<div>Since as early as the 1920s, dinitrogen tetroxide (N2O4) has been regarded as a promising oxidizer in rocket propulsion systems. In more recent times, its predecessor, mixed oxides of nitrogen (MON), remains a top contender among oxidizers, due to its unique characteristics such as low freezing temperature and compatibility with common spacecraft materials. Today, these N2O4-based oxidizers are the preferred choice in many upper stages, launch escape systems, reaction control systems, liquid apogee engines, and in-space primary propulsion systems. N2O4-based oxidizers are a key factor in rocket propulsion, and thoroughly understanding their history, development, characteristics, synthesis, and composition analysis are crucial for space exploration today and into the future.<br><br></div><div>To fully understand and predict the physical properties of a MON sample, it is important to measure and quantify its chemical composition. The recommended method for MON composition analysis, as prescribed by the Department of Defense’s Defense Specification (MIL-SPEC) document on N2O4, involves the oxidation of NO and dinitrogen trioxide (N2O3) in the MON sample to determine their amounts. An equation unofficially called the “MIL-SPEC equation” is then used to determine the amount of NO needed to mix with N2O4 to synthesize that particular MON sample. However, no explanation is given as to how the equation was derived, or its significance.<br><br></div><div>This thesis aims to collect and organize key information on the synthesis, handling, and composition analysis of MON propellant. First, the history of development of N2O4-based oxidizers was researched, and current and future uses of N2O4 and MON propellants were identified. Then a method for synthesis and composition analysis was devised and tested. Water contamination was expected of skewing the results, so the process of water contamination was examined analytically. Then a detailed derivation of the MIL-SPEC equation was conducted, to fully understand its mechanics. An attempt was then made to reverse-engineer an unexplained numerical value in the equation, labeled by the author as the “solubility factor”. Several derivations were provided with varying degrees of complexity, producing alternative solubility factors of varying accuracies. Finally, experimental data was applied to these derived, hypothetical solubility factors and the MIL-SPEC solubility factor, with the intent of determining whether improvements could be made to the MON composition determination process.<br><br></div><div>The results suggest that the MIL-SPEC equation is sufficient for providing a relatively accurate measurement of the composition of a MON sample, while also being easy to implement, both in taking the necessary measurements and in conducting the numerical calculation. However, some minor adjustments to the equation could produce consistently more accurate composition measurements without adding any more difficulty or complication.</div>

<div>The orbits of interest for potential missions are stable or nearly stable to maintain long term presence for conducting scientific studies and to reduce the possibility of rapid departure. Near Rectilinear Halo Orbits (NRHOs) offer such stable or nearly stable orbits that are defined as part of the L1 and L2 halo orbit families in the circular restricted three-body problem. Within the Earth-Moon regime, the L1 and L2 NRHOs are proposed as long horizon trajectories for cislunar exploration missions, including NASA's upcoming Gateway mission. These stable or nearly stable orbits do not possess well-distinguished unstable and stable manifold structures. As a consequence, existing tools for stationkeeping and transfer trajectory design that exploit such underlying manifold structures are not reliable for orbits that are linearly stable. The current investigation focuses on leveraging stretching direction as an alternative for visualizing the flow of perturbations in the neighborhood of a reference trajectory. The information supplemented by the stretching directions are utilized to investigate the impact of maneuvers for two contrasting applications; the stationkeeping problem, where the goal is to maintain a spacecraft near a reference trajectory for a long period of time, and the transfer trajectory design application, where rapid departure and/or insertion is of concern.</div><div><br></div><div>Particularly, for the stationkeeping problem, a spacecraft incurs continuous deviations due to unmodeled forces and orbit determination errors in the complex multi-body dynamical regime. The flow dynamics in the region, using stretching directions, are utilized to identify appropriate maneuver and target locations to support a long lasting presence for the spacecraft near the desired path. The investigation reflects the impact of various factors on maneuver cost and boundedness. For orbits that are particularly sensitive to epoch time and possess distinct characteristics in the higher-fidelity ephemeris model compared to their CR3BP counterpart, an additional feedback control is applied for appropriate phasing. The effect of constraining maneuvers in a particular direction is also investigated for the 9:2 synodic resonant southern L2 NRHO, the current baseline for the Gateway mission. The stationkeeping strategy is applied to a range of L1 and L2 NRHOs, and validated in the higher-fidelity ephemeris model.</div><div><br></div><div>For missions with potential human presence, a rapid transfer between orbits of interest is a priority. The magnitude of the state variations along the maximum stretching direction is expected to grow rapidly and, therefore, offers information to depart from the orbit. Similarly, the maximum stretching in reverse time, enables arrival with a minimal maneuver magnitude. The impact of maneuvers in such sensitive directions is investigated. Further, enabling transfer design options to connect between two stable orbits. The transfer design strategy developed in this investigation is not restricted to a particular orbit but applicable to a broad range of stable and nearly stable orbits in the cislunar space, including the Distant Retrograde Orbit (DROs) and the Low Lunar Orbits (LLO) that are considered for potential missions. Examples for transfers linking a southern and a northern NRHO, a southern NRHO to a planar DRO, and a southern NRHO to a planar LLO are demonstrated.</div>

