The Space Shuttle Columbia accident and the recent excitement surrounding Discovery's return to space brought excessive media attention to the foam products used on the External Tank (ET). In both cases, videos showed chunks of foam or ablative material falling away from the ET during lift off. This led to several years of investigation and research into the exact cause of the accident and potential solutions to avoid the problem in the future. Several design changes were made prior to the return to flight this year, but the ET still shed foam during lift off. Since the Columbia accident, the loss of foam on ETs has been a significant area of interest for NASA, United Space Alliance, and Lockheed Martin. The Columbia Accident Investigation Board did not evaluate alternative materials but certainly highlighted the need for change. The majority of the research previously concentrated on improving the design and/or the application process of the current materials. Within recent years, some research and testing has been done to determine if a glass microsphere composite foam would be an acceptable alternative, but this work was overcome by the need for immediate change to return the shuttle to flight in time to deliver supplies to the International Space Station. Through a better understanding of the foam products currently used on the ET, other products can be evaluated for future space shuttle flights and potential applications on new space vehicles. The material properties and the required functionality of alternative materials can be compared to the current materials to determine if suitable replacement products exist. This research also lends itself to the development of future space flight and unmanned launch vehicles. In this paper, the feasibility of alternative material for the space shuttle's external tank will be investigated. Research on what products are used on the ET and a set of functional requirements driving the selection of those materials will be presented. The material properties of the current ET foam products will be collected and an evaluation of how those materials' properties meet the functional requirements will be accomplished. Then significant research on polymeric foams and ablative materials will be completed to learn how these various products can be applied in this industry. With this research and analysis, the knowledge gained will be used to select and evaluate the effectiveness of an alternate product and to determine feasibility of a product change with the current ET and the importance of maintaining the shuttle launch schedule. This research will also be used to evaluate the potential application of the alternative product on future platforms. There are several possible outcomes to this research. This research could result in a recommended change to the ET foam material or a perfectly acceptable alternative material that could result in a cost or schedule impact if implemented. It is also possible that there exists no suitable alternative material given the existing functional requirements. In any case, the alternative material could have future applications on new space vehicles. A set of results from the research and analysis will be provided along with a recommendation on a future material for use on space vehicles.

This study researched the history of Space Shuttle Reusable Surface Insulation which was designed and developed for use on the United States Orbiter fleet to protect from the high heating experienced during reentry through Earth's atmosphere. Specifically the tile system which is attached to the structure by the means of an RTV adhesive has experienced situations where the bonds are identified as subnominal. The history of these subnominal conditions is presented along with a recent identification of a subnominal bond between the Strain Isolation Pad and the tile substrate itself. Tests were run to identify the cause of these subnominal conditions and also to show how these conditions were proved to be acceptable for flight. The study also goes into cases that could be used to identify subnominal conditions on tile as a non-destructive test prior to flight. Several options of non-destructive testing were identified and recommendations are given for future research into this topic. A recent topic is also discussed in the instance where gap fillers were identified during the STS-114 mission that did not properly adhere to the substrate. The gap fillers were found protruding past the Outer Mold Line of the vehicle which required an unprecedented spacewalk to remove them to allow for a safe reentry through the atmosphere.

