of momentum loss in the cylinder wake was detected with an optimal angle of 69 degrees and an optimal frequency of operation equal to …

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The Investigation Of Hypervelocity Gouging, David J. Laird Mar 2002

The Investigation Of Hypervelocity Gouging, David J. Laird

Theses and Dissertations

The slipper/rail interface of a hypervelocity rocket sled is subject to immense forces due to dynamic loads and impact of the slipper with the rail, and tremendous heating due to aerodynamic and frictional effects is produced at the interface. Under these severe loading conditions, the material in the rail will sometimes experience large non-linear deformations known as gouging. Hydrocodes are computational solvers designed to handle such non-linear, large deformation, high shock, hydrodynamic applications. The ability of the hydrocode CTH to handle gouge modeling is considered, as well as the manner in which temperature environments affect deformation and plastic strain. The …

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Computational Aerodynamic Analysis Of The Flow Field About A Hypervelocity Test Sled, Andrew J. Lofthouse Mar 2002

Computational Aerodynamic Analysis Of The Flow Field About A Hypervelocity Test Sled, Andrew J. Lofthouse

Theses and Dissertations

The flow field about the nose section of a hypervelocity test sled is computed using computational fluid dynamics. The numerical model of the test sled corresponds to the Nike O/U narrow gage sled used in the upgrade program at the High Speed Test Track facility, Holloman Air Force Base, New Mexico. The high temperatures and pressures resulting from the aerodynamic heating and loading affect the sled structure and the performance of the vehicle. The sled transitions from an air environment to a helium environment at a speed of approximately 3,300 feet per second (Mach 3 in air, Mach 1.02 in …

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Suppression Of Pilot-Induced Oscillation (Pio), Donald A. Johnson Mar 2002

Suppression Of Pilot-Induced Oscillation (Pio), Donald A. Johnson

Theses and Dissertations

Closed loop instability caused by excess phase lag induced by actuator rate limiting has been suspected in many pilot-induced oscillations (PIOs) and oscillatory departures from controlled flight. As part of the joint AFIT/TPS program, a longitudinal pilot command notch filter activated by a real-time oscillation verifier (ROVER) algorithm was developed to eliminate the PIO source for any developing, severe PIO. Closed loop computer simulations were conducted to prepare for the flight test. The HAVE ROVER flight test project was flown using the NF-16D Variable Stability In-flight Simulator Test Aircraft (VISTA). A programmable heads-up display (HUD) was used to generate a …

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Alternative Pulse Detonation Engine Ignition System Investigation Through Detonation Splitting, August J. Rolling Mar 2002

Alternative Pulse Detonation Engine Ignition System Investigation Through Detonation Splitting, August J. Rolling

Theses and Dissertations

A Pulse Detonation Engine (PDE) combusts fuel air mixtures through a form of combustion: detonation. Recent PDE research has focused on designing working subsystems. This investigation continued this trend by examining ignition system alternatives. Existing designs required spark plugs in each separate thrust tube to ignite premixed reactants. A single thrust tube could require the spark plug to fire hundreds of times per second for long durations. The goal was to minimize hardware and increase reliability by limiting the number of ignition sources. This research used a continuously propagating detonation wave as both a thrust mechanism and an ignition system …

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The Combined Effects Of Freestream Turbulence, Pressure Gradients, And Surface Roughness On Turbine Aerodynamics, Christine P. Ellering Mar 2002

The Combined Effects Of Freestream Turbulence, Pressure Gradients, And Surface Roughness On Turbine Aerodynamics, Christine P. Ellering

Theses and Dissertations

This work used scaled facsimiles of real turbine blade surfaces to characterize correlations between turbine blade roughness, freestream turbulence, pressure gradients and skin friction (Cf). Addition of roughness caused Cf to increase: up to 300% for the roughest surface. Addition of freestream turbulence resulted in 125% increase for the same surface. The combined effects showed increases up to 380%. Although decreasing roughness, freestream turbulence, and Reynolds number resulted in less dramatic results, it was concluded that the Cf increases due to combined effects were consistently higher than their corresponding sum of the parts. The combined effects of roughness and pressure …

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Investigation Of Cooperative Behavior In Autonomous Wide Search Munitions, Robert E. Dunkel Iii Mar 2002

Investigation Of Cooperative Behavior In Autonomous Wide Search Munitions, Robert E. Dunkel Iii

Theses and Dissertations

The purpose of this research is to investigate the effectiveness of wide-area search munitions in various scenarios using different cooperative behavior algorithms. The general scenario involves multiple autonomous munitions searching for an unknown number of targets of different priority in unknown locations. Three cooperative behavior algorithms are used in each scenario: no cooperation, cooperative attack only, and cooperative classification and attack. In the cooperative cases, the munitions allocate tasks on-line as a group, using linear programming techniques to determine the optimum allocation. Each munition provides inputs to the task allocation routine in the form of probabilities of successfully being able …

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An Analytical Study Of T-38 Drag Reduction In Tight Formation Flight, Eugene H. Wagner Jr. Mar 2002

An Analytical Study Of T-38 Drag Reduction In Tight Formation Flight, Eugene H. Wagner Jr.