<div>Increasing flexibility of light manipulation is vital for various domains including both biomedical and military applications, where a lack of photon control could become critical. The efforts conducted and projected within this proposal are focused on three major areas: semi-continuous planar thin film photomodification for infrared (IR) filtering, nanosphere core-shell structures for obscurance, and all-dielectric sub-wavelength focal lenses for advanced IR sensing.Through a collaborative effort with the Army Research Office, we advanced the tunability of planar plasmonic filters with cutoff wavelengths in the 10–16μm range with photomodification using a 10.6μm CO2laser. Surface-enhanced molecular absorption in concert with three-dimensional (3D) Au nano-structures with inherent broad absorption in the IR band was a novel approach utilized to create such planar filters.Expanding on these, efforts and the results of the 2-dimensional (2D) semicontinuous Au plasmonic planar filtering, we further advanced our research with 3D Au nano-coreshell structures to enable levitated long-wavelength pass filter obscurants. We exploited the radiative effects of Au nano-structures that mimic conventional apertures or antennas, though these structures are on the nanometer scale and demonstrated the filtering characteristics through flow cell.In parallel with our plasmonic filtering we designed, manufactured and tested low loss dielectric microlenses for IR radiation based on a dielectric metasurface layer by patterning a SI substrate and etching to sub-micron depths. For a proof-of-concept lens demonstration,we chose a fine patterned array of nano-pillars with variable diameters.Merging our plasmonic filtering and dielectric microlens efforts, we created a holographic lenslet by designing and simulating a low loss focusing metasurface lens with engineered nano-scaled features to converge off-axis IR radiation. An array of nano-pillars with varied diameter and fixed height and periodicity was chosen for ease of fabrication with single layer etching</div>

The main body of this thesis consists of four appended papers. The first two consider different aspects of the trajectory planning problem, while the last two deal with observer design for mobile robotic and Euler-Lagrange systems respectively. The first paper addresses the problem of designing a real time, high performance trajectory planner for aerial vehicles. The main contribution is two-fold. Firstly, by augmenting a novel safety maneuver at the end of the planned trajectory, this paper extends previous results by having provable safety properties in a 3D setting. Secondly, assuming initial feasibility, the planning method is shown to have finite time task completion. Moreover, in the second part of the paper, the problem of simultaneous arrival of multiple aerial vehicles is considered. By using a time-scale separation principle, one is able to adopt standard Laplacian control to this consensus problem, which is neither unconstrained, nor first order. Direct methods for trajectory optimization are traditionally based on a priori temporal discretization and collocation methods. In the second paper, the problem of adaptive node distribution is formulated as a constrained optimization problem, which is to be included in the underlying nonlinear mathematical programming problem. The benefits of utilizing the suggested method for online trajectory optimization are illustrated by a missile guidance example. In the third paper, the problem of active observer design for an important class of non-uniformly observable systems, namely mobile robotics systems, is considered. The set of feasible configurations and the set of output flow equivalent states are defined. It is shown that the inter-relation between these two sets may serve as the basis for design of active observers. The proposed observer design methodology is illustrated by considering a unicycle robot model, equipped with a set of range-measuring sensors. Finally, in the fourth paper, a geometrically intrinsic observer for Euler-Lagrange systems is defined and analyzed. This observer is a generalization of the observer recently proposed by Aghannan and Rouchon. Their contractivity result is reproduced and complemented by a proof that the region of contraction is infinitely thin. However, assuming a priori bounds on the velocities, convergence of the observer is shown by means of Lyapunov's direct method in the case of configuration manifolds with constant curvature. / QC 20101108

