Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 123). / This thesis investigates the potential of a space-based navigation concept known as Skymark to improve upon the accuracy of inertially-guided intercontinental ballistic missiles (ICBMs). The concept is to use an optical tracker to take line-of-sight measurements to nearby space objects with known ephemerides to update the state knowledge of the onboard inertial navigation system. The set of existing space objects that would be potentially useful for this application are tabulated, and a simulation determines their availability from realistic trajectories. A follow-on navigation simulation investigates the accuracy improvement potential in terms of Circular Error Probable at impact. Two scenarios are investigated, one in which the Skymark system is an add-on aid-to-inertial-navigation for an existing missile system, and one in which the Skymark system is completely integrated with a new inertial navigation unit. A sensitivity analysis is performed to determine how several performance factors affect Skymark accuracy. Finally, a brief discussion of some operational implementation issues is included. / by Weldon Barry Willhite. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012. / Cataloged from department-submitted PDF version of thesis. This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 123-135). / Adjoint analysis in computational fluid dynamics (CFD) has been applied to design optimization and mesh adaptation, but due to the relative expense of unsteady analysis these applications have predominantly been for steady problems. As the use of adjoint methods continues to becomes more prevalent, more problems are encountered for which steady analysis may not be appropriate. This thesis examines three aspects of unsteady adjoint analysis. First, this work investigates problems exhibiting small-scale output unsteadiness when solved with time-inaccurate iterative solvers. It is demonstrated that unconverged steady flow calculations, even with small output unsteadiness, can lead to significant variability in the estimated output sensitivity due to the arbitrary choice of unconverged state upon which the linearization is performed. Further, time-inaccurate "unsteady" iterative solutions depend on the iterative method used and may exhibit different output and output sensitivity compared to the steady flow or time-accurate unsteady flow. With the motivation for unsteady simulation established, output and output parameter sensitivities of periodic unsteady problems are sought using finite-time averaging. Periodic outputs computed over a finite time span are found to converge slowly and output sensitivities may be nonconvergent when the period of oscillation is a function of the parameter of interest. A theoretical basis for this lack of convergence is identified and output windowing is proposed to alleviate its effect. Output windowing is shown to enable the accurate computation of periodic output sensitivities and to decrease simulation time to compute periodic outputs and sensitivities. Finally, a spatial mesh adaptation approach is developed for unsteady wake problems and other problems with smooth and persistent regions of unsteadiness. For this class of problems, a higher-order discretization coupled with a single spatial mesh approach is appropriate to capture both steady and unsteady regions. The method proposed herein extends the anisotropic, output-based Mesh Optimization via Error Sampling and Synthesis (MOESS) algorithm of Yano and Darmofal to optimize the spatial mesh driven by an unsteady flow field. / by Joshua Ambre Krakos. / Ph.D.

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 (leae 39). / Piezomechanical loading of an adhesive joint is a very close analogue to the loading imposed by adherends with dissimilar thermal expansion coefficients under a temperature change. Using this concept, a double lap joint test specimen was developed to investigate the damage mechanisms in solder joints for electronic packaging applications under cyclic loading conditions. Analytical results are derived for the plastic shear strain at the free edges of such a specimen using a shear lag model. Results are also presented for the strain energy release rate for steady state crack growth. Experimental results and observations are presented for the damage processes in lead-tin eutectic solder joints between PZT-5H adherends. The lifetime of a specimen can be divided into two regimes: initiation and steady crack growth. Cracking was generally observed to initiate at voids and other defects in the solder joint. The time to initiate damage, the total joint life, and crack growth rates were quantified as a function of applied loading. Data for damage initiation was quite scattered, reflecting the variation in joint quality, but broadly conformed to a Coffin-Manson relationship. The data for crack growth rate approximately corresponded to a Paris law at higher applied voltages. At lower voltages, a strong dependence on frequency was observed, and there was evidence of a threshold strain-energy release rate. Crack growth rates increased with increasing temperature over the range 0- 25°C, but decreased up to 80°C. The appendices detail the specimen manufacturing techniques, the experimental set-up, and the testing methods and regime. An expanded literature review for this work is also provided in the appendices for further background and insight as to the issues surrounding adhesive fatigue. / by Catherine L. Sanders. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references (p. 141-144). / A trajectory optimization study for a soft landing on the Moon, which analyzed the effects of adding operationally based constraints on the behavior of the minimum fuel trajectory, has been completed. Metrics of trajectory evaluation included fuel expenditure, terminal attitude, thrust histories, etc.. The vehicle was initialized in a circular parking orbit and the trajectory divided into three distinct phases: de-orbit, descent, and braking. Analysis was initially performed with two-dimensional translational motion, and the minimally constrained optimal trajectory was found to be operationally infeasible. Operational constraints, such as a positive descent orbit perilune height and a vertical terminal velocity, were imposed to obtain a viable trajectory, but the final vehicle attitude and landing approach angle remained largely horizontal. This motivated inclusion of attitude kinematics and constraints to the system. With rotational motion included, the optimal solution was feasible, but the trajectory still had undesirable characteristics. Constraining the throttle to maximum during braking produced a steeper approach, but used the most fuel. The results suggested a terminal vertical descent was a desirable fourth segment of the trajectory. which was imposed by first flying to an offset point and then enforcing a vertical descent, and provided extra safely margin prior to landing. In this research, the relative effects of adding operational constraints were documented and can be used as a baseline study for further detailed trajectory optimization. / by Alisa Michelle Hawkins. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990. / Includes bibliographical references (leaves 62-64). / by William James Steptoe. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1993. / Includes bibliographical references (leaves 78-79). / by Andrew Kevin Barrows. / M.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998. / Includes bibliographical references. / by Jean-Marc C. Hauss. / M.Eng.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013. / This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from department-submitted PDF version of thesis / Includes bibliographical references (p. 99-102). / Multidisciplinary design optimization (MDO) is becoming an essential tool for the design of engineering systems due to the inherent coupling between discipline analyses and the increasing complexity of such systems. An important component of MDO is effective exploration of the design space since this is often a key driver in finding characteristics of systems which perform well. However, many design space exploration techniques scale poorly with the number of design variables and, moreover, a large-dimensional design space can be prohibitive to designer manipulation. This research addresses complexity management in trade-space exploration of multidisciplinary systems, with a focus on the conceptual design of Blended Wing Body (BWB) aircraft. The objectives of this thesis are twofold. The first objective is to create a multidisciplinary tool for the design of BWB aircraft and to demonstrate the performance of the tool on several example trade studies. The second objective is to develop a methodology for reducing the dimension of the design space using designer-chosen partitionings of the design variables describing the system. The first half of this thesis describes the development of the BWB design tool and demonstrates its performance via a comparison to existing methods for the conceptual design of an existing BWB configuration. The BWB design tool is then demonstrated using two example design space trades with respect to planform geometry and cabin bay arrangement. Results show that the BWB design tool provides sufficient fidelity compared to existing BWB analyses, while accurately predicting trends in system performance. The second half of this thesis develops a bi-level methodology for reducing the dimension of the design space for a trade space exploration problem. In this methodology, the designer partitions the design vector into an upper- and lower-level set, wherein the lower-level variables essentially serve as parameters, in which their values are chosen via an optimization with respect to some lower-level objective. This reduces the dimension of the design space, thereby allowing a more manageable space for designer interaction, while subsequently ensuring that the lower-level variables are set to "good" values relative to the lower-level objective. The bi-level method is demonstrated on three test problems, each involving an exploration over BWB planform geometries. Results show that the method constructs surrogate models in which the sampled configurations have a reduction in the system objective by up to 4 % relative to surrogates constructed using a standard exploration. Furthermore, the problems highlight the potential for the framework to reduce the dimension of the design space such that the full space can be visualized. / by Cory Asher Kays. / 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 99-101). / Space shuttle entry guidance with an extended analytic range corrector method is presented. The guidance method is a variation of Shuttle entry guidance in which the parameters that define the drag profile are modified using quadratic splines to make the drag profile smooth and easier to customize. In general, in order to account for off-nominal entry conditions and ensure the vehicle flies the correct range to the runway, the nominal reference drag profile is modified on-line utilizing analytic expressions for the derivative of range with respect to the relevant drag profile parameter. This new profile is then used to calculate a reference drag command in the subsequent guidance algorithm cycle. Typical implementations of Shuttle entry guidance modify the drag profile using only one variable to shift the profile by a constant value. This presents problems when the vehicle is highly constrained and can easily violate constraints such as heat load and heat rate constraints due to small drag profile variations. The methods by which the drag profile is updated are changed in order to provide multiple perturbation options. In providing multiple drag profile update parameters, a memoryless range error allocator is implemented with a vector of weights as a design variable. The allocator parameters are designed to take into account heat load while remaining within constraints using a high L/D vertical takeoff horizontal landing reusable launch vehicle simulation. The resulting algorithm seeks to leverage the high-TRL Shuttle entry guidance routine by making minimal modifications to the implementation, while increasing robustness to entry interface dispersions under tight heating constraints. A discussion of the design of the drag profile is included, in which the selection of profile update parameters is explored. Results from optimization of these parameters using a genetic algorithm are presented, as well as Monte Carlo results demonstrating that the allocator can reduce failure rates due to tight drag constraints from 42% to 0%, establishing the impact and success of this analytic range corrector method. / by Erin Elizabeth Evans. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (p. 123-125). / (cont.) (incident rate and unnecessary alert rate), the MDP-based logic can meet or exceed that of alternate logics. / This thesis describes an approach to designing hazard avoidance alerting systems based on a Markov decision process (MDP) model of the alerting process, and shows its benefits over standard design methods. One benefit of the MDP method is that it accounts for future decision opportunities when choosing whether or not to alert, or in determining resolution guidance. Another benefit is that it provides a means of modeling uncertain state information, such as unmeasurable mode variables, so that decisions are more informed. A mode variable is an index for distinct types of behavior that a system exhibits at different times. For example, in many situations normal system behavior tends to be safe, but rare deviations from the normal increase the likelihood of a harmful incident. Accurate modeling of mode information is needed to minimize alerting system errors such as unnecessary or late alerts. The benefits of the method are illustrated with two alerting scenarios where a pair of aircraft must avoid collisions when passing one another. The first scenario has a fully observable state and the second includes an uncertain mode describing whether an intruder aircraft levels off safely above the evader or is in a hazardous blunder mode. In MDP theory, outcome preferences are described in terms of utilities of different state trajectories. In keeping with this, alerting system requirements are stated in the form of a reward function. This is then used with probabilistic dynamic and sensor models to compute an alerting logic (policy) that maximizes expected utility. Performance comparisons are made between the MDP-based logics and alternate logics generated with current methods. It is found that in terms of traditional performance measures / by Lee F. Winder. / Ph.D.