Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 91-92). / This thesis explores a variety of materials and methods for creating emitter arrays for the ion electrospray propulsion system (iEPS), a compact, efficient, and scalable space propulsion system for use in a wide range of space missions. The increasing utilization of small, cheap, easy-to-launch satellites known as CubeSats has spurred demand for a propulsion system which exists at the nexus of high power efficiency, low mass, surface area, and volume, and high specific impulse. iEPS has demonstrated a unique potential to satisfy all of these stringent design requirements in a way no presently existing propulsion system can. The first part of this work explores utilizing microelectromechanical systems (MEMS) processing to increase the thrust density of iEPS. Silicon molds were designed and manufactured with differing emission site size and spacing. Additionally, a variety of materials were tested with the aim of forming a porous network within the molds prior to selective removal of the mold. A molded array is successfully fired as a result of these research efforts. The second part of this work explores creation of porous substrates for use with an existing laser ablation method of creating emitter arrays. The first iEPS thrusters tested in space used porous borosilicate glass emitter chips, which demonstrated shortcomings in terms of material uniformity, pore size, and ionic liquid fuel containment. This work explores materials and methods for improving all of these and demonstrates the successful firing of an array made by sintering a silicon dioxide nano-bead powder. / by Alexander Connor Larkin Bost. / 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 81-85). / This thesis presents a multi-fidelity methodology to enable the incorporation of high-fidelity data into a conceptual design process. The methodology is based upon a fidelity weighted combination of Gaussian Process surrogate models that takes into account both the quality of the Gaussian Process approximation and the confidence of the designer in the disciplinary model being approximated. The methodology is demonstrated on the stability and control analysis of a Blended-Wing-Body aircraft's center of gravity limits. The results show that low-fidelity data is enhanced by the presence of high-fidelity data in key areas of the design space. At the same time, the presence of even sparse high-fidelity data is key to reducing the variance in the stability and control analysis, thereby improving the quality of the predictions of the center of gravity limits. / by Alexander W. Feldstein. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1995. / Includes bibliographical references (p. 109-111). / by Masahiko Kuzume Ikuta. / M.S.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 111-112). / This thesis analyzes the effects of two algorithms that control the departure of aircraft at congested airports, with an emphasis on the uncertainty of the underlying processes. These algorithms, N-control and dynamic programming, belong to a broader class of control policies called Pushback Rate Control (PRC) policies that calculate a pushback rate for departing aircraft based on the state of the airport surface congestion. During times of congestion, these algorithms limit the amount of aircraft on the airport surface while maintaining departure throughput. This reduces the taxi-out time of aircraft, resulting in reduced fuel burn and emissions. This thesis introduces the policies and simulates their performance at LaGuardia Airport while varying two policy parameters, the length of the prediction interval and the number of prediction intervals, under several types of uncertainty, including the departure schedule and arrival rate. As will be shown, each policy results in significant taxi-out time reductions, saving airlines at least 60,000 minutes of taxiing over a 2-month period with the traditional 15-minute time window simulations. However, when accounting for the uncertainty in the algorithm inputs or the variation of policy parameters, the performance of both PRC policies degrades. By accounting for the variation of policy parameters and the different sources of uncertainty that affect airport surface management, the main contribution of this thesis provides a realistic analysis of PRC policies. / by Patrick Kough McFarlane. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 93-97). / Electrohydrodynamic (EHD) thrusters utilize ion neutral collisions in air to produce a propulsive force. The ions are generated at an emitting electrode in an asymmetric capacitor by a corona discharge. This thesis presents a Hybridized Discontinuous Galerkin (HDG) formulation for solving the EHD thruster governing equations with the exception of fluid flow equations. The problem is two-way coupled and non-linear. A smoothed charge injection model from the literature for the corona discharge is included in the HDG scheme. The formulation is validated against a model problem which has an analytical solution and parallel wire single stage and dual stage thruster performance data from the literature. The model problem consists of concentric cylinders with charge density and potential specified on the inner and outer cylinders. The inner cylinder is offset to test the charge injection boundary condition in an asymmetric solution. The single stage thruster consists of two parallel wires of different diameters separated by a 1 cm gap. The dual stage thruster consists of three inline parallel wires of different diameters separated by 1 cm and 3 cm. The HDG solution for the model problem is found to produce normalized errors on the order of 10-3 for the potential and charge density solutions. The charge density applied to the inner emitter electrode is increased over several solution iterations to resolve high charge density gradients. The charge density boundary condition applied to the offset case represented the expected qualities of a corona discharge. The smoothed boundary condition is shown to be tunable to allow for a trade-off between accuracy and numerical stability. The single stage thruster model replicated experimental thrust results within 14% error using homogeneous charge injection and the smoothed charge injection model requires a less stable setting to achieve similar accuracy. The dual stage model shows the necessity of a mixed outflow boundary condition to avoid non-unique solutions. / by Andrew Dexter. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991. / Includes bibliographical references (p. 93-94). / by Jesse Ross Gossner. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992. / Includes bibliographical references (leaves 136-143). / by Andrew D. Rothstein. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 129-136). / The optimal selection of experimental conditions is essential in maximizing the value of data for inference and prediction, particularly in situations where experiments are time-consuming and expensive to conduct. A general Bayesian framework for optimal experimental design with nonlinear simulation-based models is proposed. The formulation accounts for uncertainty in model parameters, observables, and experimental conditions. Straightforward Monte Carlo evaluation of the objective function - which reflects expected information gain (Kullback-Leibler divergence) from prior to posterior - is intractable when the likelihood is computationally intensive. Instead, polynomial chaos expansions are introduced to capture the dependence of observables on model parameters and on design conditions. Under suitable regularity conditions, these expansions converge exponentially fast. Since both the parameter space and the design space can be high-dimensional, dimension-adaptive sparse quadrature is used to construct the polynomial expansions. Stochastic optimization methods will be used in the future to maximize the expected utility. While this approach is broadly applicable, it is demonstrated on a chemical kinetic system with strong nonlinearities. In particular, the Arrhenius rate parameters in a combustion reaction mechanism are estimated from observations of autoignition. Results show multiple order-of-magnitude speedups in both experimental design and parameter inference. / by Xun Huan. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 115-117). / This thesis develops a mixed integer programming formulation to solve the proximity operations scheduling problem for autonomous orbital rendezvous. The algorithm of this thesis allows the operator to specify planned modes, which encode the chase satellite's operations. The scheduler optimally places these modes in the midst of the environmental conditions that fall out of the chase satellite's orbit parameters. The algorithm manages resources, i. e. battery state of charge, and observes temporal constraints. Experiments show that the scheduler responds to changes in a variety of situations. It accommodates changes to the constraints in the modes. Relaxing or tightening the restrictions on the resources illuminates the algorithm's responsiveness to practical resource demands. Changes to the definition of optimality via a cost function indicate that the scheduler reacts to a diverse set of parameters. / by Christopher J. Guerra. / 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. 79-80). / Increasing concern over the potential harmful effects of green house gas emissions from various sources has motivated the consideration of an aircraft certification standard as one way to reduce aircraft C02 emissions and mitigate aviation impacts on the climate. In order to develop a commercial aircraft certification standard, a fuel efficiency performance metric and the condition at which it is evaluated must be determined. The fuel efficiency metric form of interest to this research is fuel/range, where fuel and range can either be evaluated over the course of a reference mission or at a single, instantaneous point. A mission-based metric encompasses all phases of flight and is robust to changes in technology; however, definition of the reference mission requires many assumptions and is cumbersome for both manufacturers and regulators. An instantaneous metric based on fundamental aircraft parameters measures the fuel efficiency performance of the aircraft at a single point, greatly reducing the complexity of the standard and certification process; however, a single point might not be robust to future changes in aircraft technology. In this thesis, typical aircraft operations are assessed in order to develop evaluation assumptions for a mission-based metric, Block Fuel divided by Range (BF/R), and an instantaneous metric, incremental fuel burn per incremental distance (inverse Specific Air Range (1/SAR)). Operating patterns and fuel burn maps are used to demonstrate the importance of mission range on fleet fuel burn, and thus the importance of a properly defined range evaluation condition for BF/R. An evaluation condition of 40% of the range at Maximum Structural Payload (MSP) limited by Maximum Takeoff Weight (MTOW) is determined to be representative for the mission-based metric. A potential evaluation condition for 1/SAR is determined to be optimal speed and altitude for a representative mid-cruise weight defined by half of the difference between MTOW and Maximum Zero Fuel Weight (MZFW). To demonstrate suitability as a potential surrogate for BF/R, correlation of 1/SAR with BF/R is shown for the current fleet, and a case study of potential future aircraft technologies is presented to show the correlation of improvements in the 1/SAR metric with improvements in BF/R. / by Brian M. Yutko. / S.M.