This dissertation presents a new approach for identifying, assessing, mitigating, and managing the risks of failure in complex systems. It describes the paradigm commonly used today to explain such failures and proposes an alternative paradigm that expands the lens for viewing failures to include alternative theories derived from modern theories of physics. Further, it describes the foundation for each paradigm and illustrates how the paradigms may be applied to a particular system failure. Today, system failure commonly is analyzed using a paradigm grounded in classical or Newtonian physics. This branch of science embraces the principles of reductionism, cause and effect, and determinism. Reductionism is used to dissect the system failure into its fundamental elements. The principle of cause and effect links the actions that led to the failure to the consequences that result. Analysts use determinism to establish the linear link from one event to another to form the chain that reveals the path from cause to consequence. As a result, each failure has a single cause and a single consequence. An alternative paradigm, labeled contemporary, incorporates the Newtonian foundation of the classical paradigm, but it does not accept the principles as inviolate. Instead, this contemporary paradigm adopts the principles found in the theories of relativity, quantum mechanics, chaos, and complexity. These theories hold that any analysis of the failure is affected by the frame of reference of the observer. Causes may create non-linear effects and these effects may not be observable directly. In this paradigm, there are assumed to be multiple causes for any system failure. Each cause contributes to the failure to a degree that may not be measurable using techniques of classical physics. The failure itself generates multiple consequences that may be remote in place or time from the site of the failure, and which may affect multiple individuals and organizations. Further, these consequences, are not inevitable, but may be altered by actions taken prior to and responses taken after the occurrence of the failure. The classical and contemporary paradigms are applied using a single embedded case study, the failure of the space shuttle Challenger. Sources, including literature and popular press articles published prior to and after the failure and NASA documents are reviewed to determine the utility of each paradigm. These reviews are supplemented by interviews with individuals involved in the failure and the official investigations that followed. This dissertation demonstrates that a combination of the classical and contemporary paradigms provides a more complete, and more accurate, picture of system failure. This combination links the non-deterministic elements of system failure analysis to the more conventional, deterministic theories. This new framework recognizes that the complete prevention of failure cannot be achieved; instead it makes provisions for preparing for and responding to system failure. / Ph. D.

Historical accounts depict NASA's interactions with American citizens beyond government agencies and aerospace firms since the 1950s and 1960s as efforts to 'sell' its human space flight initiatives and to position external publics as would-be observers, consumers, and supporters of such activities. Characterizing citizens solely as celebrants of NASA's successes, however, masks the myriad publics, engagement modes, and influences that comprised NASA's efforts to forge connections between human space flight and citizens after Apollo 11 culminated. While corroborating the premise that NASA constantly seeks public and political approval for its costly human space programs, I argue that maintaining legitimacy in light of shifting social attitudes, political priorities, and divided interest in space flight required NASA to reconsider how to serve and engage external publics vis-à-vis its next major human space program, the Space Shuttle. Adopting a sociotechnical imaginary featuring the Shuttle as a versatile technology that promised something for everyone, NASA sought to engage citizens with the Shuttle in ways appealing to their varied, expressed interests and became dependent on some publics' direct involvement to render the vehicle viable economically, socially, and politically. NASA's ability and willingness to democratize the Shuttle proved difficult to sustain, however, as concerns evolved following the Challenger accident among NASA personnel, political officials, and external publics about the Shuttle's purpose, value, safety, and propriety. Mapping the publics and engagement modes NASA regarded as crucial to the Shuttle's legitimacy, this case study exposes the visions of public accountability and other influences -- including changing perceptions of a technology -- that can govern how technoscientific institutions perceive and engage various external publics. Doing so illuminates the prospects and challenges associated with democratizing decisions and uses for space and, perhaps, other technologies managed by U.S. government agencies while suggesting a new pathway for scholarly inquiry regarding interactions between technoscientific institutions and external publics. Expanding NASA's historical narrative, this study demonstrates that entities not typically recognized as space program contributors played significant roles in shaping the Shuttle program, substantively and culturally. Conceptualizing and valuing external publics in these ways may prove key for NASA to sustain human space flight going forward. / Ph. D.

