This research examines some of the ways to design a digital control system with particular reference to the control of yaw plane dynamics of an air-to-air missile model. Specific attention is paid to compare two methods of global digital re-design of validated analogue closed loop control system. These two methods are the multi-input multi-output (MIMO) Plant Input Mapping (PIM) method and multi-loop PIM method. The thesis will first show how a specific class of closed loop MIMO feedback systems with a single-input multi-output (SIMO) plant can be re-structured as multi-loop control systems, which includes the closed loop missile control system. Some special characteristics pertaining to SIMO systems for control system design are explored. The aforementioned two methods of PIM global digital re-design are then applied to the MIMO analogue missile control system and its re-structured multi-loop counterpart. A comparison of the two methods is made on its design procedure, implementation structure and results from computer simulation. / This thesis also touches upon the topic of controller order reduction, particularly in consideration of the PIM digital re-design of analogue feedback systems. (Abstract shortened by UMI.)

<p> A DC&ndash;thermal plasma jet is proposed as a reliable ignition source for reaction control system (RCS) thrusters employing oxygen with hydrocarbons, like methane. Industrial plasma torch systems are analyzed to understand the behavioral characteristics of DC&ndash;thermal plasmas. Nitrogen is used as a working gas for the source of plasma jet to understand the general mechanism of thermal plasma formation. DC&ndash;thermal plasmas require high electrical energy to maintain their arc discharge status which presents challenges in space systems. The purpose of this study is, therefore, to find a suitable configuration which minimizes power consumption.</p><p> Various physical and electrical conditions relate to a thermal plasma formation. In this study, the input voltage (221&ndash;332V) and pressure (5&ndash;15 psi) are applied as initial conditions. The DC&ndash;power module and starter module are designed as plasma drivers and a commercial off&ndash;the&ndash;shelf torch head is used for this research. The normalized method is developed to estimate the arc temperature. Test results show that the lowest power consumption and arc&ndash;starting voltage are 1,321W and 248.8 VDC, respectively. In addition, it is found that the current is a major factor for varying the mass flow rate.</p><p> Since the lowest power consumption is still high, future improvements and research should focus on integrating a high&ndash;power and lightweight energy source, developing a high&ndash;frequency and half&ndash;duty cycle power system, and incorporating a composite cathode. In addition, a new conceptual torch design is proposed to be considered as an igniter for RCS thrusters. The next step would be to repeat the plasma torch tests with the new configuration at ambient and vacuum conditions. These would be followed by combustion tests to verify the actual functionality of the plasma igniter for RCS thrusters with various oxidizer and fuel mixture ratios. In parallel, research should focus on miniaturization of the electrical system.</p>

<p> This dissertation interviewed a single astronaut to explore psychosocial issues relevant to long-duration space travel and how these issues relate to the astronaut's training. It examined the psychological impact of isolation, crew interaction, and the experience of microgravity with the goal of increasing understanding of how to foster crew survivability and positive small group interactions in space (Santy, 1994). It also focused on how to develop possible treatments for crews when they transition back to Earth from the extreme environment of space missions. The astronaut's responses agreed with the literature and the predictions for long-duration space missions except the participant reported no temporary or permanent cognitive or memory deficits due to microgravity exposure. The dissertation identified five frequently endorsed themes including communication, environmental stressors, personal strengths, un-researched problems, and other. The agreement found between the literature and astronaut's responses offer a strong foundation of questions and data that needs to be further studied before conducting research in space or long-duration space missions.</p>

<p> Parts machined from relatively large thickness cross sections can experience significant deformations from high residual stresses that develop in the part during the heat treatment used to form the aluminum alloy. Uphill quenching is a process that can create a part with low residual stress and stable dimensions when the process is controlled properly. The uphill quenching process involves a solution heat treat, quench, cool to liquid nitrogen, steam blast, and then age to final temper. </p><p> In this thesis two parts were modeled using ANSYS. The first part underwent the uphill quench process in the rough machined state. The second part was modeled in the stock material shape and only underwent a solution heat treat, quench, and age to final temper. After the residual stress in the second part was predicted the excess material was removed by killing the associated elements and the deformation of the final machined part was predicted. For both parts analyzed measurements were made and compared against predictions with fairly good results.</p>

