Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998. / Includes bibliographical references (p. 123). / by Alex Yen Hung Lee. / M.S.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 109-113). / Ion electrospray propulsion devices rely on the transportation of ionic liquid propellant to emission regions where ions are extracted at high velocities. One such method involves the use of porous substrates to passively transport propellant towards conically shaped features of the same porous material. Historically, the methods of fabricating such small features (~150[mu]m tapered to ~20[mu]m over a height of ~150[mu]m) are subtractive, in that material is selectively removed from a substrate to reveal the desired features. The limitations of these processes include but are not limited to: process repeatability, complex operation, material selection limited by the process, serial operation, and long/expensive fabrication time. With an understanding of these limitations, the goal of this research is to explore new materials and processes to identify candidates for electrospray propulsion applications. In particular, processes that allow for additive tip manufacturing, parallel processing, and uniformity in addition to materials that allow for variable and uniform porosity have been studied. As part of this research, the sol-gel and freeze casting methods for producing porous materials were characterized to better identify feasibility for electrospray propulsion. Characterization includes the feasibility of molding porous tips directly onto substrates. As a result of this research, porous substrates from different materials and varying pore sizes were fabricated via both methods. A porous emitter tip prepared by the sol-gel method was fired and shown to extract current at levels exceeding the state of the art. Finally, a new process, entitled sol freeze, was invented that utilizes the benefits of both the sol-gel and freeze casting methods. Additionally, porous material research for the purpose of contact electrodes was investigated. In order to lengthen the electrochemical window during electrospray thruster firing, a desire for conductive porous materials with large internal surface area was discovered. Carbon xerogel electrodes with embedded wires were designed and fabricated through this research. Specifically, carbon xerogel electrodes with internal surface areas on the order of 500 m² /g were fabricated and tested. / by Steven Mark Arestie. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1984. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Includes bibliographical references. / by Peter Frederick Lorber. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991. / Includes bibliographical references (leaves 140-145). / by Reza Shokrollah-Abhari. / 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. 113-114). / The increasing heat output of modern electronics requires concomitant advances in heat sinking technology: reductions in thermal resistance and required pumping power are necessary. This research covers the development of a novel type of air-cooled heat sink, in particular the air flow through such a heat sink. The research is carried out through theory, computation, and experiment. A nondimensionalization is carried out to determine scaling laws for such heat sinks. Correlations are provided for the prediction of performance of similar heat sinks. Using these scaling laws a heat sink with an air flow volume of 35 cm³ is described with a convection thermal resistance of 0.43 KW-1 for a pumping power of 0.72 W. / by Jonathan Michael Allison. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1974. / Vita. / Includes bibliographical references (leaves 247-253). / by Charles C. Ormsby. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 147-150). / Exploration of new environments is often conducted in search of some phenomenon of interest. Examples include the search for extreme forms of life in the deep ocean or under the ice on Europa, or localizing resource deposits on the ocean floor. Exploration of all these environments is dangerous because of uncertainty in the environment and poorly characterized disturbances that can damage the exploration vehicle. Autonomous vehicles allows exploration in those environments where it is too dangerous or expensive to send a human-operated craft. Autonomous exploration has been well-studied from the perspective of information maximization, but information gathering has not been considered with the intention of localizing specific phenomena, nor has it been considered in environments where exploration can threaten the vehicle. This thesis addresses both challenges by introducing Risk-Bounded Adaptive Search, which maximizes the number of phenomena located while bounding the probability of mission failure by a user-defined threshold. The first innovation of this thesis is the development of a new information measure that focuses on locating instances of a specific phenomenon. Search for phenomena of interest is framed as a discrete space Markov Decision Process that is solved using forward search and receding horizon planning, with a reward function specified as the information gained about unobserved instances of the phenomenon of interest from measurements. Using this reward function, the number of phenomena located is increased compared to maximizing conventional information, as it steers the agent towards locations where phenomena are thought to exist so they are not bypassed when the belief state