Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 105-113). / Blast-induced TBI has gained prominence in recent years due to the conflicts in Iraq and Afghanistan, yet little is known about the mechanical effects of blasts on the human head; no injury thresholds have been established for blast effects on the head, and even direct transmission of the shock wave to the intracranial cavity is disputed. Still less is known about how personal protective equipment such as the Advanced Combat Helmet (ACH) affect the brain's response to blasts. The goal of this thesis is to investigate the mechanical response of the human brain to blasts and to study the effect of the ACH on the blast response of the head. To that end, a biofidelic computational model of the human head consisting of 11 distinct structures was developed from high-resolution medical imaging data. The model, known as the DVBIC/MIT Full Head Model (FHM), was subjected to blasts with incident overpressures of 6 atm and 30 atm and to a 5 m/s lateral impact. Results from the simulations demonstrate that blasts can penetrate the intracranial cavity and generate intracranial pressures that exceed the pressures produced during impact; the results suggest that blasts can plausibly directly cause traumatic brain injury. Subsequent investigation of the effect of the ACH on the blast response of the head found that the ACH provided minimal mitigation of blast effects. Results from the simulations conducted with the FHM extended to include the ACH suggest that the ACH can slightly reduce peak pressure magnitudes and delay peak pressure arrival times, but the benefits are minimal because the ACH does not protect the main pathways of load transmission from the blast to brain tissue. A more effective blast mitigation strategy might involve altering the helmet design to more completely surround the head in order to protect it from direct exposure to blast waves. / by Michelle K. Nyein. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 89). / by Jean-Benoît Ferry. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged student-submitted from PDF version of thesis. / Includes bibliographical references (pages 98-101). / This research conducts a broad systems-based analysis of CubeSat engineering, with a focus on testing, failures, and their relationship to program cost, in order to assess multiple build approaches with a goal of maintaining the advantages of CubeSat missions while increasing reliability. In this work, the multiple approaches are called "beta build strategies," and we show that satellite engineering groups with minimal experience can increase their probability of success by building two flight-model versions of their satellite, allowing for more exhaustive and potentially failure-inducing testing to be conducted on the first (beta version) satellite. This differentiates itself from the standard CubeSat build approach, which is typically to build a flat sat, then an engineering model, and then a flight model of the satellite. Frequently with CubeSat development, the additional expense of building a flight-like engineering model is avoided. However, in this work we consider the probability of success and overall cost impact for multiple approaches toward the flight build. We find that by spending an additional 33% of the planned program cost, a team which plans to take this alternate approach from the beginning can build and launch two flight-model versions of their spacecraft, increasing probability of success by 30%. This cost corresponds to a 40% saving from the scenario in which the decision to build a second flight-model spacecraft is made only after the first fails. The question which this analysis tries to answer is not, "how does a group spend the least amount of money to get their first CubeSat into space?" but rather, "how does a group spend the least amount of money to get a CubeSat into space that works?" / by Zachary Scott Decker. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 129-148). / In the recent years there has been a growing interest in studying electromagnetic wave propagation at the nanoscale. The interaction of light with metallic nanostructures produces a collective excitation of conduction electrons at the metal surface, also known as surface plasmons. These plasmonic resonances enable an unprecedented control of light by confining the electromagnetic field to regions well beyond the diffraction limit, thereby leading to nearfield enhancements of the incident wave of several orders of magnitude. These remarkable properties have motivated the application of plasmonic devices in sensing, nano-resolution imaging, energy harvesting, nanoscale electronics and cancer treatment. Despite state-of-the-art nanofabrication techniques are used to realize plasmonic devices, their performance is severely impacted by fabrication uncertainties arising from extreme manufacturing constraints. Mathematical modeling and numerical simulation are therefore essential to accurately predict the response of the physical system, and must be incorporated in the design process. Nonetheless, plasmonic simulations present notable challenges. From the physical perspective, the realistic behavior of conduction electrons in metallic nanostructures is not captured by Maxwell's equations, thus requiring additional modeling. From the simulation