<p> Cold-start performance enhancement of a pump-assisted, capillary-driven, two-phase cooling loop was attained using proportional integral and fuzzy logic controls to manage the boiling condition inside the evaporator. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting fluid, was also investigated for enhancing heat transfer performance of capillary driven (passive) thermal devices was also studied. A proportional-integral control algorithm was used to regulate the boiling condition (from pool boiling to thin-film boiling) and backpressure in the evaporator during cold-start and low heat input conditions. Active flow control improved the thermal resistance at low heat inputs by 50% compared to the baseline (constant flow rate) case, while realizing a total pumping power savings of 56%. Temperature overshoot at start-up was mitigated combining fuzzy-logic with a proportional-integral controller. A constant evaporator surface temperature of 60&deg;C with a variation of &plusmn;8&deg;C during start-up was attained with evaporator thermal resistances as low as 0.10 cm<i>2</i>&ndash;K/W. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting working fluid, as a function of concentration and temperature were also investigated. Self-rewetting working fluids are promising in two-phase heat transfer applications because they have the ability to passively drive additional working fluid towards the heated surface; thereby increasing the dryout limitations of the thermal device. Very little data is available in literature regarding the surface tension of these fluids due to the complexity involved in fluid handling, heating, and experimentation. Careful experiments were performed to investigate the surface tension of n-Pentanol + water. The concentration and temperature range investigated were from 0.25%wt. to1.8%wt and 25&deg;C to 85&deg;C, respectively. </p>

<p> The current fiscally austere environment prevalent in the military and industry is driving extreme measures to save money. In the United States Air Force, this has driven enormous efforts to trim sustainment spending on extended life aircraft. The challenge to the aerospace engineer is to ensure flight safety in the midst of this economic pressure. </p><p> One method of cutting costs is to increase the time an aircraft is in service by delaying the point when the aircraft is taken out of service for depot maintenance. To ensure flight safety, in depth fatigue and fracture analysis needs to be accomplished to assess increasing the inspection interval. </p><p> The purpose of this study was to determine the sensitivity of Aluminum 2024-T351 alloy, a common material used in tension dominated aerospace applications, to two different loading spectra&mdash;one that is aggressive and the other that is benign. This was accomplished by conducting five different combinations of the two spectra, developing computer simulations using the AFGROW software and comparing with the measured data. The results showed that the material demonstrated significantly different behavior between the two spectra. These results provide a valuable tool for the aerospace engineer for fatigue life prediction and inspection interval evaluation.</p>

<p> A software prototype for autonomous 3D scanning of uncooperatively rotating orbital debris using a point cloud sensor is designed and tested. The software successfully generated 3D models under conditions that simulate some on-orbit orbit challenges including relative motion between observer and target, inconsistent target visibility and a target with more than one plane of symmetry. The model scanning software performed well against an irregular object with one plane of symmetry but was weak against objects with 2 planes of symmetry. </p><p> The suitability of point cloud sensors and algorithms for space is examined. Terrestrial Graph SLAM is adapted for an uncooperatively rotating orbital debris scanning scenario. A joint EKF attitude estimate and shape similiarity loop closure heuristic for orbital debris is derived and experimentally tested. The binary Extended Fast Point Feature Histogram (EFPFH) is defined and analyzed as a binary quantization of the floating point EFPFH. Both the binary and floating point EPFH are experimentally tested and compared as part of the joint loop closure heuristic.</p>

<p> Inverse optimal control is the problem of computing a cost function with respect to which observed state input trajectories are optimal. We present a new method of inverse optimal control based on minimizing the extent to which observed trajectories violate first-order necessary conditions for optimality. We consider continuous-time deterministic optimal control systems with a cost function that is a linear combination of known basis functions. We compare our approach with three prior methods of inverse optimal control. We demonstrate the performance of these methods by performing simulation experiments using a collection of nominal system models. We compare the robustness of these methods by analyzing how they perform under perturbations to the system. We consider two scenarios: one in which we exactly know the set of basis functions in the cost function, and another in which the true cost function contains an unknown perturbation. Results from simulation experiments show that our new method is computationally efficient relative to prior methods, performs similarly to prior approaches under large perturbations to the system, and better learns the true cost function under small perturbations. We then apply our method to three problems of interest in robotics. First, we apply inverse optimal control to learn the physical properties of an elastic rod. Second, we apply inverse optimal control to learn models of human walking paths. These models of human locomotion enable automation of mobile robots moving in a shared space with humans, and enable motion prediction of walking humans given partial trajectory observations. Finally, we apply inverse optimal control to develop a new method of learning from demonstration for quadrotor dynamic maneuvering. We compare and contrast our method with an existing state-of-the-art solution based on minimum-time optimal control, and show that our method can generalize to novel tasks and reject environmental disturbances. </p>