is high. The second innovation is a method of applying risk bounds as a function of the expected information gain of a policy over a planning horizon, in contrast to a static bound. This 'Performance-Guided Risk Bounding' system allows an MDP policy to be found that is slightly suboptimal if it has a substantially lower probability of failure, or accept more risk if the reward payoff is large. When applied to information gathering, it allows an autonomous agent to capitalize on high risk and high reward opportunities when they are seen, instead of ignoring them in an effort to conserve risk for the future, when it is ultimately less useful. Since interesting phenomena are often found in risky locations, the ability to take more risk when it is worthwhile results in more phenomena found overall. Finally, a modification to Monte Carlo Tree Search is introduced that implements Performance-Guided Risk Bounding. This allows Risk-Bounded Adaptive Search to be planned in an anytime manner. The output policy is limited to the states that are explored, but risk bounds that scale with the expected information gained over the explored states in the policy are still applied. The resulting policies are shown to converge to the results of forward search, and a few percent differences in phenomena found with an order of magnitude reduction in planning time. / by Benjamin James Ayton. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013. / This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from department-submitted PDF version of thesis. / Includes bibliographical references (p. 141-153). / Most current methods for 802.11-based indoor localization depend on either simple radio propagation models or exhaustive, costly surveys conducted by skilled technicians. These methods are not satisfactory for long-term, large-scale positioning of mobile devices in practice. This thesis describes two approaches to the indoor localization problem, which we formulate as discovering user locations using place and motion signatures. The first approach, organic indoor localization, combines the idea of crowd-sourcing, encouraging end-users to contribute place signatures (location RF fingerprints) in an organic fashion. Based on prior work on organic localization systems, we study algorithmic challenges associated with structuring such organic location systems: the design of localization algorithms suitable for organic localization systems, qualitative and quantitative control of user inputs to "grow" an organic system from the very beginning, and handling the device heterogeneity problem, in which different devices have different RF characteristics. In the second approach, motion compatibility-based indoor localization, we formulate the localization problem as trajectory matching of a user motion sequence onto a prior map. Our method estimates indoor location with respect to a prior map consisting of a set of 2D floor plans linked through horizontal and vertical adjacencies. To enable the localization system, we present a motion classification algorithm that estimates user motions from the sensors available in commodity mobile devices. We also present a route network generation method, which constructs a graph representation of all user routes from legacy floor plans. Given these inputs, our HMM-based trajectory matching algorithm recovers user trajectories. The main contribution is the notion of path compatibility, in which the sequential output of a classifier of inertial data producing low-level motion estimates (standing still, walking straight, going upstairs, turning left etc.) is examined for metric/topological/semantic agreement with the prior map. We show that, using only proprioceptive data of the quality typically available on a modern smartphone, our method can recover the user's location to within several meters in one to two minutes after a "cold start." / by Jun-geun Park. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 105-108). / by Seung H. Chung. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 71-76). / City planners use information about a city's vegetation, urban morphology, and land-use to make decisions. The availability of high-resolution imagery is now expanding the type of information that can be used for planning as well as for understanding urbanization dynamics. This research uses very high resolution orthoimagery with three bands to obtain information about specific urban structures, such as roads and pavement, buildings, and solar panels, as well as non-impervious surface areas of vegetation and water. The maximum likelihood classifier (MLC) was used for the analysis of the images, and geographical information system (GIS) techniques were used to extract features. Two case studies were done for the cities of Phoenix, Arizona for the years 2004, 2006, 2008, and 2012 and for Seattle, Washington for 2002, 2005, and 2009. Results indicate that the area of buildings and the number buildings with solar panels have increased while the area of vegetation has increased for both Phoenix.and Seattle. The area of water has decreased for Seattle while the increase in water for Phoenix could suggest that more people are installing pools. The length of roads increases slightly for Seattle but decreases for Phoenix, a potential result of parking lots being converted into parking garages. The quantitative trends in the infrastructure were then compared to power law relationships between population and urban growing and scaling indicators. / by Lisa Yang. / S.M.