Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons™

Open Access. Powered by Scholars. Published by Universities.®

Aerospace Engineering

Institution
Keyword
Publication Year
Publication
Publication Type
File Type

Articles 9451 - 9480 of 11118

Full-Text Articles in Engineering

Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick Mar 2005

Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick

Theses and Dissertations

A key area of study in air-breathing hydrocarbon-fueled scramjet combustors is the characterization of cavity-based fuel injection and flame holding. One issue concerns oscillatory disturbances caused by trapped vortices in the main flame holder cavity as a fuel-air mixing enhancement technique. Previous research demonstrates that oscillatory disturbances can be carried downstream via the shear layer and alter the oscillatory characteristics of a downstream cavity. This study investigates the mixing effectiveness of three upstream direct-fueled mixing cavities as well as the effect on the oscillatory behavior of the downstream combustion cavity by the upstream mixing cavity. The three upstream mixing cavities …

Go to article

The Use Of X-Ray Pulsars For Aiding Gps Satellite Orbit Determination, Dennis W. Woodfork Ii Mar 2005

The Use Of X-Ray Pulsars For Aiding Gps Satellite Orbit Determination, Dennis W. Woodfork Ii

Theses and Dissertations

This research proposes the use of an existing "signal of opportunity" - namely x-ray pulsars - to improve the accuracy and robustness of the GPS satellite and clock estimation algorithm. Improvement in satellite and clock accuracy results in a direct benefit to the user. A simulation has been developed to determine the effects of using x-ray pulsar measurements on the GPS Operational Control Segment. The epoch-specific position, velocity, and clock errors of all GPS satellites in the constellation were estimated using both pseudoranges and time-difference-of-arrival (TDOA) measurements from pulsars. The primary measure of accuracy is a constellation Signal-In-Space Range Error …

Go to article

Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch Mar 2005

Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch

Theses and Dissertations

While the use of relative orbit determination has reduced the difficulties inherent in tracking geosynchronous satellites that are in close proximity, the problem is often compounded by stationkeeping operations or unexpected maneuvers. If a maneuver occurs, observations will no longer fit predicted data, increasing the risk of misidentification and cross-tagging. The goal of this research was to develop a model that will estimate the magnitude, direction, and time of a suspected maneuver performed by a collocated satellite in geosynchronous orbit. Relative motion was modelled using Hill's equations, and least squares estimation was employed to create both a linear non-maneuver model …

Go to article

Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell Mar 2005

Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell

Theses and Dissertations

In response to Department of Defense (DoD) requirements for responsive and low-cost space access, this design study provides an objective empty weight analysis of potential reusable launch vehicle (RLV) configurations. Each two-stage-to-orbit (TSTO) RLV has a fixed payload requirement of 20,000 lbf to low Earth orbit. The propulsion systems considered in this study include pure rocket, pure turbine, rocket-based-combined-cycle (RBCC), and turbine-based-combined-cycle (TBCC). The hydrocarbon dual-mode scramjet (DMSJ) engines used in the RBCC and TBCC propulsion systems represent possible applications of the current research being performed in the U.S. Air Force HyTech program. Two sensitivity analyses were then performed on …

Go to article

A Numerical Analysis For Passive Attitude Stabilization Using A Tethered Balloon On A Gravity Gradient Satellite, Ernest Matias Maramba Mar 2005

A Numerical Analysis For Passive Attitude Stabilization Using A Tethered Balloon On A Gravity Gradient Satellite, Ernest Matias Maramba

Theses and Dissertations

This research effort analyzes the fundamental dynamics governing a satellite with a gravity gradient boom and a tethered balloon. Satellites that use gravity gradient booms for passive attitude control are characterized by undamped pitch oscillations and no roll control. The tethered balloon acts as a high drag device that accounts for the most drag on the satellite system. By attaching a drag device, the system resists rolling movements while also damping oscillations. This could potentially be a cost effective method for increasing satellite stabilization. The goal of this research is to model the dynamics and determine the feasibility of a …

Go to article

Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen Mar 2005

Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen

Theses and Dissertations

The purpose of this research is to investigate the effects of staging variables on Two-Stage-To-Orbit reusable launch vehicles, specifically, the question of what measurable factors play important roles in staging performance. Three different configurations (Rocket-Rocket, Turbojet-Rocket and Turbine Based Combined Cycle-Rocket) were considered. The software, Program to Optimize Simulated Trajectories (POST), was used to analyze these configurations. Vehicle coasting time, staging dynamic pressure and staging Mach number were all varied to determine their influence on the final payload.