<p> There are significant challenges involved in regulating the growing commercial human spaceflight industry. The safety of the crew and passengers should be protected; however, care should be taken not to overburden the industry with too many or too stringent, or perhaps inapplicable, regulations. </p><p> An improvement in launch success would improve the safety of the crew and passengers. This study explores the effectiveness of Mission Assurance policies to guide regulations and standards. There is a severe lack of data regarding commercial human space flights. This means that a direct test of effectiveness by looking at historical commercial human space flight data is not possible. Historical data on current expendable commercial launchers have been used in this study. The National Aeronautics and Space Administration (NASA) has strong Mission Assurance policies for its launch of civil payloads. The Office of Commercial Space Transportation at the Federal Aviation Administration (FAA/AST) regulations of commercial launches are more safety oriented. </p><p> A comparison of launches between NASA and the FAA/AST is used to gauge the effectiveness of Mission Assurance policies on launch success. Variables between the two agencies are reduced so that Mission Assurance policies are isolated as the main difference between launches. Scenarios pertinent to commercial human space flight are used so results can be applicable.</p>

<p> Historically, the National Aeronautics and Space Administration (NASA) has used rocket-powered vehicles as launch vehicles for access to space. A familiar example is the Space Shuttle launch system. These vehicles carry both fuel and oxidizer onboard. If an external oxidizer (such as the Earth's atmosphere) is utilized, the need to carry an onboard oxidizer is eliminated, and future launch vehicles could carry a larger payload into orbit at a fraction of the total fuel expenditure. For this reason, NASA is currently researching the use of air-breathing engines to power the first stage of two-stage-to-orbit hypersonic launch systems. Removing the need to carry an onboard oxidizer leads also to reductions in total vehicle weight at liftoff. This in turn reduces the total mass of propellant required, and thus decreases the cost of carrying a specific payload into orbit or beyond. However, achieving hypersonic flight with air-breathing jet engines has several technical challenges. These challenges, such as the mode transition from supersonic to hypersonic engine operation, are under study in NASA's Fundamental Aeronautics Program. </p><p> One propulsion concept that is being explored is a magnetohydrodynamic (MHD) energy- bypass generator coupled with an off-the-shelf turbojet/turbofan. It is anticipated that this engine will be capable of operation from takeoff to Mach 7 in a single flowpath without mode transition. The MHD energy bypass consists of an MHD generator placed directly upstream of the engine, and converts a portion of the enthalpy of the inlet flow through the engine into electrical current. This reduction in flow enthalpy corresponds to a reduced Mach number at the turbojet inlet so that the engine stays within its design constraints. Furthermore, the generated electrical current may then be used to power aircraft systems or an MHD accelerator positioned downstream of the turbojet. The MHD accelerator operates in reverse of the MHD generator, re-accelerating the exhaust flow from the engine by converting electrical current back into flow enthalpy to increase thrust. Though there has been considerable research into the use of MHD generators to produce electricity for industrial power plants, interest in the technology for flight-weight aerospace applications has developed only recently. </p><p> In this research, electromagnetic fields coupled with weakly ionzed gases to slow hypersonic airflow were investigated within the confines of an MHD energy-bypass system with the goal of showing that it is possible for an air-breathing engine to transition from takeoff to Mach 7 without carrying a rocket propulsion system along with it. The MHD energy-bypass system was modeled for use on a supersonic turbojet engine. The model included all components envisioned for an MHD energy-bypass system; two preionizers, an MHD generator, and an MHD accelerator. A thermodynamic cycle analysis of the hypothesized MHD energy-bypass system on an existing supersonic turbojet engine was completed. In addition, a detailed thermodynamic, plasmadynamic, and electromagnetic analysis was combined to offer a single, comprehensive model to describe more fully the proper plasma flows and magnetic fields required for successful operation of the MHD energy bypass system. </p><p> The unique contribution of this research involved modeling the current density, temperature, velocity, pressure, electric field, Hall parameter, and electrical power throughout an annular MHD generator and an annular MHD accelerator taking into account an external magnetic field within a moving flow field, collisions of electrons with neutral particles in an ionized flow field, and collisions of ions with neutral particles in an ionized flow field (ion slip). In previous research, the ion slip term has not been considered. </p><p> The MHD energy-bypass system model showed that it is possible to expand the operating range of a supersonic jet engine from a maximum of Mach 3.5 to a maximum of Mach 7. The inclusion of ion slip within the analysis further showed that it is possible to 'drive' this system with maximum magnetic fields of 3 T and with maximum conductivity levels of 11 mhos/m. These operating parameters better the previous findings of 5 T and 10 mhos/m, and reveal that taking into account collisions between ions and neutral particles within a weakly ionized flow provides a more realistic model with added benefits of lower magnetic fields and conductivity levels especially at the higher Mach numbers. (Abstract shortened by UMI.)</p>