Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 91-95). / Path planning classically focuses on avoiding environmental contact. However, some assembly tasks permit contact through compliance, and such contact may allow for more efficient and reliable solutions under action uncertainty. But optimal manipulation plans that leverage environmental contact are difficult to compute. Environmental contact produces complex kinematics that create difficulties for planning. This complexity is usually addressed by discretization over state and action space, but discretization quickly leads to computationally intractability if the optimal solution is desired. To overcome the challenge, we use the insight that only actions on configurations near the contact manifold are likely to involve complex kinematics, while segments of the plan through free space do not. Leveraging this structure can greatly reduce the number of states considered and scales much better with problem complexity. We develop the composite MDP algorithm based on this idea and show that it performs comparably to full MDP solutions at a fraction of the computational cost. However, the composite MDP still requires minutes to hours of computation, which is unsuitable for robots operating in novel environments. To overcome this limitation, we use the insight that environments are generally composed of a limited set of geometries. We can precompute the kinematic models of the dynamic object relative to these constituent geometries (constituent MDPs), and use them to assemble a kinematic model of the dynamic object relative to an environment with all constituent geometries present, by merging state spaces and transition functions. However, the straightforward assembly algorithm does not produce a sufficient computational speedup. Therefore, we introduce four assumptions to significantly reduce computation time. We demonstrate our algorithm to compute policies for novel environments on the order of seconds, without sacrificing solution quality. / by Charlie Zeyu Guan. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990. / Includes bibliographical references (leaf 73). / by Wendy Marie Power. / M.S.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 157-158). / This thesis describes the design and implementation of compact high voltage drive electronics for a multi-actuator microelectromechanical systems (MEMS) based deformable mirror (DM) for the 6U CubeSat Deformable Mirror Demonstration Mission (DeMi) with the objective of increasing the NASA Technology Readiness Level (TRL) of the MEMS DM toward its use for direct exoplanet imaging on a future large aperture space telescope mission. This thesis outlines the key requirements for DM performance, successfully develops a commercial-component based DM drive electronics board for a 140-actuator MEMS DM that is scalable to higher actuator count DMs, discusses the attributes of alternative designs in the initial trade study that were not further pursued, and summarizes the plan toward fully integrating and testing the MEMS DM drive electronics into the optical payload. / by Christian Alexander Haughwout. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007. / Includes bibliographical references (leaves 77-79). / This thesis presents a fluid model for electron behavior in the near-exit plume of a Hall thruster. The model provides 3D results and allows to study the azimuthal asymmetry induced by the hollow cathode. The model is composed by the charge and energy conservation equations and is intended to solve for the electrostatic potential and the electron temperature. It relies on the results of an external model for the ion behavior. The fluid equations are diffusive and are justified in the limit of small electron Larmor radius. They include the Hall transport, which is usually ignored in 2D approaches due to symmetry. The transport along magnetic field lines is high enough to convert the 3D problem into a 2D problem, where only the directions perpendicular to the magnetic field matter. In such a 2D formulation, the basic structure of the solution for the potential is studied analytically, with the result that the lines of constant potential can be approximately predicted. The potential can be found numerically after transforming the charge conservation equation into a convective-diffusive equation. The numerical results agree approximately with analytical predictions. The results suggest that the asymmetry induced by the hollow cathode mainly depend on how much the cathode perturbs the plasma density distribution. / by Félix Ignacio Parra Díaz. / S.M.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1964. / Microfiche copy available in Barker. / Vita. / Includes bibliographical references (leaves 118-122). / by Richard E. Kaplan. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988. / Includes bibliographical references. / by Mehtab M. Pervaiz. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaf 98). / by John M. Brookfield. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 106-109). / Small satellites are gaining popularity in the space industry and reduction in spacecraft size requires scaling down its propulsion system. Low-power electric propulsion poses a unique challenge due to various scaling penalties. Of high-performance plasma thrusters, the radio-frequency ion engine is most likely to succeed in scaling as it does not require an externally applied magnetic field and is structurally simple to construct. As part of a design package an original two-dimensional simulation code for radio-frequency ion engine discharge is developed. The code models the inductive plasma with fluid assumption and resolves the electromagnetic wave in the time domain. Major physical effects considered include magnetic field diffusion and coupling, plasma current induction and ambipolar plasma diffusion. The discharge simulation is benchmarked with data from an experimental thruster. It shows excellent performance in predicting the load power and the internal power loss of the plasma. Predictability of anode current depends on the operating power but is generally adequate. Optimum skin depth on the order of half of chamber radius is suggested by the simulation. The code also demonstrates excellent scaling ability as it successfully predicts the performance of a smaller thruster with errors less than 10%. Using the code a brief optimization study was conducted and the results suggest the maximum thrust efficiency does not necessarily occur at the same frequency that maximizes the power coupling efficiency of the matching circuit. / by Michael Meng-Tsuan Tsay. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 73-74). / The challenge of achieving safe flight comes into sharp focus in the face of adverse conditions caused by faults, damage, or upsets. When these situations occur, the corresponding uncertainties directly affect the safe operation of the aircraft. A technology that has the potential for enabling a safe flight under these adverse conditions is adaptive control. One of the main features of an adaptive control architecture is its ability to react to changing characteristics of the underlying aircraft dynamics. This thesis proposes the building blocks of an adaptable and reconfigurable control technology that ensures safe flight under adverse flight conditions. This technology enables the synthesis of such controllers as well as the systematic evaluation of their robustness characteristics. The field of adaptive control is a mature theoretical discipline that has evolved over the past thirty years, embodying methodologies for controlling uncertain dynamic systems with parametric uncertainties [1, 2, 3, 4, 5, 6]. Through the efforts of various researchers over this period, systematic methods for the control of linear and nonlinear dynamic systems with parametric and dynamic uncertainties have been developed [7, 8, 9, 10, 11, 12]. Stability and robustness properties of these systems in the presence of disturbances, time-varying parameters, unmodeled dynamics, time-delays, and various nonlinearities, have been outlined in the references [4]-[13] as well as in several journal and conference papers over the same period. / (cont.) In this thesis, we consider the control of a transport aircraft model that resembles the Generic Transport Model [14]. While the vehicles' geometry and aerodynamic model are those of a C5 aircraft, every other aspect has been made to coincide with the GTM, e.g. anti wind-up logic, time-delay due to telemetry, baseline control structure, low-pass and wash-out filters. We delineate the underlying nonlinear model of this aircraft, and introduce various damages, and failures into this model. An adaptive control architecture is proposed which combines a nominal controller that provides a satisfactory performance in the absence of adverse conditions, and an adaptive controller that is capable of accommodating various adverse conditions including actuator saturation. The specific adverse conditions considered can be grouped into the following three categories, (a) upsets, (b) damages, and (c) actuator failures. Specific cases in (a) include flight upsets in initial conditions of various states including angle of attack, cases in (b) include situations where structural failures cause changes in the location of the Center-of-Gravity (CG)[15], while cases in (c) include situations where symmetric and asymmetric failures in control surfaces and engines occur. These failures include losses in control effectiveness, and locked-in-place control surface deflections. The resilience of the adaptive controller to uncertainty is evaluated for safety using the control verification methodology proposed in [16]. / (cont.) This methodology enables the determination of ranges of uncertainty for which a prescribed set of closed-loop requirements are satisfied. This thesis studies several one-dimensional uncertainty analyzes for two flight maneuvers that focus on the longitudinal and lateral dynamics. As compared to the baseline controller, the adaptive controller enlarges the region of safe operation by a sizable margin in all but one of the cases considered. / by Megumi Matsutani. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 185-188). / The problem of performance optimization of a Common Aero Vehicle (CAV) is considered. In particular, the CAV is modeled as an unpowered high lift-to-drag ratio Earth penetrating re-entry vehicle. The CAV mission design problem is to determine a steering command that takes the CAV from a known initial state to a target on the surface of the Earth while optimizing a given performance index and satisfying all of the constraints imposed during flight. The CAV mission design problem is formulated as an optimal control problem. The optimal control problem is transformed to a nonlinear programming problem using a Legendre Pseudospectral Method. The nonlinear programming problem is then solved using a sparse nonlinear optimization algorithm. Once a solution to the CAV mission design problem is obtained, three main studies are conducted. First, the accuracy of the Legendre Pseudospectral Method is evaluated and the desirable characteristics of the solution to the CAV mission design problem are defined. Second, a study is conducted to demonstrate the effect of the parameters on the performance of the CAV. This parametric study demonstrates the use of the Legendre Pseudospectral method as a design tool and provides insight to the behavior of the CAV. Third, a preliminary investigation is performed on the real-time application of the Legendre Pseudospectral Method to the CAV mission design problem. This real-time analysis includes an assessment of the robustness of the solution to realistic environmental disturbances. / by Kimberley A. Clarke. / S.M.