Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014. / In title on title page, double underscored "x" appears as subscript. Cataloged from PDF version of thesis. / Includes bibliographical references (pages 47-49). / Aviation NOx emissions are byproducts of combustion in the presence of molecular nitrogen. In the upper troposphere, NOx emissions result in the formation of O₃ but also reduce the lifetime of CH4 , causing an indirect reduction in the formation of O₃. Meta studies by Lee et al. and Prather et al. concluded that the short-lived O₃ radiative forcing (RF) was greater than the combined long-lived CH₄ and O₃ RFs, leading to a net positive RF (4.5 to 14.3 mW/m² per Tg of NOx emissions). However, few simulations assess the surface air temperature (SAT) response, or conduct a large ensemble simulation with climate feedback in the cases where SAT is predicted. We aim to quantify the climate forcing and temperature response of aviation NOx emissions. Eight 400-member ensemble simulations are conducted with an earth system model of intermediate complexity. Inter-scenario comparisons between emissions starting in 1991, 2016 and 2036 with mid-range and high anthropogenic emissions are performed. We then determine the existence of long-term temporal heterogeneity of climate forcing and impact. The global net RF of an aviation NO, emissions inventory is positive from 1991 to 2100 while leading to a global average SAT responses of -0.068 K in 2100. Despite the positive zonal RF in the Northern Hemisphere of up to 413.9 mW/m² at 45°N, all latitudes experience cooling after 2075. In another scenario, constant aviation NOx emissions at 4.1 Tg/year cause a global net RF of near zero while leading to a SAT response of -0.020 K in 2100. The unexpected temperature behavior in both scenarios is attributed to the forcing from CH₄ destruction being 64% more effective in generating a SAT response than the O₃ forcing. Despite the positive net RF, the probability of aviation NOx emissions being cooling is 67% because of the relative difference in O₃ and CH₄ efficacies. / by Lawrence Man Kit Wong. / S.M.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND AERO. / Vita. / Bibliography: leaves 312-316. / by Steven Ray Hall. / Sc.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (leaves 58-60). / This work presents an approach to diagnosis to meet the challenging demands of modern engineering systems. The proposed approach is an architecture that is both hierarchical and hybrid. The hierarchical dimension of the proposed architecture serves to mitigate the complexity challenges of contemporary engineering systems. The hybrid facet of the architecture tackles the increasing heterogeneity of modern engineering systems. The architecture is presented and realized using a bus representation where various modeling and diagnosis approaches can coexist. The proposed architecture is realized in a simulation environment, the Specification Toolkit and Requirements Methodology (SpecTRM). This research also provides important background information concerning approaches to diagnosis. Approaches to diagnosis are presented, analyzed, and summarized according to their strengths and domains of applicability. Important characteristics that must be considered when developing a diagnostics infrastructure are also presented alongside design guidelines and design implications. Finally, the research presents important topics for further research. / by Martin Ouimet. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 123-125). / This thesis presents the design and implementation of a model predictive control based trajectory optimization method for Nap-of-the-Earth (NOE) flight. A NOE trajectory reference is generated over a subspace of the terrain. It is then inserted into the cost function and the resulting trajectory tracking error term is weighted for more precise longitudinal tracking than lateral tracking through the introduction of the TF/TA ratio. The TF/TA ratio, control effort penalties and MPC prediction horizon are tuned for this application via simulation and eigenvalue analysis for stability and performance. Steps are taken to reduce complexity in the optimization problem including perturbational linearization in the prediction model generation and the use of control basis functions which are analyzed for their trade-off between approximation of the optimal cost/solution and reduction of the optimization complexity. Obstacle avoidance including preclusion of ground collision is accomplished through the establishment of hard state constraints. These state constraints create a 'safe envelope' within which the optimal trajectory can be found. Results over a variety of sample terrains are provided to investigate the sensitivity of tracking performance to nominal velocities. The mission objective of low altitude and high speed was met satisfactorily without terrain or obstacle collision, however, methods to preclude or deal with infeasibility must be investigated as terrain severity (measured by commanded flight path angle) is increased past 30 degrees or speed is increased to and past 30 knots. / by Tiffany Rae Lapp. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 151-152). / by Akwasi Asare Apori. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. / Includes bibliographical references (p. 93). / Communications in current railroad operations are heavily based on voice links. Radio congestion is often a problem when railroad workers try to establish communication with dispatchers at the Traffic Control Center. This problem is expected to grow with the introduction of new rail services. At the same time, roadway worker fatalities still occur every year. Moreover, railroad workers' disorientations also cause accidents, and train dispatchers would often value knowing the railroad workers' locations. This report documents the design and evaluation of a GPS-aided wireless "data link" communication device used to enhance railroad worker safety. Personal safety is achieved when a person has sufficient warning before taking an action that exposes him or her to risk. The focus of the study was to understand the safety implications of both data-link and positioning technologies. The prototype device consists in a hand-held information appliance with wireless access to the Internet, connected to a GPS receiver. We demonstrated this device to railroad workers and dispatchers and their feedback has been gathered in this report. They provided excellent ideas to improve it and showed great enthusiasm. An experiment designed to evaluate the concept from the dispatcher's perspective was conducted. Although the prototype was shown to have room for improvement, the results of our experiments were encouraging. Digital interactions between dispatchers and railroad workers were slower but more accurate than the same interactions over the radio. Dispatcher valued the tracking display based on GPS information, although it increased the mental workload. / by Timothée Masquelier. / S.M.