Go to article

Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz Mar 2005

Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz

Theses and Dissertations

The purpose of this research was to develop a general, statistical model of order-to-delivery times for commercial satellite imagery. The research looked at the current four satellite providers with 3-meter or better imagers in the context of a generalized model of commercial imaging satellite operations. Existing methods use orbit analysis tools to determine the imaging time of a specified target based on defined satellite position and times, but can only develop shortest and longest times to an imaging opportunity. To address the general question of the time it takes to deliver an image for non-specific targets, this research develops a …

Go to article

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson Mar 2005

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson

Theses and Dissertations

Under certain conditions, high energy electron fluxes can increase over short periods of time in the outer radiation belt and diffuse to low altitudes. Sudden increases of high energy electron densities at low altitudes can drastically damage unsuspecting low-earth-orbit satellites. The progression of electron flux increases from a geosynchronous orbit to low-earth orbit during an electron event is somewhat unknown. If the beginning of electron flux increases at low-earth-orbits could be anticipated, warnings could be issued to space system operators allowing time to take proper measures to protect and minimize satellite damage extending satellite lifetimes and space mission operations. The …

Go to article

Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas Mar 2005

Stochastic Capability Models For Degrading Satellite Constellations, Cole W. Gulyas

Theses and Dissertations

This thesis proposes and analyzes a new measure of functional capability for satellite constellations that incorporates the instantaneous availability and mission effectiveness of individual satellites. The capability measure yields a continuous score between zero and one accounting for the degree to which the constellation meets operational requirements. The measure is computed from an average of satellite capabilities, composed of the product of the satellite's instantaneous availability and value score. Instantaneous availability is acquired by modeling the satellite degradation status as either a time-homogenous, continuous-time Markov chain (CTMC) if it possesses functions with exponential lifetime distributions, or as a time-homogenous, semi-Markov …

Go to article

An Approach For Optimizing The On-Orbit Servicing Architecture For The Space-Based Radar Constellation, Michael L. Mcconnell Mar 2005

An Approach For Optimizing The On-Orbit Servicing Architecture For The Space-Based Radar Constellation, Michael L. Mcconnell

Theses and Dissertations

Satellite systems, once operational, are essentially a consumable item with no capacity to maintain, repair, or upgrade them while on-orbit. In order to avoid having to replace costly space assets, the Defense Advanced Research Projects Agency (DARPA) and Air Force Space Command (AFSPC) are looking to developing programs to provide an on-orbit servicing capability for future satellite systems under development, such as the Space-Based Radar (SBR) system. DARPA and AFSPC are studying on-orbit servicing using the Orbital Express platform as part of an Analysis of Alternatives for the SBR program. Like their satellite clients, on-orbit servicing assets are expected to …

Go to article

Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser Mar 2005

Pulse Detonation Engine Thrust Tube Heat Exchanger For Flash Vaporization And Supercritical Heating Of Jp-8, Christen L. Miser

Theses and Dissertations

Research has shown that performance of liquid hydrocarbon fueled pulse detonation engines is limited by the time required to evaporate liquid fuel droplets within the mixture. Vaporization of liquid fuels prior to injection has been shown to decrease ignition times and also increases fuel efficiency; however, the size and efficiency of the vaporization system used are not feasible for use in future pulse detonation aircraft concepts. The purpose of this research is to harness the waste heat of pulse detonation engine thrust tubes to generate a steady-state, self-sustained flash vaporization and supercritical heating system using JP-8 as the working fluid …

Go to article

Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker Mar 2005

Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker

Theses and Dissertations

A global fourth-order solution method that incorporates compact differencing with Roe's approximate Riemann solver was investigated. This method was incorporated into a one-dimensional numerical simulation of the compressible Euler equations, and applied to a one-dimensional shock tube problem. The method was also extended to two dimensions, and applied to a two-dimensional shock tube problem and an advecting vortical structure problem on both rectilinear and curvilinear meshes. The results were compared to a third-order Roe scheme and a fourth-order compact difference scheme. An order of accuracy determination showed that it has an order of accuracy somewhere near fourth order, with absolute …

