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Master's Projects

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search.filters.applied.f.advisor: Braun, Robert D. × End date: 2009 × Start date: 2009 × search.filters.applied.f.isOrgUnitOfPublicationTitle: Daniel Guggenheim School of Aerospace Engineering × search.filters.applied.f.isSeriesOfPublicationTitle: Master's Projects ×

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Analysis of Human-System Interaction For Landing Point Redesignation

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.

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Fully-Propulsive Mars Atmospheric Transit Strategies for High-Mass Missions

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

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Experimental Determination of Material Properties for Inflatable Aeroshell Structures

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.

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Computational Fluid Dynamics Validation of a Single, Central Nozzle Supersonic Retropropulsion Configuration

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.

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