Cette thèse postule qu’il est plus heuristique pour les Relations internationales (RI) de conceptualiser les relations patron-client interétatiques comme des hiérarchies internationales fondées sur des dettes de gratitude. Elle soutient plus précisément que les théoriciens des RI peuvent attester de la présence d’une hiérarchie patron-client lorsque trois conditions sont remplies. D’abord, une dette de gratitude, contractée par l’État subalterne, doit exister au sein de la relation bilatérale. Ensuite, la puissance patronale doit faire appel à ladite dette de gratitude pour exercer de l’autorité politique sur l’État subalterne. Finalement, ce dernier doit se subordonner à l’autorité politique de la puissance patronale en guise de gratitude pour un quelconque bénéfice reçu au cours de la relation bilatérale. Plus précisément, cette thèse soutient que l’émotion de gratitude est la force impérative qui, derrière l’échange de bénéfices internationaux, légitime, d’une part, l’autorité politique exercée par la puissance patronale et, d’autre part, oblige l’État subalterne à offrir sa subordination en guise de contredon international. Les cas de Cuba-États-Unis (1898-1902) et de Cuba-URSS (1959-1963) sont utilisés pour illustrer la validité heuristique de cette proposition théorique. Ce faisant, nous invitons les théoriciens des RI à dépasser le modèle patron-client (MPC) au profit d’une conceptualisation des relations patron-client qui insère la recherche sur le patronage interétatique au sein de deux tournants théoriques de la discipline des RI : les tournants hiérarchique et émotionnel. Cette thèse fait donc une contribution à chacun des tournants précités et établit un dialogue direct entre deux programmes de recherche qui travaillent jusqu’alors en silo. / This thesis argues that it is more heuristic for International Relations (IR) to conceptualize interstate patron-client relationships as international hierarchies built on debts of gratitude. It postulates that IR theorists can attest to the presence of a patron-client hierarchy when three conditions are met. First, a debt of gratitude, incurred by the subordinate state, must exist within the bilateral relationship. Then, the patronal power must appeal to said debt of gratitude to exercise political authority. Finally, the client state must subordinate itself to the political authority of the patronal power in gratitude for any benefit received during the bilateral relationship. The emotion of gratitude is therefore the imperative force which, behind the exchange of international benefits, legitimizes, on the one hand, the political authority exercised by the patronal power and, on the other hand, obliges the client state to offer its subordination as an international gift. The cases of Cuba-USA (1898-1902) and Cuba-USSR (1959-1963) are used to show the value of this theoretical proposition. In doing so, this thesis invites IR theorists to go beyond the patron-client model (PCM) and to favor a conceptualization that inserts research on interstate patronage within two theoretical turns in IR: the hierarchical and emotional turns. It not only contributes to each of the above-mentioned theoretical turns, but also establishes a direct dialogue between two research programs that have hitherto worked in silos.

<p dir="ltr">Additive manufacturing has introduced new possibilities for the design and manufacturing of monolith catalyst beds. Many hydrogen peroxide monolith catalyst beds are made of ceramics and washcoated through a complex process. However, creating a metal monolith bed with the tried-and-true silver catalyst could provide an alternative decomposition method for 90 wt.% hydrogen peroxide with easier manufacturing methods and similar or better decomposition efficiency. 91.2 wt.% hydrogen peroxide was decomposed with a lattice-type monolithic catalyst bed additively manufactured out of 316L stainless steel that was electroplated with pure silver. The variables investigated included the catalyst bed’s mass loading, chamber pressure, pressure drop, and length-to-diameter ratio (L/D). The catalyst bed had loadings of 0.1 lb_m/s/inch², 0.25 lb_m/s/inch², and 0.4 lb_m/s/inch². One catalyst bed configuration had an L/D of 2.6, while the other configuration had an L/D of 0.85. A modular throat controlled the chamber pressures for each catalyst bed loading case. The decomposition efficiency was calculated with the theoretical and expected characteristic velocity (c*) of the catalyst beds. The chamber pressures for the lowest bed loading and highest L/D ratio varied from 52 psia to 202 psia. The hydrogen peroxide decomposition efficiency was approximately 85% for the lowest chamber pressure and approximately 100% for the highest chamber pressure. The chamber pressures for the middle and highest bed loading and high L/D were 193 psia at the lowest to 325 psia at the highest. The decomposition efficiencies for all middle and highest bed loading tests with high L/D were 90% or higher for all tests. For all of the highest L/D tests, decomposition was also confirmed by observing videos of the exhaust plume, which was clear and showed no sign of flow channeling. For all of the highest L/D tests, the pressure drops in all of the middle bed loading cases were at or below 30% of the chamber pressure. The high chamber pressure, highest bed loading cases also had a pressure loss below 30% of the chamber pressure. The smallest L/D configuration performed significantly worse than expected, with efficiencies between 15-25% at chamber pressures between 33-75 psi. The silver electroplated on the stainless steel survived the 143 s of lifetime on the catalyst bed during testing with minimal to no silver loss determined by weight and visual inspection with a microscope post-test. The higher L/D catalyst bed tests prove that silver electroplated on to an additively manufactured stainless steel monolith is a viable method for creating a catalyst bed. More research is required to determine the lowest L/D possible, which resides somewhere between the two L/D cases studied, and higher bed loadings also require investigation.</p>

