Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997. / Includes bibliographical references (v. 2, leaves 252-262). / by Mark A. Tudela. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 119-124). / Man-made space debris constitutes a major threat to the future of the space enterprise. The space surveillance community continually seeks more efficient and robust techniques for detecting and characterizing on-orbit debris. This thesis investigates the potential utility of a technique known as active polarimetry, by which a laser radar would illuminate a space object with polarized light and measure the polarization state of the reflected light. A debris fragment's polarimetric signature can help identify its material, shape, and orientation, and, by inference, its mass, origin, and other characteristics. The research takes both an experimental and modeling and simulation approach A bench-top polarimeter ([lambda] = 1064 nm) is used to determine the polarimetric Bidirectional Reflectance Distribution Function (BRDF) of several common spacecraft materials and coatings, including glossy white paint, matte black paint, black Kapton®, silver Teflon®, aluminum, and titanium. Measurements are made in both bistatic (in-plane scans for incident angles of 15°, 30°, 45°, 60°, and 75°) and monostatic (incident angles from 0° to 90°) geometries. The Mueller matrix of each material is then estimated as a function of the illumination and viewing angles. The results reveal notable trends in the materials' geometry-dependent polarimetric properties, particularly diattenuation (D), retardance (R), and depolarization power ([delta]). At specular points, metallic surfaces (i.e., aluminum and titanium) exhibit mirror-like behavior (D = 0, R = 180°, [delta] = 0), while paints and thin films (e.g., Kapton®) are diattenuating (D > 0). All the materials tend to be more depolarizing in the monostatic diffuse regime. Silver Teflon® follows the trends of a metallic surface, with the exception of its distinct retardance at the specular point (R = 115°) and range of retardance values in the bistatic diffuse region (R = 70° to 120°). Since measurements of on-orbit space debris will nominally be non-resolved (in angle), a simulation is also developed (and validated by experiments) to predict the polarimetric signature of non-resolved objects, given the measured polarimetric BRDFs of their constituent materials. The simulation is used to explore object signatures in a variety of engagement scenarios, including monostatic interrogations of stationary and tumbling objects with representative shapes (i.e., panels, spheres, and cylinders), as well as bistatic interrogations of objects with strong specular reflections. The results demonstrate that the signature of a non-resolved object is complex, but can be described as the weighted sum of the geometry-dependent polarimetric behaviors of its facets. In some cases, the signature bears a close resemblance to the behavior of the constituent material, e.g., a white-painted sphere exhibits D = 0, R = 180°, and [delta] = 0.88 in a monostatic geometry, which matches the behavior of glossy white paint in the monostatic diffuse regime. In other cases, the signature is unlike the behavior of any individual facet due to the way the facets' behaviors combine geometrically, e.g., a black-painted sphere exhibits A = 0.67, unlike the behavior of matte black paint at any angle ([delta] < 0.4). It is shown that the effective Mueller matrix of a fast tumbling object is simply the average Mueller matrix of the object over all orientations. The results reveal several opportunities for exploiting the signatures of non-resolved objects, at least in the context of the specific materials and shapes considered in this study. The signature of a stationary or slowly tumbling object can help exclude certain material identities, e.g., a slowly tumbling panel-shaped object with a diattenuation of D > 0.5 (or polarizance P > 0.5) cannot be metallic based on the distribution of possible signatures of metal surfaces. A fast-tumbling panel-shaped object covered in silver Teflon® exhibits the characteristic retardance (R = 115°) of silver Teflon* in a monostatic geometry. The monostatic signature of a fast tumbling object can still be indicative of its shape, e.g., a white-painted sphere exhibits a distinctly high depolarization power ([delta] = 0.88) compared to the low depolarization power ([delta] < 0.12) of a fast tumbling panel-shaped object or cylinder with the same coating. Since a passive system can only estimate an object's polarizance (P), current optical telescopes would not be able to determine and exploit many of these distinguishing features such as retardance and depolarization power. Several operational schemes for interrogating space objects with a ground-based polarimetric laser radar are proposed, including short- and long-duration interrogations and interrogations whose measurements are synchronized with the tumbling period of the object. The utility of polarimetric features is discussed in terms of their ability to discriminate between objects with different materials, shapes, and orientations, as well as to obtain fingerprints that can be used to identify objects in the future and monitor their changes. A look-up table is proposed to determine the number and types of measurements required for estimating different polarimetric properties. The table may be referenced to optimally plan a measurement campaign in the field that maximizes the number of objects measurable in a given period of time. The simulation tools and experimental configuration developed for this research are generally useful for assessing the utility of active polarimetry for other applications. / by Michael C. Pasqual. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1994. / Includes bibliographical references (leaves 285-294). / by Narendra Venugopal Bhat. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / Includes bibliographical references. / Legacy carriers developed hub networks to achieve a high concentration of operations, increase frequency, and serve multiple Origin-Destination markets with maximum efficiency. By contrast, the rapid emergence of low-cost carriers (LCCs) is mainly based on a low-fare entry strategy in point-to-point markets competing with the traditional connecting paths offered by the legacy carriers via their hubs. This thesis examines the traffic and revenue impacts of an LCC developing a point-to-point network in a legacy hub network environment. To this purpose, we use the Passenger Origin-Destination Simulator (PODS) to perform all quantitative evaluations. Modeling the choice of travelers with regard to flight schedules and fares, as well as the airlines' revenue management systems, PODS allows one to investigate the changes in aggregate and disaggregate airline statistics following the introduction of low-fare service on point-to-point routes. The first goal of the thesis is to review and update models of passenger choice between connecting legacy and non-stop low-cost paths. The review of the literature on air traveler choice provides parameters and benchmarks critical to the calibration of PODS. / (cont.) We then simulate a LCC entry case, and calibrate the Passenger Decision Model (PDM) embedded in PODS through sensitivity analysis. In the second part of the thesis, we analyze the introduction of LCC operations in two legacy hub networks, a theoretical symmetric and a more realistic asymmetric network. Two different LCC strategies were considered. In the first case, LCC routes are added to the legacy network with one daily frequency, while the second strategy is characterized by two daily flights in each market entered by the low-fare airline. For both networks and strategies, the analysis reveals that legacy revenues are greatly reduced whereas the decrease in legacy traffic is limited even with extended and aggressive low-cost competition, allowing the legacy carriers to maintain their network load factors at high levels. The lower fares implemented by the LCC and matched by the legacy airlines lead to the reduced legacy revenues. However, legacy carriers can rely on demand stimulation, as well as great demand in local hub markets and connecting markets not served by the LCC, to replace traffic captured by the new entrant. / by Gregory Zerbib. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1989. / Includes bibliographical references (leaves 126-128). / by Kenneth Brett Lazarus. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991. / Includes bibliographical references (leaves 122-123). / by Dwight D. Caldwell. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. / Includes bibliographical references (p. 89-91). / The National Aeronautics and Space Administration (NASA) and other entities in the aerospace industry have recently been considering distributed architectures for many space applications, such as space-based interferometry. Whether the craft in such a system are structurally connected or flown in tight formation, distribution allows for higher redundancy in case of failures as well as reducing the minimum payload footprint for launch. Designed to fly in precise formation, the SPHERES satellites rely on accurate system characteristics such as thruster strength and vehicle mass and inertia. The SPHERES testbed is described and the applications for formation flight are presented. Mass properties of the SPHERES satellites are examined because of their impact on control determination, with comparison between CAD model estimates and empirically determined values. The sensor and actuator suite, essential for closed-loop control, are also identified and characterized. A recursive least squares algorithm for determining mass properties in real time is explained and implemented both offline and online with results from test flights aboard NASA's KC-135 micro-gravity aircraft (Reduced Gravity Airplane, RGA). / by Dustin S. Berkovitz. / S.M.

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.