Go to article

A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan Mar 2005

A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan

Theses and Dissertations

This thesis further defines the position of greatest fuel savings benefit for the trail aircraft flying in a two-ship formation. The HASC95 vortex lattice code was used for the examination. Investigations of a similar formation of F-16 aircraft and a dissimilar formation of a lead KC-135 aircraft and a trail F-16 aircraft were conducted. The analyses determined the effects of varying airspeed on the optimal position. In addition, flight control surface deflections were taken into account during the analyses. Both investigations trimmed the aircraft in the yaw and roll axes to determine the optimal savings. The similar analysis was conducted …

Go to article

Full Capability Formation Flight Control, Ryan K. Osteroos Mar 2005

Full Capability Formation Flight Control, Ryan K. Osteroos

Theses and Dissertations

The subject of automatic formation flight control is of current interest to the development of Unmanned Aerial Vehicles (UAV). Previous control approaches have been refined in this work to allow more robust maneuvering and to include a fourth control parameter. The equations of motion for each aircraft as a point mass, expressed in a wind-axis coordinate system, are coupled into differential equations that model the two aircraft system dynamics. Control laws are developed that include proportional and integral action. Gains are determined based on formation performance. Lead maneuvers are simulated and the controller is gauged on its ability to maintain …

Go to article

Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt Mar 2005

Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt

Theses and Dissertations

This thesis encompasses a feasibility analysis of a parachute extracted generic precision guided munition from the cargo bay of a C-130 aircraft in flight. This analysis utilizes the USAF Beggar code and incorporates full physics effects as well as aerodynamic loading assuming an inviscid aircraft and viscous store for a time-accurate solution. Both an immediate and time varying application of the parachute force are utilized as well as two different ordnance body styles at zero and 5 degrees AOA with the store placed on centerline and offset in the cargo bay. The time accurate parachute model is based on empirical …

Go to article

Controlling Sideslip Angle To Reduce The Radar Exposure Of A Tactical, Rotary Winged Uav, Jonathan D. Bulseco Mar 2005

Controlling Sideslip Angle To Reduce The Radar Exposure Of A Tactical, Rotary Winged Uav, Jonathan D. Bulseco

Theses and Dissertations

This work investigates another way of contributing to the radar minimization solution for air vehicles in a threat environment. While much research has been conducted on structural solutions to radar exposure minimization, not much work has been done in the area of using control to continuously assess and present the smallest radar cross section of an air vehicle to oncoming threat radar systems by changing the aircraft's orientation. This work looks at the application of sideslip/beta angle feedback control of an unmanned helicopter to minimize radar cross section exposure in a hostile radar environment. A new way of controlling aircraft …

Go to article

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard Mar 2005

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard

Theses and Dissertations

The Global War on Terror with specific emphasis on the recent military operation in Afghanistan has shown the invaluable contribution that heavy lift helicopters bring to the combatant commander. However, the flight range, altitudes and lift capability required to operate effectively in such an austere environment are pushing the limits of these helicopters. In an attempt to increase the operational capability of the CH-53E, this study will investigate methods for maximizing tail rotor effectiveness at high gross weights and high altitudes. This thesis records an analytical study designed to investigate the intricacies of tail rotor design and, by the computational …

Go to article

Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith Mar 2005

Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith

Theses and Dissertations

Attitude determination of satellites is normally the job of inertial instruments, such as gyroscopes, or through sensing instruments, such as star trackers or Global Positioning Satellites (GPS). Satellite health monitoring systems watch and determine if the satellite deviates from its normal operating attitude orientation. Knowing the orientation of a satellite is essential in being able to control it in order to complete the satellite's designated mission. While there are a multitude of ways to determine a satellite's orientation, very little research has been done on determining if the attitude of a satellite can be determined directly from telemetry data of …

Go to article

Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin Mar 2005

Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin

Theses and Dissertations

This study investigated the minimum requirements to establish a satellite tracking system architecture for a microsatellite to rendezvous with a non-cooperative target satellite. A prototype optical tracking system was reviewed with emphasis on a proposed tactical employment that could be used by technologically unsophisticated state or non-state adversaries. With the tracking system architecture selected, simulated tracking data was processed with a Non-Linear Least Squares batch orbit estimation algorithm and a Bayes sequential orbit determination filter to update the target satellite's state vector.

