Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992. / Includes bibliographical references (leaves 82-83). / by John-Paul B. Clarke. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaves 112-113). / by Patrick V. Hagelauer. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013. / This thesis was scanned as part of an electronic thesis pilot project. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 107-109). / A low power, Hall-effect type plasma thruster known as the MIT-Cylindrical Cusped- Field Thruster (MIT-CCFT) has been developed and simulated using a fully-kinetic plasma model, the Plasma Thruster particle-in-cell (PTpic) model. Similar to the Diverging Cusped-Field Thruster (DCFT) previously developed in the Massachusetts Institute of Technology Space Propulsion Laboratory, this thruster uses cusped magnetic fields aligned in alternating polarity in order to confine electrons, thus slowing their flow to the anode and readily ionizing neutral gas, which is then electrostatically accelerated by the anode. The design methodology for the CCFT will be discussed, with significant emphasis on the effects of magnetic topology on thruster performance. In particular, while the topology is similar to that of the DCFT in that it also confines the discharge plasma away from the channel walls to limit wall erosion, the CCFT was also designed to minimize plume divergence. To predict the CCFTs performance and plasma dynamics, the design has been modeled and simulated with PTpic. From multiple simulations of the CCFT under different operating conditions, the thruster performance and plume characteristics were found and compared to past simulations of the DCFT. Specifically, the predicted nominal total efficiency ranged from 25 to 35 percent, providing 4-9 mN of thrust at a fixed xenon mass flow rate of 4.0 sccm, whilst consuming 90-400 W of power and with a corresponding nominal specific impulse of 1050 to 1800 s. Preliminary observations of the particle moments suggest that the magnetic confinement of the plasma isolates erosion of the channel walls of the discharge chamber to the ring cusps locations. In addition, in contrast to the DCFT, the CCFT does not have a hollow conic plume; instead, its beam profile is similar to that of traditional Hall-effect thrusters. To supplement the efforts for optimizing longevity of the cusped-field thruster, a new diagnostic tool for erosion studies, novel to the electric propulsion community, has been implemented and has undergone preliminary validation. Ion beam analysis (IBA) allows for in-situ measurements of both composition and profile of the surfaces of the discharge region of a plasma thruster during operation. The technique has been independently tested on individual coupons with the use of the Cambridge Laboratory for Accelerator Study of Surfaces (CLASS) tandem ion accelerator. The coupons, which are composed of materials with known sputtering rates and/or are commonly used as insulator material, are exposed to helicon-generated plasma to simulate the sputtering/re-deposition found in thruster discharge region. Through comparison of ion beam analysis traces taken before and after plasma exposure, the effective erosion rates were found and validated against simulated results. / by Anthony Pang. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 105-110). / We study the flow generated when a handheld fan is waved. This fluid-structure interaction problem is investigated through precision experiments, using an oscillating semi-circular elastic plate as a reduced analog model. The aerodynamic performance of the fans is systematically characterized for a variety of geometric and material parameters, as well as the amplitude of the periodic driving. We demonstrate that the bending stiffness of the structure can be tuned to maximize the output of the generated airflow, while simultaneously minimizing the input power. A design guideline is established for this optimal conditions based on matching the driving and the natural frequencies of the plate. Closer to the handheld fans, we then consider a discrete analog model comprising an array of overlapping strips. Unlike homogeneous plates, these discrete designs deform passively into shapes with finite Gaussian curvature and further enhance the generated flow. Finally, we explored the effect of corrugation on the flapping plate and found that the fan employs the interesting mechanism of reversible buckling to simultaneously increase the velocity of the flow and reduce the load. / by Grace Swee See Goon. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 153-157). / (cont.) of environmental disturbances and measurement noise.The product of this thesis is a robust planning system that is tolerant of the types of uncertainty experienced by real aircraft. This robustness has been demonstrated by more than 20 successful flights on a fully automated UAV testbed. / This thesis presents the development and testing of a unique testbed consisting of a fleet of eight unmanned aerial vehicles (UAVs) that was designed as a platform for evaluating coordination and control algorithms. A hierarchical configuration of task assignment, trajectory design, and low-level, waypoint following, are used in a receding horizon framework to control the UAV system. Future UAV teams will have to autonomously demonstrate cooperative behaviors in dynamic and uncertain environments, and this testbed can be used to compare various control approaches to accomplish these coordinated missions. Flight demonstrations are made utilizing real-time mixed-integer linear programming techniques, exercising the algorithms in realistic environments with real-world disturbances. Large disturbance sources, computational delay and measurementnoise all represent significant error sources that reduce the ability of UAV teams to interact in a coordinated fashion by increasing uncertainty on higher planning levels. This thesis develops a method that explicitly accounts for this uncertainty by including feedback loops on the task assignment and trajectory design algorithms to prescribe added robustness for the uncertainty at each stage. This approach takes into account low level controller saturation limits that might cause infeasibilities in the plans created at the higher levels of the planning system. Detailed and realistic simulation environments are useful for large-scale multi-vehicle simulations, particularly when logistics prevent flight testing on that scale. This thesis validates one such hardware-in-the-loop simulation environment through the comparison of models obtained from experimentally collected flight data and detailed modeling / by Ellis T. King. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references (p. 107-110). / Technical capabilities for improved communication, surveillance, and navigation (CNS) over the oceans are currently available. However, all aircraft operators will not equip simultaneously because of the high costs required. Consequently, as these CNS systems are integrated into oceanic air transportation architecture, the controller will have to manage the current low frequency surveillance and communication paths in parallel with future enhanced CNS. The cognitive effects of the mixed equipage environment were studied through field studies and experimental analysis. Field studies at New York Center, Oakland Center, and Reykjavik Center in Iceland were conducted to identify human-centered systems issues with the emerging mixed equipage environment. Findings show that the integration of varying communication latencies influences controller planning. The fusion of multiple surveillance sources and the application of varying separation standards based on equipage was found to limit the cognitive processes of the controller. These limitations may constrain the controller from providing full efficiency benefits to aircraft equipped with the highest capabilities, which would reduce the incentives for equipping. Experimental analysis was conducted to further study the integration of high and low frequency surveillance and the use of varying separation standards. Results show that workload increases and situation awareness degrades in the mixed surveillance environment, compared to segregated operations. The results also demonstrate that efficiency benefits attained by equipped aircraft are in fact limited in the mixed equipage environment. Implications for the design of air traffic control systems and procedures are also discussed. / (cont.) Strategies for the segregation of airspace based on equipage are suggested to alleviate controller cognitive limitations and ensure incentives for equipped aircraft. Options are given for the display of equipage information in the future environment. / by Laura M. Major. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990. / Includes bibliographical references (leaves 173-175). / by Georgia F. Denktsis. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009. / Includes bibliographical references (p. 75-76). / This thesis presents a methodology for the integration of blade row body forces, derived from axisymmetric and three- dimensional flow fields, for use in the stability analysis of axial compressors. The body force database represents the body forces as a function of the local flow coefficient times the overall flow coefficient; doing this overcomes a source of non-uniqueness in the representation. Stability calculations using body force databases from this methodology as well as from a legacy method, applied to axisymmetric streamline curvature calculations, are compared. A procedure for joining body forces extracted from axisymmetric and three-dimensional CFD calculations is presented along with an assessment of the sensitivity of the stall prediction and onset behavior to the shape of the body force curves. The slope of the body force curves near the point corresponding to peak pressure rise, as well as those near zero flow, are found to be important in determining the stall point and inception type. Comparisons to previous work and test data from a single stage research compressor are made. / by Amish A. Patel. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 120-121). / by Steven R. Braddom. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, February 2015. / Cataloged from PDF version of thesis. "October 2014." / Includes bibliographical references (pages 143-149). / This thesis investigates search scenarios in which multiple mobile, self-interested agents, cows in our case, compete to capture targets. The problems considered in this thesis address search strategies that reflect (i) the need to efficiently search for targets given a prior on their location, and (ii) an awareness that the environment in which searching takes place contains other self-interested agents. Surprisingly, problems that feature these elements are largely under-represented in the literature. Granted, the scenarios of interest inherit the challenges and complexities of search theory and game theory alike. Undeterred, this thesis makes a contribution by considering competitive search problems that feature a modest number of agents and take place in simple environments. These restrictions permit an in-depth analysis of the decision-making involved, while preserving interesting options for strategic play. In studying these problems, we report a number of fundamental competitive search game results and, in so doing, begin to populate a toolbox of techniques and results useful for tackling more scenarios. The thesis begins by introducing a collection of problems that fit within the competitive search game framework. We use the example of taxi systems, in which drivers compete to find passengers and garner fares, as a motivational example throughout. Owing to connections with a well-known problem, called the Cow-Path Problem, the agents of interest, which could represent taxis or robots depending on the scenario, will be referred to as cows. To begin, we first consider a one-sided search problem in which a hungry cow, left to her own devices, tries to efficiently find a patch of clover located on a ring. Subsequently, we consider a game in which two cows, guided only by limited prior information, compete to capture a target. We begin by considering a version in which each cow can turn at most once and show this game admits an equilibrium. A dynamic-programming-based approach is then used to extend the result to games featuring at most a finite number of turns. Subsequent chapters consider games that add one or more elements to this basic construct. We consider games where one cow has additional information on the target's location, and games where targets arrive dynamically. For a number of these variants, we characterize equilibrium search strategies. In settings where this proves overly difficult, we characterize search strategies that provide performance within a known factor of the utility that would be achieved in an equilibrium. The thesis closes by highlighting the key ideas discussed and outlining directions of future research. / by Kevin Spieser. / Ph. D.