Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (p. 130-131). / by Chang-Ching Lo Gettman. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 80-81). / Teleoperated manipulators have been invaluable tools during space missions. Arm operators work in pairs, with the primary operator controlling the arm and the secondary operator assisting by monitoring arm clearance and helping to avoid singularities. Individual ability to manipulate the arm and integrate camera views is believed to correlate with 3 subcomponents of spatial intelligence: spatial visualization (SV), mental rotation (MR) and perspective taking (PT). In particular, PT (the ability to imagine an object from another viewpoint) is thought to be important for integrating camera views. Two experiments were performed; one on primary operator performance, and one on secondary operator performance. In Experiment 1, 19 naive subjects were trained to manipulate a 6 degree of freedom (DOF) simulated arm using a pair of hand-controllers. Over 18 trials, the disparity between the arm's control frame and the cameras was varied between low (< 90 degrees) and high (> 90 degrees) conditions. We used the Cube Comparisons (CC) test to assess SV, the Vandenberg Mental Rotations Test (MRT) to assess MR, and the Purdue Spatial Visualization of Views Test (PSVT) and a Perspective Taking Ability (PTA) test to assess PT. Subjects with high PSVT scores moved the arm more directly to the target and were better at maintaining the required clearance between the arm and obstacles, even without a direct camera view. The subjects' performance degraded under the high disparity condition. In Experiment 2, 11 naive and 9 returning subjects were trained to manipulate the same simulated arm during 6 trials and then acted as a secondary operator observing an additional 32 trials. / (cont.) The MRT, PSVT, and PTA were used to assess spatial abilities. Though the primary operator task was slightly different, we confirmed many results of Experiment 1. Subjects with high PTA scores took less time, moved the arm more directly to the target, and moved the arm more fluidly, especially under the high disparity condition. High scorers on the PSVT and PTA were better at maintaining required clearance. Low PTA scorers looked from monitor to map more often. Prior experience with the arm didn't significantly improve task performance, and performance as primary operator didn't reliably predict performance as a secondary operator. However, subjects with high PSVT scores had better overall secondary operator performance and high PTA scorers were better at detecting problems before they occurred. The results of these studies could be used to customize initial training for astronauts. This research is supported by NSBRI through NASA Cooperative Agreement NCC 9-58. / by Zakiya Alexandra Tomlinson. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. / Includes bibliographical references (p. 141-143). / The trend in future space telescopes is towards large apertures and lightweight, rib-stiffened, and actively controlled deformable mirrors. These mirror architectures permit the development of segmented and deployed primary mirrors that lead to tremendous advancement in space telescope performance. Rib-stiffened and discretely actuated deformable mirrors have been shown to effectively mitigate common low order disturbances, but they are inevitably plagued by the "correction limit," or the extent to which the actuators can correct for a given shape disturbance. Improving the correctability of deformable mirrors requires understanding the origins of the correction limit, and optimizing the mirror design accordingly. This thesis details efforts to evaluate the mirror correction limit and the three predominant high spatial frequency mirror surface residual components: actuation-induced dimpling, manufacturing-induced print-through, and disturbance-induced uncorrectable error. The methods for simulating each effect are discussed, and an objective function is developed to quantify the effects of these residual components to gage the performance of each mirror design. A gradient descent algorithm is combined with the parametric capability of the Modular Optical Space Telescope (MOST) modeling tool to allow rapid trade space navigation and optimization of the mirror design across variations in mirror areal density, f-number, structural mass fractions, and rib aspect ratio. These optimization routines yield more advanced design heuristics that improve upon the simplified design techniques that are typical in industry. By forming the heuristics in terms of minimum machinable rib thickness, these new design relationships produce mirrors that satisfy manufacturing constraints and minimize uncorrectable high spatial frequency error. / by Thomas Gray. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / 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. 209-213). / The previously developed Diverging Cusped Field Thruster (DCFT) has undergone further investigations and performance characterization. The DCFT is a magnetically conned plasma thruster that uses cusped magnetic fields to confine electron ow and reduce losses to the walls. The magnetic confinement of the plasma away from the walls also reduces wall erosion to increase thruster lifetime. Additionally, modifications to the original DCFT have increased robustness and decreased mass to become more desirable for space flight. Research on reducing the plasma plume divergence of the thruster by altering the magnetic field has also been performed. The DCFT has exhibited competitive thrust and eciency performance when compared to typical Hall thrusters of similar size. Specifically, the anode eciency reached a maximum of 39.3% providing 11.8 mN of thrust with a specific impulse of 1436 s. The xenon mass ow rate to the anode was 8.5 standard cubic centimeters per minute, and the power consumption was 210 W. Two distinct modes, as well as a "mixed" mode, were observed during performance testing and had signicant, though not completely predictable, effects on thruster performance. The modes differ in plasma diffusivity and anode current. Facility effects, such as chamber back pressure and cathode coupling, on performance were also briefly y researched. In order to characterize the performance of the DCFT, the Milli-Newton Thrust Stand (MiNTS) was developed. The MiNTS is a non-conventional torsional-style thrust stand capable of measuring thrust in the range of 3 to 20 mN with an accuracy of up to 0.2 mN. Calibration of the stand is necessary to map the output of the MiNTS to the force felt by it. A calibration stand was designed to apply a known force to the MiNTS using weights. The MiNTS is controlled by a Labview Virtual Instrument that can measure and counteract the force of the DCFT. Drift forces due to external connections to the MiNTS and thermal transfer from the DCFT are also studied, and processes for negating the drift forces are provided. / by Ryan M. Daspit. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 171-181). / A nano-scale rotor supported on a cantilevered multi-wall carbon nanotube (MWNT) shaft (Stodola configuration) is proposed. The nanotube is also expected to function as the bearing, since individual walls of a MWNT are not strongly bonded and can slide on each other with low friction. While MWNT based rotors have been previously constructed, they have so far been limited to horizontally oriented nanotubes. The rotor uses a vertically aligned tube, which allows superior control of the rotor geometry, enabling improved rotor balancing and axisymmetric features such as electrodes or blades. The rotor is proposed as a test stand for measuring inter-wall friction in MWNTs. The low friction in nanotubes has been studied with simulations and experiments, and while it is agreed that relative motion between walls is possible, there is much debate about the qualitative nature of the friction force between walls. Furthermore the reported quantitative values of friction vary by as much as ten orders of magnitude. The proposed rotor might be used to gather new friction data on rotating MWNT bearings at higher speeds that previously attempted. In addition, identical rotors fabricated on nanotubes of varying size, type, and crystalline quality might provide a large dataset that could be used to find correlations between friction behavior and these factors. Applications for the rotor beyond a friction testing apparatus could include pumps to work with existing micro-chemical sensors, gyroscopes, energy storage flywheels, and turbomachinery for power generation. A fabrication process for the proposed rotor was developed, and is being refined. An isolated vertically aligned MWNT is grown by chemical vapor deposition (CVD), from a nickel catalyst dot defined with electron-beam lithography. A silicon dioxide sacrificial layer is applied, followed by a polysilicon layer from which to cut out the rotor. / (cont.) The rotor etch is performed by cryogenic reactive ion etching (RIE), patterned with electron-beam lithography. The rotor is released from the substrate by hydrofluoric acid vapor. One iteration of the fabrication process was completed, and further iterations are planned to complete a functional device. Actuation of the rotor would be achieved by directing jets of air at blades on the rotor, and an alternative electrostatic actuation concept is also proposed. A dynamic model of the rotor performance based on classical simple beam theory and rigid body dynamics indicates that speeds on the order of thousands to millions of revolutions per minute should be achievable, while avoiding the thirteen potential failure mechanisms analyzed. / by Euguene Hightower Cook. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1994. / Includes bibliographical references (p. 131-133). / by James P. Koonmen. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988. / Includes bibliographical references. / by Scott E. Schaffer. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / Includes bibliographical references (p. 59-60). / The design of hypersonic airbreathing aircraft pushes the envelope of current state-ofthe-art aerospace propulsion and materials technology. Therefore, these aircraft are highly integrated to produce adequate thrust, reduce drag, and limit surface heating. Consequently, every aircraft component (e.g., wings, fuselage, propulsion system) is sensitive to changes in every other component. Including Radar Cross Section (RCS) considerations further complicates matters. During preliminary design, this requires the rapid analysis of different aircraft configurations to investigate component interactions and determine performance trends. This thesis presents a framework and accompanying software for performing such an analysis. The intent is to optimize a hypersonic airbreathing aircraft design in terms of aerodynamic performance and RCS. Computational Fluid Dynamics (CFD) and Computational Electromagnetics (CEM) are the two main framework software components. CFD simulates airflow around the aircraft to analyze its aerodynamic performance. Alternately, CEM simulates the electromagnetic signature of the aircraft to predict its RCS. The framework begins with the generation of a three-dimensional computer aided design aircraft model. Next, a grid generator discretizes this model. The flow simulation is performed on this grid and the aircraft's aerodynamic characteristics are determined. Flow visualization aids this determination. Then, aircraft geometry refinements are made to improve aerodynamic performance. Afterward, CEM is performed on aerodynamically favorable designs at various aspect angles and frequencies. RCS values are determined and used to rank the different configurations. Also, inverse synthetic aperture radar images are generated to locate major scattering centers and aid the design refinement. The design loop continues in this fashion until an acceptable aircraft design is achieved. The NASA X-43A test vehicle was used to validate this preliminary design framework. / by Daniel L. DiCara. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 115-116). / The objective of stochastic process design is to strategically identify, measure, and reduce sources of uncertainty to guide the development of complex systems. Fundamental to this design approach is the idea that system development is driven by measurable characteristics called quantities of interest. These quantities of interest collectively describe the state of system development and evolve as the system matures. This thesis provides context for the contributions of quantities of interest to a stochastic process view of complex system development using three space hardware development projects. The CASTOR satellite provides the opportunity for retrospective identification of quantities of interest and their evolution through time. As a complement to CASTOR, the preliminary design of the REXIS x-ray spectrometer provides the foundation for applying stochastic process approaches during the early phases of system development. Lastly, a spacecraft panel structural dynamics experiment is presented that illustrates analysis techniques commonly employed in stochastic process analysis. / by George Ralph Sondecker, IV. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 93-98). / This thesis presents an overview of the design process for creating greedy decentralized task allocation algorithms and outlines the main decisions that progressed the algorithm through three different forms. The first form was called the Sequential Greedy Algorithm (SGA). This algorithm, although fast, relied on a large number of iterations to converge, which slowed convergence in decentralized environments. The second form was called the Consensus Based Bundle Algorithm (CBBA). CBBA required significantly fewer iterations than SGA but it is noted that both still rely on global synchronization mechanisms. These synchronization mechanisms end up being difficult to enforce in decentralized environments. The main result of this thesis is the creation of the Asynchronous Consensus Based Bundle Algorithm (ACBBA). ACBBA broke the global synchronous assumptions of CBBA and SGA to allow each agent more autonomy and thus provided more robustness to the task allocation solutions in these decentralized environments. / by Luke B. Johnson. / S.M.