Master of Science in Aerospace Engineering

Series

Master of Science in Aerospace Engineering

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https://hdl.handle.net/1853/73271

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Degree Series

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Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

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Now showing 1 - 10 of 141

Two studies in statistical data analysis for the space industry: cyclicality in the industry, and comparative satellite reliability analysis

(Georgia Institute of Technology, 2009-12) Hiriart, Thomas

This thesis brings statistical analyses techniques to bear on data derived from an extensive database of satellite launches and on-orbit anomalies and failures. The data collected is analyzed from two different perspectives and addresses, in two separate studies, two research objectives. The first study proposes to identify trends and cyclical patterns in the space industry, and to forecast the volume of launches for the next few years. Satellites have been rightfully described as the lifeblood of the entire space industry and the number of satellites ordered or launched per year is an important defining metric of the industry's level of activity. The structure of the space industry, its financial health and its workforce retention and development is dependent on the volume of satellites contracted. As such, trends and variability in this volume have significant strategic impact on the space industry. Over the past 40+ years, hundreds of satellites have been launched every year. Thus, an important data set is available for time series analysis and identification of trends and cycles in the various markets of the space industry. For the purpose of this first study, we collected data for over 6,000 satellites launched since 1960 on a yearly basis. We separated the satellites into three broad segments: 1) defense and intelligence satellites, 2) science satellites, and 3) commercial satellites. Several techniques are available for the analysis of time series data, both in the time domain and in the frequency domain. In this first study, we conducted spectral analysis of the time series for each of the three satellite populations and identified cycles contained in the data. In addition, once harmonic models were derived and fitted to the data, we built forecasting models of satellite launch volumes in the different market segments for the next few years. The potential implications of the results are discussed as a number of strategic matters for the space industry are contingent on the predictions or forecast of the volume of satellites contracted (the example of the U.S. auto industry is a solemn reminder of such possible strategic issues). The second study uses the previously collected launch data, confined to Earth-orbiting satellites launched between 1990 and 2008, and expanded with the failure information and retirement of each satellite to conduct a comparative analysis of satellite reliability in GEO, LEO, and MEO orbits. Reliability has long been recognized as an essential consideration in the design of space systems. However, there is limited statistical analysis of satellite reliability based on actual flight data. The objective of this second study is to conduct nonparametric satellite reliability analysis, with orbit type as a covariate, and to explore appropriate parametric fits (Weibull, lognormal, and mixture distributions). The results indicate for example that differences exist between the failure behaviors of satellites in different orbits, or that satellite infant mortality exists or dominates more clearly in a particular orbit type. The findings can be useful to satellite manufacturers as they would provide an empirical basis for reviewing and adjusting satellite testing and burn-in procedures.
Finding a representative day for simulation analyses

(Georgia Institute of Technology, 2009-11-23) Watson, Jebulan Ryan

Many models exist in the aerospace industry that attempt to replicate the National Airspace System (NAS). The complexity of the NAS makes it a system that can be modeled in a variety of ways. While some NAS models are very detailed and take many factors into account, runtime of these simulations can be on the magnitude of hours (to simulate a single day). Other models forgo details in order to decrease the runtime of their simulation. Most models are capable of simulating a 24 hour period in the NAS. An analysis of an entire year would mean running the simulation for every day in the year, which would result in a long run time. The following thesis work presents a tool that is capable of giving the user a day that can be used in a simulation and will produce results similar to simulating the entire year. Taking in parameters chosen by the user, the tool outputs a single day, multiple days, or a composite day (based on percentages of days). Statistical methods were then used to compare each day to the overall year. On top of finding a single representative day, the ability to find a composite day was added. After implementing a brute force search technique to find the composite day, the long runtime was deemed inconvenient for the user. To solve this problem, a heuristic search method was created that would search the solution space in a short time and still output a composite day that represented the year. With a short runtime, the user would be able to run the program multiple times. Once the heuristic method was implemented, it was found that it performed well enough to make it an option for the user to choose. The final version of this tool was used to find a representative day and the result was used in comparison with output data from a NAS simulation model. Because the tool found the representative day based on historical data, it could be used to validate the effectiveness of the simulation model. The following thesis will go into detail about how this tool, the Representative Day Finder, was created.
Exploring the F6 Fractionated Spacecraft Trade Space with GT-FAST

(Georgia Institute of Technology, 2009-11-12) Lafleur, Jarret M.