<p dir="ltr">Rotating detonation rocket engines (RDREs) are a quickly-growing area of research in the field of chemical rocket propulsion. The promise of increased thermodynamic efficiency from the pressure-gain combustion cycle has promoted research and development of RDRE technology for an ever-expanding range of systems. Recently, there has been interest in developing RDRE technology for in-space propulsion systems. At the Purdue Altitude Chamber facility, some of the first testing of an RDRE operating with state-of-the-art in-space propellants monomethyl hydrazine (MMH) and mixed oxides of nitrogen (MON) has been performed at simulated altitudes using an experimental 100-lbf-scale thruster from GHKN Engineering, LLC. This work presents the development, modeling, and operation of the test facility at the Maurice J. Zucrow Laboratories for the simulated-altitude testing of an RDRE using hypergolic propellants. The first chapter presents a brief history of the Purdue Altitude Chamber Facility and background information about rotating detonation rocket engines and of supersonic exhaust diffusers, which are commonly-used devices in simulated-altitude testing of rocket engines. The second chapter presents an overview of the test facility and its design, including the vacuum system, the propellant feed system, and the cold flow test stand used to support the test program. The propellant feed system is analyzed in detail to assess the accuracy of theory in predicting the behavior of the feed system in propellant delivery and measurement. The third chapter presents a computational study of the supersonic exhaust diffuser and comparison with test data. Computational methods are developed for the prediction of diffuser performance with RDREs and other annular combustion devices. While rotating detonation has not yet been observed in testing, hot-fire results corroborate the predicted behavior of an annular combustor with a second-throat exhaust diffuser. Operating an RDRE at simulated altitude and with hypergolic propellants MMH and MON represents a novel field of research in detonation-based combustion devices. The development of the test facility for this work at Zucrow Labs is a significant step towards further developing RDRE technology for in-space propulsion applications.</p>

<p dir="ltr">Burning rate as a function of pressure is one of the primary evaluation metrics of solid propellants. Most solid propellant burning rate measurements are made at a nearly constant pressure using a variety of measurement approaches. This type of burning rate data is highly discretized and requires many tests to accurately determine the burning rate response to pressure. It would be moreefficient to measure burning rate dynamically as pressures are varied. Techniques used to make transient burning rate measurements are reviewed briefly and initial results using a microwave interferometry (MI) technique are presented. The MI method used in tandem with a closed bomb enables nearly continuous measurement of burning rates for self-pressurizing burns, capturing burning rate data over a wide range of pressures. This approach is especially useful for characterization of propellants with complex burning behaviors (e.g., slope breaks or mesa burning). The burning rates of three research propellants were characterized over a pressure range of 0.101-24.14 MPa (14-3500 psi). One research propellant exhibited a slope break at a pressure of 6.63 MPa (960 psi). Using MI in a closed pressure vessel, 14 propellant strand burns resulted in a nearly continuous burning rate curve over a pressure range of 0.41-24.13MPa (60-3500psi) that reasonably matched conventional burning rate measurements. The development of this technique provides an opportunity to quickly characterize the burning rate curve of solid propellants with greater fidelity and efficiency than traditional quasi-static pressure testing techniques.</p>

Despite being the global leader in the “war on terror,” the United States has been accused of sponsoring terrorism against Cuba. The following study assesses these charges. After establishing a definition of terrorism, it examines U.S.-Cuban relations from 1808 to 1958, arguing that the United States has historically employed violence in its efforts to control Cuba. U.S. leaders maintained this approach even after the Cuban Revolution: months after Fidel Castro’s guerrilla army took power, Washington began organizing Cuban exiles to carry out terrorist attacks against the island, and continued to support and tolerate such activities until the 1970s, culminating in what was the hemisphere’s most lethal act of airline terrorism before 9/11. Since then, the United States has maintained contact with well-known anti-Castro terrorists, in many cases employing and harbouring them, despite its claims to be fighting an international campaign against terrorism.

Despite being the global leader in the “war on terror,” the United States has been accused of sponsoring terrorism against Cuba. The following study assesses these charges. After establishing a definition of terrorism, it examines U.S.-Cuban relations from 1808 to 1958, arguing that the United States has historically employed violence in its efforts to control Cuba. U.S. leaders maintained this approach even after the Cuban Revolution: months after Fidel Castro’s guerrilla army took power, Washington began organizing Cuban exiles to carry out terrorist attacks against the island, and continued to support and tolerate such activities until the 1970s, culminating in what was the hemisphere’s most lethal act of airline terrorism before 9/11. Since then, the United States has maintained contact with well-known anti-Castro terrorists, in many cases employing and harbouring them, despite its claims to be fighting an international campaign against terrorism.