Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 113-116). / by John Saunders Bellingham. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 99-100). / by Jareb D. Mirczak. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 127-129). / Accurate estimates of multistage axial compressor performance at off-design operating conditions are essential to the determination of key performance metrics of aircraft gas turbine engines, such as fuel burn, thrust output, and stable operating range. However, conventional RANS based CFD calculations of multistage axial compressors diverge at off-design operating conditions where large separation occurs and the stages are mismatched. This thesis demonstrates the feasibility of a body force based approach to capturing the three-dimensional flow field through a turbomachinery blade row at off-design conditions. A first principles based blade passage model is introduced which addresses the limitations of previous approaches. The inputs to the improved blade passage model are determined from three-dimensional, steady, single-passage RANS CFD calculations. In a first step towards modeling multistage configurations, the improved blade passage model is validated using a fan rotor test case. At the design operating conditions, the stagnation pressure rise coefficient and the work coefficient are both estimated within 5%, and the adiabatic efficiency is estimated within 1 percentage point over most of the span relative to single-passage RANS CFD simulations. At low mass flow operating conditions, where the single-passage RANS CFD diverges, the blade passage model and related body force representation are capable of computing the three-dimensional throughflow with separation and reversed flow. These results pave the way for future unsteady calculations to assess compressor stability and for multistage compressor simulations at off-design conditions. / by Maximilian Lewis Brand. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1972. / Bibliography: p. 173-177. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992. / Includes bibliographical references (p. 134-137). / by Bruno Marco Quadrelli. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Pages 129-130 blank. Cataloged from student submitted PDF version of thesis. / Includes bibliographical references (p. 115-119). / The greatest discoveries in astronomy have come with advancements in ground-based observatories and space telescopes. Latest trends in ground-based observatories have been ever increasing size of the primary mirror, providing much higher apertures for more powerful image captures. The same trend can be envisioned for space telescopes. In fact, concepts for ultra-large space telescopes (ULST) on the order of hundreds of meters in size have been emerging since the late 1990's and early 2000's. Currently, James Webb Space Telescope (JWST) scheduled to be launched in 2014 only has primary mirror diameter of 6.5 m. An important issue in the ULST is correcting for optical errors caused by large thermal deformations expected due to exposure to radiation in orbit. As of now, there are no methods for solving technical complexities involved in correcting for such deformations. Furthermore, the costs associated with weight, deployability, and maintenance hinder advancements in large space telescopes. This thesis explores the idea of using binary actuators coupled with elastic elements to offer solutions to these problems. The feasibility of using binary actuators with elastic elements for correcting the focus of the deformed structure is investigated. The investigation begins with simple representations of the primary mirror structure in one-dimensional study, then in two-dimensional study for planar analysis. The analysis includes exploration of the workspace, demonstration of deterioration of superposition, and performance measured in precision of focus correction. In general, the number of actuators required for an acceptable level of correction is about three times the number of degrees-of-freedom in the system. Ultimately, it is concluded that in the planar domain it is feasible to use binary actuators in the control of primary mirror structure for large space telescopes. / by Seung Jae Lee. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 239-252). / High power nuclear electric propulsion systems have the capability to enable many next-generation space exploration applications. To date, use of electric primary propulsion in flight systems has been limited to low-power, solar electric missions. There is a need for a large-scale research and development effort to field systems capable of meeting the demands of future high-power electric propulsion missions, especially missions utilizing nuclear power plants to power electric propulsion systems. In formulating such an effort, it is first important to identify the likely requirements around which such a system might be designed. These requirements can be effectively cast in terms of required thruster lifetime, thrust, specific impulse, output power, and power plant specific power. Projected requirements can be derived based on the mass characteristics of space-borne nuclear power plants, and the optimized trajectories of spacecraft missions enabled by the use of megawatt-level nuclear electric power systems. Detailed mass modeling of space-based Rankine cycle nuclear power plants is conducted to evaluate the achievable specific power of these systems. Based on the figures for specific power so obtained, mission modeling is next conducted using the Mission Analysis Low-Thrust Optimization software package. Optimized thrust, specific impulse and lifetime figures are derived for several missions of interest. A survey of available electric propulsion thrusters is conducted and thruster configurations presenting the lowest developmental risks in migrating to high thruster output power are identified. Design evolutions are presented for three thrusters that would enhance or enable operation at the megawatt level. First, evaluation of projected lifetime for dual-stage gridded ion thrusters is conducted using the CEX2D simulation tool to evaluate the utility of multi-stage gridded ion engines in obtaining the required thruster lifetime for operation at high specific impulse. Next, to evaluate the utility of Hall thrusters operating at high propellant mass flow rate, a numerical thruster model is developed that incorporates the effects of the neutral fluid in predicting thruster performance. Using this code, numerical simulations are conducted to investigate the effects of variations in propellant mass flow rate, magnetic field topology, and thruster channel geometry on achievable performance. Finally, the effects of variations in the channel contour of magnetoplasmadynamic thrusters on performance and efficiency are evaluated using the MACH2 software package. Incremental variations in thruster channel contour are implemented, and the effects of these variations on the performance onset condition, and electrode current distributions are observed. Conclusions regarding the utility of each of these three design evolutions in developing thrusters for multi-megawatt electric propulsion systems are discussed. Contributions stemming from this research include, first, the establishment of an appropriate requirements space for the design of advanced highpower electric power and propulsion systems. This design space is comprised of projected requirements for power plant specific power, derived from power plant mass modeling, and thruster output power, specific impulse and lifetime derived from mission modeling. Additionally, this work provides evaluation, using state-of-the-art simulation suites, of several electric thruster design evolutions of potential utility in developing electric propulsion systems designed to operate at the megawatt level. / by Daniel B. White. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 60). / Required Navigation Performance (RNP) instrument procedures guarantee high levels of navigation precision through highly accurate navigation sources (e.g. GPS) and real-time monitoring of position estimation accuracy. In recent years, the Federal Aviation Administration (FAA) has developed and published public RNP approach procedures at airports across the country. These RNP procedures offer unique capabilities such as curved segments (radius-to-fix, or RF legs), narrow containment areas, and constant descent profiles that are not seen combined in other categories of instrument approaches. Because of these capabilities, RNP approaches are regarded as highly flexible procedures that can be designed to meet specific stakeholder requirements (e.g. lower minimums in mountainous areas, minimizing fuel bum during approach, avoiding flight over populated areas for noise abatement, etc.) at the airport level. Among the various proposed benefits of RNP approaches, this study analyzed potential safety benefits related to improvements in approach stability. In total, 11,062 individual approaches at four airports were analyzed using radar (ASDE-X) data, of which 364 (3.29%) were identified as RNP procedures. Of all approaches analyzed, two non-RNP cases were identified as unsafe, while there were no unsafe RNP cases. However, due to the relatively low number of RNP approaches observed, no statistically significant evidence of improved stability on RNP approaches was found. Given the low utilization of RNP approach procedures found from radar data, further work was done to identify barriers to operational use of these procedures and to investigate strategies to accelerate the adoption of RNP across the National Airspace System (NAS). Potential factors driving the low utilization of RNP procedures were found to be the low levels of equipage and operational approval among air carriers, and difficulties in air traffic management stemming from mixed equipage operations. / by Sandro Salgueiro Rodrigues Filho. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000. / Also available online at the MIT Theses Online homepage <http://thesis.mit.edu>. / Includes bibliographical references (p. 109-112). / Artificial gravity is made through the centripetal force from a rotating chair or short-radius centrifuge. It is a very promising countermeasure, as it alone should remove all the adverse effects of microgravity. In order to effectively use artificial gravity as a long-duration space flight countermeasure, the effects of artificial gravity on the human body must be investigated. If artificial gravity is created by use of a short-radius centrifuge, the high angular velocity required, about 23 rpm, causes unexpected and illusory body motions when making head turns. My work in artificial gravity consisted of two parts, a study that investigated the vestibular response to head movements during centrifugation and regulator feedback control of the centrifuge. This experiment studied the perceived illusory body sensations and heart rate changes induced by head movements in both the yaw and pitch planes while supine during centrifugation. Yaw right, yaw left, and pitch head movements yielded successively significantly higher heart rate than baseline. Results show that 68% of subjects in the yaw plane and 48% of subjects in the pitch plane experienced illusory body tilt as predicted by a model of the vestibular system while 13% in yaw and 40% in pitch experienced body tilt in the opposite direction from the predicted model. Pitch head movements yielded significantly higher magnitude and duration of illusory tilt. These side effects are serious and will need to be controlled if short-radius centrifugation is to be a successful countermeasure. Regulator feedback control has been implemented on the centrifuge with both an optical encoder and an accelerometer. Tachometer development, automatic control, and classical PID control theory was used to develop the gain and integrator time constants, which lead to K=1.5 and Ti=1 sec. This results in an improved steady state error by 99.8% and a more accurate response of the centrifuge by 5.7% for the accelerometer and 52% for the encoder feedback system from the open loop system. / by Carol C. Cheung. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007. / Includes bibliographical references (p. 131-133). / Physical information is transferred between technical systems through wires, beams, and other physical attributes, while more intangible information is typically transferred between communities of people through artifacts such as documents, e-mails, etc. This research attempts to characterize these communication interfaces better by analyzing the use of artifacts at these interfaces by means of a boundary object attribute model. Boundary objects, the metric of analysis of this thesis, are artifacts used to bridge information and knowledge gaps between different communities of practice. The US Army's Future Combat System (FCS) was chosen as a case study primarily because of its complex programmatic characteristics. The information gathered in the FCS case study was combined with knowledge from previous boundary object literature to generate an attributes model. Once developed, the boundary object attributes model was validated on the US Air Force Transformational Communications Satellite System (TSAT) program focusing specifically on the TSAT Mission Operations System (TMOS) segment of the program. Data were collected on the frequency and type of resources used to understand information and the dependencies that individuals have with each other for documented information. Furthermore, five communication artifacts were critiqued for their effectiveness as boundary objects. Statistical tests were conducted to highlight trends in resource dependencies and attributes common in effective boundary objects. An implication of this research is that the most important attributes for a boundary object are inclusivity, traceability, and synchronization. This research also found that people generally tend to rely much more on other people for information than artifacts. This introduces problems of exhausting valuable human resources and creating unnecessary bottlenecks. / (cont.) A second implication of this research is that spending the extra time and effort to design artifacts with high inclusivity and freshness will add significant value to the overall system. In addition, a third implication of this research is that having the right boundary objects alone is not enough for effective collaborative interfaces. A fourth implication of this research is that designing a boundary object whose form follows its function is critical for its effectiveness. These suggestions can provide relief to a program highly taxing to its human resources and reduce transaction costs of the overall system. Furthermore, this model may be extended for the purpose of determining the roles and responsibilities of system integrators. / by Allan Fong. / S.M.