Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992. / Includes bibliographical references (leaves 214-219). / by Dava Jean Newman. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student submitted PDF version of thesis. / Includes bibliographical references (p. 99-109). / Human physiological systems, especially the cardiovascular and musculo-skeletal systems, are well-known to decondition during spaceflight. Several countermeasures that are in use today have been rigorously developed over the decades to combat this deconditioning. However, these countermeasures are system specific and have proven to be only partially effective. Artificial gravity has been persistently discussed as a countermeasure that potentially has salutary effects on all physiological systems, though few ground-based studies have been performed in comparison to other countermeasures. The current analysis attempts to elucidate the effectiveness of artificial gravity by directly comparing results of previously published and unpublished deconditioning studies with those of more traditional, ground-based countermeasures (i.e. resistive exercise, aerobic exercise, lower body negative pressure, or some variation of these). Animal studies were also evaluated to supplement the knowledge base and to fill gaps in the human countermeasure literature. Designs of published studies, such as study duration, deconditioning paradigm, subject selection criteria, measurements taken, etc., were confounding variables; however, studies that had some measure of consistency between these variables were compared, although notable differences were cited in the analysis and discussion. Results indicate that for prolonged spaceflight an artificial gravity-based countermeasure may provide benefits equivalent to traditional countermeasures for the cardiovascular system. Too few comparable, human studies have been performed to draw any conclusions for the musculo-skeletal system, although animal studies show some positive results. Gaps in the current knowledge of artificial gravity are identified and guidance for future deconditioning studies is offered. Based on the results of this study, a comprehensive artificial gravity protocol is proposed and future research topics using this countermeasure are addressed. / by Justin David Kaderka. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Statement of responsibility on t.p. reads: 2nd Lieutenant Timothy J. Spaulding, USAF. / Includes bibliographical references (p. 139-142). / by Timothy J. Spaulding. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995. / Includes bibliographical references (leaves 141-151). / by Jason R. Maddocks. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Vita. / Includes bibliographical references (p. 66). / Computer aided design has allowed many design decisions to be made before hardware is built through "virtual" prototypes: computer simulations of an engineering design. To produce robust systems noise factors must also be considered (robust design), and should they should be considered as early as possible to reduce the impact of late design changes. Robust design on the computer requires a method to analyze the effects of uncertainty. Unfortunately, the most commonly used computer uncertainty analysis technique (Monte Carlo Simulation) requires thousands more simulation runs than needed if noises are ignored. For complex simulations such as Computational Fluid Dynamics, such a drastic increase in the time required to evaluate an engineering design may be probative early in the design process. Several uncertainty analysis techniques have been developed to decrease the number of simulation runs required, but none have supplanted Monte Carlo. Gaussian Quadrature (GQ) is presented here as a new option with significant benefits for many types of engineering problems. Advantages of GQ include: as few as 2*(number of noise factors) simulation runs required to estimate performance mean and variance, errors dependent only on the ability to approximate performance using polynomials for each noise factor, and the ability to estimate gradients without further simulation rims for use in computer aided optimization of mean or variance. The mathematically basis for GQ is discussed along with case studies demonstrating its utility. / by Geoffrey Scott Reber. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 79-83). / by Adam Theodore Hendriks. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1974. / Bibliography: p. 87-88. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 399-412). / System architecting is concerned with exploring the tradespace of early, high-level, system design decisions with a holistic, value-centric view. In the last few years, several tools and methods have been developed to support the system architecting process, focusing on the representation of an architecture as a set of interrelated decisions. These tools are best suited for applications that focus on breadth - i.e., enumerating a large and representative part of the architectural tradespace -as opposed to depth - modeling fidelity. However, some problems in system architecting require good modeling depth in order to provide useful results. In some cases, a very large body of expert knowledge is required. Current tools are not designed to handle such large bodies of knowledge because they lack scalability and traceability. As the size of the knowledge base increases, it becomes harder: a) to modify existing knowledge or add new knowledge; b) to trace the results of the tool to the model assumptions or knowledge base. This thesis proposes a holistic framework for architecture tradespace exploration of large complex systems that require a large body of expert knowledge. It physically separates the different bodies of knowledge required to solve a system architecting problem (i.e., knowledge about the domain, knowledge about the class of optimization or search problem, knowledge about