perspective, the disparity in length scales stemming from the extreme field localization exceeds the capabilities of most numerical simulation schemes. In addition, relevant data such as optical constants or geometry specifications are typically subject to measurement and manufacturing errors, hence simulations need to accommodate uncertainty in the data. In this thesis we present a collection of numerical methods to efficiently simulate electromagnetic wave propagation through metallic nanostructures. Firstly, we develop the hybridizable discontinuous Galerkin (HDG) method for Maxwell's equations augmented with the hydrodynamic model for metals, which accounts for the nonlocal interactions between electrons that become predominant at nanometric regimes. Secondly, we develop a reduced order modeling (ROM) framework for Maxwell's equations with the HDG method, enabling the incorporation of material and geometric uncertainties in the simulations. The result is a family of surrogate models that produces accurate yet inexpensive simulations of plasmonic devices. Finally, we apply these approaches to the study of periodic annular nanogaps, and present parametric analyses, verification with experimental data and design of novel structures. / by Ferran Vidal-Codina. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988. / Includes bibliographical references. / by Michael R. Fisher, Jr. / Ph.D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007. / Includes bibliographical references (p. 307-324). / The capability to routinely perform autonomous docking is a key enabling technology for future space exploration, as well as assembly and servicing missions for spacecraft and commercial satellites. Particularly, in more challenging situations where the target spacecraft or satellite is tumbling, algorithms and strategies must be implemented to ensure the safety of both docking entities in the event of anomalies. However, difficulties encountered in past docking missions conducted with expensive satellites on orbit have indicated a lack of maturity in the technologies required for such operations. Therefore, more experimentation must be performed to improve the current autonomous docking capabilities. The main objectives of the research presented in this thesis are to develop a guidance, navigation and control (GN&C) architecture that enables the safe and fuel-efficient docking with a free tumbling target in the presence of obstacles and anomalies, and to develop the software tools and verification processes necessary in order to successfully demonstrate the GN&C architecture in a relevant environment. The GN&C architecture was developed by integrating a spectrum of GN&C algorithms including estimation, control, path planning, and failure detection, isolation and recovery algorithms. / (cont.) The algorithms were implemented in GN&C software modules for real-time experimentation using the Synchronized Position Hold Engage and Reorient Experimental Satellite (SPHERES) facility that was created by the MIT Space Systems Laboratory. Operated inside the International Space Station (ISS), SPHERES allow the incremental maturation of formation flight and autonomous docking algorithms in a risk-tolerant, microgravity environment. Multiple autonomous docking operations have been performed in the ISS to validate the GN&C architecture. These experiments led to the first autonomous docking with a tumbling target ever achieved in microgravity. Furthermore, the author also demonstrated successful docking in spite of the presence of measurement errors that were detected and rejected by an online fault detection algorithm. The results of these experiments will be discussed in this thesis. Finally, based on experiments in a laboratory environment, the author establishes two processes for the verification of GN&C software prior to on-orbit testing on the SPHERES testbed. / by Simon Nolet. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 235-239). / I envision a future where collaboration between humans and robots will be indispensable to our work in numerous domains, ranging from surgery to space exploration. The success of these systems will depend in part on the ability of robots to integrate within existing human teams. The goal of this thesis is to develop robot partners that we can work with easily and naturally, inspired by the way we work with other people. My hypothesis is that human-robot team performance improves when a robot teammate emulates the effective coordination behaviors observed in human teams. I design and evaluate Chaski, a robot plan execution system that uses insights from human-human teaming to make human-robot teaming more natural and fluid. Chaski is a task-level executive that enables a robot to robustly anticipate and adapt to other team members. Chaski also emulates a human's response to implicit communications, including verbal and gestural cues, and explicit commands. Development of such an executive is challenging because the robot must be able to make decisions very quickly in response to a human's actions. In the past, the ability of robots to demonstrate these capabilities has been limited by the time-consuming computations required to anticipate a large set of possible futures. These computations result in execution delays that endanger the robot's ability to fulfill its role on the team. I