Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 99-100). / by Samuel A. Schweighart. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999. / Includes bibliographical references (p. 145-150). / The pressure ratio of axial compressor stages can be significantly increased by controlling the development of blade and endwall boundary layers in regions of adverse pressure gradient by means of boundary layer suction. This concept is validated and demonstrated through the design and analysis of two unique aspirated compressor stages: a low-speed stage with a design pressure ratio of 1.6 at a tip speed of 750 ft/s, and a high-speed stage with a design pressure ratio of 3.5 at a tip speed of 1500 ft/s. The aspirated compressor stages were designed using a new procedure which is a synthesis of low speed and high speed blade design techniques combined with a flexible inverse design method which enabled precise independent control over the shape of the blade suction and pressure surfaces. Integration of the boundary layer suction calculation into the overall design process is an essential ingredient of the new procedure. The blade design system consists of two axisymmetric through-flow codes coupled with a quasi three-dimensional viscous cascade plane code with inverse design capability. Validation of the completed designs were carried out with three-dimensional Euler and Navier-Stokes calculations. A single spanwise slot on the blade suction surface is used to bleed the boundary layer. The suction mass flow requirement for the low-speed and high-speed stages are 1 % and 4% of the inlet mass flow, respectively. Additional suction between 1-2% is also required on the compressor end walls near shock impingement locations. The rotor is modeled with a tip shroud to eliminate tip clearance effects and to discharge the suction flow radially from the flowpath. Three-dimensional viscous evaluation of the designs showed good agreement with the quasi three-dimensional design intent, except in the endwall regions. The suction requirements predicted by the quasi three-dimensional calculation were confirmed by the three-dimensional viscous calculations. The three-dimensional viscous analysis predicted a peak pressure ratio of 1.59 at an isentropic efficiency of 89% for the low-speed stage, and a peak pressure ratio of 3.68 at an isentropic efficiency of 94% for the high-speed rotor. / by Ali M. Merchant. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 79-81). / A primary goal in compressor design for jet engines is the reduction of size and weight. This can be achieved by increasing the work output per stage, thereby reducing the required number of stages. In this thesis, the aerodynamic design of a high speed compressor that produces a pressure ratio of 9.1:1 in only two stages (rather than the typical six or seven) is presented. This is accomplished by employing blade aspiration in conjunction with rotor counter-rotation. Aspiration has been shown to make feasible significantly increased blade loading and counter-rotation provides a means of taking full advantage of this potential throughout a multistage compressor. The aspirated counter-rotating compressor was designed using a one-dimensional stage analysis program coupled with an axisymmetric throughflow code and a quasi-three- dimensional cascade code for blade design. The design of each stage focused on maximizing pressure ratio within diffusion factor and relative inlet Mach number (i.e. shock loss) constraints. The exit angle of the first stator was optimized to maximize the pressure ratio of the counter-rotating (second) rotor. The blade design code MISES allowed for each feature of the blade sections, including aspiration, to be precisely designed for the predicted conditions. To improve the process of designing blades with MISES, extensive analysis of previously designed high-speed aspirated blades was performed to identify the relationships between various blade features. / by Jody Kirchner. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 47-49). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / In scientific and engineering contexts, physical systems are represented by mathematical models, characterized by a set of parameters. The inverse problem arises when the parameters are unknown and one tries to infer these parameters based on observations. Solving the inverse problem can require many model simulations, which may be expensive for complex models; multiple models of varying fidelity and complexity may be available to describe the physical system. However, inferring the parameters may only be an intermediate step, and what is ultimately desired may be a low-dimensional Quantity of Interest (QoI); we refer to this as the goal-oriented inverse problem. We present a novel algorithm for solving the goal-oriented inverse problem, which allows one to manage the fidelity of modeling choices while solving the inverse problem. We formulate a hierarchy of models, and assume that the QoI obtained by inferring the parameters with the highest-fidelity model is the most accurate QoI. We derive an estimate for the error in the QoI from inferring the parameters using a lower-fidelity model instead of the highest-fidelity model. This estimate can be localized to individual elements of a discretized domain, and this element-wise decomposition can then be used to adaptively form mixed-fidelity models. These mixed-fidelity models can be used to infer the parameters, while controlling the error in the QoI. We demonstrate the method with two pairs of steady-state models in 2D. In one pair, the models differ in the physics included; in the other pair, the models differ in the space to which the parameters belong. In both cases, we are able to obtain a QoI estimate with a small relative error without having to solve the inverse problem with the high-fidelity model. We also demonstrate a case where solving the inverse problem with the high-fidelity model requires a more complex algorithm, but where our method gives a mixed-fidelity model with which we can infer parameters using a simple Newton solver, while achieving a low error in the QoI. / by Harriet Li. / S.M.

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.