Theses and Dissertations

This thesis explores the benefits of flying in a tight formation, mimicking the natural behavior of migratory birds such as geese. The first phase of the research was to determine an optimal position for the wingman of a tight formation flight of T-38 Talon aircraft using the HASC95 vortex lattice code. A second wingman was then added to determine the benefit derived by increasing formation size. The second wingman was predicted to derive an even greater induced drag benefit than the first wingman for T-38s operating at Mach 0.54 at a 10,000-foot altitude. The predicted values were 17.5% savings for …

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Periodic Methods For Controlling A Satellite In Formation, Erin Y. Carraher Mar 2002

Periodic Methods For Controlling A Satellite In Formation, Erin Y. Carraher

Theses and Dissertations

Precise position determination and control is necessary to accomplish proposed satellite formation flying missions of ground movement target indication and synthetic aperture radar. This thesis combines the estimation and control techniques of past AFIT theses with various time-varying and time-invariant LQG control methods. Linear time-invariant control is ideal for on-board satellite estimation and control applications, freeing-up the satellite's limited computational capacity. Using a dynamics frame transformation from the nodal frame to an orbital frame, a higher fidelity, time-periodic model produced nearly identical results for either time-varying or time-invariant control for many scenarios. Scenarios included initial perturbations in the radial, in-track, …

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Orbital Maneuvering Using Electrodynamic Tethers, Hakan San Mar 2002

Orbital Maneuvering Using Electrodynamic Tethers, Hakan San

Theses and Dissertations

Considerably short electrodynamic tethers can be used as a low-thrust propulsion system with minimum or no mass expenditure. The propulsive force is generated by inducing a current flow through the tether which interacts with the magnetosphere of the planet (i.e. Earth, Jupiter and other planetary bodies with magnetosphere). The basics of electrodynamic tether systems have been studied and successful experiments such as boost and de-boost of spacecraft have been conducted in the past. This study presents a simple guidance scheme for the current in the tether in order to perform orbital maneuvers. The general perturbation equations are used to develop …

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Commercial Regional Space/Airborne Imaging, Ugur Akyazi, Ali Durmus, Birce Boga Bakirli, Arif Arin Mar 2002

Commercial Regional Space/Airborne Imaging, Ugur Akyazi, Ali Durmus, Birce Boga Bakirli, Arif Arin

Theses and Dissertations

In this work goal programming is used to solve a minimum cost multicommodity network flow problem with multiple goals. A single telecommunication network with multiple commodities (e.g., voice, video, data, etc.) flowing over it is analyzed. This network consists of: linear objective function, linear cost arcs, fixed capacities, specific origin-destination pairs for each commodity. A multicommodity network flow problem with goals can be successfully modeled using linear goal programming techniques. When properly modeled, network flow techniques may be employed to exploit the pure network structure of a multicommodity network flow problem with goals. Lagrangian relaxation captures the essence of the …

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Air Vehicle Path Planning, Jeffrey M. Hebert Dec 2001

Air Vehicle Path Planning, Jeffrey M. Hebert

Theses and Dissertations

This dissertation explores optimal path planning for air vehicles. An air vehicle exposed to illumination by a tracking radar is considered and the problem of determining an optimal planar trajectory connecting two prespecified points is addressed. An analytic solution yielding the trajectory minimizing the received radar energy reflected from the target is derived using the Calculus of Variations. Additionally, the related problem of an air vehicle tracked by a passive sensor is also solved. Using the insights gained from the single air vehicle radar exposure minimization problem, a hierarchical cooperative control law is formulated to determine the optimal trajectories that …

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Reduced Order Modeling For High Speed Flows With Moving Shocks, David J. Lucia Dec 2001

Reduced Order Modeling For High Speed Flows With Moving Shocks, David J. Lucia

Theses and Dissertations

The use of Proper Orthogonal Decomposition (POD) for reduced order modeling (ROM) of fluid problems is extended to high-speed compressible fluid flows. The challenge in using POD for high-speed flows is presented by the presence of moving discontinuities in the flow field. To overcome these difficulties, a domain decomposition approach is developed that isolates the region containing the moving shock wave for special treatment. The domain decomposition implementation produces internal boundaries between the various domain sections. The domains are linked using optimization-based solvers which employ constraints to ensure smoothness in overlapping portions of the internal boundary. This approach is applied …

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Modeling Axisymmetric Optical Precision Piezoelectric Membranes, James W. Rogers Jr. Oct 2001

Modeling Axisymmetric Optical Precision Piezoelectric Membranes, James W. Rogers Jr.