Go to article

Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey Mar 2005

Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey

Theses and Dissertations

The near-space region of earth's atmosphere above 20 kilometers altitude is greatly underutilized. Lighter-than-air maneuvering vehicles, or airships, using the principle of buoyancy can take advantage of this region to become potential platforms for precision navigation, environmental monitoring, communication relays, missile warning, surveillance, and weapon delivery. These vehicles purportedly provide persistent coverage over large areas of the earth's surface at substantially lower costs than orbiting satellites. This study investigated the technical requirements to loiter an operational payload within this high altitude region using a lighter-than-air maneuvering platform. A parametric analysis was conducted to identify the critical technologies needed to achieve …

Go to article

Analysis Of Online-Delaunay Navigation For Time Sensitive Targeting, David Chow Mar 2005

Analysis Of Online-Delaunay Navigation For Time Sensitive Targeting, David Chow

Theses and Dissertations

Given the drawbacks of leaving time-sensitive targeting (TST) strictly to humans, there is value to the investigation of alternative approaches to TST operations that employ autonomous systems. This paper accomplishes five things. First, it proposes a short-hop abbreviated routing paradigm (SHARP) - based on Delaunay triangulations (DT), ad-hoc communication, and autonomous control - for recognizing and engaging TSTs that, in theory, will improve upon persistence, the volume of influence, autonomy, range, and situational awareness. Second, it analyzes the minimum timeframe need by a strike (weapons enabled) aircraft to navigate to the location of a TST under SHARP. Third, it shows …

Go to article

Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin Mar 2005

Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin

Theses and Dissertations

This study investigated the use of ballistic and Double-Dip'' aerobraking reentry to return the Space Maneuver Vehicle (SMV) from geotransfer orbit in no more than two atmosphere passes. Lift and drag accelerations were applied to the two-body problem when either of their magnitudes exceeded 1/1000 g. Lift and drag coefficients, along with the SMV model, were taken from Investigation of Atmospheric Reentry for the Space Maneuver Vehicle by Captain McNabb, AFIT/GA/ENY/04-M03. Target perigees were formulated using the two-body problem. The orbit from each target perigee was numerically integrated around a planar earth model using a fourth order Runge-Kutta method. Ballistic …

Go to article

Katysat: Kids Aren’T Too Young For Satellites, Robert J. Twiggs, Ben Yuan Feb 2005

Katysat: Kids Aren’T Too Young For Satellites, Robert J. Twiggs, Ben Yuan

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs and Bob Yuan titled "Katysat: Kids Aren’t Too Young for Satellites" from February 8, 2005.

Go to article

Modelling And Validation Of A Propellant Mixer For Controller Design, Hanz Richter, Enrique Barbieri, Fernando Figueroa Nasa Stennis Space Center Feb 2005

Modelling And Validation Of A Propellant Mixer For Controller Design, Hanz Richter, Enrique Barbieri, Fernando Figueroa Nasa Stennis Space Center

Mechanical Engineering Faculty Publications

A mixing chamber used in rocket engine testing at the NASA Stennis Space Center is modelled by a system of two nonlinear ordinary differential equations. The mixer is used to condition the thermodynamic properties of cryogenic liquid propellant by controlled injection of the same substance in the gaseous phase. The three inputs of the mixer are the positions of the valves regulating the liquid and gas flows at the inlets, and the position of the exit valve regulating the flow of conditioned propellant. Mixer operation during a test requires the regulation of its internal pressure, exit mass flow, and exit …

Go to article

Experimental Verification Of The Aerodynamics Of Stream Thrust Probes, Robert S. Hiers Iii, James R. Sirbaugh, Capt Barrett T. Mccann, Russell M. Cummings, Cadet Laura S. Luft, Cadet Dimitrios P. Grillos Jan 2005

Experimental Verification Of The Aerodynamics Of Stream Thrust Probes, Robert S. Hiers Iii, James R. Sirbaugh, Capt Barrett T. Mccann, Russell M. Cummings, Cadet Laura S. Luft, Cadet Dimitrios P. Grillos

Aerospace Engineering

Determining the local stream thrust (a vector quantity) from a measured pitot pressure (a scalar quantity) requires either knowledge of the flow direction or a probe shape that compensates for flow direction. This compensation ideally would make the measured pressure directly proportional to the component of momentum along the probe axis. The flow angle sensitivity required to resolve this component of momentum was previously determined theoretically. A proposed probe nose shape was analyzed using computational fluid dynamics (CFD) and was found to produce a flow angle sensitivity close to the required sensitivity. In the current work, the proposed nose shape …