This thesis examines the growth of the space elevator community in America from 1975 to 2010. It argues that the continued practical failures of the space elevator, a proposed technology for efficiently transporting payloads and people into space without conventional propulsion sources, resulted from a technological paradigm built around the rocket and supported by a traditional engineering culture. After its triumph in landing men on the Moon from 1969 to 1972, the United States' National Aeronautics and Space Administration (NASA) sought to advance novel concepts for further space exploration, but it fumbled in pursuing nontraditional notions of escaping the atmosphere such as the space elevator. Employing interviews with space elevator advocates Bradley Edwards and Michael Laine and other primary and secondary sources, this thesis also draws on concepts such as technological paradigms, engineering cultures, and the technological sublime. It concludes by demonstrating how success eluded the marginalized space elevator researchers who found themselves grappling with the vast social and technical system that supported the rocket's hegemony. / Master of Arts / This thesis examines the growth of the space elevator community in America from 1975 to 2010. It argues that the continued practical failures of the space elevator, a proposed technology for efficiently transporting payloads and people into space without conventional propulsion sources, resulted from a technological paradigm built around the rocket and supported by a traditional engineering culture. The technological paradigm of the rocket encompassed all of the people and practices that made the rocket work. After its triumph in landing men on the Moon from 1969 to 1972, the United States' National Aeronautics and Space Administration (NASA) sought to advance novel concepts for further space exploration, but it fumbled in pursuing nontraditional notions of escaping the atmosphere such as the space elevator. Much of this failure is owed to an engineering culture within NASA that looked down upon challenging the rocket. This thesis demonstrates how success eluded the marginalized space elevator researchers who found themselves grappling with the vast social and technical system that supported the rocket's hegemony.

On January 14, 2004, President George W. Bush announced the Vision for Space Exploration (VSE). The goals of the vision include developing a new generation launch capability while completing assembly of the International Space Station (ISS) and retiring the Space Shuttle by 2010. In support of this goal, the Space Shuttle Program (SSP) initiated evaluation of hardware, infrastructure, and workforce skill mix needed to continue Space Shuttle flights until the projected 2010 retirement. The SSP also studied how NASA will deploy personnel from, and use the facilities of, the SSP to ensure that the Space Shuttle operates safely through its final flight, and to ensure personnel and facilities from the SSP are effectively transitioned to NASA’s exploration programs. NASA funding, like other federal agencies, is affected by various factors including domestic and international political environments, current and emerging technologies available to meet agency goals, and sustainability and potential economic return of federal expenditures. In this paper I will present a retrospective analysis of federal budget allocations to NASA as a percentage of the Federal Budget from years 1958 to 2010 (adjusted to 1979 dollars). The classic method for calculating net present value (NPV) is not well suited for projecting potential value of future R&D technologies. A quantitative analysis of R&D technologies transferred to private industry will be presented, as well as a description of a method of evaluating their significance will discussed relative to current budgetary considerations will likely for past, current and upcoming funding cycles. The opportunity at hand for NASA’s transition from SSP to Constellation in support of the VSE initiative is to advocate their culture as R&D innovators and emphasize the future benefit of increased funding. / text

Despite the critical importance of project completion timeliness, management practices in place today remain inadequate for addressing the persistent problem of project completion tardiness. Uncertainty has been identified as a contributing factor in late projects. This uncertainty resides in activity duration estimates, unplanned upsetting events, and the potential unavailability of critical resources. This research developed a comprehensive simulation based methodology for conducting quantitative project completion-time risk assessments. The methodology enables project stakeholders to visualize uncertainty or risk, i.e. the likelihood of their project completing late and the magnitude of the lateness, by providing them with a completion time distribution function of their projects. Discrete event simulation is used to determine a project's completion distribution function. The project simulation is populated with both deterministic and stochastic elements. Deterministic inputs include planned activities and resource requirements. Stochastic inputs include activity duration growth distributions, probabilities for unplanned upsetting events, and other dynamic constraints upon project activities. Stochastic inputs are based upon past data from similar projects. The time for an entity to complete the simulation network, subject to both the deterministic and stochastic factors, represents the time to complete the project. Multiple replications of the simulation are run to create the completion distribution function. The methodology was demonstrated to be effective for the on-going project to assemble the International Space Station. Approximately $500 million per month is being spent on this project, which is scheduled to complete by 2010. Project stakeholders participated in determining and managing completion distribution functions. The first result was improved project completion risk awareness. Secondly, mitigation options were analyzed to improve project completion performance and reduce total project cost.