Theses and Dissertations

The US Department of Defense (DOD), as well as the National Aeronautics and Astronautics Administration (NASA) and the Jet Propulsion Laboratory (JPL) are interested in developing and deploying precise, compliant, light-weight, space-based structures. More specifically, the Air Force’s core competencies ‘Aerospace Superiority’ and ‘Information Superiority’ demand ever-increasing depth and breadth of capability. Whether used for energy transmission or optical reconnaissance, current launch restraints limit rigid space-based optical reflector size. To support this requirement, the Air Force Research Laboratory (AFRL) is developing a large space-based optical membrane telescope. Inflatable reflectors can conceptually break this barrier, but controlling such a compliant structure …

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Techniques For Reduced Order Modeling Of Aeroelastic Structures With Deforming Grids, John S. R. Anttonen Oct 2001

Techniques For Reduced Order Modeling Of Aeroelastic Structures With Deforming Grids, John S. R. Anttonen

Theses and Dissertations

Reduced order modeling (ROM) seeks to make the modeling of aeroelastic behavior practical by reducing computation time for design codes. Deforming grids are often used in aeroelastic problems to account for the deformation of the structure. Proper Orthogonal Decomposition (POD/ROM) is a ROM technique that operates in an index-space for computations, not accounting for changes in grid dynamics, and must be modified to reflect grid deformation properly. To investigate and account for the effects of grid deformation on POD/ROM, a new algorithm is developed that incorporates modifications to the usual formulation. Evaluation of the new algorithm is accomplished through application …

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Adaptive And Reconfigurable Flight Control, Yih Shiun Huang Mar 2001

Adaptive And Reconfigurable Flight Control, Yih Shiun Huang

Theses and Dissertations

An indirect adaptive and reconfigurable flight control system is developed. The three-module controller consists of: (1) a system identification module, (2) a parameter estimate smoother, and (3) a proportional and integral compensator for tracking control. Specifically: (1) The identification of a linear discrete-time control system's open-loop gain is addressed. The classical Kalman filter theory for linear control systems is extended and the control system's state and loop gain are jointly estimated on-line. Explicit formulae for the loop gain's estimate and estimation error covariance are derived. The estimate is unbiased and the predicted covariance is reliable. (2) An adaptive smoother is …

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The Use Of Systems Engineering Processes And Tools To Develop A System Dynamic Simulation Model Of Engineering Support During The Development Phase Of An Acquisition Program, Jason E. Bartolomei Mar 2001

The Use Of Systems Engineering Processes And Tools To Develop A System Dynamic Simulation Model Of Engineering Support During The Development Phase Of An Acquisition Program, Jason E. Bartolomei

Theses and Dissertations

Due to the increase of system complexity and the existing draw down of manpower allocations, today's acquisitions environment desperately needs a systems approach to decision making. Many studies have been performed to model the entire government acquisition environment. Due to the high degree of aggregation, front line decision-makers have had no use for the information these models provide. This research focuses on the Air Force's largest functional support element in aircraft systems development, engineering. I will only consider one phase of the government acquisition cycle the Engineering, Manufacturing, and Development (EMD). This is the development cycle, which begins with initial …

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Estimation Of Relative Satellite Formation Elements In Near Circular Orbits, Ralph E. Bordner Iii Mar 2001

Estimation Of Relative Satellite Formation Elements In Near Circular Orbits, Ralph E. Bordner Iii

Theses and Dissertations

Precise relative position determination of satellite formation elements in near circular orbits is the focus of this thesis. A Bayes filter is used for the estimator with the dynamics solution obtained by solving the time periodic, linearized system via Floquet theory. This approach is similar to that of the traditional Clohessy-Wiltshire treatment, however much more of the system's behavior is retained by using a linear, time periodic system. The dynamics model includes all zonal harmonics of the Earth as well as sectoral, tesseral, and air drag perturbations. The filter algorithm was fed three types of simulated measurements: relative Carrier-Phases Differential …

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Environmental Disturbance Modeling For Large Inflatable Space Structures, Donald J. Davis Mar 2001

Environmental Disturbance Modeling For Large Inflatable Space Structures, Donald J. Davis

Theses and Dissertations

Tightening space budgets and stagnating spacelift capabilities are driving the Air Force and other space agencies to focus on inflatable technology as a reliable, inexpensive means of deploying large structures in orbit. Recent improvements in rigidization techniques make the use these inflatable structures feasible for a growing number of missions. For many of these missions, the primary design requirement is dimensional accuracy of the structure. Finite element analysis offers a means of predicting structural behavior in orbit. The analysis requires knowledge of external loads. This thesis examines the environmental disturbances which act upon large, orbiting structures. Calculations are made on …

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Rigex: Preliminary Design Of A Rigidized Inflatable Get-Away-Special Experiment, John D. Disebastian Iii Mar 2001

Rigex: Preliminary Design Of A Rigidized Inflatable Get-Away-Special Experiment, John D. Disebastian Iii

Theses and Dissertations

As space structures grow in size and complexity, their weight and cost increase considerably. The use of inflatable and rigidizable structures offers drastic improvements in all areas of spacecraft design. The goal of this experiment is to verify and validate ground testing of inflation and rigidization methods for inflatable space structures. The Rigidized Inflatable Get-Away-Special Experiment is an autonomous, self-contained space shuttle experiment that will inflate and rigidize several structures. After inflation, the experiment will perform a structural analysis by exciting the rigidized structures and collecting vibration data. A systems engineering approach is utilized to make design decisions based on …

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