Go to article

Computational Aerodynamics Goes To School: A Course In Cfd For Undergraduate Students, Russell M. Cummings, Scott A. Morton Jan 2005

Computational Aerodynamics Goes To School: A Course In Cfd For Undergraduate Students, Russell M. Cummings, Scott A. Morton

Aerospace Engineering

As aerodynamics education has evolved over the past decades, a slow transition from important analytic methods to increasingly powerful computational methods has taken place. While a basic understanding of theoretical aerodynamics should always be included in coursework, the realities of modern design practices make the usefulness of the traditional approach less and less practical. A new undergraduate course in computational aerodynamics has been developed that attempts to give students experience with the modern computational tools of aerodynamics, primarily from an applications perspective. While introducing students to the important computational topics of accuracy and stability, the course stresses the practical tools …

Go to article

Des Turbulence Modeling On The C-130 Comparison Between Computational And Experimental Results, Malcom P. Claus, Scott A. Morton, Russell M. Cummings, Yannick Bury Jan 2005

Des Turbulence Modeling On The C-130 Comparison Between Computational And Experimental Results, Malcom P. Claus, Scott A. Morton, Russell M. Cummings, Yannick Bury

Aerospace Engineering

This paper represents the results from the initial phase of a research program to determine the flow characteristics of the C-130 Hercules transport aircraft. The initial phase of the program consists of evaluation and comparison of the flow-field obtained from flow visualization methods. Specifically CFD (Computational Fluid Dynamics) results are compared with experimental Hot Wire results produced by wind tunnel tests on the C-130 in clean configuration. This paper outlines the results to date and provides a description of further work. The CFD element of this research features the use of Detached Eddy Simulation (DES) in order to extend its …

Go to article

Deformation Of Unstructured Viscous Grids, Denis B. Kholodar, Scott A. Morton, Russell M. Cummings Jan 2005

Deformation Of Unstructured Viscous Grids, Denis B. Kholodar, Scott A. Morton, Russell M. Cummings

Aerospace Engineering

A mesh deformation algorithm for unstructured grids is presented. It is designed for high Reynolds number flow problems. Such grids are employed in aerodynamic and aeroelastic studies of wings or complete aircraft configurations in flows where the viscous effects are important. Given a surface deformation, the method efficiently recalculates new locations of high aspect ratio cells that make up the viscous layers of the grid and then deforms the inviscid part of the grid using an established method based on a torsional spring analogy technique. Results are presented for monitoring the deterioration of the quality of the grid during subsequent …

Go to article

Robust Control Techniques For State Tracking In The Presence Of Variable Time Delays, Jarrett Goodell, Marc Compere, Miguel Simon, Wilford Smith, Ronnie Wright, Mark Brudnak Jan 2005

Robust Control Techniques For State Tracking In The Presence Of Variable Time Delays, Jarrett Goodell, Marc Compere, Miguel Simon, Wilford Smith, Ronnie Wright, Mark Brudnak

Publications

In this paper, a distributed driver-in-the-Ioop and hardware-in-the-Ioop simulator is described with a driver on a motion simulator at the U.S. Army TARDEC Ground Vehicle Simulation Laboratory (GVSL). Realistic power system response is achieved by linking the driver in the GVSL with a full-sized hybrid electric power system located 2,450 miles away at the TARDEC Power and Energy Systems Integration Laboratory (P&E SIL), which is developed and maintained by Science Applications International Corporation (SAIC). The goal is to close the loop between the GVSL and P&E SIL over the Internet to provide a realistic driving experience in addition to realistic …

Go to article

Engineering Tools For Variable Stiffness Vibration Suppression And Isolation, Michael F. Winthrop Jan 2005

Engineering Tools For Variable Stiffness Vibration Suppression And Isolation, Michael F. Winthrop

Theses and Dissertations

With the advent of smart materials, the concept of semi-active control or dynamic control of stiffness and/or damping for vibration control of structures has become practical and has seen limited use. Semi-active control has advantages over active and passive control methods, since it provides almost as much capability as active control while requiring much less power. Its main disadvantage is its inherent nonlinearity, greatly complicating engineering design. The purpose of this research is to extend semi-active control vibration isolation tools and methods considering space launch and on-orbit systems.

Go to article

First Prev Next Last