Cette thèse porte sur le développement d'une loi de guidage autonome par platitude pour les véhicules de rentrée atmosphérique. La problématique associée au développement d'une loi de guidage autonome porte sur l'organisation globale, l'intégration et la gestion de l'information pertinente jusqu'à la maîtrise du système spatial durant la phase de rentrée. La loi de guidage autonome proposée dans ce mémoire s'appuie sur le concept de platitude, afin d'effectuer un traitement des informations à bord, dans le but double d'attribuer un niveau de responsabilité et d'autonomie au véhicule, déchargeant ainsi le segment sol de tâches opérationnelles "bas niveau", pour lui permettre de mieux assumer son rôle de coordination globale. La première partie de ce mémoire traite de la caractérisation formelle de sorties plates pour les systèmes non linéaires régis par des équations différentielles ordinaires, ainsi que pour les systèmes linéaires à retards. Des algorithmes constructifs sont proposés afin de calculer des sorties plates candidates sous un environnement de calcul formel standard. Dans la seconde partie, une méthodologie complète et générique de replanification de trajectoires de rentrée atmosphérique est proposée, afin de doter la loi de guidage d'un certain niveau de tolérance à des pannes actionneur simple/multiples pouvant survenir lors des phases critiques d'une mission de rentrée atmosphérique. En outre, une méthodologie d'annexation superellipsoidale est proposée afin de convexifier le problème de commande optimale décrit dans l'espace des sorties plates. La loi de guidage proposée est ensuite appliquée étape par étape à une mission de rentrée atmosphérique pour la navette spatiale américaine STS-1. / This thesis deals with the design of an autonomous guidance law based on flatness approach for atmospheric reentry vehicles. The problematic involved by the design of an autonomous guidance law relates to the global organization, the integration and the management of relevant data up to the mastering of the spacecraft during the re-entry mission. The autonomous guidance law proposed in this dissertation is based on flatness concept, in order to perform onboard processing so as to locally assign autonomy and responsibility to the vehicle, thus exempting the ground segment from "low level" operational tasks, so that it can ensure more efficiently its mission of global coordination. The first part of the manuscript deals with the formal characterization of flat outputs for nonlinear systems governed by ordinary differential equations, as well as for linear time-delay systems. Constructive algorithms are proposed in order to compute candidate flat outputs within a standard formal computing environment. In the second part of the manuscript, a global and generic reentry trajectory replanning methodology is proposed in order to provide a fault-tolerance capability to the guidance law, when facing single/multiple control surface failures that could occur during the critical phases of an atmospheric reentry mission. In addition, a superellipsoidal annexion method is proposed so as to convexify the optimal control problem described in the flat outputs space. The proposed guidance law is then applied step by step to an atmospheric reentry mission for the US Space Shuttle orbiter STS-1.

<div>Optimal control theory (OCT) exists since the 1950s. However, with the advent of modern computers, the design community delegated the task of solving the optimal control problems (OCPs) largely to computationally intensive direct methods instead of methods that use OCT. Some recent work showed that solvers using OCT could leverage parallel computing resources for faster execution. The need for near real-time, high quality solutions for OCPs has therefore renewed interest in OCT in the design community. However, certain challenges still exist that prohibits its use for solving complex practical aerospace problems, such as landing human-class payloads safely on Mars.</div><div><br></div><div>In order to advance OCT, this thesis introduces Epsilon-Trig regularization method to simply and efficiently solve bang-bang and singular control problems. The Epsilon-Trig method resolves the issues pertaining to the traditional smoothing regularization method. Some benchmark problems from the literature including the Van Der Pol oscillator, the boat problem, and the Goddard rocket problem verified and validated the Epsilon-Trig regularization method using GPOPS-II.</div><div><br></div><div>This study also presents and develops the usage of trigonometry for incorporating control bounds and mixed state-control constraints into OCPs and terms it as Trigonometrization. Results from literature and GPOPS-II verified and validated the Trigonometrization technique using certain benchmark OCPs. Unlike traditional OCT, Trigonometrization converts the constrained OCP into a two-point boundary value problem rather than a multi-point boundary value problem, significantly reducing the computational effort required to formulate and solve it. This work uses Trigonometrization to solve some complex aerospace problems including prompt global strike, noise-minimization for general aviation, shuttle re-entry problem, and the g-load constraint problem for an impactor. Future work for this thesis includes the development of the Trigonometrization technique for OCPs with pure state constraints.</div>