Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (leaves 66-69). / by Jun Luo. / 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. / The goal of this research is to characterize the distribution and costs of spacecraft discrepancies found at the system level of integration and test, as well as understand the implications of those distributions and costs for the spacecraft enterprise as a whole. If discrepancies can be better understood, they can potentially be reduced or even eliminated. Reducing discrepancies will result in cycle time reduction and cost savings, as well as increased product quality and reliability. All of these potential outcomes are indications of successful progress toward becoming a lean organization. Data on discrepancies at the system level of integration were gathered from spacecraft vendor databases, while interviews with key program managers and engineers provided perspective and insight into the data. Results are based on 224 spacecraft representing at least 20 different programs or product lines, and encompassing 23,124 discrepancies. The spacecraft date from 1973-1999, and represent different vendors as well as a mix of commercial and government spacecraft. Spacecraft discrepancies are analyzed in this work on the basis of ten categories: the spacecraft mission, the spacecraft subsystem where the discrepancy occurred, the date of the discrepancy occurrence, the discrepancy report open duration, the immediate action taken to fix the discrepancy (disposition), the root cause of the discrepancy, the long-term corrective action prescribed to prevent the discrepancy from happening again on future spacecraft, the labor time spent on the discrepancy, and the cycle time lost due to the discrepancy. Statistical measures of central tendency, correlation and normality are presented for each category. This statistical analysis forms the basis for research findings at the enterprise level in the areas of quality yield, resource utilization, stakeholder satisfaction and flow time. Recommendations to enterprise stakeholders for increasing the value derived from system-level integration and test follow from the enterprise-level findings. / by Annalisa L. Weigel. / 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 87-92). / While measurement covariances are often taken to be constant in many robotic state estimation systems, many sensors exhibit different interactions with their environment. Accurate covariance estimation allows graph-based estimation techniques to better optimize state estimates by reasoning about the utility of different methods relative to each other. This thesis describes a method of learning compact feature representations for real-time covariance estimation. A direct log-likelihood optimization technique is used to train a deep convolutional neural network to predict the covariance matrix of a Gaussian measurement model, given representative data. This method is algorithm-agnostic, and therefore does not require the handcoding of representative features. Quantative results are presented, showing that improved measurement covariances on a frame-to-frame visual odometry system reduce trajectory errors after a loop closure is applied. / by Katherine Y. Liu. / 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 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.