Released in July 2007, the Broad Agency Announcement for DARPA’s System F6 outlined goals for flight demonstration of an architecture in which the functionality of a traditional monolithic satellite is fulfilled with a fractionated cluster of free-flying, wirelessly interconnected modules. Given the large number of possible architectural options, two challenges facing systems analysis of F6 are (1) the ability to enumerate the many potential candidate fractionated architectures and (2) the ability to analyze and quantify the cost and benefits of each architecture. This paper applies the recently developed Georgia Tech F6 Architecture Synthesis Tool (GT-FAST) to the exploration of the System F6 trade space. GT-FAST is described in detail, after which a combinatorial analysis of the architectural trade space is presented to provide a theoretical contribution applicable to future analyses clearly showing the explosion of the trade space as the number of fractionatable components increases. Several output metrics of interest are defined, and Pareto fronts are used to visualize the trade space. The first set of these Pareto fronts allows direct visualization of one output against another, and the second set presents cost plotted against a Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) score aggregating performance objectives. These techniques allow for the identification of a handful of Pareto-optimal designs from an original pool of over 3,000 potential designs. Conclusions are drawn on salient features of the resulting Pareto fronts, important competing objectives which have been captured, and the potential suitability of a particularly interesting design designated PF0248. A variety of potential avenues for future work are also identified.
Dynamics of longitudinally forced bluff body flames with varying dilatation ratios

(Georgia Institute of Technology, 2009-11-09) Plaks, Dmitriy Vital

This thesis focuses on experimentally measuring the response of varying dilatation ratio bluff body flames under harmonic excitation. Such flames are often encountered in jet engine afterburners and are susceptible to combustion instabilities. Previous work has been done modeling such flames, however, only limited experimental data has been obtained at these conditions and is the motivation for this thesis. The focus of this work is to measure the transfer function of longitudinally forced, varying dilatation ratio bluff body flames. The transfer function is obtained by measuring flame position and flame luminosity fluctuations at the forcing frequency. Specifically, the amplitude and phase of the fluctuations are characterized as a function of flow velocity, axial location, and perturbation amplitude. These measurements are also compared to available theoretical predictions, showing that qualitative measured trends are consistent with theory. In addition, a detailed quantitative comparison is performed at one condition, showing good agreement between predictions and measurements in the near and mid-field of the flame response. However, agreement is not obtained in the far-field, indicating that continued theoretical work is needed to understand the flame response characteristics in this region.
Investigation of a stop-fold tiltrotor

(Georgia Institute of Technology, 2009-07-09) Bosworth, Jeff

In 1967 the US Air Force solicited proposals for ``low-disc-loading [Vertical Takeoff and Landing] configurations suitable for high speed flight.' Bell Helicopter elected to respond with a proposal after initial analysis on configurations including a stopped edgewise disc and a trail rotor. They concluded that a folding proprotor design would best meet the requirements laid forth. Initial analysis work began on this folding proprotor (stop-fold) design in the same year and concluded in 1972 with a full scale 25 foot diameter pylon and rotor assembly wind tunnel test at the NASA-Ames Large Scale Wind Tunnel. The project was concluded at this point and never resulted in a production or research aircraft. The original proposed stop-fold tiltrotor design by Bell Helicopter allowed for vertical takeoff and landing, a transition sequence rotating the pylon rotor assembly from helicopter to airplane mode, a conversion sequence during which the rotor stopped and blades folded along the pylon, and a transition from prop thrust to auxiliary jet engine power while the rotor was being stopped. This configuration effectively removes the high-speed restraints typical of a prop-driven aircraft and instead opens a flight envelope comparable to a fixed-wing jet. This project entails both the simulation and basic analysis of the stop-fold concept with special attention to frequency responses and potential coupling between modes.
Analysis of Human-System Interaction For Landing Point Redesignation

(Georgia Institute of Technology, 2009-05-26) Chua, Zarrin K.

Despite two decades of manned spaceflight development, the recent thrust for increased human exploration places significant demands on current technology. More information is needed in understanding how human control affects mission performance and most importantly, how to design support systems that aid in human-system collaboration. This information on the general human-system relationship is difficult to ascertain due to the limitations of human performance modeling and the breadth of human actions in a particular situation. However, cognitive performance can be modeled in limited, well-defined scenarios of human control and the resulting analysis on these models can provide preliminary information with regard to the human-system relationship. This investigation examines the critical case of lunar Landing Point Redesignation (LPR) as a case study to further knowledge of the human-system relationship and to improve the design of support systems to assist astronauts during this task. To achieve these objectives, both theoretical and experimental practices are used to develop a task execution time model and subsequently inform this model with observations of simulated astronaut behavior. The experimental results have established several major conclusions. First, the method of LPR task execution is not necessarily linear, with tasks performed in parallel or neglected entirely. Second, the time to complete the LPR task and the overall accuracy of the landing site is generally robust to environmental and scenario factors such as number of points of interest, number of identifiable terrain markers, and terrain expectancy. Lastly, the examination of the overall tradespace between the three main criteria of fuel consumption, proximity to points of interest, and safety when comparing human and analogous automated behavior illustrates that humans outperform automation in missions where safety and nearness to points of interest are the main objectives, but perform poorly when fuel is the most critical measure of performance. Improvements to the fidelity of the model can be made by transgressing from a deterministic to probablistic model and incorporating such a model into a six degree-of-freedom trajectory simulator. This paper briefly summarizes recent technological developments for manned spaceflight, reviews previous and current efforts in implementing LPR, examines the experimental setup necessary to test the LPR task modeling, discusses the significance of findings from the experiment, and also comments on the extensibility of the LPR task and experiment results to human Mars spaceflight.
Experimental Determination of Material Properties for Inflatable Aeroshell Structures

(Georgia Institute of Technology, 2009-05-26) Hutchings, Allison L.