Thesis (M.Eng.)--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. 94-96). / This thesis focuses on developing a recommended architecture for the next generation of design centers for integrated concurrent engineering in an academic environment and identifying and implementing an enabling sub-system for the architecture. During the development of this architecture a systems engineering process was used to structure the efforts of the team and maintain traceability to the customer needs throughout the design. Site visits were undertaken to benchmark existing design centers. Customer needs were compiled and analyzed to develop the system requirements that were input into a product matrix. This enabled the team to generate a wide array of implementations to synthesize multiple architectures. The recommended architecture should help to promote active learning in a distributed design team environment. Further, a concept for an On-Line Teaching Assistant (OLTA) was developed designed to help designers throughout the process of developing complex systems. The OLTA may be considered an "expert system" that will retain and filter an accumulating knowledge database of student work entities. A proof-of-concept prototype was developed to demonstrate this concept. Results of the architecture show a significant relative improvement over the currently proposed architecture and preliminary responses for the OLTA are very positive with one advisor stating "OLTA could revolutionize engineering education as we know it." Two faculty members agreed to utilize a prototype in their upcoming classes and the Aeronautics and Astronautics Department is very interested in implementing the system in its capstone design classes. / by Bruce J. Farnworth. / M.Eng.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 97-100). / While the introduction of CubeSats has enabled the scientific, commercial, and governmental communities to launch space missions more quickly at lower costs, the communication subsystems of the platform are limited by a heavily regulated and overcrowded RF spectrum. Scientific instruments with increasing capabilities on CubeSats are generating massive amounts of data and are quickly pushing the boundaries of the data rates of current RF communication systems. An alternative to the traditional RF communication system is the free space optical (FSO) communication system. With higher power efficiency, FSO communication, or lasercom, can potentially provide higher data rates using less power and also avoid the RF spectrum regulatory process. MIT's Nanosatellite Optical Downlink Experiment (NODE) is an effort to demonstrate low cost and high speed optical downlink from LEO for CubeSats, and this thesis focuses on alignments in the optomechanical system and transmitter system of the NODE payload. First, simulation and analyses are performed on an optomechanical model of NODE to study the effects potential misalignments of hardware components can have on the overall system. Second, we present an autonomous optimization algorithm that monitors the conditions of the transmitter system and compensates for wavelength misalignments between the transmitter optical components caused by variations in the thermal environment. / by Myron Lee. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 161-164). / Alerting systems are becoming pervasive in process operations, which may result in the potential for dissonance or conflict in information from different alerting systems that suggests different threat levels and/or actions to resolve hazards. Little is currently available to help in predicting or solving the dissonance problem. This thesis presents a methodology to model and analyze dissonance between alerting systems, providing both a theoretical foundation for understanding dissonance and a practical basis from which specific problems can be addressed. A state-space representation of multiple alerting system operation is generalized that can be tailored across a variety of applications. Based on the representation, two major causes of dissonance are identified: logic differences and sensor error. Additionally, several possible types of dissonance are identified. A mathematical analysis method is developed to identify the conditions for dissonance originating from logic differences. A probabilistic analysis methodology is developed to estimate the probability of dissonance originating from sensor error, and to compare the relative contribution to dissonance of sensor error against the contribution from logic differences. A hybrid model, which describes the dynamic behavior of the process with multiple alerting systems, is developed to identify dangerous dissonance space, from which the process can lead to disaster. Methodologies to avoid or mitigate dissonance are outlined. Two examples are used to demonstrate the application of the methodology. First, a / (cont.) conceptual In-Trail Spacing example is presented. The methodology is applied to identify the conditions for possible dissonance, to identify relative contribution of logic difference and sensor error, and to identify dangerous dissonance space. Several proposed mitigation methods are demonstrated in this example. In the second example, the methodology is applied to address the dissonance problem between two air traffic alert and avoidance systems: the existing Traffic Alert and Collision Avoidance System (TCAS) vs. the proposed Airborne Conflict Management system (ACM). Conditions on ACM resolution maneuvers are identified to avoid dynamic dissonance between TCAS and ACM. / by Lixia Song. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 121-123). / Reference trajectory design for atmospheric reentry vehicles can be accomplished through trajectory optimization using optimal control techniques. However, this method generally focuses on nominal vehicle performance and does not include robustness considerations during trajectory design. This thesis explores the use of linear covariance analysis to directly include trajectory robustness in the design process. The covariance matrix can be propagated along a trajectory to provide the expected errors about the nominal trajectory in the presence of uncertainties. During the optimization process, the covariance matrix is used as a performance metric to be minimized, directly penalizing expected errors so that the trajectory is shaped to reduce its sensitivity to uncertainties. This technique can penalize the open-loop covariance of the trajectory or the closed-loop covariance with the inclusion of a feedback guidance law. This covariance shaping technique is applied to reference trajectory design for a generic small reentry vehicle. A baseline trajectory is generated without any robustness considerations, along with an open-loop covariance shaped trajectory and a closed-loop covariance shaped trajectory, which uses a feedback guidance law based on a linear quadratic regulator scheme. Uncertainties in initial conditions, atmospheric density, aerodynamic coefficients, and unmodeled dynamics are applied to each trajectory and performance is analyzed using linear covariance analysis and Monte Carlo simulations. The results show that when the vehicle is flown closed-loop with feedback, shaping using the open-loop covariance produces a trajectory that is less robust than the baseline trajectory, while shaping using the closed-loop covariance generates a trajectory with reduced sensitivity to uncertainty for more robust performance. / by Benjamin R. Saunders. / S.M.