significantly improve the ability of a robot to adapt on-the-fly by generalizing the state-of-the-art in dynamic plan execution to support just-in-time task assignment and scheduling. My methods provide a novel way to represent the robot's plan compactly. This compact representation enables the plan to be incrementally updated very quickly. I empirically demonstrate that, compared to prior work in this area, my methods increase the speed of online computation by one order of magnitude on average. I also show that 89% of moderately-sized benchmark plans are updated within human reaction time using Chaski, compared to 24% for prior art. I evaluate Chaski in human subject experiments in which a person works with a mobile and dexterous robot to collaboratively assemble structures using building blocks. I measure team performances outcomes for robots controlled by Chaski compared to robots that are verbally commanded, step-by-step by the human teammate. I show that Chaski reduces the human's idle time by 85%, a statistically significant difference. This result supports the hypothesis that human-robot team performance is improved when a robot emulates the effective coordination behaviors observed in human teams. / by Julie A. Shah. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 161-172). / Engineering systems of the modern day are increasingly complex, often involving numerous components, countless mathematical models, and large, globally-distributed design teams. These features all contribute uncertainty to the system design process that, if not properly managed, can escalate into risks that seriously jeopardize the design program. In fact, recent history is replete with examples of major design setbacks due to failure to recognize and reduce risks associated with performance, cost, and schedule as they emerge during the design process. The objective of this thesis is to develop methods that help quantify, understand, and mitigate the effects of uncertainty in the design of engineering systems. The design process is viewed as a stochastic estimation problem in which the level of uncertainty in the design parameters and quantities of interest is characterized probabilistically, and updated through successive iterations as new information becomes available. Proposed quantitative measures of complexity and risk can be used in the design context to rigorously estimate uncertainty, and have direct implications for system robustness and reliability. New local sensitivity analysis techniques facilitate the approximation of complexity and risk in the quantities of interest resulting from modifications in the mean or variance of the design parameters. A novel complexity-based sensitivity analysis method enables the apportionment of output uncertainty into contributions not only due to the variance of input factors and their interactions, but also due to properties of the underlying probability distributions such as intrinsic extent and non-Gaussianity. Furthermore, uncertainty and sensitivity information are combined to identify specfic strategies for uncertainty mitigation and visualize tradeoffs between available options. These approaches are integrated with design budgets to guide decisions regarding the allocation of resources toward improving system robustness and reliability. The methods developed in this work are applicable to a wide variety of engineering systems. In this thesis, they are demonstrated on a real-world aviation case study to assess the net cost-benet of a set of aircraft noise stringency options. This study reveals that uncertainties in the scientific inputs of the noise monetization model are overshadowed by those in the scenario inputs, and identifies policy implementation cost as the largest driver of uncertainty in the system. / by Qinxian He. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 85-87). / In numerous scientific and engineering fields, sensitivity analysis tools are essential for design optimization as well as uncertainty quantification. For instance, adjoint algorithms are common place in aerospace engineering when it comes to optimize the shape of an airfoil, the configuration of a rocket or to quantify the impact of a manufacturing imperfection on the performance of a product. The quantities of interest are long-time averaged outputs such as the average drag on a plane wing. However, these conventional methods fail to compute the right sensitivity when the physical model exhibits chaos. This is the case of many turbulent fluid flows and atmospheric modelisations. A recently developed method, Least Squares Shadowing or simply LSS, tackles this problem and proposes an alternative approach to compute the desired sensitivities. The results are very promising and this thesis is intended to lay the mathematical foundations of this new algorithm. A latter part is dedicated to some improvements of LSS which make it faster and more reliable. / by Mario Chater. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 115-122). / Extravehicular Activity (EVA) is a critical component of human spaceflight. Working in gas-pressurized space suits, however, causes fatigue, unnecessary energy expenditure, and injury. The problem of injury is particularly acute and is exacerbated with the additional hours astronauts spend training inside the suit, especially underwater in NASA's Neutral Buoyancy Laboratory (NBL). Although space suit performance and improved system designs have been investigated, relatively little is known about how the astronaut moves and interacts with the space suit, what factors lead to injury, and how to prevent injury. At the outset of this research effort there were no technologies suitable to evaluate human movement and contact within the space suit during dynamic movements. The objective of this thesis is to help understand human-space suit interaction and design hardware to assess and ultimately mitigate injury. This is accomplished through two specific aims. The first specific aim is to use data mining techniques to uncover trends in space suit configuration, training environment, and anthropometry, which may lead to injury. Two groups of subjects were analyzed: those whose reported shoulder injury incidence is specifically attributable to the NBL or working in the space suit, and those whose shoulder problems began in active duty, meaning working in the suit could have been a contributing factor. The first statistical model correctly identifies 39% of injured subjects, while the second model correctly identifies 68% of injured subjects. For both models, percent of training incidence in the space suit planar hard upper torso (HUT) was the most important predictor variable. Frequency of training and recovery between training were also identified as significant metrics. These variables can be monitored and modified operationally to reduce the impacts on the astronaut's health. Several anthropometric dimensions were also found to have explanatory power for injury. Expanded chest depth was included in both models, while bi-deltoid breadth was relevant for identifying injured NBL subjects and shoulder circumference was relevant for identifying injured Active subjects. These dimensions may be targeted as particularly important to accommodate in future designs of the HUT or any advanced concept space suits. Finally, for the NBL subjects, previous record of injury was found to be an important factor. Further descriptive analysis implies that analyzing the HUT style and size together may be critical for future detailed studies on fit and accommodation. These results quantitatively elucidate the underlying mechanisms of shoulder injuries for astronauts working inside the space suit. The second specific aim is to develop a wearable pressure sensing capability to quantitatively measure areas on the body's surface that the space suit impacts during normal EVA movement. A low-pressure sensing system was designed and constructed for the upper body during dynamic movements inside the space suit environment. Sensors were designed to measure between 5-60 kPa with approximately 1 kPa resolution. The sensors are constructed from hyper-elastic silicone imbedded with a microfluidic channel. The channel is filled with liquid conductive metal, galinstan, such that an applied pressure corresponds to a change in resistance of the liquid metal. The system of 12 pressure sensors accommodates anthropometry from a 50th percentile female to a 95th percentile male upper body dimensions with near shirt-sleeve mobility. The wiring was intentionally designed to achieve the best trade between flexibility, resistance, and stretch ability, but ultimately was the greatest limitation in system durability. The electronics architecture utilizes onboard data storage with more than 4 hours of use. The entire system was designed with extreme environments in mind, where considerations of shock, battery hazards, and material properties in mixed gas, pressurized atmosphere were minimized to ensure user safety. The pressure sensing system was used in a human subject experiment to characterize human-suit interaction. Three experienced subjects were asked to perform a series of 3 isolated joint movements and 2 functional tasks, all focused on upper body movement. Movements were repeated 12 times each and pressure responses were evaluated both by quantifying peak pressure and full profile responses. Comparing subjective feedback to the quantitative pressure data allows a sense of the variability of movement and minor changes in loading on the body while performing suited motions. Users generally felt they were consistent for all movements. However, using a nonparametric H-test, 53% of movements were found to be biomechanically inconsistent (p < 0.05). This experiment provided the first "window" inside the suit to evaluate contact pressures and sequential indexing of the person inside the suit for realistic EVA movement. It cannot be extrapolated how changes in contact pressure would affect a subject's propensity for injury as injuries accumulate over long time scales. However, changes in pressure may be due to alterations in biomechanical strategies or fatigue, both of which could be precursors for injury and discomfort. This work focuses on the upper body, but the methods may be extended to the full body as future work. It provides solutions that could be applied beyond the field of aerospace to assess human-garment interactions and recommending armor protection for defense applications to alleviate fall impacts for medical applications. The contributions to the field include the development of a protection system that assesses and prevents injury inside gas-pressurized space suits. / by Allison Anderson. / Ph. D.