As part of a deployable aeroshell development effort, system design, materials evaluation, and analysis methods are under investigation. One specific objective is to validate finite element analysis techniques used to predict the deformation and stress fields of aeroshell inflatable structures under aerodynamic loads. In this paper, we discuss the results of an experimental mechanics study conducted to ensure that the material inputs to the finite element models accurately predict the load elongation characteristics of the coated woven fabric materials used in deployable aeroshells. These coated woven fabrics exhibit some unique behaviors under load that make the establishment of a common set of test protocols difficult. The stiffness of a woven fabric material will be influenced by its biaxial load state. Uniaxial strip tensile testing although quick and informative may not accurately capture the needed structural model inputs. Woven fabrics, when loaded in the bias direction relative to the warp and fill axes, have a resultant stiffness that is quite low as compared with the warp and fill directional stiffness. We evaluate the experimental results from two load versus elongation test devices. Test method recommendations are made based on the relevance and accuracy of these devices. Experimental work is conducted on a sample set of materials, consisting of four fabrics of varying stiffness and strength. The building blocks of a mechanical property database for future aeroshell design efforts are constructed.
Computational Fluid Dynamics Validation of a Single, Central Nozzle Supersonic Retropropulsion Configuration

(Georgia Institute of Technology, 2009-05) Cordell, Christopher E., Jr.

Supersonic retropropulsion provides an option that can potentially enhance drag characteristics of high mass entry, descent, and landing systems. Preliminary flow field and vehicle aerodynamic characteristics have been found in wind tunnel experiments; however, these only cover specific vehicle configurations and freestream conditions. In order to generate useful aerodynamic data that can be used in a trajectory simulation, a quicker method of determining vehicle aerodynamics is required to model supersonic retropropulsion effects. Using computational fluid dynamics, flow solutions can be determined which yield the desired aerodynamic information. The flow field generated in a supersonic retropropulsion scenario is complex, which increases the difficulty of generating an accurate computational solution. By validating the computational solutions against available wind tunnel data, the confidence in accurately capturing the flow field is increased, and methods to reduce the time required to generate a solution can be determined. Fun3D, a computational fluid dynamics code developed at NASA Langley Research Center, is capable of modeling the flow field structure and vehicle aerodynamics seen in previous wind tunnel experiments. Axial locations of the jet terminal shock, stagnation point, and bow shock show the same trends which were found in the wind tunnel, and the surface pressure distribution and drag coefficient are also consistent with available data. The flow solution is dependent on the computational grid used, where a grid which is too coarse does not resolve all of the flow features correctly. Refining the grid will increase the fidelity of the solution; however, the calculations will take longer if there are more cells in the computational grid.
Fully-Propulsive Mars Atmospheric Transit Strategies for High-Mass Missions

(Georgia Institute of Technology, 2009-04-29) Marsh, Christopher L.

A systems analysis focused on the use of propulsion during the EDL sequence at Mars for high-payload missions is presented. Trajectory simulation and mass sizing are performed to analyze the feasibility of a fully-propulsive descent. A heat rate boundary and associated control law are developed in an effort to limit the heating loads placed on the vehicle. Analysis is performed to explore the full-propulsive EDL strategy’s sensitivity to the vehicle’s propulsive capabilities and aero-propulsive and vehicle models. The EDL strategy is examined for ranges of initial masses and heat rate constraints, outlining an envelope of feasibility. The proposed architecture is compared against EDL systems in which significant aeroassist technology is employed. With this information, an overview of the impact of a fully-propulsive EDL system on spacecraft design and functionality is offered
Resonance Hopping Transfers Between Moon Science Orbits

(Georgia Institute of Technology, 2009-04-22) Brinckerhoff, Adam T.

Resonance hopping transfers between science orbits around two circular, coplanar moons of a common planet are designed using series of alternating V-infinity leveraging maneuvers and zero-point patched conic gravity assists. When this technique is combined with an efficient global search based on Bellman’s Principle, the end result is an exhaustive set of fuel and time optimal trajectories between the two moons in question. The associated Pareto front of solutions represents the classic fuel versus flight time trade study sought in preliminary mission design. Example numerical results are produced for orbital transfers between scientifically interesting moons in the Jovian system due to NASA and ESA’s particular interest in executing future tour missions in this environment. Finally, resonant transfers between neighboring pairs of moons are patched together to obtain fuel and flight time estimates for a full Jovian system tour between intermediate previously discovered circulating eccentric science orbits. Results from this fast, preliminary design procedure are intended to serve as useful starting points for higher fidelity multi-body mission design. In general, the resonant hopping design approach and the associated design procedure are found to be most relevant for missions with short flight time requirements.