the particular instance of problem) by using a rule-based expert system. It provides a generic population-based heuristic algorithm for search, which can be augmented with rules that encode knowledge about the domain, or about the optimization problem or class of problems. It identifies five major classes of system architecting problems from the perspective of optimization and search, and provides rules to enumerate architectures and search through the architectural tradespace of each class. A methodology is also defined to assess the value of an architecture using a rule-based approach. This methodology is based on a decomposition of stakeholder needs into requirements and a systematic comparison between system requirements and system capabilities using the rules engine. The framework is applied to the domain of Earth observing satellite systems (EOSS). Three EOSS are studied in depth: the NASA Earth Observing System, the NRC Earth Science Decadal Survey, and the Iridium GEOscan program. The ability of the framework to produce useful results is shown, and specific insights and recommendations are drawn. / by Daniel Selva Valero. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. / Includes bibliographical references (p. 117-118). / This thesis presents an approach to applying Systems Architecture methods to the development of large, complex, commercial systems, particularly offshore oil and gas productions systems. The aim of this research was to assist BP in the development of concepts for a multi-billion dollar oil production system, particularly in the unprecedented deep water arctic locations prone to seismic activity, as well as in existing fields that must be extended. The thesis demonstrates that these systems can be decomposed and analyzed using rigorous, methodical system architecture thinking that archives and represents tacit knowledge in several graphical frameworks. The thesis breaks the architecture of oil and gas production systems into two problems. The first problem is the architecture of one facility and one reservoir; a classic problem of assigning function to form. The second problem is the architecture of multiple facilities and multiple reservoirs; a classic problem of connection and routing. For the first problem, the production process is decomposed using Object Process Methodology (OPM). The decompositions provide a methodology to capture industry knowledge that is not always explicitly stated and provides a framework to explore the entire architectural design space. The thesis then describes how these decompositions of general and specific oil systems can be used to develop software models, using the meta-language tool OPN (Object Process Network), that successfully generate thousands of architecture concepts. This set of feasible architectures can be prioritized and better understood using metrics in an effort to down-select to a handful of preferred concepts to be carried forward for more detailed study and eventual development. / (cont.) The approach to the second problem demonstrates that even a modest set of facilities and reservoirs have a huge number of connection possibilities. This space of connection possibilities is large and daunting, and typically is not fully explored. To solve the second problem the thesis presents two models that generate all the possible connection schemes between elements in a system, in this case oil facilities and reservoirs. It is then demonstrated that these possibilities can be prioritized through the use of metrics. The thesis presents a method that can identify new concepts, highlight preferred sets of concepts, and underline patterns common to those concepts. This method increases the architects' overall knowledge and understanding of the entire space of possibilities, and ensures that all options are considered in the development of complex systems. / by James Keller. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 69-74). / Composites have seen an increasing role in aerospace structures that demand lightweight, strong, and stiff materials. Composites are attractive structural materials with outstanding mechanical and physical properties, as well as directional fabrication control and tailorability, though these advantages come with increased complexity and challenging failure modes. Matrix-rich regions at ply interfaces especially are susceptible to damage and matrix cracking, leading to delamination and a reduction of mechanical properties. Several manufacturing solutions such as stitching, z-pinning, and braiding have been developed by the aerospace industry to provide through-thickness reinforcement and improve interlaminar properties, though these improvements come with concomitant reductions in important in-plane properties. This thesis describes the design, manufacturing, and testing of woven composites with aligned carbon nanotubes (CNTs) integrated into the bulk composite, focusing here particularly on interlaminar reinforcement at ply interfaces. Implementing aligned CNTs takes advantage of their scale and superior specific stiffness and strength, with in-plane properties maintained while interlaminar properties are enhanced by the CNTs bridging across matrix-rich interfaces. Significant improvement in Mode I fracture toughness is observed experimentally with over 60% increase in both initiation and steady-state Mode I fracture toughnesses (steady-state toughness improves from 2.1 to 3.7 kJ/m² ). This enhancement is attributed to CNT crackbridging and pullout, in agreement with a first-order model, confirming the viability of CNTs to improve composite interlaminar properties. Future work to follow this thesis will focus on development of a vacuum-assisted infusion manufacturing process implementation of the 'fuzzy'-fiber reinforced nano-engineered composite architecture with alternate fiber and polymer systems, and exploring multifunctional applications of these materials. / by Sunny S. Wicks. / S.M.