Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997. / Includes bibliographical references (p. 91-93). / by Christian M. Jacquemont. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1996. / Includes bibliographical references (p. 165-168). / by Leonard Lublin. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 153-163). / This thesis presents a novel framework for safe online trajectory planning of unmanned vehicles through partially unknown environments. The basic planning problem is formulated as a receding horizon optimization problem using mixed-integer linear programming (MILP) to incorporate kino-dynamic, obstacle avoidance and collision avoidance constraints. Agile vehicle dynamics are captured through a hybrid control architecture that combines several linear time-invariant modes with a discrete set of agile maneuvers. The latter are represented by affine transformations in the state space and can be described using a limited number of parameters. We specialize the approach to the case of a small-scale helicopter flying through an urban environment. Next, we introduce the concept of terminal feasible invariant sets in which a vehicle can remain for an indefinite period of time without colliding with obstacles or other vehicles. These sets are formulated as affine constraints on the last state of the planning horizon and as such are computed online. They guarantee feasibility of the receding horizon optimization at future time steps by providing an a priori known backup plan that is dynamically feasible and obstacle-free. / (cont.) Vehicle safety is ensured by maintaining a feasible return trajectory at each receding horizon iteration. The feasibility and safety constraints are essential when the vehicle is maneuvering through environments that are only partially characterized and further explored online. Such a scenario was tested on an unmanned Boeing aircraft using scalable loiter circles as feasible invariant sets. The terminal feasible invariant set concept forms the basis for the construction of a provably safe distributed planning algorithm for multiple vehicles. Each vehicle then only computes its own trajectory while accounting for the latest plans and invariant sets of the other vehicles in its vicinity, i.e., of those whose reachable sets intersect with that of the planning vehicle. Conflicts are solved in real-time in a sequential fashion that maintains feasibility for all vehicles over all future receding horizon iterations. The algorithm is applied to the free flight paradigm in air traffic control and to a multi-helicopter relay network aimed at maintaining wireless line of sight communication in a cluttered environment. / by Tom Schouwenaars. / Ph.D.

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.